Liquid Chromatography-tandem Mass Spectrometric Method Research Articles

Lipid radicals and oxidized cholesteryl esters in low- and high-density lipoproteins in patients with β-thalassemia: Effects of iron overload and iron chelation therapy

Iron overload results in lipid peroxidation (LPO) and the oxidative modification of circulating lipoproteins, which contributes to cardiovascular complications in patients with β-thalassemia. Investigating LPO may provide opportunities for the development of novel therapeutic strategies; however, the chemical pathways underlying iron overload-induced LPO in β-thalassemia lipoproteins remain unclear. In this study, we identified various species of lipid radicals (L•), the key mediators of LPO, and oxidized cholesteryl esters (oxCE) derived from the in vitro oxidation of major core lipids, cholesteryl linoleate (CE18:2) and cholesteryl arachidonate (CE20:4); the levels of these radical products in low-density lipoproteins (LDL) and high-density lipoproteins (HDL) were measured and compared between β-thalassemia patients and healthy subjects by using a specific fluorescent probe for L• with a liquid chromatography-tandem mass spectrometric method. Our results demonstrated that iron overload substantially decreased the levels of CE18:2 and CE20:4 substrates and α-tocopherol, resulting in higher levels of full-length and short-chain truncated L• and oxCE products. In particular, CE epoxyallyl radicals (•CE-O) were observed in the lipoproteins of β-thalassemia, revealing the pathological roles of iron overload in the progression of LPO. In addition, we found that intermission for two weeks of iron chelators can increase the production of these oxidized products; therefore, suggesting the beneficial effects of iron chelators in preventing LPO progression. In conclusion, our findings partly revealed the primary chemical pathway by which the LPO of circulating lipoproteins is influenced by iron overload and affected by iron chelation therapy. Moreover, we found that •CE+O shows potential as a sensitive biomarker for monitoring LPO in individuals with β-thalassemia.

Rapid and sensitive liquid chromatographic–tandem mass spectrometric methods for quantitation of Dolutegravir in human plasma and breast milk

BackgroundDolutegravir (DTG) is part of a first-line antiretroviral therapy (ART) for HIV management in drug-naïve individuals and is recommended for the treatment of HIV during pregnancy. Robust analytical tools to quantify DTG are necessary to support clinical trials that characterize its multi-compartment drug distribution. MethodsPotassium EDTA (K2EDTA) plasma or whole breast milk was spiked with DTG and an isotopically labeled internal standard. Samples were prepared via protein precipitation prior to LC–MS/MS analysis. The assays were validated in accordance with regulatory recommendations. ResultsAnalytical measuring ranges for DTG quantitation in plasma and breast milk were 100–10,000 ng/mL and 0.500 to 1,000 ng/mL, respectively. Inter-assay precision and accuracy were 2.73 % to 3.41 % and −10.6 % to −5.37 % for plasma, and 4.24 % to 12.4 % and −5.63 % to 7.49 % for breast milk, respectively. DTG was stable for three freeze–thaw cycles and for at least 72 h at room temperature in matrix (plasma or breast milk). Additionally, whole blood was stable for 24 h at room temperature and 2 h under conditions of extended heat and humidity. Matrix effects for DTG in plasma and breast milk ranged from 101–108 % and 78.2–99.3 %, respectively. Quantitation in remnant plasma samples yielded measurable concentrations within the primary linearity of the assay. ConclusionsMethods to quantify DTG in human plasma and breast milk have been developed and validated. These assays were designed to satisfy all criteria for implementation in clinical and clinical trial settings.

Quantification of 700 mycotoxins and other secondary metabolites of fungi and plants in grain products

This work reports on the validation of a liquid chromatography–tandem mass spectrometric method for the simultaneous quantification of more than 700 mycotoxins and other secondary fungal metabolites and plant toxins in pasta, biscuits, crackers and musli. The “dilute and shoot” approach was found to be fully applicable to these complex matrices, as only 7–14% of the analytes exhibited significant matrix effects while recoveries of the extraction were outside the target range of 70–120% for only 26 compounds. Data on repeatability (based on 7 brands per matrix) and on intermediate precision was compliant to the related < 20% criterion for 95–98% and 99% of all analytes, respectively. The limits of quantification were much lower than the related regulatory limits set for mycotoxins in cereal products. Application of the method to 157 samples from the European market revealed the presence of enniatins and deoxynivalenol in the majority of the samples. No regulatory limits were exceeded except the sum of ergot alkaloids being higher in a few samples than the 50–150 µg/kg to be implemented as of July 2024.

