Electrospray Ionization-triple Quadrupole Mass Spectrometry Research Articles

A high performance liquid chromatography-tandem mass spectrometry assay for therapeutic drug monitoring of 10 drug compounds commonly used for antimicrobial therapy in plasma and serum of critically ill patients: Method optimization, validation, cross-validation and clinical application

Background and aimsIntensive care antibiotic treatment faces challenges due to substantial pharmacokinetic differences in critically ill patients. Individualized antibiotic dosing guided by therapeutic drug monitoring (TDM) is considered to minimize the risk of treatment failure and toxicity. This study aimed to develop a valid method for simultaneous LC-MS/MS quantification of 10 drugs frequently used in intensive care antibiotic therapy for which TDM-guided dosing is recommended: piperacillin, meropenem, flucloxacillin, cefuroxime, vancomycin, colistin A and B, linezolid, ciprofloxacin and tazobactam. Methods and ResultsThorough optimization of sample preparation and chromatography resulted in a fast and simple method based on protein precipitation of 50 µL plasma or serum and gradient elution using an Acquity UPLC HSS-T3 column. Electrospray ionization-triple quadrupole mass spectrometry in dynamic multiple reaction monitoring was used for quantification, covering the therapeutic range of each drug compound. Validation following EMA and FDA recommendations, including inter-platform validation and inter-laboratory comparison, demonstrated high accuracy, precision and robustness of the new method. The assay was successfully used to monitor plasma antibiotic levels of critically ill patients (n = 35). ConclusionThe established multiplex method covers major drug classes with documented dosing challenges, provides a reliable basis for the implementation of high-throughput TDM, and its application confirmed the clinical impact of TDM in a real-world setting.

Simultaneous quantitation of 17 endogenous adrenal corticosteroid hormones in human plasma by UHPLC-MS/MS and their application in congenital adrenal hyperplasia screening.

Accurate investigation of adrenal hormone levels plays a vital role in pediatric endocrinology for the detection of steroid-related disorders. This study aims to develop a straightforward, sensitive UHPLC-MS/MS method to quantify 17 endogenous adrenal corticosteroid hormones in human plasma. These hormones are the main ingredients in the synthetic and metabolic pathways of adrenal corticosteroid hormones. Chromatographic separation was achieved on a C18 column before electrospray ionization triple-quadrupole mass spectrometry in multiple reaction monitoring mode with a run time of 7 min. The samples were extracted by liquid-liquid extraction and required no derivatization. Analytical performance was evaluated, including linearity, analytical sensitivity, accuracy, precision, and specificity. Plasma specimens from 32 congenital adrenal hyperplasia (CAH) patients and 30 healthy volunteers were analyzed to further reveal the diagnostic value of multiple steroid hormones in the synthetic and metabolic pathways of adrenal corticosteroid in CAH diagnosis. All hormones were effectively extracted and separated using our method. The method was essentially free from potential interference of isomers or structural analogues. The imprecisions were <10%. The lower limits of quantification varied from 0.05 to 15.0 ng/ml. Good linearity coefficients (r 2 > 0.998) were also obtained for most hormones in the required concentration range, except for 21-deoxycortisol (r 2 = 0.9967) and androstenediol (r 2 = 0.9952). The recoveries for the steroid hormones ranged from 91.7 to 109.8%. We developed the UHPLC-MS/MS method for the simultaneous measurement of steroid hormones. The results showed that measurement of steroid hormones simultaneously could improve the diagnostic efficiency of CAH.

