Abstract: Nonionic surfactants of the alkylphenol ethoxylate class are relatively nonvolatile analytes that are typically analyzed by LLE and HPLC or GC after derivatization. Solid-phase microextraction (SPME) has seen many GC applications, but recently the ability to hyphenate SPME with HPLC was investigated. In this paper, a new SPME/HPLC method for analysis of Triton X-100 and other alkylphenol ethoxylates is described. Normal-phase gradient elution with detection by UV absorbance at 220 nm was used for the analysis. Several new coated phases, currently in the developmental stage, were evaluated. New Carbowax/template resin and Carbowax/divinylbenzene coatings allowed successful analysis of alkylphenol ethoxylates with a linear range of 100-0.1 mg/L. These coatings provided the best agreement between the ethoxamer distribution of surfactants after extraction and that in the original surfactant. Limits of detection of the individual ethoxamers were determined to be in the low microgram per liter to submicrogram per liter range. Some applications of the method have been demonstrated for sewage sludge samples.

Abstract: The methodologies for the analysis of D-amino acids in biological materials have been reviewed, including the use of enzymes, gas and liquid chromatography with chiral stationary phases and diastereomer derivatization with chiral reagents followed by GC or HPLC separation. The distribution of D-amino acids in the body, their origin, metabolism and possible roles in human diseases are discussed.

Abstract: Understanding arsenic toxicity and metabolism requires quantitation of individual arsenic species. However, it has been difficult to separate many biochemically and environmentally important arsenic species on a single chromatography column. We have studied the separation of 11 arsenic compounds by using ion pair chromatography at 30, 50, and 70 °C column temperatures. The use of elevated column temperature improved separation efficiency and dramatically reduced chromatographic retention time for arsenobetaine, arsenocholine, tetramethylarsonium, and arsenosugars. On-line microwave derivatization combined with hydride generation and atomic fluorescence spectrometry (HGAFS) was used for detection, which was able to differentiate more toxic from less toxic arsenic species. The speciation technique was successfully applied to a study of metabolism of arseno sugars present in commercial seaweed products. Two uncharacterized arsenic-containing metabolites were detected in urine samples collected 20−33 h after ...

Abstract: A novel, selective precolumn derivatization reaction was introduced and evaluated in the fluorescence labeling of phenoxy acid herbicides with 7-aminonaphthalene-1,3-disulfonic acid (ANDSA). The ANDSA-phenoxy acid derivatives were readily detected by capillary electrophoresis/laser-induced fluorescence (CE-LIF) at 0.2 ppb, a concentration at which environmental herbicide samples are expected to occur. The precolumn derivatization was very quantitative (99.7% yield) and produced stable derivatives and no side products. Furthermore, the ANDSA-phenoxy acid herbicide enantiomers exhibited higher chiral resolution than their underivatized counterparts in the presence of cyclodextrin (CD) in the running electrolyte. Several native and modified CDs were investigated in the enantiomeric separation of chiral phenoxy acid herbicides. The best enantioselectivity was achieved when 2,3,6-tri-O-methyl-β-cyclodextrin (TM-β-CD) was used as the chiral selector. To effect the enantiomeric resolution of a large number of AN...

Abstract: We report investigations into the conversion of trimethylsilylcellulose multilayers to ultrathin cellulose films, the derivatization of these films with succinic anhydride and the utilization of the regenerated and modified cellulose films for adsorption studies

Abstract: Two methods for determination of cholesterol in fat and muscle of pig were evaluated: extraction with chloroform:methanol (2:1, v/v) followed by saponification (method 1) and direct saponification (method 2). HPLC and GC were used to determine cholesterol concentrations. GC analysis was performed with a capillary column of 100 μm using a PTV injector in the modes of cold split and solvent venting. Cholesterol was analyzed without derivatization. Both methods of extraction did not present significant differences (p > 0.01). Sample analysis by GC with solvent venting injection and HPLC showed the lowest % r.s.d. but GC in the cold split mode allowed to obtain a shorter analysis time. Cholesterol concentrations obtained by HPLC were not statistically different from the results obtained by GC with solvent venting injection and were slightly lower than those previously reported. Cholesterol concentrations in fat and muscle tissues respectively ranged from 52 to 77 mg/100 g and from 55 to 65 mg/100 g.

Abstract: A method for the rapid and convenient identification of chemical interferences in the determination of aldehydes and ketones in air samples using the 2,4-dinitrophenylhydrazine (DNPH) method is described. The ratio of absorptions at 360 and 300 nm is characteristic for groups of related aldehydes and ketones as well as for the main interferents. It has been determined by UV/visible spectroscopy of pure standard compounds and confirmed by HPLC analysis with UV/visible detection of complex hydrazone mixtures. The application of this method has led to the identification of 2,4-dinitrochlorobenzene as another interfering compound after sampling of air with high nitrogen dioxide content when using hydrochloric acid as catalyst. The possibilities and limitations of the dual-wavelength detection with the DNPH method are discussed for mixtures of standards and real samples from car exhaust.