Indicator displacement-based colorimetric assay for dibutyl phthalate in pharmaceutical products with titanium(IV)-pyridylazo resorcinol (PAR)

Taking advantage of the competitive binding affinity towards Ti(IV) between 4-(2-pyridylazo) resorcinol (PAR) and phthalate, a simple indicator displacement (ID)–based colorimetric assay was designed for indirect determination of a well-known phthalic acid ester, dibutyl phthalate (DBP). The indicator PAR and Ti(IV) formed a purplish-red-colored Ti(IV)-PAR complex (λmax = 540 nm) at a 1:1 ratio. In the presence of pre-hydrolyzed DBP, colorless complex formation of phthalate ion (emerging from alkaline hydrolysis of DBP) with Ti(IV) resulted in a hypsochromic shift in absorbance maximum, accompanying a color change from purplish-red to yellowish-orange (λmax = 390 nm) by the release of PAR from Ti(IV)-PAR system. Based on this mechanism, the linear response range of the system for DBP was found to lie between 0.16 and 0.37 mmol L–1 with an experimental detection limit of 11.6 µmol L–1. The recommended Ti(IV)-PAR system was successfully applied to DBP-containing pharmaceutical products (as real sample) after a simple clean-up process for removing possible water-soluble interferents. The analytical results obtained from the recommended method (by applying the standard addition approach) and the reference liquid chromatography-tandem mass spectrometric (LC–MS/MS) method were statistically compared using DBP-extract of the drug samples. Consequently, a simple and selective colorimetric ID strategy was proposed for the analysis of DBP in pharmaceuticals for the first time.

In-Vitro Dissolution Study of Solid Dispersion Adsorbate of Nateglinide by Eco-Friendly Liquid Chromatography-Tandem Mass Spectrometric Method through Harmonized Approach of White Analytical Chemistry and Analytical Quality by Design

In-Vitro Dissolution Study of Solid Dispersion Adsorbate of Nateglinide by Eco-Friendly Liquid Chromatography-Tandem Mass Spectrometric Method through Harmonized Approach of White Analytical Chemistry and Analytical Quality by Design

A simple and sensitive ultra-high performance liquid chromatography tandem mass spectrometry method for the quantitative analysis of VX-548 in monkey plasma: Method validation and application to pharmacokinetic study.

VX-548 is an orally active and highly selective NaV 1.8 inhibitor that is undergoing development for the treatment of acute pain. The aim of this study was to develop a liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for the measurement of VX-548 in monkey plasma. VX-548 was extracted from the plasma using acetonitrile-mediated protein precipitation. The quantitative analysis was performed on a Thermo Vantage TSQ mass spectrometer with ibrutinib as an internal standard. Chromatography was performed on a Waters ACQUITY UPLC BEH C18 column with 0.1% aqueous formic acid and acetonitrile as mobile phase. The precursor-to-product ion transitions were m/z 474.2 > 165.0 and m/z 441.2 > 138.1 for VX-548 and internal standard, respectively. This developed method was successfully validated in the concentration range of 1-1000 ng/mL. The calibration curve showed excellent linearity with a correlation coefficient of >0.999. The precision expressed as relative standard deviation (RSD) was <8.4%, whereas the accuracy denoted as relative error (RE) ranged from -5.0% to 9.1%. The mean recovery was >84%. VX-548 was stable in monkey plasma after storage under certain conditions. The validated method was successfully applied to the pharmacokinetic study of VX-548 in monkey plasma after single oral (2 mg/kg) and intravenous (1 mg/kg) administrations.

Multiple mycotoxins associated with maize (Zea mays L.) grains harvested from subsistence farmers’ fields in southwestern Ethiopia

