Weak Anion Exchange Cartridges Research Articles

Automation of Copper-Mediated 18F-Fluorination of Aryl Pinacol Boronates Using 4-Dimethylaminopyridinium Triflate

Currently, the copper-mediated radiofluorination of aryl pinacol boronates (arylBPin) using the commercially available, air-stable Cu(OTf)2Py4 catalyst is one of the most efficient synthesis approaches, greatly facilitating access to a range of radiotracers, including drug-like molecules with nonactivated aryl scaffolds. Further adjustment of this methodology, in particular, the [18F]fluoride recovery step for the routine preparation of radiotracers, has been the focus of recent research. In our recent study, an organic solution of 4-dimethylaminopyridinium trifluoromethanesulfonate (DMAPOTf) was found to be an efficient PTC for eluting radionuclides retained on the weak anion exchange cartridge, Oasis WAX 1cc, employing the inverse sorption–elution protocol. Notably, the following Cu-mediated radiofluorination of arylBPin precursors in the presence of the Cu(OTf)2(Py)4 catalyst can be performed with high efficiency in the same solvent, bypassing not only the conventional azeotropic drying procedure but any solvent replacement. In the current study, we aimed to translate this methodology, originally developed for remote-controlled operation with manual interventions, into the automated synthesis module on the TRACERlab automation platform. The adjustment of the reagent amounts and solvents allowed for high efficiency in the radiofluorination of a series of model arylBPin substrates on the TRACERlab FXFE Pro synthesis module, which was adapted for nucleophilic radiofluorinations. The practical applicability of the developed radiofluorination approach with DMAPOTf elution was demonstrated in the automated synthesis of 6-L-[18F]FDOPA. The radiotracer was obtained with an activity yield (AY; isolated, not decay-corrected) of 5.2 ± 0.5% (n = 3), with a synthesis time of ca. 70 min on the TRACERlab FX N Pro automation platform. The obtained AY was comparable with one reported by others (6 ± 1%) using the same boronate precursor, while a slightly higher AY of 6-L-[18F]FDOPA (14.5 ± 0.5%) was achieved in our previous work using commercially available Bu4NOTf as the PTC.

Determination of perfluorinated compounds in Eichhornia crassipes (Mart.) Solms using LC-MS/MS in combination with sample preparation by ultrasound-assisted extraction and solid-phase extraction

Fifteen perfluorinated compounds, including perfluorocarboxylic acids and perfluoroalkyl sulfonate salts (with 4 to 12 carbon atoms in their structure) in Eichhornia crassipes (Mart.) Solms samples underwent analysis using Liquid Chromatography- tandem Mass Spectrometry (LC-MS/MS). This analysis was conducted alongside sample preparation employing ultrasound-assisted extraction and solid-phase extraction. The optimization of solvent extraction involved the use of 5 ml of methyl tert-butyl ether (MTBE), 10 minutes of sonication, and three repeated extraction cycles. The weak anion exchange (WAX) cartridge was selected after evaluating and comparing the solid-phase extraction efficiencies of both WAX and C18 cartridges. The evaluated method demonstrated successful analysis of all 15 PFCs in plant samples, achieving favorable recoveries ranging from 71 to 116% (with a coefficient of variation of 1.2-6.6%). The quantification limits for these 15 PFCs in Eichhornia crassipes (Mart.) Solms samples ranged between 0.30 to 0.54 ng/g.
 ® 2023 Journal of Science and Technology - NTTU

