Chromatography-atmospheric Pressure Chemical Ionization-mass Spectrometry Research Articles

Simultaneous quantification of vinblastine and desacetylvinblastine concentrations in canine plasma and urine samples using LC–APCI–MS/MS

A highly sensitive and specific liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (LC/APCI–MS/MS) method has been developed and validated for simultaneous quantification of vinblastine and its metabolite, desacetylvinblastine, in canine plasma and urine samples. Plasma and urine samples were processed by a solid phase extraction procedure. The optimal chromatographic behavior of these analytes was achieved on pentafluorophenyl (PFP) propyl analytical column (5μm, 50×2.1mm) under isocratic elution of 0.75mL/min with a mobile phase of 5mM ammonium acetate and methanol. The samples were analyzed in positive ion, multiple reaction monitoring mode. The calibration curves were linear over 0.125–2ng/mL (lower calibration curve); 2–100ng/mL (higher calibration curve) and 0.125–5ng/mL for vinblastine and desacetylvinblastine in plasma, and over 1–2000ng/mL and 0.5–100ng/mL for vinblastine and desacetylvinblastine in urine samples, respectively. The limits of quantitation of vinblastine and desacetylvinblastine were 0.125ng/mL in both matrices. The intra and interday accuracy was above 89% and precision below 8.6% for both analytes in both matrices. The developed method was successfully applied to ongoing in vivo vinblastine pharmacokinetic studies in dogs.

Bioequivalence Assessment of Two Formulations of Spironolactone in Chinese Healthy Male Volunteers

The bioavailability of a new spironolactone ((7alpha,17alpha)-7-(acetylthio)-17-hydroxy-3-oxopregn-4-ene-21-carboxylic acid gamma-lactone, CAS 52-01-7) formulation (test) was compared with a commercially available original formulation (reference) of the drug in 20 Chinese healthy male volunteers, aged between 21 and 27. The trial was designed as an open, randomized, single blind two-sequence, two-period crossover study. Under fasting conditions, each subject received a single oral dose of 100 mg spironolactone as a test or reference formulation with a 7-day washout period between the two formulations. The plasma concentrations of spironolactone and its active metabolite canrenone (CAS 976-71-6) were analyzed by a sensitive liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) method. The pharmacokinetic parameters included AUC(0.t), AUC(0-infinity), C(max), t1/2, and T(max). Values of AUC(0-t) demonstrate nearly identical bioavailability of spironolactone from the examined formulations. The AUC(0.12) of spironolactone was 148.35 +/- 39.5 and 144.39 +/- 53.02 ng x h/ml for the test and reference formulation, respectively. The AUC(0-60) of the metabolite canrenone was 1873.36 +/- 318.10 and 1911.28 +/- 355.60 ng h/ml for test and reference formulation, respectively. The maximum plasma concentration (C(max)) of spironolactone was 48.34 +/- 21.16 ng/ml for the test and 47.40 +/- 23.40 ng/ml for the reference product and the C(max) of the metabolite was 122.90 +/- 27.70 and 123.35 +/- 27.29 ng/ml for the test and reference product, respectively. No statistical differences were observed for C(max) and the area under the plasma concentration-time curve for both spironolactone and its active metabolite canrenone. 90% confidence limits calculated for C(max) and AUC from zero to infinity (AUC(0-infinity)) of spironolactone and its metabolite were included in the bioequivalence range (80%-125% for AUC). This study shows that the test formulation is bioequivalent to the reference formulation for spironolactone and its main active metabolite canrenone.

Methylation of Catechins and Procyanidins by Rat and Human Catechol-O-Methyltransferase: Metabolite Profiling and Molecular Modeling Studies

Catechins and procyanidins are major polyphenols in plant-derived foods. Despite intensive studies in recent years, neither their biochemical nor their toxicological properties have been clarified sufficiently. This study aimed to compare the methylation of catechins and procyanidins by the enzyme catechol-O-methyltransferase (COMT) in vitro. We conducted incubations with rat liver cytosol and human placental cytosol including S-adenosyl-l-methionine. The set of substrates comprised the catechins (-)-epicatechin (EC) and (+)-catechin (CAT), the procyanidin dimers B1, B2, B3, B4, B5, and B7 as well as procyanidin trimer C1. After extraction, metabolites were analyzed by means of liquid chromatography-electrospray ionization-mass spectrometry and liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry. EC and CAT were converted to two monomethylated metabolites each by human and rat COMT, with the 3'-O-methyl derivatives being consistently the main metabolites. Furthermore, the flavanyl units of procyanidins were methylated consecutively, leading to monomethylated and dimethylated dimeric metabolites as well as monomethylated, dimethylated, and trimethylated C1 metabolites. The methylation status of each flavanyl unit was determined by means of mass spectrometric quinone-methide fragmentation patterns. In addition, molecular modeling studies were performed with the aim to predict the preferred site of methylation and to verify the experimental data. In conclusion, our results indicate that the degree and position of methylation depend clearly on the three-dimensional structure of the entire substrate molecule.

