Ion-Pair Single-Drop Microextraction Determinations of Degradation Products of Chemical Warfare Agents in Water

Ion-pair single-drop microextraction (SDME) coupled to gas chromatography–mass spectroscopy (GC–MS) methods for the determination of four degradation products of chemical warfare agents were investigated in water. Acidic analytes were converted into their ion-pair complexes with cation surfactants in aqueous sample and then extracted into the organic single drop containing the derivatising agent. Upon injection, the analytes were derivatised in the GC injection hot port. Parameters, such as type of extraction solvent, ion-pairing (IP) reagent, reagent concentration, salt concentration, stirring speed and pH, were all optimized. This method is reproducible for spiked water sample for four different analytes (RSDs < 9.33 %, n = 5) and linear (r ² > 0.9945). The limit of detection (LOD) is in the range of 0.08–0.01 ng mL⁻¹ (S/N = 5) under GC–MS selected ion monitoring mode. The method was successfully applied to the proficiency test samples from the Organization for Prohibition of Chemical Weapons (OPCW).

     

Ultrasonic-Assisted Drop-to-Drop Solvent Microextraction in a Capillary Tube for Analyzing Trace Benzene, Toluene, Xylene in One Drop of a Water Sample

A novel analytical technique termed ultrasonic-assisted drop-to-drop solvent microextraction (USA-DDSME) in a capillary tube was developed to determine trace benzene, toluene, xylene in one drop of a water sample, which was combined with gas chromatography–flame ionization detection (GC–FID). The advantages of this method are rapidity, convenience, ease of operation, simplicity of the device, and extremely little solvent and sample consumption. Extraction conditions including the type of extraction solvent, the volume of extraction solvent, the volume of sample, extraction time and effect of salt concentration were optimized. The best optimum parameters for extraction were achieved with 3 μL of extraction solvent. Chloroform was divided into four equal divisions in 20 μL water sample (without salt addition) in a capillary tube and ultrasonicated for 10 min, centrifugated at 2,500 rpm for 5 min to let the extraction solvent settle at the bottom of the capillary tube, then 1 μL of the separated extraction solvent was injected into the GC–FID for analysis. Linearity of the method was determined by analyzing spiked water samples over a concentration range of 0.1–50 μg mL^?1. Correspondingly, the LOD values were 0.01 μg mL^?1. All calibration curves were found to have good linearity with correlation coefficients (r ²) > 0.995. The precision (RSD) of the system, measured by six repeated determinations of the analytes at 1 μg mL^?1 were in the range of 1.6–3.5%.     

GC Methods for the Determination of Methanol and Ethanol in Insulating Mineral Oils as Markers of Cellulose Degradation in Power Transformers

Methanol and ethanol in transformer oils have been recently proposed as new markers of thermal and mechanical degradation of cellulose (the solid insulation in power transformers). In this work, we optimized and compared the performance of two headspace gas chromatographic methods based on flame ionization (HS–GC–FID) and mass spectrometry detection (HS–GC–MS) to determine methanol and ethanol in insulating mineral oil. For methanol and ethanol, the detection limits were 12 and 27 μg kg^?1 (HS–GC–FID) and 1.3 and 3.1 μg kg^?1 (HS–GC–MS). Repeatability was evaluated in transformer oils for both the methods at different concentration levels of analytes and RSD values were found to lie between 1.8 and 16 %. The accuracy of the methods was assessed under a proficiency test (Cigré JWG A2/D1.46). The methods were compared by a F-test and a one-sided paired t test performed on 21 transformer oils in service. Correlations of methanol and ethanol content in sampled oils against their actual time of service are provided. For each sample, the content of traditional markers (furan-2-carbaldehyde and CO₂) was also measured, finding a correlation between light alcohols and CO₂ content. This indicates that methanol and ethanol determination may be helpful in providing further information on the thermal degradation conditions of transformers’ solid insulation. The method developed is currently routinely applied by the laboratories of Sea Marconi Technologies for the assessment of transformers’ conditions.     