Qualitative and quantitative analysis of multi-components in Xing-Su-Ning Capsules for quality improvement

Xin-Su-Ning Capsules (XSNC) is an effective prescription for the treatment of arrhythmia composed of eleven Chinese herbs. With the wide application of XSNC in clinic, its quality control issues have also received increasing attention. Based on the multi-components characteristics of Chinese herbal compound, there is an urgent need to establish a quality evaluation system. Gas chromatography-mass spectrometry (GC-MS) and ultra high-performance liquid chromatography quadrupole electrostatic orbitrap high resolution mass spectrometry (UHPLC-Q-Exactive-Orbitrap-MS) were performed to identify the preliminary chemical profile of XSNC. Subsequently, a rapid ultra high-performance liquid chromatography coupled with electrospray ionization triple-quadrupole mass spectrometry (UHPLC-QQQ-MS/MS) method was developed to evaluate the quality of XSNC through a simultaneous determination of 16 components. A total of 21 volatile components and 59 non-volatile compounds were tentatively identified from the XSNC, each identified compound is marked on the corresponding chromatogram. Moreover, sixteen chemical constituents (sophocarpine, matrine, febrifugine, berberine, palmatine, Tangeratin, nobiletin, liensinine, neferine, scopoletin, isoliquiritigenin, liquiritigenin, naringenin, naringin, hesperidin and glycyrrhizic acid) were quantified by the developed UHPLC-QQQ-MS/MS method. The method validation of the sixteen compounds was performed with acceptable linearity (R 2 , 0.9990-1.0000), precision (RSD, 0.25-2.06%), repeatability (RSD, 0.93-2.90%) and recovery (99.65%-104.03%, RSD≤4.35%). This qualitative analysis method sensitive and reliable for searching the volatile and non-volatile compounds from XSNC. The linearity, accuracy and precision of the quantitative analysis method were satisfactory. It is proposed that the methods described here can be applied for rapid evaluation, quality control and authenticity establishment of XSNC.

A UFLC-MS/MS Method for the Simultaneous Analysis of Urinary Podocin and Podocalyxin in Patients with Nephrotic Syndrome.

To create an efficient and robust mass spectrometric method for the simultaneous quantitation of podocin and podocalyxin in urine samples and to evaluate urinary podocin and podocalyxin levels in patients with nephrotic syndrome (NS). A mass spectrometric method was generated for the measurement of tryptic peptides in urine sediment. Separation of peptides was achieved via liquid chromatography, and mass spectrometric analyses were conducted by electrospray ionization triple-quadrupole mass spectrometry in the multiple reaction monitoring mode. Intra- and interassay precision values were below 12% and accuracies ranged from 87% to 111% for both of peptides. The validated method was successfully applied to detect these peptides in patients with NS. Urine podocin and podocalyxin levels were significantly higher in patients with NS compared to healthy controls. This proposed mass spectrometric method provides technological evidence that will benefit the clinical field in the early diagnosis and follow-up of NS.

Experimental and Computational Studies on the Gas-Phase Acidity of 5,5-Dialkyl Barbituric Acids.

The gas phase acidities (GA) of 5,5-alkylbarbituric acids have been experimentally determined by electrospray ionization-triple quadrupole (ESI-TQ) mass spectrometry and by using the extended kinetic Cooks method (EKCM). The GAs of C–H (1330.9 ± 10.0 kJ mol–1) and N–H (1361.5 ± 10.5 kJ mol–1) deprotonated sites of bifunctional barbituric acid were determined from the selective production of their corresponding heterodimers. The GA value in the N–H site was confirmed by measuring the GAs of 5,5-dimethyl- and 5,5-diethyl barbituric acids (∼1368 kJ mol–1). The experimental results have been rationalized and discussed with the support of quantum chemical calculations with Gaussian-n (G3 and G4) composite methods, which confirmed the excellent consistency of the results.