Fifty-four maize grain samples freshly harvested from subsistence farmers’ fields in southwestern Ethiopia were analyzed for multiple mycotoxins using liquid chromatography-tandem mass spectrometric (LC-MS/MS) method following extraction by acetonitrile/water/acetic acid on a rotary shaker. The grain samples were contaminated with a total of 164 metabolites, of which Fusarium and Penicillium metabolites were the most prevalent accounting for 27 and 30%, respectively. All the major mycotoxins and derivatives except one (citrinin) were of Fusarium origin. Zearalenone was the most frequent major mycotoxin occurring in 74% of the samples at concentrations of 0.32–1310 µg/kg. It was followed by nivalenol (63%), zearalenone-sulfate (44%), and fumonisin B1 (41%). Nivalenol, nivalenol glucoside, and fusarenon-X were detected at unusually high levels of 8–1700 µg/kg, 21–184 µg/kg, and 33–149 µg/kg, respectively. Deoxynivalenol and DON-3 glucoside contaminated 32% of the samples, each at levels of 15.9–5140 µg/kg and 10–583 µg/kg, respectively. Moniliformin and W493B occurred in 96 and 22% samples at levels of 3.27–4410 µg/kg and 3–652 µg/kg, respectively. Fumonisins were also detected in the samples at levels of 9–6770 µg/kg (B1), 16–1830 µg/kg (B2), 9.5–808 µg/kg (B3), and 1.3–128 µg/kg (A1). This study confirmed the presence of an array of mycotoxins contaminating maize grains right from the field. The effect of the co-occurring mycotoxins on consumers’ health should be investigated along with that of the newly emerging ones. Results of the current study call for application of pre-harvest mycotoxin mitigation strategies to safeguard maize-based food and feed.

Simultaneous Determination of D and L Enantiomers of 2-Hydroxyglutarate by UHPLC-MS/MS Method in Human Biological Fluids and its Clinical Application.

2-hydroxyglutarate has limited abundance in normal tissues but a high level under certain pathologic conditions. To clarify the diagnostic value of two chiral isomers of 2-hydroxyglutarate in plasma and urine of Chinese cancer patients, an ultra-high performance liquid chromatography-tandem mass spectrometric method was developed for simultaneous quantification of D-/L-2-hydroxyglutarate. The selected D-/L-2-hydroxyglutarate-d5 as internal standards were added to samples before the SPE on Waters Oasis® MAX 96-Well plate (30μm, 60mg). A derivatization step with (+)-O,O'-diacetyl-L-tartaric anhydride permitted the chromatography separation of D-/L-2-hydroxyglutarate on an ACQUITY UPLC-HSS T3 column (50 × 2.1mm, i.d. 1.8μm) with acetonitrile and water (containing 0.1% formic acid and 10mmol ammonium acetate) as the mobile phase. The calibration curves showed good linearity (R ≥ 0.99) over the concentration ranges of 200-5,000ng/mL and 500-20,000ng/mL for analysis of D-/L-2-hydroxyglutarate in plasma and urine samples, respectively. Intra- and inter-run precision were ≤ 12.33%, and the accuracy was within the range of -10.44 to 13.90%. This method was further successfully applied to clinical sample analysis in isocitrate dehydrogenase 1/2 mutated Chinese cancer patients.

Simplified processing and rapid quantification of buprenorphine, norbuprenorphine, and their conjugated metabolites in human plasma using UPLC-MS/MS: Assessment of buprenorphine exposure during opioid use disorder treatment.

Opioid use disorder (OUD) is a chronic neurobehavioral ailment and is prevalent in pregnancy. OUD is commonly treated with methadone or buprenorphine (BUP). Pregnancy is known to alter the pharmacokinetics of drugs and may lead to changes in drug exposure and response. A simple, specific, and sensitive analytical method for measuring the parent drug and its metabolites is valuable for assessing the impact of pregnancy on drug exposure. A new liquid chromatography-tandem mass spectrometric method that utilized a simple protein precipitation procedure for sample preparation and four deuterated internal standards for quantification was developed and validated for BUP and its major metabolites (norbuprenorphine [NBUP], buprenorphine-glucuronide [BUP-G], and norbuprenorphine-glucuronide [NBUP-G]) in human plasma. The standard curve was linear over the concentration range of 0.05-100 ng/mL for BUP and NBUP, and 0.1-200 ng/mL for BUP-G and NBUP-G. Intra- and inter-day bias and precision were within ±15% of nominal values for all the analytes. Quality controls assessed at four levels showed high recovery consistently for all the analytes with minimal matrix effect. Adequate analyte stability was observed at various laboratory conditions tested. Overall, the developed method is simple, sensitive, accurate and reproducible, and was successfully applied for the quantification of BUP and its metabolites in plasma samples collected from pregnant women in a clinical study assessing BUP exposure during OUD treatment.

