Determination of trace amounts of off-flavor compounds in drinking water by stir bar sorptive extraction and thermal desorption GC-MS

Volatile organic compounds in preen oil and feathers - a review

For a long time birds were assumed to be anosmic or at best microsmatic, with olfaction a poorly understood and seldom investigated part of avian physiology. The full viability of avian olfaction was first discovered through its functions in navigation and foraging. Subsequently, researchers have investigated the role of olfaction in different social and non-social contexts, including reproduction, kin recognition, predator avoidance, navigation and foraging. In parallel to the recognition of the importance of olfaction for avian social behaviour, there have been advances in the techniques and methods available for the sampling and analysis of trace volatiles and odourants, leading to insights into the chemistry underlying chemical communication in birds. This review provides (i) an overview of the current state of knowledge regarding the volatile chemical composition of preen oil and feathers, its phylogenetic coverage, chemical signatures and their potential functions, and (ii) a discussion of current methods used for the isolation and detection of volatiles. Finally, lines for future research are proposed.

An automated micro solid phase extraction gas chromatography-mass spectrometry (μSPE-GC-MS) detection method for geosmin and 2-methylisoborneol in drinking water

Geosmin and 2-methylisoborneol (2-MIB) are amongst the most common earthy and musty taste and odour (T&O) compounds found in drinking water. With low odour threshold detection limits below 10 ng L^-1, and the complexity of raw water matrices, these two compounds provide a significant challenge for water companies globally. In this research, for the first time, a novel and fully automated micro-solid phase-extraction (μSPE) method coupled with gas chromatography (GC)-mass spectrometry (MS) has been developed for the detection of geosmin and 2-MIB for drinking water analysis. The new automated method described herein is environmentally friendly requiring low raw water sample volumes, of 25 mL, and only 50 μL of elution solvent. Our μSPE-GC-MS method exhibits excellent linearity for both compounds (R² > 0.999) and low limits of detection of 2.0 ng L^-1 and 4.3 ng L^-1 for geosmin and 2-MIB, respectively. The method showed excellent recovery rates (95.1-100.1%) and good precision (RSD < 7%) in raw sample matrices. Our approach is fully automated onto a robotic workstation which can be readily integrated into a laboratory workflow for routine water analysis. Furthermore, the method has excellent potential to be incorporated within a portable system for onsite analysis.

Quality Evaluation of Drinks Based on Liposome Shape Changes Induced by Flavor Molecules

The flavors of ethyl caproate and isoamyl acetate and their precursors are crucial in sake brewing for fermentation and evaluation of the corresponding quality of drinks. However, the quality evaluation of drinks containing these flavors is challenging. Therefore, sake quality was evaluated via dynamic membrane transformation on cell-sized liposomes while adding flavor-containing solutions. Flavor varieties have been reported to influence dynamic shape change patterns. This study reports the observed difference in the dynamic shape change of each flavor. Based on these results, proper quality evaluation of drinks is expected.

Off-Flavors in Aquacultured Fish: Origins and Implications for Consumers

Off-flavors in fish and water are considered a worldwide problem. Several factors, such as the presence of phosphorus, micronutrients, and organic matter, contribute to phytoplankton proliferation and the production of off-flavors. Geosmin and 2-methylisoborneol are the most common off-flavors that confer the smell of earth or mold to water and fish. These metabolites are not considered toxic, but they can be easily transferred from water to living organisms and accumulate in the biota, up the trophic levels and to consumers, including fish species. Numerous processes have been studied to eliminate or reduce the presence of off-flavors in recirculating aquaculture systems. Managing off-flavors must be eco-friendly and consumer-friendly. Strategies against off-flavors must be efficient and low-cost. However, these solutions may be different for each fish production system. We review herein the main compounds produced by cyanobacteria that can accumulate in fish used in aquaculture that can affect the quality of food, as well as production costs and consumer preference.