Simultaneous Analysis of Hexaconazole, Myclobutanil, and Tebuconazole Residues in Apples and Soil by SPE Clean-Up and GC with Nitrogen–Phosphorus Detection

A facile and sensitive method utilizing capillary gas chromatography with nitrogen phosphorus detection (GC–NPD) has been developed and validated for simultaneous analysis of hexaconazole, myclobutanil, and tebuconazole, three broad-spectrum systemic fungicides, in apples and soil. Two samples were fortified with the three pesticides and subjected to ultrasonic extraction, followed by solid-phase extraction (SPE) to remove coextractives, before analysis by GC–NPD. SPE procedures were performed on PSA cartridges (500 mg, 3 mL), the analytes being eluted with n-hexane–acetone (9:1 v/v, 2 mL). Recovery of three pesticides from the fortified apple and soil samples ranged from 94.5 to 107.3% with relative standard deviations less than 9.7% at the three spike levels (0.01, 0.1, and 0.5 mg kg^?1). Limits of quantification of the method for apple and soil were 0.01 mg kg^?1, sufficiently below the maximum residue limits. Direct confirmation of the analytes in samples was achieved by gas chromatography–mass spectrometry (GC–MS).     

Large Volume Headspace Analysis Using Solid-Phase Microcolumn Extraction

A rapid and simple large volume headspace (HS) sampling technique termed headspace solid-phase microcolumn extraction (HS-SPMCE) is described. HS gas above a liquid or solid sample is aspirated by attaching a gas-tight syringe onto a glass thermal desorption tube filled with Tenax sorbent. The trapped analytes are recovered by thermal desorption for gas chromatography–mass spectrometry (GC–MS) analysis. Benzene, toluene, ethylbenzene and the xylene isomers (BTEX) are used as model compounds to demonstrate the application of the extraction procedure for water samples. The results of the tests of the effect of agitation time and aspiration rate on recovery of the analytes show a good robustness of the method. BTEX are determined in the linear range from 0.5 to 50.0 μg L^?1 with limits of detection (3 σ) ranging within 0.09–0.14 μg L^?1 (MS was in scan mode). The method provides a good repeatability (RSD < 9%) and only a negligible carryover effect was observed ( ≤0.05%) when analysing BTEX at concentration 50.0 μg L^?1.     

Sequential Injection Ion Chromatography with Flow Injection Post Column Derivatization Capable of Using the Unstable Reagent Murexide to Determine Calcium and Magnesium in a Mixture

A hyphenated sequential injection ion chromatography–flow injection analysis (SIIC–FIA) system is proposed for post column derivatization capable of using murexide, an unstable but commonly available reagent, for the determination of calcium and magnesium in a mixture. A short ion exchange column was modified from a 4.6 mm × 10 mm C18 monolithic guard column. Calcium/magnesium mixture and murexide were used as model analytes and derivatizing agent, respectively. The FIA post column allows the use of unstable chromogenic reagents. The continuous flow of liquid also helped to stabilize the signal baseline during detection. A single concentration based calibration graph was demonstrated. The system requires low volumes of standard/sample (5–50 µL) and mobile phase (4.50 mL), and offers sample throughput at 8 h^?1 without the need for long column calibration. Detection limits were 0.5 and 0.1 µg for Ca²⁺ and Mg²⁺, respectively. Working ranges were 1–5 µg Ca²⁺ and 0.2–1 µg Mg²⁺. Analyses of well and drinking water samples were demonstrated and validated with the standard complexometric titration.     

