N，N－二甲基甘氨酸乙酯分解反应机理的理论研究

利用量子化学计算方法MP2／6－31＋G^*研究了N，N－二甲基甘氨酸乙酯在气 相中热分解反应机理，并计算了反应的协同性，得出此反应是一个多步反应过程。 主要有两个阶段：第一个阶级是N，N－二甲基甘氨酸乙酯热分解产生N，－N二甲基 甘氨酸中间体和乙烯，第二个阶段是N，N－二甲基甘氨酸进一步分解生成三甲氨和 二氧化碳。第一个反应阶段为速率控制步骤。研究表明，该反应机理是一个非协同 的质子转移过程。计算结果与实验值吻合。     

Head-space chromatography in determination of enzymatic activity: microdetermination of the urinary kallikrein as arginine esterases

Many enzymatic reactions yield volatile products either directly or by cascade sequences, so it seems possible that head-space chromatography might be used to determine enzymatic activity. The activity of urinary kallikrein, as arginine esterase, has been determined in this way by using the N(alpha)-acetyl-L-phenylalanyl-L-arginine ethyl ester as substrate and measuring the ethanol yielded on incubation for 10 min at 30 degrees, followed by quenching of the reaction. The method has been applied to aqueous solutions and urine.     

Assay for N tau-methylimidazoleacetic acid, a major metabolite of histamine, in urine and plasma using capillary column gas chromatography-negative ion mass spectrometry

A gas chromatographic-mass spectrometric assay has been developed for the measurement of N tau-methylimidazoleacetic acid in urine and plasma. The method uses the isopropyul ester 3,5-bistrifluoromethylbenzoyl derivative of N tau-methylimidazoleacetic acid and electron capture negative ion chemical ionisation mass spectrometry. The derivative has very good chromatographic properties and a negative ion mass spectrum which contains only a molecular ion at m/z 422. When this ion is specifically monitored, an amount of derivative equivalent to 1 pg of parent compound can be detected. A deuterated analogue of N tau-methylimidazoleacetic acid was synthesised for use as an internal standard and this allowed the development of an assay for N tau-methylimidazoleacetic acid, in urine with a precision of 2.9% and in plasma with a precision of 1.5%.     

Gas chromatographic method for the determination of N-acetyl-S-(N-methylcarbamoyl)cysteine, a metabolite of N,N-dimethylformamide and N-methylformamide, in human urine

A simple method has been developed for the determination of N-acetyl-S-(N-methylcarbamoyl)cysteine in human urine. Treatment of a urine sample (1 ml) with ethanol (2 ml) and potassium carbonate (1.5 g) produces ethyl N-methylcarbamate, which is extracted into ethanol and measured by packed column gas chromatography with nitrogen-sensitive detection. The limit of quantitation in human urine is 1 microgram/ml and the between-sample coefficient of variation is 5-11%. Simultaneously, N,N-dimethylformamide, N-methylformamide and formamide can also be determined.     

Rapid method for the measurement of methylprednisolone and its hemisuccinate in plasma and urine following "pulse therapy" by high-performance liquid chromatography

A rapid method for the measurement of methylprednisolone and its 21-hemisuccinate ester in plasma and urine following high dose pulse therapy is described. The drugs were extracted using Extrelut columns, eluted with ethyl acetate which was evaporated to dryness and the residue was reconstituted in chromatographic mobile phase. High-performance liquid chromatography was performed on a reversed-phase column using a mobile phase of acetonitrile-acetate buffer with detection at 251 nm. No interference from any drugs or endogenous compounds has been observed. The method has been used to analyse over 200 plasma and 150 urine samples from patients with rheumatoid disease or renal failure who have received high dose methylprednisolone hemisuccinate infusions.     

Direct derivatization of alprenolol and its 4-hydroxy metabolite in urine with phosgene and methanol prior to analysis by capillary column gas chromatography

A method for the determination of alprenolol and its 4-hydroxy metabolite has been developed. The urine sample is made alkaline with buffer (pH 12) and derivatized with 60 microliter of 2 M phosgene in toluene with vigorous shaking. In the presence of 2.5% methanol, an oxazolidineone methyl carbonate is formed from 4-hydroxy alprenolol. The now neutral derivatives are extracted with an equal volume of dichloromethane. After evaporation of the organic phase, the residue is taken up in a small volume of ethyl acetate and subjected to capillary column gas chromatography with CP-Sil 8 as the stationary phase. The precision was 2.1% at the 3.3 micrograms/ml level of the metabolite in urine (n = 8). The isopentylamino analogue was used as the internal standard.     

Mass fragmentographic quantitation of ethotoin and some of its metabolites in human urine.