A simple and easy-to-perform liquid chromatography–mass spectrometry method for the quantification of tacrolimus and its metabolites in human whole blood. Application to the determination of metabolic ratios in kidney transplant patients

Tacrolimus is the cornerstone of immunosuppressive therapy in solid organ transplantation and its blood concentrations are routinely monitored. Tacrolimus is extensively metabolized into metabolites that are supposed to be nephrotoxic. Yet, few analytical methods have been described to simultaneously quantify tacrolimus and its main metabolites. We developed and validated a simple liquid chromatography-mass spectrometry method for the quantification of tacrolimus and its three desmethylated metabolites, 13-O, 15-O, and 31-O-desmethylated tacrolimus (M−I, M−III, and M−II respectively) in human whole blood. Protein precipitation of 50 µL of whole blood with 100 µL methanol and zinc sulfate was used as a single-extraction procedure. Tacrolimus and its metabolites were quantified using electrospray ionization-triple quadrupole mass spectrometry in combination with selected reaction monitoring detection in the positive ionization mode. The method was validated following FDA recommendations. This method was precise (intra- and inter-assay coefficients of variation: 2.88–7.81% and 3.96–12.10% for low and high levels of internal quality controls, respectively) and accurate (intra- and inter-assay biases: −1.67–10.30%, and −0.77–-9.36%, respectively).In adult kidney transplant patients who were treated with tacrolimus prolonged release formulation, the median (10th-90th percentiles) trough concentrations (n = 16) of tacrolimus, M−I, and M−III were 5.85 (3.37–7.09), 0.100 (0.037–0.168), 0.051 (0.03–0.104), respectively. M−II was measured in only 2 trough samples. The metabolic ratios M−I/tacrolimus and M−III/tacrolimus were 0.017 (0.009–0.027) and 0.009 (0.006–0.015) when measured on trough concentration and 0.022 (0.011–0.037) and 0.008 (0.006–0.015) when measured on area under the curves 0–24 h.This method is a suitable and easy-to-perform tool for future pharmacokinetic-pharmacodynamics studies investigating the importance of tacrolimus and its metabolites blood exposure for solid organ graft survival.

Quantitative analysis of the relationship of derivatization reagents and detection sensitivity of electrospray ionization-triple quadrupole tandem mass spectrometry: Hydrazines as prototypes

Chemical derivatization-assisted electrospray ionization-triple quadrupole mass spectrometry (ESI-QqQ-MS) has become an efficient tool for the quantification of low-molecular-weight molecules. Many studies found that the derivatives of the same analytes derivatized by different derivatization reagents with the same reaction group had different detection sensitivity, even under the same conditions of electrospray ionization-mass spectrometry (ESI-MS). This phenomenon was suggested to be caused by the different modifying groups in the derivatization reagents. However, there is still a lack of systematic study on how modifying groups in the derivatization reagents affect the detection sensitivity of their corresponding derivatives of analytes, especially theoretical investigations. In this study, we employed a quantitative structure-activity relationship (QSAR) modeling approach to explore the relationship between modifying group structures and the detection sensitivity of derivatization reagents and their derivatives during ESI-MS detection. A total of 110 derivatization reagents of the hydrazine family and their hexanal derivatives (substituted hydrazones) were selected as the prototypes to construct QSAR models. The established models suggested that several molecular descriptors, related to hydrophobicity, electronegativity, and molecular shape, were related to the detection sensitivity of hexanal derivatives induced by different modifying groups in the derivatization reagents. Besides, we found that the detection sensitivity of compounds detected in selected ion mode (SIM) showed a positive correlation with that obtained in multiple reaction monitoring mode (MRM), and the ionization efficiency was the key factor on the detection sensitivity in both modes.

Facile preparation of magnetic covalent organic framework-metal organic framework composite materials as effective adsorbents for the extraction and determination of sedatives by high-performance liquid chromatography/tandem mass spectrometry in meat samples.