An Improved Method for Determination of Polychlorinated Biphenyls and Polybrominated Diphenyl Ethers in Sediment by Ultrasonic Solvent Extraction Followed by Stir Bar Sorptive Extraction Coupled to TD–GC–MS

An improved simple, fast and miniaturized method for the determination of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in freshwater sediment using ultrasonic solvent extraction followed by stir bar sorptive extraction–thermal desorption–gas chromatography–mass spectrometry (USE-SBSE/TD–GC–MS) is presented. The sediment sample (0.2 g) is extracted with methanol (1:1.2, 2:1.0 mL) in an ultrasonic bath (two 5-min extraction cycles). The combined extracts are made up to 5 mL with water, and from the resulting solution, the analytes are preconcentrated on a stir bar coated with polydimethylsiloxane during 1 h of stirring. The loaded sorptive stir bar is then thermally desorbed and online analysed by GC–MS. For the analytes in river sediment, a linear dynamic range of 0.5–50 ng g^?1 was established and limits of detection in sub nanogram-per-gram level were achieved. Recoveries and repeatability were obtained in the ranges 62.8–91.5 % and 3.6–15.0 %, respectively. The method accuracy was confirmed by the analysis of PCBs and PBDEs in a certified reference material. The main improvement in comparison with similar published methods is in shortening the sample handling time and the method miniaturization.     

Optimization and Simultaneous Determination of Alkyl Phenol Ethoxylates and Brominated Flame Retardants in Water after SPE and Heptafluorobutyric Anhydride Derivatization followed by GC/MS

A gas chromatography–mass spectrometry (GC–MS) method was investigated for the simultaneous analysis of two types of endocrine disrupting compounds (EDCs), i.e., alkylphenol ethoxylates and brominated flame retardants (BFRs), by extraction and derivatization followed by GC–MS. Different solid phase extraction (SPE) cartridges (Cleanert PestiCarb, C₁₈, Cleanert-SAX and Florosil), solvents (toluene, tetrahydrofuran, acetone, acetonitrile and ethyl acetate) and bases (NaHCO₃, triethylamine and pyridine) were tested and the best chromatographic analysis was achieved by extraction with Strata-X (33 μm, Reverse Phase) cartridge and derivatization with heptafluorobutyric anhydride at 55 °C under Na₂CO₃ base in hexane. It was observed that APE together with lower substituted PBBs (PBB1, PBB10, PBB18 and PBB49), HBCD and TBBPA can be determined simultaneously under the same GC conditions. This simple and reliable analytical method was applied to determining trace amounts of these compounds from wastewater treatment plant samples. The recoveries of the target compounds from simulated water were above 60 %. The limit of detection ranged from 0.01 to 0.15 μg L⁻¹ and the limit of quantification ranged from 0.05 to 0.66 μg L⁻¹. There were no appreciable differences between filtered and unfiltered wastewater samples from Leeuwkil treatment plant although concentration of target analytes in filtered influent was slightly lower than the concentration of target analytes in unfiltered influent water. The concentrations of the target compounds from the wastewater treatment were determined from LOQ upwards.

     

Flow-assisted automated solid-phase microextraction for the determination of chloroethers in aqueous matrices

In this study a method of flow-assisted automated solid-phase microextraction (FA-SPME) was developed for the determination of organic pollutants in aqueous samples. A CTC Combi-PAL autosampler coupled with gas chromatography–mass spectrometry (GC–MS) was used to automate the entire extraction process. In this method, the SPME fibre was exposed to 100 mL of sample in a direct immersion mode for 10 min. After exposure, the fibre was desorbed at the injection port of GC–MS. To demonstrate the applicability of FA-SPME, chloroethers were selected as model compounds. Good linear correlation was found over a concentration range of 0.5–100 µg/L. The detection limits of the method were determined between 0.02 and 0.05 µg/L with the coefficients of determination (R²) from 0.9980 to 0.9996. The relative standard deviations (RSDs) of the FA-SPME for three sequential FA-SPME analyses were determined to be in the range between 1.2% and 6.2% (n = 3). The applicability of the method was assessed by means of recovery studies and satisfactory values for all compounds were obtained. This optimised method was used in the analysis of water and human urine samples to show the matrix effect on FA-SPME. This FA-SPME/GC–MS is substantially faster and suitable for the routine continuous flow-mode environmental monitoring applications.     

