Efficient quantification of water content in edible oils by headspace gas chromatography with vapour phase calibration

BACKGROUND

An automated and accurate headspace gas chromatographic (HS-GC) technique was investigated for rapidly quantifying water content in edible oils. In this method, multiple headspace extraction (MHE) procedures were used to analyse the integrated water content from the edible oil sample. A simple vapour phase calibration technique with an external vapour standard was used to calibrate both the water content in the gas phase and the total weight of water in edible oil sample. After that the water in edible oils can be quantified.

RESULTS

The data showed that the relative standard deviation of the present HS-GC method in the precision test was less than 1.13%, the relative differences between the new method and a reference method (i.e. the oven-drying method) were no more than 1.62%.

CONCLUSION

The present HS-GC method is automated, accurate, efficient, and can be a reliable tool for quantifying water content in edible oil related products and research. © 2017 Society of Chemical Industry.

Synthesis of Alkyl-Glycerolipids Standards for Gas Chromatography Analysis: Application for Chimera and Shark Liver Oils

Natural O-alkyl-glycerolipids, also known as alkyl-ether-lipids (AEL), feature a long fatty alkyl chain linked to the glycerol unit by an ether bond. AEL are ubiquitously found in different tissues but, are abundant in shark liver oil, breast milk, red blood cells, blood plasma, and bone marrow. Only a few AEL are commercially available, while many others with saturated or mono-unsaturated alkyl chains of variable length are not available. These compounds are, however, necessary as standards for analytical methods. Here, we investigated different reported procedures and we adapted some of them to prepare a series of 1-O-alkyl-glycerols featuring mainly saturated alkyl chains of various lengths (14:0, 16:0, 17:0, 19:0, 20:0, 22:0) and two monounsaturated chains (16:1, 18:1). All of these standards were fully characterized by NMR and GC-MS. Finally, we used these standards to identify the AEL subtypes in shark and chimera liver oils. The distribution of the identified AEL were: 14:0 (20-24%), 16:0 (42-54%) and 18:1 (6-16%) and, to a lesser extent, (0.2-2%) for each of the following: 16:1, 17:0, 18:0, and 20:0. These standards open the possibilities to identify AEL subtypes in tumours and compare their composition to those of non-tumour tissues.

Standard Reference Material (SRM) 2378 fatty acids in frozen human serum. Certification of a clinical SRM based on endogenous supplementation of polyunsaturated fatty acids

Dietary fatty acids can be both beneficial and detrimental to human health depending on the degree and type of saturation. Healthcare providers and research scientists monitor the fatty acid content of human plasma and serum as an indicator of health status and diet. In addition, both the Centers for Disease Control & Prevention (CDC) and the National Institutes of Health - Office of Dietary Supplements are interested in circulating fatty acids (FAs) because they may be predictive of coronary heart disease. The National Institute of Standards and Technology (NIST) provides a wide variety of reference materials (RMs) and Standard Reference Materials® (SRM®s) including blood, serum, plasma, and urine with values assigned for analytes of clinical interest. NIST SRM 2378 Fatty Acids in Frozen Human Serum was introduced in 2015 to help validate methods used for the analysis of FAs in serum, and consists of three different pools of serum acquired from (1) healthy donors who had taken fish oil dietary supplements (at least 1000 mg per day) for at least one month (level 1 material), (2) healthy donors who had taken flaxseed oil dietary supplements (at least 1000 mg per day) for at least one month (level 2 material), and (3) healthy donors eating "normal" diets who had not taken dietary supplements containing fish or plant oils (level 3 material). The use of dietary supplements by donors provided SRMs with natural endogenous ranges of FAs at concentrations observed in human populations. Results from analyses using two methods at NIST, including one involving a novel microwave-assisted acid hydrolysis procedure, and one at the CDC are presented here. These results and their respective uncertainties were combined to yield certified values with expanded uncertainties for 12 FAs and reference values with expanded uncertainties for an additional 18 FAs.

Sensitive and Simplified Detection of Antibiotic Influence on the Dynamic and Versatile Changes of Fecal Short-Chain Fatty Acids

Short-chain fatty acids (SCFAs), produced by anaerobic fermentation of mainly indigestible dietary carbohydrates by gut microbiota, have a profound influence on intestinal function and host energy metabolism. Antibiotics may seriously disturb the balance of fecal SCFAs. To evaluate the impacts of antibiotics on fecal SCFAs produced by gut microbiota, a simple, reproducible and accurate gas chromatography (GC) method, which can simultaneously analyze seven SCFAs in fecal samples, was developed and validated. The ranges of detection and quantitation of the SCFAs reached 0.0868 ~ 0.393 and 0.261 ~ 1.18 μg·mL-1 respectively, in an optimized protocol for SCFAs extraction and analysis that used 10 mL 75% ethanol aqueous solution containing 1% HCl, without ultrasonication. The technique exhibited excellent intra-day (relative standard deviation (RSD) ≤ 2.54%) and inter-day (RSD ≤ 4.33%) precisions for all the SCFAs. Later, we administered broad-spectrum antibiotics, cefdinir or azithromycin to rats and analyzed the alterations in fecal SCFAs. The total amount, types and distribution of nearly all fecal SCFAs were significantly altered during the administration and even after withdrawal of the antibiotics in rats. The effects of cefdinir on the SCFAs were more pronounced than those of azithromycin. Our findings suggest SCFAs may serve as sensitive indicators to monitor the influences of antibiotics on SCFAs originated by intestinal bacteria. Our improved SCFAs analysis method is a potential platform for a standard clinical test of the effects of new antibiotics on SCFAs.

Validation of QuEChERS method for the determination of 36 pesticide residues in fruits and vegetables from Ghana, using gas chromatography with electron capture and pulsed flame photometric detectors

In this study, "Quick, Easy, Cheap, Effective, Rugged and Safe" 'QuEChERS' method was modified for the determination of 36 pesticides fortified at (0.01-1.0) mg kg(-1) in three vegetables and a fruit (lettuce, carrot, tomatoes and pineapples respectively) from Ghana. The method involved extraction with acetonitrile, phase separation with primary secondary amine and magnesium sulfate; the final injection solution was reconstituted in ethyl acetate. Organochlorine and synthetic pyrethroids residues were detected with electron capture detector whereas organophosphorus, pulsed flame photometric detector was used. The recoveries at different concentration levels (0.01, 0.1 and 1.0 mg kg(-1)) were in the range of 83% and 93% with relative standard deviation ranging from 2% to 10% (n = 5) and the coefficient of determination (R(2)) was greater than 0.99 for all the 36 pesticides. The method was successfully tested on 120 real samples from Accra markets and this proved to be useful for monitoring purposes particularly in laboratories that have no gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry.