Abstract: A chromatographic system for the on-line derivatization of drugs using column switching is described. The system uses a 20 mm × 2.1 mm i.d. precolumn packed with a unmodified ODS stationary phase. This column is used for sample cleanup and enrichment of the analytes. Next, the trapped analytes are derivatized by injection of the derivatization reagent into the precolumn. Finally, the derivatives are transferred to the analytical column for their separation under reversed-phase conditions. The influence of several parameters such as the reaction time, the amount of derivatization reagent, or the system design has been studied using some amphetamines as model compounds and three derivatization reagents: sodium 1,2-naphthoquinone-4-sulfonate, o-phthaldialdehyde, and 9-fluorenylmethyl chloroformate. The potential of the described approach is illustrated by determining amphetamine and methamphetamine in untreated urine at ambient temperature.

Abstract: Hydrolysis with acetic acid carried out in a low-power focused microwave field in the presence of sodium tetraethylborate and nonane is shown to shorten the sample preparation time for gas chromatographic determination of organotin compounds in biological materials. After a 3-min reaction time, ethyl derivatives of mono-, di-, and tributyltin, and triphenyltin are quantitatively (>95%) found in the supernatant organic phase that is injected onto a capillary GC column. Two rapid one-step analytical procedures, using flame photometric and atomic emission detection, respectively, were developed on this basis and validated by analyzing the NIES11 certified reference fish tissue.

Abstract: A sensitive HPLC-fluorescence method for determining total endogenous plasma homocysteine (Hcy), cysteine (Cys) and cysteinylglycine (Cys-Gly) following derivatization with ammonium 7-fluoro 2,1,3-benzoxadiazole-4-sulphonate (SBD-F) is described. Quantitation utilizes an internal standard, 2-mercaptoethylamine. The derivatization procedure has been optimized for concentration of SBD-F, reducing agent (tributylphosphine) and temperature. Findings indicate that values for plasma determinations vary according to the nature of the matrix in which calibration standards are made up. If quantitation is based on a peak height ratio, then standards should be made up in either pH 7.4 phosphate buffered saline or plasma taking into account the endogenous thiol concentration. These findings are based on calibration data, and 30 plasma samples quantified using thiol standards made up in plasma, pH 7.4 and pH 9.5 buffers. By defining how this matrix/pH effect influences thiol quantitation, it should be possible to make a more meaningful comparison of Hcy measurements between laboratories. The chromatographic separation was investigated at several mobile-phase pH values with the following conditions ascertained to be optimal: a mobile phase consisting of 5% (v/v) acetonitrile in 0.1 M KH2PO4, pH 2.15 was run at a flow rate of 0.5 mL/min. It was used in conjunction with a Supelco LC-18 base deactivated analytical column (150 x 4.6 cm i.d. 3 microM bonded silica). The internal standard and thiols were measured by fluorescence detection at 385 nm excitation and 515 nm emmission. Plasma levels are easily measured in a 100 microL volume. Storage for 2 months at -20 degrees C resulted in no deterioration of thiols. Furthermore, no difference in thiol levels was observed between bloods collected in lithium heparin and EDTA. Collected blood should, however, be separated as soon as possible to avoid red cell metabolism of Hcy which was observed in a case of hyperhomocysteinemia. Once derivatized, thiols are stable for at least one week at +4 degrees C.

Abstract: An LC–UV method using dibutylamine (DBA) as derivatization reagent for airborne monomeric and polymeric isocyanates is presented. Isocyanates were collected in impingers containing 0.01 mol l–1 DBA in 10 ml of toluene. Stable isocyanate–DBA (urea) derivatives were rapidly formed in the sampling solution and the reaction was completed within 10 s. After evaporation of the solvent and excess reagent, the urea derivatives were analysed using reversed-phase LC–UV at 240 nm. Linear calibration graphs were obtained for toluene 2,4-and 2,6-diisocyanate (TDI) and methylene diphenyl-4,4′-diisocyanate (MDI) in the range 0.4–20 nmol ml–1. The overall precision for a DBA solution spiked at concentrations of 540 µg l–1 of 2,4-TDI, 540 µg l–1 of 2,6-TDI and 520 µg l–1 of 4,4′-MDI were found to be 1.1, 5.0 and 3.0%(n= 6), respectively. The detection limit was 0.5–0.8 µg m–3 for a 15 l air sample. Ratio chromatograms between λ1= 240 nm and λ2= 254 nm demonstrated an increased selectivity. Interferences from morpholine, ethanol, phenol, toluene-2,4-and 2,6-diamine, 4,4′-methylenedianiline and water were studied by spiking the sampling solution with 6.2 µmol of each chemical, corresponding to an air concentration of 10 ppm. No losses of the urea derivatives were found. Air samples of TDI were simultaneously collected with impingers containing 9-(N-methylaminomethyl)anthracene (n= 10) and DBA (n= 10). No significant differences between the results obtained with the two methods were observed. Sampling of isocyanates in the work environment based on derivatization with DBA was demonstrated to be a robust method. DBA is especially well suited for the determination of complex mixtures of airborne isocyanates.

Abstract: A gas-liquid chromatographic method for the determination of gabapentin (Neurontin®) is described. The method involves extracting 0.5 mL of acidified sample by C 18 solid-phase column, derivatization with MTBSTFA plus 1% tBDMCS, and analysis on an HP-1 column with a flame-ionization detector. Quantitation was performed with peak-height ratios of gabapentin to a gabapentin analogue [(1-aminomethyl-1-cycloheptyl) acetic acid] as the internal standard. The assay had a limit of detection of 0.2 mg/L and a linear range from 0.5 to 30.0 mg/L. Several compounds were analyzed for potential interference, and none interfered with the assay.