Characterization of cheesy odor formed during fermentation of soy drink with Agrocybe aegerita

The market for plant protein-based substitutes for cheeses is growing, but the sensory properties are distinctively different from the original products. Hence, natural and vegan cheesy flavors are needed to aromatize the products. A cheesy, sweaty and parmesan-like aroma was produced by fermentation of soy drink with Agrocybe aegerita. Aroma dilution analysis revealed short-chain fatty acids (SCFAs) as main influencing cheesy odorants analyzed by gas chromatography-mass spectrometry-olfactometry. In comparison to the five cheese varieties, the SCFA profile of the fermented soy drink revealed similarities with Parmesan and Emmental cheese. Meanwhile, principal component analysis showed an approximation of the aroma profile after fermentation with A. aegerita to those of cheeses. 3-Methylbutanoic acid was synthesized from the protein fraction, while the oil fraction contributed to the formation of unbranched SCFAs like butanoic acid. Accordingly, the production of these compounds can be increased by addition of the fractions.

[Study for Formation Root of Off-Flavor Substance 2-Iodo-4-methylphenol in Milk]

Food can sometimes contain odors not normally associated with that food. These odors are called off-flavors, and cow milk is known to contain off-flavors such as hexanal depending on the feed or physical condition of the cows. We previously discovered and revealed the structure of 2-Iodo-4-methylphenol (2I4MP), an off-flavor component in commercially available cow milk. We were the first group to discover 2I4MP is an off-flavor component in cow milk.This study investigated the following three questions. First, what compounds serve as the starting materials in generating 2I4MP? Organic synthesis techniques were used to identify p-cresol as a candidate starting material. Second, how is 2I4MP generated in the cowshed? Using cow dung, we confirmed that 2I4MP was generated by the effects of iodine on cow dung. Based on these findings, measures were proposed to prevent contamination of cow milk by 2I4MP. Third, how is 2I4MP transferred to raw milk? 2I4MP movement was estimated by creating a desiccator-based model that showed 2I4MP is potentially transferred to raw milk in the cowshed. These involve that the iodine-based disinfectants, used to disinfect teats during milking, should not be used excessively. Furthermore, ensuring the disinfectants do not fall onto cow dung or bedding. Adopting these measures is vital for preventing contamination of cow milk by 2I4MP.

The formation, analysis, and control of chlor(am)ination-derived odor problems: A review

Odors and tastes have become universal problems related to drinking water quality. In addition to the typical odor problems caused by algae or microorganisms, the occurrence of odors derived from drinking water disinfection have attracted attention. The chlor(am)ination-derived odor substances have certain toxicity and odor-causing characteristics, and would enter the tap water through water distribution systems, directly affecting drinking water safety and customer experience. This study provided a comprehensive overview of the occurrence, detection, and control of odor substances derived from drinking water chlor(am)ination disinfection. The occurrence and formation mechanisms of several typical types of disinfection derived odor substances were summarized, including haloanisoles, N-chloroaldimines, iodotrihalomethanes, and halophenoles. They are mainly derived from specific precursors such as halophenols, anisoles, and amino acids species during the disinfection or distribution networks. In addition, the change of disinfectant during chlor(am)ination was also one of the causes of disinfection odors. Due to the extremely low odor threshold concentrations (OTCs) of these odor substances, the effective sample pre-enrichment for instrument identification and quantification are essential. The control strategies of odor problems mainly include adsorption, chemical oxidation, and combined processes such as ozonation and biological activated carbon processes (O₃/BAC) and ultraviolet-based advanced oxidation processes (UV-AOPs). Finally, the challenges and possible future research directions in this research field were discussed and proposed.

Size of Cells and Physicochemical Properties of Membranes are Related to Flavor Production during Sake Brewing in the Yeast Saccharomyces cerevisiae

Ethyl caproate (EC) and isoamyl acetate (IA) are key flavor components of sake. Recently, attempts have been made to increase the content of good flavor components, such as EC and IA, in sake brewing. However, the functions of EC and IA in yeast cells remain poorly understood. Therefore, we investigated the effects of EC and IA using cell-sized lipid vesicles. We also investigated lipid vesicles containing EC and/or caproic acid (CA) as well as IA and/or isoamyl alcohol (IAA). CA and IAA are precursors of EC and IA, respectively, and are important flavors in sake brewing. The size of a vesicle is influenced by flavor compounds and their precursors in a concentration-dependent manner. We aimed to establish the conditions in which the vesicles contained more flavors simultaneously and with different ratios. Interestingly, vesicles were largest in a mixture of 50% of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) with 25% EC and 25% CA or a mixture of 50% DOPC with 25% IA and 25% IAA. The impact of flavor additives on membrane fluidity was also studied using Laurdan generalized polarization. During the production process, flavors may regulate the fluidity of lipid membranes.