Determination of phosphine in plant materials: method optimization and validation in interlaboratory comparison tests

The optimization and validation of a method for the determination of phosphine in plant materials are described. The method is based on headspace sampling over the sample heated in 5% sulfuric acid. Critical factors such as sample amount, equilibration conditions, method of quantitation, and matrix effects are discussed, and validation data are presented. Grinding of coarse samples does not lead to lower results and is a prerequisite for standard addition experiments, which present the most reliable approach for quantitation because of notable matrix effects. Two interlaboratory comparisons showed that results varied considerably and that an uncertainty of measurement of about 50% has to be assessed. Flame photometric and mass spectrometric detection gave similar results. The proposed method is well reproducible within one laboratory, and results from the authors' laboratories using different injection and detection techniques are very close to each other. The considerable variation in the interlaboratory comparison shows that this analysis is still challenging in practice and further proficiency testing is needed.

The development, validation and application of a GC-dual detector (NPD-ECD) multi-pesticide residue method for monitoring bee poisoning incidents

A simple multiresidue method based on matrix solid phase dispersion (MSPD) combined with clean-up has been developed for the simultaneous screening of 153 pesticides in honeybees suspected of suffering from pesticide poisoning during field spraying. Extraction and clean-up were carried out in a glass column containing anhydrous sulphate, 2.0g of octadecyl (C18) and a 2.0-g sample of bees (23 insects on average) macerated with 4.0g of Florisil. An additional layer of anhydrous sodium sulphate was added, and acetonitrile was used as the elution solvent. This combination of clean-up steps ensured an efficient purification. A gas chromatograph with dual selective detectors for electron capture and nitrogen-phosphorous was used. The results presented in this paper demonstrate that matrix solid-phase dispersion (MSPD) with the one-step clean-up procedure is the most effective extraction technique. MSPD method recoveries ranged from 70 to 118%, with precision values expressed as a relative standard of <20%, except for 10 pesticides that had recoveries of 50-70% and two with 120-130%. Low limits of detection (0.003-0.04μg/g) and quantification (0.005-0.05μg/g) were readily achieved with this method for all tested pesticides. A "top down" empirical model was used to estimate the expanded uncertainty at 28% on average (coverage factor k=2, confidence level 95%). The MSPD method was successfully used on real bee samples to analyse four acaricides, 55 fungicides, 16 herbicides and 78 insecticides from various regions of Poland. A total of 33 honeybee samples from suspected pesticide poisoning incidents were analysed, in which 17 different pesticides were determined (14 insecticides and three fungicides). The pesticides most often found in honeybees were cypermethrin (in 51% of the samples, 0.008-0.563µg/bee), chlorpyrifos (27%, 0.001-51.5µg/bee) and biphentin (21%, 0.002-0.012µg/bee).

Comparison of GC stationary phases for the separation of fatty acid methyl esters in biodiesel fuels

The fatty acid methyl ester (FAME) content of biodiesel fuels has traditionally been determined using gas chromatography with a polar stationary phase. In this study, a direct comparison of the separation of FAMEs present in various biodiesel samples on three polar stationary phases and one moderately polar stationary phase (with comparable column dimensions) was performed. Retention on each column was based on solubility in and polarity of the phase. Quantitative metrics describing the resolution of important FAME pairs indicate high resolution on all polar columns, yet the best resolution, particularly of geometric isomers, is achieved on the cyanopropyl column. In addition, the separation of four C18 monounsaturated isomers was optimized and the elution order determined on each column. FAME composition of various biodiesel fuel types was determined on each column to illustrate (1) chemical differences in biodiesels produced from different feedstocks and (2) chemical similarities in biodiesels of the same feedstock type produced in different locations and harvest seasons.

Determination of acetaldehyde in saliva by gas-diffusion flow injection analysis

The consumption of ethanol is known to increase the likelihood of oral cancer. In addition, there has been a growing concern about possible association between long term use of ethanol-containing mouthwashes and oral cancer. Acetaldehyde, known to be a carcinogen, is the first metabolite of ethanol and it can be produced in the oral cavity after consumption or exposure to ethanol. This paper reports on the development of a gas-diffusion flow injection method for the online determination of salivary acetaldehyde by its colour reaction with 3-methyl-2-benzothiazolinone hydrazone (MBTH) and ferric chloride. Acetaldehyde samples and standards (80 μL) were injected into the donor stream containing NaCl from which acetaldehyde diffused through the hydrophobic Teflon membrane of the gas-diffusion cell into the acceptor stream containing the two reagents mentioned above. The resultant intense green coloured dye was monitored spectrophotometrically at 600 nm. Under the optimum working conditions the method is characterized by a sampling rate of 9h(-1), a linear calibration range of 0.5-15 mg L(-1) (absorbance=5.40×10(-2) [acetaldehyde, mg L(-1)], R(2)=0.998), a relative standard deviation (RSD) of 1.90% (n=10, acetaldehyde concentration of 2.5 mg L(-1)), and a limit of detection (LOD) of 12.3 μg L(-1). The LOD and sampling rate of the proposed method are superior to those of the conventional gas chromatographic (GC) method (LOD=93.0 μg L(-1) and sampling rate=4 h(-1)). The reliability of the proposed method was illustrated by the fact that spiked with acetaldehyde saliva samples yielded excellent recoveries (96.6-101.9%), comparable to those obtained by GC (96.4-102.3%) and there was no statistically significant difference at the 95% confidence level between the two methods when non-spiked saliva samples were analysed.

