Silica Solid-phase Extraction Column Research Articles

Silver-coated monolitic silica column for separation of benzo[a]pyrene from petroleum

Monolithic silica solid-phase extraction column has been successfully applied for the rapid fractionation and subsequent gas chromatographic analysis of benzo[a]pyrene from the diesel and oil matrix. Due to π-π electronic interactions between silver nanoparticles on the sorbent surface and aromatic analyte specific retention was achieved. It was demonstrated that only 0.2 g of the sorbent and 6 ml of the organic solvent are enough for such separation.

Low concentration DNA extraction and recovery using a silica solid phase.

DNA extraction from clinical samples is commonly achieved with a silica solid phase extraction column in the presence of a chaotrope. Versions of these protocols have been adapted for point of care (POC) diagnostic devices in miniaturized platforms, but commercial kits require a high amount of input DNA. Thus, when the input clinical sample contains less than 1 μg of total DNA, the target-specific DNA recovery from most of these protocols is low without supplementing the sample with exogenous carrier DNA. In fact, many clinical samples used in the development of POC diagnostics often exhibit target DNA concentrations as low as 3 ng/mL. With the broader goal of improving the yield and efficiency of nucleic acid-based POC devices for dilute samples, we investigated both DNA adsorption and recovery from silica particles by using 1 pg– 1 μg of DNA with a set of adsorption and elution buffers ranging in pH and chaotropic presence. In terms of adsorption, we found that low pH and the presence of chaotropic guanidinium thiocyanate (GuSCN) enhanced DNA-silica adsorption. When eluting with a standard low-salt, high-pH buffer, > 70% of DNA was unrecoverable, except when DNA was initially adsorbed with 5 M GuSCN at pH 5.2. Unrecovered DNA was either not initially adsorbed or irreversibly bound on the silica surface. Recovery was improved when eluting with 95°C formamide and 1 M NaOH, which suggested that DNA-silica-chaotrope interactions are dominated by hydrophobic interactions and hydrogen bonding. While heated formamide and NaOH are non-ideal elution buffers for practical POC devices, the salient results are important for engineering a set of optimized reagents that could maximize nucleic acid recovery from a microfluidic DNA-silica-chaotrope system.

Determination of oxygenates in methanol-to-olefin gasoline byproducts and methanol-to-gasoline product with solid phase extraction-gas chromatography

Silica solid phase extraction (SPE) column was used for sample pretreatment to enrich the target analytes and simplify background. Due to its high efficiency, reliability and simplicity, the technique has been widely used in many fields. The byproduct gasoline of methanol-to-olefin (MTO) and the product of methanol-to-gasoline (MTG) mainly consist of hydrocarbons along with small amounts of oxygenates. Trace amounts of oxygenates are hard to identify because of their complex hydrocarbon components. With the SPE technique, the samples were separated into two major classes, oxygenates and hydrocarbons. Oxygenates were then determined with gas chromatography-mass spectrometry (GC-MS). The elution conditions of the silica solid phase extraction column were optimized with the standard sample. Under the optimized elution conditions, the hydrocarbons were first eluted from the SPE column with 5 mL dichloromethane, the oxygenates were then eluted with 3 mL acetonitrile. The recoveries of standard samples were tested before and after pretreatment. The standard recoveries were 87.7%-95.3%. The oxygenates except methanol and ethanol were then quantified by gas chromatography-flame ionization detection (GC-FID) and internal standard method. Methanol and ethanol were then quantified by extracting characteristic ion chromatograms and external standard method. The results show that the oxygenates of MTO byproduct gasoline and MTG product mainly consist of ketones and aldehydes. The method improves the sensitivities of the target compounds and reduces the interference of the background.

Development of an analytical method to quantify PBDEs, OH-BDEs, HBCDs, 2,4,6-TBP, EH-TBB, and BEH-TEBP in human serum.

