Analysis of polycyclic aromatic hydrocarbons (PAHs) in environmental samples: a critical review of gas chromatographic (GC) methods

Polycyclic aromatic hydrocarbons (PAHs) are frequently measured in the atmosphere for air quality assessment, in biological tissues for health-effects monitoring, in sediments and mollusks for environmental monitoring, and in foodstuffs for safety reasons. In contemporary analysis of these complex matrices, gas chromatography (GC), rather than liquid chromatography (LC), is often the preferred approach for separation, identification, and quantification of PAHs, largely because GC generally affords greater selectivity, resolution, and sensitivity than LC. This article reviews modern-day GC and state-of-the-art GC techniques used for the determination of PAHs in environmental samples. Standard test methods are discussed. GC separations of PAHs on a variety of capillary columns are examined, and the properties and uses of selected mass spectrometric (MS) techniques are presented. PAH literature on GC with MS techniques, including chemical ionization, ion-trap MS, time-of-flight MS (TOF-MS), and isotope-ratio mass spectrometry (IRMS), is reviewed. Enhancements to GC, for example large-volume injection, thermal desorption, fast GC, and coupling of GC to LC, are also discussed with regard to the determination of PAHs in an effort to demonstrate the vigor and robustness GC continues to achieve in the analytical sciences.

Large volume splitless injection with concurrent solvent recondensation: Keeping the sample in place in the hot vaporizing chamber

An injector liner packed with a plug of glass wool is compared with a laminar and a mini laminar liner for large volume (20-50 microL) splitless injection with concurrent solvent recondensation (CSR-LV splitless injection). Videos from experiments with perylene solutions injected into imitation injectors show that glass wool perfectly arrested the sample liquid and kept it in place until the solvent had evaporated. The sample must be transferred from the needle to the glass wool as a band, avoiding 'thermospraying' by partial solvent evaporation inside the needle. The liquid contacted the liner wall when the band was directed towards it, but from there it was largely diverted to the glass wool. In the laminar liners, part of the liquid remained and evaporated at the entrance of the obstacle, while the other proceeded to the center cavity. Vapors formed in the center cavity drove liquid from the entrance of the obstacle upwards, but the importance of such problems could not be verified in the real injector. Some liquid split into small droplets broke through the obstacle and entered the column. Breakthrough through the laminar liners was confirmed by a chromatographic experiment. An improved design of a laminar liner for large volume injection is discussed as a promising alternative if glass wool causes problems originating from insufficient inertness.

Optimized method for the determination of organophosphorus pesticides in meat and fatty matrices

A method was developed and optimized for determination of residues of organophosphorous pesticides (OPs) in meat and fatty matrices. The method was developed for the national Danish monitoring programme, whereby priority was given to simplify the clean-up, avoid use of toxic and harmful organic solvents and allow quantification at ppb level using GC with nitrogen-phosphorus detection (NPD). Homogenized meat was extracted using ethyl acetate, the co-extracted water being removed using anhydrous Na2SO4. The clean-up was done through fat precipitation by cooling the extract flowed by solid-phase extraction on C18 mini-columns. Pesticide residues were determined by GC-NPD using a DB1701 capillary column. The limit of detection was 1 to 20 ppb and limit of determination was 2 to 33 ppb and the method is feasible for control of fat-soluble OPs according to the maximum residue limits set by the European Communities. The method developed covers a broad polarity range from polar OPs, such as acephate and methamidophos, through medium polar OPs to non-polar pesticides, such as prothiofos.

The methyl-5 alpha-dihydrotestosterones mesterolone and drostanolone; gas chromatographic/mass spectrometric characterization of the urinary metabolites

Before including the detection of the methyl-5 alpha-dihydrotestosterones mesterolone (1 alpha-methyl-17 beta-hydroxy-5 alpha-androstan-3-one) and drostanolone (2 alpha-methyl-17 beta-hydroxy-5 alpha-androstan-3-one) in doping control procedures, their urinary metabolites were characterized by gas chromatography/mass spectrometry. Several metabolites were found after enzymatic hydrolysis and conversion of the respective metabolites to their trimethylsilyl-enol-trimethylsilyl ether derivatives. The major metabolites of mesterolone and drostanolone were identified as 1 alpha-methyl-androsterone and 2 alpha-methyl-androsterone, respectively. The parent compounds and the intermediate 3 alpha,17 beta-dihydroxysteroid metabolites were detected as well. The reduction into the corresponding 3 beta-hydroxysteroids was a minor metabolic pathway. All metabolites were found to be conjugated to glucuronic acid.

