Quantitative Detection Limit Research Articles

Determination of Xylazine and 2,6‐Xylidine in Animal Tissues by Liquid Chromatography—Tandem Mass Spectrometry

Xylazine is a potent α2-adrenergic agonist used in veterinary medicine for sedation, analgesia, muscle relaxation, and so on. Its residue in animal-derived food may cause the food safety problem. Moreover, the metabolite 2,6-xylidine was reported to be a genotoxic and carcinogenic compound. Therefore, it is necessary to develop a high sensitive method for analyzing xylazine and metabolite residue in animal products. Here, we described a LC-MS/MS method for simultaneous determination of xylazine and 2,6-xylidine in 4 animal tissues: liver, meat, kidney, and fat. The samples were extracted by acetonitrile, and further clean up by hexane. The analysis was performed on a C18 reversed-phase column and API 5000 Triple Quadrupole mass spectrometry with positive electrospray ionization interface operating in the multiple-reaction monitoring mode. For all of the investigated sample matrix, the limit of detection (limit of quantitation) for xylazine and 2,6-xylidine were 0.06 (0.2) and 1.5 (5) μg/kg, respectively, the recoveries were between 63.5% and 90.8%. The precision was within the range of required criteria for method development. The presented method is sensitive and reproducible, and thus suitable for accurate quantification of xylazine and metabolite residue in animal-derived food products.

Development and comparison of two dispersive liquid–liquid microextraction techniques coupled to high performance liquid chromatography for the rapid analysis of bisphenol A in edible oils

In this study, two novel sample extraction methods for the analysis of bisphenol A (BPA) in edible oils were developed by using liquid–liquid extraction followed by a dispersive liquid–liquid microextraction (LLE-DLLME) and reversed-phase dispersive liquid–liquid microextraction (RP-DLLME). RP-DLLME showed a superior characteristic over LLE-DLLME and other previously reported procedures because of its easy operation, short extraction time, high sensitivity, low organic solvent consumption and waste generation. The optimized extraction conditions of RP-DLLME for 1.0g of edible oil diluted in 4mL of n-hexane were: extractant, 100μL 0.2M sodium hydroxide solution (80% methanol, v/v); extraction time, 1min; centrifugation, 3min. The determination of BPA was carried out by high performance liquid chromatography coupled with a DAD detector. The method offered excellent linearity over a range of 0.010–0.5μgg−1 with a correlation coefficient of r>0.997. Intra-day and inter-day repeatability values expressed as relative standard deviation were 1.9% and 5.9%, respectively. The quantitation limit and detection limit were 6.3 and 2.5ngg−1. The target analyte was detected in 5 out of 16 edible oil samples. The recovery rates in real samples ranged from 89.5 to 99.7%.

Establishment and clinical application of TapMan real-time RT-PCR method for detection of HHV-6

To establish a rapid, sensitive and specific real-time PCR method for detection of Human Herpesvirus-6 (HHV-6). According to the reference, a pair of primers and a probe were designed located in U65-66 gene and to set up the standards. We established a real-time RT-PCR method for detection of HHV-6, and to verify the specificity, sensitivity, reproducibility. The correlation coefficient was 0.999, E = 97.9%, the coefficient of variation values of Ct were 0.61% and 3.13% in real-time PCR assay for inter and intra assay, respectively. The results of all viruses were negative except of HHV-6 for the assay. The quantitative detection limit of the assay was 3 x 10(0) copies/microl. The real-time PCR assay is highly specific, sensitive and reproducible, which can be used to quatitative detecting clinical samples.