Complementary biomarker detection for bisphosphonate use in racehorses

Determining the use of off-label bisphosphonates (BPs) in young horses (< 4 years old) is of interest due to the threat to racing integrity and welfare associated with this class of drugs that have the potential to manipulate bone structure. The analysis of BPs in biological matrices is challenging by liquid chromatography coupled to mass spectrometry (LC-MS/MS) and alternative sample preparation approaches are needed to detect their misuse in racehorses. There are currently two classes of BPs: non-nitrogen and nitrogen-containing with each having a distinct mode of action. Currently two non-nitrogenous based BPs are available for use in horses, tiludronic acid (or tiludronate) and chlodronate for the treatment of navicular syndrome (Mitchell et al. BMC Veterinary Research 2019;15(1):211) in horses over the age of 4. There is, however, evidence that BPs can persist in the bone for several years after administration since they can form hydroxyapatite crystals prior to being fully absorbed by active osteoclasts where full inhibitory action is performed (Riggs et al. Equine veterinary journal 2021;53(6):1287–1295). Therefore, with this prolonged detection time for the BPs, it is necessary to investigate whether the use of metabolomic biomarkers can provide a complementary method for the detection of their misuse. The aim of this research was to develop a biomarker approach for complementary direct detection of bisphosphonate drugs in equine plasma. BPs are hydrophilic therefore the targeted detection of tiludronic acid in equine plasma required an orthogonal solid phase extraction (SPE) method using both a polymeric reversed-phase sorbent and a weak anion exchange cartridge prior to derivatisation using trimethyl orthoacetate and reverse LC-MS/MS. Endogenous lipids and corticosteroids in equine plasma were detected after protein precipitation and SPE with a polymeric reverse phase cartridge prior to liquid chromatography high-resolution mass spectrometry. Data was analysed using the Shimadzu Insight Explore software to determine up- or down-regulation of biomarkers. Results were then profiled using a Parametric Empirical Bayes algorithm to propose individual reference limits (IRLs). Tiludronic acid was detected up to the final collection point of 28 days post-administration. Following a targeted approach, up- and down-regulation of the eicosanoid and corticosteroid ratios were observed with the corticosteroid ratio exceeding both the proposed population reference limit (PRL) and IRL. Using a semi-targeted approach, several additional lipids were identified to have activity during the administration and will require further confirmatory analysis. Monitoring the impact on endogenous biomarkers following an administration of Tiludronic Acid in racehorses is limited therefore little is known if BPs have a direct or indirect effect on the inflammatory pathways. However, research in humans has linked BPs with possible effects of analgesia in addition to bone remodelling that BPs are primarily used for. Therefore, it is necessary to further extend detection capabilities to ensure endogenous eicosanoids and corticosteroids are monitored. This, however, should not negate the need for the detection of the drug itself as tiludronic acid has the potential to be detected as far as 28 days post-administration. Therefore, a complementary biomarker approach would be preferable for the detection of non-nitrogen-based BPs, which can be further applied for the nitrogen-based BPs. A complementary biomarker approach to direct detection of administered drugs can improve the understanding of effect and support non-targeted detection strategies for analogues of specific drug classes.

Extraction and Matrix Cleanup Method for Analyzing Novel Per- and Polyfluoroalkyl Ether Acids and Other Per- and Polyfluoroalkyl Substances in Fruits and Vegetables.

Per- and polyfluoroalkyl ether acids (PFEAs) are a subclass of per- and polyfluoroalkyl substances (PFAS) that are detected with increasing frequency in environmental matrices. Diet can be an important route of PFEA exposure, but the presence of PFEAs in food is poorly understood. Extraction methods for food samples exist for traditionally studied PFAS, but their suitability for PFEAs and other novel PFAS remains unknown. In this study, an extraction and matrix cleanup method was developed to quantify 45 PFAS, including 13 PFEAs, 3 perfluoroalkane sulfonamides, and 6 fluorotelomer carboxylic acids in 10 types of fruits and vegetables. Homogenized samples were extracted with basic methanol, and resulting extracts were diluted with water and cleaned up using solid-phase extraction with weak anion-exchange cartridges. The method was validated by performing spike-recovery experiments at spike levels of 1 ng/g in all 10 matrices and 0.1 ng/g in 2 matrices. For PFAS without a corresponding isotopically labeled internal standard (IS), adopting an IS with a similar chromatographic retention time generated the most accurate recoveries. Dependent upon the matrix, recoveries of 38-44 PFAS (including 10-13 PFEAs) fell within 50-150% for samples spiked at 1 ng/g. Recoveries of 40 and 38 PFAS in blueberries and corn, respectively, fell within 50-150% for samples spiked at 0.1 ng/g. Method quantification limits (MQLs) of PFAS in pure solvents were determined as the lowest calibration level with an accuracy between 70 and 130%. To compensate for matrix effects, a matrix factor was applied on the basis of the analyte response in different matrices relative to the pure solvent. The MQLs of 45 PFAS (including 13 PFEAs) in 10 matrices ranged from 0.025 to 0.25 ng/g. Overall, this method is capable of sensitively quantifying 45 PFAS in many fruits and vegetables.

