Positive Ion Chemical Ionization Mode Research Articles

GC-MS Studies on Derivatization of Creatinine and Creatine by BSTFA and Their Measurement in Human Urine.

In consideration of its relatively constant urinary excretion rate, creatinine (2-amino-1-methyl-5H-imidazol-4-one, MW 113.1) in urine is a useful endogenous biochemical parameter to correct the urinary excretion rate of numerous endogenous and exogenous substances. Reliable measurement of creatinine by gas chromatography (GC)-based methods requires derivatization of its amine and keto groups. Creatinine exists in equilibrium with its open form creatine (methylguanidoacetic acid, MW 131.1), which has a guanidine and a carboxylic group. Trimethylsilylation and trifluoroacetylation of creatinine and creatine are the oldest reported derivatization methods for their GC-mass spectrometry (MS) analysis in human serum using flame- or electron-ionization. We performed GC-MS studies on the derivatization of creatinine (d0-creatinine), [methylo-2H3]creatinine (d3-creatinine, internal standard) and creatine (d0-creatine) with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) using standard derivatization conditions (60 min, 60 °C), yet in the absence of any base. Reaction products were characterized both in the negative-ion chemical ionization (NICI) and in the positive-ion chemical ionization (PICI) mode. Creatinine and creatine reacted with BSTFA to form several derivatives. Their early eluting N,N,O-tris(trimethylsilyl) derivatives (8.9 min) were found to be useful for the precise and accurate measurement of the sum of creatinine and creatine in human urine (10 µL, up to 20 mM) by selected-ion monitoring (SIM) of m/z 271 (d0-creatinine/d0-creatine) and m/z 274 (d3-creatinine) in the NICI mode. In the PICI mode, SIM of m/z 256, m/z 259, m/z 272 and m/z 275 was performed. BSTFA derivatization of d0-creatine from a freshly prepared solution in distilled water resulted in formation of two lMate-eluting derivatives (14.08 min, 14.72 min), presumably creatinyl-creatinine, with the creatininyl residue existing in its enol form (14.08 min) and keto form (14.72 min). Our results suggest that BSTFA derivatization does not allow specific analysis of creatine and creatinine by GC-MS. Preliminary analyses suggest that pentafluoropropionic anhydride (PFPA) is also not useful for the measurement of creatinine in the presence of creatine. Both BSTFA and PFPA facilitate the conversion of creatine to creatinine. Specific measurement of creatinine in urine is possible by using pentafluorobenzyl bromide in aqueous acetone.

GC Analysis of Seven Seed Oils Containing Conjugated Fatty Acids

The fatty acid compositions, including isomer compositions, of seven seed oils containing conjugated fatty acids (CFA) were determined. Seed oils were extracted using a modified Folch extraction, converted to fatty acid methyl esters, and analyzed by gas chromatography (GC) with mass spectrometry and flame ionization detection. The MS detector was operated in positive-ion chemical ionization mode using methane reagent gas. GC was performed using two columns providing different retention characteristics: a poly(ethylene glycol) column and a more polar biscyanopropyl column. The complimentary information provided by the two columns was crucial to peak identification in several cases. The major CFA species in the samples are well known but all contained lesser amounts of additional CFA that have not been widely reported. All samples contained multiple species of conjugated linolenic acid, and two samples also contained small amounts of conjugated linoleic acid. The seed oils of Jacaranda mimosifolia and Calendula officinalis were found to contain 8c,10t,12t-18:3, the natural occurrence of which has only been recently reported in some other samples. The seed oil of Impatiens balsamina has been reported to contain four conjugated 18:4 species, and we present evidence for a fifth conjugated 18:4 isomer.

