Determination of amino acids in human cerebrospinal fluid by gas chromatography

In the present study, the use of gas chromatography (GC) for the determination of amino acids in human cerebrospinal fluid (CSF) is described. Although some amino acids may be determined using a packed column following the removal of glucose, the major interfering component, the inadequate resolution of other amino acids from remaining unidentified components results in poor quantitation. The use of wide bore columns improves reproducibility considerably, but still it does not provide sufficient resolution to enable quantitative determination of all amino acids in human CSF. Good reproducibility data, with CV values for all amino acids of 7% or less and recoveries generally between 80% and 100%, can only be obtained using the fused silica open tubular (FSOT) column. Normal amino acid levels are presented for 10 samples of human CSF, which compare well with data previously reported in the literature.     

Direct GC determination of methylmercury chloride on HBr-methanol-treated capillary columns

Summary Gas chromatography with electron capture detection (GC-ECD) for the analysis of methylmercury choloride (MMC) using a packed column and a capillary column has been investigated. The columns were 2% silicone OV-227 Uniport HP glass column and a DB-17 capillary column, each pretreated by about ten injections of HBr-methanol solution. MMC was separated as a sharp peak by the HBr-teated column and determined directly by ECD without derivatisation. The mass spectrum of MMC indicated that halide exchange from chloride to bromide proceeded during separation. The minimum detectable concentrations were approximately 5 ng mL⁻¹ on the packed column, and 2 ng mL⁻¹ on the capillary. Calibration curves showed good linearity between 5–200 ng mL⁻¹ for the packed column, and between 2–200 ng mL⁻¹ for the capillary. Relative standard deviations of peak areas were 0.95% for the packed column and 0.43% for the capillary at the level of 100 ng mL⁻¹ in both cases. The column treatment technique was applicable to determination of methylmercury in fish samples.     

Determination of methylmercury in biological samples by capillary gas chromatography with electron capture detection

A precise and accurate method has been developed for the determination of methylmercury in biological material using capillary gas chromatography with electron-capture detection. Homogenized fish or mussel samples were digested with acid, spiked with ethylmercury chloride as an internal standard and extracted with toluene. After treatment of the solvent extract with sodium thiosulphate and cupric bromide the alkylmercurials were extracted into benzene as their bromide derivatives and analyzed using an OV-275 coated glass capillary column. The detection limit of the method for methylmercury was 5 g/kg tissue.     

Comparison of high-selectivity gas chromatographic methods, including column switching, for the determination of felodipine in plasma

The selectivity required for the determination of low concentrations of felodipine in plasma was achieved by either mass-selective detection, optimization of stationary phase selectivity or column-switching gas chromatography (GC) with a dual-oven chromatograph, the latter two with electron-capture detection. The three approaches were evaluated in terms of selectivity, detectability, precision and suitability for routine applications with automated injection. Using mass-selective detection, the detectability in plasma samples was limited by the performance of the mass spectrometer. The detection limit (signal-to-noise ratio = 3) was 4.7 pmol (1.8 pg) of felodipine. Pre-concentration of extracts permitted quantitation in plasma down to 0.2 nmol/1. Using electron-capture detection, the detectability was determined by the selectivity and bleeding characteristics of the columns. For single-column separation, a 35% phenyl phase was selected. The detection limit was 3.0 fmol (1.2 pg). The limit of quantitation in plasma was 1 nmol/1. In column-switching GC, bleeding products from the first column will separate on the second column and may interfere in separations for trace analysis. Bleeding products from a 50% phenyl phase (DB-17) were characterised by GC-mass spectrometry. With a dual-column system, employing a DB-17 (50% phenyl) column for selective introduction on to a CP-Sil 5 (0% phenyl) column, the signal-to-noise ratio was limited by the low-bleeding second column, provided that the bleeding products from the first column were adequately separated from felodipine. The detection limit in this instance was significantly lower 0.35 fmol (0.13 pg). Direct injection of plasma extracts permitted quantitation down to 0.4 nmol/l. All three methods were well suited for use with autosamplers.     

气相色谱法测定太白洋参中的甘露醇含量

介绍了应用气相色谱法－氢火焰离子化检测器检测太白洋参中甘露醇的方法,采用OV－225填充柱分离该法平均回收率为90．66％,检出限为0．1mg/kg。     

Coupling miniaturized liquid chromatography to capillary gas chromatography (micro-LC-CGC): Possibilities of reversed phase LC

Retention gaps with different polarity treatments were evaluated for reversed phase solvents. Aminopropyl- and cyanopropyl-deactivated retention gaps showed the best results for methanol-water mixtures. A reversed phase packed fused silica capillary LC column is connected on-line with a capillary gas chromatography column. The combination was used for the analysis of diazepam in urine. Volume overloading on packed fused silica columns without loss of too much efficiency was demonstrated for propranolol.     

