Weak Anion Exchange Solid-phase Extraction Research Articles

A Fast and Simple Solid Phase Extraction-Based Method for Glucosinolate Determination: An Alternative to the ISO-9167 Method.

Glucosinolates (GLSs) are a well-studied sulfur-containing compound found in Brassicaceae plants that play critical roles in plant resistance and human health. Correctly identifying and reliably quantifying the total and individual GLS content is of great importance. An improved method as an alternative to the ISO 9167-1 (ISO) method is developed in the present study. An efficient extraction and purification procedure is proposed with a commercially available dimethylaminopropyl (DEA)-based weak anion exchange solid-phase extraction (SPE) cartridge instead of using the self-prepared ion-exchange columns in the ISO method. The GLSs are identified and quantified by ultra high-performance liquid chromatography (UHPLC) high-resolution mass spectrometry (HRMS). The method demonstrates a comparable quantification of total and individual GLSs on certified rapeseeds and other Brassicaceae vegetables when compared to the ISO method. The developed SPE method is simpler and more efficient, thus allowing for applications to a large sample size with reduced analysis time, improved repeatability and accuracy, and possible automation.

A Rapid Derivatization for Quantitation of Perfluorinated Carboxylic Acids from Aqueous Matrices by Gas Chromatography-Mass Spectrometry.

Ultrashort-chain perfluorinated carboxylic acids (PFCAs) are receiving more attention due to their ever-increasing presence in the environment. Methods have been established for the analysis of short- and long-chain PFCAs, while robust quantitation of ultrashort-chain species is scarce. Here, we develop a novel derivatization method using diphenyl diazomethane for quantitation of C2-C14 PFCAs in aqueous matrices. The method is highlighted by rapid completion of derivatization (<1 min) and retention and separation of ultrashort-chain (C2/C3) PFCA derivatives using H2 carrier gas (R > 1.5). A weak anion exchange solid-phase extraction procedure for analyte recovery from representative aqueous samples was developed and validated by spike and recovery from ultrapure water, synthetic ocean water, and simulated denuder extracts used for collecting gaseous PFCAs. Recoveries for PFCAs ranged from 83 to 130% for the majority of analytes and matrices. The instrument detection limits (IDLs) range from 8 to 220 fg per injection, and method detection limits (MDLs) range from 0.06 to 14.6 pg/mL for 500 mL aqueous samples, which are within an order of magnitude to conventional LC-MS/MS methods. The method was applied to the analysis of real samples of tap water, rainwater, ocean water, and annular denuder extracts. The overall method provides a cost-effective alternative to conventional LC-MS/MS methods, overcoming the typical GC-MS drawbacks of high detection limits and long sample preparation times while being able to simultaneously analyze the complete spectrum of environmentally relevant PFCAs.

High-resolution mass spectrometry-based strategies for the target analysis and suspect screening of per- and polyfluoroalkyl substances in aqueous matrices

Per- and polyfluoroalkyl substances (PFASs) are a man-made diverse group of highly fluorinated aliphatic molecules, entailing risks to the ecosystems and human health. Herein, a streamlined, single-shot, HRMS-based analytical workflow for the quantitation and suspect screening of various PFAS was developed. Sample preparation was based on weak-anion exchange solid phase extraction, while instrumental analysis was performed by highly sensitive liquid chromatography Orbitrap–high-resolution mass spectrometry. The target method was optimized and validated for drinking water, surface water, and wastewater, while it was also modified to be efficient for leachates. Method performance was excellent in terms of linearity (R2 > 0.99), detection/quantification limits (reaching even at pg L−1 scale), recoveries (70–108 %, for most of the compounds), and precision (<20%). Isotopically labelled internal standards and matrix-matched calibration curves were used for quantification. The suspect analysis performed on a single-stage HRMS method operating in data-dependent ‘discovery’ mode. Thus, content-rich spectra were acquired and once combined with suspect screening features such as peak picking, feature alignment, and compound annotation enabled the putative annotation of the tested PFAS with high confidence. After evaluation, the presented fully elaborated workflow was applied to real samples to explore the putative annotation of the tested PFAS with high confidence for the first time in Greece for five different matrices, revealing maximum concentrations for PFOS 1.5 ng L−1 in tap water and 394.4 ng L−1 in effluent wastewater, and PFHxA 4284.8 ng L−1 in leachates.