Influence of Ethyl Caproate on the Size of Lipid Vesicles and Yeast Cells

Ethyl caproate (EC) is a key flavor component of sake. Recently, in sake brewing, an effort has been underway to increase the content of aromatic components such as EC. However, the function of EC in yeast cells remains poorly understood. Therefore, we investigated the effects of EC using cell-sized lipid vesicles. We found that vesicle size decreases in a concentration-dependent manner when EC is contained in lipid vesicles. Furthermore, yeast experiments showed that a strain producing high quantities of EC in its stationary phase decreased in size during EC production. Given caproic acid's (CA) status as the esterification precursor of EC in yeast, we also compared lipid vesicles containing CA with those containing EC. We found that CA vesicles were smaller than EC vesicles of the same concentration. These results suggest that EC production may function apparently to maintain cell size.

Development of a liquid chromatography atmospheric pressure chemical ionization mass spectrometry method for determining off-flavor compounds and its application toward marine recirculating aquaculture system monitoring and evaluation of aeration as a depuration approach

The off-flavor compounds geosmin and 2-methylisoborneol (2-MIB) are well-known to impact the quality of farmed freshwater fish species, but little is known about off-flavors in marine aquaculture. To begin addressing this knowledge gap, a method for determining geosmin and 2-MIB using LC with atmospheric pressure chemical ionization (APCI) MS detection was developed. While 2-MIB was readily detected using LC-APCI/MS, geosmin exhibited on-column degradation that was independent of column chemistry and could not be eliminated. Optimized conditions were identified that balanced the separation and ionization efficiency of 2-MIB and geosmin while minimizing geosmin degradation, but the overall method sensitivity for geosmin was reduced by the on-column losses. The method was used with direct aqueous injections to determine the volatilization rates of geosmin and 2-MIB at ppb levels during aeration under laboratory conditions in both salt water and pure water to simulate marine and fresh water aquaculture, respectively. The volatilization rates of both compounds were 30% faster in salt water than in fresh water with or without aeration, but aeration was found to enhance the rate by a factor of 2.5 in both water types. The LC-APCI/MS method was combined with stir bar sorptive extraction (SBSE) to achieve greater sensitivity for determining off-flavors in recirculating aquaculture system (RAS) water. Using SBSE-LC-APCI/MS, the LODs for geosmin and 2-MIB were 70 ng/kg (part per trillion) and 6 ng/kg, respectively. The on-column losses resulted in a relatively high LOD for geosmin that renders this method unsuitable for determining geosmin at the low ng/kg levels expected in RAS. SBSE using both grab water samples and an in-situ diving unit were used to evaluate 2-MIB levels in the culture water of two separate marine RAS that were supporting the growth of European sea bass but had differing levels of water treatment. 2-MIB was readily detected using both SBSE approaches in the RAS with less sophisticated treatment when the animal stocking density was at its highest (50 kg/m³) but was not detected in the more sophisticated RAS regardless of stocking density. Geosmin was not detected in either system, but the results were inconclusive given its higher LOD. These limited results suggest that the anaerobic water treatment components, present only in the more sophisticated RAS, maintained the level of 2-MIB below the LOD.

The role of algae and cyanobacteria in the production and release of odorants in water

This review covers literatures pertaining to algal and cyanobacterial odor problems that have been published over the last five decades. Proper evaluation of algal and cyanobacterial odors may help establish removal strategies for hazardous metabolites while enhancing the recyclability of water. A bloom of microalgae is a sign of an anthropogenic disturbance in aquatic systems and can lead to diverse changes in ecosystems along with increased production of odorants. In general, because algal and cyanobacterial odors vary in chemistry and intensity according to blooming pattern, it is necessary to learn more about the related factors and processes (e.g., changes due to differences in taxa). This necessitates systematic and transdisciplinary approaches that require the cooperation of chemists, biologists, engineers, and policy makers.

