Gas chromatographic analysis of free fatty acids and glycerides of milk fat using tetramethylammonium hydroxide as catalyste

Summary Tetramethylammonium hydroxide in methanol has been proposed as a catalyst for preparing methyl esters of both free fatty acids and glycerides of fats. Nevertheless, procedures normally recognized as suitable can be inadequate when the fat under study contains noticeable amounts of low relative molecular mass esters. The method using tetramethylammonium hydroxide has been examined and modified in order to analyze milk fats by capillary GC. The pyrolysis methylation of free fatty acids in capillary injectors has been also studied. The modified method was satisfactory for both neutral and acid milk fats.     

Separation of pesticides by capillary gas chromatography. Part 1: s-Triazines and substituted urea herbicides

The authors have shown that capillary columns are perfectly adequate for the separation of s-triazine herbicides and urea herbicides. The method presented remains adequate when the initial molecules are accompanied by some of their metabolites.     

Gas chromatographic analysis of phenylurea herbicides following catalytic hydrolysis on silica gel

Summary A method is described for the rapid catalytic hydrolysis of phenylurea herbicides on silica gel at elevated temperatures. After derivatisation of the anilines produced with heptafluorobutyric acid anhydride final analysis is done on a gas chromatograph equipped with an electroncapture detector. Detection limits are in the 1–5 picogram range. The method has successfully been applied to residue analysis of water samples at the 1 ppb level. The determination of free anilines present in water samples and the potential of various techniques to be used to discriminate between free anilines and parent herbicides are also discussed.     

Analysis of some chlorophenoxy acids and carbamate herbicides in water and soil as amide derivatives using gas chromatography-mass spectrometry

A newly developed method for determining three phenoxy acids and one carbamate herbicide in water and soil samples using gas chromatography with mass spectrometric detection is developed. Phenoxy acids are derivatized through a condensation reaction with a suitable aromatic amine. 1,1-Carbonyldiimidazole is used as a condensation reagent. Derivatization conditions are optimized with respect to the amount of analyte, amine, solvent, and derivatization reagent. The optimum derivatization yield is accomplished in acetonitrile. 4-Methoxy aniline is used as a derivatizing agent. Obtained derivatives are stable indefinitely. Enhancement in sensitivity is achieved by using the single-ion monitoring mass spectrometric mode. The effectiveness of the developed method is tested by determining investigated compounds in water and soil samples. Analytes are concentrated from water samples using liquid-phase extraction and solid-phase extraction. Soil samples are extracted using methanol. Detection limits of 1.00, 50.00, 100.00, and 1.00 ng/mL are obtained for 2-(1-methylethoxy)phenyl methylcarbamate (Baygon), 2-(3-chlorophenoxy)-propionic acid (Cloprop), 2,4,5-trichlorophenoxyacetic acid, and 4-(2,4-dichlorophenoxy)butyric acid, respectively. LPE for spiked water samples yields recoveries in the range of 60.6-95.7%, with relative standard deviation (RSD) values of 1.07-7.85% using single component calibration curves. Recoveries of 44.8-275.5%, with RSD values ranging from 1.43% to 8.61% were obtained using a mixed component calibration curves. SPE from water samples and soil samples showed low recoveries. The reason is attributed to the weak sorption capabilities of soil and Al(2)O(3).     

Derivatisation in gas chromatographic determination of acidic herbicides in aqueous environmental samples

This paper reviews derivatisation processes applied in chromatographic determination of acidic herbicides (with carboxyl and phenol groups), mainly in aqueous environmental samples. The discussion focuses on the basic derivatisation reactions used to convert herbicides to derivatives to make them analysable by gas chromatography, and possibly to reduce detection limits and/or increase extraction recovery from aqueous samples. The reactions are transesterification, esterification, silylation, alkylation, and extractive and pyrolytic alkylation. The reagents used to conduct the reactions are numerous. Diazomethane is a very efficient methylation reagent but explosive and toxic. Methyl iodide also ensures rapid and efficient methylation. Benzyl bromide can be used directly in water but derivatisation yield is low and reproducibility is poor. Butyl chloroformate and dimethyl sulfite can also be used for derivatisation in water, and acetic anhydride can be used for in-situ derivatisation of phenolic herbicides. For increasing selectivity of GC detection pentafluorobenzyl bromide (for ECD) and (2-cyanethyl)dimethyl(diethylamino)silane (for NPD) have been applied. Very characteristic ions are produced in mass spectra if silyl groups are introduced, e.g. by using bis(trimethylsilyl)trifluoroacetamide. Tetramethylammonium, trimethylphenylammonium, tetraalkylammonium, and trimethylsulfonium hydroxides and salts can by used for derivatisation at elevated temperature in the GC injection port. Extractive alkylation is relatively efficient if tetraalkylammonium salts with long chain alkyl groups are used.     