Membrane Sampling Separates Naphthenic Acids from Biogenic Dissolved Organic Matter for Direct Analysis by Mass Spectrometry.

Oil sands process waters can release toxic naphthenic acids (NAs) into aquatic environments. Analytical techniques for NAs are challenged by sample complexity and interference from naturally occurring dissolved organic matter (DOM). Herein, we report the use of a poly(dimethylsiloxane) (PDMS) polymer membrane for the on-line separation of NAs from DOM and use direct infusion electrospray ionization mass spectrometry to yield meaningful qualitative and quantitative information with minimal sample cleanup. We compare the composition of membrane-permeable species from natural waters fortified with a commercial NA mixture to those derived from weak anion exchange solid-phase extraction (SPE) using high-resolution mass spectrometry. The results show that SPE retains a wide range of carboxylic acids, including biogenic DOM, while permeation through PDMS was selective for petrogenic classically defined NAs (CnH2n+zO2). A series of model compounds (log Kow ∼1–7) were used to characterize the perm-selectivity and reveal the separation is based on hydrophobicity. This convenient sample cleanup method is selective for the O2 class of NAs and can be used prior to conventional analysis or as an on-line analytical strategy when coupled directly to mass spectrometry.

Use of liquid chromatography-tandem mass spectrometry for foscarnet quantification in human serum and cerebrospinal fluid.

Foscarnet (FCV) is used to treat cytomegalovirus, human herpesvirus, and human immunodeficiency virus infections. It is a low-molecular-weight compound containing carboxylate and phosphate groups. There are no reports on the use of liquid chromatography-tandem mass spectrometry (LC/MS/MS) to analyze FCV via bioanalysis. In the present study, we developed the ion-pair LC/MS/MS method to analyze FCV in human serum and cerebrospinal fluid (CSF). FCV was extracted from human serum and CSF by weak anion exchange (WAX) solid-phase extraction. The LC/MS/MS systems were coated with 0.1% phosphoric acid in methanol to avoid nonspecific absorption. FCV was detected using ion-pair LC/MS/MS with dibutylammonium acetate. Selected reaction monitoring transition of FCV in the negative ion mode was selected at m/z 125.1 → 62.9. FCV was selectively detected in human serum and CSF, and the liner range was 5-1000 μM (R2 = 0.99). The intraday and interday accuracy and precision were within ±15%. FCV was constantly extracted from human serum and CSF by WAX solid-phase extraction (recovery ratio = 76.0-77.9%). No matrix effect was observed. A robust LC/MS/MS method to analyze FCV was successfully developed. FCV was selectively measured using LC/MS/MS in very low extract volumes (20 μL). The method will be useful in evaluating the FCV level in human serum and CSF.

Purification and Analysis of Nucleotides and Nucleosides from Plants.

This protocol describes necessary steps to isolate and quantify nucleotides and nucleosides from plant samples. Proper sample preparation in combination with liquid chromatography coupled to mass spectrometry enables the sensitive detection and quantification of metabolites of low abundance. Utilizing a liquid-liquid extraction in combination with a weak anion-exchange solid phase extraction enables the separation of negatively charged molecules from uncharged metabolites or cations.

Developments in Molecular Level Characterization of Naphthenic Acid Fraction Compounds Degradation in a Constructed Wetland Treatment System

