Acetonitrile Methanol Mixtures Research Articles

Liquid chromatography-tandem mass spectrometry for determination of fingolimod and its active metabolite fingolimod phosphate in whole blood of patients with multiple sclerosis.

Fingolimod is an oral drug for the escalation of treatment of relapsing-remitting multiple sclerosis in patients with persistent disease activity on first-line drugs or in patients with rapidly progressive severe relapsing-remitting multiple sclerosis. An ultra-high-performance liquid chromatography-tandem mass spectrometry method for determining the concentrations of fingolimod and its active metabolite fingolimod phosphate in whole blood has been developed and validated. The advantages of this method are the easy, fast and cheap sample preparation using protein precipitation from blood with a mixture of acetonitrile-methanol (40:60, v/v). Chromatographic separation was performed on a ultra-high performance liquid chromatography BEH C18 1.7 μm (100 × 2.1mm) column. Two modes of ionization, electrospray ionization and atmospheric pressure chemical ionization, were tested and compared. For validation, the electrospray ionization mode was chosen. As internal standard, isotopically labeled fingolimod-D4 was used to quantify the analytes. The method was validated according to the rules of the European Medicines Agency. The coefficients of variation for fingolimod were in the range of 1.13-11.88%, and the recovery was 98.80-106.00%. The coefficients of variation for fingolimod phosphate were in the range of 2.73-9.31%, and the recovery was 90.08-107.00%. The method is quite easy and fast and can be used for routine analysis.

Development and validation of a chiral UPLC-MS/MS method for quantifying S-Oxiracetam and R-Oxiracetam in human plasma, urine and feces: Application to a phase-I clinical pharmacokinetic study

A chiral UPLC-MS/MS method was developed and validated to determine oxiracetam enantiomers in human plasma, urine, and feces. The R-Oxiracetam and S-Oxiracetam were quantified using a CHIRALPAK ®AD3 column at 25 ℃, and the resolution was greater than 3.2. The S-Oxiracetam is the eutomer that isresponsible for the treatment of various brain damage. Isocratic elution was conducted at a flow rate of 0.9 mL/min for 6 min using the mixture of methanol and acetonitrile (methanol:acetonitrile, 15:85) containing 0.3‰ formic acid. The methods showed linearity at the range of 0.5–100 µg/mL for each oxiracetam enantiomer. A comprehensive validation process was carried out, covering aspects including linearity, selectivity, carryover, accuracy, precision, interferences, matrix effect, recovery, dilution integrity and stability in matrix and solution. The validated methods were successfully applied to quantifying R-Oxiracetam and S-Oxiracetam in human plasma, urine, and feces of 12 healthy subjects treated with either a single dose of 2 g S-Oxiracetam injection or 4 g Oxiracetam injection in a phase-I clinical trial. There was no significant difference for plasma pharmacokinetic parameters of S-Oxiracetam between the two regimens (P＞0.05). The S-Oxiracetam and Oxiracetam were primarily eliminated through urine in their original form, with cumulative excretion rates of 92.16% and 85.92%, respectively, within 24 h after administration. Enantiomers interconversion was not observed in the plasma, urine, or feces. The results of this study suggest that replacing 4 g Oxiracetam injection with 2 g S-Oxiracetam injection could offer clinical benefits by lowering the dosage and mitigating potential risks, based on the pharmacokinetic characteristics.

A combination of FTIR and DFT to study the microstructure properties of ionic liquid–acetonitrile–methanol systems

Understanding the structural properties of ionic liquids (ILs) in azeotrope mixtures is crucial for designing and synthesizing IL entrainers tailored for extractive distillation. While extensive research has been conducted to comprehend the molecular properties of IL systems, much of this work has been limited to IL-cosolvent binary mixtures and fails to fully capture the essence of breaking azeotropy. In this study, we utilized Fourier-transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations to study the microstructure of the IL-azeotropic system. Leveraging the high resolution of excess spectroscopy and employing the methanol hydroxyl group as an effective probe, our research focused on the IL–acetonitrile–methanol mixtures. This approach enabled us to pinpoint species transformations during the mixing process, revealing the nature of phase equilibrium changes within the azeotrope. Consequently, our findings offer valuable insights into the microstructures of multicomponent solutions.

