Measurement of methsuximide and N-desmethylmethsuximide using solid-phase extraction and wide-bore capillary gas chromatography

A method for the determination of the anti-epileptic drug methsuximide (MSM) and its active metabolite N-desmethylmethsuximide (NDM) is presented. 5-Methyl-5-phenylhydantoin is used as the internal standard. A simple solid-phase extraction procedure utilizing disposable reversed-phase C18 columns is described. Samples are analyzed by gas chromatography with flame ionization detection using a wide-bore capillary column with a permanently bonded, non-polar stationary phase. The MSM assay possesses linearity to 6.0 micrograms/mL, sensitivity to 0.5 microgram/mL, recovery ranging from 93 to 110%, and precision reflected by a SD of +/- 0.37 microgram/mL. The NDM assay displays linearity up to 80.0 micrograms/mL, sensitivity to 5.0 micrograms/mL, recovery of 90 to 100%, and precision reflected by a SD +/- 0.90 microgram/dL. Lack interference is documented for 6 commonly prescribed anti-epileptic drugs and 4 drugs with similar retention times on this stationary phase; only guaifenesin was found to potentially interfere with the determination of methsuximide. We conclude that the method reported here is ideally suited for monitoring therapeutic and toxic levels of this anti-epileptic drug.     

Determination of tri-n-butylphosphate in plasma using solid phase extraction and capillary gas chromatography

A simple method for the quantitative determination of tri-n-butylphosphate in blood plasma preparations is described. The sample is passed through an octadecyl extraction column from which tri-n-butylphosphate is eluted with chloroform. By capillary GC 50 micrograms/l tri-n-butylphosphate can be detected with a recovery of more than 90%.     

Measurement of rimantadine in plasma by capillary gas chromatography/mass spectrometry with a deuterium-labeled internal standard

Rimantadine is a synthetic antiviral agent used in prophylaxis and in treating the early stages of uncomplicated influenza A illness. We describe a stable isotope-dilution assay involving capillary gas chromatography/mass spectrometry. We used 200 ng of d3-rimantadine, added to 1 mL of plasma, as the internal standard. The rimantadine was extracted from the plasma with a Bond-Elut CN column, the column was washed with water, and the rimantadine was eluted with methanol, dried, and treated to form the t-butyldimethylsilyl derivative. The mass spectrometer was operated in the selected ion monitoring mode. Ions at m/z 236 and m/z 239 were monitored, corresponding to the loss of C4H9 from the rimantadine derivative and d3-rimantadine, respectively. Within-run precision (CVs) ranged from 8.9% at 29 micrograms/L to 3.2% at 1666 micrograms/L. Corresponding data for between-run precision were 5.4% and 1.7%. Treated volunteers (n = 86) provided plasma samples with a concentration range of 153 to 1127 micrograms/L. This simplified method allows rapid, precise assay of rimantadine in plasma.     

A system for toxicological screening by capillary gas chromatography with use of a drug retention index based on nitrogen-containing reference compounds

Capillary gas chromatography with nitrogen-specific detection allows rapid screening of numerous drugs of toxicological interest. However, for accurate identification of individual peaks, the system must be well calibrated, e.g., through the use of retention indices (RI). To overcome problems associated with the use of RI's based on homologous series determined with nitrogen-specific detectors, we have developed an RI reference system based on molecular masses and retention times of nitrogen-containing compounds. The standards chosen are easily available in highly purified form and can be detected by the unmodified nitrogen-specific detector. By using temperature programming, we can obtain a linear relationship between the molecular masses of standards and their retention times. Used in conjunction with microcomputer data handling, this screening system is rugged and reliable, operating 22 h per day. In the past two years, we have screened greater than 3000 samples (blood, serum, urine, gastric lavage) without major problems.     

The screening of inborn errors of metabolism in sick Chinese infants by tandem mass spectrometry and gas chromatography/mass spectrometry

BackgroundAnalyses of amino acid/acylcarnitines in dried blood spots (DBS) and organic acids in urine are the primary tests for inborn errors of metabolism (IEMs). Automated tandem mass spectrometry (MS/MS) and gas chromatography/mass spectrometry (GC/MS) can rapidly and simultaneously detect numerous metabolic compounds with high precision and sensitivity.MethodsThree thousand four hundred and twenty-nine DBSs and 2781 urine samples were collected from our hospital patients with suspected IEMs, and analyzed for amino acid/acylcarnitines and organic acids by MS/MS and GC/MS, respectively. The results were used in a coincidental survey to determine the efficacy of these methods for the diagnosis of IEMs.ResultsNineteen different types of IEMs were detected in 121 affected cases (1.95% of 6210 samples). There were 66.12% amino acid disorders, 29.75% organic acid disorders and 4.13% with fatty acid oxidation disorders. Conclusions: the sick infants tested in this study had high prevalence rates of neonatal intrahepatic cholestasis, methylmalonic acidemia, hyperphenylalaninemia, tyrosinemia type I, and urea cycle disorders.ConclusionThe combined use of MS/MS and GC/MS is an appropriate tool for screening of IEMs in sick infants.     