Facile Synthesis of Mixed-Mode Weak Anion-Exchange Microspheres via One-Step Pickering Emulsion Polymerization for Efficient Simultaneous Extraction of Strongly and Weakly Acidic Drugs from Reservoir Water.

Poly(2-(diethylamino)ethyl methacrylate-co-divinylbenzene) (poly(DEAEMA-co-DVB)) microspheres with mixed-mode weak anion-exchange (WAX) character were successfully fabricated for the first time via facile one-step Pickering emulsion polymerization. The obtained poly(DEAEMA-co-DVB) particles had good spherical geometry, uniform particle size in the range of 30–40 µm, a large specific surface area of 575 m2/g, and a pore size range of 5–30 nm, according to the SEM and nitrogen adsorption–desorption results. Using these mixed-mode WAX microspheres as packing material, a reliable and robust analytical method based on solid phase extraction and high performance liquid chromatography with ultraviolet detection (SPE-HPLC-UV) was developed for simultaneous determination of six strongly and weakly acidic nonsteroidal anti-inflammatory drugs (NSAIDs, niflumic acid, diflunisal, naproxen, ketoprofen, mefenamic acid, and diclofenac) in reservoir water. Under optimized conditions, it was applicable to preconcentrate up to 500 mL of reservoir water samples on the WAX cartridges with satisfying recoveries (88–96%) for all the NSAIDs tested. The limits of detection were in the range of 0.002–0.025 μg L−1, respectively. Our results showed that the developed mixed-mode WAX poly(DEAEMA-co-DVB) phase containing a tertiary amine with a pKa value of approximately 10.7 could be used for simultaneous clean-up and preconcentration of strongly and weakly acidic organic pollutants in real environmental water, which could not be achieved by single use of quaternary ammonium strong anion-exchange phase or weaker primary and secondary amine anion-exchange.

Permethylation and Microfractionation of Sulfated Glycans for MS Analysis.

Sulfated glycans are barely detectable in routine mass spectrometry (MS)-based glycomic analysis due to ion suppression by the significantly more abundant neutral glycans in the positive ion mode, and sialylated non-sulfated glycans in the negative ion mode, respectively. Nevertheless, the negative charge imparted by sulfate can be advantageous for selective detection in the negative ion mode if the sialic acids can first be neutralized. This is most conveniently achieved by a concerted sample preparation workflow in which permethylation is followed by solid phase fractionation to isolate the sulfated glycans prior to MS analysis. Importantly, we demonstrated that conventional NaOH/DMSO slurry permethylation method can retain the sulfates. Instead of extracting permethylated glycans into chloroform for sample clean-up, reverse phase C18 cartridge coupled with self-packed amine-tip or mixed mode weak anion exchange cartridge can be utilized to obtain in good yield the non-sulfated, mono-sulfated, and multiply sulfated permethylated glycans in separate fractions for sulfoglycomic analysis.

A single analytical method for the determination of 53 legacy and emerging per- and polyfluoroalkyl substances (PFAS) in aqueous matrices.