Fabry-Pérot cavity sensor-based optofluidic gas chromatography using a microfabricated passive preconcentrator/injector

This study reports on dual on-column Fabry-Pérot (FP) cavity sensor-based gas chromatography (GC) of mixtures of volatile organic compounds (VOCs) utilizing an on-chip device, the so called "microfabricated passive preconcentrator/injector (μPPI)". Comprehensive analysis of the sampling, desorption/injection, and compound separation performance of the μPPI-based optofluidic GC system is described. Here, the combined use of the μPPI and on-column FP cavity sensors in a common GC platform enabled diffusion-based passive sampling, rapid (<7 min) chromatographic separation, and optical detection for the quaternary VOC mixtures of benzene, TCE, toluene, and m-xylene at sub-ppm concentrations with a simpler fluidic setup than conventional GC systems. The FP cavity sensor arrangement provided the means to study the dynamics of the thermal desorption/injection of VOCs by the μPPI and its effect on the GC separation resolution. Our analysis of obtained chromatograms revealed a presence of the competitive adsorptions of VOC mixtures onto the adsorption sites of trapping materials in the μPPI, which decreased the effective sampling rate by ~50% for compounds with high volatility. The validated performance of the optofluidic GC system promises future development of a field deployable GC microsystem incorporating the μPPI and the FP cavity sensors.

Determination of ethanol content in medicated syrups by static headspace gas chromatography

Liquid drug preparations are the most convenient for pediatric patients. Unfortunately, these formulations very often contain ethanol, which may have an impact on children development. Moreover, medicines containing alcohol may cause undesirable interactions in conjunction with other drugs. This work reports complete validated method for the quantitation of ethanol in commercial medicated syrups. For determination of ethanol headspace gas chromatography and different methods of quantitative analysis were used. The analyzed samples of commercial medicated syrups available on the home marked contained from 3.37 to 8.65% (v/v) of ethanol. The estimated theoretical values of blood ethanol concentration for children after single recommended dose ingestion were at least twice lower than 0.125 g/mL. The process of validation showed that the applied GC method is selective, sensitive, linear and precise. The use of internal standard makes it accurate. The developed method could be considered as an analytical tool for the quality control of various liquid drug preparations.

Simultaneous determination of four sesquiterpenoids in Atractylodes Macrocephala Rhizoma by GC-FID: optimisation of an ultrasound-assisted extraction by central composite design

INTRODUCTION

Atractylodes Macrocephala Rhizoma (AMR) is a traditional Chinese medicine containing several sesquiterpenoids with a series of effects. These bioactive compounds may be used as chemical markers for the quality control of AMR. It is necessary to optimise the extraction method and conditions in order to improve extraction productivity.

OBJECTIVE

To develop a simple and effective method for the extraction of sesquiterpenoids from AMR and then to simultaneously determine four sesquiterpenoids, selina-4 (14), 7(11)-dien-8-one (SA), atractylenolide II (AII), atractylenolide III (AIII) and atractylenolide VII (AVII), in AMR.

METHODOLOGY

Ultrasound-assisted extraction (UAE) was optimised by central composite design (CCD) to obtain the maximum efficiency. The gas chromatography method was validated and applied for the quantification of four sesquiterpenoids.

RESULTS

The optimum values of factors were: particle size (120 mesh), extraction time (26 min), extraction temperature (39°C) and 31 mL of chloroform. The selectivity, linear range, limits of detection (LOD) and quantification (LOQ), accuracy, precision and repeatability of the method developed indicated its validity. The application of the method showed that the contents of four sesquiterpenoids in AMR were rather variable.

CONCLUSION

The results indicated that the described GC method could be used for the quality control of AMR and its related preparations. Meanwhile, this research revealed that UAE under optimum conditions could be considered as a powerful tool for the extraction of phytochemicals from plants.

A multifunctional test mixture for chiral cyclodextrin GC columns

Gas chromatography (GC) is a powerful tool in the separation science of chiral analytes. The development of a new chiral test mixture for cyclodextrin (CD) coated GC columns allows comparing, choosing and identifying most suitable columns for a given separation challenge. This test mixture contains 12 enantiomer pairs of a broad range of functional groups and it is the first mixture suitable for all types of modified cyclodextrin capillary columns. Column changes can be observed and system performance can be monitored by means of this test mixture, which is therefore a base for reliable results. Furthermore, this publication is thought to be a start-up aid for chiral GC.

Self-referenced composite Fabry-Pérot cavity vapor sensors

We develop a versatile, self-referenced composite Fabry-Pérot (FP) sensor and the corresponding detection scheme for rapid and precise measurement of vapors. The composite FP vapor sensor is formed by etching two juxtaposed micron-deep wells, with a precisely controlled offset in depth, on a silicon wafer. The wells are then coated with a vapor sensitive polymer and the reflected light from each well is detected by a CMOS imager. Due to its self-referenced nature, the composite FP sensor is able to extract the change in thickness and refractive index of the polymer layer upon exposure to analyte vapors, thus allowing for accurate vapor quantitation regardless of the polymer thickness, refractive index, and light incident angle and wavelength. Theoretical analysis is first performed to elucidate the underlying detection principle, followed by experimental demonstration at two different incident angles showing rapid and consistent measurement of the polymer changes when the polymer is exposed to three different analytes at various concentrations. The vapor detection limit is found to be on the order of a few pico-grams (~100 ppb).

[Correction of the alkylnitrite method for the detection of ethanol in blood taking into account toxico-kinetic and anthropometric data]

The correction coefficient for the systemic inaccuracy arising during determination of blood ethanol by alkylnitrite gas chromatography and concomitant calibration of aqueous solutions was estimated to equal 0.82; this finding was confirmed by the results of the toxico-kinetic assay for the measurement of total body water (TBW) from the kinetic curve characterizing the time dependence of ethanol concentration in the exhaled air, saliva, capillary and venous blood in combination with 4 anthropometric methods and (in several cases) direct physical detection of TBW. When detecting the blood ethanol level with a correction coefficient of 0.82, the mutual position of the kinetic curves for ethanol concentrations in the blood and the exhaled air (recalculated for the blood level with a coefficient of 2100) as well as in the blood and saliva agreed with that reported in the available literature; it significantly differed from the position of the curves obtained with a correction coefficient of 0.95. The causes accounting for the systematic inaccuracy and erroneous values of the correction coefficients in earlier studies are discussed.