Application of gas chromatography/mass spectrometry instrument techniques to forensic urine drug testing

Appropriate GC/MS analytical techniques can provide conclusive confirmatory evidence for the presence of drugs and metabolites in forensic urine drug testing. Although forensic laboratories are required to utilize GC/MS, they have flexibility in selecting instrumentation, modes of operation, and actual analytical methods. Because a laboratory's accreditation status, reputation, and economic well-being depend on consistently accurate results, it is important to use optimal analytical procedures so that reliability and accuracy are maximized. Pitfalls in conventional EI SIM techniques can lead to high rates of false-positive and false-negative results. Different mass spectrometric operating modes such as CI and full-scan can be used to complement SIM analyses. These modes are useful in solving difficult identification problems and in enhancing both specificity and sensitivity. Newer types of GC/MS systems based on ion trapping offer the promise of technologic advances in enhanced analytical performance and productivity gains. Knowledge of the advantages and potential pitfalls of different GC/MS systems as well as different ionization and detection modes is helpful in optimizing the accuracy of compound identification.     

Determination of serum triglycerides by capillary on-column gas chromatography

We report an accurate method, based on capillary on-column gas chromatography, for determining triglycerides in human serum. After serum extraction and chemical hydrolysis, glycerol is directly measured by gas chromatography (GC). With our extraction method no free glycerol is extracted from serum. The accuracy of this method was compared with that of a method based on the original procedure of Carlson (J. Atheroscler. Res. 3, 334-336 (1963)) and which is standardized by the Centers for Disease Control (CDC, Atlanta, U.S.A.). Orthogonal regression analysis of the GC method (y) and the CDC reference method (X) resulted in y = 0.996 X + 0.000 with a correlation coefficient of 0.999. The variances of analytical data, collected over a two month period showed that, for the GC method, the within-day coefficient of variation (CV) was less than 1.43%; the between-day CV less than 1.35%. The data for the CDC method were less than 3.36% (within-day) and less than 6.38% (between-days). The CDC method is linear up to 3.7 mmol/l and the GC method to 22 mmol/l.     

Method for screening urinary steroids by gas chromatography

Numerous methods are available for measuring urinary steroids in evaluating endocrine dysfunctions. Measurements of these particular steroids, or groups of them, usually involve tedious isolation methods, corrections for interferences and losses of the steroid, and (or) expensive reagents. We show how gas-liquid chromatography provides a rapid, sensitive, and direct method for several steroid metabolites in urine. Androstanol, androsterone, etiocholanolone, dehydroisoandrosterone, pregnanediol, pregnanetriol, 11-keto-17-ketosteroids, and the 11beta-hydroxy-17-ketosteroids can be identified and quantified.     

Rendering the "poppy-seed defense" defenseless: identification of 6-monoacetylmorphine in urine by gas chromatography/mass spectroscopy

We report a sensitive, rapid, quantitative gas chromatographic/mass spectroscopic method for measuring the 6-monoacetylmorphine (6-MAM) metabolite of heroin in 0.5 mL of human urine. After a simple liquid-liquid extraction and derivatization, the trimethylsilyl derivative of 6-MAM is identified from its retention time (total ion current) and by selected ion monitoring. The limit of detection was 10 micrograms/L, corresponding to 0.2 ng of trimethylsilyl-6-MAM injected into the gas chromatograph/mass spectrometer. The presence of 6-MAM in urine is indicative of heroin. 6-MAM is not present in poppy seeds or in urine after the ingestion of products containing poppy seed.     

Specific quantitation of plasma medroxyprogesterone acetate by gas chromatography/mass spectrometry

Investigation of various derivatives (O-methyloxime, trifluoroenol acetate and t-butyldimethylsilyl enol ether) coupled with the efficient preparation of a trideuterated analogue of medroxyprogesterone acetate, has allowed the development of a rapid and accurate assay for its quantitation in plasma by isotope dilution gas chromatography/mass spectrometry. High oral doses (2.8 g weekly) of medroxyprogesterone acetate are shown to lead consistently to plasma levels of less than 16 ng.ml-1.     

Measurement of glucose and fructose in clinical samples using gas chromatography/mass spectrometry

Objective:The impact of increased fructose consumption on carbohydrate metabolism is a topic of current interest, but determination of serum level has been hindered due to low concentration and interference from serum glucose. We are reporting a method for the quantification of glucose and fructose in clinical samples using gas chromatography/mass spectrometry (GC/MS). The accuracy and precision of GC/MS and an enzymatic assay were compared.Design and methods:Mass spectrometry fragmentation patterns of methyloxime peracetate derivatized aldose and ketose were determined. Unique fragments for glucose and fructose were used for quantitative analysis using isotope labeled recovery standards.Results:Methyloxime peracetate derivatives of glucose and fructose showed characteristic loss of acetate (M-60) or ketene (M-42) under chemical ionization (CI). Under electron impact (EI) ionization, a unique C1–C2 fragment of glucose was formed, while a C1–C3 fragment was formed from keto-hexoses. These unique fragments were used in the quantitative assay of glucose and fructose in clinical samples. In clinical samples, the GC/MS assay has a lower limit of detection than that of the enzymatic assay. In plasma samples from patients evaluated for diabetes the average serum glucose and fructose were 6.19 ± 2.72 mM and 46 ±  25.22 μM. Fructose concentrations in many of these samples were below the limit of detection of the enzymatic method.Conclusion:Derivatization of aldose and ketose monosaccharides to their respective O-methyloxime acetates for GC/MS analysis is a facile method for determination of serum/plasma glucose and fructose samples.     