Sedatives, which are prone to cause residues in animals, have been abused in modern animal husbandry. Long-term consumption of contaminated meat products would be unfavorable to the human nervous system. Taking into account public health and food safety, it was essential to develop an effective method for the enrichment and detection of sedatives in meat. Fe3 O4 @TbBd@ZIF-8 composites were synthesized by using Fe3 O4 nanoparticles as a magnetic core and 1,3,5-triformylbenzene (Tb) and benzidine (Bd) as two building blocks to form Fe3 O4 @TbBd. Furthermore, the zeolitic imidazolate framework-8 (ZIF-8) was modified on the surface of the Fe3 O4 @TbBd. In addition, Fe3 O4 @TbBd@ZIF-8 was used as a magnetic solid-phase extraction (MSPE) adsorbent of typical animal sedatives in pork samples. Mass spectrometry analysis was conducted by electrospray ionization triple-quadrupole mass spectrometry in positive-ion multiple reaction monitoring mode. By combining the optimized MSPE approach with high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS), an accurate and sensitive method for the determination of sedatives was developed. The method exhibited good linearity in the range of 0.03-70 μg/kg with the correlation coefficient (R2 ) ranging from 0.9982 to 0.9999, high sensitivity with limits of detection (LODs) ranging from 0.04 to 0.2 μg/kg, and high precision with relative standard deviation (RSD) less than 5.5%. The adsorption behaviors of Fe3 O4 @TbBd@ZIF-8 towards sedatives were more suitably described by a pseudo-second-order kinetic and Freundlich isotherm model. The proposed MSPE-HPLC/MS/MS method was successfully applied to the determination of sedatives in real samples and showed excellent applicability. Several sedatives were detected in the selected meat samples. The developed method was shown to be facile, sensitive and accurate for sedative detection and also showed great prospects for determination of sedatives from other complex samples.

Determination of Tryptophan and Kynurenine by LC–MS/MS by Using Amlodipine as an Internal Standard

Tryptophan is an essential amino acid that plays an important role in cell metabolism, and kynurenine is its main metabolic pathway. By using ultra-high-performance liquid chromatography coupled to electrospray ionization triple-quadrupole mass spectrometry, tryptophan and kynurenine were determined using amlodipine as an internal standard. The analysis was carried out on an ACE-C18 (4.6 mm × 50 mm, 5 μm) reversed-phase analytical column using the gradient elution mode. For quantitative determination, amlodipine was used as an internal standard. Detection was performed using multiple reaction monitoring in electrospray ionization mode at m/z 205.1 → 117.7 and 187.9 for tryptophan, m/z 209.1 → 146 and 93.9 for kynurenine, and m/z 409.2 → 294.1 for the internal standard. Good linearity of the analyte to internal standard peak area ratios was seen in the concentration range 1.25-4000 ng/mL for tryptophan and 0.5-1600 ng/mL for kynurenine. The method showed excellent linearity with regression coefficients of 0.99 for kynurenine and 0.996 for tryptophan. The limits of quantification were 0.55 ng/mL for tryptophan and 0.47 ng/mL for kynurenine. The % RSD for all analytes ranged from 0.3 to 3.4% for intraday and 0.4 to 8.9% for interday experiments. A simple LC-MS/MS method has been developed and validated for measuring Kyn and Trp by using an affordable and more easily available internal standard, which is amlodipine.

Differentiation of FUB-JWH-018 positional isomers by electrospray ionization–triple quadrupole mass spectrometry

Analytical differentiation of the positional isomers of synthetic cannabinoids (SCs) is a notable issue in forensic drug analysis, because only one or two of the imaginable isomers are controlled legally in most cases. Two series of fluorine-substituted SCs, differing in the substituent positions, were examined by electrospray ionization–triple quadrupole mass spectrometry (ESI-QqQ MS) to assess the capabilities of this technique to differentiate their positional isomers. The mass spectra of (1-(4-fluorobenzyl)-1H-indol-3-yl)(naphthalen-1-yl)methanone (FUB-JWH-018) and its positional isomers were recorded while the collision energy was varied (5–90 eV), and the fragment ions of the protonated precursor ions [M+H]+ were characterized. The applicability of ESI-QqQ MS in the positive mode was demonstrated by analyzing the naphthalen-2-yl derivative of FUB-JWH-018 and its positional isomers. The statistical analysis of the principal fragment ions in the 80 eV spectra of each synthetic cannabinoid allowed the authors to significantly differentiate its isomers based on their m/z (127:109) ratio.