Simultaneous assessments of occurrence, ecological, human health, and organoleptic hazards for 77 VOCs in typical drinking water sources from 5 major river basins, China

Owing to the growing public awareness on the safety and aesthetics in water sources, more attention has been given to the adverse effects of volatile organic compounds (VOCs) on aquatic organisms and human beings. In this study, 77 target VOCs (including 54 common VOCs, 13 carbonyl compounds, and 10 taste and odor compounds) were detected in typical drinking water sources from 5 major river basins (the Yangtze, the Huaihe, the Yellow, the Haihe and the Liaohe River basins) and their occurrences were characterized. The ecological, human health, and olfactory assessments were performed to assess the major hazards in source water. The investigation showed that there existed potential ecological risks (1.30 × 10 ≤ RQtotals ≤ 8.99 × 10) but little human health risks (6.84 × 10(-7) ≤ RQtotals ≤ 4.24 × 10(-4)) by VOCs, while that odor problems occurred extensively. The priority contaminants in drinking water sources of China were also listed based on the present assessment criteria.

Simultaneous determination of ten taste and odor compounds in drinking water by solid-phase microextraction combined with gas chromatography-mass spectrometry

Taste and odor (T&O) problems in drinking water frequently occur because of many compounds present in the water, of which trans-1,10-dimethyl-trans-9-decalol (geosmin) and 2-methylisoborneol (MIB) are well-known. In this study, a fast and effective method was established for simultaneous determination of 10 T&O compounds, including geosmin, MIB, 2,4,6-trichloroanisole (TCA), 2-methylbenzofuran, 2-isopropyl-3-methoxypyrazine (IPMP), 2-isobutyl-3-methoxypyrazine (IBMP), cis-3-hexenyl acetate, trans,trans-2,4-heptadienal, trans, cis-2,6-nonadienal, and trans-2-decenal in water samples by headspace solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry. An orthogonal array experimental design was used to optimize the effects of SPME fiber, extraction temperature, stirring rate, NaCI content, extraction time, and desorption time. The limits of detection ranged from 0.1 to 73 ng/L were lower than or close to the odor threshold concentrations (OTCs). All the 10 T&O compounds were detected in the 14 water samples including surface water, treatment process water and tap water, taken from a waterworks in Lianyungang City, China. MB and geosmin were detected in most samples at low concentration. Six T&O compounds (IPMP, IBMP, trans,cis-2,6-nonadienal, 2-methylbenzofuran, trans-2-decenal, and TCA) were effectively decreased in water treatment process (sedimentation and filtration) that is different from cis-3-hexenyl acetate, MIB and geosmin. It is noted that the TCA concentrations at 15.9-122.3 ng/L and the trans,cis-2,6-nonadienal concentrations at 79.9-190.1 ng/L were over 10 times higher than their OTCs in tap water. The variation of the analytes in the all water samples, especially distribution system indicated that distribution system cannot be ignored as a T&O compounds source.

Simultaneous quantitation of volatile compounds in citrus beverage through stir bar sorptive extraction coupled with thermal desorption-programmed temperature vaporization

Due to disparate concentrations and physiochemical properties of analytes, difficulties in terms of sensitivity and reproducibility are commonly encountered in flavour analysis. In this study, we attempted to improve the performance of stir bar sorptive extraction coupled with thermal desorption and programmed temperature vaporization (SBSE-TD-PTV) based on a model citrus beverage. Through response surface methodology, thermal desorption conditions (i.e. desorption flow, thermal desorption time and cryofocusing temperature) were optimised based on constrained optimisation. Solute discrimination during injection was alleviated by normalising the variability of peak responses of different analytes. In addition, the effects of extraction conditions (i.e. ionic strength, stirring speed, extraction time, temperature and pH) were also investigated using partial factorial design. The obtained method showed high precision and good linearity over the concentration ranged from 0.10 to 20.00 μg L(-1) with the correlation coefficients higher than 0.991 for most of the selected chemicals, except indole. The limit of detection ranged from 0.03 to 3.89 μg L(-1). Hence, our results indicated that through the systematic study, SBSE-TD-PTV method became much less solute discriminative and more reliable to quantitate complex analytes.

