Chromatography-atmospheric Pressure Chemical Ionization-mass Spectrometry Research Articles

Response of Bacteriohopanepolyols to Hypoxic Conditions in the Surface Sediments of the Yangtze Estuary and Its Adjacent Areas

Bacteriohopanepolyols (BHPs), as a novel bacterial biomarker, show clear potential for tracking organic matter sources and environmental change. To evaluate BHPs as indicators of seasonal hypoxia in the Yangtze Estuary and its adjacent areas, the composition, distribution, and source of BHPs in surface sediments were analyzed using high-performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (HPLC-APCI-MS). A total of 12 BHPs were detected with a normalized TOC concentration of 3.79-269 μg·g-1. The BHPs present in the surface sediments were dominated by bacteriohopanetetrol (BHT), 2-methyl-BHT, amino-BHPs, and adenosylhopane and its homologues, accounting for 40%, 22%, 12%, and 4% of the total BHPs, respectively. Each of these components and their corresponding indices show clear spatial trends. Specifically, BHT showed an "offshore increase" trend, which was mainly attributed to marine autochthonous inputs; and soil marker BHPs including adenosylhopane, which were dominated by terrestrial sources, showed an "offshore decrease" trend. The Rsoil index indicated a similar spatial pattern to the soil marker BHPs, with the relative contribution of terrestrial organic matter decreasing from 61.5% in coastal waters to 1.66% in the open ocean. This suggests that the organic matter in the coastal waters was mainly derived from terrestrial sources while marine sources were dominant in the open ocean. BHT-Ⅱ, the BHT stereoisomer, was derived from anaerobic ammonium oxidizing bacteria. High BHT-Ⅱ ratios were consistent with seasonal hypoxic zones in the Yangtze Estuary and, furthermore, these ratios were significantly negatively correlated with dissolved oxygen (DO) concentrations in the bottom waters. These observations indicate that hypoxic environments are beneficial to BHT-Ⅱ production, implying that BHT-Ⅱ can be used as an indicator of marine hypoxia.

Data-Independent Identification of Suspected Organic Pollutants Using Gas Chromatography-Atmospheric Pressure Chemical Ionization-Mass Spectrometry.

The identity of an unknown environmental pollutant is reflected by the mass and dissociation chemistry of its (quasi)molecular ion. Gas chromatography-atmospheric pressure chemical ionization-mass spectrometry (GC-APCI-MS) increases the yield of molecular ions (compared to conventional electron ionization) by collisional cooling. Scanning quadrupole data-independent acquisition (SQDIA) permits unbiased, unattended selection of (quasi)molecular ions and acquisition of structure-diagnostic collision-induced dissociation mass spectra, while minimizing interferences, by sequentially cycling a quadrupole isolation window through the m/z range. This study reports on the development of a suspect screening method based on industrial compounds with bioaccumulation potential. A comparison of false and correct identifications in a mixed standard containing 30 analytes suggests that SQDIA results in a markedly lower false-positive rate than standard DIA: 5 for SQDIA and 82 for DIA. Electronic waste dust was analyzed using GC and quadrupole time-of-flight MS with APCI and SQDIA acquisition. A total of 52 brominated, chlorinated, and organophosphorus compounds were identified by suspect screening; 15 unique elemental compositions were identified using nontargeted screening; 17 compounds were confirmed using standards and others identified to confidence levels 2, 3, or 4. SQDIA reduced false-positive identifications, compared to experiments without quadrupole isolation. False positives also varied by class: 20% for Br, 37% for Cl, 75% for P, and >99% for all other classes. The structure proposal of a previously reported halogenated compound was revisited. The results underline the utility of GC-SQDIA experiments that provide information on both the (quasi)molecular ions and its dissociation products for a more confident structural assignment.