H-beta zeolite-based dispersive solid-phase strategy for the multi-residue determination of pesticides

In this work, electrostatic interactions, hydrogen bonding and other interactions between a variety of pesticides and H-beta zeolite are discussed based on thermodynamics (Gibbs free energy, enthalpy, and entropy). Combined with the physical properties of the target compounds (octanol-water partition coefficient and molar volume), the characteristics of the physical adsorption on the synthetic zeolite were analyzed, the results of H-beta zeolite adsorption showed that the adsorption rate had a nonlinear relationship with the physical properties, and the adsorption reaction was dominated by the adsorption on the surface and in the pores of the H-beta zeolite. Based on the principle of zeolite adsorption, the parameters of absorbent amount, adsorption time, sample pH, ion strength, sample volume and desorption solvent were optimized, a vortex-assisted dispersive solid-phase extraction procedure coupled with liquid chromatography-tandem mass spectrometry was developed for the analysis of multiple pesticides in surface water. The sample was adjusted by phosphate buffer or hydrochloric acid to pH 4, then adsorbed by 50 mg of zeolite within 10 min, adding 2% (g/v) sodium chloride to the solution. The absorbent was eluted with a mixture of acetonitrile-methanol containing 0.5% formic acid after separation, then filtered prior to analysis. The optimized vortex-assisted dispersive solid-phase extraction method simultaneously achieved a low adsorbent dosage, a high enrichment factor of 25, rapid pre-concentration for 30 min, a low solvent usage of 2 mL and multi-target simultaneous analysis. Method performance in terms of accuracy, precision, limit of detection, and limit of quantitation was performed to validate the reliability of the procedure. The proposed protocol achieved acceptable accuracy (recoveries between 62% and 107%), and precision (relative standard deviation < 20%). The limit of detection of the method was below 0.1 μg/L, and the limit of quantitation was 0.08 μg/L or 0.2 μg/L. The results indicated that zeolite is a promising adsorbent with high adsorption capacity. It has the advantages of being a fast, simple, green and economical method for determining residual pesticides in water.

Sample preparation and quantification of polar drug, allopurinol, in human plasma using LCMSMS.

A fast, selective and reproducible LC-MS/MS method with simple sample preparation was developed and validated for a polar compound, allopurinol in human plasma, using acyclovir as internal standard (IS). Chromatographic separation was achieved using Agilent Poroshell 120 EC-C18 (100 × 2.1 mmID, 2.7 µm) analytical column. The mobile phase was comprised of 0.1%v/v formic acid-methanol (95:05; v/v), at a flow rate of 0.45 mL/min. The effect of different protein precipitation agents used in sample preparation such as methanol, acetonitrile, a mixture of acetonitrile-methanol and a mixture of acetonitrile-acetone were evaluated to optimize the extraction efficiency of allopurinol and IS. The use of acetone-acetonitrile (50:50, v/v) as protein precipitating agent shortened the sample preparation time and improved the recovery of allopurinol to above 93%. The IS-normalised matrix factors at two concentration levels were 1.0, with CV of 5.1% and 4.2%. Allopurinol in plasma was stable at benchtop for 24 h, in autosampler tray for 48 h, in instrumentation room for 48 h, in freezer after 7 freeze-thaw cycles and in freezer for 140 days. Allopurinol stock standard solutions were stable for 140 days at room temperature and in the chiller. The short sample run time of the validated bioanalytical method allowed high throughput analysis of plasma samples in pharmacokinetic study of an allopurinol formulation. The robustness and reproducibility of the bioanalytical method was reaffirmed through incurred sample reanalysis (ISR).

