Determination of polychlorinated biphenyls by liquid chromatography–atmospheric pressure photoionization–mass spectrometry

This study presents the atmospheric pressure photoionization (APPI) of high‐chlorinated (five or more chlorine atoms) polychlorinated biphenyls (PCBs) using toluene as dopant, after liquid chromatographic separation. Mass spectra of PCB 101, 118, 138, 153, 180, 199, 206 and 209 were recorded by using liquid chromatography‐APPI‐tandem mass spectrometry (LC‐APPI‐MS/MS) in negative ion full scan mode. Intense peaks appeared at m/z that correspond to [M ? Cl + O]^? ions, where M is the analyte molecule. Furthermore, a detailed strategy, which includes designs of experiments, for the development and optimization of LC‐APPI‐MS/MS methods is described. Following this strategy, a sensitive and accurate method with low instrumental limits of detection, ranging from 0.29 pg for PCB 209 to 8.3 pg for PCB 101 on column, was developed. For the separation of the analytes, a Waters XSELECT HSS T3 (100 mm × 2.1 mm, 2.5 µm) column was used with methanol/water as elution system. This method was applied for the determination of the above PCBs in water samples (surface water, tap water and treated wastewater). For the extraction of PCBs from water samples, a simple liquid–liquid extraction with dichloromethane was used. Method limits of quantification, ranged from 4.8 ng l^?1, for PCB 199, to 9.4 ng l^?1, for PCB 180, and the recoveries ranged from 73%, for PCB 101, to 96%, for PCB 199. The estimated analytical figures were appropriate for trace analysis of high‐chlorinated PCBs in real samples. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparison of release and penetration of tacrolimus ointment reference and trial formulation after dermal application to pigs by liquid chromatography–electrospray ionization tandem mass spectrometry

To investigate the consistency and bioequivalence of tacrolimus ointment reference and trial formulation, the tacrolimus concentrations in blood and skin were determined by HPLC‐ESI‐MS/MS following topical application of two kinds of ointment in porcine skin in a parallel, cross‐over trial. The plasma protein of blood was precipitated by acetonitrile and the tacrolimus in skin was extracted by acetonitrile before HPLC‐ESI‐MS/MS analysis. The internal calibration method (diazepam was the internal standard) was used for quantification analysis (R² > 0.9999), with linear range from 0.05 to 5 ng/mL for blood samples and from 1 to 200 ng/mL for skin samples. The limits of detection for the porcine blood and skin were 0.005 and 0.5 ng/mL, respectively. The average recoveries for the porcine blood and skin spiked at three levels were 97.56–109.53 and 96.48–103.57%, respectively. The precision expressed in RSDs was from 3.43 to 10.83% for porcine blood and from 3.10 to 8.69% for porcine skin. For the same pig, the tacrolimus concentrations and variation with time of the two kinds of ointment in porcine skin were similar, although variation occurred with different individuals. These results showed that the release and penetration of tacrolimus from the reference and trial formulation are similar. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of PCDD/Fs and dioxin-like PCBs in food and feed using gas chromatography-triple quadrupole mass spectrometry

A method was developed on a gas chromatograph coupled to a triple quadrupole mass spectrometer(GC-MS/MS) for trace level determination of polychlorinated dibenzo-p-dioxins/dibenzofurans(PCDD/Fs) and dioxin-like polychlorinated biphenyls(DL-PCBs) in food and feed. The results demonstrated good sensitivity and repeatability for PCDD/Fs and DL-PCBs at an extremely low level(10 pg mL~(-1) for 2,3,7,8-TCDD/F), as well as wide linear response of over 3 or 4 orders of magnitude in concentration ranges; 0.5–200 ng mL~(-1) for PeCDD/F and 0.2–2000 ng mL~(-1) for DL-PCBs. The method detection limits for PCDD/Fs and DL-PCBs were in the range from 0.018–0.17 pg g~(-1) to 0.13–0.36 pg g~(-1), respectively. The performance of the GC-MS/MS for food and feed sample analysis showed high precision and accuracy compared to the high resolution gas chromatograph/high resolution mass spectrometer. The results indicated the feasibility of GC-MS/MS as a confirmatory method for the measurement of PCDD/Fs and DL-PCBs in food and feed as required by European Union legislation.     