Highly sensitive, quick and simple quantification method for mono and disaccharides in aqueous media using liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (LC–APCI–MS)

A highly sensitive, rapid LC–APCI–MS method for identification and quantification of mono and disaccharides in simple or complex aqueous phase has been developed. This original method is easy to use, no derivation and no post-column injection are needed. The separation is performed with a hydrophilic amino interaction (HILIC) column allowing high-throughput analysis with analysis times of 15 min for monosaccharides to 22 min for disaccharides. The development of the method carried out with 9 standard saccharides allowed to point out a dynamic range from 0.1–25.6 to 1–256 μg mL −1 depending on the considered sugar. Next, the method was validated on saccharides at known concentrations in water and on 2 real samples: orange juice and aqueous phase obtained after enzymatic hydrolysis of sunflower seeds.

A Review of Analytical Techniques for Determination of Glimepiride: Present and Perspectives

Glimepiride is an oral antidiabetic drug in the sulfonylurea class, which is widely used in treatment of Type 2 diabetes and it is currently available in more than 60 countries worldwide. As a result of the importance of this oral hypoglycemic agent in the treatment of noninsulin-dependent diabetes mellitus, this work aims to compile the published analytical methods reported so far in the literature for determination of glimepiride in biologic samples and pharmaceutical formulations. Techniques like high-performance liquid chromatography with ultraviolet, array-diode, mass spectroscopy, evaporative light scattering and charged aerosol detections, liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry, liquid chromatography-electrospray ionization-tandem mass spectrometry, semimicrobore high-performance liquid chromatography with column-switching, micellar electrokinetic chromatography, high-performance thin layer chromatography, polarography, and spectrophotometry have been used for analysis, from which it can be seen that high-performance liquid chromatography methods have been used most extensively.

LC–APCI–MS Simultaneous Determination of Barbital, Amobarbital, Phenobarbital and Secobarbital in Human Plasma

A sensitive and simple liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (LC–APCI–MS) method was developed and validated for determination of barbital, amobarbital, phenobarbital and secobarbital in human plasma. Barbiturate drugs extracted from plasma samples using ethyl ether and separation were carried out on an Agilent Zorbax SB-C18 column (2.1 mm × 150 mm, 5 μm) at 30 °C, acetonitrile–water used as mobile phase with gradient elution. APCI source was applied and operated in negative ion mode, and selective ion monitoring mode used to quantify barbiturate drugs. The method showed excellent intra-assay and inter-assay precision (relative standard deviation and bias <15%) for quality control samples spiked at concentrations of 10, 400 and 1,600 ng mL−1 and the r 2 > 0.99 over the range were investigated (10–2,000 ng mL−1). Lower limits of quantification were estimated to be 10 ng mL−1. This method is simple and sensitive for quantitation of barbiturate drugs in plasma, suitable for use in the clinical and forensic medical laboratory.