Validation of GC method for quantitative determination of residual 2-(2-chloroethoxy)ethanol (CEE) and N-methyl-2-pyrrolidinone (NMP) in pharmaceutical active substance

The gas chromatography method with direct injection for quantitative determination of residual nonvolatile solvents such as 2-(2-chloroethoxy)ethanol (CEE) and N-methyl-2-pyrrolidinone (NMP) in quetiapine--the pharmaceutical active substance has been validated. Validation was performed according to the requirement of ICH validation guidelines Q2A and Q2B. Specificity, precision, accuracy, linearity, limits of detection and quantitation and robustness were determined and excellent results were obtained.

[Improvement of method for detecting volatile fatty acids in air]

The authors demonstrated possible use of capillary columns to detect volatile fatty acids in air. Tenax TA as adsorbent is recommended.

Assessment of circulating sex steroid levels in prepubertal and pubertal boys and girls by a novel ultrasensitive gas chromatography-tandem mass spectrometry method

CONTEXT

Estrogens and androgens play key roles for pubertal onset and sexual maturation. Most currently used immunoassays are not sensitive enough to accurately measure the low circulating levels of sex steroids in children without any signs of puberty. However, this does not exclude that sex steroids have important biological roles in prepubertal children.

OBJECTIVES

To accurately determine levels of sex steroid hormones and their metabolites in serum of healthy children before any physical signs of puberty and to evaluate possible sex differences.

MAIN OUTCOME MEASURES

Total (unconjugated plus conjugated) serum levels of 17beta-testosterone, 17alpha-testosterone, 5alpha-dihydrotestosterone, 5beta-dihydrotestosterone, androsterone, etiocholanolone, estradiol, and estrone measured by an ultrasensitive method based on gas chromatography-tandem mass spectrometry in samples from 81 healthy schoolchildren (42 boys) without any signs of puberty. For comparison, 48 pubertal children were studied.

RESULTS

17beta-Estradiol levels in prepubertal boys were undetectable or extremely low (median < 3.7 pmol/liter), whereas levels in prepubertal girls were significantly higher (median 9.6 pmol/liter, P < 0.001). Among the older prepubertal children (>8 yr), girls had significantly higher androsterone (4.07 vs. 1.45 nmol/liter, P < 0.05), etiocholanolone (5.45 vs. 1.95 nmol/liter, P < 0.0001), 5alpha-dihydrotestosterone (0.11 vs. <0.10 nmol/liter, P < 0.01), and 17beta-testosterone concentrations (0.69 vs. 0.47 nmol/liter, P < 0.05) compared with similarly aged prepubertal boys.

CONCLUSION

Using an accurate and sensitive method, we found significantly higher levels of estrogens as well as androgen metabolites in prepubertal girls compared with age-matched boys. The higher prepubertal sex steroid levels in girls may contribute to their earlier onset of puberty including pubic hair development.

Effect of a purification step and the type of internal standard used on fatty acid determination of grass and maize silages

The fatty acid (FA) analysis of grass and maize silages was studied by application of a direct transesterification method (DT) followed by purification by solid-phase extraction (SPE). The choice of the internal standard (IS) for quantification of FA by gas-liquid chromatography (GLC) was also studied. The acidic DT method applied to grass silage samples produced a high amount of non-fatty acid methyl ester compounds (non-FAME) compared with those formed in maize silages. The application of the SPE cleanup step reduced significantly the amount of non-FAME compounds in both samples. Five FAs were tested as IS; among them, 3 were naturally present in all silages, however their use as IS did not affect quantification of total FA composition. Nevertheless, some minor FAs present in silages were significantly affected by the IS used. Additionally, application of corrections to the GLC peak areas did not significantly influence quantification of total FA composition of silages.

Determination of organotins in aquatic food by gas chromatography with pulsed flame photometric detection

A method based on gas chromatography (GC)-pulsed flame photometric detection (PFPD) was developed to determine the levels of organotins in aquatic food. After being purified by gel-permeation chromatography in ethyl actate-tetrahydrofuran, the organotin compounds were derivatized by pentylmagnesium bromide. The derivative products were injected into the GC system and detected by PFPD (sulfur mode). The method was validated by analysis of the certified reference material and spiked samples. Recoveries of organotins ranged from 84.1 to 116.6% with relative standard deviation between 1.3 and 16.0% when spiked at levels of 2, 10, and 40 microg/kg. The limits of detection varied from 0.1 to 1.2 microg/kg for shellfish and 0.1 to 0.5 microg/kg for fish. The proposed method was suitable for determining organotins in aquatic foods.

Trace phthalate and adipate esters contaminated in packaged food

A method for trace analysis of two plasticizers, di-2-ethylhexyl phthalate (DEHP) and di-2-ethylhexyl adipate (DEHA), contaminated in packaged curry paste were investigated by gas chromatography with flame ionization detector (GC-FID). Curry paste samples were extracted by ultrasonic and solid phase extraction using Florisil(R) cartridge. Analysis by the GC-FID system provided limits of detection for DEHA and DEHP at 12 and 25 microg L(- 1) and a linear dynamic range between 25 microg L(- 1) to 60 mg L(- 1) with a coefficient of determination (R(2)) greater than 0.99. High recoveries were obtained, ranged from 91 to 99% and 88 to 98% for DEHP and DEHA with RSD lower than 7 and 10% respectively. The method detection limit and limits of quantitation were ranged from 27 to 30 and 90 to 100 microg L(- 1). The analysis of curry paste samples showed concentrations of DEHP and DEHA in the range of 4.0 ng g(- 1) to 0.61 microg g(- 1).

Validation of an efficient method for the determination of pesticide residues in fruits and vegetables using ethyl acetate for extraction

In this study, a version of the "quick, easy, cheap, effective, rugged, and safe" (QuEChERS) method was modified to use ethyl acetate (EtOAc) rather than acetonitrile (MeCN) for extraction in the determination of multiple pesticide residues in fruits and vegetables. EtOAc is better suited than MeCN for gas chromatographic (GC) analysis with electron capture detection (ECD) and nitrogen-phosphorus detection (NPD). The method entailed extraction of 30 g chopped sample plus 5 g NaHCO(3) and 30 g anhydrous Na(2)SO(4) with 60 mL EtOAc using a probe blender. After a centrifugation step, removal of residual water and cleanup were performed using dispersive solid-phase extraction (dispersive-SPE) with MgSO(4) and primary secondary amine (PSA) sorbent. (14)C-labeled chlorpyrifos with liquid scintillation counting was used to assist in optimizing and characterizing the method, and GC-ECD and GC-NPD were used for analysis of 24 selected pesticides. The method was validated using tomato, apple and frozen green bean matrices spiked at 0.05, 0.5, and 5 mg/kg. For 22 of the analytes, recoveries averaged 93% for all three commodities over the validation range with a relative standard deviation of 10% (n = 1182). Lower recoveries of dichlorvos were obtained with the method and iprodione determination was compromised in the green beans by an interfering peak. Typical limits of detection were 0.005-0.01 mg/kg with the method.