The reclamation of oil sands process-affected water (OSPW) is a matter of environmental importance because of the aquatic toxicity to biota. This study describes refinements in advanced analytical methods to assess the performance of biological treatment systems for OSPW, such as constructed wetland treatment systems (CWTSs). Assessment of treatment efficiency by measurement of the degradation of naphthenic acid fraction compounds (NAFCs) in OSPW is challenging in CWTS due to potentially interfering constituents such as humic acids, organic acids, salts, and hydrocarbons. Here we have applied a previous weak anion exchange (WAX) solid-phase extraction (SPE) method and high-resolution Orbitrap-mass spectrometry (MS) to remove major interferences from the NAFC analysis. The refinements in data processing employing principal component analysis (PCA) indicates that the relative abundance of NAFCs decreased with time in the treated OSPW relative to the untreated OSPW. The most saturated NAFCs with higher carbon numbers were relatively more degraded as compared to unsaturated NAFCs. The use of Kendrick plots and van Krevelen plots for assessment of the performance of the CWTS is shown to be well-suited to detailed monitoring of the complex composition of NAFCs as a function of degradation. The developments and application of analytical methods such as the WAX SPE method and high-resolution Orbitrap-MS are demonstrated as tools enabling the advancement of CWTS design and optimization, enabling passive or semi-passive water treatment systems to be a viable opportunity for OSPW treatment.

High-Throughput and Sensitive Analysis of Free and Total 8-Isoprostane in Urine with Isotope-Dilution Liquid Chromatography-Tandem Mass Spectrometry.

Oxidative stress (OS) plays a major role in the pathogenesis of various diseases in humans. OS is a result of an imbalance between reactive oxygen species (ROS) and the biologically available antioxidants that prevent or repair damage that ROS inflict on the host cells. ROS are naturally generated during normal mitochondrial respiration and by oxidative burst during the immune response. Many factors may influence OS, including genetics, diet, exercise, and exposure to environmental toxicants (e.g., tobacco smoke). A nonenzymatic peroxidation product of arachidonic acid (AA), 8-iso-PGF2α (8-isoprostane), is a validated biomarker of OS that is present in urine as both glucuronide conjugate and free acid. Previous studies report that the conjugated forms of 8-isoprostane can vary between 30 and 80% of the total 8-isoprostane levels. By hydrolyzing the conjugated forms, it is possible to obtain a total (free + conjugated) measurement of 8-isoprostane in urine samples. Here, we describe a robust, automated, and high-throughput method for measuring total urinary 8-isoprostane using a polymeric weak anion-exchange solid-phase extraction (SPE) and isotope-dilution ultrahigh performance liquid chromatography electrospray ionization–tandem mass spectrometry (UHPLC–MS/MS). This method, using a 96-well plate platform, showed good sensitivity (8.8 pg/mL LOD) and used only 400 μL of the sample volume with a cycle time of 11 min. The inter- and intraday precision, calculated from 20 repeated measurements of two quality control pools, varied from 4 to 10%. Accuracy, calculated from the recovery percentage at three spiking levels, ranged from 92.7 to 106.7%. We modified this method to allow for the exclusive measurement of free 8-isoprostane by removing the hydrolysis step. We measured both free and total 8-isoprostane in urine collected from 30 cigarette smokers (free: 460 ± 78.8 pg/mL; total: 704 ± 108 pg/mL) and 30 nonusers of tobacco products (free: 110 ± 24.2 pg/mL; total: 161 ± 38.7 pg/mL). This method is robust, accurate, and easily adaptable for large population studies.

Detection of in utero ethanol exposure via ethyl glucuronide and ethyl sulfate analysis in umbilical cord and placenta

Alcohol exposure during pregnancy constitutes one of the leading preventable causes of birth defects, mental retardation and neurodevelopmental disorders in the exposed children. The ethanol marker ethyl glucuronide (EtG) is a specific long-term marker of ethanol in utero exposure in meconium; however, currently, there are scarce or no data about EtG and ethyl sulfate (EtS) in umbilical cord and placenta. These tissues are alternative matrices to meconium that offer critical advantages, such as always being available at birth with noninvasive and easy collection. We developed and validated a method for the determination of EtG and EtS in umbilical cord and placenta. Tissues were homogenized in methanol, extracted using weak anion-exchange solid-phase extraction (SPE) and analyzed by liquid chromatography–tandem mass spectrometry. The umbilical cord and placenta method was applied to 59 authentic samples from newborns whose meconium samples were positive for EtG (EtG > 5 ng/g). The method in umbilical cord and placenta was fully validated, with a limit of quantification at 5 ng/g in umbilical cord and 10 ng/g in placenta for both compounds. EtG and/or EtS were detected in 25 umbilical cord samples (4.4–529 and 4.3–39 ng/g, respectively) and in 8 placenta samples (26.5–267 and 11–24.3 ng/g, respectively). EtG and EtS showed a homogenous distribution throughout umbilical cord tissue (n = 5). We developed and validated a sensitive and specific method for the determination of EtG and EtS in umbilical cord and placenta. To date, this is the first method to investigate both direct metabolites of ethanol in umbilical cord and placenta samples for prenatal ethanol exposure.