Halobenzoquinones in Swimming Pool Waters and Their Formation from Personal Care Products

Halobenzoquinones (HBQs) are a class of disinfection byproducts (DBPs) of health relevance. In this study, we aimed to uncover which HBQs are present in swimming pools. To achieve this goal, we developed a new method capable of determining eight HBQs while overcoming matrix effects to achieve reliable quantification. The method provided reproducible and quantitative recovery (67-102%) and detection limits of 0.03-1.2 ng/L for all eight HBQs. Using this new method, we investigated water samples from 10 swimming pools and found 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) in all the pools at concentrations of 19-299 ng/L, which was as much as 100 times higher than its concentration in the input tap water (1-6 ng/L). We also identified 2,3,6-trichloro-(1,4)benzoquinone (TriCBQ), 2,3-dibromo-5,6-dimethyl-(1,4)benzoquinone (DMDBBQ), and 2,6-dibromo-(1,4)benzoquinone (2,6-DBBQ) in some swimming pools at concentrations of <0.1-11.3, <0.05-0.7, and <0.05-3.9 ng/L, respectively, but not in the input tap water. We examined several factors to determine why HBQ concentrations in pools were much higher than in the input tap water. Higher dissolved organic carbon (DOC), higher doses of chlorine and higher temperatures enhanced the formation of HBQs in the pools. In addition, we conducted laboratory disinfection experiments and discovered that personal care products (PCPs) such as lotions and sunscreens can serve as precursors to form additional HBQs, such as TriCBQ, 2,6-dichloro-3-methyl-(1,4)benzoquinone (DCMBQ), and 2,3,5,6-tetrabromo-(1,4)benzoquinone (TetraB-1,4-BQ). These results explained why some HBQs existed in swimming pools but not in the input water. This study presents the first set of occurrence data, identification of new HBQ DBPs, and the factors for their enhanced formation in the swimming pools.

Application of a Reliable LC-MS/MS Method for Determination of Rizatriptan in Healthy Subject Samples: Demonstration of Assay Reproducibility by Incurred Sample Reanalysis

A reliable, rapid, and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay has been proposed for the determination of rizatriptan in human plasma using sumatriptan as internal standard (IS). The analyte and IS were extracted from 300 μL human plasma via liquid-liquid extraction and the chromatography was achieved on Hypurity C18 (50 mm × 4.6 mm, 5 μm) column under isocratic conditions. Detection of rizatriptan and IS was done by tandem mass spectrometry, operating in positive ionization and multiple-reaction monitoring mode. The limit of detection and lower limit of quantitation of the method were 0.04 and 0.20 ng/mL, respectively, with a linear dynamic range of 0.20–60.0 ng/mL. The intrabatch and interbatch precision (% CV) was ≤8.4% while the mean extraction recovery was &gt;78% across quality control levels. Bench top stability, freeze and thaw stability, processed sample stability, and long-term stability in plasma were evaluated at two quality control levels. It was successfully applied to a bioequivalence study of 10 mg rizatriptan orally disintegrating tablet formulation in 40 and 32 healthy Indian male subjects under fasting and fed conditions, respectively. The reproducibility in the measurement of study data was demonstrated by reanalysis of 254 incurred samples.

Quantitation of aldosterone in human plasma by ultra high performance liquid chromatography tandem mass spectrometry

Aldosterone is a mineralocorticoid steroid hormone whose measurement in the clinical laboratory is principally performed for the investigation of primary hyperaldosteronism. Traditionally measurement of aldosterone has been performed by radioimmunoassay, however these assays lack specificity as they are prone to interference from structurally related steroid hormones. Herein, we have developed a novel, sensitive and specific method utilising solid phase extraction and quantitation of aldosterone from human plasma by UPLC–MS/MS. Standards, quality controls and samples (250μL) were extracted using Oasis® HLB 96-well plates. Extract (30μL) was injected onto a Krudcatcher UPLC In-Line Filter, 0.5μm guard column, coupled to a Kinetex PFP, 100mm×2.1mm, 2.6μm column with methanolic mobile phase gradient elution. Eluant was connected to a Waters® Xevo TQS tandem mass spectrometer operating in electrospray negative mode. We detected multiple reaction monitoring (MRM) transitions of m/z 359.0>189.1 for aldosterone and 366.0>194.1 for d7-aldosterone respectively, which co-eluted at 2.65min. Ion suppression was negligible. Mean recovery was 89.6%, limit of detection and lower limit of quantitation were 26pmol/L and 30pmol/L respectively. The assay was linear up to 3200pmol/L (r2=0.9999). Mean intra- and inter-assay imprecision and bias were all <10%. Comparison of the UPLC–MS/MS method with an immunoassay in routine clinical use in the UK yielded the equation UPLC–MS/MS=0.789(RIA)–41.7, linear regression r2=0.88, n=54. We have developed a sensitive and specific method for the extraction and measurement of aldosterone from human plasma. The method features a simple 96-well plate solid phase extraction procedure, highly selective column chemistry and short chromatographic run times.