A mass-balanced definition of corrected retention volume in gas chromatography

The mass balance equation of a chromatographic system using a compressible moving phase has been compiled for mass flow of the mobile phase instead of traditional volumetric flow allowing solution of the equation in an analytical form. The relation obtained correlates retention volume measured under ambient conditions with the partition coefficient of the solute. Compared to the relation in the ideal chromatographic system the equation derived contains an additional correction term accounting for the compressibility of the moving phase. When the retention volume is measured under the mean column pressure and column temperature the correction term is reduced to unit and the relation is simplified to those known for the ideal system. This volume according to International Union of Pure and Applied Chemistry (IUPAC) is called the corrected retention volume.

Ruggedness and robustness testing

Due to the strict regulatory requirements, especially in pharmaceutical analysis, analysis results with an acceptable quality should be reported. Thus, a proper validation of the measurement method is required. In this context, ruggedness and robustness testing becomes increasingly more important. In this review, the definitions of ruggedness and robustness are given, followed by a short explanation of the different approaches applied to examine the ruggedness or the robustness of an analytical method. Then, case studies, describing ruggedness or robustness tests of high-performance liquid chromatographic (HPLC), capillary electrophoretic (CE), gas chromatographic (GC), supercritical fluid chromatographic (SFC), and ultra-performance liquid chromatographic (UPLC) assay methods, are critically reviewed and discussed. Mainly publications of the last 10 years are considered.

Evaluation of Gas Chromatographic Isotope Fractionation and Process Contamination by Carbon in Compound-Specific Radiocarbon Analysis

The relevance of both modern and fossil carbon contamination as well as isotope fractionation during preparative gas chromatography for compound-specific radiocarbon analysis (CSRA) was evaluated. Two independent laboratories investigated the influence of modern carbon contamination in the sample cleanup procedure and preparative capillary gas chromatography (pcGC) of a radiocarbon-dead 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169) reference. The isolated samples were analyzed for their 14C/12C ratio by accelerator mass spectrometry. Sample Delta14C values of -996 +/- 20 and -985 +/- 20 per thousand agreed with a Delta14C of -995 +/- 20 per thousand for the unprocessed PCB 169, suggesting that no significant contamination by nonfossil carbon was introduced during the sample preparation process at either laboratory. A reference compound containing a modern 14C/12C ratio (vanillin) was employed to evaluate process contamination from fossil C. No negative bias due to fossil C was observed (sample Delta14C value of 165 +/- 20 per thousand agreed with Delta14C of 155 +/- 12 per thousand for the unprocessed vanillin). The extent of isotopic fractionation that can be induced during pcGC was evaluated by partially collecting the vanillin model compound of modern 14C/12C abundance. A significant change in the delta13C and delta14C values was observed when only parts of the eluting peak were collected (delta13C values ranged from -15.75 to -49.91 per thousand and delta14C values from -82.4 to +4.71 per thousand). Delta14C values, which are normalized to a delta13C of -25 per thousand, did not deviate significantly (-58.9 to -5.8 per thousand, considering the uncertainty of approximately +/-20 per thousand). This means that normalization of radiocarbon results to a delta13C of -25 per thousand, normally performed to remove effects of environmental isotope fractionation on 14C-based age determinations, also cor-rects sufficiently for putative isotopic fractionation that may occur during pcGC isolation of individual compounds for CSRA.

Effect of residues remaining in the injection liner of a gas chromatograph on the quantification of polycyclic aromatic hydrocarbons by isotope dilution mass spectrometry using deuterium-labeled internal standards

We have investigated the differences in response ratios of native polycyclic aromatic hydrocarbons (native PAHs)/13C-labeled PAHs (13C-PAHs) and of native PAHs/deuterium-labeled PAHs (PAHs-d) in a calibration solution containing at trace concentrations (< 1 microg mL(-1)) by gas chromatography-mass spectrometry. Only the ratios of native PAHs/PAHs-d decreased significantly (p < 0.05) accompanied with increase of residue amounts originated from immediately before injected solution. Since the analytical results using PAHs-d as internal standards were significantly lower than those using 13C-PAHs whatever solutions were injected immediately before (p < 0.05, 1.9-13.2%), 13C-PAHs gave more accurate results.

Determination of eight synthetic pyrethroids in bovine fat by gas chromatography with electron capture detection

Synthetic pyrethroids are among the most widely used classes of insecticides, and their uses are varied, including plant protection, animal dips, and as a treatment for human clothing and bedding in very hot climates. Veterinary applications include ear tags, pour-on formulations, sprays, and dips. Persistent residues have been reported in livestock, and routine monitoring programs in other countries have found detectable residues of various pyrethroids in fat. A method has been developed using solid-phase extraction that reduces the quantities of solvents used, the time required, and the amount of glassware used compared to an earlier method on which it was based. The scope of analytes tested included the 5 compounds cited in the earlier method (flucythrinate, permethrin, cypermethrin, fenvalerate, and deltamethrin) and, in addition, cyfluthrin, lambda-cyhalothrin, and fluvalinate. Sample extracts were analyzed by gas chromatography with electron capture detection using selected chromatographic peaks characteristic of each compound. Limits of quantification for the compounds were from 25-50 microg/kg, with a linear response for all compounds to 200 microg/kg. Recoveries ranged from 80 to 123%.

Homocysteine

Elevated homocysteine levels are associated with a variety of vascular diseases. Specifically, hyperhomocysteinemia is a risk factor for coronary artery disease, cerebrovascular disease, and peripheral arterial disease. Laboratory-based strategies for its detection and quantification have evolved to meet the increasing need for accuracy in risk prediction. Although new technologies have been developed over the past 2 decades that have enhanced the precision of measurement, universal guidelines for circulating homocysteine determination remain lacking.