Determination of Acidic Dyes in Pharmaceutical Capsules by Solid-Phase Extraction and High-Performance Liquid Chromatography

ABSTRACTA rapid and simple method was established for the determination of acidic dyes in pharmaceutical capsules using solid-phase extraction and high-performance liquid chromatography with a diode array detector. The capsules were dissolved in water using an ultrasonic bath at 55 ± 5°C, and pH was adjusted to 1 with 0.2 mol/L hydrochloric acid. The resulting solution was purified using a weak anion exchange solid-phase extraction cartridge. Chromatographic separation was performed on a reversed phase C18 column with gradient elution using acetonitrile and 20 mmol/L aqueous ammonium acetate (pH = 4.5) as the mobile phase. The chromatography was monitored at 420, 480, 520, and 600 nm. Under the optimized conditions, the recoveries of the analytes were from 60.5 ± 1.59 to 99.1 ± 0.84%. The intraday and interday relative standard deviations were from 0.29 to 10.6% and from 1.08 to 10.8%, respectively. The limits of quantification were between 0.11 and 0.50 µg/g.

Trace enrichment and characterization of polyphenols in Bistort Rhizoma using weak anion-exchange solid phase extraction and high performance liquid chromatography-quadrupole time-of-flight mass spectrometry

The analysis of trace constituents in herbal medicines has always been a challenge due to complex matrices and structural diversities. In this work, a pH-sensitive solid phase extraction (SPE) procedure capable of enriching trace polyphenols in Bistort Rhizoma (BR) was proposed and preliminary chemical characterization was accomplished by high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-QTOF MS). A weak anion-exchange SPE column packed with divinylbenzene/vinylpyrrolidone bonding quaternary amine group was employed for anionic extraction, and the target fraction was obtained by eluting with acidic methanol (apparent pH 1.9). On the other hand, the MS/MS fragmentation rules of four reference polyphenols in negative ion mode were outlined. Using these rules, a total of 31 polyphenols including 20 benzoyl derivatives and 11 caffeoyl derivatives were screened out from BR extract, of which 26 trace members were found for the first time in this herb. Those findings demonstrated that the anion-exchange SPE could enhance the detection capability and selectivity for plant polyphenols in the LC–MS analysis and the strategy for deducing structures could be applied for analysis of polyphenols in BR and other herbal medicines.

Determination of Perfluorochemicals in Cow’s Milk Using Liquid Chromatography-Tandem Mass Spectrometry

This study describes a new method developed for detection of 10 different perfluorochemicals (PFCs) in cow's milk, seven perfluorinated carboxylates and three perfluorinated sulfonate salts. After attempting multiple methods employing both acidic and basic extractions, a basic extraction using 10 mM sodium hydroxide in methanol digestion along with weak anion-exchange solid-phase extraction was employed. Vortex mixing and varying sonication times were compared as part of sample processing. Results show that sonication during sample processing yield decreased recovery of longer chain perfluorinated carboxylates. The final method developed was used to determine the concentration of PFCs in 12 raw and 49 retail milk samples from across the United States. With the exception of a single raw milk sample obtained from a dairy farm that had applied PFC containing biosolids to its fields, there were no milk samples containing PFCs.