Quantification of Transformation Products of Unsymmetrical Dimethylhydrazine in Water Using SPME and GC-MS

Quantification of trace concentrations of transformation products of rocket fuel unsymmetrical dimethylhydrazine (UDMH) in water requires complex analytical instrumentation and tedious sample preparation. The goal of this research was to develop a simple and automated method for sensitive quantification of UDMH transformation products in water using headspace (HS) solid-phase microextraction (SPME) in combination with GC-MS and GC-MS/MS. HS SPME is based on extraction of analytes from a gas phase above samples by a micro polymer coating followed by a thermal desorption of analytes in a GC inlet. Extraction by 85 µm Carboxen/polydimethylsiloxane fiber at 50 °C during 60 min provides the best combination of sensitivity and precision. Tandem mass spectrometric detection with positive chemical ionization improves method accuracy and selectivity. Detection limits of twelve analytes by GC-MS/MS with chemical ionization are about 10 ng L^?1. GC-MS provides similar detection limits for five studied analytes; however, the list of analytes detected by this method can be further expanded. Accuracies determined by GC-MS were in the range of 75–125% for six analytes. Compared to other available methods based on non-SPME sample preparation approaches (e.g., liquid–liquid and solid-phase extraction), the developed method is simpler, automated and provides lower detection limits. It covers more UDMH transformation products than available SPME-based methods. The list of analytes could be further expanded if new standards become available. The developed method is recommended for assessing water quality in the territories affected by space activities and other related studies.     

Simultaneous Analysis of Herbicide Metribuzin and Quizalofop-p-ethyl Residues in Potato and Soil by GC-ECD

A robust and sensitive method was developed for the simultaneous analysis of metribuzin and quizalofop-p-ethyl residues in potato and soil, based on solid-phase extraction (SPE) coupled to capillary gas chromatography with electron capture detector (GC-ECD). Residues of two herbicides were extracted from potato and soil with acetone and methanol–water, followed by SPE to remove coextractives, before analysis by GC-ECD. SPE procedures were performed on Florisil cartridges (500 mg, 3 mL), the analytes from potato and soil matrix were eluted with petroleum ether-acetic ether (9:1 v/v, 5 mL) and petroleum ether-acetic ether (8:2 v/v, 2 mL), respectively. Limits of quantification of the method were 0.01 mg kg^?1, and the mean recoveries ranged from 72.9 to 109.5% with relative standard deviation ranging from 0.7 to 9.2% at the three spike levels (0.01, 0.1, and 0.5 mg kg^?1). The proposed method was successfully applied to the analysis of metribuzin and quizalofop-p-ethyl residues in potato and soil samples from an experimental field. Direct confirmation of the analytes in real samples was achieved by gas chromatography-mass spectrometry (GC–MS).     

Monitoring of Polychlorinated Biphenyls in Surface Water Using Liquid Extraction,GC/MS,and GC/ECD

Abstract

A rapid and reliable analytical method, at trace level concentration was developed and validated for monitoring polychlorinated biphenyls (PCBs) in Jordanian surface water. The method combines the advantage of liquid extraction together with gas chromatography‐mass spectrometry (GC/MS) and gas chromatography‐electron capture detector (GC/ECD). The performance of the method was evaluated by analyzing certified reference material (CRM) of the analytes and applied on real water samples collected from different sites in Jordan. A mixture of 60∶40 dichloromethan‐petroleum ether was chosen as a convenient binary solvent for liquid–liquid extraction. The GC conditions for GC/MS were optimized using He as a carrier gas, temperature programming, and chlorpropham as an internal standard (IS).

The conditions for GC/ECD were performed using N₂ gas and a temperature program from 160 to 280°C with different increasing rates. The method of GC/MS in the selective ion mode (SIM) gave linear relationships for all PCBs tested between 0.60–6.0 µg/l with R ²=0.9934 (n=7×18). Recoveries from spiked water samples ranged between 87.6 and 91.4%. The mean accuracy and precision obtained were 4.9% and 2.16%, respectively. The mean of detection limit was 0.14±0.04 µg/l. In GC/ECD, linear relationships for all PCBs examined over the range of 0.3–2.4 µg/l was verified as characterized by a linear regression equation and correlation coefficient, R ²=0.9915 (n=12). The average precision and accuracy were 4.86% and 5.21%, respectively. Analyses results clarified that none of the examined Jordanian water samples contained any of the searched for PCBs within the detection limit achieved.     