Development of polypropylene coated hollow fiber membranes as passive sampler for field equilibrium sampling of odorous compounds in environmental waters

A new passive sampling device was developed for field equilibrium sampling of geosmin (GSM) and 2-methylisoborneol (MIB) in surface water. The sampling device was prepared by coating a 50 cm length polypropylene hollow fiber tubing (50 μm wall thickness, 280 μm inner diameter) with polypropylene glycol 4000. The sampler was brought into equilibrium with the sample in the field, and then transferred and immersed into 100 μL of methanol held in a little desorption device for room temperature desorption and preservation of the sampled analytes. After being transported to the laboratory, the analytes were determined by headspace solid-phase microextraction-GC-MS. The large surface area-to-volume ratio of the developed sampler facilitated the reaching of sampling equilibrium in 1 h, while the equilibrium sampling minimized the effects of environmentally relevant sampling conditions. Variation of sample pH (4.0-9.0) and salinity (0-100 mM NaCl) had no significant effects on the distribution coefficients of analytes to the sampler. The desorption device, constructed with a 200 μL glass insert, and a 2 mL brown glass vial with PTFE sealed screw cap, has no loss of analytes during the storage of the sampler. The proposed procedure had detection limits of 4 and 9 ng L-1 for GSM and MIB, respectively. This developed sampler was successfully applied to field sampling in Taihu Lake (China), with MIB and GSM detected in the range of 0.11-0.61 μg L-1 during a medium out-break of blue-green algae bloom.

Formation of pyrazines in Maillard model systems of lysine-containing dipeptides

Whereas most studies concerning the Maillard reaction have focused on free amino acids, little information is available on the impact of peptides and proteins on this important reaction in food chemistry. Therefore, the formation of flavor compounds from the model reactions of glucose, methylglyoxal, or glyoxal with eight dipeptides with lysine at the N-terminus was studied in comparison with the corresponding free amino acids by means of stir bar sorptive extraction (SBSE) followed by GC-MS analysis. The reaction mixtures of the dipeptides containing glucose, methylglyoxal, and glyoxal produced 27, 18, and 2 different pyrazines, respectively. Generally, the pyrazines were produced more in the case of dipeptides as compared to free amino acids. For reactions with glucose and methylglyoxal, this difference was mainly caused by the large amounts of 2,5(6)-dimethylpyrazine and trimethylpyrazine produced from the reactions with dipeptides. For reactions with glyoxal, the difference in pyrazine production was rather small and mostly unsubstituted pyrazine was formed. A reaction mechanism for pyrazine formation from dipeptides was proposed and evaluated. This study clearly illustrates the capability of peptides to produce flavor compounds that can differ from those obtained from the corresponding reactions with free amino acids.

Application of a headspace sorptive extraction method for the analysis of volatile components in South African wines

A headspace sorptive extraction (HSSE) in combination with thermal desorption gas chromatography-mass spectrometry (TD-GC-MS) method for the analysis of volatile components (alcohols, esters, carbonyls, acids, phenols and lactones) in wine samples was developed. Extraction conditions such as salting-out effects, sorption time, stirring speed, phase ratio, extraction temperature, and effect of pH were thoroughly evaluated as part of method validation. The method was very sensitive with LODs and LOQs between 50 pg/L to 299 microg/L and 0.2 ng/L to 0.996 microg/L, respectively. Repeatability for all the compounds was between 3 and 22%. The intermediate repeatability was obtained within the acceptable range. Out of 39 volatile compounds selected, 37 were detected and quantitated. The method was found to be simple, cost-effective, sensitive, and use a small sample volume. The method was successfully applied for the routine analysis of 79 young red and white wine samples from various South African districts.

