Quantification of hepcidin using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Hepcidin is known to be a key systemic iron‐regulatory hormone which has been demonstrated to be associated with a number of iron disorders. Hepcidin concentrations are increased in inflammation and suppressed in hemochromatosis. In view of the role of hepcidin in disease, its potential as a diagnostic tool in a clinical setting is evident. This study describes the development of a matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) assay for the quantitative determination of hepcidin concentrations in clinical samples. A stable isotope labeled hepcidin was prepared as an internal standard and a standard quantity was added to urine samples. Extraction was performed with weak cation‐exchange magnetic nanoparticles. The basic peptides were eluted from the magnetic nanoparticles using a matrix solution directly onto a target plate and analyzed by MALDI‐TOF MS to determine the concentration of hepcidin. The assay was validated in charcoal stripped urine, and good recovery (70–80%) was obtained, as were limit of quantitation data (5 nmol/L), accuracy (RE <10%), precision (CV <21%), within ‐day repeatability (CV <13%) and between‐day repeatability (CV <21%). Urine hepcidin levels were 10 nmol/mmol creatinine in healthy controls, with reduced levels in hereditary hemochromatosis (P < 0.000005) and elevated levels in inflammation (P < 0.0007). In summary a validated method has been developed for the determination of hepcidin concentrations in clinical samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification and profiling of targeted oxidized linoleic acid metabolites in rat plasma by quadrupole time‐of‐flight mass spectrometry

Linoleic acid (LA) and LA‐esters are the precursors of LA hydroperoxides, which are readily converted to 9‐ and 13‐hydroxy‐?octadecadienoic acid (HODE) and 9‐ and 13‐oxo‐?octadecadienoic acid (oxo ODE) metabolites in vivo. These four oxidized LA metabolites (OXLAMs) have been implicated in a variety of pathological conditions. Therefore, their accurate measurement may provide mechanistic insights into disease pathogenesis. Here we present a novel quadrupole time‐of‐flight mass spectrometry (Q‐TOFMS) method for quantitation and identification of target OXLAMs in rat plasma. In this method, the esterified OXLAMs were base‐hydrolyzed and followed by liquid–liquid extraction. Quantitative analyses were based on one‐point standard addition with isotope dilution. The Q‐TOFMS data of target metabolites were acquired and multiple reaction monitoring extracted‐ion chromatograms were generated post‐acquisition with a 10 ppm extraction window. The limit of quantitation was 9.7–35.9 nmol/L depending on the metabolite. The method was reproducible with a coefficient of variation of <18.5%. Mean concentrations of target metabolites in rat plasma were 57.8, 123.2, 218.1 and 57.8 nmol/L for 9‐HODE, 13‐HODE, 9‐oxoODE and 13‐oxoODE, respectively. Plasma levels of total OXLAMs were 456.9 nmol/L, which correlated well with published concentrations obtained by gas chromatography/mass spectrometry (GC/MS). The concentrations were also obtained utilizing a standard addition curve approach. The calibration curves were linear with correlation coefficients of >0.991. Concentrations of 9‐HODE, 13‐HODE, 9‐oxoODE and 13‐oxoODE were 84.0, 138.6, 263.0 and 69.5 nmol/L, respectively, which were consistent with the results obtained from one‐point standard addition. Target metabolites were simultaneously characterized based on the accurate Q‐TOFMS data. This is the first study of secondary LA metabolites using Q‐TOFMS. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.     

A rapid and sensitive LC–MS/MS method for quantification of quercetin‐3‐O‐β‐d‐glucopyranosyl‐7‐O‐β‐d‐gentiobioside in plasma and its application to a pharmacokinetic study