LC-ESI-MS/MS Method for Simultaneous Determination of Triterpenoid Glycosides and Aglycones in Centella asiatica L.

A new and rapid method for simultaneous identification and estimation of bioactive triterpenoid glycosides [asiaticoside (AS) and madecassoside (MS)] and their aglycones [asiatic acid (AA) and madecassic acid (MA)] in Centella asiatica was developed by using high-performance liquid chromatography (HPLC) coupled with triple-quadrupole mass spectrometry (MS/MS). Estimation was based on multiple reaction monitoring (MRM) using the precursor → product ion combination for determination of four analytes using Alltima C18 column (50 × 4.6 mm, 3 µm). An electrospray ionization (ESI) tandem interface in positive mode was employed prior to mass-spectrometric detection. The method was subjected to a thorough validation procedure in terms of linearity, limit of detection (LOD) and quantification (LOQ), accuracy, and precision. Six-point calibration curves were linear in the range of 50–500 ng mL⁻¹ for AS and MS, and 25–250 ng mL⁻¹ for AA and MA, with excellent linearity (R ² > 0.98). With the optimized conditions, the four analytes were detected accurately within 10 min. LOD and LOQ ranged from 2.5 to 5 and 10 to 15 ng mL⁻¹, respectively. Method accuracy in terms of average recoveries of all four analytes ranged between 98.61 and 102.85 % at three spiking levels with intra- and interday precision relative standard deviation (RSD, %) of 1.01–4.62 and 1.13–4.16, respectively. The new method was successfully applied to estimate the concentration of these four bioactive compounds in extracts of C. asiatica prepared by nonpolar-to-polar solvents.

     

Gas chromatography–triple quadrupole tandem mass spectrometry: a powerful tool for the (ultra)trace analysis of multiclass environmental contaminants in fish and fish feed

A new method for rapid determination of 73 target organic environmental contaminants including 18 polychlorinated biphenyls, 16 organochlorinated pesticides, 14 brominated flame retardants and 25 polycyclic aromatic hydrocarbons in fish and fish feed using gas chromatography coupled with triple quadrupole tandem mass spectrometry (GC–MS/MS) was developed and validated. GC–MS/MS in electron ionization mode was shown to be a powerful tool for the (ultra)trace analysis of multiclass environmental contaminants in complex matrices, providing measurements with high selectivity and sensitivity. Another positive aspect characterizing the newly developed method is a substantial simplification of the sample preparation, which was achieved by an ethyl acetate QuEChERS (quick, easy, cheap, effective, rugged and safe) based extraction followed by silica minicolumn clean-up. With use of this sample preparation approach the sample laboratory throughput was increased not only because six samples may be prepared in approximately 1 h, but also because all the above-mentioned groups of contaminants can be determined in a single GC–MS/MS run. Under the optimized conditions, the recoveries of all target analytes in both matrices were within the range from 70 to 120 % and the repeatabilities were 20 % or less. The method quantification limits were in the range from 0.005 to 1 μg kg^–1 and from 0.05 to 10 μg kg^–1 for fish muscle tissue and fish feed, respectively. The developed method was successfully applied to the determination of halogenated persistent organic pollutants and polycyclic aromatic hydrocarbons in fish and fish feed samples.     