Deep hydroconversion of ethanol-soluble portion from the ethanolysis of Dahuangshan lignite to clean liquid fuel over a mordenite supported nickel catalyst

A highly active mordenite (M)-supported nickel catalyst Ni/M was prepared via a modified deposition-percipitation and used for catalyzing hydroconversion of ethanol-soluble portion (ESP) from the ethanolysis of Dahuangshan lignite. The Ni nanoparticles were uniformly dispersed on the support without apparent agglomeration. Moreover, the number and yields of the species detected in ESP are obviously different from those detected in catalytically hydrogenated ESP (CHESP). The contents of aromatic ring (AR)-containing compounds and/or heteroatom-containing compounds (HACCs, some of which also contain an AR or ARs) in CHESP are significantly lower than those in ESP, while the alkanes (30.4%) and cyclanes (54.7%) contents in CHESP are much higher than those in ESP according to the analysis with a gas chromatograph/mass spectrometer. Furthermore, according to the analysis with a quadrupole exactive orbitrap mass spectrometer using atmospheric-pressure chemical ionization in positive-ion mode, the number and yields of HACCs in CHESP are significantly lower than those in ESP. The catalytic hydroconversion of lignite-related model compounds further confirms that the synergy between Ni nanoparticles and the M skeleton plays a crucial role in activating H2 to H···H and further activating H···H to H· and H+, which is the key to achieving the AR hydrogenation and the heteroatom removal at 160 °C.

Quantitative Determination of Anastrozole by Liquid Chromatography–Tandem Mass Spectrometry

Anastrozole is a potent and selective non-steroidal aromatase inhibitor and is used for therapy of postmenopausal women with hormone-receptor-positive breast cancer. This paper provides a detailed description of the determination of anastrozole in human plasma by liquid chromatography–mass spectrometry (LC–MS–MS). Plasma-sample pretreatment involved solid-phase extraction using Accubond SPE ODS-C18 cartridges. Chromatographic separation was carried out on a Zorbax Bonus-RP column with a mobile phase consisting of aqueous formic acid (0.2%) (eluent A) and MeOH (eluent B) with a ratio A:B = 30:70 (v/v) that was supplied at flow rate 0.2 mL/min. Detection was performed on an Agilent 6410-2K triple quadrupole tandem mass spectrometer by multiple reaction monitoring in the preset mass range 294.2 → 225.1 using atmospheric-pressure chemical ionization in positive-ion mode. A calibration curve for anastrozole was linear (R2 ≥ 0.97) over the concentration range 0.5 – 20.0 ng/mL with a lower detection limit of 0.5 ng/mL. The described procedures can be applied successfully to both therapeutic monitoring of anastrozole and drug bioequivalence studies.

Organophosphate and phthalate esters in standard reference material 2585 organic contaminants in house dust

The levels of 22 phthalate diesters (phthalates) and organophosphate triesters (organophosphates) have been investigated in standard reference material 2585 (SRM 2585) "organic contaminants in house dust." Ultrasonic-assisted solvent extraction and solid-phase extraction on a Florisil adsorbent were used as the extraction and cleanup steps combined with analysis using gas chromatography-tandem mass spectrometry in positive ion chemical ionization mode. Seven phthalates were detected in the concentration range 1-570 μg/g. Di(2-ethylhexyl) phthalate was the major phthalate present at 570 μg/g. Ten organophosphates were detected in SRM 2585. Tris(2-butoxyethyl) phosphate was the predominant organophosphate at 82 μg/g, and nine organophosphates were determined at concentrations ranging from 0.19 to 2.3 μg/g. Five organophosphates were below the method detection limit, of which two were in level with the procedural blank. The applied extraction and cleanup method was evaluated for the analysis of SRM 2585. The extraction yield was ≥99%, except for tris(2-chloroethyl) phosphate (97%) and diethyl phthalate (98.5%). The problem of calibration curvature is addressed, and it is shown that the use of deuterated standards improves the analysis. The concentrations of ten organophosphate esters were determined in SRM 2585, and seven of these were compared with existing data. To our knowledge, this is the first report of the levels of the seven phthalates esters in SRM 2585 "organic contaminants in house dust."