A rapid and sensitive LC–MS/MS method with good accuracy and precision was developed and validated for the pharmacokinetic study of quercetin‐3‐O‐β‐d ‐glucopyranosyl‐7‐O‐β‐d ‐gentiobioside (QGG) in Sprague–Dawley rats. Plasma samples were simply precipitated by methanol and then analyzed by LC–MS/MS. A Venusil® ASB C₁₈ column (2.1 × 50 mm, i.d. 5 μm) was used for separation, with methanol–water (50:50, v/v) as the mobile phase at a flow rate of 300 μL/min. The optimized mass transition ion‐pairs (m/z) for quantitation were 787.3/301.3 for QGG, and 725.3/293.3 for internal standard. The linear range was 7.32–1830 ng/mL with an average correlation coefficient of 0.9992, and the limit of quantification was 7.32 ng/mL. The intra‐ and inter‐day precision and accuracy were less than ±15%. At low, medium and high quality control concentrations, the recovery and matrix effect of the analyte and IS were in the range of 89.06–92.43 and 88.58–97.62%, respectively. The method was applied for the pharmacokinetic study of QGG in Sprague–Dawley rats. Copyright © 2016 John Wiley & Sons, Ltd.     

LC‐MS/MS analysis of Δ9‐tetrahydrocannabinolic acid A in serum after protein precipitation using an in‐house synthesized deuterated internal standard

An assay based on liquid chromatography/tandem mass spectrometry is presented for the fast, precise and sensitive quantitation of Δ9‐tetrahydrocannabinolic acid A (THCA) in serum. THCA is the biogenetic precursor of Δ9‐tetrahydrocannabinol in cannabis and has aroused interest in the pharmacological and forensic field especially as a potential marker for recent cannabis use. After addition of deuterated THCA, synthesized from D₃‐THC as starting material, and protein precipitation, the analytes were separated using gradient elution on a Luna C18 column (150 × 2.0 mm × 5 µm) with 0.1% formic acid and acetonitrile/0.1% formic acid. Data acquisition was performed on a triple quadrupole linear ion trap mass spectrometer in multiple reaction monitoring mode with negative electrospray ionization. After optimization, the following sample preparation procedure was used: 200 μL serum was spiked with internal standard solution and methanol and then precipitated ‘in fractions’ with 500 μL ice‐cold acetonitrile. After storage and centrifugation, the supernatant was evaporated and the residue redissolved in mobile phase. The assay was fully validated according to international guidelines including, for the first time, the assessment of matrix effects and stability experiments. Limit of detection was 0.1 ng/mL, and limit of quantification was 1.0 ng/mL. The method was found to be selective and proved to be linear over a range of 1.0 to 100 ng/mL using a 1/x weighted calibration model with regression coefficients >0.9996. Accuracy and precision data were within the required limits (RSD ≤ 8.6%, bias: 2.4 to 11.4%), extractive yield was greater than 84%. The analytes were stable in serum samples after three freeze/thaw cycles and storage at ?20 °C for one month. Copyright © 2012 John Wiley & Sons, Ltd.     

Newborn screening for 3‐hydroxy‐3‐methylglutaric aciduria using direct analysis in real‐time mass spectrometry

A novel method utilizing ambient thermal desorption ionization with a direct analysis in real‐time source integrated with mass spectrometry (DART‐MS) was established and applied to the rapid analysis of 3‐hydroxy‐3‐methylglutaric (3‐HMG) acid in the neonatal urine. Instrument parameter settings were optimized to obtain high sensitive and accurate determination of 3‐HMG acid. The use of helium gas heated to temperature of 400°C was observed to permit deprotonation, 3‐HMG acid producing an abundant (M‐H)^? (m/z 161) in the negative ion mode. The calibration curve was determined to be linear over the range of 0.05‐5 mg/L, with the correlation coefficient r = 0.9988 and the relative standard deviations (n = 6) in the range of 1.5‐11.8%. The limit of detection was 0.002 mg/L, and the limit of quantitation was 0.007 mg/L. The recoveries ranged from 88.0% to 123.1%. Four urine samples from patients and four simulated urine samples were investigated. The results of DART‐MS were in agreement with the values determined using established methods at the hospitals. The proposed method demonstrated significant potential in the application of the high‐throughput screening in newborn screening.     