Simultaneous LC–MS–MS Analysis of Danshensu, Salvianolic Acid B, and Hydroxysafflor Yellow A in Beagle Dog Plasma, and Application of the Method to a Pharmacokinetic Study of Danhong Lyophilized Powder for Injection

A reliable and sensitive liquid chromatographic–tandem mass spectrometric method, with rutin as internal standard, has been developed and validated for simultaneous determination of danshensu, salvianolic acid B (SAB), and hydroxysafflor yellow A (HSYA) in beagle dog plasma. Plasma samples spiked with the analytes were extracted by solid-phase extraction and the analytes were separated on a 250 × 4.6 mm i.d., 5-μm particle, C₁₈ column with methanol–acetonitrile–0.5% formic acid 20:25:55 (v/v) as mobile phase at a flow rate of 1 mL min^?1. LC–MS–MS analysis was performed with a Finnigan TSQ triple-quadrupole tandem mass spectrometer operated in negative-ion selected-reaction-monitoring mode, using electrospray ionization. The accuracy and precision of the method were acceptable and linearity was good over the range 20–4,000 ng mL^?1 for danshensu, 50–10,000 ng mL^?1 for SAB, and 10–2,000 ng mL^?1 for HSYA. The method was successfully applied to a pharmacokinetic study of a traditional Chinese medicinal preparation, Danhong lyophilized powder for injection.     

Stir Bar Sorptive Extraction and LC–MS/MS for Trace Analysis of UV Filters in Different Water Matrices

A simple, selective and highly sensitive method was developed and optimized to determine the most commonly used UV filters with endocrine-disrupting potential in water, namely benzophenone-3 (BP-3), octocrylene (OC), ethylhexyl dimethyl p-aminobenzoate (OD-PABA), ethylhexyl methoxycinnamate, ethylhexyl salicylate (EHS) and homosalate (HMS). Samples were extracted by stir bar sorptive extraction followed by liquid desorption (SBSE-LD). The important factors influencing SBSE-LD were optimized. Under optimal conditions, assays were performed on 50 mL of water sample using stir bars (0.5 mm in film thickness, 10 mm in length) at room temperature. The analytes were determined by liquid chromatography–tandem mass spectrometry with triple quadrupole analyzer using atmospheric pressure chemical ionization. The main parameters in HPLC–APCI–MS/MS were also optimized to provide the best performances for all analytes. Moreover, matrix effect was investigated using two methods the post-column infusion system and the method of spiked matrices after extraction. As a result, no significant matrix effect on the analysis was observed. The method showed good linearity (R ² coefficients greater than 0.996 in different water samples after SBSE-LD). Recoveries of the analytes were close to 90%, except for BP-3 (64%) and OC (76%) with relative standard deviation lower than 11%. Detection limits were between 0.6 and 3.3 ng L⁻¹ for all the analytes except for HMS (94 ng L⁻¹) and EHS (114 ng L⁻¹). This methodology was applied to measure UV filters in seawater, river water and wastewater in different sites of Liguria; BP-3 and OC were found in most of the considered samples at rather low concentration level.

     

An automated method for the simultaneous measurement of azole antifungal drugs in human plasma or serum using turbulent flow liquid chromatography-tandem mass spectrometry

Azole antifungal drugs are important in the prophylaxis and treatment of invasive aspergillosis. Therapeutic drug monitoring may be indicated to (1) monitor adherence, (2) guide dosage and (3) minimise the risk of drug–drug interactions and dose-related toxicity. TurboFlow^TM technology offers online, automated sample preparation. An Aria Transcend^TM TLX-II coupled with a TSQ Vantage^TM MS was used. Centrifuged samples (25 μL) were mixed with internal standard solution (975 μL) and 30 μL injected directly onto a C18-P-XL TurboFlow column. Analytes were focussed onto a Phenomenex Gemini Phenyl analytical column and eluted using a methanol/water gradient (flow-rate, 0.8 mL/min). Analytes were monitored in selected reaction monitoring mode (two transitions per analyte, positive mode APCI). Calibration ranges were as follows: itraconazole, hydroxyitraconazole, and posaconazole 0.05–5.0 mg/L; voriconazole and fluconazole 0.1–10 mg/L. Total analysis time was 12 min. TurboFlow column recovery was >77% for all analytes. Calibration was linear (R ²?>?0.99) for all analytes. Inter- and intra-assay imprecision (% RSD) was <8% and accuracy (nominal internal quality control values) 90–105% for all analytes. The limit of detection was 0.01 mg/L for all analytes. No matrix effects were observed. This method is simple, robust and suitable for measuring these compounds at concentrations attained during therapy.     