Activation of ferrate by carbon nanotube for enhanced degradation of bromophenols: Kinetics, products, and involvement of Fe(V)/Fe(IV)

Very recently, several studies have found that homogeneous reducing agents (e.g., sodium thiosulfate (Na2S2O3), and sodium sulfite (Na2SO3)) can activate ferrate to enhance the degradation of selected contaminants. In this work, it was found that heterogeneous carbon nanotube (CNT) could accelerate ferrate (Fe(VI)) for the degradation of bromophenols (BrPs) of environmental concerns and alleviate the appearance of undesired by-products in effluent. Fe(VI) could react with BrPs over a wide pH range of 6–10 with apparent second-order rate constants of 1.8–1850 M−1 s−1. Electrospray ionization-triple quadrupole mass spectrometry (ESI-QqQMS) analysis showed that dibrominated dihydroxylated biphenyls and dibrominated phenoxyphenols were possibly formed via coupling reaction of BrPs radicals generated from Fe(VI) oxidation through one-electron transfer. The presence of CNT could remarkably accelerate the degradation rates of BrPs by Fe(VI) in a wide pH range from 7 to 10. Moreover, the formed undesired polybrominated products during Fe(VI)/CNT oxidation were absorbed on CNT surface and thus removed from treated water. The Fe(VI)/CNT system was capable of selectively oxidizing electron-rich pollutants (e.g., BrPs, and sulfamethoxazole (SMX)), but reluctant to iopamidol (IPM) and nitrobenzene (NB). High-valent metal-oxo intermediates Fe(V)/Fe(IV) formed in situ from the reaction of CNT with Fe(VI) were likely responsible for this activation effect of CNT, which was further confirmed via using methyl phenyl sulfoxide (PMSO) as a probe compound. Comparatively, homogeneous reducing agent Na2S2O3 could enhance Fe(VI) degradation of BrPs at pH 7 and 8, while undesired polybrominated products were detected in effluent from Fe(VI)/Na2S2O3 system. These findings have crucial implications for the development of a promising oxidation process by combination of Fe(VI) and CNT for water and wastewater treatment.

Qualitative and quantitative analysis on the chemical constituents in Orthosiphon stamineus Benth. using ultra high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A sensitive and efficient method was established and validated for qualitative and quantitative analysis on the chemical constituents in Orthosiphon stamineus Benth. (O. stamineus) using ultra high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Based on the retention time and MS spectra, 61 compounds were detected by using ultra high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry. 52 chemical structures in the O. stamineus extracts including 26 phenolic acids, 11 flavonoids, 6 diterpenoids, 4 fatty acids and 5 tanshinones were tentatively identified without the time-consuming process of isolation. Moreover, five chemical constituents (Danshensu, Caffeic acid, Rosmarinic acid, Sinensetin and Eupatorin) were quantified in three different batches of O. stamineus samples by the developed ultra high-performance liquid chromatography coupled with electrospray ionization triple-quadrupole mass spectrometry method in 10 min. The method validation of the five compounds was performed with acceptable linearity (R2, 0.9930–0.9997), precision (RSD, 1.87–10.36%), repeatability (RSD, 0.59–4.87%) and recovery (105.30–110.53%, RSD ≤ 13.90%).

A facile and green pretreatment method for nonionic total organic halogen (NTOX) analysis in water – Step I. Using electrodialysis to separate NTOX and halides