Simultaneous Determination of Aluminum,Cadmium and Lead in Whole Blood by Simultaneous Atomic Absorption Spectrometry with Oxygen Charring

A method for the simultaneous determination of aluminum (Al), cadmium (Cd) and lead (Pb) in whole blood has been developed by using simultaneous atomic absorption spectrometry (SIMAAS) with oxygen charring. The optimized conditions for the simultaneous determination of Al, Cd and Pb were obtained in the presence of palladium (Pd) as the chemical modifier, using 600 °C and 2400 °C as the pyrolysis and the atomization temperature, respectively. The whole blood samples were diluted 1+5 (v/v) directly with 0.1% (v/v) Triton X‐100. Oxygen was employed to eliminate the interference of carbonaceous residues in the charring step before pyrolysis. The calibration curves were carried out with aqueous standard solutions and the linear ranges were 0–40 ng mL⁻¹, 0–4 ng mL⁻¹ and 0–40 ng mL⁻¹ for Al, Cd and Pb, respectively. The detection limits were 0.96 ng mL⁻¹ (19.2 pg) for Al, 0.03 ng mL⁻¹ (0.6 pg) for Cd and 0.60 ng mL⁻¹ (12.0 pg) for Pb. The spiked recoveries of Al, Cd and Pb in whole blood were 98.0%, 100.0% and 101.7%, respectively. The accuracy of the proposed method was evaluated with the analysis of a whole blood certified reference material (Seronorm, level 2). The found concentrations were in agreement with the recommended values. The proposed method has been successfully applied to the simultaneous determination of Al, Cd and Pb in whole blood of healthy volunteers before and after eating barbecued foods.     

High‐sensitive LC‐MS/MS method for the simultaneous determination of mirodenafil and its major metabolite,SK‐3541, in human plasma: Application to microdose clinical trials of mirodenafil

A high‐sensitivity LC/MS/MS method was developed and validated for the simultaneous determination of mirodenafil and its major metabolite, SK‐3541, in human plasma. Mirodenafil, SK‐3541, and udenafil as an internal standard were extracted from plasma samples with methyl tert‐butyl ether. Chromatographic separation was performed on a Luna phenyl‐hexyl column (100 × 2.0 mm) with an isocratic mobile phase consisting of 5 mM ammonium formate and ACN (23:77, v/v) at a flow rate of 0.35 mL/min. Detection and quantification were performed using a mass spectrometer in selected reaction monitoring mode with positive ESI at m/z 532.3 → 296.1 for mirodenafil, m/z 488.1 → 296.1 for SK‐3541, and m/z 517.3 → 283.2 for udenafil. The calibration curves were linear over a concentration range of 2–500 pg/mL using 0.5 mL plasma for the microdose of mirodenafil (100 μg). Analytical method validation of the clinical dose (100 mg), with a calibration curve range of 2–500 ng/mL using 0.025‐mL plasma, was also conducted. The other LC‐MS/MS conditions were similar to those used for the microdosing. Each method was applied successfully to pharmacokinetic studies after a microdose or clinical dose of mirodenafil to six healthy Korean male volunteers.     

Development and validation of an LC–MS/MS procedure for environmental monitoring of eight cytostatic drugs in pharmacies

An LC–MS/MS multi-method for the simultaneous determination of the structurally different and frequently used cytostatic drugs 5-fluorouracil, gemcitabine, methotrexate, cyclophosphamide, ifosfamide, etoposide, docetaxel and paclitaxel was developed and validated. In order to perform repeated ambient monitoring in 130 German pharmacies all steps of the monitoring procedure such as sample collection, transport, storage, sample preparation and HPLC–MS/MS analysis have been adapted and optimised. Thus sensitivity and reliability as well as sample throughput were increased. The final method consists of wipe sampling from 900?cm² surfaces and extraction of the tissues with an aqueous pH 3 solution. The limits of quantification range from 3.7 to 37?pg?cm^?2. Validation showed that sampling via the individual pharmacy personnel does not affect the overall results. Recovery rates below 70% were observed on rough surfaces for the taxanes docetaxel and paclitaxel. Likewise, neither the storage nor the shipping conditions affected the results significantly.     