Development of a validated UPLC–MS/MS method for determination of humantenmine in rat plasma and its application in pharmacokinetics and bioavailability studies

Humantenmine (HMT), the most toxic compound isolated from Gelsemium elegans Benth , is a well‐known active herbal compound. A rapid and sensitive ultra‐performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method was developed and validated to estimate the absolute oral bioavailability of HMT in rats. Quantification was performed by multiple reaction monitoring using electrospray ionization operated in positive ion mode with transitions of m/z 327.14 → m/z 296.19 for HMT and m/z 323.20 → m/z 236.23 for gelsemine (internal standard, IS). The linear range of the calibration curve was 1–256 nmol/L, with a lower limit of quantification at 1 nmol/L. The accuracy of HMT ranged from 89.39 to 107.5%, and the precision was within 12.24% (RSD). Excellent recovery and negligible matrix effect were observed. HMT remained stable during storage, preparation and analytical procedures. The pharmacokinetics of HMT in rats showed that HMT reached the concentration peak at 12.50 ± 2.74 min with a peak concentration of 28.49 ± 6.65 nmol/L, and the corresponding area under the concentration–time curve (AUC_0–t ) was 1142.42 ± 202.92 nmol/L min after 200 μg/kg HMT was orally administered to rats. The AUC_0–t of HMT given at 20 μg/kg by tail vein administration was 1518.46 ± 192.24 nmol/L min. The calculated absolute bioavailability of HMT was 7.66%.     

Simultaneous determination of plasma creatinine,uric acid,kynurenine and tryptophan by high‐performance liquid chromatography: method validation and in application to the assessment of renal function

A high‐performance liquid chromatography with ultraviolet detection method has been developed for the simultaneous determination of a set of reliable markers of renal function, including creatinine, uric acid, kynurenine and tryptophan in plasma. Separation was achieved by an Agilent HC‐C₁₈ (2) analytical column. Gradient elution and programmed wavelength detection allowed the method to be used to analyze these compounds by just one injection. The total run time was 25 min with all peaks of interest being eluted within 13 min. Good linear responses were found with correlation coefficient >0.999 for all analytes within the concentration range of the relevant levels. The recovery was: creatinine, 101 ± 1%; uric acid, 94.9 ± 3.7%; kynurenine, 100 ± 2%; and tryptophan, 92.6 ± 2.9%. Coefficients of variation within‐run and between‐run of all analytes were ≤2.4%. The limit of detection of the method was: creatinine, 0.1 µmol/L; uric acid, 0.05 µmol/L; kynurenine, 0.02 µmol/L; and tryptophan, 1 µmol/L. The developed method could be employed as a useful tool for the detection of chronic kidney disease, even at an early stage. Copyright © 2014 John Wiley & Sons, Ltd.     

Salt‐assisted acetonitrile extraction and HPLC‐QTOF‐MS/MS detection for residues of multiple classes of pesticides in human serum samples

Detecting pesticide residues in human serum is a challenging process. In this study we developed and validated a method for the extraction and recovery of residues of multiple classes of pesticides from serum using one reagent. Salt‐assisted acetonitrile extraction and high‐performance liquid chromatography with quadrupole time of flight tandem mass spectrometry were used to quantitate 34 pesticides classified in nine groups of chemicals in human serum samples, which are frequently detected in food. The recoveries for 33 of analyzed pesticides ranged from 86 to 112% with relative standard deviations below 15%. The limits of quantitation and linearity of 31 of the pesticides were 1 µg/L and >0.990, respectively. The lower limit of quantitation has been reported in the literature particularly for multi‐classes pesticide mixtures in human serum. The salt–acetonitrile reagent was allowed to achieve good recoveries and detection limits, which could be attributed to salt altering the solvent polarity, preferentially collecting the organic phase in the solution, and promoting the extraction. The developed method was applied for two organophosphate pesticide metabolites, diethylphosphate and 3,5,6‐trichloro‐2‐pyridinol, in serum from rats that were fed a nonlethal quantity of chlorpyrifos. The concentrations of these two were 252.18 ± 15.47 and 0.63 ± 0.23 µg/L, respectively.     