Adsorbable organic halogen (AOX) is a bulk organic parameter conventionally used to indicate all adsorbable halogenated organic disinfection byproducts formed in disinfected water. Analytically, AOX is determined by three sequential steps: 1) concentration and separation of AOX from halides with activated carbon, 2) conversion of AOX into halides with pyrolysis, and 3) quantification of halides via microcoulometry or ion chromatography (IC). Because the approach is relatively costly and cannot effectively recover non-adsorbable compounds, we herein proposed a facile and green pretreatment tool to measure the nonionic portion of total organic halogen (NTOX) with a new three-step approach: 1) separation of NTOX and halides with electrodialysis (ED), 2) conversion of NTOX into halides with ultraviolet, and 3) analysis of halides with IC. To verify this proposal, this study presented the efficiency of ED in separating halides and NTOX under a variety of operational and environmental conditions. The results showed that ED removed ≥98.5% of fluoride, chloride, bromide, and iodide from all tested waters (up to 1000 mg-X/L) within 1.5 h. Meanwhile, ED recovered an average of 87.9% of fourteen small molecular weight model compounds with each at 100 μg/L. By using electrospray ionization-triple quadrupole mass spectrometry, the whole pictures of high molecular weight compounds in a chlorinated drinking water before and after ED pretreatment were compared, which revealed 79.7% and 83.6% recoveries of overall polar chlorinated and brominated compounds, respectively. In addition, the quantity and property of the dissolved organic matter were largely maintained by ED, and the retained organics may be used for later characterization. The study hence presents a novel use of ED as a pretreatment tool to enable subsequent NTOX measurement.

A facile and green pretreatment method for nonionic total organic halogen (NTOX) analysis in water – Step II. Using photolysis to convert NTOX completely into halides

Adsorbable organic halogen (AOX) is a parameter conventionally used to indicate the sum of organic halogenated disinfection byproducts (DBPs), which are formed from the reactions of disinfectants with dissolved organic matter, bromide and iodide in water. To overcome the issues of the AOX analytical method, we proposed a new facile and green pretreatment method to enable the analysis of nonionic total organic halogen (NTOX) via the following three steps: 1) separation of NTOX and halides with electrodialysis, 2) conversion of NTOX with ultraviolet (UV) photolysis, and 3) analysis of halides with ion chromatography. To verify this proposal, we mainly evaluated the efficiency of vacuum ultraviolet (VUV) coupled with UV photolysis (VUV−UV) in converting NTOX into halides. Results showed that by applying VUV irradiation for 60 min and UV irradiation at pH 10–11 for another 30 min, over 85.5% of each halide from 20 representative small molecular weight DBPs (each at 100 μg-X/L level) was recovered. The purpose of UV photolysis under alkaline conditions was to reduce oxyhalides (such as bromate and iodate) formed in the VUV process back to halides. With the aid of electrospray ionization-triple quadrupole mass spectrometry, we captured the whole pictures of high molecular weight polar DBPs in a chlorinated drinking water before and after VUV−UV, through which averagely 96.4% of dehalogenation with the VUV−UV treatment was observed. An illustrative comparison of the conventional AOX method and the proposed NTOX method indicates that although the detected NTOX was lower (by 2.3–30.6%) than AOX, the results of the two methods were highly correlated (R2 > 0.97). All these hence verified the photolysis as a mature yet novel tool for sample pretreatment in environmental analytical chemistry.

Oxidation of bromophenols by carbon nanotube activated peroxymonosulfate (PMS) and formation of brominated products: Comparison to peroxydisulfate (PDS)

Recently, we have examined the oxidation kinetics and products of bromophenols (BrPs) by nonradical activation of peroxydisulfate (PDS) in the presence of carbon nanotubes (CNT). In this work, the transformation of BrPs by CNT activated peroxymonosulfate (PMS) was comparatively investigated. It was found that both radical (i.e., sulfate radical (SO4−) and hydroxyl radical (OH)) and nonradical species (i.e., singlet oxygen (1O2) and reactive PMS-CNT complexes) contributed to BrPs degradation by the PMS/CNT system. Their relative contributions to BrPs degradation were very close irrespective of solution pH, while high temperature strengthened the contribution of radicals due to thermo activation of PMS. The effects of chloride ion, bicarbonate and natural organic matter (NOM) on BrPs transformation were mainly attributed to their scavenging effects for SO4− and OH. Additionally, NOM could hinder the interaction of PMS with CNT active sites, thus inhibiting BrPs degradation. The analysis by electrospray ionization-triple quadrupole mass spectrometry showed the formation of brominated polymeric products (i.e., hydroxylated polybrominated diphenyl ethers and hydroxylated polybrominated biphenyls) on CNT surface rather than in aqueous solution when BrPs were treated by the PMS/CNT system, similar to the case of PDS. Meanwhile, inorganic Br− was released but its potential oxidation by SO4− and OH leading to bromate formation was rather negligible, probably due to the fact that CNT as a reducing agent could rapidly convert reactive bromine intermediates back to Br−. Therefore, both PMS/CNT and PDS/CNT systems are promising strategies for effectively removing BrPs with alleviation of toxic byproducts in treated water effluents, while the former involving both nonradical and radical species is more advantageous in treatment of diverse pollutants (e.g., electron-rich moieties containing organics and refractory compounds).