Polybrominated diphenyl ethers (PBDEs) flame retardants (FRs) were phased-out in the mid-2000s (penta- and octaBDE) and 2013 (decaBDE); however, their hydroxylated metabolites (OH-BDEs) are still commonly detected in human serum. Today, novel FRs such as Firemaster® 550, a mixture that contains two brominated compounds, EH-TBB and BEH-TEBP are used as replacements for PBDEs in some applications, and there is a need to develop a comprehensive analytical method to assess exposure to both legacy PBDEs and novel FRs. This study developed a solid-phase extraction (SPE)-based method to analyze PBDEs, OH-BDEs, 2,4,6-tribromophenol (TBP), hexabromocylcododecane isomers (HBCDs), EH-TBB, and BEH-TEBP in human serum. Briefly, serum proteins were first denatured with formic acid, and then the target analytes were isolated using a SPE column. Finally, the extract was cleaned and fractioned using a silica SPE column. Method performance was assessed by spiking fetal bovine serum with 1-2ng of the target analytes, and method accuracy was quantified by comparison to a serum Standard Reference Material (SRM). The developed method showed good recovery and accuracy for all target analytes with the exception of the very low and very high molecular weight PBDE congeners. Using this method, 43 serum samples collected from the Healthy Pregnancy, Healthy Baby Study (HPHB) cohort in Durham, NC, USA were analyzed for FRs. A novel finding was the ubiquitous detection of 2,4,6-TBP, at levels greater than the individual PBDE congeners. Furthermore, 2,4,6-TBP was positively correlated with PBDEs, suggesting that they may have a similar source of exposure, or that 2,4,6-TBP may result from metabolism of PBDEs in vivo.

Determination of three estrogens in animal liver and kidney tissues by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the determination of estrone, 17beta-estradiol, estriol in animal liver and kidney tissues. The sample was extracted by tert-butyl methyl ether, and the extract was evaporated by nitrogen at 45 degrees C. The residue was redissolved in hexane-dichloromethane (6:4, v/v), then purified on a silica solid-phase extraction column. The eluant was evaporated by nitrogen, dissolved in acetonitrile-water (7:3, v/v) and then analyzed by LC-MS/MS. The separation of estrogens was performed on a Poroshell 120 EC-C18 column with the mobile phases of acetonitrile and water with a gradient elution. The identification and quantification of estrogens were carried out by negative electrospray ionization in the multiple reaction monitoring mode using external standard method. The calibration curves showed good linearity in the range of 1.0-20.0 microg/kg with the correlation coefficients above 0.99. The limit of quantification was 1.0 microg/kg for each estrogen. The average recoveries of the estrogens spiked at 1.0, 2.0, 10.0 microg/kg levels in different matrices were between 70.2% and 114%, and the relative standard deviations were between 2.01% and 14.5%. The method is simple, rapid, sensitive, good in purification effect. It is suitable for the confirmation and quantification of estrogens in animal liver and kidney tissues.

Analysis of Stilbene Residues in Aquacultured Finfish Using LC-MS/MS

This analytical method was developed for the determination of three stilbene residues, diethylstilbestrol (DES), dienestrol (DEN), and hexestrol (HEX), in edible tissues of finfish including catfish, salmon, trout, and tilapia. Fortified fish samples were extracted with acetonitrile and further cleaned up using silica solid phase extraction columns. Stilbene residues were separated from matrix components by reversed phase high-performance liquid chromatography on a C8 column and analyzed using a tandem mass spectrometer with negative electrospray ionization. The overall average residue recoveries using post-fortified matrix-matched calibrants were 119, 99, and 104% with %RSDs of 18, 11, and 15% for DEN, DES, and HEX, respectively. Method detection limits of DEN, DES, and HEX in each matrix were found to be at or below 0.21 ng/g, and the limit of quantification averaged 0.3 ng/g and ranged from 0.18 to 0.65 ng/g for all analytes in all matrices.

Simultaneous determination of four coccidiostats in eggs and broiler meat: Validation of an LC-MS/MS method

A published confirmatory method for the quantitative determination of four ionophoric coccidiostats (lasalocid, monensin, salinomycin and narasin) in eggs and broiler meat has been further developed. It is proposed for replacement of liquid chromatography methods previously used in analysis of ionophoric coccidiostats. The samples were extracted with acetonitrile and purified on a silica solid phase extraction column. Purified samples were analysed by liquid chromatography – mass spectrometry and the method, was validated according to the Commission Decision 2002/657/EC. The validation parameters selectivity, linearity, specificity, precision, recovery, decision limit (CCα) and detection capability (CCβ) were determined. The recoveries of coccidiostats analysed ranged from 64–99% in eggs and 62–100% in broiler meat. CCα varied from 0.8–1.4 µg/kg in eggs and from 1.5–2.5 µg/kg in broiler meat. CCβ varied from 0.9 µg/kg to 2.0 µg/kg in eggs and from 1.7–3.2 µg/kg in broiler meat.