Determination of chlorophenoxy acid herbicides and their esters in soil by capillary high performance liquid chromatography with ultraviolet detection, using large volume injection and temperature gradient

A simple method for the simultaneous determination of chlorophenoxy acid herbicides and their esters in soil is presented. Compounds studied are: 2,4-dichlorophenoxyacetic acid (2,4-D), 4-(2,4-dichlorophenoxy)butanoic acid (2,4-DB), 2,4-dichlorophenoxyacetic-1-butyl ester (2,4-D-1-butyl ester), and 2,4-dichlorophenoxyacetic-1-methyl ester (2,4-D-1-methyl ester).

The chromatographic analysis was carried out by HPLC, after ultrasonic extraction, on a C₁₈ packed capillary column with temperature gradient, large injection volumes and UV detection at 232 nm. Samples were spiked with amounts between 2.5 and 6.0 μg g⁻¹ of each herbicide; recoveries obtained were between 72 and 97% (n=3 for each spiked level) and detection limits were between 0.3 and 0.5 μg g⁻¹.

Application of this procedure to the analysis of herbicides in ester and acid forms showed the effectiveness of the methodology proposed.     

Photodegradation study of some triazine-type herbicides

Triazines are amongst the most widely used herbicides. Since triazines can be found in many environmental compartments, their fate in ecosystems and the characterization of their degradation pathways in the environment are to be determined. In this paper we report on a study intended to investigate the photodegradation of some triazine-type herbicides: atrazine, cyanazine, terbuthylazine and terbutryn. The rate of photodegradation process was determined, and degradation schemes were outlined for the compounds studied. Moreover, experiments with different degrading energies were carried out in order to gain information about the effect of total degrading energy on the photodegradation process. The most significant processes of photodegradation of triazines are the partial or complete loss of side-chains, or rather the substitution of the heteroatom-containing side-chain to hydroxyl-group. Besides consecutive processes, loss of the different side-chains takes place parallely also, thus, different metabolites will be formed having mixed side-chains, until the cyanuric acid and 2-amino-4,6-dihydroxy-1,3,5-s-triazine are formed by losing all the side-chains. The presence of the dimer products could be detected during the degradation of all triazines. This proves the radical character of processes occurring during the photodegradation. Increasing the degradation energy (15 to 125 W) has raised the degradation rate by 2-5, and the chlorine containing metabolite—which was still present in the completely degraded mixture during the low-energy experiments—has completely disappeared from the mixture, thus, the increased degrading energy is favorable to the formation of less dangerous, nature identical metabolites.     

The use of activated (S)-(+)-naproxen for the gas chromatographic resolution of some amino acid methyl esters

Summary A GC method has been elaborated for the separation of enantiomers of some amino acid methyl esters after derivatization with activated (S)-(+)-naproxen. Nine amino acid ester paris were completely resolvede in a single run on a fused silica capillary column.     

Determination of fatty acid methyl esters derived from algae Scenedesmus dimorphus biomass by GC–MS with one‐step esterification of free fatty acids and transesterification of glycerolipids

Algae can synthesize, accumulate and store large amounts of lipids in its cells, which holds immense potential as a renewable source of biodiesel. In this work, we have developed and validated a GC–MS method for quantitation of fatty acids and glycerolipids in forms of fatty acid methyl esters derived from algae biomass. Algae Scenedesmus dimorphus dry mass was pulverized by mortar and pestle, then extracted by the modified Folch method and fractionated into free fatty acids and glycerolipids on aminopropyl solid‐phase extraction cartridges. Fatty acid methyl esters were produced by an optimized one‐step esterification of fatty acids and transesterification of glycerolipids with boron trichloride/methanol. The matrix effect, recoveries and stability of fatty acids and glycerolipids in algal matrix were first evaluated by spiking stable isotopes of pentadecanoic‐2,2‐d₂ acid and glyceryl tri(hexadecanoate‐2,2‐d₂) as surrogate analytes and tridecanoic‐2,2‐d₂ acid as internal standard into algal matrix prior to sample extraction. Later, the method was validated in terms of lower limits of quantitation, linear calibration ranges, intra‐ and inter‐assay precision and accuracy using tridecanoic‐2,2‐d₂ acid as internal standard. The method developed has been applied to the quantitation of fatty acid methyl esters from free fatty acid and glycerolipid fractions of algae Scenedesmus dimorphus .     