Determination of erythrocyte methotrexate polyglutamates by liquid chromatography/tandem mass spectrometry after low-dose methotrexate therapy in Chinese patients with rheumatoid arthritis

Methotrexate (MTX) is currently one of the most widely used drugs for treatment of rheumatoid arthritis (RA) through polyglutamation of methotrexate polyglutamates (MTXPGs), a process attaching sequential γ-linked glutamic residues to MTX. A new and sensitive LC/MS/MS method was developed and validated for determination of whole-blood MTX and total MTX (MTX+MTXPGs), and then concentration of MTXPGs was calculated. To determine whole-blood MTX, whole blood was precipitated with 50% trifluoroacetic acid, and extraction was performed using ethyl acetoacetate. Analytes were subjected to LC/MS/MS analysis using positive electrospray ionization. To determine whole-blood total MTX, whole blood was incubated with ascorbic acid (200mM) at 37°C for 3h to enzymatically convert the MTXPGs to MTX, and then processed with the same method mentioned above. Recoveries of spiked MTX at ppb (ng/mL) level were between 26.2% and 37.8% with intra- and inter-day precision less than 15.8% and 11.8%, respectively. The lower limit of detection (LLOD) and lower limit of quantitation (LLOQ) were 0.5ng/mL and 1ng/mL, respectively. The sensitive LC/MS/MS method was fully validated with high selectivity and acceptable accuracy and precision, which was successfully applied to determine the erythrocyte methotrexate polyglutamates in patients with RA.

The Evaluation of Statistical Methods for Estimating the Lower Limit of Detection

In estimating a quantitative assay's lower limit of detection (LOD), standard deviation (SD) is the most common measure used to quantify the dispersion of the data, yet this LOD calculation method assumes that the low concentration samples follow a Gaussian distribution, which is not always true in reality. Here, a few LOD estimating methods that are based on different dispersion measures were investigated; each method's performance was evaluated across various distribution scenarios. Nine methods for LOD estimation that use different measures of data dispersion-SD, mean absolute deviation (MD), median absolute deviation, Gini's mean difference (GMD), percentiles (PCT), Algorithm A, S(n), Q(n), and inter-quartile range-were evaluated using both simulations and real-life datasets. LOD estimates calculated using different variability measures were compared to the true LOD value under different scenarios. A method was judged to be good if the method had a relatively stable formula, low bias, confidence interval that had shorter width, and achieved the desired level of frequency in covering the true value of LOD (coverage probability [CP]). First, the nine methods were screened for formula consistency across different distribution scenarios. Methods showing the greatest formula variation were removed from further analysis; the remaining methods were then examined and compared. The GMD-based method had a relatively stable formula and demonstrated the best overall performance with low bias, confidence interval of shorter width, and good CP across all situations. The PCT-based method only performed well if sample size was large. The MD-based method in general had larger bias than the GMD-based estimator. LOD estimates based on SD that assumes Gaussian distribution in all scenarios will often generate poor results. Instead, the GMD-based estimator, a method with a simple formula so is easy to use in practice, demonstrated robust performance across varying situations.

Determination of Mercury and Other Metals in Red Yeast Rice

Chromium, arsenic, cadmium, nickel, selenium, mercury and lead have been determined in red yeast rice samples by ICP-MS and a Hydra-C mercury analyzer. Less than 0.010 μg/g mercury was found in all but one sample, which had 0.011 μg/g. The amounts of chromium, arsenic, cadmium, nickel, selenium, cadmium and lead varied from 0.05–0.83 (Cr), 0.05–0.35 (As), 0.004–0.139 (Cd), 0.13–2.05 (Ni), 0.028–0.222 (Se), and 0.000–0.517 (Pb) μg/g. Percent recoveries of spiked samples ranged from 77 – 111%. Recoveries of mercury in two different standard reference materials were 83 and 110%. The minimum detection limit and limit of quantitation for mercury were 0.2 and 1.0 ng, respectively.