Investigation of reagent gases for the positive chemical ionization of select polybrominated diphenyl ethers

Abstract Polybrominated diphenyl ethers (PBDEs) fall into the class of compounds known as brominated flame retardants and their incorporation in a multitude of products is responsible for saving numerous lives. However, toxicology studies have alerted researchers to the potential adverse health effects that may develop as a result of prolonged or extreme exposure to these compounds. Frequent disposal and subsequent leaching has focused concern on environmental concentrations and current reports cite increasing levels. Method development continues in support of this research and the present work examines the feasibility of utilizing gas chromatography ion trap mass spectrometry operating in positive ion chemical ionization mode. In the evaluation of reagents for chemical ionization (methane, methanol and acetonitrile), comparative results of all three reagents demonstrated more difficult protonation as the number of bromine atoms increased. Methane, possessing the lowest proton affinity, provided the highest response for the analytes. Further, when methane chemical ionization was compared to electron impact ionization, the tetra-congener showed approximately 8× greater sensitivity and the penta- and hexa-congeners demonstrated approximately 2× greater. CI parameters, such as ionization and reaction times, were optimized to provide the highest analyte response and this was followed by the investigation of the employment of MS n . In the this mode, optimal excitation amplitude delivered sufficient fragmentation while maintaining maximum signal, yielding final instrument detection limits in the sub µg L − 1 range.

Gas Chromatography-Mass Spectrometry Detection of a Norfluoxetine Artifact in Hydrolyzed Urine Samples May Falsely Indicate Tranylcypromine Ingestion

In several cases, fluoxetine, its metabolites, its known artifacts, and supposedly tranylcypromine were detected in urine using the authors' systematic toxicological analysis (STA) procedure based on acid hydrolysis, extraction, and acetylation. As fluoxetine and tranylcypromine are absolutely contraindicated drugs and in none of the cases was tranylcypromine prescribed, the question of whether the detected compound might have been formed by fluoxetine and/or its metabolites arose. Therefore, rat urine taken after dosing with fluoxetine was screened in the same way. In addition, aqueous solutions of fluoxetine, norfluoxetine, tranylcypromine, and a mixture of the latter two drugs were worked-up and analyzed according to the STA and without hydrolysis. In urine specimens obtained from rats dosed with fluoxetine, tranylcypromine was detected as well as in the solution of worked-up norfluoxetine including hydrolysis. Its underlying mass spectrum could be identified by detailed interpretation of the fragmentation patterns as acetylated 3-phenyl-propyl-2-ene-amine. This compound could be postulated as hydrolysis product of norfluoxetine formed by ether cleavage and water elimination. Although this spectrum shows nearly the same fragmentation patterns as that of acetylated tranylcypromine, both compounds could finally be differentiated by their retention indices and by using the positive-ion chemical ionization mode.

Determination of antidepressants in human postmortem blood, brain tissue, and hair using gas chromatography–mass spectrometry

A gas chromatographic-mass spectrometric (GC-MS) method in positive ion chemical ionization mode in combination with a solid phase extraction was optimized for new-generation antidepressants and their metabolites in postmortem blood, brain tissue, and hair. Twelve antidepressants and their active metabolites (i.e., mirtazapine, viloxazine, venlafaxine, citalopram, mianserin, reboxetine, fluoxetine, fluvoxamine, sertraline, maprotiline, melitracen, paroxetine, desmethylfluoxetine, desmethylmianserin, desmethylmirtazapine, desmethylsertraline, desmethylmaprotiline, desmethylcitalopram, and didesmethylcitalopram) could be quantified. In this article, in addition to the validation of the GC-MS method, four postmortem cases are discussed to demonstrate the usefulness of the described method in forensic toxicology. In these cases, sertraline, fluoxetine, citalopram, and trazodone in combination with their active metabolites were quantified. Blood concentrations ranged from subtherapeutic to toxic concentrations, while brain to plasma ratios ranged from 0.8 to 17. Hair concentrations ranged from 0.4 to 2.5 ng/mg depending on the compound and hair segment.

GC–MS assay for hepatic DDAH activity in diabetic and non-diabetic rats by measuring dimethylamine (DMA) formed from asymmetric dimethylarginine (ADMA): Evaluation of the importance of S-nitrosothiols as inhibitors of DDAH activity in vitro and in vivo in humans