Determining Vitamin D Status: A Comparison between Commercially Available Assays

BackgroundVitamin D is not only important for bone health but can also affect the development of several non-bone diseases. The definition of vitamin D insufficiency by serum levels of 25-hydroxyvitamin D depends on the clinical outcome but might also be a consequence of analytical methods used for the definition. Although numerous 25-hydroxyvitamin D assays are available, their comparability is uncertain. We therefore aim to investigate the precision, accuracy and clinical consequences of differences in performance between three common commercially available assays.Methodology/Principal FindingsSerum 25-hydroxyvitamin D levels from 204 twins from the Swedish Twin Registry were determined with high-pressure liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (HPLC-APCI-MS), a radioimmunoassay (RIA) and a chemiluminescent immunoassay (CLIA). High inter-assay disagreement was found. Mean 25-hydroxyvitamin D levels were highest for the HPLC-APCI-MS technique (85 nmol/L, 95% CI 81–89), intermediate for RIA (70 nmol/L, 95% CI 66–74) and lowest with CLIA (60 nmol/L, 95% CI 56–64). Using a 50-nmol/L cut-off, 8% of the subjects were insufficient using HPLC-APCI-MS, 22% with RIA and 43% by CLIA. Because of the heritable component of 25-hydroxyvitamin D status, the accuracy of each method could indirectly be assessed by comparison of within-twin pair correlations. The strongest correlation was found for HPLC-APCI-MS (r = 0.7), intermediate for RIA (r = 0.5) and lowest for CLIA (r = 0.4). Regression analyses between the methods revealed a non-uniform variance (p<0.0001) depending on level of 25-hydroxyvitamin D.Conclusions/SignificanceThere are substantial inter-assay differences in performance. The most valid method was HPLC-APCI-MS. Calibration between 25-hydroxyvitamin D assays is intricate.

Possible Anandamide and Palmitoylethanolamide involvement in human stroke

BackgroundEndocannabinoids (eCBs) are ubiquitous lipid mediators that act on specific (CB1, CB2) and non-specific (TRPV1, PPAR) receptors. Despite many experimental animal studies proved eCB involvement in the pathogenesis of stroke, such evidence is still lacking in human patients. Our aim was to determine eCB peripheral levels in acute stroke patients and evaluate their relationship with clinical disability and stroke volume.MethodsA cohort of ten patients with a first acute (within six hours since symptoms onset) ischemic stroke and a group of eight age- and sex-matched normal subjects were included. Groups were also matched for metabolic profile. All subjects underwent a blood sample collection for anandamide (AEA), 2-arachidonoylglycerol (2-AG) and palmitoylethanolamide (PEA) measurement; blood sampling was repeated in patients on admission (T0), at 6 (T1) and 18 hours (T2) thereafter. Patients neurological impairment was assessed using NIHSS and Fugl-Meyer Scale arm subitem (FMSa); stroke volume was determined on 48 h follow-up brain CT scans. Blood samples were analyzed by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry.Results1)T0 AEA levels were significantly higher in stroke patients compared to controls. 2)A significant inverse correlation between T0 AEA levels and FMSa score was found. Moreover a positive correlation between T0 AEA levels and stroke volume were found in stroke patients. T0 PEA levels in stroke patients were not significantly different from the control group, but showed a significant correlation with the NIHSS scores. T0 2-AG levels were lower in stroke patients compared to controls, but such difference did not reach the significance threshold.ConclusionsThis is the first demonstration of elevated peripheral AEA levels in acute stroke patients. In agreement with previous murine studies, we found a significant relationship between AEA or PEA levels and neurological involvement, such that the greater the neurological impairment, the higher were these levels.

Decomposition of N‐hydroxylated compounds during atmospheric pressure chemical ionization

N-Hydroxylated polyamine derivatives were found to decompose during the ionization process of liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) experiments. The phenomenon was studied with a model compound, a synthetic N-hydroxylated tetraamine derivative. It was found that reduction, oxidation and water elimination occurred during APCI to generate the corresponding amine, N-oxide, and imine. The investigation further revealed that decomposition of hydroxylamines during APCI depends upon the concentration of the analyte and on the acidity of the solution introduced into the ionization source. The pH-dependence of decomposition was utilized for the development of an MS method that allows for the unambiguous identification of N-OH functionalities. This method was applied for the study of natural products including polyamine toxins from the venom of the spider Agelenopsis aperta and mayfoline, a cyclic polyamine derivative of the shrub Maytenus buxifolia.

Determination of ethylenethiourea in urine by liquid chromatography–atmospheric pressure chemical ionisation–mass spectrometry for monitoring background levels in the general population

This study reports a sensitive analytical method suitable for the quantitative analysis of ethylenethiourea (ETU) in human urine and its application to samples from the general population. Sample preparation involved the use of diatomaceous earth extraction columns to remove matrix interferences. Quantification was achieved by liquid chromatography–mass spectrometry using positive ion atmospheric pressure chemical ionisation. Within-day and between-day variability of 14% ( n = 10) and 11% ( n = 6), respectively, were obtained at 98 nmol/l (10 μg l −1). The assay was linear over the investigated range 2.5–245 nmol/l, with a limit of detection of 2.5 nmol/l. The method was applied to monitoring background levels of ETU in urine samples from the general population in the UK. Results obtained from 361 spot samples contained ETU levels ranging from less than the detection limit (54% of samples) to a maximum of 15.8 μmol/mol creatinine (14.3 μg/g creatinine). The 95th percentile was 5.7 μmol/mol creatinine (5.2 μg/g creatinine).