A method for the determination of ethotoin and its p-hydroxylated and dealkylated metabolites in urine has been developed. Ethotoin and the metabolites were extracted from acidified urine with ethyl acetate and silylated before injection into a combined gas chromatograph--mass spectrometer. Four partly identified metabolites were recorded, but their exact quantitation was not possible as pure reference substances were not available. The limit of sensitivity was far below the amounts of ethotoin and of its metabolites found in urine from patients treated with therapeutic doses of ethotoin.     

Quantitative measurement of N-acetyl-L-aspartic acid in urine by gas chromatography with negative-ion chemical ionization mass spectrometry.

A highly specific and sensitive assay for N-acetyl-L-aspartic acid has been developed. The trideuterated compound was synthesized and used as an internal standard for gas chromatography with negative-ion chemical ionization mass spectrometry. Urine samples were acidified and extracted with ethyl acetate, and the compounds converted into their pentafluorobenzyl ester derivatives. Under these conditions, sub-picogram amounts of the pure derivatives could be detected. Thus, only microliter volumes of urine samples have to be processed to achieve reliable quantification of "basal" levels of N-acetyl-L-aspartic acid.     

Concentration profiles of cocaine, pyrolytic methyl ecgonidine and thirteen metabolites in human blood and urine: determination by gas chromatography-mass spectrometry

When cocaine is smoked, a pyrolytic product, methyl ecgonidine (anhydroecgonine methyl ester), is also consumed with the cocaine. The amount of methyl ecgonidine formed depends on the pyrolytic conditions and composition of the illicit cocaine. This procedure describes detection of cocaine and 10 metabolites--cocaethylene, nor-cocaine, nor-cocaethylene, methyl ecgonine, ethyl ecgonine, benzoylecgonine, nor-benzoylecgonine, m-hydroxybenzoylecgonine, p-hydroxybenzoylecgonine and ecgonine--in blood and urine. In addition, the detection of pyrolytic methyl ecgonidine and three metabolites--ecgonidine (anhydroecgonine), ethyl ecgonidine (anhydroecgonine ethyl ester) and nor-ecgonidine (nor-anhydroecgonine)--are included. The newly described metabolites, ethyl ecgonidine and nor-ecgonidine, were synthesized and characterized by gas chromatography-mass spectrometry (GC-MS). All 15 compounds were extracted from 3 mL of blood or urine by solid-phase extraction and identified by a GC-MS method. The overall recoveries were 49% for methyl ecgonine, 35% for ethyl ecgonine, 29% for ecgonine and more than 83% for all other drugs. The limits of detection were between 0.5 and 4.0 ng/mL except for ecgonine, which was 16 ng/mL. Linearity for each analyte was established and in all cases correlation coefficients were 0.9985-1.0000. The procedure was applied to examine the concentration profiles of analytes of interest in post-mortem (PM) blood and urine, and in urine collected from living individuals (LV). These specimens previously were shown to be positive for the cocaine metabolite, benzoylecgonine. Ecgonidine, the major metabolite of methyl ecgonidine, was present in 77% of PM and 88% of the LV specimens, indicating smoking as the major route of cocaine administration. The new pyrolytic metabolites, ethyl ecgonidine and nor-ecgonidine, were present in smaller amounts. The urine concentrations of nor-ecgonidine were 0-163 ng/mL in LV and 0-75 ng/mL in PM specimens. Ethyl ecgonidine was found only in PM urine at concentrations 0-39 ng/mL. Ethanol-related cocaine metabolites, ethyl ecgonine or cocaethylene, were present in 69% of PM and 53% of cocaine-positive LV specimens, implying alcohol consumption with cocaine use. The four major metabolites of cocaine--benzoylecgonine, ecgonine, nor-benzoylecgonine and methyl ecgonine--constituted approximately 88 and 97% of all metabolites in PM and LV specimens, respectively. The concentrations of nor-cocaine and nor-cocaethylene were consistently the lowest of all cocaine metabolites. At benzoylecgonine concentrations below 100 ng/mL, ecgonine was present at the highest concentrations. In 20 urine specimens, benzoylecgonine and ecgonine median concentrations (range) were 54 (0-47) and 418 ng/mL (95-684), respectively. Therefore, detection of ecgonine is advantageous when benzoylecgonine concentrations are below 100 ng/mL.     