Application of a rapid and sensitive liquid chromatography–tandem mass spectrometry method for determination of bumetanide in human plasma for a bioequivalence study

A rapid, selective and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay has been proposed for the determination of bumetanide in human plasma using tamsulosin as internal standard (IS). The analyte and IS were extracted from 200 μL of human plasma via solid phase extraction and the chromatographic separation was achieved on Peerless Basic C18 (100 mm × 4.6 mm, 3 μm) column under isocratic conditions. Detection of bumetanide and IS was done by tandem mass spectrometry, operating in positive ionization and multiple reaction monitoring (MRM) acquisition mode. The protonated precursor to product ion transitions monitored for bumetanide and IS were m/z 365.2→240.2 and 409.2→228.2 respectively. The method was fully validated as per the US FDA guidelines. The limit of detection and lower limit of quantitation of the method were 0.03 and 0.30 ng/mL respectively with a linear dynamic range of 0.30-200.0 ng/mL for bumetanide. The intra-batch and inter-batch precision (% CV) was ≤6.9% while the mean extraction recovery was >90% across quality control levels. The method is selective in presence of four diuretic drugs and some commonly used medications by healthy volunteers. It was successfully applied to a bioequivalence study of 2mg bumetanide tablet formulation in 10 healthy Indian male subjects under fasting condition. The reproducibility in the measurement of study data was demonstrated by reanalysis of 42 incurred samples.

Dried blood spot (DBS) sample collection for determination of the oxidative stress biomarker 8‐epi‐PGF2α in humans using liquid chromatography/tandem mass spectrometry

F2-isoprostanes are a series of prostaglandin F2-like compounds that are formed by free-radical-catalyzed peroxidation of arachidonic acid (ARA). Several F2-isoprostanes, but in particular 8-epi-PGF(2α), are widely used as oxidative stress biomarkers. In this study we have developed an analytical tool for finger-tip blood sampling and analysis of 8-epi-PGF(2α) from dried blood spots (DBS). We have applied solid-phase extraction (SPE) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the extraction, separation and detection of 8-epi-PGF(2α) in DBS and have studied the stability of this marker using the DBS collection platform. The mass limit of detection (mLOD) for 8-epi-PGF(2α) extracted from DBS samples was 1.5 pg while the concentration limit of detection (cLOD) and concentration limit of quantitation (cLOQ) were 6 pg/mL and 18 pg/mL, respectively. All values based on triplicate analysis. Sufficient stability of 8-epi-PGF(2α) in DBS was achieved by preconditioning DBS paper with vitamin E and BHT. The developed method is sensitive, specific, robust, efficient, and can accurately measure endogenous concentrations of 8-epi-PGF(2α) in DBS. Thus, it offers an analytical approach to measure 8-epi-PGF(2α) by a novel sample collection technique that is less invasive and costly than conventional techniques.

Application of polymerase chain reaction with disposable amplicon detection device for identification of regulatory gene introduced into genetically modified maize

A novel genetically modified organism (GMO) detection method was developed using a simple and rapid procedure to identify a regulatory gene introduced into genetically modified (GM) maize. After DNA extraction from GM maize flours, fragments of the conserved sequence of the cauliflower masaic virus (CaMV) 35S promoter gene along with a competitive internal control gene were amplified using duplex polymerase chain reaction (PCR). Amplification products were then detected using a disposable detection device. The quantitative detection limit for GM maize 59122 was found to be 1.0% (w/w). Because the combination-method involving PCR technology coupled with a disposable detection device does not require expensive instrumentation or expertise, it will serve as a valuable alternative to immunoassays and traditional PCR-based tests in the detection of GMOs.