Chemical characterization, antioxidant and enzyme inhibitory effects of Mitracarpus hirtus extracts

Mitracarpus hirtus (L.) DC. (Family: Rubiaceae) is a tropical annual herb commonly found in America and Mexico. In the present study, the methanol, ethyl acetate, dichloromethane and aqueous extracts of the plant were tested for total phenolic (TPC) and flavonoid content (TFC) and antioxidant activities were evaluated using a battery of assays including 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), cupric reducing antioxidant capacity, total antioxidant capacity (TAC) (phosphomolybdenum) and metal chelating. Enzyme inhibitory effects were investigated using acetylcholinesterase (AChE), tyrosinase, α-amylase and α-glucosidase as target enzymes. The phytochemical profile was obtained using liquid chromatography-diode array detection-electrospray ionization-mass spectrometry (LC-DAD-ESI-MSn), liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MSn) and nuclear magnetic resonance (NMR) experiments. Results showed that the dichloromethane and ethyl acetate extracts yielded the highest TPC (29.10 ± 0.07 mg gallic acid equivalent/g) and TFC (38.14 ± 0.91 mg rutin equivalent/g), respectively. Aqueous extract showed weak activity against tested enzymes but demonstrated the strongest ABTS scavenging activity (59.39 ± 1.19 mg trolox equivalent/g) and is the strongest Fe3+ reducer (59.42 ± 0.59 mg trolox equivalent/g). Phytochemical analysis revealed the presence of phenolics, pyrrolizidine alkaloids and triterpene acid. This is the first report gathering scientific data on antioxidant, enzyme inhibitory activities and phytochemical composition of M. hirtus and the obtained results can be used as starting point for further investigation on this traditional medicinal herb.

Sebomic identification of sex- and ethnicity-specific variations in residual skin surface components (RSSC) for bio-monitoring or forensic applications

Background“Residual skin surface components” (RSSC) is the collective term used for the superficial layer of sebum, residue of sweat, small quantities of intercellular lipids and components of natural moisturising factor present on the skin surface. Potential applications of RSSC include use as a sampling matrix for identifying biomarkers of disease, environmental exposure monitoring, and forensics (retrospective identification of exposure to toxic chemicals). However, it is essential to first define the composition of “normal” RSSC. Therefore, the aim of the current study was to characterise RSSC to determine commonalities and differences in RSSC composition in relation to sex and ethnicity.MethodsSamples of RSSC were acquired from volunteers using a previously validated method and analysed by high-pressure liquid chromatography–atmospheric pressure chemical ionisation–mass spectrometry (HPLC-APCI-MS). The resulting data underwent sebomic analysis.ResultsThe composition and abundance of RSSC components varied according to sex and ethnicity. The normalised abundance of free fatty acids, wax esters, diglycerides and triglycerides was significantly higher in males than females. Ethnicity-specific differences were observed in free fatty acids and a diglyceride.ConclusionsThe HPLC-APCI-MS method developed in this study was successfully used to analyse the normal composition of RSSC. Compositional differences in the RSSC can be attributed to sex and ethnicity and may reflect underlying factors such as diet, hormonal levels and enzyme expression.

Determination of sterols and steroid hormones in surface water and wastewater using liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry

The development and optimization of an analytical method for simultaneous extraction, determination and reliable confirmation of twenty steroids from different classes (human/animal and plant sterols, and natural and synthetic steroid hormones) in environmental water and wastewater at ngL−1 levels are described. Water samples were prepared using solid-phase extraction and extracts were analyzed by liquid chromatography-linear ion trap-tandem mass spectrometry. Improved instrumental method was developed for complete chromatographic separation of analytes with identical fragmentation reactions, based on the use of a single C8 column and acetonitrile as organic solvent in the mobile phase. The optimized method provided high recoveries (70–114%) for both water matrices with the RSDs generally lower than 20%. Low limits of detection were achieved for both surface water (0.7–15.0ngL−1) and wastewater (1.7–15.0ngL−1). Method displayed good linearity in the tested concentration ranges. As a result of method application to real water samples, cholesterol was detected in all fifteen analyzed river water samples (in the concentration range 176–5162ngL−1) and all seven wastewater samples (1092–4808ngL−1). Also, coprostanol, stigmasterol, campesterol, β-sitosterol and sitostanol were found in the investigated samples. Steroid hormones were not detected in any of the analyzed water samples.