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis, is hydrolyzed to dimethylamine (DMA) and l-citrulline by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). In the present article we report on a GC–MS assay for DDAH activity in rat liver homogenate in phosphate buffered saline. The method is based on the quantitative determination of ADMA-derived DMA by GC–MS as the pentafluorobenzamide derivative. Quantification was performed by selected-ion monitoring of the protonated molecules at m/ z 240 for DMA and m/ z 246 for the internal standard (CD 3) 2NH in the positive-ion chemical ionization mode. The assay was applied to determine the enzyme kinetics in rat liver, the hepatic DDAH activity in streptozotocin-induced (50 mg/kg) diabetes in rats, and to evaluate the importance of S-nitrosothiols as DDAH inhibitors. The K M and V max values were determined to be 60 μM ADMA and 12.5 pmol DMA/min mg liver corresponding to 166 pmol DMA/min mg protein. Typical DDAH activity values measured in rat liver homogenate were 8.7 pmol DMA/min mg liver at added ADMA concentration of 100 μM. DDAH activity was found to be 1.7-fold elevated in diabetic as compared to non-diabetic rats ( P = 0.01). The SH-specific agents HgCl 2, S-nitrosocysteine ethyl ester (SNACET), a synthetic lipophilic S-nitrosothiol, S-nitrosoglutathione (GSNO), S-nitrosocysteine (CysNO) and S-nitrosohomocysteine (HcysNO) were found to inhibit DDAH activity in rat liver homogenate. The IC 50 values for HcysNO, SNACET, CysNO and GSNO were estimated to be 300, 500, 700 and 1000 μM, respectively. Oral administration of 15N-labelled SNACET to two healthy volunteers (1 μmol/kg) resulted in elevated urinary excretion of 15N-labelled nitrite and nitrate, but did not reduce creatinine-corrected excretion of DMA in the urine. Our results suggest that inhibition of DDAH activity on the basis of reversible nitros(yl)ation or irreversible N-thiosulfoximidation of the sulfhydryl group of the cysteine moiety involved in the catalytic process is most likely not a rationale design of DDAH inhibitors. A major advantage of the present GC–MS assay over other assays is that DDAH activity is assessed by measuring the formation of the specific enzymatic product DMA but not the formation of unlabelled or (radio)labelled l-citrulline or the decay of the substrate ADMA. The GC–MS assay reported here should be suitable to probe for DDAH activity in various disease models.

LC–MS Determination of Sterols in Olive Oil

Sterols in olive oils have been analyzed by liquid chromatography coupled to mass spectrometry with atmospheric-pressure chemical ionization in positive-ion mode. A simple procedure based on saponification and extraction of the compounds from olive oils was studied. Validation of the method included calibration and determination of recovery and repeatability was carried out. Good linearity was obtained up to 100 mg kg−1 for all the sterols studied except β-sitosterol, for which linearity was obtained up to 2,000 mg kg−1. Recovery ranged from 88 to 110%, detection limits from 0.9 to 3.1 mg kg−1, and precision was good. The method has been successfully used for analysis of sterols in different types of oil. The predominant sterol was β-sitosterol; other minor components, for example sitostanol and cholesterol, were also detected. Total sterol content depended on the type of oil, and ranged from 687 to 2,479 mg kg−1. Stigmasterol and the amount of erythrodiol plus uvaol can be used to distinguish between olive oil and seed oil.

Accurate quantification of dimethylamine (DMA) in human plasma and serum by GC–MS and GC–tandem MS as pentafluorobenzamide derivative in the positive-ion chemical ionization mode

Dimethylamine (DMA) circulates in human blood and is excreted in the urine. Major precursor for endogenous DMA is asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis. ADMA is hydrolyzed to DMA and l-citrulline by dimethylarginine dimethylaminohydrolase (DDAH). In previous work, we reported a GC–MS method for the quantification of DMA in human urine. This method involves simultaneous derivatization of endogenous DMA and the internal standard (CD 3) 2NH by pentafluorobenzoyl chloride (PFBoylCl) and extraction of the pentafluorobenzamide derivatives by toluene. In the present work, we optimized this derivatization/extraction procedure for the quantitative determination of DMA in human plasma. Optimized experimental parameters included vortex time and concentration of PFBoylCl, carbonate and internal standard. The GC–MS method was thoroughly validated and applied to measure DMA concentrations in human plasma and serum samples. GC–MS quantification was performed by selected-ion monitoring of the protonated molecules at m/ z 240 for DMA and m/ z 246 for (CD 3) 2NH in the positive-ion chemical ionization mode. Circulating DMA concentration in healthy young women ( n = 18) was determined to be 1.43 ± 0.23 μM in serum, 1.73 ± 0.17 μM in lithium heparin plasma, and 9.84 ± 1.43 μM in EDTA plasma. DMA was identified as an abundant contaminant in EDTA vacutainer tubes (9.3 ± 1.9 nmol/monovette, n = 6). Serum and lithium heparin vacutainer tubes contained considerably smaller amounts of DMA (0.42 ± 0.01 and 0.95 ± 0.01 nmol/monovette, respectively, each n = 6). Serum is recommended as the most appropriate matrix for measuring DMA in human blood. The present GC–MS method should be useful for the determination of systemic and whole body DDAH activity by measuring circulating and excretory DMA in experimental and clinical studies.