Simultaneous Determination of Two Metabolites of Gelsemium elegans by LC-MS/MS in Rat Urine and its Application to Pharmacokinetic Study

Background: G. elegans is a highly useful medicinal plant with broad and superior clinical pharmacological effects. However, it also exhibits high toxicity to humans, so it must be used with extreme caution in clinical practice. Previous studies on G. elegans have mainly focused on its main ingredients from perspectives of pharmaceutical analysis, pharmacokinetics, and pharmacodynamics. The kinetic behavior of G. elegans' main metabolites in vivo has not yet been reported, which is also crucial for studying the herb's toxification and detoxification process. Aims: This study aimed to establish a quantitative method to describe the metabolic profile of the two main metabolites of koumine after oral administration of G. elegans to rats. Objective: The objective of this study was to test two major metabolites of G. elegans in rat urine after administration using a rapid and sensitive high-performance liquid chromatographic-tandem mass spectrometric (HPLC-MS/MS) method developed in advance. Methods: A Kromasil C18 column was used as the stationary phase for chromatographic separation, with an isocratic mobile phase consisting of mixture of water (2 mM ammonium formate), formic acid, and methanol (25:0.05:75, v/v/v) at a flow rate of 0.40 mL/min. The mass spectrometer was equipped with an electrospray ionization (ESI) source operating in positive ionization mode, and detection was performed using a selective reaction monitoring (SRM) mode. Detection was performed in selective reaction monitoring (SRM) mode. Protein precipitation was used to pretreat the rat urine samples before analysis, with acetonitrile as the precipitation solvent. In this study, a "relative quantification" strategy was employed, which avoided the expensive and time-consuming separation of standard substances. The assay was validated in terms of specificity, linearity, precision, stability, recovery, and other aspects. Results: The intra- and inter-day precision values were less than 12.7%. The recoveries at three different concentrations were all above 73.1%. The stability study showed that the analytes were stable during the experiment. The method was then used to study the kinetic profiles of N-demethylkoumine and N-oxidatekoumine in rat urine for the first time. Conclusion: In this study, the established LC/MS method was fully validated and proven to be sensitive and accurate for the simultaneous determination of the two main metabolites of G. elegans in rats' urine samples. These results could provide references for the safe use of koumine and G. elegans in clinical applications.

Bioequivalence Study of Two Tablet Formulations of Clonazepam 2mg: A Randomized, Open-Label, Crossover Study in Healthy Mexican Volunteers Under Fasting Conditions.

The prevalence of neurological disorders is high among the Mexican population. Clonazepam is primarily indicated to treat panic disorders, certain kinds of epilepsy such as status epilepticus, childhood motor seizures (petit mal absence, Lennox-Gastaut syndrome, and infantile spasms), anxiety, and muscle spasm. This study was performed to compare bioequivalence between two oral tablet formulations of clonazepam 2mg in healthy Mexican volunteers under fasting conditions. This phaseI, randomized, open-label, two-treatment, crossover study included 30healthy volunteers. Subjects were randomly assigned to either test or reference formulation of clonazepam 2mg. Each study period was separated by 21-day washout period. Blood samples were collected at pre-dose and up to 72h after drug administration. Clonazepam concentrations were determined using a validated ultra-flow liquid chromatography-tandem mass spectrometric method. Pharmacokinetic parameters were determined using a non-compartmental method. Two formulations were considered bioequivalent if geometric mean ratios (test/reference) were between 80% and 125%. Safety was evaluated by recording adverse events. Pharmacokinetic parameters were comparable between test and reference formulations. The mean maximum plasma concentration (Cmax) was ≈ 13ng/mL, area under the plasma concentration-time curve from time0 to last measurable concentration (AUC0-t) was ≈ 360ngh/mL, time to reach maximum plasma concentration (Tmax) was ≈ 3h, and elimination half-life (t1/2) was ≈ 43h. Geometric mean ratios (90% confidence interval) of Cmax (99.2-115.3%), AUC0-t (100.6-110.6%), and AUC0-∞ (98.5-111.6%) were within the bioequivalence range. Seven non-serious adverse events (mostly asymptomatic hypotension) were recorded. The test and reference formulations of clonazepam 2mg were bioequivalent and well tolerated in healthy Mexican volunteers under fasting conditions. 213301410B0051 (Approved on April 13, 2021).