Dioxin and polychlorinated biphenyl analysis: Automation and improvement of clean‐up established by example of spices

To analyze polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDDs/PCDFs) and polychlorinated biphenyls (PCBs) in spices by gas chromatography-mass spectrometry, a new clean-up method had to be developed owing to the high content of essential oils in the samples. A solid-phase extraction (SPE) column with activated silica endowed with sulfuric acid and sodium hydroxide was used. Under these conditions, clean-up was achieved using at least 5-7 g of pepper and even higher amounts of other spices. The automatized clean-up comprised three additional chromatographic steps after accelerated solvent extraction (ASE) followed by gel permeation: chromatography on a florisil SPE column, extract cleaning with the above-mentioned silica SPE column and chromatography with an activated charcoal column. On the basis of this automatized clean-up, a method that is more effective, rapid, simplified and economical than the available methods for PCDD/PCDF and PCB analysis is proposed. In model studies, the average recoveries for PCDDs/PCDFs ranged between 82.6% and 105.6% and for the PCBs between 71.3% and 113.3%.

Quantification of Bacillus cereus Emetic Toxin (Cereulide) in Figs Using LC/MS

An LC/MS method is described for the quantification of cereulide, the emetic toxin of Bacillus cereus in figs. The method can also be used for the determination of cereulide in rice. The sample was extracted with a mixture of acetone–tetrahydrofurane, methanol, and water, after which the organic layer was separated from water with chloroform and evaporated to dryness. The dry residue was diluted in chloroform–hexane and purified using a silica solid phase extraction column. The detection limit was 1 ng/g.

Confirmation of Phenylbutazone Residues in Bovine Kidney by Liquid Chromatography/Mass Spectrometry

A confirmatory method is described for phenylbutazone (PB) residues in bovine kidney tissue. Ground kidney tissue is diluted with water, and the mixture is made basic with 25% ammonium hydroxide in water; the lipids are extracted with ethyl and petroleum ethers. The ether layer is discarded, and the tissue is acidified with 6N HCl. PB residues are extracted with tetrahydrofuranhexane (1 + 4). The extract is passed through a silica solid-phase extraction column, and the eluate is evaporated to dryness. The residue is dissolved in acidified acetonitrile-water-acetic acid (50 + 49.4 + 0.6). A single quadrupole mass spectrometer coupled to a liquid chromatograph with an electrospray interface is used to confirm the identity of the PB residues in the kidney extract. Negative-ion detection with selected-ion monitoring of 4 ions is used. Sets of control and fortified-control kidney tissues (at 50, 100, and 200 ppb PB) and several kidney tissue field samples were analyzed for method validation. The method was tested further during the course of a survey to determine the incidence of PB residues in bovine kidney samples obtained from slaughterhouses across the country. In addition, the method was tested for use with an ion-trap mass spectrometer coupled to a liquid chromatograph, which allowed confirmation of PB at lower levels (5-10 ppb) in kidney tissue.

Determination of Two Oxy-Pyrimidine Metabolites of Diazinon in Urine by Gas Chromatography/Mass Selective Detection and Liquid Chromatography/Electrospray Ionization/Mass Spectrometry/Mass Spectrometry

An analytical method was developed for the determination in urine of 2 metabolites of diazinon: 6-methyl-2-(1-methylethyl)-4(1H)-pyrimidinone (G-27550) and 2-(1-hydroxy-1-methylethyl)-6-methyl-4(1H)-pyrimidinone (GS-31144). Two of the urine sample preparation procedures presented rely on gas chromatography/mass selective detection (GC/MSD) in the selected ion monitoring mode for determination of G-27550. For fast sample preparation and a limit of quantitation (LOQ) of 1.0 ppb, urine samples were purified by using ENV+ solid-phase extraction (SPE) columns. For analyte confirmation at an LOQ of 0.50 ppb, classical liquid/liquid partitioning was used before further purification in a silica SPE column. An SPE sample preparation procedure and liquid chromatography/electrospray ionization/mass spectrometry/mass spectrometry (LC/ESI/MS/MS) were used for both G-27550 and GS-31144. The limit of detection was 0.01 ng for G-27550 with GC/MSD, and 0.016 ng when LC/ESI/MS/MS was used for both G-27550 and GS-31144. The LOQ was 0.50 ppb for G-27550 when GC/MSD and the partitioning/SPE sample preparation procedure were used, and 1.0 ppb for the SPE only sample preparation procedure. The LOQ was 1.0 ppb for both analytes when LC/ESI/MS/MS was used.