Investigation to find a suitable reference material for use as an inverse gas chromatography system suitability test

The purpose of this study was to find a suitable material for use as a system suitability test material for inverse gas chromatography (IGC). The purpose of a system check is to measure the variability of the instrument being used rather than the material being analysed. Having such a system check for IGC enables a basic GMP requirement to be met. IGC results can then be used in regulatory submissions to support other already established techniques for characterising pharmaceutical materials. Alpha-alumina was chosen because it is inorganic, stable at high temperatures, resistant to hydration and is already established as a system check material for surface area determination by nitrogen adsorption. Two columns (1 and 2) packed from the same reference sample jar of alpha-alumina and analysed under the same conditions yielded dispersive surface energies of 34.8+/-0.8 and 35.3+/-0.8 mJ/m(2), respectively, at 15% RH. Column 1 was analysed on a second IGC system, and gave a dispersive surface energy of 34.7+/-0.2 mJ/m(2). No significant change was evident after 7 months storage under laboratory ambient conditions. Analysis of material from a second reference sample jar of alpha-alumina produced results not noticeably different to those of the first, yielding a dispersive surface energy of 35.3+/-0.1 mJ/m(2). A change was seen to occur in the surface properties alpha-alumina when the humidity was varied, but the change appeared to be consistent across the two columns reported. Based upon the data in this experimental, alpha-alumina appears to be a suitable material for use as a system suitability test material for IGC.

Determination of volatile residual solvents in pharmaceutical products by headspace liquid-phase microextraction gas chromatography-flame ionization detector

This paper demonstrates headspace liquid-phase microextraction (HS-LPME) as used for the determination of volatile residual solvents in pharmaceutical products. This method is based on headspace liquid-phase microextraction capillary column gas chromatography. Under optimum conditions, the linerary of the method ranged from 1 to 1,000 mg l(-1). The limits of detection are 0.2-6.0 [corrected] mg l(-1) and relative standard deviations (RSD) for most of the volatile solvents were below 10%. This novel method is applied to the analysis of volatile residual solvents in pharmaceutical products with satisfactory results.

Application of ethyl esters and d3-methyl esters as internal standards for the gas chromatographic quantification of transesterified fatty acid methyl esters in food

Ethyl esters (FAEE) and trideuterium-labeled methyl esters (d3-FAME) of fatty acids were prepared and investigated regarding their suitability as internal standards (IS) for the determination of fatty acids as methyl esters (FAME). On CP-Sil 88, ethyl esters of odd-numbered fatty acids eluted approximately 0.5 min after the respective FAME, and only coelutions with minor FAME were observed. Depending on the problem, one or even many FAEE can be added as IS for the quantification of FAME by both GC-FID and GC-MS. By contrast, d3-FAME coeluted with FAME on the polar GC column, and the use of the former as IS requires application of GC-MS. In the SIM mode, m/z 77 and 90 are suggested for d3-methyl esters of saturated fatty acids, whereas m/z 88 and 101 are recommended for ethyl esters of saturated fatty acids. These m/z values give either no or very low response for FAME and can thus be used for the analysis of FAME in food by GC-MS in the SIM mode. Fatty acids in sunflower oil and mozzarella cheese were quantified using five saturated FAEE as IS. Gravimetric studies showed that the transesterification procedure could be carried out without of loss of fatty acids. GC-EI/MS full scan analysis was suitable for the quantitative determination of all unsaturated fatty acids in both food samples, whereas GC-EI/MS in the SIM mode was particularly valuable for quantifying minor fatty acids. The novel GC-EI/MS/SIM method using fatty acid ethyl esters as internal standards can be used to quantify individual fatty acids only, that is, without determination of all fatty acids (the common 100% method), although this is present. This was demonstrated by the exclusive quantification of selected fatty acids including methyl-branched fatty acids, erucic acid (18:1n-9trans), and polyunsaturated fatty acids in cod liver oil and goat's milk fat.

An improved gas chromatography for rapid measurement of CO2, CH4 and N2O

Combining improved injector, gas line and valve-driving modules, a GC equipped with FID and ECD, could simultaneously measure CH4, CO2 and N2O in an air sample within 4 min. Test results showed that the system has high sensitivity, resolution and precision; the linear response range of the system meets the requirement of in situ flux measurements. Thus, the system is suitable for monitoring fluxes of main greenhouse gases in terrestrial ecosystem since it is easy to use, efficacious, stable and reliable to collect data.

Development of quantitative structure gas chromatographic relative retention time models on seven stationary phases for 209 polybrominated diphenyl ether congeners

Quantitative structure retention relationships (QSRRs) were developed to predict the gas chromatographic (GC) relative retention times (RRTs) for 209 polybrominated diphenyl ether (PBDE) congeners using the heuristic method included in the computer software Comprehensive Descriptors for Structural and Statistical Analysis (CODESSA). A total of 445 constitutional, topological, geometrical, electrostatic, and semi-empirical quantum chemical descriptors were derived for all PBDEs. Using experimental RRT data for 126 PBDE congeners from the literature, predictive regression models were built for seven individual GC capillary columns differing in stationary phases. Each model includes four descriptors which included Wiener index, Randic index, polarity parameter, etc., selected by CODESSA. High predictability was obtained. High multiple correlation coefficients R(2) indicated that >98.5% (except for stationary phase CP-Sil 19) of the total variation in the predicted RRTs is explained by the fitted models. The models were subsequently used to predict the RRTs of the remaining 83 PBDE congeners on seven different stationary phases. The statistical results show that, compared with others, DB-XLB column not only produces the least number of peak overlaps but also results in shorter retention times.