Analysis of perfluorinated phosponic acids and perfluorooctane sulfonic acid in water, sludge and sediment by LC–MS/MS

Residues of perfluorinated phosphonic acids (PFPAs) and perfluorooctane sulfonic acid (PFOS) were investigated in various Dutch surface waters, sludge and sediments. For this purpose, a liquid chromatographic (LC) method was optimized by testing several columns with different mobile phases. Atmospheric pressure chemical ionization (APCI) was chosen for the LC tandem mass spectrometry (MS/MS) analysis. An ion-pair reagent was added to the injection solvent to improve peak shape. Different solvents were studied for the extraction from solid samples. For clean-up and pre-concentration, weak anion-exchange solid-phase extraction cartridges were used. Water samples were extracted using the same cartridges. The method was used for screening PFPAs in the Dutch aquatic environment. PFPAs were not observed in sediment or sludge samples. PFOPA was found at 1ngL−1 in one surface water sample. PFOS was found at levels between 0.07ngg−1 and 48ngg−1 (dry weight) in sediments and sewage sludge samples. PFOS concentrations in surface water ranged from 3.3ngL−1 to 25.4ngL−1.

Sensitive determination of domoic acid in shellfish by on-line coupling of weak anion exchange solid-phase extraction and liquid chromatography–diode array detection–tandem mass spectrometry

An automated method based on the use of on-line solid-phase extraction (SPE) coupled to liquid chromatography with diode array detection and tandem mass spectrometry (LC–DAD–MS/MS) has been developed for the determination of domoic acid in shellfish. The on-line coupling of SPE and liquid chromatography was accomplished by a column switching approach. A weak anion exchange (WAX) sorbent was selected for the SPE procedure, allowing a selective cleanup of shellfish extracts. High sensitivity was achieved by on-line pre-concentration of large volume injections (50–1000μL). A simple protein precipitation cleanup with acetone was used to efficiently remove proteins from shellfish extracts, preventing possible column clogging during chromatographic separation.The proposed method showed good performance in terms of linearity, limits of detection (LODs), precision and accuracy. Quantitative recovery and satisfactory inter-day precision (RSD ⩽7%) was achieved. LODs in the in the sub-nanogram per gram level (0.23–0.32ngg−1) were obtained with MS/MS detection. Matrix effects were assessed by post-extraction addition method and no signal enhancement or suppression was observed during MS detection.This method was successfully applied to the determination of domoic acid in several shellfish samples, including scallops, oysters, mussels, Manila clams, common cockles and razor clams.

Analysis of perfluorinated alkyl substances in Spanish sewage sludge by liquid chromatography–tandem mass spectrometry

The present article describes the development of an analytical method for the determination of 13 perfluorinated alkyl substances (PFAS), as well as its application to real sewage sludge samples to confirm the presence of these compounds. The isolation of the analytes was performed by agitation, sonication and centrifugation techniques, followed by EnviCarb cleanup and weak anion exchange solid-phase extraction. Sensitive and selective determination was carried out by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Six mass-labelled internal standards were used to ensure the accuracy of the analytical results following isotopic dilution method. Several mobile phases (acetonitrile, methanol, mixtures of both and water with ammonium acetate or acetic acid) have been tested to reach the best resolution and reproducibility results. Other parameters related to MS/MS conditions were optimized. The reliability of the method was confirmed by the evaluation of linearity (R(2) = 0.995-0.999), accuracy (84-99%) and injection repeatability and reproducibility (relative standard deviation below 19 and 23%, respectively). Limits of detection ranged from 0.007 to 2.217 pg. Recoveries show values higher than 80% for most of the target compounds. The application of this method to twenty real samples demonstrates its efficiency and accuracy, as well as provides for the first time to our knowledge, PFAS levels in sewage sludges from Spain.