The effect of reagents solvation on change in the stability of coordination compounds of silver(I) ion with pyridine in mixed methanol–acetonitrile solvents

In this study, potentiometric titration was used to determine the stability constants of mono- and bis(pyridine) complexes with silver(I) in mixed methanol–acetonitrile solvents. Gibbs free energies of transfer of pyridine from methanol to methanol–acetonitrile mixtures were determined by the method of distribution between two immiscible phases. The effect of solvent composition on change in the solvation state of pyridine was analyzed. The replacement of methanol by acetonitrile leads to the desolvation of pyridine. The resolvation of pyridine occurs predominantly due to the resolvation of the nitrogen atom at the concentration of acetonitrile >0.5 mol fr. The enthalpic contribution was shown to have a major contribution in ΔtrG0(Py)MeOH→(MeOH-AN). The effect of reagents solvation on the stability of [AgPy]+ and [AgPy2]+ complexes upon the change of the solvent composition was investigated. The resolvation of silver(I) was established to be a key factor controlling the stability of both complexes in MeOH-AN mixtures. The possibility of predictive calculation of the stability constants [AgPy]+ in individual and mixed non-aqueous solvents through the change in the Gibbs free energy of the solvation of the complexing ion was shown. Proper data are compared with data reported in the literature.

Pharmacokinetic comparison between Tanreqing Capsules Substitute and Tanreqing Capsules in rats by LC-MS/MS

Due to the limited resource of bear bile powder, the major raw material of Tanreqing Capsules(TRQ), cultured bear bile powder is used as a replacement to develop the Tanreqing Capsules Substitute(TRQS). An LC-MS/MS method was established in this study for simultaneous quantitation of 8 compounds from TRQS in rat plasma: tauroursodeoxycholic acid(TUDCA), taurocheno-deoxycholic acid(TCDCA), ursodeoxycholic acid(UDCA), chenodeoxycholic acid(CDCA), ferulic acid, wogonoside, baicalin, and forsythoside A. Thereby, the pharmacokinetic behaviors of TRQ and TRQS were evaluated. Concentration of endogenous compounds TUDCA, TCDCA, UDCA, and CDCA was determined with the stable isotope surrogate analytes: D4-TUDCA, D4-TCDCA, D4-UDCA, and D4-CDCA. Plasma samples were extracted by acetonitrile-induced protein precipitation. The LC conditions are as follows: Waters BEH C_(18) column(2.1 mm×100 mm, 1.7 μm), mobile phase of 10 mmol·L~(-1) ammonium formate aqueous solution(containing 0.01% formic acid) and acetonitrile-methanol mixture(1∶5). MS conditions are as below: multiple reaction monitoring(MRM), ESI~(+/-). Concentration of UDCA, CDCA, TUDCA, and TCDCA was corrected with a response factor, which is the ratio between the responses recorded for the surrogate and the authentic analyte at the equal concentration. Each of the plasma components showed good linearity(r &gt; 0.995 1). Accuracy and precision met the criteria(inter-day RSD&lt;7.0%, RE 89.98%-112.0%; intra-day RSD&lt;12%, RE 90.41%-111.2%). The recovery was 64.83%-119.9% and matrix effect was 87.15%-113.8%. The validated method was applied for pharmacokinetic study of TRQS and TRQ(po, 0.94 g·kg~(-1)). There was no significant difference in C_(max) and AUC_(0-24 h) of baicalin, UDCA, TUDCA, and TCDCA between the two groups, indicating similar pharmacokinetic behaviors between TRQS and TRQ in rats.

Simultaneous determination of 30 antibiotics in soil by ultra-high performance liquid chromatography-tandem mass spectrometry