Selective determination of organophosphate flame retardants and plasticizers in indoor air by gas chromatography, positive‐ion chemical ionization and collision‐induced dissociation mass spectrometry

Gas chromatography/ion trap mass spectrometry with in-source ionization and dissociation was used in positive-ion chemical ionization (PICI) mode for the determination of organophosphate triesters in indoor air. These compounds are widely used as additive flame retardants and plasticizers in different types of materials and have become ubiquitous pollutants in indoor environments. When using collision-induced dissociation in PICI mode the fragmentation of the organophosphate triesters can be performed in a more controllable way than in electron ionization (EI) mode. The developed selected-reaction monitoring method provided high selectivity for the investigated compounds. For 8-h air measurements (corresponding to 1.5 m3 of sampled air) the limit of detection of the method was determined to be in the range 0.1-1.4 ng m(-3), which is comparable with nitrogen-phosphorus detection and about 50-fold lower than when using EI in selected-ion monitoring mode. The presented method was applied to samples from three common indoor environments, in which a number of organophosphate triesters were identified and quantified. The dominating compound was found to be tris(2-chloropropyl) phosphate, which occurred at levels up to 0.8 microg m(-3).

Analysis of the Labial Gland Secretions of the Male Bumblebee Bombus griseocollis (Hymenoptera: Apidae)

The labial gland secretions from males of the bumblebee Bombus (Separatobombus) griseocollis De Geer, a bumblebee exhibiting perching behaviour, were analysed by gas chromatography/mass spectrometry (GC/MS) in the electron impact and positive ion chemical ionization mode. The major compound of the complex mixture of alkenols, acetates, hydrocarbons, wax type esters and steroids is tetradecyl acetate, considerable amounts of hexadecyl, geranyllinaloyl, geranylgeranyl, docosyl, tetracosenyl and hexacosenyl acetate were also found. 1,3-Tetradecanediol diacetate, detected as a minor component, has not yet been identified in male bumblebee labial gland secretions. Besides small amounts of primary alcohols (tetradecanol and hexadecanol) the tertiary alcohol geranyllinalool (3,7,11,15-tetramethyl-hexadeca-1,6,10,14-tetraene-3-ol) was also present. The primary alcohols were also present as esters of butanoic, dodecanoic, tetradecanoic, and hexadecanoic acid. Besides the usual mixture of un- and mono-unsaturated straight chain hydrocarbons, the labial gland contains the isoprenoid hydrocarbons beta-springene [(6E, 10E)-7,11,15-trimethyl-3-methylene-hexadeca-1,6,10,14-tetraene] and two isomers of a-springene [(3Z,6E,10E)- and (3E,6E,10E)-3,7,11,15-tetramethyl-hexadeca-1,3,6,10,14-pentaene]. The close relationship in chemical composition in male bumblebees with perching and flight pass behaviour is discussed.

Analysis of the labial gland secretions of the male bumble bee Bombus perplexus Cresson (Hymenoptera: Apidae) from North America.

The labial gland secretions from males of the bumble bee Bombus (Pyrobombus) perplexus Cresson were analysed by gas chromatography/mass spectrometry (GC/MS) in the electron impact and positive ion chemical ionization mode. The major compound of the complex mixture of alkenols, alkenals, fatty acids, hydrocarbons, wax type esters and steroids is 3,7,11,15-tetramethyl-2,6,10-hexadecatrien-1-ol (geranylcitronellol), considerable amounts of hexadecan-1-ol and Z-9-hexadecen-1-ol were also found. All alcohols were present as esters of the detected acids. In older samples both the acids and the alcohols sometimes could not be detected in the GC; therefore, the possibility to check the detected acid-alcohol pattern by interpreting the wax type ester peaks is very instructive. Moreover, the labial gland contains a rich mixture of mono- and di-unsaturated straight chain hydrocarbons. The similarity in composition of the labial glands of the North American B. (Pyrobombus) perplexus with the Eurasian species B. (Pyrobombus) hypnorum corroborates the assumption that the two species are conspecific. The likely supposition that the hydrocarbons could play an essential role in the chemical communication in bumble bees is discussed.