Body mass but not vitamin D status is associated with bone mineral content and density in young school children in northern Sweden

BackgroundHigh latitude of residence where sun exposure is limited affects vitamin D status. Although vitamin D levels have been associated with poor bone health, cut-off values for optimising bone health are yet to be decided.ObjectiveTo assess vitamin D intake and status among young school children living at latitude 63–64 °N, in northern Sweden and to examine the association between vitamin D status and bone mineral content (BMC) and bone mineral density (BMD).DesignIn a cross-sectional study, diet was assessed by a 4-day food diary and a food frequency questionnaire in 8- to 9-year-old children (n=120). Energy, vitamin D, and calcium intakes were calculated. Physical activity was assessed using a pedometer for 7 days. Serum 25-hydroxyvitamin D (S-25[OH]D) levels were analysed by high-pressure liquid chromatography-atmospheric pressure chemical ionisation-mass spectrometry (n=113). BMC and BMD were assessed by dual energy X-ray absorptiometry scan. Height and weight were measured by standard procedures and BMI z-score was calculated using WHO AnthroPlus programme.ResultsThe majority of children, 91%, did not reach the recommended vitamin D intake of 7.5 µg/day and 50% had insufficient S-25[OH]D levels defined as <50 nmol/l. The highest concentrations of S-25[OH]D were observed during the summer months (p=0.01). Body mass (p<0.01) but not S-25[OH]D was associated with measures of BMC and BMD. Furthermore, boys had higher total BMC (p=0.01), total body less head BMC (p=0.02), fat free mass (p<0.01), and a higher degree of physical activity (p=0.01) compared to girls.ConclusionsBody mass was related to BMC and BMD measures in a population of prepubertal school children living at high latitudes in Sweden. Despite insufficient S-25[OH]D levels and low vitamin D intake, this did not appear to affect bone parameters. Prospective studies with repeated assessment of vitamin D status are needed to examine cut-off values for optimising bone health.

An approach based on ultrahigh performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry allowing the quantification of both individual phytosteryl and phytostanyl fatty acid esters in complex mixtures

A method for the analysis of both individual phytosteryl and phytostanyl fatty acid esters in complex mixtures was established. The approach was based on a previously not described combination of three elements: (i) the formation of [M−FA+H]+ fragment ions via APCI (atmospheric pressure chemical ionization), (ii) a highly efficient UHPLC-based separation on a 1.7μ C8 column, previously established for phytostanyl fatty acid esters, allowing the distinction of individual fatty acid esters sharing the same sterol/stanol nucleus and of isotope peaks of phytosteryl fatty acid esters and corresponding phytostanyl fatty acid esters based on these [M−FA+H]+ fragment ions, and (iii) the adjustment of the APCI conditions allowing the differential APCI–MS–SIM (single ion monitoring) detection of phytostanyl esters of linoleic and linolenic acid based on their distinct formation of a [M+H]+ ion. The usefulness of the methodology was demonstrated by the analysis of a commercially available enriched margarine. Two runs per sample allowed the quantification of 35 target analytes; the total amounts of esters were between 124.7 and 125.3g/kg, being in good agreement with the labelled 125g/kg. Validation data were elaborated for 35 individual fatty acid esters of sitosterol, campesterol, brassicasterol, stigmasterol, sitostanol and campestanol. Recovery rates ranged from 95 to 106%; the coefficients of variation were consistently <5%, except for stigmasteryl-18:1. The approach describes for the first time a quantification of both individual phytosteryl and phytostanyl fatty acid esters and thus closes an analytical gap related to this class of health-relevant food constituents.