土壤基质复杂,土壤中残留的抗生素种类繁多,浓度多为痕量水平,高灵敏度的仪器方法、有效的净化和富集方法、多种类抗生素的同时检测是土壤中抗生素检测的重点和难点。该研究建立了固相萃取-超高效液相色谱-串联质谱法同时测定土壤中7类(磺胺类、氟喹诺酮类、四环素类、大环内酯类、β-内酰胺类、酰胺醇类和林可酰胺类)30种抗生素的方法。首先,通过参数优化确定最佳质谱条件,选择BEH-C18色谱柱,以0.1%(v/v)甲酸甲醇溶液-0.1%(v/v)甲酸水溶液为流动相,10%(v/v)甲醇水溶液为进样溶剂。然后,通过提取条件(萃取剂种类及体积)和固相萃取条件(上样液pH、淋洗液有机溶剂比例、洗脱液种类及体积)的优化,确定使用10 mL乙腈和Na2EDTA-McIlvaine缓冲液的混合溶液(1:1, v/v)为萃取剂,萃取液pH调节至8.0后,采用HLB小柱进行固相萃取,并以10 mL超纯水淋洗净化,最后用10 mL甲醇-乙腈(1:1, v/v)洗脱目标分析物。在优化的分析条件下,该方法的定量限为0.043~4.04 μg/kg,目标化合物的标准曲线线性关系良好,相关系数在0.992~1.00的范围内,在20、100、200 μg/kg的添加浓度下,大多数目标化合物的加标回收率范围为44.8%~164%,相对标准偏差为0.700%~14.8%。将该方法用于6个实际土壤样品的分析,结果显示在30种抗生素中,17种抗生素有检出,其中12种抗生素的检出率为100%。环丙沙星和诺氟沙星是土壤样品中含量最高的两种抗生素,它们的含量范围分别是13.7~32.1和15.6~43.6 μg/kg。本研究建立的方法简单、快速、溶剂使用量少,能用于土壤样品中痕量水平的7类30种抗生素的同时测定。

Chemoenzymatic synthesis of enantiomerically enriched diprophylline and xanthinol nicotinate

A concise chemoenzymatic route toward enantiomerically enriched active pharmaceutical ingredients (API) – diprophylline and xanthinol nicotinate – is reported for the first time. The decisive step is an enantioselective lipase-mediated methanolysis of racemic chlorohydrin-synthon acetate, namely 1-chloro-3-(1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7H-purin-7-yl)propan-2-yl acetate, performed under kinetically-controlled conditions on a preparative 500 mg-scale. The best results in terms of reaction enantioselectivity (E = 14) were obtained for the enantiomers resolution performed with lipase type B from Candida antarctica immobilized on acrylic resin (CAL-B, Novozym 435) suspended in homophasic acetonitrile-methanol mixture. The elaborated biocatalytic system furnished the key chlorohydrin intermediate (in 71% ee and 38% yield), which was then smoothly converted into enantioenriched active agents: (R)-(–)-diprophylline (57% ee) and (S)-(+)-xanthinol nicotinate (65% ee). To support the assignment of absolute configurations of EKR-products as well as to confirm the stereochemical outcome of the remaining reaction steps, docking studies toward the prediction of enantiomers binding selectivity in CAL-B active site as well as the respective chemical correlations with enantiomerically enriched analytical standards obtained from commercially available (R)-(–)-epichlorohydrin, were applied. In addition, single-crystal X-ray diffraction (XRD) analyses were performed for the synthesized optically active APIs furnishing by this manner a first crystal structures of nicotinic acid salt of xanthinol.

Simultaneous determination of five bioactive components of XiaoJin Capsule in normal and mammary gland hyperplasia rat plasma using LC-MS/MS and its application to a pharmacokinetic study.

XiaoJin Capsule (XJC) is a classic Traditional Chinese Medicine formula for clinical treatment of thyroid nodules, mammary gland hyperplasia and breast cancer. For the specification and rational application of XJC in the future, an accurate and specific LC-MS/MS method was developed and validated for quantitative determination of five components in rat plasma after oral administration of XJC. The collected plasma samples were extracted by protein precipitation with methanol-acetonitrile (1:3, v/v) mixture solvent and separated on a C18 column using a gradient elution system. Mass spectrometry was performed on a triple quadrupole mass spectrometer, and samples were detected in positive ionization and multiple reactions monitoring mode. The method was properly validated in terms of linearity, precision, accuracy, recovery, matrix effect and stability. All calibration curves showed good linearity (r2 > 0.9910) over their concentration ranges. The intra- and inter-day precisions (RSD) were within 11.0%, and the LLOQ was 0.1, 0.2, 0.5, 7.5 and 7.5 ng/ml for aconine, songorine, neoline, 3-acetyl-11-keto-β-boswellic acid and 11-keto-β-boswellic acid, respectively. Extraction recovery, matrix effect and stability were satisfactory in rat plasma. This established method was successfully applied to a pharmacokinetics study of five compounds after oral administration of XJC to normal and mammary gland hyperplasia model rats.