Evaluation of a mixed anionic–nonionic surfactant modified eggshell membrane as an advantageous adsorbent for the solid‐phase extraction of Sudan I–IV as model analytes

The coadsorption of mixed anionic–nonionic surfactants, sodium dodecylbenzenesulfonate with Triton X‐100, on the surface of eggshell membrane was investigated based on adsorption isotherms to improve the solid‐phase extraction performance of eggshell membrane toward organic contaminants. Results showed that even though excess Triton X‐100 might inhibit the adsorption of sodium dodecylbenzenesulfonate, a low dosage of Triton X‐100 can significantly improve sodium dodecylbenzenesulfonate modification and enhance the extraction efficiency of eggshell membrane from 73.7 to 100.4% because of the formation of mixed hemimicelles. The highest recovery was achieved at 2:8 (Triton X‐100/sodium dodecylbenzenesulfonate mass ratios), and multiple mechanisms involving π–π interactions, hydrophobic effect, and π–π electron donor–acceptor interactions contributed to the strong extraction affinity. When mixed, the Triton X‐100 and sodium dodecylbenzenesulfonate modified eggshell membrane packed cartridge coupled with high‐performance liquid chromatography was applied for the simultaneous determination of trace Sudan I–IV, and low detection limits (0.16–0.26 ng/L) were achieved with satisfactory linearity (R ² > 0.999) in 10–10 000 μg/L. For real samples, Sudan II and III in one chilli sauce sample were found at 4.3 and 1.7 μg/kg. Sudan I–IV recoveries at three spiked levels were 87.4–102.9% with precisions <6.8%. Comparison with commonly used solid‐phase extraction adsorbents and methods further reflected the superiorities of the proposed adsorbent in sensitivity, retention ability, and applicability.     

Simultaneous determination of atorvastatin,amlodipine, ramipril and benazepril in human plasma by LC‐MS/MS and its application to a human pharmacokinetic study

A rapid, simple, sensitive and specific LC‐MS/MS method has been developed and validated for the simultaneous estimation of atorvastatin (ATO), amlodipine (AML), ramipril (RAM) and benazepril (BEN) using nevirapine as an internal standard (IS). The API‐4000 LC‐MS/MS was operated under the multiple‐reaction monitoring mode using electrospray ionization. Analytes and IS were extracted from plasma by simple liquid–liquid extraction technique using ethyl acetate. The reconstituted samples were chromatographed on C₁₈ column by pumping 0.1% formic acid–acetonitrile (15:85, v/v) at a flow rate of 1 mL/min. A detailed validation of the method was performed as per the FDA guidelines and the standard curves were found to be linear in the range of 0.26–210 ng/mL for ATO; 0.05–20.5 ng/mL for AML; 0.25–208 ng/mL for RAM and 0.74–607 ng/mL for BEN with mean correlation coefficient of ≥0.99 for each analyte. The intra‐day and inter‐day precision and accuracy results were well with in the acceptable limits. A run time of 2.5 min for each sample made it possible to analyze more than 400 human plasma samples per day. The developed assay method was successfully applied to a pharmacokinetic study in human male volunteers. Copyright © 2010 John Wiley & Sons, Ltd.     

Soapwort (Saponaria officinalis L.) Extract vs. Synthetic Surfactants—Effect on Skin-Mimetic Models