Solid-phase extraction of technetium--amine complexes onto C18 silica and its application to the isolation of 99Tc

The extraction of Tc-tripentylamine complexes onto C18 silica solid-phase extraction columns is evaluated for the selective removal of 99Tc from other isotopes. The Tc-amine complex is quantitatively extracted from sulfuric acid and can be recovered from the column by elution with dilute alkali. A clean separation of Tc from all likely contaminants, including Ru, is achieved showing that C18 silica solid-phase extraction columns are a viable and attractive alternative to the solvent extraction of 99Tc.

DETERMINATION OF AMPROLIUM, ETHOPABATE, LASALOCID, MONENSIN, NARASIN, AND SALINOMYCIN IN CHICKEN TISSUES, PLASMA, AND EGG USING LIQUID CHROMATOGRAPHY-MASS SPECTROMETRY

A liquid chromatographic-atmospheric pressure ionization ion spray method for the determination of some coccidiostatics in chicken egg, fat, liver, muscle, and plasma is presented. The samples were extracted with acetone-tetrahydrofuran. The water and the organic layer was then separated using a liquid-liquid extraction step and the organic phase was then evaporated to dryness. The dry residue was diluted in hexane and a portion of the organic phase was cleaned-up with a simple step for ethopabate analyses while the rest of the organic phase was purified using a silica solid phase extraction column to analyse lasalocid, monensin, narasin, and salinomycin. The water phase (amprolium analyses) was diluted with water, filtered, and injected into the LC-MS. Three different analytical columns were used. The detection limits were from 1 ng/g to 7 ng/g for chicken tissue and from 4 to 10 ng/mL for plasma.

Determination of methotrexate in human urine at trace levels by solid phase extraction and high-performance liquid chromatography/tandem mass spectrometry.

For biological monitoring of hospital personnel occupationally exposed to antineoplastic agents, highly sensitive and specific methods are required. In order to detect trace MTX urinary concentrations, a precise and accurate high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) procedure, incorporating solid phase extraction, has been developed. Urine samples were purified by solid phase extraction (SPE) on octadecyl bonded, endcapped silica SPE columns. After eluting with methanol, the solvent was evaporated obtaining a 25-fold concentration of the analyte. This procedure was validated by using 7-OHMTX as internal standard. Calibration curves had correlation coefficients always higher than 0.999, and the limit of detection was assessed at 0.2 microg L(-1). High specificity of the HPLC-MS/MS technique assures that no interfering substances are detected rather than the analyte of interest.

HPLC-UV method for the quantitation of nevirapine in biological matrices following solid phase extraction

Nevirapine (VIRAMUNE®) is a non-nucleoside reverse transcriptase inhibitor with activity against human immunodeficiency virus type 1 (HIV-1), currently marketed for the treatment of HIV-1 infected adults. A reverse phase HPLC-UV method was optimized and validated for the determination of nevirapine in human plasma, serum, milk and cerebrospinal fluid. The analyte was extracted from 250 μl of biofluid using a bonded silica solid phase extraction column, and resolved chromatographically on a reversed-phase, 15×0.46 cm i.d. 5 μm particle Supelco LC-8 analytical column with an isocratic mobile phase of 63% phosphate buffer (0.025 M, pH 6.0) with 1-butanesulfonic acid as anion-pair reagent: 21.5% methanol: 15.5% acetonitrile. The peaks were detected at a flow rate of 1.0 ml min −1, at a wavelength of 280 nm, with a run time of 10 min. The assay was linear over a range of 25 to 10 000 ng ml −1. This method has been used for the clinical development of nevirapine.

Determination of Ivermectin in Salmon Muscle Tissue by Liquid Chromatography with Fluorescence Detection

A liquid chromatographic method was developed for determination of ivermectin B1a (IVR) extracted from raw fortified and incurred Atlantic salmon muscle tissues. The method was also used to determine fortified doramectin (DOR) in Atlantic salmon. Tissue extract was applied to C8 solid-phase extraction (SPE) column, followed by a silica SPE column. Residues in the eluate were treated with trifluoroacetic anhydride and methylimidazole to dehydrate the IVR molecule and form an aromatic fluorescent moiety with a trifluoroacetic ester. This product was subsequently treated with ammonium acetate in methanol to cleave the ester and convert the functional group back to a stable alcohol form. The analytes were determined by fluorescence with excitation at 272 nm and emission at 465 nm. A C18 Hypersil column was used for analysis with a mobile phase of acetonitrile-water (90 + 10, v/v) and an oven temperature of 65 degrees C. IVR and DOR were determined at 5 fortification levels (1, 5, 10, 20, and 40 ppb). Intra-assay absolute recoveries ranged from 75 to 89% for IVR and from 73 to 85% for DOR. Relative standard deviations (RSDs) were < 7% in all cases. The limit of detection (3 x baseline noise) was 0.25 ppb extracted from tissue. Incurred tissues had an average concentration of 32 ppb, with an RSD of 3%.