Stir bar sorptive extraction for the determination of pyrethroids in water samples

Stir bar sorptive extraction (SBSE) was applied to the enrichment of pyrethroids in water samples. Analysis was done by retention time-locked GC/MS in selected ion-monitoring (SIM) mode using trans-permethrin-d(6) as internal standard. Thermal desorption (TD) was performed in a classical split/splitless inlet equipped with a flip-top sealing system and in a dedicated thermal desorption unit. These two thermal desorption methods were compared to liquid desorption with ethyl acetate. Sensitivity was the highest for thermal desorption in the dedicated system and the lowest for liquid desorption even at injection volumes of 10 microL. The SBSE-TD-GC/MS method is able to determine pyrethroids at ultra-trace level (<1 ng/L) with RSD% smaller than 15 (n=6).

Application of a polysiloxane-based extraction method combined with large volume injection-gas chromatography-mass spectrometry of organic compounds in water samples

This work describes a novel, simple, and inexpensive approach for an absorptive extraction of organic contaminants from aqueous samples applying polysiloxane tubes. After the extraction, the tubes were desorbed with 200 microL of an organic solvent and 50 microL of the extract were transferred via large volume injection (LVI) into a gas chromatography-mass spectrometry system (GC-MS). Fourteen organic compounds covering a broad range in polarity with log K(o/w)-values between 2.6 (atrazine) and 7 (polychlorinated biphenyl 138, PCB 138) were chosen as model compounds. The experimental parameters affecting the efficiency of the process such as desorption solvents, the addition of salt and pH-change, the extraction and desorption time were carefully optimised. The recoveries were compared with theoretical values. The limits of detection (LODs) were in the range of 0.5-5 ng/L and the precision was 7-15%. The method was successfully applied to the analysis of a contaminated river water sample.

Stir bar sorptive extraction for trace analysis

Stir bar sorptive extraction (SBSE) was introduced in 1999 as a solventless sample preparation method for the extraction and enrichment of organic compounds from aqueous matrices. The method is based on sorptive extraction, whereby the solutes are extracted into a polymer coating on a magnetic stirring rod. The extraction is controlled by the partitioning coefficient of the solutes between the polymer coating and the sample matrix and by the phase ratio between the polymer coating and the sample volume. For a polydimethylsiloxane coating and aqueous samples, this partitioning coefficient resembles the octanol-water partitioning coefficient. In comparison to solid phase micro-extraction, a larger amount of sorptive extraction phase is used and consequently extremely high sensitivities can be obtained as illustrated by several successful applications in trace analysis in environmental, food and biomedical fields. Initially SBSE was mostly used for the extraction of compounds from aqueous matrices. The technique has also been applied in headspace mode for liquid and solid samples and in passive air sampling mode. In this review article, the principles of stir bar sorptive extraction are described and an overview of SBSE applications is given.

Automated trace determination of earthy-musty odorous compounds in water samples by on-line purge-and-trap–gas chromatography–mass spectrometry

An automated technique based on purge-and-trap coupled to gas chromatography with mass spectrometric detection has been developed and optimized for the trace determination of five of the most important water odorants; 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, 2-methylisoborneol, 2,4,6-trichloroanisole and geosmin. The extraction method was absolutely solvent-free. Analytes were purged from 20 ml of water sample containing sodium chloride at room temperature by a flow of He and trapped on a Tenax sorbent. The desorption step was performed with helium and temperature programming and desorbed analytes were directly transferred to a gas chromatograph coupled to a mass spectrometer for separation and determination. The method was reproducible (RSD<8%) and linear over the calibration range (10-200 ngl(-1)). The relative recoveries of the analytes from ground water sample were calculated and were between 80 and 103% and limits of detection (LOD) below odor thresholds were achieved for most of the compounds.