Cysteamine ophthalmic hydrogel for the treatment of ocular cystinosis

Ocular cystinosis is a rare disease characterised by the deposition on the corneal surface of cystine crystals that hinder the eyesight of patients. Oral cysteamine is administered as cysteamine bitartrate; however, due to the lack of corneal vascularization it does not reach the cornea and must be administered by the topical ocular route. The aim of the present study was to determine the stability of an ophthalmic hydrogel of cysteamine under different preservation conditions during a follow-up of 30 days. This hydrogel could be prepared in hospital pharmacy services.Several physical and chemical parameters were assessed: osmolality, pH, and cysteamine concentration, which was measured using an ultra-performance liquid chromatography-tandem mass spectrometer (UPLC-MS/MS) method. Descriptive tests were also performed, such as transparency measurements and microbiological assays in order to verify sterility. The results show that cysteamine hydrogel is stable over 30 days and should be preserved under refrigeration.

Liquid Chromatography Tandem Mass Spectrometric Method Development and Validation for the Quantification of Orlistat in Biological Matrices

A specific, linear and precise liquid chromatographic-tandem mass spectrometric method was established and validated for the quantitation of orlistat in sample plasma. Zorbax C18 (4.6 mm i.d.× 50.0 mm; 5.0 μm) stationary phase was utilized to achieve chromatography elution, through a flowing rate of 0.90 mL/min. Isocratic elution was done using methanol, acetonitrile and 0.10% v/v HCOOH in a fraction of 80:10: 10 v/v/v as the mobile phasic system. For drug and internal standard separation, the precipitation extraction technique used acetonitrile as solvent. A triple quadrupole mass detector was employed for the quantification of ions. Electrospray ionization in a positive ionizing method, which was executed in multiple reaction monitorings (MRM) with parent/product ion transitions of m/z 496.4→337.31 for orlistat and 506.23→57.07 for amprenavir internal standard. The calibration graph was executed between the concentrations of 4.75–190.0 ng/mL and the resulting equation was y = 0.0058x + 0.0022 with r2 value of more than 0.99. Orlistat recovery values were found to be more than 93.65%, and its accuracy, measured in relative error, was in the range of -4.48 to 3.49%. Accuracy findings, sensitivity and recovery values of orlistat in the sample plasma for the established technique evidences its importance in pharmacokinetic and bioequivalence study.

Pharmacokinetics Study and Simultaneous Quantification of Eight Schisandra Lignans in Normal Rats by LC-MS/MS after Oral Administration of Schisandra Lignan Extract

Background: Schisandra chinensis has been widely used. It has many pharmacological activities. Lignans, including schizandrol A, schizandrin A, schisandrin B, schisanhenol, gomisin E, gomisin H, gomisin J, gomisin N, etc., are the major active ingredients of Schisandra chinensis. Objective: In the present study, the liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed for the simultaneous quantification of Schisandra lignans in normal rats. Methods: Nifedipine was used as an internal standard, and chromatographic separation was achieved on Agela Venusil C18 Plus (4.6*100mm, 3μm). Aqueous solution containing 0.1% (v/v) formic acid was used as the mobile phase A, and methanol solution containing 0.1% (v/v) formic acid was used as the mobile phase B for gradient elution. The flow rate was 0.8 mL/min. Multiple reaction monitoring (MRM) mode with positive electrospray ionization was used to detect the analytes. Results: The calibration curves provided reliable responses at concentrations of 0.5-200 ng/ml for schizandrin A, schisandrin B, schisanhenol, gomisin E, gomisin H, gomisin N, concentrations of 10-200 ng/ml for schizandrol A, and concentrations of 5-200 ng/ml for gomisin J. The inter- and intra-day coefficients of variations (CVs) for the precision ranged from 6.70% (3.44%) to 11.66% (10.38%). The inter- and intra-day accuracies of eight lignans ranged from 95.70% (93.89%) to 104.59% (106.13%). No significant variation of any of the lignans occurred in the stability tests. Conclusion: The established method can be successfully applied to the pharmacokinetic study of the Schisandra lignan extract in normal rats.

Comparative Study of the Bioactive Constituents of Raw and Ripe Zizyphi Spinosi Semen

High-performance liquid chromatographic-tandem mass spectrometric (HPLC-MS-MS) methods were developed for the analysis of 13 bioactive constituents of Zizyphi Spinosae Semen ( ZSS), and for samples of ZSS fried at different temperatures and from different production areas. The results showed that the content of bioactive constituents increased with the increase in frying time from 65 to 80 min at 150 °C; among the 14 samples of ZSS from different production areas, those from Shanxi Changzhi, Shandong Jining, and Hebei Xingtai had a higher content of bioactive constituents. This analytical method can accurately and quickly analyze the bioactive constituents of ZSS and provide a scientific basis for its quality control.