Development and validation of a sensitive LC‐MS/MS‐ESI method for the determination of ivabradine in human plasma: application to a pharmacokinetic study

A sensitive, rapid assay method for estimating ivabradine in human plasma has been developed and validated using liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive‐ion mode. The procedure involved extraction of ivabradine and the internal standard (IS) from human plasma by solid‐phase extraction. Chromatographic separation was achieved using an isocratic mobile phase (0.1% formic acid–methanol, 60:40, v/v) at a flow rate of 1.0 mL/min on an Aglient Eclipse XDB C₈ column (150 × 4.6 mm, 5 µm; maintained at 35°C) with a total run time of 4.5 min. Detection was achieved using an Applied Biosystems MDS Sciex (Concord, Ontario, Canada) API 3200 triple‐quadrupole mass spectrometer. The MS/MS ion transitions monitored were 469–177 for ivabradine and 453–177 for IS. Method validation was performed according to Food and Drug Administration guidelines, and the results met the acceptance criteria. The calibration curve was linear over a concentration range of 0.1–200 ng/mL. The lower limit of quantitation achieved was 0.1 ng/mL. Intra‐ and inter‐day precisions were in the range of 1.23–14.17% and 5.26‐8.96%, respectively. Finally, the method was successfully used in a pharmacokinetic study that measured ivabradine levels in healthy volunteers after a single 5 mg oral dose of ivabradine. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantitation of small molecules using high‐resolution accurate mass spectrometers – a different approach for analysis of biological samples

The quantitative capabilities of a linear ion trap high‐resolution mass spectrometer (LTQ‐Orbitrap™) were investigated using full scan mode bracketing the m/z range of the ions of interest and utilizing a mass resolution (mass/FWHM) of 15000. Extracted ion chromatograms using a mass window of ±5–10 mmu centering on the theoretical m/z of each analyte were generated and used for quantitation. The quantitative performance of the LTQ‐Orbitrap™ was compared with that of a triple quadrupole (API 4000) operating using selected reaction monitoring (SRM) detection. Comparable assay precision, accuracy, linearity and sensitivity were observed for both approaches. The concentrations of actual study samples from 15 Merck drug candidates reported by the two methods were statistically equivalent. Unlike SRM being a tandem mass spectrometric (MS/MS)‐based detection method, a high resolution mass spectrometer operated in full scan does not need MS/MS optimization. This approach not only provides quantitative results for compounds of interest, but also will afford data on other analytes present in the sample. An example of the identification of a major circulating metabolite for a preclinical development study is demonstrated. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterizing protein glycosylation sites through higher‐energy C‐trap dissociation

Assigning glycosylation sites of glycoproteins and their microheterogeneity is still a very challenging analytical task despite the rapid advancements in mass spectrometry. It is shown here that glycopeptide ions can be fragmented efficiently using the higher‐energy C‐trap dissociation (HCD) feature of a linear ion trap orbitrap hybrid mass spectrometer (LTQ Orbitrap). An attractive aspect of this dissociation option is the generation of distinct Y1 ions (peptide+GlcNAc), thus allowing unequivocal assignment of N‐glycosylation sites of glycoproteins. The combination of the very informative collision‐induced dissociation spectra acquired in the linear ion trap with the distinct features of HCD offers very useful information aiding in the characterization of the glycosylation sites of glycoproteins. The HCD activation energy needed to obtain optimum Y1 ions was studied in terms of glycan structure and charge state, and size and structure of the peptide backbone. The latter appeared to be primarily dictating the needed HCD energy. The distinct Y1 ion formation in HCD facilitated an easy assignment of such an ion and its subsequent isolation and dissociation through multiple‐stage tandem mass spectrometry. The resulting MS³ spectrum of the Y1 ion facilitates database searching and de novo sequencing thus prompting the subsequent identification of the peptide backbone and associated glycosylation sites. Moreover, fragment ions formed by HCD are detected in the Orbitrap, thus overcoming the 1/3 cut‐off limitation that is commonly associated with ion trap mass spectrometers. As a result, in addition to the Y1 ion, the common glycan oxonium ions are also detected. The high mass accuracy offered by the LTQ Orbitrap mass spectrometer is also an attractive feature that allows a confident assignment of protein glycosylation sites and the microheterogeneity of such sites. Copyright © 2010 John Wiley & Sons, Ltd.     