Determination of triazine herbicides in human body fluids by solid-phase microextraction and capillary gas chromatography

Summary Eight triazine herbicides, prometon, propazine, atrazine, simazine, prometryn, ametryn, metribuzin, and cyanazine, have been extracted from human whole blood and urine samples by headspace solid-phase microextraction (SPME) with a polydimethylsiloxane-coated fiber and quantified by capillary gas chromatography with nitrogen-phosphorus detection. Extraction efficiencies for all compounds were 0.21–0.99% for whole blood, except for cyanazine (0.06%). For urine, the extraction efficiencies for prometon, propazine, atrazine, prometryn and ametryn were 13.6–38.1%, and those of simazine, metribuzin and cyanazine were 1.35–8.73%. The regression equations for the compounds extracted from whole blood were linear within the concentration ranged 0.01–1 μg (0.5 mL)⁻¹ for prometon, propazine, atrazine, prometryn, and ametryn, and 0.02–1 μg (0.5 mL)⁻¹ for simazine, metribuzin, and cyanazine. For urine, regression equations for all compounds were linear within the concentration range 0.005–0.25 μg mL⁻¹. Compound detection limits were 2.8–9.0 ng (0.5 mL)⁻¹ and 0.4–2.0 ng mL⁻¹ for whole blood and urine, respectively. The coefficients of within-day and day-to-day variation were satisfactory for all the compounds, and not greater than 10.3 and 14.2%, respectively. Data obtained from determination of atrazine in rat whole blood after oral administration of the compound are also presented.     

Analysis of herbicides in water using temperature-responsive chromatography and an aqueous mobile phase

A simple and rapid method has been developed for herbicides in water using temperature-responsive liquid chromatography (LC) and a column packed with poly(N-isopropylacrylamide) (PNIPAAm), a polymer anchored on the stationary-phase surface of modified silica. PNIPAAm reversibly changes its hydrophilic/hydrophobic properties in water in response to temperature. The method was used to determine five sulfonylurea and three urea herbicides. Separation was achieved with a 10 mM ammonium acetate (pH 3.0) isocratic aqueous mobile phase, and by changing the column temperature. The analytes were extracted from water by off-line solid-phase extraction (SPE) with an N-vinyl-pyrrolidone polymer cartridge. The average recoveries of the eight herbicides from spiked pure water, tap water and river water were 70-130% with relative standard deviations (RSDs) of <10%. The limits of quantitation (LOQ) of the eight herbicides were between 1 and 4 microg l(-1).     

Evaluation of fast gas chromatography and gas chromatography-mass spectrometry in the analysis of lipids

Fast and conventional gas chromatography (GC) techniques were applied to nine different lipidic matrices (butter, lard, tallow, and peanut, corn, sunflower, soya, olive, menhaden oils). Simultaneous methylic transesterification was performed on all samples prior to GC analysis. Several practical aspects concerning high speed analysis were investigated, such as the great increase in linear velocity, the use of fast temperature ramps, column sample capacity and detection systems. Analytical results showed certain losses in resolution, balanced by a consistent reduction in analysis time. The actual time savings were variable (60-70 min) as they were dependent on the complexity of the sample while the speed enhancement factor was equal to 10.5. Peak identification was achieved by means of different information sources, such as fast GC-mass spectrometry (MS), linear retention indices and comprehensive two-dimensional (2D) gas chromatography group patterns. The method developed was shown to be applicable in routine applications on complex natural samples.     

Gas chromatographic analysis of aromatic,carboxylic acids in the presence of C1−C5 fatty acids and C2−C7 dicarboxylic acids esterified in aqueous solutions as the n-butyl esters

Summary The direct esterification and gas chromatographic analysis of aromatic carboxylic acids as n-butyl esters is described.Derivatization is performed in aqueous solution with n-butanol in the presence of sulfuric acid. The butyl esters of benzoic, phthalic, hemimellitic, trimellitic, trimesic and pyromellitic acids permit their gas chromatographic separation from each other and from fatty acids and alipatic dicarboxylic acids. At mole ratios of [H₂O]/ [n-BuOH]0.04 the water present does not interfere with the esterification reaction. At mole ratios above 0.04 anhydrous sodium sulfate is used for binding the water, at mole ratios of [Na₂SO₄ anh.]/[H₂O]=0.25–0.75.     