Method for determination of pentobarbital in dry dog food by gas chromatography/mass spectrometry.

A procedure has been developed and validated for measuring the concentration of pentobarbital residues in dry, extruded animal feed in the range of 3-200 ng/g (ppb) with an estimated limit of quantitation of 2 ppb. The method was developed for surveillance purposes: to measure the concentration of euthanizing agent which might be present in feeds incorporating rendered products which themselves might include some fraction of euthanized animals. A previously published qualitative procedure was modified by adding isotopically labelled pentobarbital as an internal standard. Dry feed was ground and extracted with methanol. The extract was loaded on a mixed-mode (C-18, anion exchange) solid-phase extraction cartridge designed for barbiturate residues. Pentobarbital was eluted and derivatized for gas chromatography/mass spectrometry in positive ion chemical ionization mode. Quantitation was based on the ratio of dimethyl-pentobarbital MH+ (m/z 255) vs dimethyl-pentobarbital-d(5) (m/z 260) in standards and extracts. Accuracy ranged from 112% at 3 ppb to 96% at 200 ppb, with relative standard deviations ranging from 4% at 3 ppb to 2% at 200 ppb.

Quantitative analysis of l-alpha-acetylmethadol, l-alpha-acetyl-N-normethadol, and l-alpha-acetyl-N,N-dinormethadol in human hair by positive ion chemical ionization mass spectrometry.

A sensitive and specific method was developed for the quantitative analysis of l-alpha-acetylmethadol (LAAM), l-alpha-acetyl-N-normethadol (norLAAM), and l-alpha-acetyl-N,N-dinormethadol (dinorLAAM) in hair. In the development of this method, it was determined that sample pretreatment methods performed by the laboratory greatly affect the measured concentrations of drug and metabolite in hair. Deuterated internal standards were added to 20-mg hair samples and the samples digested overnight in a buffered solution of Protease Type VIII enzyme. Digests were extracted by modification of a liquid-liquid extraction procedure developed previously in our laboratory for the analysis of plasma and tissues. Derivatized extracts were analyzed on a Finnigan MAT 4500 mass spectrometer in positive ion chemical ionization mode using methane and ammonia reagent gases, helium carrier gas, and a DB-5MS (30 m, 0.25-micron film thickness) capillary column. The assay was linear to 50 ng/mg hair (r = 0.99) for all three compounds with a limit of quantitation experimentally determined to be 0.5 ng/mg for LAAM and 0.3 ng/mg for norLAAM and dinorLAAM. Intra-assay precision ranged from 1.0 to 10.5% for the three analytes at concentrations of 0.5, 5.0, and 25.0 ng/mg of hair. Interassay precision ranged from 4.7 to 12.9%. The performance of the method was also evaluated for its utility in detecting and quantitating LAAM, norLAAM, and dinorLAAM in hair from rats (n = 6) that had been administered 3 mg/kg LAAM intraperitoneally once daily for five days. LAAM, norLAAM and dinorLAAM were detectable in pigmented hair at concentrations of 1.27 ng/mg (+/-0.04), 1.28 ng/mg (+/-0.014), and 2.89 ng/mg (+/-0.014), respectively. Five laboratory wash solvents were then evaluated for their effect on the measured concentration of LAAM and metabolites in the rat hair. Phosphate buffer and 1% SDS washes substantially reduced the measured LAAM, norLAAM, and dinorLAAM concentrations by at least 30%, which suggests that drug incorporated into hair is removed (extracted) during the laboratory wash procedures. Wash procedures using methanol, methylene chloride, or water reduced the measured concentrations by no more than 20%. Because measured concentrations of LAAM, norLAAM, and dinorLAAM in hair appear to depend on the specific wash procedures used by a laboratory, quantitative data must be interpreted cautiously based on the sample pretreatment conditions.