An expedient reverse‐phase high‐performance chromatography (RP‐HPLC) based method for high‐throughput analysis of deferoxamine and ferrioxamine in urine

The present study was planned to optimize and validate an expedient reverse‐phase high chromatography (RP‐HPLC) based protocol for the analysis of deferoxamine (DFO) and ferrioxamine (FO) in urinary execration of patients suffering β ‐thalassemia major. The optimized RP‐HPLC method was found to be linear over the wide range of DFO and FO concentration (1–90 μg/mL) with appreciable recovery rates (79.64–97.30%) of quality controls at improved detection and quantitation limits and acceptable inter and intraday variability. Real‐time analysis of DFO and FO in the urine of thalassemic patients (male and female) at different intervals of Desferal®(Novartis Pharmaceuticals Corporation) injection revealed DFO and FO excretion at significantly (p < 0) different rates. The maximum concentrations of DFO (76.7 ± 3.06 μg/mL) and FO (74.2 ± 3.25 μg/mL) were found in urine samples, collected after 6 h of drug infusion while the minimum levels of DFO (1.10 ± 0.12 μg/mL) and FO (2.97 ± 0.13 μg/mL) were excreted by patients after 24 h. The present paper offers balanced conditions for an expedient, reliable and quick determination of DFO and FO in urine samples.     

Determination of Estrogenic Nonylphenol and Bisphenol a in River Water by Solid‐Phase Extraction and Gas Chromatography‐Mass Spectrometry

A simple and sensitive method is presented for the analysis of nonylphenol (NP) and bisphenol A (BPA), two well known hormonally active agents (HAAs), in the samples of river water. The method involves extraction of the sample by a graphitized carbon black (GCB) solid‐phase extraction, and determination by an ion‐trap gas chromatography‐mass spectrometry (GC‐MS). The large‐volume injection technique provides high precision and sensitivity for NP and BPA, to quantitation at < 0.05 μg/L in 200 mL of water samples. Recovery of NP and BPA in spiked water samples ranged from 80% to 85%. Relative standard deviations (RSD) of replicate analyses ranged from 1.6% to 6.9%. The concentrations of NP in rivers were in the range between 0.4 to 2.4 μg/L, which were below the threshold concentration (10 μg/L) for vitellogenin induction in fish, but 78%) of water samples from five rivers exceeded the predicted‐no‐effect concentration (PNEC) of 0.7 μg/L as proposed recently. The concentrations of BPA ranged from < 0.05 μg/L to 3.0 μg/L, which all were below the PNEC of 64 μg/L.     

Collision‐induced dissociation of oligonucleotide anions fully modified at the 2'‐position of the ribose: 2'‐F/‐H and 2'‐F/‐H/‐OMe mix‐mers

Gas‐phase dissociation of various 2'‐position modified oligonucleotide anions has been studied as a function of precursor ion charge state using ion trap and low energy beam‐type collision‐induced dissociation (CID). For a completely 2'‐O‐methyl modified 6‐mer, all possible dissociation channels along the phosphodiester linkage, generating complementary (a‐B)/w‐, b/x‐, c/y‐, d/z‐ion series, were observed with no single dominant type of dissociation pathway. Full sequence information was generated from each charge state via ion trap CID. More sequential fragmentation was noted under beam‐type CID conditions. Comparison with model DNA, in which all 2'‐OH groups are converted to 2'‐H, and RNA anions suggests that the 2'‐OMe substitution stabilizes the phosphodiester linkage with respect to fragmentation relative to both DNA and RNA oligomers. For modified mix‐mer anions, comprised of DNA nucleotides and 2'‐F substituted nucleotides or a mixture of DNA nucleotides and 2'‐O‐methyl (2'‐OMe) and 2'‐F substituted nucleotides, 3'‐side backbone cleavage was found to be inhibited by the 2'‐OMe or 2'‐F modification on the nucleotides under ion trap CID conditions. Thus, the sequence information was limited to the a‐Base/w‐fragments from the cleavage of the 3' C‐O bond of the 2'‐H (DNA) nucleotides. Under beam‐type CID conditions, limited additional cleavage adjacent to 2'‐OMe substituted nucleotides was noted but 2'‐F modified residues remained resistant to cleavage. Copyright © 2012 John Wiley & Sons, Ltd.     