Circulating and hepatic endocannabinoids and endocannabinoid-related molecules in patients with cirrhosis

Endocannabinoids include anandamide (AEA) and 2-arachidonoylglycerol (2-AG). Endocannabinoid-related molecules like oleoyl-ethanolamine (OEA) and palmitoyl-ethanolamine (PEA) have also been identified. AEA contributes to the pathogenesis of cardiovascular alterations in experimental cirrhosis, but data on the endocannabinoid system in human cirrhosis are lacking. Thus, we aimed to assess whether circulating and hepatic endocannabinoids are upregulated in cirrhotic patients and whether their levels correlate with systemic haemodynamics and liver function. The endocannabinoid levels were measured in peripheral and hepatic veins and liver tissue by isotope-dilution liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry. Systemic haemodynamics were assessed by the transthoracic electrical bioimpedance technique. Portal pressure was evaluated by hepatic venous pressure gradient. Circulating AEA and, to a greater extent, PEA and OEA were significantly higher in cirrhotic patients than in controls. PEA and OEA were also increased in the cirrhotic liver tissue. AEA, OEA and PEA levels were significantly higher in peripheral than in the hepatic veins of cirrhotic patients, while the opposite occurred for 2-AG. Finally, circulating AEA, OEA and PEA correlated with parameters of liver function, such as serum bilirubin and international normalized ratio. No correlations were found with systemic haemodynamics. The endocannabinoid system is upregulated in human cirrhosis. Peripheral AEA is increased in patients with a high model of end-stage liver disease score and may reflect the extent of liver dysfunction. In contrast, the 2-AG levels, the other major endocannabinoid, are not affected by cirrhosis. The upregulation of the endocannabinoid-related molecules, OEA and PEA, is even greater than that of AEA, prompting pharmacological studies on these compounds.

Determination of 20(S)-Ginsenoside Rh1 and its Aglycone 20(S)-Protopanaxatriol in Rat Plasma by Sensitive LC-APCI-MS Method and its Application to Pharmacokinetic Study

Liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) method has been developed for the measurement of the concentrations of 20(S)-ginsenoside Rh1 and its aglycone 20(S)-protopanaxatriol in rat plasma with panaxatriol as internal standard. The method involved single liquid-liquid extraction of both 20(S)-ginsenoside Rh1 and 20(S)-protopanaxatriol from plasma samples with n-butanol. The limit of quantification (LOQ) was 5 ng mL(-1) for both compounds. The method was validated within the linear range 5-2000 ng.mL(-1) for both compounds. The correlation coefficient for the calibration regression line was 0.999 or better. Intra-day and inter-day accuracy were better than 15%. The method has been successfully used for the pharmacokinetic studies in rats. After intravenous administrations, the mean retention times of 20(S)-ginsenoside Rh1 and 20(S)-protopanaxatriol were 17.1 +/- 2.0 min and 3.46 +/- 0.33 h, respectively.

Highly sensitive quantification of key regulatory oxysterols in biological samples by LC-ESI-MS/MS

We describe a highly sensitive and specific method for the quantification of key regulatory oxysterols in biological samples. This method is based upon a stable isotope dilution technique by liquid chromatography-tandem mass spectrometry (LC-MS/MS). After alkaline hydrolysis of human serum (5 microl) or rat liver microsomes (1 mg protein), oxysterols were extracted, derivatized into picolinyl esters, and analyzed by LC-MS/MS using the electrospray ionization mode. The detection limits of the picolinyl esters of 4beta-hydroxycholesterol, 7alpha-hydroxycholesterol, 22R-hydroxycholesterol, 24S-hydroxycholesterol, 25-hydroxycholesterol, 27-hydroxycholesterol, and 24S,25-epoxycholesterol were 2-10 fg (5-25 amol) on-column (signal-to-noise ratio = 3). Reproducibilities and recoveries of these oxysterols were validated according to one-way layout and polynomial equation, respectively. The variances between sample preparations and between measurements by this method were calculated to be 1.8% to 12.7% and 2.9% to 11.9%, respectively. The recovery experiments were performed using rat liver microsomes spiked with 0.05 ng to 12 ng of oxysterols, and recoveries of the oxysterols ranged from 86.7% to 107.3%, with a mean recovery of 100.6%. This method provides reproducible and reliable results for the quantification of oxysterols in small amounts of biological samples.