Routine analysis of off-flavor compounds in water at sub-part-per-trillion level by large-volume injection GC/MS with programmable temperature vaporizing inlet

"Earthy-musty" off-flavor problem in water samples are due to organic compounds present at the sub-part-per-trillion level. Most of the developments in the analysis of tastes and odorous compounds focus on the extraction pre-concentration technique, with detection at picogram per liter level of the earthy-musty off-flavor compounds difficult to be achieved. The objective of this study is to develop a new method involving the large-volume injection (LVI) GC/MS via programmable temperature vaporizing (PTV) inlet and continuous liquid-liquid extraction, to attain analytical sensitivity equal to or better than olfactory sensitivity. Six "earthy-musty" organic compounds, 2-methylisoborneol (MIB), geosmin, 2,4,6-trichloroanisole, 2,3,6-trichloroanisole, 2,3,4-trichloroanisole and 2,4,6-tribromoanisole, were used as probes for this study. It was found that LVI via PTV could greatly improve system sensitivity towards off-flavor compound detection. Variable instrument conditions and sample preparation conditions were studied in detail. This reliable and efficient method has been optimized and validated. The method detection limit were found to be from 35 to 70 pg/L for haloanisoles, 50 pg/L for geosmin and 0.34 ng/L for MIB, with relative standard deviation of calibration curve ranging from 4.7% to 15.1% and recovery ranging from 58% to 96%. This method has been successfully applied to test off-flavor compounds in different types of water samples with satisfactory results.

Dual derivatization–stir bar sorptive extraction–thermal desorption–gas chromatography–mass spectrometry for determination of 17β-estradiol in water sample

A novel method for the trace analysis of 17beta-estradiol (E2) in river water sample was developed, which involved stir bar sorptive extraction (SBSE) with in situ acylation (first derivatization) and thermal desorption (TD) with quartz wool assisted (QWA) in tube silylation (second derivatization), followed by gas chromatography-mass spectrometry (GC-MS), and is called the "dual derivatization method." The optimum conditions for SBSE with in situ acylation, such as the volume of acetic acid anhydride and the extraction time, were investigated. In addition, the optimum conditions for TD with QWA in tube silylation, such as the volume of N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and the TD temperature and hold time, were investigated as well. The detection limit (S/N = 3) and the quantitation limit (S/N>10) of E2 in the river water sample were 0.5 and 2 pg ml(-1) (ppt), respectively, by the dual derivatization method. In addition, the detection limit was 0.1 pg ml(-1) by using dual derivatization method with multi-shot mode. The calibration curve for E2 was linear in the range of 0.002-10 ng ml(-1) with correlation coefficients >0.999. The average recoveries of E2 (n = 6) at the concentrations of 0.05 and 1.0 ng ml(-1) from the river water sample were 93.1 (RSD: 1.4%) and 98.4% (RSD: 0.8%), respectively, with correction using the added surrogate standard, 17beta-estradiol-(13)C(4). This simple, accurate, sensitive and selective analytical method may be applicable to the determination of trace amounts of E2 in water samples.

Determination of 2-methylisoborneol and geosmin in aqueous samples by static headspace-gas chromatography-mass spectrometry with ramped inlet pressure

A method for determining the earthy and musty odors 2-methylisoborneol (2-MIB) and geosmin in drinking water using static headspace-GC-MS is described. To achieve lower detection limits, split ratio was optimized with ramped inlet pressure for large headspace sampling volume. The ramped inlet pressure, which held higher pressure (higher column flow rate) only during injection, allowed us to inject 3-mL volume to GC with very low split ratio (2:1). Although sequential analysis with a stainless steel ion source often changed the mass spectrum of 2-MIB, this spectral change was eliminated by using an inert ion source with a 6 mm drawout plate. The detection limits of this method were 0.36 and 0.14 ng/L, respectively, for 2-MIB and geosmin. The repeatabilities (n = 30) were 6.6 and 4.8%, respectively, at 1 ng/L for 2-MIB and geosmin.