Anti-CD19 BiTE Blinatumomab Induces High Complete Remission Rate In Adult Patients with Relapsed B-Precursor ALL: Updated Results of An Ongoing Phase II Trial

Abstract 252Adult patients with relapsed/refractory B-precursor acute lymphoblastic leukemia (ALL) have a dismal prognosis with low complete remission (CR) rates with intensive salvage chemotherapy which are not durable.Blinatumomab is a bispecific T-cell engaging (BiTE®) antibody construct that directs cytotoxic T-cells to CD19 expressing B-cells. In collaboration with the German Multicenter Study Group for Adult Lymphoblastic Leukemia (GMALL), an open-label, multicenter, single-arm, exploratory phase II trial is being conducted to evaluate efficacy and safety of blinatumomab in adult patients with relapsed/refractory B-precursor ALL.The primary endpoint for this trial is the rate of patients who reach CR or CR with partial hematological recovery (CRh*) within 2 cycles of blinatumomab treatment. Secondary endpoints are the rate of minimal residual disease (MRD) response (defined by an MRD level below the quantitative detection limit of 10−4), time to hematological relapse and overall survival.Blinatumomab is administered by continuous intravenous infusion for 28-days followed by a 14-day treatment-free interval. Responding patients could proceed to allogeneic hematopoietic stem cell transplantation (HSCT) or receive a total of up to 5 cycles of blinatumomab treatment. Three dose levels have been explored as shown in Table 1.Table 1Summary of Dose Cohorts and OutcomesCohortPatients TreatedInitial Dose Week 1, Cycle 1 μg/m2/dayDose Week 2, Cycle 1 μg/m2/dayDose Weeks 3–4, Cycle 1 μg/m2/dayMaintenance Dose, Subsequent Cycles μg/m2/dayCR or CRh*Serious Adverse EventsnPts171515151551562a551515154222b65153030354310 planned5151515n.a.n.a.n.a.As of June 30, 2011, 43 cycles have been administered to a total of 18 patients (range 1–5; median 2). Twelve out of 18 patients have reached a complete remission within the first 2 cycles of single agent blinatumomab corresponding to a response rate of 67%. Of these 12 responding patients, 75% had complete hematologic recovery of peripheral blood counts. All 12 responders reached MRD negativity within the first 2 cycles and included 3 patients with t(4;11) and 1 patient with Ph-positive B-precursor ALL. Four responders proceeded to allogeneic HSCT; one experienced a CD19-negative hematological relapse after HSCT. Two responders relapsed during treatment; one had a CD19-positive extramedullary, and one a CD19-negative bone marrow relapse. The remaining 6 non-transplanted responders are still in hematological complete remission.The most common adverse events were pyrexia and chills. In cohort 1, one patient with a high tumor burden developed disseminated intravascular coagulation (DIC)/cytokine release syndrome (CRS) leading to treatment discontinuation. The implementation of a cytoreductive pre-phase and a lower initial dosing at 5μg/m2/day during the first week prevented further treatment discontinuations in such patients. Four patients had fully reversible CNS serious adverse events that led in 1 patient to discontinuation of treatment, and in 3 patients to temporary interruption of treatment. These 3 patients resumed treatment at a lower dose without further interruptions during the following cycles. There were no deaths related to blinatumomab.Blinatumomab as single agent induced an unprecedented high rate of complete hematological and MRD responses in adult patients with relapsed/refractory B-precursor ALL. A lower dose of 5μg/m2/day for the initial week of treatment, as tested in cohort 2a, demonstrated a favorable safety profile while maintaining efficacy. A maintenance dose of 30μg/m2/day, as tested in cohort 2b, did not further improve the already high efficacy but increased the number of adverse events. Therefore, the dosing of cohort 2a was selected as the basis for cohort 3 and will be applied to further clinical development in this patient population. Updated results of the study will be presented. Disclosures:Topp:Micromet: Consultancy, Honoraria. Goekbuget:Micromet: Consultancy. Zugmaier:Micromet: Employment. Klappers:Micromet AG: Employment. Mergen:Micromet Inc: Employment. Bargou:Micromet: Consultancy, Honoraria.