LC-MS/MS Method for the Quantification of PARP Inhibitors Olaparib, Rucaparib and Niraparib in Human Plasma and Dried Blood Spot: Development, Validation and Clinical Validation for Therapeutic Drug Monitoring.

Poly (ADP-ribose) polymerase inhibitors (PARPis) are becoming increasingly meaningful in oncology, and their therapeutic drug monitoring (TDM) might be beneficial for patients. Several bioanalytical methods have been reported for PARPis quantification in human plasma, but advantages might be obtained using dried blood spot (DBS) as a sampling technique. Our aim was to develop and validate a liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for olaparib, rucaparib, and niraparib quantification in both human plasma and DBS matrices. Additionally, we aimed to assess the correlation between the drug concentrations measured in these two matrices. DBS from patients was obtained using Hemaxis DB10 for volumetric sampling. Analytes were separated on a Cortecs-T3 column and detected with electrospray ionization (ESI)-MS in positive ionization mode. Validation was performed according to the latest regulatory guidelines, in the range (ng/mL) 140-7000 for olaparib, 100-5000 for rucaparib, and 60-3000 for niraparib, within the hematocrit (Hct) range 29-45%. The Passing-Bablok and Bland-Altman statistical analyses revealed a strong correlation between plasma and DBS for olaparib and niraparib. However, due to the limited amount of data, it was challenging to establish a robust regression analysis for rucaparib. To ensure a more reliable assessment, additional samples are required. The DBS-to-plasma ratio was used as a conversion factor (CF) without considering any patient-related hematological parameters. These results provide a solid basis for the feasibility of PARPis TDM using both plasma and DBS matrices.

Visual colorimetric sensor for nitroguanidine detection based on hydrogen bonding−induced aggregation of uric acid−functionalized gold nanoparticles

A colorimetric assay is proposed for the quantification of nitroguanidine (NQ), based on triggering the aggregation of uric acid−modified gold nanoparticles (AuNPs@UA) by intermolecular hydrogen bonding interaction between uric acid (UA) and NQ. The red-to-purplish blue (lavender) color change of AuNPs@UA with increasing NQ concentrations could be perceived with the naked eye or detected by UV–vis spectrophotometry. The absorbance versus concentration correlation gave a linear calibration curve in the range of 0.6–3.2 mg L−1 NQ, with a correlation coefficient of 0.9995. The detection limit of the developed method was 0.063 mg L−1, lower than those of noble metal aggregation methods in the literature. The synthesized and modified AuNPs were characterized using UV–vis spectrophotometry, scanning transmission electron microscopy (STEM), dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). Some critical parameters such as modification conditions of AuNPs, UA concentration, solvent environment, pH, and reaction time were optimized for the proposed method. The non-interference of common explosives (i.e., nitroaromatic, nitramine, nitrate ester, insensitive and inorganic explosives), common soil and groundwater ions (Na+, K+, Ca2+, Mg2+, Cu2+, Fe2+, Fe3+, Cl−, NO3−, SO42−, CO32−, PO43−) and possible interfering compounds (used as camouflage agents for explosives; D-(+)-glucose, sweeteners, acetylsalicylic acid (aspirin), household powder detergents, and paracetamol) on the proposed method was demonstrated, proving that the procedure was fairly selective for NQ, due to special hydrogen bonding interactions between UA−functionalized AuNPs and NQ. Finally, the proposed spectrophotometric method was applied to NQ−contaminated soil, and the obtained results were statistically compared with those of the liquid chromatography-tandem mass spectrometric (LC-MS/MS) method in the literature.