Simultaneous picogram determination of “earthy-musty” odorous compounds in water using solid-phase microextraction and gas chromatography–mass spectrometry coupled with initial cool programmable temperature vaporizer inlet

"Earthy-musty" off-flavor problem in water samples are due to organic compounds present at the sub-part-per-trillion level. Most of the developments in the analysis of tastes and odorous compounds focus on the extraction pre-concentration technique, with detection at picogram per liter level of the earthy-musty off-flavor compounds difficult to be achieved. In this study, a simple, efficient and sensitive method for the analysis of odorous compounds has been developed by the application of solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) with initial cool programmable temperature vaporizer (PTV) inlet for the first time. Compared with initial hot PTV inlet, the initial cool inlet could greatly improve the system sensitivity, especially for the compounds with good volatility, e.g. 2-methylisoborneol (MIB). StableFlex divinylbenzene/Carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber was found to possess the best extraction efficiency towards these odorous compounds in water. Various SPME and PTV conditions have been studied and optimized in detail. The optimized method has been validated with good linearity, precision and accuracy. The method detection limits (MDL) of the targeted odorous compounds were found to be 0.32ng/L for 2,4,6-trichloroanisole (2,4,6-TCA), 0.14ng/L for 2,3,6-trichloroanisole (2,3,6-TCA), 0.16ng/L for 2,3,4-trichloroanisole (2,3,4-TCA), 0.38ng/L for 2,4,6-tribromoanisole (2,4,6-TBA), 0.16ng/L for gesomin and 0.15ng/L for MIB. To the best of our knowledge, this represents the best sensitivity achieved for analysis of gesomin and MIB in water via the simple and efficient SPME method. The current method has been successfully applied in the analyses of different water samples.

Identification of 2,4,6-Trichloroanisole (TCA) causing a musty/muddy off-flavor in sake and its production in rice koji and moromi mash

2,4,6-Trichloroanisole (TCA), which has been identified as the main component responsible for the cork taint in wine, was detected in sake samples having a musty/muddy off-flavor by stir bar sorptive extraction (SBSE). We confirmed that TCA is one of the components causing this off-flavor in sake, as in other alcoholic beverages, from a sensory analysis showing the correlation between TCA concentration and the intensity of the musty/muddy off-flavor. We investigated the route of TCA production in the rice koji preparation process and in the moromi mash process for sake brewing. We found that TCA is produced mainly by the biomethylation of 2,4,6-trichlorophenol (TCP) by rice koji in brewing and that TCP originates from the wooden tools used in preparing rice koji.

Optimization of a multi-residue screening method for the determination of 85 pesticides in selected food matrices by stir bar sorptive extraction and thermal desorption GC-MS

A multi-residue method to determine 85 pesticides, including organochlorine pesticides, carbamates, organophosphorus pesticides, and pyrethroids, in vegetables, fruit, and green tea, has been developed. The method is based on stir bar sorptive extraction (SBSE) coupled to thermal desorption (TD) and retention time locked (RTL) GC-MS operating in the scan mode. Samples are extracted with methanol and diluted with water prior to SBSE. Dilution of the methanol extract before SBSE was optimized to obtain high sensitivity and to minimize adsorption onto the glass wall of the extraction vessel as well as to minimize sample matrix effects (particularly for the pesticides with high log K(o,w) values). The optimized method consists of a dual SBSE extraction performed simultaneously on respectively a twofold and a fivefold diluted methanol extract. After extraction, the two stir bars are placed in a single glass thermal desorption liner and are simultaneously desorbed. The method showed good linearity (r2 > 0.9900) and high sensitivity (limit of detection: < 5 microg kg(-1)) for most of the target pesticides. The method was applied to the determination of pesticides at low microg kg(-1) in tomato, cucumber, green soybeans, spinach, grapes, and green tea.

Changes in the aroma compounds of sake during aging

Changes in the aroma of sake during aging were investigated by aroma extract dilution analysis (AEDA) and quantitative analysis using the stir bar sorptive extraction method. In AEDA, more odor zones were detected in aged sake than in fresh sake. The dilution factors of aldehydes, polysulfides, and some esters were greater in the aged sake, and their increase during aging was confirmed through a quantitative analysis of sake stored for 0-35 years. Among these compounds, 3-methylbutanal, methional, and dimethyltrisulfide (DMTS) were present in aged sake at concentrations exceeding their odor thresholds, and the highest odor active value was observed for DMTS. Sensory tests showed that supplementation with DMTS contributed to both the total odor intensity and the sulfury odor of aged sake aroma.