LC--APCI-MS--MS Method for the Tissue Distribution of Viaminate After Oral Administrations to Rats

Fast and sensitive liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) method for the specific determination of viaminate in 14 kinds of rat tissues pre-treated with simple procedure was developed and validated. Biological samples were prepared by direct precipitation to skin, stomach, intestine, and liver and extracted by liquid-liquid extraction to lung, kidney, muscle, spleen, brain, fat, testes (male and female), eye, and heart. After addition of menaquinon as internal standard to tissue homogenate, the supernatant was injected into the isocratic chromatographic system using a Waters Symmetry C8 column and methanol-water-formic acid (93:7:0.1) as the eluent. The eluate was completely led into an APCI interface with selected ion monitoring mode and the analytes were quantified using triple quadrupole MS. The assays were successfully validated in the ranges 0.02-20 ng/mL for lung, 0.02-10 ng/mL for kidney, spleen, muscle, brain, fat, eye, and heart, 0.05-10 ng/mL for testicle, 0.4-100 ng/mL for liver, skin and intestine, and 1.0-200 ng/mL for stomach. The accurate and precise studies showed good reproducibility with coefficients of variation below 8.5% and the recoveries range from 90 to 109%. The analytes were chemically stable under all relevant conditions and the assays were applied in tissue distribution study. The results showed that the viaminate concentration was high in skin, low in kidney, and almost undetectable in eye and brain.

Highly sensitive analysis of sterol profiles in human serum by LC-ESI-MS/MS

We have developed a highly sensitive and specific method for the analysis of serum sterol profiles. Sterols in 1 mul of dried serum were derivatized into picolinyl esters (3beta-picolinate) and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using the electrospray ionization (ESI) mode. In addition to cholesterol, 19 cholesterol precursors, cholestanol, campesterol, sitosterol, and sitostanol were identified simultaneously. Quantitative analyses for the picolinyl esters of 11 available sterols were performed, and detection limits were found to be less than 1 pg on-column. Reproducibilities and recoveries of 8 noncholesterol sterols were validated according to one-way layout and polynomial equation, respectively. The variances between sample preparations and between measurements by this method were calculated to be 1.6% to 8.2% and 2.5% to 16.5%, respectively. The recovery experiments were performed using 1 mul aliquots of normal human serum spiked with 1 ng to 6 ng of sterols, and recoveries of the sterols ranged from 88.1% to 102.5% with a mean recovery of 98.1%. The present method provides reliable and reproducible results for the identification and quantification of neutral sterols, especially in small volumes of blood samples, which is useful for serological diagnosis of inherited disorders in cholesterol metabolism and for noninvasive evaluation of cholesterol biosynthesis and absorption in humans.

Analysis of large oxygenated and nitrated polycyclic aromatic hydrocarbons formed under simulated diesel engine exhaust conditions (by compound fingerprints with SPE/LC-API-MS).

The analysis of organic compounds in combustion exhaust particles and the chemical transformation of soot by nitrogen oxides are key aspects of assessment and mitigation of the climate and health effects of aerosol emissions from fossil fuel combustion and biomass burning. In this study we present experimental and analytical techniques for efficient investigation of oxygenated and nitrated derivatives of large polycyclic aromatic hydrocarbons (PAHs), which can be regarded as well-defined soot model substances. For coronene and hexabenzocoronene exposed to nitrogen dioxide under simulated diesel exhaust conditions, several reaction products with high molecular mass could be characterized by liquid chromatography-atmospheric pressure chemical (and photo) ionization-mass spectrometry (LC-APCI-MS and LC-APPI-MS). The main products of coronene contained odd numbers of nitrogen atoms (m/z 282, 256, 338), whereas one of the main products of hexabenzocoronene exhibited an even number of nitrogen atoms (m/z 391). Various reaction products containing carbonyl and nitro groups could be tentatively identified by combining chromatographic and mass spectrometric information, and changes of their relative abundance were observed to depend on the reaction conditions. This analytical strategy should highlight a relatively young technique for the characterization of various soot-contained, semi-volatile, and semi-polar reaction products of large PAHs. FigureLC-APCI-MS analysis of nitrated coronene (and HBC): Total-Ion-Chromatogram (TIC), Extracted Ion Chromatograms (EICs) and corresponding mass spectrum (top).