Investigation of compound-independent calibration and partial molecular formula determination by gas chromatography–atomic-emission detection for characterisation of organophosphorus and organosulfur agents related to the chemical weapons convention

Atomic-emission detection (AED) is a technique particularly-well suited to screening complex samples for multiple compounds containing heteroatoms such as phosphorus, sulfur, or nitrogen, which are especially relevant in verification of chemical disarmament. Among other GC detectors, AED has unique characteristics such as compound-independent calibration and possible raw-formula determination. Because contradictory results have been reported on these points, we set up a study with the objectives not only of applying these techniques to chemical weapons convention-related chemicals but of determining under which conditions they would yield satisfactory results. The extensive data collected in this study are evidence that the response of the detector, particularly for the phosphorus line, is very dependent on the molecular mass and concentration of the chemicals analysed whereas molecular structure seems to have less effect on the AED signal. Most interestingly, compound-independent calibration and subsequent partial molecular formula determination usually seem satisfactory when the reference compounds used to calibrate the system have GC retention times and molecular masses close to those of the unknown analytes (whose molecular mass may be determined by GC-CI-MS). We therefore suggest the use of a reference set of compounds covering a large chromatographic window, which enables the selection, within this set, of the most appropriate reference compound for calibration and for determination of the raw formula of an unknown analyte. For optimal performance, the use of a new discharge tube is also recommended.

Long-term stability of pure standards and stock standard solutions for the determination of pesticide residues using gas chromatography

The regular replacement of pure standards used in pesticide residue analysis laboratories and frequent preparation of stock standard solutions, both required by many accreditation bodies, impose considerable demands on a laboratory's resources. In this study, pure standards for all but one (heptenophos) of 118 different pesticides amenable to analysis by GC, and stock standard solutions (1000 microg/ml) prepared from these in toluene, acetone or ethyl acetate have been shown to be stable at < or = -20 degrees C over long periods: 4-13 and 2-8 years, respectively, for pure standards and solutions. Suitable solvents, containers and handling procedures are essential to avoid evaporation from solutions.

Predicting gas chromatographic retention times of 209 polybrominated diphenyls (PBBs) for different temperature programs

A method has been developed to predict the retention times of 209 individual polybrominated diphenyl congeners for different temperature programs. The retention equations lnk'=A+B/T of five PBBs in gas chromatography (GC) were used to evaluate the properties of the regression coefficients A and B, which are widely accepted as being highly reliable chromatographic retentions. The quantitative relationships between the A and B values of PCBs and those of PBBs were found. The regression equations derived have coefficients of determination greater than 0.999. The A, B values of any PBB can be predicted by using the A, B values of the PCB according to these relationships. Using these predicted A and B values, the retention times of all PBBs can be predicted. This is an important advance in the identification of PBBs because at present there are only a few PBB standards available.

A simplified method for analysis of polyunsaturated fatty acids

Background

Analysis of fatty acid composition of biological materials is a common task in lipid research. Conventionally, preparation of samples for fatty acid analysis by gas chromatography involves two separate procedures: lipid extraction and methylation. This conventional method is complicated, tedious and time consuming. Development of a rapid and simple method for lipid analysis is warranted.

Results

We simplified the conventional method by combining the extraction and methylation into a single step (omitting the procedure of prior extraction). Various biological samples including cultured cells, animal tissues and human specimens have been tested using the new method. Statistical analysis indicates that the recovery of long chain fatty acids from tissue samples by the simplified method is significantly higher than that by the traditional method, but there is no difference in relative fatty acid composition between the two methods. This simplified method can significantly save time and materials, and reduce the potentials of sample loss and contamination.

Conclusion

The lipid extraction procedure prior to methylation employed conventionally in lipid analysis can be omitted without affecting the recovery of long chain (≥ 18 C) fatty acids and their composition. The simplified method is rapid, easy-to-use, suitable for analysis of total long chain polyunsaturated fatty acid contents (e.g. n-6 and n-3 fatty acids) in various biological samples, especially when the number of samples to be analyzed is large and/or the specimen size is small.

Trichothecenes: reference materials and method validation

The frequent contamination of food and feed with trichothecene mycotoxins, the high consumption of these products, and the potential risk associated herewith, has led to an increasing public awareness and therefore to the establishment of measures to control trichothecene contamination. The analytical difficulty and the economic importance of controlling trichothecenes in food and feed support the need for certified reference materials (CRMs) and validated methods. They form invaluable tools to ensure comparability and traceability in analytical measurements and are very useful for the implementation of written standards, legislation/regulations and laboratory accreditation. The present paper provides an overview of previous work, current strategies and prospectives for the production of CRMs and validation of analytical methods in the field of trichothecene analysis. Additional information is given on methodological demands, normative frameworks and commonly accepted procedures.

Interlaboratory comparison to evaluate a standardized calibration procedure for the headspace analysis of aromatic solvents in blood

The determination of volatile organic compounds in blood by headspace gas chromatography is one of the central and long-established analytical techniques in occupational medical biomonitoring. Nevertheless, the relatively low success rate in intercomparison programs shows that the headspace technique is insufficiently standardized. A critical stage of the analytical procedure seems to be the preparation of calibration standards in biological matrices. As part of an extensive interlaboratory comparison by the Analyses of Hazardous Substances in Biological Materials working group of the DFG Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area, three typical procedures were compared with one another using typical aromatic solvents as an example. The best correlations between the participating laboratories and the best results for the analyses of samples from interlaboratory comparisons were obtained when highly concentrated stock solutions of the aromatic compounds in ethanol were first diluted with physiological saline and then used for spiking horse blood in headspace vials. This procedure can be easily standardized and is therefore recommended by the Analyses of Hazardous Substances in Biological Materials working group for the preparation of headspace calibration standards for aromatic compounds.

Validation of a gas chromatographic method for determining fatty acids that compose D003 in 10 mg film-coated tablets

D003 is a new product composed of a mixture of aliphatic fatty acids (C(24:0) to C(36:0)), which shows antiplatelet, antithrombotic, antioxidant, and cholesterol-lowering effects in experimental models and human beings. A gas chromatographic method using a DB-5 wide-bore column and 1-nonadecanoic acid as internal standard was developed and validated in order to determine D003 in 10 mg film-coated tablets. The acids were analysed as methyl esters derivatives, prepared using 5% aqueous HCl-methanol. Developed method was specific for the active principle, even when samples were subjected to stress conditions. Good linearity (correlation coefficient > 0.99) and accuracy (total average recovery = 100.29%) were proven over a range 50-150% of the nominal concentration. Within-day and intermediate precisions at the nominal dose (100%) were < 1.5%. Robustness was examined through an intralaboratory study, quantification and resolution were only affected by the injection volume increase and no other of the 7 operational changes evaluated affected the results. The method was suitable for quality control and stability studies of these tablets.