Quantitative determination of codeine and its major metabolites in human hair by gas chromatography-positive ion chemical ionization mass spectrometry: a clinical application.

A highly sensitive method was developed for the quantitative analysis of codeine and morphine in human hair. After addition of deuterated internal standards, hair samples were digested overnight in 1N NaOH at 37 degrees C. Hydrolysis was performed on certain digests by addition of 1 mL 6N HCl. Digest solutions were extracted using a solid-phase procedure with Bond Elut Certify extraction columns. Derivatized extracts were analyzed on a Finnigan ion trap mass spectrometer (Magnum) in the positive ion chemical ionization mode using acetone as the reagent gas, helium as the carrier gas, and a DB-5 MS (30 m x 0.25-mm i.d.) capillary column. The assay was linear to 75 ng/mg (r = 0.99) and was capable of detecting 10 pg of codeine and morphine on-column. Intra-assay precision ranged from 8 to 20%. The method was used to quantitate codeine in human hair obtained from two male volunteers with dark brown to black hair after a single oral dose of 120 mg codeine phosphate liquid. Hair samples were plucked from the scalp for 28 days and then cut at the scalp. Codeine was detectable in 1-cm long hair (containing the bulb) at 12 h following the dose and remained detectable in the hair shaft for at least 8 weeks. Codeine metabolites were not detected in the hair of these two subjects. The method is currently being used in dose-response disposition studies to quantitate codeine and its major metabolites in human subjects.

Application of capillary supercritical fluid chromatography combined with benchtop mass spectrometry for the analysis of the macrolide antibiotic midecamycin A1

A capillary supercritical fluid chromatograph interfaced to an unmodified benchtop quadrupole mass spectrometer has enabled the relative molecular mass determination of midecamycin A1 in positive ion chemical ionization mode.

Positive and negative ion mass spectrometry of ten xanthine derivatives and their rapid clean-up with Sep-Pak C 18 cartridges from biological samples

Positive ion electron impact (PIEI), positive ion chemical ionization (PICI) and negative ion chemical ionization (NICI) mass spectra are presented for ten xanthine derivatives; and each fragmentation pathway has been analyzed. In the PIEI mode, molecular ions were generall intense and constituted base peaks in five compounds. Peaks at m z 42 (NCO) appeared in all compounds; fragment cations at m z 55, 68 (or 67) and 82 were observed in many compounds. In the PICI mode, all drugs showed intense [M+H] + quasi-molecular peaks together with small peaks at m z M+C 2H 5 and M+C 3H 5; fragment peaks at m z 44, 58, 72 and/or 84 (or 86) were also observed. In the NICI mode, [M−H] − quasi-molecular peaks appeared in nine compounds and constituted base peaks in five compounds; adduct anions at m z M+32 and/or M+C 3H 7, and fragment anions at m z 42, 165 and/or 179 were also observed in many compounds. Detection limits for total ion monitoring of the drugs in the PIEI, PICI and NICI modes were 2.2–10 ng, 11–28 ng and 7.8–14 ng on column, respectively. Xanthine derivatives present in human plasma or urine could be rapidly extracted by use of Sep-Pak C 18 cartridges with chloroform/methanol as elution solvent; recovery of the drugs from the plasma and urine was > 75%. They were also detected by capillary gas chromatography (GC) with both flame ionization detection (FID); their limits were 1.6–8.3 ng on column.

Characterization and purification of polyunsaturated fatty acids from microalgae by gas chromatography-mass spectrometry and countercurrent chromatography

The present study was undertaken in order to characterize then to purify fatty acids from marine phytoplankton. From a crude mixture of fatty acid methyl esters it was possible to isolate by countercurrent chromatography a mixture of four polyunsaturated fatty acid methyl ester identified as being hexadecatrienoic acid methyl ester, octadecatetraenoic acid methyl ester, eicosapentaenoic acid methyl ester and docosahexaenoic acid methyl ester by gas chromatography coupled with mass spectrometry in electron impact and in positive-ion chemical ionization mode. The four polyunsaturated fatty acids are in different ratios in mixtures from the two microorganisms:Skeletonema costatum andIsochrysis galbana.