A quantitative method for the determination of per- and polyfluoroalkyl substances (PFAS) using liquid chromatography (LC) tandem mass spectrometry (MS/MS) was developed and applied to aqueous wastewater, surface water, and drinking water samples. Fifty-three PFAS from 14 compound classes (including many contaminants of emerging concern) were measured using a single analytical method. After solid-phase extraction using weak anion exchange cartridges, method detection limits in water ranged from 0.28 to 18ng/L and method quantitation limits ranged from 0.35 to 26ng/L. Method accuracy ranged from 70 to 127% for 49 of the 53 extracted PFAS, with the remaining four between 66 and 138%. Method precision ranged from 2 to 28% RSD, with 49 out of the 53 PFAS being below < 20%. In addition to quantifying > 50 PFAS, many of which are currently unregulated in the environment and not included in typical analytical lists, this method has efficiency advantages over other similar methods as it utilizes a single chromatographic separation with a shorter runtime (14min), while maintaining method accuracy and stability and the separation of branched and linear PFAS isomers. The method was applied to wastewater influent and effluent; surface water from a river, wetland, and lake; and drinking water samples to survey PFAS contamination in Australian aqueous matrices. The compound classes FTCAs, FOSAAs, PFPAs, and diPAPs were detected for the first time in Australian WWTPs and the method was used to quantify PFAS concentrations from 0.60 to 193ng/L. The range of compound classes detected and different PFAS signatures between sample locations demonstrate the need for expanded quantitation lists when investigating PFAS, especially newer classes in aqueous environmental samples. Graphical abstract.

Determination of 23 perfluorinated alkylated substances in water and suspended particles by ultra-performance liquid chromatography/tandem mass spectrometry

A practical multi-residue method based on ultra-performance liquid chromatography/tandem mass spectrometry was developed for the simultaneous determination of 23 perfluorinated alkylated substances (PFASs) in water and suspended particles. Suspended particle samples were extracted with 1% formic acid–acetonitrile and cleaned by matrix solid phase dispersion extraction using a C18 sorbent and graphitized carbon black. Water samples were filtered through 0.7-μm glass fiber membranes and enriched utilizing weak anion exchange cartridges. The eluent was dried under a gentle stream of N2 at 45°C and suspended in 1 mL acetonitrile–5 mM ammonium acetate (1:1, vol:vol). Gradient elution for chromatographic separation utilized acetonitrile and 5 mM ammonium acetate as mobile phases on a reverse phase C18 column. The compounds were quantified using an internal standard method in multiple reaction-monitoring mode. Limits of detection and quantitation of the 23 PFAS test compounds in water samples were 0.5–10 ng L−1 and 2–20 ng L–1, respectively. Recoveries at three fortified levels of 20, 50, and 200 ng L–1 ranged from 68.5% to 118% with relative standard deviations below 9.6%. We used this method to determine PFAS levels in real water and suspended particle samples and found high sensitivity and good reproducibility.

Analytical method applied for perfluororinated chemicals in water, sediment and fish by liquid chromatography with tandem mass spectrometry

Abstract: 12 perfluororinated chemicals including perflourocarbocylic acids and perfluoroankyl sulfonates (containing C4 to C12) in environmental media such as water, sediment and fish were deternined by liquid chromatography with tandem mass spectrometric detector (LC-MS/MS) using weak anion exchange cartridge (WAX) in solid phase extraction for sample preparation. The result of method validation showed that the recoveries of 12 PFCs for water and fish samples were in a range from 87 to 112% ( 4-17% CV) and a range from 81 to125% (3-12% CV), respectively. The method was a reliable analysis for 10 PFCs compounds of sediment sample which recieved the recoveries in a range from 80 to121% (3-16% CV), except PFUdA and PFDoA. The detection limits of 12 PFCs were from 0.06 to 0.6 ng/L for water and from 0.01 to 0.06 ng/g for sediment and fish samples.&#x0D;

Analysis of a broad range of perfluoroalkyl acids in accipiter feathers: method optimization and their occurrence in Nam Co Basin, Tibetan Plateau.