Our skin is continuously exposed to different amphiphilic substances capable of interaction with its lipids and proteins. We describe the effect of a saponin-rich soapwort extract and of four commonly employed synthetic surfactants: sodium lauryl sulfate (SLS), sodium laureth sulfate (SLES), ammonium lauryl sulfate (ALS), cocamidopropyl betaine (CAPB) on different human skin models. Two human skin cell lines were employed: normal keratinocytes (HaCaT) and human melanoma cells (A375). The liposomes consisting of a dipalmitoylphosphatidylcholine/cholesterol mixture in a molar ratio of 7:3, mimicking the cell membrane of keratinocytes and melanoma cells were employed as the second model. Using dynamic light scattering (DLS), the particle size distribution of liposomes was analyzed before and after contact with the tested (bio)surfactants. The results, supplemented by the protein solubilization tests (albumin denaturation test, zein test) and oil emulsification capacity (using olive oil and engine oil), showed that the soapwort extract affects the skin models to a clearly different extent than any of the tested synthetic surfactants. Its protein and lipid solubilizing potential are much smaller than for the three anionic surfactants (SLS, ALS, SLES). In terms of protein solubilization potential, the soapwort extract is comparable to CAPB, which, however, is much harsher to lipids.     

Application of ion mobility spectrometry in study of surfactants adsorbed on different dish surfaces

Sodium lauryl sulfate (SLS) and sodium lauryl ether sulfate (SLES) are commonly used in many dishwashing liquids. These chemicals are adsorbed on the dish surface during the washing process and then transferred to food or drink in the cooking process. In this work, the adsorption of SLS and SLES on different dish surfaces in aqueous solution was studied. Stainless steel, copper, aluminum, Pyrex, Teflon and arcopal china ware were used in this study. The adsorbed chemical remained on the surface after rinsing was measured by thermal desorption using an ion mobility spectrometer as the detector. Although arcopal china ware showed the maximum amount of adsorption, and Pyrex and stainless steel dishes showed the minimum amount of residual chemical, the results showed that the amount of adsorbed chemicals on dish surfaces is less than 428 ng.cm^?2, which is well below the health risk dosage. The released SLS and SLES from dish surfaces into cold or hot water were also measured and compared for different dishes.     

Gold and silver nanoparticles‐based laser desorption/ionization mass spectrometry method for detection and quantification of carboxylic acids

A comparison of ionization efficiency for gold and silver nanoparticles used as an active media of matrix‐less laser desorption/ionization (LDI) mass spectrometry (MS) methods was made for carboxylic acids including fatty acids. The matrix‐assisted laser desorption/ionization (MALDI)‐type targets containing monoisotopic cationic ¹⁰⁹Ag nanoparticles (¹⁰⁹AgNPs) and Au nanoparticles (AuNPs) were used for rapid MS measurements of 10 carboxylic acids of different chemical properties. Carboxylic acids were directly quantified in experiments with 10 000‐fold concentration change conditions ranging from 1 mg/ml to 100 ng/ml which equates to 1 μg to 100 pg of carboxylic acids per measurement spot.     

Rapid simultaneous determination of codeine and morphine in plasma using LC‐ESI‐MS/MS: Application to a clinical pharmacokinetic study

A rapid and sensitive high‐performance LC‐MS/MS method was developed and validated for the simultaneous quantification of codeine and its metabolite morphine in human plasma using donepezil as an internal standard (IS). Following a single liquid‐liquid extraction with ethyl acetate, the analytes were separated using an isocratic mobile phase on a C₁₈ column and analyzed by MS/MS in the selected reaction monitoring mode using the respective [M+H]⁺ ions, mass‐to‐charge ratio (m/z) 300/165 for codeine, m/z 286/165 for morphine and m/z 380/91 for IS. The method exhibited a linear dynamic range of 0.2–100/0.5–250 ng/mL for codeine/morphine in human plasma, respectively. The lower LOQs were 0.2 and 0.5 ng/mL for codeine and its metabolite morphine using 0.5 mL of human plasma. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 300 human plasma samples per day. The validated LC‐MS/MS method was applied to a pharmacokinetic study in which healthy Chinese volunteers each received a single oral dose of 30 mg codeine phosphate.     

Simultaneous determination of sesquiterpene lactones isoalantolactone and alantolactone isomers in rat plasma by liquid chromatography with tandem mass spectrometry: Application to a pharmacokinetic study

A selective, sensitive, and accurate LC–MS/MS method for the simultaneous determination of isoalantolactone and alantolactone in rat plasma has been developed using psoralen as the internal standard. LC–MS/MS analysis was carried out on a Triple Quadrupole mass spectrometer using positive ion ESI and the selected reaction monitoring mode. The assays were linear in the range of 7.5–750 ng/mL for isoalantolactone and 5.5–550 ng/mL for alantolactone. The average recoveries in plasma samples both were better than 85%. The intra‐ and inter‐day precision and accuracy values were found to be within the assay variability criteria limits according to the US FDA guidelines. The method was successfully applied to pharmacokinetic studies of the two structural isomers after an intravenous injection of Inula helenium formulation to rats.     