Development of a nano-liquid chromatography on chip tandem mass spectrometry method for high-sensitivity hepcidin quantitation

Microfluidic LC systems present undeniable advantages over classical LC in terms of sensitivity. Hepcidin, a peptide marker of clinical disorders linked to iron metabolism, was used as model to demonstrate peptide quantification potentialities of LC-chip coupled to a nanoelectrospray source ion trap mass spectrometer in an aqueous sample. First, stable isotope labelled hepcidin was chosen as internal standard and gradient as well as sample compositions were optimised using design of experiments as development tool. The method was then prevalidated using accuracy profiles in order to select the most appropriate response function and to confirm the ability of the technique to quantify low hepcidin concentration. A reliable and very sensitive quantitation method was finally obtained using this integrated microfluidic technology. Indeed, good results with respect to accuracy, trueness and precision were achieved, as well as a very low limit of quantitation (0.07 ng/ml). Method suitability of nano-LC on chip tandem mass spectrometry for hepcidin quantitation was also demonstrated in complex media such as human plasma.     

Optimization of a quadrupole ion storage trap as a source for time‐of‐flight mass spectrometry

Designs of a quadrupole ion trap (QIT) as a source for time‐of‐flight (TOF) mass spectrometry are evaluated for mass resolution, ion trapping, and laser activation of trapped ions. Comparisons are made with the standard hyperbolic electrode ion trap geometry for TOF mass analysis in both linear and reflectron modes. A parallel‐plate design for the QIT is found to give significantly improved TOF mass spectrometer performance. Effects of ion temperature, trapped ion cloud size, mass, and extraction field on mass resolution are investigated in detail by simulation of the TOF peak profiles. Mass resolution (m/Δm) values of several thousand are predicted even at room temperature with moderate extraction fields for the optimized design. The optimized design also allows larger radial ion collection size compared with the hyperbolic ion trap, without compromising the mass resolution. The proposed design of the QIT also improves the ion–laser interaction volume and photon collection efficiency for fluorescence measurements on trapped ions. Copyright © 2011 John Wiley & Sons, Ltd.     

Sensitive determination of glucose in Dulbecco's modified Eagle medium by high‐performance liquid chromatography with 1‐phenyl‐3‐methyl‐5‐pyrazolone derivatization: application to gluconeogenesis studies

A new pre‐column derivative high‐performance liquid chromatography (HPLC) method for determination of d ‐glucose with 3‐O‐methyl‐d ‐glucose (3‐OMG) as the internal standard was developed and validated in order to study the gluconeogenesis in HepG2 cells. Samples were derivatized with 1‐phenyl‐3‐methy‐5‐pyrazolone at 70°C for 50 min. Glucose and 3‐OMG were extracted by liquid–liquid extraction and separated on a YMC‐Triart C₁₈ column, with a gradient mobile phase composed of acetonitrile and 20 mm ammonium acetate solution containing 0.09% tri‐ethylamine at a flow rate of 1.0 mL/min. The eluate were detected using a UV detector at 250 nm. The assay was linear over the range 0.39–25 μm (R² = 0.9997, n = 5) and the lower limit of quantitation was 0.39 μm (0.070 mg/mL). Intra‐ and inter‐day precision and accuracy were <15% and within ±3%, respectively. After validation, the HPLC method was applied to investigate the gluconeogenesis in Dulbecco's modified Eagle medium (DMEM) cultured HepG2 cells. Glucose concentration was determined to be about 1–2.5 μm in this gluconeogenesis assay. In conclusion, this method has been shown to determine small amounts of glucose in DMEM successfully, with lower limit of quantitation and better sensitivity when compared with common commercial glucose assay kits. Copyright © 2015 John Wiley & Sons, Ltd.     

The Analysis of Chlorinated Phenol Solutions by Capillary Electrophoresis Coupled with Direct and Indirect Amperometric Detection Using a Boron‐Doped Diamond Microelectrode