Enantiomeric analysis of simendan on polysaccharide-based stationary phases by polar organic solvent chromatography.

Herein, the enantiomeric separation of simendan by high-performance liquid chromatography with ultraviolet detection using polysaccharide-based chiral stationary phases in polar organic mode is described. Three chiral columns (Chiralpak AD-H, Chiralcel OD-H, and Chiralpak AS) were screened using pure methanol and acetonitrile without additives under isocratic conditions. A reversed elution order was observed on the Chiralpak AD-H column when the methanol content in the mobile phase (methanol-acetonitrile mixtures) was above 10%, whereby levosimendan eluted prior to dextrosimendan. Further, it was found that increasing temperature effectively improved the enantioresolution on the Chiralpak AD-H column. Van't Hoff analysis was performed to evaluate the contribution of enthalpy and entropy to the chiral discrimination process. The best enantioseparation (α=3.00, Rs=12.85) was obtained on the Chiralpak AD-H column with methanol as the mobile phase at 40°C. Thus, a quantitative method for the resolution of dextrosimendan was established and validated, which could be used as a reference for the determination of dextrosimendan in levosimendan products.

Novel 4,4'-Fluoresceinoxy Bisphthalonitrile Showing Aggregation-Induced Enhanced Emission and Fluorescence Turn off Behavior to Fe3+ Ions.

A novel 4,4'-fluoresceinoxy bisphthalonitrile FPN is synthesized from fluorescein and 4-nitrophthalonitrile by aromatic nucleophilic ipso nitro substitution reaction. The structure of FPN constitutes phthalonitrile-fluorescein-phthalonitrile, acceptor-donor-acceptor, A-D-A form and the solvatochromic study of newly synthesized compound FPN was done in hexane, cyclohexane, CHCl3, DCM, DMF, acetonitrile, ethanol and in methanol. The aggregation behavior of FPN was investigated in good-poor solvent mixture DMF-water in various proportions and the molecule was found to be exhibiting Aggregation Induced Emission Enhancement AIEE for volume percentage of water beyond 50% with a significant hypsochromic shift of 70nm in the emission maxima from 458 to 388nm. This phenomenon is termed as Aggregation Induced Blue Shifted Emission Enhancement AIBSEE and was reported in substituted phthalonitrile for the first time. The chemo sensing activity of FPN with various transition metal ions also has been checked by fluorescence spectroscopy where the new molecule FPN exhibited fluorescence turn OFF behaviour towards Fe3+ ion in acetonitrile-methanol ACN-MeOH solution. The binding stoichiometry of FPN with Fe3+ was verified by Job's plot analysis and Density Functional Theory DFT-B3LYP computational methodology by using Gaussian 09 software. Graphical Abstract A novel 4,4'-fluoresceinoxy bisphthalonitrile FPN was synthesized by base catalyzed coupling reaction of fluorescein with 4 nitrophthalonitrile. The newly synthesized compound has been characterized using UV-vis, FTIR, 1HNMR, fluorescence spectral data and single crystal X-ray diffraction studies. The compound FPN was found to be exhibiting positive solvatochromism in various organic solvents and Aggregation Induced Blue Shifted Emission Enhancement AIBSEE in DMF-aqueous mixture when water volume exceed above 50%. As a metal ion chemo sensor FPN exhibited a selective fluorescence turn OFF behavior towards Fe3+ ion in the stoichiometric ratio 1:2 in acetonitrile-methanol mixture and limit of detection LOD of Fe3+ by FPN was calculated to be 3.665μM.

New approach for determination of the degradation products of fenspiride hydrochloride found in oral liquid formulations.