Development of a stable isotope dilution UPLC‐MS/MS method for quantification of dexmedetomidine in a small amount of human plasma

Dexmedetomidine (Dex) is a selective central α2‐agonist with anesthetic properties and has been used in clinical practice for sedation in the intensive care unit (ICU) after operations. In this study, an analytical assay for the determination of Dex in a small amount of plasma was developed for the application to pediatric ICU trials. The quantification of Dex was constructed using the original stable isotope Dex‐d₃ for electrospray ionization‐tandem mass spectrometry (ESI‐MS/MS) in the selected reaction monitoring mode. A rapid ultra‐performance liquid chromatography technique was adopted using ESI‐MS/MS with a runtime of 3 min. Efficacious concentration levels (50 pg/mL to 5 ng/mL) could be evaluated using a very small amount of plasma (10 μL) from patients. The lower limit of the quantification was 5 pg/mL in the plasma (100 µL). For sample preparation, a solid‐phase extraction was used along with the OASIS‐HLB cartridge type. Recovery values ranged from 98.8 to 100.3% for the intra‐ [relative standard deviation (RSD), 0.9–1.3%] and inter‐ (RSD, 0.9–1.5%) day assays. A stable test had recovery values that ranged from 97.8 to 99.7% with an RSD of 1.0–1.9% for the process/wet extract, bench‐top, freeze–thaw and long‐term tests. This method was used to measure the Dex levels in plasma from pediatric ICU patients. In the clinical ICU trial, the small amount of blood (approximate plasma volume, 200 μL) remaining from blood gas analysis was reused and targeted for the clinical analysis of Dex in plasma. Copyright © 2013 John Wiley & Sons, Ltd.     

The development and validation of a high‐throughput LC–MS/MS method for the analysis of endogenous β‐hydroxy‐β‐methylbutyrate in human plasma

A high‐throughput, sensitive, and rugged liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the rapid quantitation of β ‐hydroxy‐β ‐methylbutyrate (HMB) in human plasma has been developed and validated for routine use. The method uses 100 μL of plasma sample and employs protein precipitation with 0.1% formic acid in methanol for the extraction of HMB from plasma. Sample extracts were analyzed using LC–MS/MS technique under negative mode electrospray ionization conditions. A ¹³C–labeled stable isotope internal standard was used to achieve accurate quantitation. Multiday validation was conducted for precision, accuracy, linearity, selectivity, matrix effect, dilution integrity (2×), extraction recovery, freeze–thaw sample stability (three cycles), benchtop sample stability (6 h and 50 min), autosampler stability (27 h) and frozen storage sample stability (146 days). Linearity was demonstrated between 10 and 500 ng/mL. Inter‐day accuracies and coefficients of variation (CV) were 91.2–98.1 and 3.7–7.8%, respectively. The validated method was proven to be rugged for routine use to quantify endogenous levels of HMB in human plasma obtained from healthy volunteers.     

Multi-Matrix Approach for the Analysis of Bicalutamide Residues in Oncology Centers by HPLC–FLD

Cytostatics are toxic pharmaceuticals, whose presence in surfaces puts healthcare workers at risk. These drugs might also end up in hospital effluents (HWW), potentially damaging aquatic ecosystems. Bicalutamide is a cytostatic extensively consumed worldwide, but few analytical methods exist for its quantification and most of them require advanced techniques, such as liquid chromatography mass spectrometry (LC-MS), which are very complex and expensive for large monitoring studies. Therefore, a simple but reliable multi-matrix high performance liquid chromatographic method, with fluorescence detection, was developed and validated to rapidly screen abnormal concentrations of bicalutamide in HWW and relevant contamination levels of bicalutamide in indoor surfaces (>100 pg/cm²), prior to confirmation by LC-MS. The method presents good linearity and relatively low method detection limits (HWW: 0.14 ng/mL; surfaces: 0.28 pg/cm²). Global uncertainty was below 20% for concentrations higher than 25 ng/mL (HWW) and 50 pg/cm² (surfaces); global uncertainty was little affected by the matrix. Therefore, a multi-matrix assessment could be achieved with this method, thus contributing to a holistic quantification of bicalutamide along the cytostatic circuit. Bicalutamide was not detected in any of the grab samples from a Portuguese hospital, but an enlarged sampling is required to conclude about its occurrence and exposure risks.     