Determination of gas–liquid partition coefficients by gas chromatography

This review covers theoretical principles and experimental procedures for the determination of gas-liquid partition coefficients, KL, by gas chromatography. In order to precisely define the relationship between KL, retention time and experimental parameters, the retention theory, both for ideal and for imperfect gas phase, is expounded. The most important sources of systematic error, as peak asymmetry, mixed retention mechanisms, column hold-up time and stationary phase mass determination, are discussed. Although the review is focussed on packed columns, comparison to capillary columns is discussed in those aspects in which these last show advantages.

Determination of endosulfan residues in eggplant (Solanum melongena) by ELISA

Eggplant samples were analyzed for endosulfan residues using ELISA, a technique recognized as a promising tool for screening environmental contaminants. Calibration curve for endosulfan was standardized using kits developed by CFTRI Mysore. Farm gate samples of eggplant from 12 different locations were analyzed. The matrix effect was removed by charcoal clean-up. The results were compared with gas chromatographic (GC) analysis. The residues in different samples were in the range of 5-226 ppb. Correlation coefficient between the two methods was found to be 0.98.

Challenges with fats and fatty acid methods

The content and chemical nature of lipids in feedstuffs is heterogeneous. It has long been known that ether extraction by the Weende procedure inadequately characterizes the fat content of feedstuffs, yet it remains the official method. Diethyl ether (or hexanes that are often used) extracts significant amounts of nonnutritive, nonsaponifiable lipids from forages, and often incompletely extracts lipids of nutritional value, especially fatty acids present as salts of divalent cations. Preextraction hydrolysis of insoluble fatty acid salts with acid releases these fatty acids, and this step is included in the official procedure for certain feedstuffs in the United Kingdom; however, acid hydrolysis increases analysis time and decreases precision. Acid hydrolysis also causes confusion as to the proper definition of the fat content of feedstuffs. A preferred method of fat analysis determines the total fatty acid concentration in feed samples by converting fatty acid salts, as well as the acyl components in all lipid classes, such as triacylglycerols, phospholipids, and sphingolipids, to methyl esters using a simple, direct one-step esterification procedure. Fatty acid methyl esters are then quantified by GLC, which provides information on both fatty acid quantity and profile in a single analysis. Adjustments in conditions and reagents may be necessary to overcome difficulty in quantitatively preparing esters from certain types of fatty acids and their derivatives in commercial fat supplements. After correction for glycerol content, analysis of oils by this procedure provides information on the content of nonsaponifiable material, such as chlorophyll, waxes, and indigestible polymers formed from heat- or oxidatively damaged fats. The correct description of feedstuffs for energy value of fats is the content of total fatty acids.

Development of a gas chromatography/ion trap mass spectrometry based method for the quantification of polybrominated diphenyl ethers and polychlorinated biphenyls in adipose tissue

A combined gas chromatographic mass spectrometric (GC/MS/MS) method for the determination of seven polybrominated diphenyl ethers (PBDEs) and seven marker polychlorinated biphenyls (PCBs) in adipose tissue has been developed. Adipose tissue was melted and filtered through anhydrous sodium sulphate to obtain pure fat. Clean-up was performed using a glass column containing acidified silica, deactivated alumina and anhydrous sodium sulphate. Polybrominated biphenyl (PBB) 155 and Mirex were added as internal standards for PBDEs and PCBs, respectively. Injection standards, PBB 103 and PCB 143, for PBDEs and PCBs, respectively, were added before analysis with GC/MS/MS. The developed GC/MS/MS method has the advantage of being more selective than single MS methods because matrix effects are largely eliminated. Validation of this method was conducted according to Commission Decision 2002/657/EC. Decision limits for PBDEs and PCBs ranged from 0.06-0.15 ng g(-1) and from 0.35-1.22 ng g(-1), respectively. Detection capabilities were all between 0.23-0.55 ng g(-1) for PBDEs and between 0.98-2.29 ng g(-1) for PCBs. Precision, recovery, bias and selectivity were tested, with satisfactory results.

An Improved Method for the Analysis of Dimethyl Sulfoxide in Water Samples

An analytical method for dimethyl sulfoxide (DMSO) in aqueous samples at nanomolar levels has been improved. DMSO was reduced to dimethyl sulfide (DMS), concentrated on an adsorbent, and measured by gas chromatography. In the presence of iron chloride, the sodium borohydride (NaBH4) reduction of DMSO proceeded smoothly and efficiently, and the repeatability of this reaction was significantly improved. The detection limit was 0.27 nM for DMSO, and its repeatability of the peak-area measurement was 4.1% as RSD (n = 5).

Interlaboratory variability in the quantification of new generation antiepileptic drugs based on external quality assessment data

PURPOSE

To assess interlaboratory variability in the determination of serum levels of new antiepileptic drugs (AEDs).

METHODS

Lyophilised serum samples containing clinically relevant concentrations of felbamate (FBM), gabapentin (GBP), lamotrigine (LTG), the monohydroxy derivative of oxcarbazepine (OCBZ; MHD), tiagabine (TGB), topiramate (TPM), and vigabatrin (VGB) were distributed monthly among 70 laboratories participating in the international Heathcontrol External Quality Assessment Scheme (EQAS). Assay results returned over a 15-month period were evaluated for precision and accuracy.

RESULTS

The most frequently measured compound was LTG (65), followed by MHD (39), GBP (19), TPM (18), VGB (15), FBM (16), and TGB (8). High-performance liquid chromatography was the most commonly used assay technique for all drugs except for TPM, for which two thirds of laboratories used a commercial immunoassay. For all assay methods combined, precision was <11% for MHD, FBM, TPM, and LTG, close to 15% for GBP and VGB, and as high as 54% for TGB (p < 0.001). Mean accuracy values were <10% for all drugs other than TGB, for which measured values were on average 13.9% higher than spiked values, with a high variability around the mean (45%). No differences in precision and accuracy were found between methods, except for TPM, for which gas chromatography showed poorer accuracy compared with immunoassay and gas chromatography-mass spectrometry.

CONCLUSIONS

With the notable exception of TGB, interlaboratory variability in the determination of new AEDs was comparable to that reported with older-generation agents. Poor assay performance is related more to individual operators than to the intrinsic characteristics of the method applied. Participation in an EQAS scheme is recommended to ensure adequate control of assay variability in therapeutic drug monitoring.