Fenspiride hydrochloride (FNS) is used in treating chronic inflammatory diseases, most commonly as a liquid oral solution. FNS produces degradation products along with fenspiride N-oxide (FNO) and 1-phenylethyl-4-hydroxy-4-aminomethyl piperidine hydrochloride (PHAP). We aimed to develop and validate a chromatographic method in order to identify the main degradation products in the presence of other compounds from a liquid preparation. The method used a dual gradient using two buffer solutions: the first with pH 4.5 (buffer 1, pH 4.5-MeOH 90:10%, v/v) and the second with pH 2.9 (buffer 2, pH 2.9-acetronitrile-methanol, 65:15:10%, v/v/v). As mentioned, there was a modification of the organic mixture, starting with 10% methanol and ending with a mixture of acetonitrile-methanol (15:10%, v/v). The flow-rate was 1.5 mL/min. According to the elution program, experimental conditions started with 100% solution S1, which decreased to 0% and, simultaneously, solution S2 increased to 100% during the first 10 min and was maintained for a further 5 min. After 15 min, initial conditions were re-established. The linearity interval was 0.5-2 μg/mL and the minimum correlation coefficient was 0.999. The recovery factor was 100.47-103.17% and the limit of quantification was 0.19-0.332 μg/mL. Intra-day maximum precision was 4.08% for FNS and 2.65% for PHAP. This double-gradient mobile phase produced good specificity in relation to the degradation products of FNS and other constituents of the oral liquid formulation. Forced degradation studies revealed other related substances that were confirmed in mass balance analyses. Degradation products were confirmed in acidic, basic and oxidative media.

Air assisted dispersive liquid-liquid microextraction with solidification of the floating organic droplets (AA-DLLME-SFO) and UHPLC-PDA method: Application to antibiotics analysis in human plasma of hospital acquired pneumonia patients

An ultra high-performance liquid chromatographic (UHPLC) method with PDA detection was developed and validated for the simultaneous quantification of metronidazole, meropenem, ciprofloxacin, linezolid and piperacillin in human plasma and applied to patients suffering from hospital acquired pneumonia (HAP). The method uses an air assisted dispersive liquid-liquid microextraction for sample preparation. All parameters in the extraction step, including selection of extractant, amount of extractant, ionic strength, pH, and extraction cycles, were investigated and optimized. Chromatography was carried out using a Poroshell 120 SB C18 (50 × 2.1 mm I.D. 2.6 μm particle size) column and a gradient mobile phase consisting of ammonium acetate buffer (10 mM, pH 4.0) (eluent A); and a mixture of acetonitrile-methanol in a ratio (80/20)(eluent B). Ulifloxacin was used as internal standard. The method demonstrated good linearity with correlation coefficients, r2 > 0.9995 for the drugs, as well as high precision (RSD% ≤ 9.87%), accuracy ranged from −8.14% to +8.98. The enrichment factor (EF) obtained ranged within 87 and 121. During the validation, the concentrations of the analytes were found to be stable after 3 freeze-thaw cycles and for at least 24 h after extraction. Subsequently, this method was used to quantify the drugs in patients with HAP in order to establish if the dosage regimen given was sufficient to eradicate the infection at the target site.

Rapid method for the quantification of 13 sulphonamides in milk by conventional high-performance liquid chromatography with diode array ultraviolet detection using a column packed with core-shell particles

In the present study, a column packed with core-shell particles was used for the separation and the quantification of 13 sulphonamides in milk by conventional high-performance liquid chromatography coupled with diode array ultraviolet detection (HPLC/UV-DAD). Preliminary experiments were carried out to investigate selectivity of different stationary phases. Best results were achieved using a C18 column packed with 2.6μm core-shell particles (diameter 4.6mm, length 75mm). A binary gradient elution based on acetate buffer solution at pH 4.50 and a mixture of methanol acetonitrile 50:50 (v/v) was employed at the flow rate of 1.2mLmin−1 with an injection volume of 6μL. These chromatographic conditions allowed the efficient separation of 13 sulphonamides in about 8min. To evaluate the suitability of the method for official control analysis, the most important validation parameters were investigated according to the European Decision 657/2002/EC as established for analysis of drug residues in food. Sulphonamides were recovered from milk samples by a simple and quick preparation procedure consisting of an extraction step with chloroform/acetone and a purification step with n-hexane. Mean recoveries from raw milk ranged between 55% and 86% at the Maximum Residual Limit of 100μgkg−1, and RSDs% resulted lower than Thompson and Horwitz RSD% reference values for all sulphonamides. The LOQ value (2.7–15μgkg−1) was low enough to satisfy legal limits suggested by European Regulation 37/2010/EC.