Perfluoroalkyl acids (PFAAs) are ubiquitous in the environment. They are prone to accumulate in organisms and have raised public attention in recent decades. Feather samples have been successfully applied as nondestructive indicators for several contaminants. However, a sophisticated analytical method for determining PFAAs in feathers is still lacking. In the present study, a series of conditions, such as the use of the solid-phase extraction cartridge type and extraction/digestion methods, were optimized for the analysis of 13 PFAAs in feathers. According to the spiked recoveries, a weak-anion exchange cartridge was chosen and the methanol was selected as the extraction solvent. In the present study, an optimized pretreatment procedure combined with high-performance liquid chromatography-electrospray ionization-tandem mass spectrometric (HPLC-ESI-MS/MS) method was established for the determination of PFAAs in feathers. The recoveries and method detection limits of the PFAAs ranged from 71 to 120% and 0.16 to 0.54ng/g, respectively. Finally, 13 PFAAs in four accipiter feather samples from Nam Co Basin, Tibetan Plateau, were analyzed, indicating that PFOS was the predominant PFAA in accipiter feathers, with an average of 4.67ng/g, followed by the short-chain PFAAs, PFBS and PFBA, with averages of 1.91 and 1.39ng/g, respectively. These results partly indicated the current situation of PFAA pollution in the Nam Co Basin, especially the existence of short-chain PFAAs in this region.

Comparative lipidomics of mouse brain exposed to enriched environment

Several studies have shown that housing conditions and environmental exposure to a series of stimuli lead to behavior improvement in several species. While more works have been focused on illustrating changes of the proteome and transcriptome following enriched environment exposure in mice, little has been done to understand changes in the brain metabolome in this paradigm due to the complexity of this type of analysis. In this paper, lipidomics focused on phospholipids and gangliosides were conducted for brain tissues of mice exposed to enriched or impoverished conditions. We optimized previously reported method and established a reliable relative comparison method for phospholipids and gangliosides in brain tissue using prefractionation with weak anion exchange cartridge. We used liquid chromatography mass spectrometry to explore metabolic signatures of the cerebral cortex and hippocampus after confirming the animals had significant memory differences using the fear conditioning paradigm and brain immunohistochemistry. Although both cerebral cortex and hippocampus regions did not show major alterations in ganglioside composition, we found significant differences in a series of phospholipids containing 22:6 fatty acid in the prefrontal cortex, indicating that environmental enrichment and impoverished housing conditions might be a relevant paradigm to study aberrant lipid metabolism of docosahexaenoic acid consumption. Our study highlights the hypothesis-generating potential of lipidomics and identifies novel region-specific lipid changes possibly linked not only to change of memory function in these models, but also to help us better understand how lipid changes may contribute to memory disorders.

Determination of perfluorinated compounds in human plasma and serum Standard Reference Materials using independent analytical methods

Perfluorinated compounds (PFCs) were measured in three National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs) (SRMs 1950 Metabolites in Human Plasma, SRM 1957 Organic Contaminants in Non-fortified Human Serum, and SRM 1958 Organic Contaminants in Fortified Human Serum) using two analytical approaches. The methods offer some independence, with two extraction types and two liquid chromatographic separation methods. The first extraction method investigated the acidification of the sample followed by solid-phase extraction (SPE) using a weak anion exchange cartridge. The second method used an acetonitrile extraction followed by SPE using a graphitized non-porous carbon cartridge. The extracts were separated using a reversed-phase C(8) stationary phase and a pentafluorophenyl (PFP) stationary phase. Measured values from both methods for the two human serum SRMs, 1957 and 1958, agreed with reference values on the Certificates of Analysis. Perfluorooctane sulfonate (PFOS) values were obtained for the first time in human plasma SRM 1950 with good reproducibility among the methods (below 5% relative standard deviation). The nominal mass interference from taurodeoxycholic acid, which has caused over estimation of the amount of PFOS in biological samples, was separated from PFOS using the PFP stationary phase. Other PFCs were also detected in SRM 1950 and are reported. SRM 1950 can be used as a control material for human biomonitoring studies and as an aid to develop new measurement methods.