Analytical Method for the Determination of Atrazine and Its Dealkylated Chlorotriazine Metabolites in Urine by Gas Chromatography/Mass Selective Detection.

A multiresidue method is reported for the determination of atrazine and its chloro dealkylated metabolites in urine. Urine samples were subjected to a protein precipitation procedure followed by further purification using strong anion exchange and silica solid-phase extraction columns. Final analysis was accomplished using gas chromatography/mass selective detection in the selected ion monitoring mode. The limits of detection were 0.050 ng injected for 2,4-diamino-6-chloro-s-triazine (G-28273) and 0.025 ng injected for 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 2-amino-4-chloro-6-(isopropylamino)-s-triazine (G-30033), and 2-amino-4-chloro-6-(ethylamino)-s-triazine (G-28279). The limits of quantification were 1.0 ppb for atrazine and G-30033 and 2.0 ppb for G-28279 and G-28273. The mean procedural recoveries obtained during the method validation were 115, 113, 112, and 97% and the standard deviations were 10.6, 10.2, 9.5, and 16.1% for atrazine, G-30033, G-28279, and G-28273, respectively. Additional recovery data were obtained during a worker exposure study and during an outside ruggedness trial. All studies were conducted under U.S. EPA FIFRA Good Laboratory Practice Standards 40 CFR 160.

Detection and identification of thyreostats in the thyroid gland by gas chromatography-mass spectrometry

Because thyreostatic compounds, also named thyreostats, are banned in Europe (directive 86/469/EEC), methods have to be developed to prevent the illegal use of these substances. The analytical procedure described herein involves the detection and identification at the low ng g −1 level of the main thyreostats known to be used for growth promotion by gas chromatography coupled to mass spectrometry (GC-MS). The assay is based on a liquid/liquid extraction of the thyroid gland, derivatization with pentafluorobenzyl bromide (PFBBr), purification on a silica solid phase extraction column and finally a trimethylsilylation prior to GC-MS. Good thyreostat recoveries were obtained (from 40% to 70%) as well as at acceptable repeatability. The target analytes were detectable below the 1 ng g −1 level on a quadrupole mass spectrometer with negative chemical ionization (NCI) using ammonia as reagent gas and the selected ion monitoring (SIM) acquisition mode. This limit of detection was also reached in the SIM high resolution mode. An improved specificity (more diagnostic ions) was obtained under electronic impact (EI) conditions and positive chemical ionization (PCI) with methane as reagent gas. Identification of thyreostats according to the EU (European Union) criteria (93/256/EEC decision) was made on the basis of two independent GC-MS techniques; the limit of identification was close to 5 ng g −1 for most thyreostats, which represents a real improvement for their control.

Determination of Aflatoxin Bi in Pistachio Kernels and Shells

A method was developed for accurate measurement of aflatoxin B1 in the edible portion of pistachio nuts. Twenty-nine samples of kernels with and without their shells were slurried with a Mega Ultra Turrax. A subsample of the homogenate was extracted with water-methanol, defatted with petroleum ether, purified with a silica solid-phase extraction column, and redissolved in methanol. After separation on an octadecyl column and postcolumn reaction with on-line electrochemically generated bromine, the aflatoxin B1 derivative was detected fluorometrically. The shells contained less than 1% of the aflatoxin B1 found in the edible kernel, and they accounted for 41.7-46.8% of the weight of the whole pistachio. These observations indicate it is possible to analyze an entire sample, up to 25 kg, as a whole and still be able to judge whether it meets the legal tolerance limit of 5 micrograms aflatoxin B1/kg edible part, as set by the Dutch Food Act.

Determination of ionophores in the tissues of food animals by liquid chromatography.

A liquid chromatographic method for determining residues of ionophores in bovine, porcine, and avian tissues is described. Tissues were extracted with iso-octane-ethyl acetate and the extracts purified on silica solid-phase extraction columns. Monensin, narasin and salinomycin were detected by UV absorbance following post-column derivatization with vanillin, and lasalocid was detected underivatized using fluorescence. In muscle, kidney and fat, all drugs were determined from a single sample extract. In liver, a separate extraction was done to determine lasalocid. The detection limit for lasalocid, narasin and salinomycin was 5 ppb; for monensin it was 2 ppb. Average recoveries were: lasalocid-71.0%; monensin-94.3%; salinomycin-97.2%; narasin-94.1%.