Determination of oxpentifylline and four metabolites in plasma and urine by automated capillary gas chromatography using nitrogen-selective detection

A capillary gas chromatographic assay for the determination of oxpentifylline and four hydroxylated metabolites is described. Oxpentifylline, metabolites and internal standards are extracted from basified plasma or urine with chloroform and the metabolites are converted to their O-trifluoroacetates before analysis by capillary gas chromatography using nitrogen-selective detection. A high throughput of samples is achieved by use of an autosampler and a split injection technique which allows the samples to be analysed isothermally. The detection limits of the compounds are in the range 2-10 ng/ml for plasma and 0.1-0.2 microgram/ml for urine. The assay has been applied to the analysis of plasma and urine samples after the oral administration of oxpentifylline.

Urinary steroid profiles in pregnancy by capillary column gas chromatography

A qualitative and quantitative method for the estimation of urinary steroids during pregnancy by capillary column gas chromatography has been developed. Steroid conjugates were hydrolysed by enzymes and free steroids isolated by extraction using SEP-PAK C18 cartridges. Methoxime-trimethylsilyl derivatives of the steroids were characterized by packed column gas chromatography-mass spectrometry and subsequently by their retention indices on capillary column gas chromatography. Of the 48 peaks resolved on the profiles about 35 were identified as steroids. The retention indices of reference steroids were very reproducible in the short term showing a mean coefficient of variation of 0.015%. The columns allowed 95% valley resolution of steroids whose retention indices differed by only 7 units. The use of an on-column injection technique contributed to the high precision for replicate injections (coefficient of variation less than 1%) while for reference steroids, and well-resolved peaks in the urine profile, the mean coefficient of variation for the complete assay was less than 10%. To the best of our knowledge this is the first report concerning the quantitation, with good precision, of a large number of steroids in pregnancy urine.

Semi-micro quantitative analysis of complex urinary steroid mixtures in healthy and diseased states

A method for the determination of urinary steroid hormones in healthy and diseased states is described. The use of a Van den Berg all-glass injector coupled to a fused silica column has shown a dramatic increase in sensitivity and a significant reduction in gas chromatography analytical time. The increase in sensitivity also eliminates the need for processing large volumes of urine. The method has proven to be rapid, precise, reproducible and sensitive. Also, column life is increased due to the absence of solvent. This technique has shown to have broad applications in the analysis of such classes of compounds as sugars, steroids, prostaglandins and fatty acids.

Capillary GLC assay for carbinoxamine and hydrocodone in human serum using nitrogen-sensitive detection

Capillary gas chromatography using an open tubular fused silica column and NP-FID was applied to the simultaneous analysis of the antihistamine, carbinoxamine, and the antitussive, hydrocodone, in human serum. Carbinoxamine and hydrocodone were extracted into methylene chloride-2-propanol (9:1) under alkaline conditions along with their respective internal standards, brompheniramine and N-ethylhydrocodone. The basic drugs were back-extracted into 0.1 N sulfuric acid and reextracted into benzene after making the aqueous phase alkaline with potassium hydroxide. The benzene extracts were evaporated to dryness and the residues were reconstituted with 40 microliter of n-nonyl alcohol-methanol (19:1). Samples (1-2 microliter) were injected onto the capillary column in the splitless mode (solvent effect) at 185 degrees and the temperature programmed to 250 degrees. Calibration curves using spiked serum standards were linear to at least 20 ng/ml for both drugs. Coefficients of variation averaged +/- 6.1% for carbinoxamine and +/- 5.0% for hydrocodone in the 2-15 ng/ml range. Sensitivity was estimated to be approximately 0.2 ng/ml for a 2-ml serum sample. Serum levels of carbinoxamine and hydrocodone were determined in a human volunteer administered these drugs.