Post-Blast Analysis of Hexamethylene Triperoxide Diamine using Liquid Chromatography-Atmospheric Pressure Chemical Ionization-Mass Spectrometry

A qualitative method using liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC/APCI-MS) has been developed and validated for the identification of trace hexamethylene triperoxide diamine (HMTD) using three structurally-specific ions. Residues are extracted with deionized water (DI) and identified using a gradient mobile phase program and positive ion full scan mode on a Thermo Finnigan LCQ Ion Trap Mass Spectrometer. This method was validated according to several performance characteristics for the qualitative identification of an analyte using the characteristic ions, demonstrating the method’s reliability for use on forensic applications. The method’s limit of detection (LOD) can identify HMTD in an extract from a cotton matrix to which 20μg of HMTD has been applied (equivalent to 10ppm in extract). Previous scientific publications using LC/MS have not demonstrated post-blast HMTD residue analyses and suffer from a lack of chromatographic retention, sufficient number of mass spectral ions with validation, or require more complex/expensive instrumental methods (accurate mass or MS/MS). Post-blast analyses were successfully conducted with two syringe detonations that verified the efficacy of the method on the analysis of debris and residues following detonation.

Analysis of Phenolic Compounds in Some Medicinal Herbs by LC-MS.

In this paper, a liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry in negative mode method was developed for the identification and quantitative determination of 13 individual phenolics (chlorogenic acid, caffeic acid, coumaric acid, ferulic acid, (+)-catechin, (-)-epicatechin, rutin, quercitrin, isoquercitrin, fisetin, isorhamnetin, hesperidin and chrysin) from ethanolic extracts [30, 50 and 70% (w/v)] of Calendula officinalis, Hypericum perforatum, Galium verum and Origanum vulgare and some commercial extracts of these medicinal herbs. Correlation coefficients (r(2)) from calibration curves for all the compounds were between 0.9971 and 0.9996. Limit of detection was in the range of 0.070-0.280 µg/mL and limit of quantification was from 0.233 to 0.932 µg/mL. The method was partially validated and the results obtained are: the intra- and interday relative standard deviation values were within 0.086 and 2.821% and recovery values vary from 95.84% (coumaric acid) to 103.20% (rutin).

Simultaneous liquid chromatography-mass spectrometry quantification of cefixime and clavulanic acid in human plasma.

A simple and specific liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) assay method has been developed and fully validated for the simultaneous quantification of cefixime (CX) and clavulanic acid (CA) in human plasma. Analytes and internal standard were extracted from human plasma by a solid phase extraction technique using a Sam prep (3 mL, 100 mg) extraction cartridge. The extracted samples were chromatographed on a reverse phase C18 column using a mixture of methanol : acetonitrile : 2 mM ammonium acetate (pH 3.5) (25 : 25 : 50, v/v/v) as the mobile phase at a flow rate of 0.8 mL/min. Quantification of the analytes were carried out using single quadrupole LC-APCI-MS through selected ion monitoring at m/z 452 and 198, respectively, for CX and CA. The assay was linear over the concentration range of 0.05-10.0 and 0.1-10.0 μg/mL, respectively, for CX and CA. The mean plasma extraction recoveries of the CX and CA were found to be 95.20-96.27% and 94.67-95.58%, respectively. The method was successfully applied for the determination of pharmacokinetics of CX and CA after oral administration of single dosage CX/CA (200/125 mg) pill to the humans (n = 12).

Evaluation of the Potential of GC-APCI-MS for the Analysis of Pesticide Residues in Fatty Matrices

A method based on gas chromatography-atmospheric pressure chemical ionization-mass spectrometry (GC-APCI-MS) has been developed for the analysis of pesticides in meat by using quadrupole-time of flight mass spectrometry (QTOF-MS). Ionization and MS conditions were studied for 71 compounds, although only 51 showed acceptable performance. The protonated form of the analytes was mainly found ([M + H]⁺), although some compounds generated the molecular ion (M⁺(•)). A fast and generic extraction procedure was applied in sample pretreatment. The analytical method was suitable for qualitative analysis, and it was also evaluated for quantitative analysis, obtaining adequate recovery and precision values for most of the studied analytes at two concentration levels (50 and 150 μg/kg). Several operational drawbacks were found with this instrument, such as slow stabilization and moderate sensitivity, although the fast switching between LC and GC allows the increase of its applicability.