Novel aspects of quantitation of immunogenic wheat gluten peptides by liquid chromatography–mass spectrometry/mass spectrometry

A novel, specific and sensitive non-immunological liquid chromatography–mass spectrometry (LC–MS) based assay has been developed to detect and quantify trace levels of wheat gluten in food and consumer products. Detection and quantification of dietary gluten is important, because gluten is a principle trigger of a variety of immune diseases including food allergies and intolerances. One such disease, celiac sprue, can cause intestinal inflammation and enteropathy in patients who are exposed to dietary gluten. At present, immunochemistry is the leading analytical method for gluten detection in food. Consequently, enzyme-linked immunosorbent assays (ELISAs), such as the sandwich or competitive type assays, are the only commercially available methods to ensure that food and consumer products are accurately labeled as gluten-free. The availability of a comprehensive, fast and economic alternative to the immunological ELISA may also facilitate research towards the development of new drugs, therapies and food processing technologies to aid patients with gluten intolerances and for gluten-free labeling and certification purposes. LC–MS is an effective and efficient analytical technique for the study of cereal grain proteins and to quantify trace levels of targeted dietary gluten peptides in complex matrices. Initial efforts in this area afforded the unambiguous identification and structural characterization of six unique physiologically relevant wheat gluten peptides. This paper describes the development and optimization of an LC–MS/MS method that attempts to provide the best possible accuracy and sensitivity for the quantitative detection of trace levels of these six peptides in various food and consumer products. The overall performance of this method was evaluated using native cereal grains. Experimental results demonstrated that this method is capable of detecting and quantifying select target peptides in food over a range from 10 pg/mg to 100 ng/mg (corresponding to approximately 0.01–100 ppm). Limits of detection (LOD) and quantification (LOQ) for the six target peptides were determined to range from 1 to 30 pg/mg and 10–100 pg/mg respectively. Reproducibility of the assay was demonstrated by evaluation of calibration data as well as data collected from the analysis of quality control standards over a period of four consecutive days. The average coefficient of determination (R²) for each peptide was consistently found to be >0.995 with residuals ranging from approximately 80% to 110%. Spike recovery data for each peptide in various matrices was evaluated at a concentration level near the approximate LOQ for each, as well as at higher concentration levels (30 and 60 ng/mg). The average range of accuracy of detection for all peptides at the lower concentration level was determined to be 90% (±11), while accuracy at the 30 and 60 ng/mg levels was 98% (±5%) and 98% (±3%), respectively. The usefulness and capabilities of this method are presented in a practical application to prospectively screen a variety of common commercially available (native and processed) gluten-containing and gluten-free foods and products.     

Fundamental properties of a touchable high‐power pulsed microplasma jet and its application as a desorption/ionization source for ambient mass spectrometry