Gas chromatographic analysis of aromatic carboxylic acids in the presence of C1−C22 fatty acids and C2−C16 dicarboxylic acids esterified in aqueous solutions as the n-propyl esters

Summary The direct esterification and gas chromatographic analysis of aromatic carboxylic acids as n-propyl esters is described.Derivatization is performed in aqueous solution with n-propanol in the presence of sulfuric acid. The n-propyl esters of benzoic, phthalic, trimellitic and pyromellitic acids permit their gas chromatographic separation from each other and from fatty acids and aliphatic dicarboxylic acids. At mode ratios of [H₂O]/[n-PrOH]0.03 the water present does not interfere with the esterification reaction. At mole ratios above 0.03 anhydrous sodium sulfate is used for binding the water, at mole ratios of [Na₂SO₄anh.]/[H₂O]=0.51–1.52 and of [H₂SO₄]/[Na₂SO₄anh.]=0.43–1.28, respectively.     

Quantification of fatty acids as methyl esters and phospholipids in cheese samples after separation of triacylglycerides and phospholipids

Determination of the individual fatty acid composition of neutral- and phospholipids as well as the phospholipid content of dairy food and other foodstuffs are important tasks in life sciences. For these purposes, a method was developed for the separation of lipids (standards of triolein and diacylphosphatidylcholines as well as three cheese samples) by solid-phase extraction using a self-packed column filled with partly deactivated silica. Non-halogenated solvents were used for the elution of the lipid classes. Cyclohexane/ethyl acetate (1:1, v/v) served for the elution of neutral lipids, while polar lipids were eluted with three solvents (ethyl acetate/methanol, methanol, and methanol/water) into one fraction. The separated lipid fractions were transesterified and the individual fatty acids were quantified by using gas chromatography coupled to electron ionization mass spectrometry (GC/EI-MS) in the selected ion monitoring (SIM) mode. The recovery rate for standard phosphatidylcholines was ∼90% and cross-contamination from neutral lipids was negligible. The method was applied to cheese samples. Quantitative amounts of individual fatty acids in the phospholipid fraction were <0.002-0.29% of total lipids from camembert, <0.002-0.12% of total lipids from mozzarella, and <0.002-0.18% of total lipids in a goat cream cheese. Differences in the fatty acid pattern of neutral and polar lipids were detected. The quantity of the fatty acids determined in the phospholipid fraction was divided by the factor 0.7 in order to convert the fatty acid content into the phospholipid content of the cheese samples. This factor is based on the contribution of 16:0 to dipalmitoylphosphatidylcholine (DPPC). The resulting DPPC equivalents (DPPC_eq) were found to be representative for the average contribution of fatty acids to all classes of phospholipids in dairy products. Using this approach, the phospholipid content of lipids from mozzarella, camembert, and goat cream cheese was 0.60%, 1.42% and 0.79%, respectively.     

Esterification of amino acids to n-butyl and isobutyl esters in aqueous solutions for their gas chromatographic analysis

Summary Amino acids have been esterified with n-butanol and isobutanol in the presence of perchloric acid. It has been established that in the concentration range of [H₂O]/[n-BuOH]=0.10–0.40 esterification can be utilized for the determination of alanine, glycine, valine, leucine, proline, methionine, aspartic acid, phenylalanine, tyrosine, glutamic acid, lysine, arginine, histidine and cystine. In the case of [H₂O]/[i-BuOH] =0.05–0.20 the esterification yield decreases from 100% to 70%, in proportion to the water content.     

Simultaneous gas chromatographic determination of methanol and free glycerol in biodiesel

Summary The methanol and free glycerol content of vegetable oil methyl esters used as diesel fuel (biodiesel) is very important in describing the quality of this fuel and is therefore limited by specifications. A previously described GLC method for the determination of free glycerol in biodiesel has been further developed and also allows the simultaneous determination of methanol. Sample preparation includes dissolving in dimethylformamide, silylation with bis-trimethylsilyltrifluoracetamide (BSTFA) and separation on a methylsilicone fluid, coated-capillary column using either FID or MS-detection. Ethanol and 1,4-butanediol were used as internal standards. Both detection systems show sufficient sensitivity for concentrations relevant to biodiesel samples. The recovery was tested using a RME-sample containing known amounts of methanol and glycerol.