Analysis of aqueous solutions containing chlorinated phenol pollutants was accomplished by capillary electrophoresis with direct and indirect amperometric detection using a boron‐doped diamond microelectrode. The microelectrode was prepared by (i) coating a thin film of boron‐doped polycrystalline diamond on a sharpened platinum wire (76‐μm diameter) and (ii) sealing the coated wire in a polypropylene pipet tip. The diamond microelectrode, used in end‐column detection, exhibited a low and stable background current with low peak‐to‐peak noise and good electrochemical activity for the pollutants without any conventional pretreatment. The electrode performance was evaluated in terms of the linear dynamic range, sensitivity, limit of quantitation, and response precision for the detection of several priority pollutants (2‐chlorophenol, 3‐chlorophenol, 4‐chlorophenol, 2,4‐dichlorophenol, 2,4,6‐trichlorophenol, and pentachlorophenol). The diamond microelectrode gave good detection figures of merit for these contaminants in the direct amperometric mode with no evidence of any electrode fouling. As an example, the concentration limit of quantitation for 2‐chlorophenol was 100 nM or 13 ppb (S/N=3) and the relative standard deviation of the peak height for 9 injections was 4.7±0.5% (est. 1.1 nL inj.). The separation efficiency was greater than 100 000 plates/m for all seven solutes. The microelectrode was also employed for the indirect detection of the chlorinated phenols. In this approach, which is useful for detecting electroinactive solutes, ferrocene carboxylic acid was added to the run buffer as the electrophore. Good detection figures of merit were also achieved for the separation and detection of 2‐chlorophenol, 3‐chlorophenol, and 2,4‐dichlorophenol in this mode, although the linear dynamic range was not as wide and the limit of quantitation was not as low as in direct amperometry. For example, the concentration limit of quantitation for these pollutants was in the mid micromolar range (1–10 ppm) with excellent response reproducibility of 3.2±0.8%, or less.     

Star‐shaped and photocrosslinked poly(1,5‐dioxepan‐2‐one): Synthesis and characterization

New star‐shaped and photocrosslinked poly(1,5‐dioxepan‐2‐one) (PDXO) has been synthesized through ring‐opening polymerization initiated by SnOct₂/pentaerythritol. The star‐shaped PDXO was end‐functionalized by acrolyol chloride to form acrylate end groups. The end‐functionalized PDXO was photocrosslinked initiated by 2,2‐dimethoxy‐2‐phenylacetophenone. The gel content ranged from 80 to 99%, indicating a high degree of crosslinking. The thermal properties of the star‐shaped PDXO and the photocrosslinked PDXO were analyzed by differential scanning calorimetry. The glass‐transition temperature was determined to approximately ?32 °C for the crosslinked PDXO. The viscosity numbers were determined for star‐shaped PDXO, with reference to linear homologues. The star‐shaped PDXO had lower viscosity numbers than the linear counterparts. The crosslinked PDXO showed a rather hydrophilic surface as compared with other resorbable polyesters. The advancing contact angle was 64 ± 2, and the receding angle was 57 ± 4. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2049–2054, 2002     

Qualitative and quantitative analysis of THC, 11‐hydroxy‐THC and 11‐nor‐9‐carboxy‐THC in whole blood by ultra‐performance liquid chromatography/tandem mass spectrometry

A qualitative and quantitative analytical method was developed for the simultaneous determination of Δ⁹‐tetrahydrocannabinol (THC), 11‐hydroxy‐Δ⁹‐tetrahydrocannabinol (11‐OH‐THC) and l1‐nor‐9‐carboxy‐Δ⁹‐tetrahydrocannabinol (THC‐COOH) in whole blood. The samples were prepared by solid‐phase extraction followed by ultra‐performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) analysis using positive ion electrospray ionization and multiple reaction monitoring. The chromatographic separation was performed with an Acquity UPLC® HSS T3 (50 × 2.1 mm i.d., 1.8 µm) reversed‐phase column using a methanol/2 mM ammonium formate (formic acid 0.1%) gradient in a total run time of 9.5 min. MS/MS detection was achieved with two precursor‐product ion transitions per substance. The method was fully validated, including selectivity and capacity of identification, according to the identification criteria (two transitions per substance, signal‐to‐noise ratio, relative retention time and ion ratio) without the presence of interferences, limit of detection (0.2 µg/L for THC and 0.5 µg/L for 11‐OH‐THC and THC‐COOH), limit of quantitation (0.5 µg/L for all cannabinoids), recovery (53–115%), carryover, matrix effect (34‐43%), linearity (0.5‐100 µg/L), intra‐assay precision (CV < 10% for the relative peak area ratios and <0.1% for the relative retention time), inter‐assay accuracy (mean relative error <10%) and precision (CV <11%). The method has already been successfully used in proficiency tests and subsequently applied to authentic samples in routine forensic analysis. Copyright © 2011 John Wiley & Sons, Ltd.