OH-terminated cyanopropyl silicones

Due to their high polarity and unique selectivity, cyanopropyl silicones are basic stationary phases for high resolution capillary gas chromatography. Different OH-terminated cyanopropyl silicones, containing a high cyanopropyl content, were synthesized and chromatographically evaluated. Special attention was paid to the degree of immobilization of the phases in FSOT columns. Depending on the problem at hand, a choice has to be made between immobilization and maximum selectivity.     

Noncryogenic FSOT column separation of sulfur-containing gases

Fused silica open tubular (FSOT) capillary column GC separations of low molecular weight, reactive sulfur-containing gases (S-gases) are significant improvements over packed column separations in terms of resolution, detection limits, and conditioning effects. Nevertheless, some of the problems with current FSOT capillary systems include matrix Injection incompatibilities; detector dead volumes; the necessity for cryogenic initial oven temperatures to separate CO₂, H₂S, COS, and SO₂; and relatively long analysis times to separate later, closely eluting compounds. A noncryogenic FSOT GC-FPD system that either reduces or eliminates these problems is reported. Baseline separation of seven common S-gases (H₂S-DMDS) is achieved in less than 5 min with ambient initial oven temperatures via this system, which is a combination of (1) a cryogenic sample concentration/injection design that is flow compatible with a wide-bore FSOT column; (2) a combined DB-1/DB-WAX thick phase, wide-bore FSOT column for greater capacity, retention, and tuned selectivity; and (3) a reduced dead volume FPD to minimize peak width and tailing.     

气相色谱法测定爱迪注射液中的斑蟊素

 研究了斑蟊素在几种萃取体系中的分配行为,测定了它的分配系数。选定二氯甲烷为萃取剂,在相比为1∶10时,只需一次萃取便可以使斑蟊素定量富集。选用OV-17填充柱、外标法定量。方法的分离效果令人满意,检测限低,结果的准确性和精密度良好。     

Large diameter open tubular columns in gas chromatographic analysis

Large diameter open tubular columns provide the packed column chromatographer with a simple route to higher resolution gas chromatography. They can be operated in a high-flow (lower resolution) mode that permits their direct substitution for a packed column, or they can be operated in a low-flow (higher resolution) mode that maximizes separation at the cost of longer analysis times. Inlet design and column installation can influence both the chromatographic results and quantiative reliability. Make-up gas is not required in the high-flow mode, and its benefits in the low-flow mode are restricted to enhanced detector sensitivity, provided the outlet end of the column resides in the detector jet (FID). The columns seem fully compatible with all common modes of detection.     

整体柱和填充柱离子对色谱-间接紫外检测法分析四乙基铵根离子

建立了整体柱离子对色谱-间接紫外检测和填充柱离子对色谱-间接紫外检测分析四乙基铵根离子的两种方法。用反相整体柱和反相填充柱,以咪唑离子液体-离子对试剂-有机溶剂为流动相,研究了背景紫外吸收试剂、检测波长、离子对试剂、有机溶剂、柱温和流速对测定四乙基铵根离子的影响,比较了两种色谱柱的差异,并讨论了保留规律。在优化的实验条件下,两种方法测定四乙基铵根离子的保留时间分别是2.40和3.02 min;检出限分别是0.04和0.07 mg/L;峰面积的相对标准偏差分别是0.16%和0.11%;保留时间的相对标准偏差分别是0.02%和0.01%。将这两种方法用于分析实验室合成的溴化四乙基铵离子液体,加标回收率分别为98.2%和99.1%。两种方法均能满足四乙基铵根离子测定的需要。     

Gas chromatography of hydrocarbons using packed liquid chromatographic capillary columns

Capillary columns of 0.3-0.5 mm i.d. packed with 3- to 30-μm silica-based stationary phases for liquid chromatography were used for gas chromatographic separation of hydrocarbons. Column efficiencies were evaluated for various commercially available packing material. The best column efficiency was achieved with 5-μm octadecyl group bonded silica gel, the surface of which was coated with a poly (dimethylsiloxane) film. The 30-cm column produced 11,000 theoretical plates.     

Direct Urine Injection with Micellar Liquid Chromatography-Amperometric Detection for Dopamine Monitoring

Abstract

Micellar liquid chromatography with amperometric detection was evaluated for the determination of dopamine in urine. The samples were injected directly without time-consuming protein precipitation. The separations were carried out in an analytical column packed with C18. The mobile phase was 0. 01M SDS with 3% n-propanol added at pH 4. 15. The limit of detection for dopamine is 4 pg. Eight urine samples were analyzed. The results were in a reasonable range.     

Determination of methylmercury in natural waters at the sub-nanograms per litre level by capillary gas chromatography after adsorbent preconcentration

Methylmercury was preconcentrated from water on to a sulph-hydryl cotton fibre adsorbent, using the column technique or the batch-column two-stage technique. A small volume of 2 M HCl was used to elute methylmercury and to separate it from inorganic mercury; 0.4–0.6 ml of benzene was used to extract methylmercury from the eluate. Analysis was performed by capillary gas chromatography with electron-capture detection. The detection limit for methylmercury was <0.05 ng l^?1 in a 4-l water sample. Four surface waters were analysed to test the agreement of methylmercury concentration between the two preconcentration methods, and to test the interference of humic substances on the filtered and unfiltered surface water. The methylmercury concentrations found in different surface water samples ranged from 0.08 to 0.48 ng l^?1.     