Routine Therapeutic Drug Monitoring of Haloperidol in Human Serum by Liquid Chromatography-Tandem Mass Spectrometry

Therapeutic drug monitoring (TDM) is a suitable and accepted tool for optimizing therapy with many antipsychotics. The guidelines of AGNP-TDM Expert Group strongly recommend TDM for haloperidol. We evaluated chromatographic conditions and mass spectrometry detection for its quantification in human serum to increase the number of monitored drugs in our hospital. Simple sample preparation using protein precipitation by mixture of acetonitrile-methanol (40:60, v/v) with zinc sulfate and fast gradient liquid chromatography-tandem mass spectrometry provided an effective method for the use in routine clinical settings. The separation was performed on a BEH C18 column (2.1 x 50 mm, 1.7µm) by using binary mobile phase (A: 0.1% formic acid in water, v/v; B: 0.1% formic acid in acetonitrile, v/v). Alprenolol was applied as an internal standard. Mass spectrometric detection was carried out in the positive electrospray ionization mode. The method was validated over the concentration range of 0.13–100 ng/mL with overall recovery of haloperidol 96.7 % - 100.0 %. The intra-day and inter-day precisions determined at the three concentration levels were in the range of 1.4 % to 9.7 %. Selected reaction monitoring and negligible matrix effect allow to achieve a required quantification limit. The presented method is applicable to routine therapeutic drug monitoring of haloperidol in clinical practice with a reasonable short analysis time (5 min).

Highly sensitive LC–MS/MS method to estimate doxepin and its metabolite nordoxepin in human plasma for a bioequivalence study

A selective, sensitive and rugged liquid chromatography–tandem mass spectrometry (LC–MS/MS) assay has been developed for the simultaneous determination of doxepin (Dox) and its pharmacologically active metabolite, nordoxepin (NDox) in human plasma. The analytes and their internal standards (IS) were extracted from 500µL of human plasma by liquid-liquid extraction using methyl tert-butyl ether. Chromatographic separation was achieved on Hypurity C8 column (100mm × 4.6mm, 5µm) using a mixture of acetonitrile-methanol (95:5, v/v) and 2.0mM ammonium formate in 93:7 (v/v) ratio. Detection was accomplished by tandem mass spectrometry in the positive ionization and multiple reaction monitoring acquisition mode. The protonated precursor to product ion transitions studied for Dox, NDox, and their corresponding ISs, propranolol and desipramine, were m/z 280.1→107.0, 266.0 →107.0, 260.1→116.1 and 267.1→72.1, respectively. A linear dynamic range of 15.0–3900pg/mL for Dox and 5.00–1300pg/mL for NDox was established with mean correlation coefficient (r2) of 0.9991 and 0.9993, respectively. The extraction recovery ranged from 86.6%–90.4% and 88.0%–99.1% for Dox and NDox, respectively. The intra-batch and inter-batch precision (% CV) across quality control levels was ≤ 8.3% for both the analytes. Stability evaluated under different storage conditions showed no evidence of degradation and the % change in stability samples compared to nominal concentration ranged from 4.7% to 12.3%. The method was successfully applied to a bioequivalence study of 6mg doxepin hydrochloride orally disintegrating tablet in 41 healthy Indian subjects under fasting and fed conditions.

A simple LC-MS/MS method for the simultaneous quantification of resveratrol and its major phase II metabolites: Assessment of their urinary and biliary excretions in rats.