Accurate quantitation of pentaerythritol tetranitrate and its degradation products using liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry

After an explosion of pentaerythritol tetranitrate (PETN), its degradation products pentaerythritol trinitrate (PETriN), dinitrate (PEDiN) and mononitrate (PEMN) were detected using liquid chromatography–atmospheric-pressure chemical-ionization–mass spectrometry (LC–APCI–MS). Discrimination between post-explosion and naturally degraded PETN could be achieved based on the relative amounts of the degradation products. This information can be used as evidence when investigating a possible relationship between a suspect and a post-explosion crime scene. The present work focuses on accurate quantitation of PETN and its degradation products, using PETriN, PEDiN and PEMN standards specifically synthesized for this purpose. With the use of these standards, the ionization behavior of these compounds was studied, and a quantitative method was developed. Quantitation of PETN and trace levels of its degradation products was shown to be possible with accuracy between 85.7% and 103.7% and a precision ranging from 1.3% to 11.5%. The custom-made standards resulted in a more robust and reliable method to discriminate between post-explosion and naturally-degraded PETN.

CHEMOMETRIC APPROACHES FOR THE CHARACTERIZATION OF TURKISH RHODODENDRON AND HONEYDEW HONEYS DEPENDING ON AMINO ACID COMPOSITION

The amino acid composition of twenty-five honey samples obtained from different regions of Turkey (rhododendron and honeydew honey) was determined by a liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (LC–APCI–MS). Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to characterize and classify the honey samples. In rhododendron honeys, major amino acids were detected as aspartic acid, lysine, and arginine, for honeydew honeys, lysine, arginine, and histidine were found, following the proline. Five principal components (PCs) and four main clusters were obtained from the chemometric analysis that classifies the samples. Five PCs were detected to be explanatory of more than 79% of the total variance in the data matrix. It can be concluded that free amino acids are good indicators for determination of botanical origins and chemometric studies are highly useful for honey characterization.

Determination of Vitamins E, D3, and K1 in Plasma by Liquid Chromatography-Atmospheric Pressure Chemical Ionization-Mass Spectrometry Utilizing a Monolithic Column

This paper reports a rapid, simple, and sensitive method for determination of vitamin D3, vitamin E acetate, and vitamin K1 in plasma using atmospheric pressure chemical ionization –high performance liquid chromatography–mass spectrometry. Plasma samples were prepared using solid phase extraction. The separation of compounds was achieved using a C18 monolithic column and a mobile phase composed of methanol and 0.1% formic acid in gradient elution mode at a flow rate of 1.0 mL min−1. Analytes were ionized using atmospheric chemical ionization in positive mode. Mass spectra were recorded at m/z = 385.23, 473.47, and 451.41 for vitamin D3, vitamin E, and vitamin K1, respectively. Vitamin D2 was used as an internal standard and its mass spectra was recorded at 397.28 m/z. The method was validated using ICH guidelines. The system suitability responses were calculated for retention time, number of theoretical plates, capacity factor, resolution, and the selectivity factor. System validation was evaluated for precision, specificity, and linearity of all compounds. The limits of detection for vitamin D3, vitamin E, and vitamin K1 were determined to be 0.1, 1.36, and 0.052 ng mL−1, respectively. The accuracy, evaluated as % of recovery, was in the range of 96.4 to 102.4% and precision determined as the coefficient of variation was between 1.24 and 3.6%. The validated method was applied to real plasma samples.