Plasma‐based ambient desorption/ionization mass spectrometry (ADI–MS) has attracted considerable attention in many fields because of its capacity for direct sample analyses. In this study, a high‐power pulsed microplasma jet (HPPMJ) was developed and investigated as a new plasma desorption/ionization source. In an HPPMJ, a microhollow cathode discharge is generated in a small hole (500 µm in diameter) using a pulsed high‐power supply. This system can realize a maximum power density of 5 × 10⁸ W/cm³. The measured electron number density, excitation temperature and afterglow gas temperature of the HPPMJ were 3.7 × 10¹⁵ cm^‐3, 7000 K at maximum and less than 60 °C, respectively, which demonstrate that the HPPMJ is a high‐energy, high‐density plasma source that is comparable with an argon inductively coupled plasma while maintaining a low gas temperature. The HPPMJ causes no observable damage to the target because of its low gas temperature and electrode configuration; thus, we can apply it directly to human skin. To demonstrate the analytical capacity of ADI–MS using an HPPMJ, the plasma was applied to direct solid sample analysis of the active ingredients in pharmaceutical tablets. Caffeine, acetaminophen, ethenzamide, isopropylantipyrine and ibuprofen were successfully detected. Application to living tissue was also demonstrated, and isopropylantipyrine on a finger was successfully analyzed without damaging the skin. The limits of detection (LODs) for caffeine, isopropylantipyrine and ethenzamide were calculated, and LODs at the picogram level were achieved. These results indicate the applicability of the HPPMJ for high‐sensitivity analysis of materials on a heat‐sensitive surface. Copyright © 2014 John Wiley & Sons, Ltd.     

Simultaneous analysis of ten low‐molecular‐mass organic acids in the tricarboxylic acid cycle and photorespiration pathway in Thalassiosira pseudonana at different growth stages

A method using high‐performance liquid chromatography coupled with tandem mass spectrometry was developed for the simultaneous determination of organic acids in microalgae. o‐Benzylhydroxylamine was used to derivatize the analytes, and stable isotope‐labeled compounds were used as internal standards for precise quantification. The proposed method was evaluated in terms of linearity, recovery, matrix effect, sensitivity, and precision. Linear calibration curves with correlation coefficients >0.99 were obtained over the concentration range of 0.4–40 ng/mL for glycolic acid, 0.1–10 ng/mL for malic acid and oxaloacetic acid, 0.02–2 ng/mL for succinic acid and glyoxylic acid, 4–400 ng/mL for fumaric acid, 20–2000 ng/mL for isocitric acid, 2–200 ng mL⁻¹ for citric acid, 100–10000 ng mL⁻¹ for cis‐aconitic acid, and 1–100 ng mL⁻¹ for α‐ketoglutaric acid. Analyte recoveries were between 80.2 and 115.1%, and the matrix effect was minimal. Low limits of detection (0.003–1 ng/mL) and limits of quantification (0.01–5 ng/mL) were obtained except cis‐aconitic acid. Variations in reproducibility for standard solution at three different concentrations levels were <9%. This is the first report of the simultaneous analysis of ten organic acids in microalgae, which promotes better understanding of their growth state and provides reference value for high‐yield microalgae cultures.     

Selected ion storage versus tandem MS/MS for organochlorine pesticides determination in drinking waters with SPME and GC-MS

The use of two modes for mass spectrometry (MS) detection with an ion trap instrument, selected ion storage (SIS) and tandem mass spectrometry (MS/MS), are compared for the solid-phase microextraction (SPME)–gas chromatography (GC) coupled to mass spectrometry (GC-MS) determination of 16 priority organochlorine pesticides (OCPs) in drinking water samples at the ultratrace levels (ng?L^?1) required by official guidelines in the European legislation. Experimental parameters investigated for the SPME sample preparation were: the type of coating (100?µm polydimethylsiloxane, PDMS, and 65?µm poly(dimethylsiloxane)–divinylbenzene, PDMS/DVB), SPME modality, extraction and desorption times and desorption temperature and the methanol percentage in the SPME working solution. Under the calculated optimal conditions two methodologies were developed, one for SIS and the other for MS/MS modes. The detection limits, precision and accuracy were evaluated for both alternatives and were appropriate to the official guidelines requirements. The SPME–GC-MS(SIS) methodology offered LODs from 0.2–6.6?ng?L^?1, precision below 13% and recoveries between 83 and 110%. The SPME–GC–MS/MS methodology provided limits of detection (LODs) ranging from 0.3 to 7.6 ng?L^?1, % RSD were ≤14% and recoveries of 79–108% were achieved. After the results observed within an Interlaboratory Exercise, the latest MS methodology was selected for the pursued analysis in real drinking water samples. Also, the good results in this round-robin exercise validate the proposed SPME–GC–MS/MS methodology.