Rapid Determination of Fumagillin Residues in Honey by Liquid Chromatography–Tandem Mass Spectrometry Using the QuEChERS Method

A new, rapid, and efficient method for determining the fumagillin residues in honey was developed. The samples extracted were analyzed using LC/MS/MS. Chromatographic separation of fumagillin was performed in gradient mode on a C8 column (100 x 2.0 mm, 5 microm) at 40 degrees C. The mobile phase consisted of a mixture of 2 mM ammonium formate-0.01% formic acid solution and methanol; the flow rate was set to 0.2 mL/min. Under these conditions, it was possible to measure fumagillin and its isomers as a single peak. The sample preparation procedure used is based on the QuEChERS (quick, easy, cheap, effective, rugged, and safe) method, which is fast (approximately 30 min) and uses less organic solvent. The fumagillin was extracted with acetonitrile containing 0.1% formic acid, then purified using a solid-phase extraction method with an Oasis mixed-mode weak anion-exchange cartridge. The overall recovery of fumagillin ranged from 88.1 to 99.4%; the intra- and interassay CVs were <4.5% and <4.9%, respectively. The LOQ was 0.1 microg/kg. LC/MS/MS coupled with the QuEChERS method showed strong potential as a method for determining fumagillin residues in honey.

Quantification of dialkylphosphate metabolites of organophosphorus insecticides in human urine using 96-well plate sample preparation and high-performance liquid chromatography–electrospray ionization-tandem mass spectrometry

Organophosphorus (OP) pesticides kill by disrupting a targeted pest's brain and nervous systems. But if humans and other animals are sufficiently exposed, OP pesticides can have the same effect on them. We developed a fast and accurate high-performance liquid chromatography–tandem mass spectrometry method for the quantitative measurement of the following six common dialkylphosphate (DAP) metabolites of organophosphorus insecticides: dimethylphosphate (DMP), dimethylthiophosphate (DMTP), dimethyldithiophosphate (DMDTP), diethylphosphate, (DEP), diethylthiophosphate (DETP), and diethyldithiophosphate (DEDTP). The general sample preparation included 96-well plate solid phase extraction using weak anion exchange cartridges. The analytical separation was performed by high-performance liquid chromatography with a HILIC column. Detection involved a triple quadrupole mass spectrometer with an ESI probe in negative ion mode using multiple reaction monitoring. Repeated analyses of urine samples spiked at 150, 90 and 32 ng/mL with the analytes gave relative standard deviations of less than 22%. The extraction efficiency ranged from 40% to 98%. The limits of detection were in the range of 0.04–1.5 ng/mL. The throughput is 1152 samples per week, effectively quadrupling our previous throughput. The method is safe, quick, and sensitive enough to be used in environmental and emergency biological monitoring of occupational and nonoccupational exposure to organophosphates.

Determination of Vedaprofen in Livestock Products and Seafoods by Liquid Chromatography-Tandem Mass Spectrometry

A novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the trace residue determination of vedaprofen (VPF) in livestock products and seafoods. VPF was extracted from each sample with acidified acetone, and the crude extract was re-extracted with ethyl acetate and NaCl solution. Clean-up was performed using a weak anion exchange cartridge (Bond Elut DEA). The LC separation was performed on a C18 column using acetonitrile-0.0025 mol/L formic acid (3 : 2) as the mobile phase and MS was run in the negative ion electrospray ionization mode. The calibration curve was linear in the range of 0.001-0.1 µg/mL VPF. The mean recoveries from equine muscle, cattle muscle, cattle liver, cattle fat, salmon, eel, corbicula, milk, egg and buckwheat honey were 72-94%, and the relative standard deviations (RSDs) were 1.1-2.0%. Limits of quantitation (LOQs) ranged from 0.001 to 0.007 µg/g.

Analysis of fluorotelomer alcohols, fluorotelomer acids, and short- and long-chain perfluorinated acids in water and biota

