Abstract: A method previously used for the analysis of organic acids in silage has been applied to the detection and quantification of acidic fermentation products (C1 to C6 volatile fatty acids, lactic and succinic acid) of rumen bacteria and anaerobic fungi grown in pure culture The acids were converted to tertiary butyldimethylsilyl derivatives prior to separation on a 30 m DB1 capillary gas chromatographic column The quantitative recoveries of formic and succinic acids were found to be comparable to the recoveries of other acids reported in the original study The quantitative recovery of lactic acid was found to be dependent on storage of the samples at ambient temperature for at least 24 h following derivatization The simultaneous determination of a wide range of volatile and non-volatile acidic products is an important feature of this method

Abstract: Homocysteine exists in human plasma as various (mixed) disulfides. Most plasma homocysteine (about 70%) is protein bound, probably via a disulfide bond to albumin, whereas homocysteine-cysteine mixed disulfide is the predominating form in the free fraction. We here present a method for the determination of total homocysteine, which includes both fractions. Plasma was initially treated with sodium borohydride to reduce the disulfide bonds, and the liberated thiols were derivatized with monobromobimane. The derivatized sample, still containing the plasma proteins, was injected onto a strong cation-exchange column, from which the homocysteine derivative was directed by column switching into a cyclohexyl silica (CH) column. The homocysteine derivative was top-concentrated on the CH column, then rapidly eluted with a steep gradient of methanol. Both the derivatization procedure and chromatography were performed with a combined sample processor and sample injector from Gilson (Model 232-401). Within-run and between-run precision (CV) was less than 4%, and the detection limit of 0.2 pmol was sufficiently low for monitoring homocysteine in plasma. We verified the assay against two established manual methods for the determination of total homocysteine in plasma. This, the first fully automated assay for total plasma homocysteine, allows the unattended analysis of 70 samples per 24 h.

Abstract: A precolumn phenylisothiocyanate derivatization method is described for the determination of amino acids in protein hydrolysates from a wide variety of complex food matrixes, with and without performic acid oxidation pretreatment. Analysis of samples that were not pretreated with performic acid was necessary since this pretreatment destroyed an average of 25% of the histidine and 87% of the tyrosine present in the food samples. This method is rapid and reproducible; coefficients of variation between duplicate analyses of the same food item were less than 5% for a majority of the amino acids. Occasionally, variation between duplicate analyses for histidine and tyrosine was greater than 10%. Recoveries of amino acids added to samples were in the 100% range.

Abstract: High-resolution open-tubular columns coated with solutions of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (Phase I) or heptakis(2,6-di-O-methyl-3-O-trifluoroacetyl)-β-cyclodextrin (Phase II) in moderately polar polysiloxanes such as OV-1701 (5% cyanopropyl/7% phenyl/88% methylpolysiloxane) and OV-225 (25% cyanopropyl/50% phenyl/25% methylpolysiloxane) are used for the gas chromatographic enantiomer separation of volatiles belonging to different classes of compounds. No derivatization procedures are necessary for most of the resolved chiral molecules. The chiral stationary phases can be operated between 25 and 190°C for extended periods of time. The enantiomer separation of saturated, unfunctionalized hydrocarbons clearly demonstrates the importance of molecular inclusion in chiral recognition using cyclodextrins for this class of compounds. The different, and in some cases complementary, selectivity of the Phases I and II is demonstrated.

Abstract: High-performance liquid chromatography (HPLC) coupled with a segmented-flow analyzer was used for the analysis of aldehydes. The aldehydes, which were separated on a reversed-phase C_(18) column, were derivatized with 3-methyl-2-benzothiazolinonhe ydrazone (MBTH) and detected at 640 nm. MBTH reacts readily with all aliphatic aldehydes to form MBTH derivatives with high molar absorptivities. Aldehydes below 1 µM can be easily detected by this method. Because aldehydes and other solutes are separated by HPLC before derivatization, free aldehydes are detected without interference. Aldehydes in cloud- and fogwater samples were analyzed. Form-aldehyde, acetaldehyde, glyoxal, and methylglyoxal concentrations were determined. Results obtained with the MBTH method were consistent with those obtained with the 2,4-dinitrophenylhydrazine (DNPH) method. The MBTH method allows for the rapid determination of the concentration of free aldehydes; the DNPH method will yield similar results, although the procedure is more cumbersome and time consuming.

Abstract: A new approach to the derivatization and analysis of long chain polyunsaturated fatty acids is described. The method is based on the formation of 2-alkenyl-4,4-dimethyloxazolines by condensation of the starting material with 2-amino-2-methylpropanol. The derivatization method is rapid, efficient and specific with respect to the chain feature of the parent acids. Volatility, comparable with that of the corresponding simple esters, and improved gas chromatographic separation are achieved without difficulty. The derivatives exhibit clear and regular fragmentation patterns that allow easy discrimination of positional isomers and assignment of double bond location in the chain.

Abstract: J A urine assay for methamphetamine and amphetamine that is compatible with our existing high-volume GC/MS assays for other drugs of abuse has been developed. Trlchloroacetic anhydride is used for derivatizatJon and its derivative is substantially less volatile than other commonly used derivatives. The internal standard is the primary amine 2-methylphenethylamine. The procedure utilizes an initial liquid-liquid extraction, a llquid-IiquId back extraction for specimen cleanup, and derivatization for removal of excess trichloroaceti c anhydride and acid by-product. A GC temperature of about 180~ results In retention times of approximately 2.8, 3.2, and 4.3 mln for amphetamine, the internal standard, and methamphetamine, respectively. Five ions are monitored: 91 +, 118+, 188+ for amphetamine; 105+, 118+ for 2-methylphenethylamine; and 91 +, 118+, 202 + for methamphetamJne. Full scan GC/MS data from a variety of other derivatives are examined and used to illustrate the advantages of derJvatlzing molecules with strongly electronegative atoms near the reaction site. This situation forces fragmentation patterns in which positive charges are located on larger and structurally acceptable identifying mass fragments of the original methamphetamine or amphetamine molecule.

Abstract: A reproducible and interference-free method is presented for simultaneous determination of individual tri-, di- and monoalkyltin species present in aqueous systems The ionic methyltin and butyltin compounds are extracted from water into pentane as diethyldithiocarbamate complexes at pH 5 The organic phase is then evaporated to dryness under reduced pressure, after which derivatization withn-pentyl (Pe) Grignard reagent is carried out in a microvolume ofn-octane to form pentylated alkyltin compounds RnSnPe(4-n) (R = Methyl, Me or Butyl, Bu) The quantitation is subsequently performed by gas chromatography with quartz furnace atomic absorption spectrometric detection (GC-AAS) Absolute detection limits range between 016 ng and 040 ng Sn for the various organotin species, allowing speciation in natural water down to the 4-10 ng ⁗ 1−1 level

Abstract: The separation of polar compounds by supercritical fluid chromatography is a difficult problem to solve. In this work, we have used a pre-derivatization method to obtain apolar or less polar compounds. Amino acids have been chosen as model polar compounds of biological interest, and 9-fluorenylmethyl chloroformate (FMOC) and (+)-1-(9-fluorenyl)ethyl chloroformate (FLEC) have been used as derivatizating reagents. With this procedure, the amino acids studied have been separated in less than 40 minutes with a good efficiency. Furthermore, with FLEC reagent, the enantiomeric separation was rapid in comparison with liquid chromatography techniques and the selectivities obtained were in the same order of magnitude.