Simultaneous quantitation of endogenous estrone, 17β-estradiol, and estriol in human serum by isotope-dilution liquid chromatography-tandem mass spectrometry for clinical laboratory applications.

Estrogen measurements are important in the assessment of female reproductive function and have expanding roles in other fields. A simple, accurate, highly sensitive and specific isotope-dilution liquid chromatography-tandem mass spectrometry method was developed and evaluated to simultaneously measure three endogenous estrogens in serum: estrone (E1), 17β-estradiol (E2), and estriol (E3). Chromatographic separation was achieved on a C18 column before electrospray ionization triple-quadrupole mass spectrometry in multiple reaction monitoring mode. The sample preparation in this assay requires no derivatization and extraction by liquid-liquid extraction. After optimization of the extraction conditions, the final extraction efficiency of E1, E2, and E3 was 83.8%, 78.9%, and 77.3% respectively. The metabolites and structural analogs that have the same molecular masses as the estrogens were separated under the optimized liquid chromatography conditions. Method validation showed satisfactory linearity over the concentration range of 20-10000pgmL-1 for all three estrogens (r 2 > 0.997). The limits of quantification were 5, 10, and 10pgmL-1 for E1, E2, and E3 respectively, and their recoveries ranged from 94.7% to 103.5%. The accuracy of the proposed method was further evaluated with use of certified reference materials BCR-576, BCR-577, and BCR-578 for E2 and 2014 International Federation of Clinical Chemistry and Laboratory Medicine External Quality Assessment Scheme for Reference Laboratories in Laboratory Medicine samples for E3, whose certified values were determined by reference methods. Great agreement was observed between the measured values and the certified values. Satisfactory precision (coefficients of variation less than 7.44%) was also obtained for the three estrogens. Moreover, the proposed method was successfully applied to measure the three estrogens in serum samples of pregnant women in the second trimester and to assess the accuracy of chemiluminescent immunoassays in clinical laboratories by determination of E2 and unconjugated E3 in serum samples. Graphical Abstract Schematic representation of the simultaneous quantitation of three major endogenous estrogens in human serum by ID-LC-MS/MS.

Liquid chromatography/tandem mass spectrometry for simultaneous determination of undeclared corticosteroids in cosmetic creams.

Undeclared corticosteroids in creams intended for frequent use might cause serious side-effects, especially in children. In order to prevent this or find the cause, it was essential to develop a method for quick detection and quantification of low levels of corticosteroids. Eleven corticosteroids were used in this study: prednisolone, methylprednisolone, prednisolone-21-acetate, fluocinolone acetonide, fluocinolone acetonide-21-acetate, hydrocortisone-21-acetate, dexamethasone, betamethasone, betamethasone dipropionate, clobetasol propionate and triamcinolone. Separation was achieved via liquid chromatography (LC), and mass spectrometric analysis was conducted by electrospray ionization triple-quadrupole mass spectrometry (MS/MS) in the multiple reaction monitoring mode using corticosterone as internal standard. Good separation by using a gradient-elution LC/MS/MS method with run time of 25 min enabled the use of a segmented detection method and consecutive decrease in detection limits. The proposed method has been validated in the linearity range of 10-1000 ng/mL with coefficients of determination higher than 0.990. The method has shown to have very low limits of quantification (0.75-3 ng/mL) with satisfactory precision and accuracy for each of the corticosteroids. An LC/MS/MS method for the rapid and simultaneous determination of low levels of eleven topical corticosteroids in creams was developed, optimized and validated. The proposed method can be used for testing of different products indicated for the treatment of atopic dermatitis, including "natural products", and "herbal creams" with "miraculous effects".