Factors determining flow rate in chromatographic columns

Summary It is shown that the flow in chromatography is nearly always laminar in nature. Starting from the Darcy equation, expressions are given for the flow rate in both gas and liquid chromatography columns. The concepts of specific permeability, chromatographic permeability and column resistance factor are discussed for packed as well as open tubular columns. The experimental determination of all these factoers is demonstrated. The influence of the shape and pore volume of porous and non-porous supports on the column resistance factor and the chromatographic permeability is discussed.     

Enzyme activity determination by radio gas chromatography on capillary columns

Androgen 5α-reductase from the foreskin of 48 boys in prepubertal age was analyzed by evaluation of the apparent K_m-and V_max- values after tissue incubation. Reaction rates were calculated after determination of specific radioactivity of distinct metabolites, by comparison to the radioactivity of the precursor. Reaction products were separated by radio gas chromatography on capillary columns. The chromatography system was based on multicolumn equipment with column switching facilities and a variable splitter at the outlet of the separation column. A radioactivity monitor (gas proportional counter) was used for measurement of radioactivity in the column effluents. An electron capture detector was used for mass detection of steroid acyl derivatives.     

Evaluation of restricted access media for high-performance liquid chromatographic analysis of sulfonamide antibiotic residues in bovine serum.

Three commercially-available high-performance liquid chromatographic columns packed with restricted access media were evaluated for suitability in multi-residue direct injection analysis at the ng/ml level. The internal surface reversed-phase and shielded hydrophobic phase columns were not sufficiently retentive to separate all analytes from the tail of the matrix peak. Coelution of some of the analytes was also observed with these columns. The semi-permeable surface column was significantly more retentive and selective, providing good separation of analyte and matrix peaks. With this column, an analytical protocol requiring no organic solvents was developed for the assay of six sulfonamides at a detection limit of 25 ng/ml.     

Use of specially designed columns for antioxidants and antimicrobials enrichment by preparative supercritical fluid chromatography

A new, specially designed column has been developed for fractionation of supercritical fluid extract of rosemary by using a preparative supercritical fluid chromatography system (Prep-SFC). The column evaluated in this work was prepared using a new packing method consisting of a combination of slurry and supercritical CO2 with commercial silica particles coated with a stationary phase commonly used in gas chromatography, such as SE-54 (5% phenyl-, 95% methylsilicone). The new packing procedure provided columns with reasonable efficiencies, with high stability and useful at high-pressure range. A 25 cm x 10 mm i.d. column packed with silica particles coated with 3% of SE-54 was prepared, and its separation power was tested for isolating fractions with high antioxidant and/or antimicrobial activity from a supercritical rosemary extract. The SFC conditions were selected based on a previous work done with a commercial LC-Diol packed column (130 bar, 80 degrees C), and different percentages of modifier in the mobile phase were tested (5 and 10%). Two cyclones were employed to collect the fractions which were then characterized by HPLC-diode array detection (DAD), GC, and in vitro antioxidant and antimicrobial assays. The use of coated packed columns allowed the fractionation of a complex mixture of rosemary supercritical extract with a minimum amount of modifier in the mobile phase (5% ethanol). At the optimum conditions it was possible to obtain two very active fractions in terms of antioxidant and antimicrobial activity, with no residual rosemary aroma and with improved activities compared to the original supercritical extract.     

Column-switching high-performance liquid chromatographic detection of pholcodine and its metabolites in urine with fluorescence and electrochemical detection.

A sensitive and selective method for the detection of pholcodine and its metabolite morphine in urine using high-performance liquid chromatography is described. It involves on-line clean-up of urine on a trace enrichment column packed with a polymeric strong cation-exchange material. Pholcodine and its metabolites were separated on two analytical columns with different selectivities. Pholcodine was detected by a fluorescence detector and morphine was detected electrochemically. One system, based on reversed-phase chromatography, applied a polystyrene-divinylbenzene column and gradient elution. The other system was based on normal-phase chromatography with a silica column and isocratic elution. Morphine was confirmed to be a metabolite of pholcodine by reversed-phase chromatography and electrochemical detection. Two unidentified metabolites of pholcodine were separated from pholcodine by normal-phase chromatography and detected by fluorescence detection.     

New dynamic axial compression columns with means for monitoring floating adapter position. Column design and utilisation in low pressure LC on soft packings

Summary The design of new dynamic, axial-compression columns with a system for continous packed bed adjustment and monitoring of the floating adapter position is described. The columns are meant for liquid chromatography at low pressures (up to 8 bar) in aqueous and organic media with stationary phases of all types. The columns have adapter position pickups for continuous automatic monitoring of the bed height (original “swellographic” monitoring). The column described with gas pressurisation was tested with soft Sephadex G-10 and G-25. In spite of the reduction in external porosity there was no dramatic increase in back-pressure. The column proved to provide long-term stability of the packed bed and improvement in resolution. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996