Evaluation of gas chromatography-atmospheric pressure chemical ionization-mass spectrometry as an alternative to gas chromatography-electron ionization-mass spectrometry: Avocado fruit as example

Although GC-APCI-MS was developed more than 40 years ago this coupling is still far from being a routine technique. One of the reasons explaining the limited use of GC-APCI so far is the lack of spectral database which facilitates the identification of the compounds under study. The first application of a very recently developed GC-APCI database to identify as many compounds as possible in a complex matrix such as avocado fruit is presented here. The results achieved by using this database has been checked against those obtained using traditional GC-EI-MS and a comparison of the MS signals observed in both ionization sources has been carried out. 100 compounds belonging to different chemical families were identified in the matrix under study. Considering the results of this study, the wide range of application (in terms of polarity and size of analytes) and the robustness of APCI as interface, the high quality of TOF spectra, and our library as a publicly available resource, GC-APCI-TOF MS is definitively a valuable addition to the “metabolomics toolbox”.

Determination and differentiation of triacylglycerol molecular species in Antarctic and non-Antarctic yeasts by atmospheric pressure-chemical ionization-mass spectrometry

Yeast, particularly Saccharomyces cerevisiae, has long served as a model eukaryotic system for studies on the regulation of lipid metabolism. We developed a high performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry method for the detailed analysis of triacylglycerols (TAGs) in 14 species of yeast consisting of seven Antarctic yeasts (grown at 15°C and 5°C) and seven non-Antarctic yeasts (grown at 25°C and 15°C), the latter including 3 strains of S. cerevisiae. Analysis of TAG molecular species established that the sn-2 position was invariably occupied by an unsaturated fatty acyl moiety. In S. cerevisiae the preference was for oleic acid 18:1>palmitoleic acid 16:1, in Candida albicans, Cryptococcus humicolus and Rhodotorula mucilaginosa 18:1>linoleic acid 18:2 and in Zygosaccharomyces rouxii 18:2>18:1. In the Antarctic yeasts (Cryptococcus watticus, Cryptococcus victoriae, Cryptococcus nyarrowii, Leucosporidium antarcticum, Leucosporidium fellii, Candida psychrophila and Rhodotorula mucilaginosa) the general pattern was for the sn-2 position to be occupied by 18:1, 18:2 or linolenic acid 18:3. A trend towards synthesis of increased unsaturated fatty acid in TAGs was observed as the growth temperature was lowered. The application of principal component analysis demonstrated that the yeasts were differentiated into three distinct groups. One group consisted of the three S. cerevisiae strains, a second the other four non-Antarctic yeasts and the third the seven Antarctic yeasts. The data for the Antarctic yeasts, to the best of our knowledge, have not been previously reported.

Analysis of Carotenoids in 25 Indigenous Korean Coral Extracts

In this study, methanol extracts from 25 indigenous Korean corals were prepared and their carotenoid constituents were analyzed by high-performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (HPLC-APCI-MS). Among them, extracts from nine species showed detectable peaks in the HPLC chromatogram at 450 nm and the ultraviolet/visible spectra exhibiting carotenoid-specific characteristics were chosen. The mass data of carotenoid peaks revealed that only peridinin could be identified based on literature comparison and suggested the potential presence of novel carotenoid structures. This is the first reported investigation of indigenous Korean coral carotenoids and further work is needed to explore the carotenoids and their potential roles in the ecosystem of indigenous Korean corals.

Simultaneous pharmacokinetic assessment of cefadroxil and clavulanic acid in human plasma by LC–MS and its application to bioequivalence studies