High-performance liquid chromatographic determination of a cysteine protease inhibitor and its ethyl ester in mouse serum and muscle by pre-column fluorescence derivatization

A simple and sensitive high-performance liquid chromatographic method has been developed for the determination of a cysteine protease inhibitor (E-64-c) and its ethyl ester in mouse serum and muscle samples. After deproteinization with acetone, E-64-c is converted into a fluorescent derivative by reaction with 3-bromomethyl-6,7-dimethoxy-1-methyl-2(1H)-quinoxalinone. The derivative is separated on a reversed-phase column by isocratic elution of aqueous acetonitrile and monitored fluorimetrically. The ethyl ester is hydrolysed to E-64-c by carboxyl esterase and then derivatized in the same way as E-64-c. The limits of detection, at a signal-to-noise ratio of 3, of E-64-c and the ester are 500 pmol/ml in serum (10 microliters) and 300 pmol/g in muscle (20 mg), corresponding to ca. 0.5 pmol each in a 50-microliters injection volume. The method allows the determination of E-64-c and the ethyl ester in mouse serum and muscle after oral administration of these compounds.     

气相色谱-氮磷检测法检测尿中劳拉西泮

 报道了尿中劳拉西泮的气相色谱 氮磷检测器的检测方法。检测时以 2 羟乙基氟西泮为内标 ,用 β 葡萄糖醛酸苷酶水解后于碱性条件下用乙醚萃取 ,将萃取液浓缩后进行检测。劳拉西泮的萃取率 (mean±SD)为 ( 83 4±3 1) % ,检出限为 5 μg/L。萃取物用N ,O 双 (三甲硅烷基 )三氟乙酰胺 (BSTFA)衍生化后进行三甲基硅烷 (TMS)衍生物检测。     

稀土对大鼠代谢产物影响的核磁共振研究

以高场核磁共振技术为研究手段,通过分析腹腔注射０．２、２、１０、２０ｍｇ／ｋｇ体重剂量的Ｌａ（ＮＯ３）３后大鼠尿液中代谢物浓度、物种的变化,研究了稀土化合物在动物体内的作用情况,结果表明,稀土的引入使动物肾脏和肝脏都受到一定程度的损伤,并在代谢物中挑选出了合适的ＮＭＲ ｍａｒｋｅｒｓ,其变化可以反映稀土离子作用后大鼠的异常代谢。     

Development of a screening method for cocaine and cocaine metabolites in urine using solvent microextraction in conjunction with gas chromatography

A simple, quick and inexpensive screening method for cocaine and cocaine metabolites has been developed. Drug extraction was achieved using the relatively new technique of solvent microextraction (SME). Complete analysis is achieved in 13 min, using, a 6-min extraction with a 2-microl drop followed by separation on a gas chromatograph. The developed procedure was tested as a screening method for cocaine and cocaine metabolites in spiked urine samples. Using SME, concentrations as low as 0.125 microg ml(-1) of cocaine, ecgonine methyl ester, cocaethylene and anhydroecgonine methyl ester were measurable with relative standard deviation values averaging 9.0%.     

Preparation of eicosapentaenoic acid ethyl ester from fish oil ethyl esters by continuous batch chromatography

Fish oils are rich in eicosapentaenoic acid, which has the wide‐ranging biological activities. The rapid and efficient separation of eicosapentaenoic acid ethyl ester from fish oils ethyl ester is still regarded as a challenge. In this study, we described an effective and flexible chromatography for eicosapentaenoic acid ethyl ester preparation, named continuous batch chromatography, which combined the batch chromatography with the continuous chromatographic operation mode. After continuous batch chromatography experiment, the recovery of eicosapentaenoic acid ethyl ester was 82.01%, the average relative purity and the relative highest purity of eicosapentaenoic acid ethyl ester were 97.82 and 98.98%. The productivity of continuous batch chromatography was 5.48 times higher than that of batch chromatography, while the solvent consumption of eicosapentaenoic acid ethyl ester was 78% of the batch chromatography. This study provided a reference for the separation of the targeted chemical component from multi‐component mixtures.     

Gas chromatographic analysis of urinary dimercaptosuccinic acid

The therapeutic use of disulfhydryl compounds such as 2,3-dimercaptosuccinic acid (DMSA) for the treatment of heavy metal poisoning has generated a requirement for specific and sensitive methods to determine those compounds in biological media. We have developed a gas chromatographic assay for DMSA in urine. The use of capillary column technology eliminates the requirement for a preliminary clean-up step. Samples are first reduced electrochemically to liberate DMSA present as disulfides. The reduced product is then extracted into ethyl acetate and the organic phase removed by evaporation. The residue is derivatized with N,O-bis (trimethylsilyl) acetamide for gas chromatography. The silylated DMSA derivative is then detected with a flame ionization detector. The detection limit for DMSA is 1.9 nmol per 1-microliter aliquot of derivatized extract injected on column (detector sensitivity at 1.10(-11) A/mV). The utility of the method was demonstrated by analyzing the urine of rats orally dosed with DMSA.     