Perfluorinated phosphonic acids in Canadian surface waters and wastewater treatment plant effluent: Discovery of a new class of perfluorinated acids

The environmental prevalence of a new class of perfluorinated acids, the perfluorinated phosphonic acids (PFPAs), was determined in Canadian surface waters and wastewater treatment plant (WWTP) effluent. For quality control and comparison, the C8- to C11-perfluorinated carboxylic acids and perfluorooctane sulfonic acid were included in the analysis. Water samples were extracted using weak anion-exchange solid-phase extraction cartridges. Perfluorinated phosphonic acids were observed in 80% of surface water samples and in six of the seven WWTP effluent samples. The C8-PFPA was observed at concentrations ranging from 88 +/- 33 to 3400 +/- 900 pg/L in surface waters and from 760 +/- 270 to 2500 +/- 320 pg/L in WWTP effluent. To our knowledge, this is the first observation of PFPAs in the environment. Given their structural similarities with perfluorinated carboxylic and sulfonic acids, PFPAs are expected to be persistent. The observation of PFPAs in the majority of samples analyzed here suggests they are prevalent environmental contaminants and should be considered in future environmental monitoring campaigns to better understand the total burden of fluorinated materials in the environment.

Isolation and quantification by high-performance liquid chromatography–ion-trap mass spectrometry of androgen sulfoconjugates in human urine

Together with steroid glucuronides, sulfoconjugates may be used as markers of steroid administration as well as endogenous steroid production. A fast and sensitive analytical procedure has been developed for the simultaneous separation, determination and quantification of sulfate and glucuronide derivatives of testosterone (T), epitestosterone (E), androsterone (A), etiocholanolone (Etio) and dehydroepiandrosterone (DHEA) in human urine. First, a weak anion-exchange solid-phase extraction support (SPE Oasis WAX) was used for complete and rapid separation of sulfates and glucuronides in two extracts after loading of urine sample (2 mL). Then sulfates were analyzed directly by high-performance liquid chromatography–ion-trap mass spectrometry (LC–MS/MS) with electrospray ionization in negative mode. Chromatographic separation of the targeted sulfoconjugates was achieved using a Waters XBridge C 18 column (150 mm × 4.6 mm I.D., 5 μm) with gradient elution. Assay validation demonstrated good performance for instance for T sulfate (TS) and E sulfate (ES) in terms of trueness (89–107%), repeatability (3.4–22%) and intermediate precision (5.8–22%) over the range of 2–200 ng/mL (corresponding to 1.5–147 ng/mL as free steroids). Results obtained on biological samples demonstrated the suitability of this analytical strategy for direct measurement of androgen sulfoconjugates and glucuroconjugates in human urine.

Determination of S-Adenosylmethionine and S-Adenosylhomocysteine in Plasma and Cerebrospinal Fluid by Stable-Isotope Dilution Tandem Mass Spectrometry

Available methods for the determination of nanomolar concentrations of S:-adenosylmethionine (SAM) and S:-adenosylhomocysteine (SAH) in plasma and cerebrospinal fluid (CSF) are time-consuming. We wished to develop a method for their rapid and simultaneous measurement. We used tandem mass spectrometry (MS/MS) for the simultaneous determination of SAM and SAH, with stable-isotope-labeled internal standards. The (13)C(5)-SAH internal standard was enzymatically prepared using SAH-hydrolase and [(13)C(5)]adenosine. The method comprises a weak anion-exchange solid-phase extraction procedure serving as clean-up step for the deproteinized plasma and CSF samples. After clean-up, samples were injected on a C(18) HPLC column, which was connected directly to the tandem mass spectrometer, operating in MS/MS mode. In plasma samples, the intraassay CVs for SAM and SAH were 4.2% and 4.0%, respectively, and the interassay CVs were 7.6% and 5. 9%, respectively. In CSF, the intraassay CVs for SAM and SAH were 6. 8% and 6.9%, respectively, and the interassay CVs were 4.2% and 5.5%, respectively. Mean recovery of SAM and SAH for both matrices at two concentrations was 93%. Detection limits for SAM and SAH in samples were 7.5 and 2.5 nmol/L, respectively. Concentrations of SAM and SAH in plasma from healthy subjects were within the previously reported ranges. In 10 CSF samples, the mean concentrations (range) were 248 (137-385) nmol/L for SAM and 11.3 (8.9-14.1) nmol/L for SAH. SAM and SAH can be analyzed by MS/MS, taking optimal advantage of the speed and high sensitivity and specificity of this relatively new analytical technique.