A simple, rapid and selective liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (LC–APCI–MS) assay method has been developed and fully validated for the simultaneous quantification of cefadroxil (CF) and clavulanic acid (CA) in human plasma. Analytes and internal standard (IS) were extracted from human plasma by solid-phase extraction (SPE) technique using Sam prep (3mL, 100mg) extraction cartridge. The extracted samples were chromatographed on a reverse phase C18 column using a mixture of methanol: acetonitrile: 2mM ammonium acetate (pH 3.5) (25:25:50, v/v/v) as the mobile phase at a flow rate of 0.8mL/min. Quantification of the analytes and IS were carried out using single quadrupole LC–APCI–MS through selected-ion monitoring (SIM) at m/z 362 and m/z 198, for CF and CA, respectively. Method validation was performed as per the FDA guidelines and the results met the acceptance criteria. Plasma concentration of CF and CA followed by the oral administration of CF/CA (500/125mg) pill to healthy male volunteers (n=12) was measured. Area under plasma concentration–time curve from 0 to 12h (AUC0–12h) and 0h extrapolated to infinity (AUC0−∞) were calculated. The ratio of AUC0–12h/AUC0−∞ was found to be >85% for all the subjects, as recommended by the FDA guidelines.

Simultaneous quantification of cefpodoxime proxetil and clavulanic acid in human plasma by LC–MS using solid phase extraction with application to pharmacokinetic studies

A simple, rapid and selective high performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (HPLC-APCI-MS) method was developed and validated for the simultaneous estimation of cefpodoxime proxetil (CDPX) and clavulanic acid (CA) in human plasma. Extraction of samples was done by solid phase extraction technique (SPE) and chloramphenicol used as internal standard. Chromatographic separation was carried out on a reverse phase Princeton SPHER C18 (150mm×4mm i.d., 5μm) column using mixture of methanol: acetonitrile: 2mM ammonium acetate (25:25:50, v/v, pH 3.5) at 0.8mL/min flow rate. Detection was performed on a single quadrupole MS by selected ion monitoring (SIM) mode via APCI source. The calibration curve was linear within the concentration range, 0.04-4.4μg/mL and 0.1-10.0μg/mL for CDPX and CA respectively. Pharmacokinetic parameters of tablet (CDPX 200mg, CA 125mg) were evaluated. Cmax, Tmax, T1/2, elimination rate constant (Kel), AUC0-t, and AUC0-∞ of tablet were 2.13±0.06μg/mL, 2h, 3.05±0.15h, 0.24±0.37h(-1), 6.81±0.14μg h/mL and 7.72±0.23μg h/mL respectively for cefpodoxime (CP), 5.34±0.28μg/mL, 2h, 2.73±0.25h, 0.26±0.31h(-1), 15.37±0.16μg h/mL and 16.59±0.53μg h/mL respectively for CA.

In situ production of branched glycerol dialkyl glycerol tetraethers in a great basin hot spring (USA)

Branched glycerol dialkyl glycerol tetraethers (bGDGTs) are predominantly found in soils and peat bogs. In this study, we analyzed core (C)-bGDGTs after hydrolysis of polar fractions using liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry and analyzed intact P-bGDGTs using total lipid extract (TLE) without hydrolysis by liquid chromatography-electrospray ionization-multiple stage mass spectrometry. Our results show multiple lines of evidence for the production of bGDGTs in sediments and cellulolytic enrichments in a hot spring (62–86°C) in the Great Basin (USA). First, in situ cellulolytic enrichment led to an increase in the relative abundance of hydrolysis-derived P-bGDGTs over their C-bGDGT counterparts. Second, the hydrolysis-derived P- and C-bGDGT profiles in the hot spring were different from those of the surrounding soil samples; in particular, a monoglycosidic bGDGT Ib containing 13,16-dimethyloctacosane and one cyclopentane moiety was detected in the TLE but it was undetectable in surrounding soil samples even after sample enrichments. Third, previously published 16S rRNA gene pyrotag analysis from the same lignocellulose samples demonstrated the enrichment of thermophiles, rather than mesophiles, and total bGDGT abundance in cellulolytic enrichments correlated with the relative abundance of 16S rRNA gene pyrotags from thermophilic bacteria in the phyla Bacteroidetes, Dictyoglomi, EM3, and OP9 (“Atribacteria”). These observations conclusively demonstrate the production of bGDGTs in this hot spring; however, the identity of organisms that produce bGDGTs in the geothermal environment remains unclear.