Fluorotelomer alcohols and fluorotelomer acids have been proposed as a source of the perfluorinated carboxylic acids found in remote marine locations. To examine the sources and fate of perfluorinated acids in the environment, a method to determine a wide range of poly- and perfluorinated acids in environmental and biological matrices is needed. In this study, a method has been developed to measure a suite of neutral and acidic fluorochemicals including, fluorotelomer alcohols, fluorotelomer acids, and short- and long-chain perfluorinated acids, in water and biological samples. The method involves solid-phase extraction with weak anion exchange (WAX) cartridges, followed by sequential elution with sodium acetate buffer, methanol, and 0.1% NH 4OH in methanol. For biological samples, prior to solid-phase extraction, tissues are digested in 0.5N potassium hydroxide/methanol, diluted in water, and passed through the WAX cartridge. Neutral compounds and telomer alcohols are separated from other poly- and perfluorinated acids. The method is robust (i.e., capable of measuring neutral and acidic compounds), and can be applied for the analysis of a range of poly- and perfluorinated acids, including telomer alcohols, telomer acids, perfluoroalkylcarboxylates, and perfluoroalkylsulfonates in water and biota. With the use of high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), a method detection limit in the range of several tens to hundreds of parts-per-quadrillion (pg/L) in water and at a few tens to hundreds of parts-per-trillion (pg/g) levels in biological matrices can be achieved.

Forensic Toxicological Determination of Surfactant by Liquid Chromatography/Electrospray lonization Mass Spectrometry and Liquid Chromatography/Electrospray lonization Tandem Mass Spectrometry.

A procedure for identifying surfactants was investigated by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) and liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) from the forensic toxicological point of view. The analysis of anionic, cationic, and nonionic surfactants in both negative and positive mode revealed that anionic and cationic surfactants are detected as M- ions in the negative mode and M+ ions in the positive mode, respectively, while [M+H]+ ions or [M+NH4]+ ions appeared for nonionic surfactants in the positive mode. Anionic surfactants (linear alkylbenzene sulfonate and polyoxyethylene alkyl ether sulfate) were successfully extracted using a weak anion exchange cartridge, with recovery rates of 53.8-76.7%. Cationic surfactant (benzalkonium) was also easily extracted using a weak cation exchange cartridge with a recovery rate of 107%. When aqueous solutions of cationic, anionic, and nonionic surfactants were concentrated to dryness, the recovery rates ranged from 65.8% to 124%. By analyzing anionic surfactants (alpha-olefine sulfate, polyoxyethylene alkyl ether sulfate, and linear alkylbenzene sulfonate) in the product ion scan mode in LC/ESI-MS/MS, it was possible to identify the structure of the hydrophilic group of surfactants, and MS/MS was confirmed to be a powerful technique for classification.

Determination of acetamiprid, imidacloprid, and nitenpyram residues in vegetables and fruits by high-performance liquid chromatography with diode-array detection.

Determination of 3 neonicotinoid insecticides, nitenpyram, imidacloprid, and acetamiprid, was studied. Vegetables and fruits were extracted with acetonitrile. The crude extract was passed through a weak anion-exchange cartridge (PSA). The effluent was subjected to silica gel cartridge. Imidacloprid and acetamiprid were eluted with 10 mL of 4:6 (v/v) acetone/hexane, followed by nitenpyram with acetone (20 mL). Pesticides were determined by HPLC with a C-18 column and diode-array detection system. Imidacloprid and acetamiprid were recovered at about 90% at the spike levels with 0.2 and 2 mg/kg in cucumber, potato, tomato, eggplant, Japanese radish, and grape. Nitenpyram was recovered at 64-80%. Relative standard deviations were less than 10% throughout all the recovery tests. In the residue analysis, agriculturally incurred pesticides at 0.08-0.14 mg/kg were designated with UV spectra compared with respective reference standards.

Enzymes adsorbed on an ion exchanger as a post-column reactor: application to acetylcholine measurement

Enzymes can be used in high-performance liquid chromatography post-column reactors to improve sensitivity and specificity of detection for some compounds by converting the compounds to easily detectable products. The enzymes can be covalently bound to a post-column reactor, but a simpler approach is to bind them by adsoption to an ion exchanger or a hydrophobic interaction support. This technique has been applied to electrochemical detection of acetylcholine by using adsorption of choline oxidase and cholinesterase to a 3-cm long commercially available weak anion-exchange cartridge. Conversion of acetylcholine to peroxide is quantitative during the 10-sec residence time in the cartridge. Enzyme elution from the cartridge is negligible when low ionic strength mobile phases are used. Fresh enzyme needs to be added to the cartridge at only 1–2 week intervals.