Determination of Ofloxacin using a Highly Selective Photo Probe Based on the Enhancement of the Luminescence Intensity of Eu3+—Ofloxacin Complex in Pharmaceutical and Serum Samples

A rapid, simple and sensitive spectrofluorimetric method for determination of trace amount of ofloxacin was developed. At pH 5.1 the ofloxacin enhances the luminescence intensity of the Eu(3+) ion in Eu(3+)- ofloxacin complex at λ(ex) = 365 nm. The produced luminescence intensity of Eu(3+)-ofloxacin complex was in proportional to the concentration of ofloxacin. The working range for the determination of ofloxacin was 5.0 × 10(-9)-5.0 × 10(-6) mol L(-1) with lower detection limit (LOD) and quantitative detection limit (QDL) of 3 × 10(-9) and 9 × 10(-9) mol L(-1), respectively. The enhancement mechanism of the luminescence intensity in the Eu(3+)-ofloxacin system has been also explained. The method revealed good selectivity for ofloxacin in the presence of coexisting substances and used successfully for the assay of ofloxacin in pharmaceutical preparations and serum. A comparison with other standard methods was also discussed.

Gluten-free barley malt beers

About 75% of the barley proteins are gluten, with 50% prolamins and 25% glutenins. Gluten is related to gluten allergy and celiac disease. Malting and brewing processes removes much of the protein. More than 40 Belgian brewed commercial beers (gluten-free labeled, pils/lager, abbey, trappist, strong blond, amber, old brown, kriek and gueuze) and some foreign commercial beers are analyzed with R5 antibody sandwich ELISA gluten kit and competitive ELISA celiac-toxic peptide kits. The gluten content of the gluten-free labeled beers is in the range 5–8 ppm. The other beers have a gluten content from lower than the quantitative detection limit (5 ppm) to 101 ppm. Preliminary lab scale brewing experiments (60 Liter pilot brewery) and an industrial brewing case study revealed that the gluten content in the final beer can clearly be diminished by either using prolyl endopeptidase and/or tannins during the brewing processes. Even 100% barley malt beers can obtain a final gluten content much lower than the threshold of 20 ppm for food products to be declared ‘gluten-free’.

Detection of rolling circle amplified DNA molecules using probe-tagged magnetic nanobeads in a portable AC susceptometer

Here, the volume-amplified magnetic nanobead detection assay (VAM-NDA) is for the first time applied for detection of rolling circle amplified (RCA) DNA molecules in a portable, commercial AC susceptometer that operates at ambient temperatures and with an analysis time of about 20min. The performance of the assay is investigated using three different magnetic nanobead sizes: 50, 130 and 250nm. The performance of the assay using the AC susceptometer is compared to the performance achieved using a superconducting quantum interference device (SQUID).It is found that the performance of the assay is comparable in the two setups with a quantitative detection limit of ∼4pM for all bead sizes under study.The findings show that the VAM-NDA holds promise for future wide-spread implementation in commercial AC susceptometer setups thus opening up for the possibility to perform magnetic bead-based DNA detection in point-of-care and outpatient settings.

Development and validation of a selective and sensitive LC–MS/MS method for determination of cycloserine in human plasma: Application to bioequivalence study

A selective and sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) assay for the determination of cycloserine in human plasma is developed using niacin as internal standard (IS). The analyte and IS were extracted from 500 μL of human plasma via solid phase extraction on Waters Oasis MCX cartridges. Chromatographic separation was achieved on a Peerless Basic C18 (100 mm × 4.6 mm, 3 μm) column under isocratic conditions. Detection of analyte and IS was done by tandem mass spectrometry, operating in positive ion and multiple reaction monitoring (MRM) acquisition mode. The protonated precursor to product ion transitions monitored for cycloserine and niacin were at m/z 103.1 → 75.0 and 124.1 → 80.1 respectively. The method was fully validated for its selectivity, interference check, sensitivity, carryover check, linearity, precision and accuracy, reinjection reproducibility, recovery, matrix effect, ion suppression/enhancement, stability and dilution integrity. The limit of detection (LOD) and lower limit of quantitation of the method were 0.0013 and 0.20 μg/mL respectively with a linear dynamic range of 0.20–30.00 μg/mL for cycloserine. The intra-batch and inter-batch precision (%CV) across six quality control levels was less than 8.0% for cycloserine. The method was successfully applied to a bioequivalence study of 250 mg cycloserine capsule formulation in 24 healthy Indian male subjects under fasting condition.