Urinary steroid profiles in pregnancy by capillary column gas chromatography

A qualitative and quantitative method for the estimation of urinary steroids during pregnancy by capillary column gas chromatography has been developed. Steroid conjugates were hydrolysed by enzymes and free steroids isolated by extraction using SEP-PAK C18 cartridges. Methoxime-trimethylsilyl derivatives of the steroids were characterized by packed column gas chromatography-mass spectrometry and subsequently by their retention indices on capillary column gas chromatography. Of the 48 peaks resolved on the profiles about 35 were identified as steroids. The retention indices of reference steroids were very reproducible in the short term showing a mean coefficient of variation of 0.015%. The columns allowed 95% valley resolution of steroids whose retention indices differed by only 7 units. The use of an on-column injection technique contributed to the high precision for replicate injections (coefficient of variation less than 1%) while for reference steroids, and well-resolved peaks in the urine profile, the mean coefficient of variation for the complete assay was less than 10%. To the best of our knowledge this is the first report concerning the quantitation, with good precision, of a large number of steroids in pregnancy urine.     

Rapid analysis of parathion in biological samples using headspace solid-phase micro-extraction (HS-SPME) and gas chromatography/mass spectrometry (GC/MS).

A simple and rapid method for the analysis of parathion in biological samples is presented. The method consists of the extraction of parathion from blood samples by headspace solid-phase micro-extraction (SPME), followed by capillary gas chromatography and mass spectrometry detection. The recoveries in the blood samples after addition of ammonium sulphate and sulphuric acid were between 85% and 89% compared to samples prepared in water. Linearity was established over a concentration range of 0.1-5 microg/g blood with acceptable coefficients of correlation and limits of detection reached 0.02-0.05 microg/g. The time for an analysis is 57 minutes for one sample, including the extraction step. In conclusion, HS-SPME in combination with GC/MS is an effective method for the determination and quantification of parathion-ethyl and parathion-methyl in biological material.     

Determination of six organophosphorus pesticides in water samples by three-dimensional graphene aerogel-based solid-phase extraction combined with gas chromatography/mass spectrometry

In the present study, a three-dimensional graphene aerogel (3D-GA), synthesised by chemical reduction of an aqueous solution of graphene oxides (GOs) with ethylenediaminethermal by a simple water bath method followed by freeze-drying treatment, was used for the solid-phase extraction (SPE) of six organophosphorus pesticides (OPPs) (i.e. trichlorfon, dimethoate, ethoprophos, parathion, fenitrothion and fenthion) from water samples. The target analytes were extracted using packed SPE cartridges and then eluted with tetrahydrofuran. The eluate was collected and dried with high-purity nitrogen gas at room temperature. After redissolving in acetone, the residue was analysed using gas chromatography/mass spectrometry (GC/MS). The proposed method demonstrated a good linearity between 0.5 and 500 μg L⁻¹ with the correlation coefficient of 0.9990–0.9998. The limits of detection (LODs) (S/N = 3) and the limits of quantification (LOQs) (S/N = 10) for the six OPPs pesticides were in the range of 0.12–0.58 μg L⁻¹ and 0.41–1.96 μg L⁻¹, respectively. The accuracy of the present method was evaluated by measuring the recovery of the spiked samples, which ranged from 93.8% to 104.2% with relative standard deviations (RSDs) of 1.1–5.6%. The established method was successfully applied to the determination of the target analytes in environmental water samples including tap water, river water, drinking water and lake water, demonstrating its great potential for the determination of OPPs in water.

3D graphene aerogel fabricated via chemical reduction followed by freeze-drying treatment was used as SPE sorbent to extract OPPs from water sample.     

Quantitative determination of unconjugated pterins in urine by gas chromatography/mass fragmentography

A gas chromatographic/mass fragmentographic method is described which permits the determination of unconjugated pterins in urine. After the addition of 6,7-dimethylpterin as an internal standard, the acidified urine samples are purified by liquid chromatography on Dowex-50 and Dowex-1 columns. The pterins are then converted to their corresponding trimethylsilyl derivatives and the base peaks of biopterin ($\text{m}\text{e}\text{409}$), neopterin ($\text{m}\text{e}\text{409}$) and 6,7-dimethylpterin ($\text{solm}\text{e}\text{320}$) are determined. The method is sensitive and specific and permits the processing of large numbers of samples. By means of this method, the urinary excretion of biopterin and neopterin from 9 healthy subjects has been determined.