Trans-resveratrol (Res) is rapidly metabolized, extensively distributed into various tissues and mainly excreted by urine. The present study aimed to establish a simple LC-MS/MS method to simultaneously quantify Res and its major phase II metabolites (Res-3-O-β-d-glucuronide, R3G; Res-4'-O-β-d-glucuronide, R4'G; Res-resveratrol 3-sulfate, R3S; and Res-4'-sulfate, R4'S), and apply this method to assess their urinary and biliary excretions in rats. A simplified salting-out assisted liquid-liquid extraction (SALLE) strategy was developed to prepare samples with acetonitrile-methanol mixture (8:2, v/v) as extractant and ammonium acetate solution (10M) as salting-out reagent. The method validation demonstrated an acceptable recovery (>80%), good accuracy (85-115%), low deviation of detection (<15%) and no obvious matrix effect (<20%). Then the validated method was successfully applied to analyze the excretion of Res and its metabolites after intragastric administration of Res at 50mg/kg in rats. Only a minor proportion of Res (0.51nmol) and its metabolites (R3S, 35.8nmol; R4S, 0.25nmol; R3G, 142.3nmol; R4'G, 0.19nmol) were eliminated via bile, while the majority of Res (1670.2nmol), R3G (14,089.0nmol) and R3S (2975.6nmol) were excreted through urine. The major forms found in feces were Res and R3S, which were accumulated up to 241.8 and 250.8nmol, respectively. In summary, the SALLE technique simplified the samples preparation and could be well popularized, especially for those highly polar compounds in biosamples like urine, bile and feces, where various endogenous substances could significantly affect the extraction recovery and detection response.

Development of an HPLC-DAD Method for the Determination of Five Sulfonamides in Shrimps and Validation According to the European Decision 657/2002/EC

A method for the determination of five sulfonamide drugs: sulfadiazine (SDZ), sulfamethazine (SMTH), sulfisoxazole (SIX), sulfadimethoxine (SDMX), sulfaquinoxaline (SQX) in shrimps was developed using a high-pressure liquid chromatography–diode array detection (HPLC–DAD) instrumentation. The drugs were extracted from the samples using a solid-liquid extraction, with a mixture of acetonitrile-methanol and aqueous solution of acetic acid. The separation was achieved with LiChroCART-LiChrospher® 100 RP-18 (5 μm, 250 × 4 mm), and the mobile phase consisted of (A) aqueous solution of acetic acid 0.1% (65%) and (B) mixture of ACN-MeOH 50:50 v/v (35%), delivered at a flow rate of 0.8 mL/min isocratically. A DAD detector was used for the detection of the sulfonamides at 265 nm. The method was validated according to the 657/2002/EC decision of the European Union. The recoveries for within-day repeatability were 90.2–109.0% and for between-day precision 88.6–108.4%. The limit of quantitation for all five suflonamides was 50 μg/kg, and the limit of detection was 15 μg/kg.

Core-Shell in Liquid Chromatography: Application for Determining Sulphonamides in Feed and Meat Using Conventional Chromatographic Systems.

A C18 column packed with core-shell particles was used for the chromatographic separation of sulphonamides in feed and meat by a conventional high performance liquid chromatography system coupled with a diode array detector. Two analytical methods, already used in our laboratory, have been modified without any changes in the extraction and clean-up steps and in the liquid chromatography instrumentation. Chromatographic conditions applied on a traditional 5-µm column have been optimized on a column packed with 2.6 µm core-shell particles. A binary mobile phase [acetate buffer solution at pH 4.50 and a mixture of methanol acetonitrile 50: 50 (v/v)] was employed in gradient mode at the flow rate of 1.2 mL with an injection volume of 6 µL. These chromatographic conditions allow the separation of 13 sulphonamides with an entire run of 13 minutes. Preliminary studies have been carried out comparing blanks and spiked samples of feed and meat. A good resolution and the absence of interferences were achieved in chromatograms for both matrices. Since no change was made to the sample preparation, the optimized method does not require a complete revalidation and can be used to make routine analysis faster.