Fast separation of selected cathinones and phenylethylamines by supercritical fluid chromatography

The chromatographic behaviour of eleven synthetic cathinones and four phenylethylamines under supercritical/subcritical fluid conditions was investigated. Four stationary phases with sub-2μm particles (Waters Acquity UPC2 BEH silica, BEH 2-ethylpyridine, CSH Fluoro-Phenyl, and HSS C18SB) were evaluated in terms of isomer resolution, chromatographic peak shape, and analysis time. Methanol, water, formic acid, ammonium hydroxide, ammonium acetate, and ammonium formate were mixed with carbon dioxide to test their influence on analyte retention and peak shapes. Methanol and ammonium cations were essential for successful separations. Efficient separations of four isomeric pairs (R>1), and most of the remaining analytes, were achieved in less than 3.3min on BEH and Fluoro-Phenyl columns with gradient of methanolic ammonium hydroxide in CO2. Drugs were detected by positive electrospray ionization–triple quadrupole mass spectrometry in selected reaction monitoring mode. Added detection specificity and faster separation of isomers on the BEH column using a steep gradient and high flow rate reduced analysis time of the mixture of 15 drugs to 1.6min.

Degradation of trimethoprim by thermo-activated persulfate oxidation: Reaction kinetics and transformation mechanisms

Trimethoprim (TMP) is a dihydrofolate reductase inhibitor that is synergistically prescribed with sulfonamides to treat infectious disease in humans and animals. The widespread occurrence of TMP in natural environment may pose ecotoxicological risks to aquatic organisms and microalgae. In this work, we investigated the kinetics and mechanisms of TMP degradation by thermo-activated persulfate (PS) oxidation process in aqueous solution. Experimental results revealed that TMP could be effectively destructed at the temperature range of 50–65°C. Acidic pH facilitated the degradation of TMP. The pyrimidine moiety in TMP molecule was identified as the primary reactive site by comparison to substructural analogs. Solid phase extraction (SPE) coupled with liquid chromatography–electrospray ionization-triple quadrupole mass spectrometry (LC–ESI-MS/MS) was employed to identify the intermediate products. Thermo-activated PS oxidation of TMP produced several intermediates via hydroxylation and oxidation with α-hydroxytrimethoprim (TMPOH) and α-ketotrimethoprim (TMPO) being the major products. Water matrix affected TMP removal significantly, e.g., natural organic matter (NOM) and bicarbonate (HCO3−) inhibited the degradation while halides promoted it. Results from this study showed that thermo-activated PS oxidation could be an efficient approach to remove TMP from waters; however, the removal efficiency could be influenced by coexisting species.

A method for analysis of vanillic acid in polar ice cores

Abstract. Biomass burning generates a wide range of organic compounds that are transported via aerosols to the polar ice sheets. Vanillic acid is a product of conifer lignin combustion, which has previously been observed in laboratory and ambient biomass burning aerosols. In this study a method was developed for analysis of vanillic acid in melted polar ice core samples. Vanillic acid was chromatographically separated using reversed-phase liquid chromatography (HPLC) and detected using electrospray ionization–triple quadrupole mass spectrometry (ESI-MS/MS). Using a 100 μL injection loop and analysis time of 4 min, we obtained a detection limit of 77 ppt (parts per trillion by mass) and an analytical precision of ±10%. Measurements of vanillic acid in Arctic ice core samples from the Siberian Akademii Nauk core are shown as an example application of the method.