Chiral separation of racemic closantel and ultratrace detection of its enantiomers in bacteria by enhanced liquid chromatography-tandem mass spectrometry combined with postcolumn infusion of ammonia

Reliable analysis of ultratrace antibiotics in bacterial cells may become a new means to elucidate the antibacterial mechanism, drug resistance and environmental fate. In this work, an ultrahigh-sensitive, accurate and enhanced liquid chromatography-tandem mass spectrometric method was first developed for chiral separation and detection of racemic closantel, as an antibacterial adjuvant. Optimizing acetonitrile-water-formic acid system that is compatible with mass spectrometry as a mobile phase, the baseline separation of two enantiomers was achieved by using EnantioPak® Y1-R chiral column, and the resolution of the two analytes was more than 1.95. Further adopt the strategy of postcolumn infusion of ammonia, the mobile phase pH was reversed from acidic condition suitable for the optimal chromatographic separation of R- and S-closantel to alkaline, so that closantel could realize efficient electrospray ionization under the preferred negative ion mode. The bacterial cells were subjected to be frozen-cracked, and the analytes were extracted with acetonitrile after clipping the pointed bottom of the Eppendorf tube into a new tube. The method was linear over concentration ranges of 0.5–50 pg/mL (r2≥0.99) for R- and S-closantel. The detection limits of target analytes were all 0.15 pg/mL in bacterial cells. The average recoveries of two enantiomers ranged from 81.2% to 107.8% with relative standard deviations below 15%. The method proposed might be important support for the deep research of the stereoselectivity of biological activity, toxicity and metabolism of closantel enantiomers.

A Sensitive Ultra-performance Liquid Chromatography-Tandem Mass Spectrometric Method for Determination of Secalonic Acid F in Rat Plasma and Its Application to Pharmacokinetic Study.

Secalonic acid F (SAF) is a fungal secondary metabolite exhibited interesting pharmacological effect. In this study, a simple and sensitive ultra-performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS) method was developed and validated for the determination of SAF in rat plasma. Emodin was selected as the internal standard (IS), and plasma samples were prepared by liquid-liquid extraction with ethyl acetate. Chromatographic separation was operated on an Agilent SB-C18 column, and the mobile phase was a mixture of 0.5% formic acid in water and methanol (V:V =20:80) at a flow rate of 0.3mL/min. Detection was carried out with a 6460 triple-quadrupole mass spectrometer using electrospray ionization in the multiple-reaction monitoring mode. The MS/MS ion transitions monitored were m/z 639.3→415.4 and 269.0→225.1 for SAF and IS, respectively. Results showed the calibration curve of SAF was linear in the range of 2-500ng·mL-1 with the correlation coefficient > 0.99. The matrix effect, extraction recovery, dilution effect, intraday and inter-day precision and accuracy were all in acceptable limits. The analytes were also stable under different conditions. The validated method was successfully applied to a pharmacokinetic study after oral administration in Sprague-Dawleyrats at a dose of 10mg/kg.

High-throughput quantitation of serological dimethylarginines by LC/MS/MS: Potential cardiovascular biomarkers for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by systemic inflammation of the joints and extra-articular tissues. The incidence of cardiovascular disease (CVD) remains the main cause of morbidity and mortality in patients with RA. Despite the development of new therapeutics targeting the articular manifestations, the relief of the cardiovascular burden is still an unmet medical need during the management of RA. So, the early prognosis of RA-associated CVD plays a crucial role in improving the clinical outcomes of RA patients. Recently, circulating dimethylarginines have gained attention as potential biomarkers for CVDs. Here, we present the development and validation of a high-throughput liquid chromatography-tandem mass spectrometric (LC/MS/MS) method for simultaneous quantification of creatinine, arginine, and dimethylarginines in human serum within 2 mins by isotope dilution mass spectrometry. This method employed a protein precipitation method for rapid sample preparation, trichloroacetic acid (TCA)-based ion pairing chromatography for fast analyte separation, and multiple reaction monitoring (MRM) with stable isotope-labeled internal standards (ISs) for simultaneous quantitation. To assure the quality, our method was validated against the FDA guidelines for lower limit of quantitation (0.2 µM), linearity (square of coefficient correlation>0.99), precision (intra-&inter-assay imprecision < 10 %), accuracy (intra-&inter-assay inaccuracy < 10 %), sample preparation recovery (recovery ≥ 90 %), stability (instability < 10 %), matrix effect (signal suppression < 55 %), and carryover ( < 0.01 %). Afterward, we applied the validated method to a retrospective cross-sectional study. We aimed to evaluate the utility of serological dimethylarginines as potential cardiovascular biomarkers in the development of RA-associated CVD. Our results revealed that the serological ratio of asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), an indicator of physiological arginine methylation status, was significantly elevated in patients with RA. This finding might provide value in detecting CVD to improve clinical outcomes in RA management.