Determination of five polar herbicides in water samples by ionic liquid dispersive liquid-phase microextraction

A simple, rapid and efficient ionic liquid based on dispersive liquid-phase microextraction (IL-DLPME) method was developed for the determination of three triazine and two phenylurea herbicides in water samples. IL (1-hexyl-3-methylimidazolium hexafluorophosphate [C₆MIM][PF₆]) that dispersed completely into the water solution under controlled temperature was used as the extraction solvent. The analytes were easily concentrated into the ionic liquid phase. This technique combined the process of extraction and concentration of the analytes into one step and avoided use of the more common, toxic organic solvents. The factors affecting the extraction efficiency such as the IL volume, sample pH, extraction time, centrifugal time, dissoluble temperature and ionic strength were optimized. The extracts were analyzed by high-performance liquid chromatography (HPLC) coupled with diode array detector (DAD). Under the optimized conditions, recoveries (50.5–109.1%) were obtained for the target analytes in water samples. The calibration curves were linear and the correlation coefficient ranged from 0.9947 to 0.9973 in the concentration levels of 5–100 μg L^?1. The relative standard deviations (RSDs, n?=?5) were 6.80–10.78%. The limit of detections (LODs) for the five polar herbicides were between 0.46 μg L^?1 and 0.89 μg L^?1.     

Development and Validation of a Column-Switching LC–ESI–MS Assay for Determination of Huperzine A in Rat Plasma and Cerebrospinal Fluid

A simple and rapid method using liquid chromatography-mass spectrometry was developed and applied to determine the concentration of huperzine A in rat plasma or cerebrospinal fluid following a single intravenous injection or nasal administration. The chromatographic separation of the analytes was performed by column switching. A Zorbax SB-C₁₈ pre-column was used as the first column for sample clean-up, and then the analytes were eluted onto a Zorbax SB-C₁₈ column, the second column, and detected by electrospray ionization MS using single ion monitoring in positive mode. Hup B was used as internal standard. Linear calibration curve was achieved over a dynamic range of 0.5–500 ng mL^?1 for Hup A in plasma sample and 0.5–200 ng mL^?1 in CSF sample. The inter- and intra-assay coefficients of variation for the analysis were within ±6.67%. The mean absolute recoveries of Hup A from plasma were between 94.7 and 106.7%.     

Hydrophilic interaction liquid chromatography/positive ion electrospray ionization mass spectrometry method for the quantification of perindopril and its main metabolite in human plasma

A validated method based on liquid chromatography/positive ion electrospray–mass spectrometry (LC-ESI/MS) is described for the quantification of perindopril and its active metabolite, perindoprilat, in human plasma. The assay was based on 500-μL plasma samples, following solid-phase extraction using Oasis HLB cartridges. All analytes and the internal standard (trandolapril) were separated by hydrophilic interaction liquid chromatography using a SeQuant Zic-HILIC analytical column (150.0?×?2.1 mm i.d., particle size 3.5 μm, 200 Å) with isocratic elution. The mobile phase consisted of 10% 5.0 mM ammonium acetate water solution in a binary mixture of acetonitrile/methanol (60:40, v/v) and pumped at a flow rate of 0.10 mL min^?1. Quantitation of the analytes was performed with selected ion monitoring (SIM) in positive ionization mode using electrospray ionization interface. The assay was found to be linear in the concentration range of 5.0–500.0 ng mL^?1 for perindopril and perindoprilat. Intermediate precision were found less than 3.5% over the tested concentration ranges. A run time of less than 6.0 min for each sample made it possible to analyze a large number of human plasma samples per day. The method is the first reported application of HILIC in the analysis of angiotensin-converting enzyme inhibitors and can be used to quantify perindopril and perindoprilat in human plasma covering a variety of pharmacokinetic or bioequivalence studies.