The development of an ultra performance liquid chromatography-coupled atmospheric pressure chemical ionization mass spectrometry assay for seven adrenal steroids

An ultra performance liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (UPLC–APCI–MS) method was developed for the separation and quantification of adrenal steroid metabolites from heterologous expression media. Steroids were extracted by liquid–liquid extraction, separated on a Waters UPLC BEH C18 column, ionized by APCI, and detected using a triple quadrupole mass spectrometer in APCI positive mode with single ion monitoring. The incorporation of UPLC enabled the detection of seven structurally closely related steroids at between 5 and 40 ng/ml using run times of 11 min. The adrenal steroidogenic enzyme cytochrome P450 17-hydroxylase/17,20-lyase (CYP17) was expressed in the yeast Pichia pastoris and in nonsteroidogenic COS-1 cells, and used as a model system to evaluate the detection and quantification of adrenal steroid metabolites by UPLC–APCI–MS.

Analysis of Cyclic Peptides in Pseudostellaria heterophylla (Miq.) Pax by HPLC–APCI–MS

A new method for the analysis of cyclic peptides (Pseudostellarins) in traditional Chinese medicine, Pseudostellaria heterophylla (Miq.) Pax, was established by high performance liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (HPLC–APCI–MS). The real samples were separated by a reversed-phase C18 column using a binary eluent under gradient conditions. Six cyclic peptides were isolated and detected with a DAD detector. The Pseudostellarins components were identified by APCI–MS in a negative mode. In the negative ion APCI mode, the best sensitivity and the lowest detection limit for Pseudostellarins were obtained by using a mobile phase consisting of acetonitrile and pure water. The APCI spectra were characterized by [M-H]− peak. The parent ions [M-H]− with highest intensity was used for quantification of one cyclic peptide-Pseudostellarin B.

HPLC–APCI–MS for the determination of teprenone in human plasma: Method and clinical application

A sensitive high performance liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (HPLC–APCI–MS) method for the determination of teprenone (GGA) in human plasma using menatetrenone as the internal standard (I.S.) was established. After protein precipitation with ethanol, the plasma sample was extracted by cyclohexane and separated by high performance liquid chromatography on a reversed phase C 8 HPLC column with a mobile phase of water–methanol (4:96, v/v). GGA was determined with atmospheric pressure chemical ionisation–mass spectrometry (APCI–MS). HPLC–APCI–MS was performed in the selected ion monitoring (SIM) mode using target ions at [ M + H] + m/ z 331.3 for GGA and [ M + H] + m/ z 445.4 for the I.S. Calibration curve was linear over the range of 0.3–1000 ng/ml. The lower limit of quantification was 0.3 ng/ml. The intra- and inter-batch variability values were less than 7.8% and 8.7%, respectively. The method was successfully applied in the pharmacokinetic study in which plasma concentrations of GGA in 20 healthy Chinese volunteers were determined up to 24 h after administration of capsule containing 50 mg GGA. The maximum GGA plasma concentration ( C max) was 246.9 ± 85.4 ng/ml, the elimination half-life ( t 1/2) was 3.38 ± 1.20 h, and the time to the C max was 5.35 ± 1.39 h.

Use of porous graphitic carbon for the analysis of nitrate ester, nitramine and nitroaromatic explosives and by-products by liquid chromatography–atmospheric pressure chemical ionisation-mass spectrometry

A new LC/MS method was developed for the analysis of sixteen different analytes including the most common organic explosives encountered in forensic investigations. The separation was achieved using a porous graphitic carbon (PGC) column with a binary gradient elution. Molecular modeling suggested a possible interpretation for the elution order of explosive compounds on PGC. The introduction of ammonium formate in the mobile phase resulted in the formation of characteristic adduct ions thus enhancing the mass spectrometric detection of nitrate ester and nitramine compounds. Atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) were compared in terms of sensitivity. The final LC/APCI-MS method allowed easy identification of investigated compounds with limits of detection ranging from 0.04 to 1.06 ng/μl. The analysis of simulated forensic samples confirmed the performance of the method.