A bias in quantitative RT-PCR limit of detection is induced by the use of cancer cell lines in the molecular detection of circulating tumor cells

9 species of caddisflies (Trichoptera) are reported for the first time in Saxony, (Germany): Rhyacophila philopotamoides, Synagapetus iridipennis, Hydroptila vectis, Orthotrichia tragetti, Ithytrichia lamellaris, Plectrocnemia brevis, Hydropsyche tennis, Phacopteryx brevipennis, Ylodes simulans. Additional 12 species were rediscovered in reference to Robert (2001): Hydroptila forcipata, Hydropsyche fulvipes, Oligostomis reticulata, Brachycentrus maculatus, Ironoquia dubia, Drusus chrysotus, Grammotaulius nitidus, Limnephilus subcentralis, Halesus tesselatus, Ceraclea annulicornis, Ceraclea nigronervosa, Oecetis testacea.

On‐line solid‐phase extraction LC‐MS/MS for the determination of Ac‐SDKP peptide in human plasma from hemodialysis patients

We developed a high-throughput method based on on-line solid-phase extraction liquid chromatography tandem mass spectrometry (SPE-LC-MS/MS) to determine N-terminal thymosin-β fragment peptide (N-acetyl-seryl-aspartyl-lysyl-proline, Ac-SDKP) in human plasma samples. Quantification of Ac-SDKP was performed using direct injection for on-line SPE based on C(18), reversed-phase LC separation and stable isotope dilution electrospray ionization-MS/MS in multiple reaction-monitoring (MRM) mode. The Ac-SDKP-(13)C(6), (15)N(2) (m/z 496 → 137) was synthesized for the internal standard. The MRM ion for Ac-SDKP was m/z 488 → 129 (quantitative ion)/226. The limit of detection and lower limit of quantitation were 0.05 and 0.1 ng/mL in standard solution, respectively. Recovery values were 98.3-100.4% with inter-day (relative standard deviation, RSD, 0.4-14.1%) and intra-day (RSD, 0.8-19.7%) assays. This method was applied to the measurement of Ac-SDKP levels in plasma from hemodialyzed subjects. Concentrations were 0.59 ± 0.23 ng/mL (pre-hemodialyzed subjects, n = 9) and 0.44 ± 0.19 ng/mL (post-hemodialyzed subjects, n = 9). All plasma Ac-SDKP levels were decreased by dialysis. Thus, plasma Ac-SDKP was decreased through dialysis in chronic kidney disease. The findings in this study will be useful for the treatment of anemia in chronic kidney disease with dialysis.

Spectrofluorimetric Determination of Triamterene in Different Body Fluids and Pharmaceutical Tablets

A spectrofluorimetric method is used to determine 6-phenylpteridine-2,4,27-triamine inpharmaceutical dosage form, Urine and human serum samples. The method is simple, sensitive, and accurateand based on the fluorescence enhancement with increasing concentration of the highly fluorescent triamterenecontaining three amino groups in methanol at pH 6.7. The dynamic range for the determination of triamtereneis 5×10-10 – 9.5×10-7 mol L-1 with detection limit and quantitative detection limit (LOD and LOQ) of 2x10-10 and 6.6x10-10, mol L-1, respectively. The low values of LOD and LOQ indicate the high sensitivity of theproposed method if compared to previous methods for the determination of triamterene. Percentage recoverieswere found to be 99.30 ± 0.65, 98.6 ± 0.75, and 96.60 ± 0.85 for the pharmaceutical tablets, urine, and serumsamples, respectively. The results demonstrated the accuracy as well as the precision of the proposed method.