Determination of carnitine by high-performance liquid chromatography using 9-anthryldiazomethane

The high-performance liquid chromatographic determination of carnitine chloride was investigated by using 9-anthryldiazomethane (ADAM) as a pre-column derivatization reagent. Carnitine chloride and the internal standard N,N-dimethylglycine reacted with ADAM to give a stable ester derivative in the presence of sodium dodecyl sulphate (SDS) used to mask the basic function. The ADAM derivative of carnitine was separated from decomposition products of the reagent and related compounds such as amino acid derivatives on a silica gel column eluted with methanol-5% aqueous SDS-phosphoric acid (990:10:1). The calibration plot was linear over a sample concentration range from 0.02 to 100 ng per injection. The detection limit for carnitine chloride was about 1 pg per injection (signal to noise ratio = 4), by fluorometric detection.     

液液萃取-气相色谱-质谱联用法同时检测烟用水基胶中的23种酯类化合物

建立了一种同时检测烟用水基胶中23种酯类化合物的液液萃取-气相色谱-质谱联用方法。23种酯类化合物包括乙酸酯类、丙烯酸酯类、甲基丙烯酸酯类、邻苯二甲酸酯类化合物。水基胶样品经水分散后,用含内标物丙酸苯乙酯的正己烷溶液振荡萃取,萃取液离心后过0.45 μm有机相滤膜,用DB-WAXETR气相色谱柱(60 m×0.25 mm×0.25 μm)分离,质谱选择离子模式监测,内标法定量。结果表明,23种酯类化合物在0.4~50.0 mg/L范围内线性关系良好,线性相关系数大于0.998,样品加标回收率为81.8%~109.1%,相对标准偏差(RSD, n=5)小于4%,检出限为0.02~0.76 mg/kg,定量限为0.04~2.52 mg/kg。该方法前处理简便、快速、分析时间短、灵敏度高、重复性好,可用于烟用水基胶中23种酯类化合物的同时检测。     

Stir bar sorptive extraction-thermal desorption-capillary GC-MS applied to biological fluids

A new sample preparation method, stir bar sorptive extraction (SBSE), has been evaluated for the enrichment of organic solutes from biological fluids such as urine and blood. In SBSE, a stir bar coated with a polydimethylsiloxane layer is stirred for a given time in the sample. After sampling the stir bar is placed in a thermal desorption unit coupled on-line to capillary gas chromatography-mass spectrometry (SBSE-TD-CGC-MS). The principle and operation of SBSE are presented. Total profiling and target compound analysis have been selected as applications to illustrate the performance of SBSE-TD-CGC-MS (MSD). It is demonstrated that a variety analytes ranging from biological markers (phenols, hormones, fatty acids) to artificial contaminants (recreational drugs, plasticizers) can be enriched with high sensitivity. For polar solutes, in-situ derivatization can enhance both recovery into the polydimethylsiloxane (PDMS) layer and chromatographic analysis. Two types of derivatization have been applied, derivatization with ethyl chloroformate and with acetic acid anhydride. Linearity, detectability, and repeatability are illustrated by the determination of 1-hydroxypyrene in a urine sample from a smoker.     

Measurement of imidazoleacetic acid in urine by gas chromatography-mass spectrometry

Imidazoleacetic acid (IAA), a histamine and histidine metabolite, was quantified in human urine by gas chromatography-mass spectrometry (GC-MS). The acid was separated by ion-exchange chromatography, derivatized as the n-butyl ester with boron trifluoride-butanol and the derivative extracted with chloroform. GC-MS analysis was carried out by selected-ion monitoring of ions m/z 81 and m/z 83 corresponding, respectively, to IAA and [15N,15N']IAA used as internal standard. The mean IAA content in urine was about 8.02 nmol/mg of creatinine. The specificity of measurement was rigorously established by GC retention time, peak shape, ion abundance ratios, and recovery experiments. The method is capable of quantifying IAA in 0.05 ml of urine and in amounts as low as 0.20 nmol.     

Preparation,characterisation and gas transport properties of trifluoroacetylated ethyl cellulose

A mixed ester of ethyl cellulose (EC) has been prepared by reaction of trifluoroacetic anhydride with the residual hydroxy groups of ethyl cellulose. The mixed ester is soluble in tetrahydrofuran, dichloromethane, chloroform, benzene and pyridine. FTIR and NMR spectra show that hydroxy groups of ethyl cellulose were replaced by trifluoroacetoxy groups. The trifluoroacetyl ethyl cellulose (TFAEC) has higher selectivity for oxygen relative to nitrogen, in gas transport, than unmodified EC. Annealing at an elevated temperature further improves selectivity for oxygen, whilst subsequent ageing at ambient temperature partially reduces oxygen selectivity. The tensile strength of TFAEC is virtually the same as that of unmodified EC, but the elongation to break is 200% higher than for EC.