Comparison of different solid phase extraction materials and techniques by application of multiresidue methods for the determination of pesticides in water by high-performance liquid chromatography (HPLC)

Solid phase extraction materials and techniques (C-18 EMPORE^® disks, polystyrenedivinylbenzene (SDB) EMPORE^® disks, C-18 BondElut cartridges and ENVI-Carb cartridges) are compared for the preconcentration of 33 basic/neutral and 10 acidic/phenolic pesticides and three metabolites in water. The efficiency of the different extraction procedures was investigated by application of appropriate multiresidue separation methods by reversed phase-high performance liquid chromatography with UV-diode-array detection. Calibrations were performed with multicomponent standard mixtures and recoveries, relative standard deviations and determination limits were calculated for comparing the described enrichment methods. Experiences made in practical application of the different techniques and materials were also considered for the final evaluation.     

Detection of Phthalate Esters in Environmental Water Samples-Comparison of Nylon6 Nanofibers Mat-based Solid Phase Extraction and Other Conventional Extraction Methods

In this article, a new method for simultaneous determination of six phthalate esters was developed by a combination of electrospun nylon6 nanofibers mat‐based solid phase extraction with high performance liquid chromatography‐ultraviolet detector (HPLC‐UV). The six phthalate esters were dimethyl phthalate (DMP), diethyl phthalate (DEP), butyl benzyl phthalate (BBP), di‐n‐butyl phthalate (DBP), di‐(2‐ethylhexyl) phthalate (DEHP) and dioctyl phthalate (DOP). Under optimized conditions, all target analytes in 50 mL environmental water samples could be completely extracted by 2.5 mg nylon6 nanofibers mat and eluted by 100 µL solvent. Compared with C18 cartridges solid phase extraction, C18 disks solid phase extraction and national standard method (China), nylon6 nanofibers mat‐based solid phase extraction was advantageous in aspects of simple and fast operation, low consumption of extraction materials and organic solvents. The four methods were applied to analysis of environment water samples. All the results indicated that the determination values of target compounds with the proposed method were consistent with C18 cartridges and C18 disks solid phase extraction method, and the new method was better than the national standard method in aspects of recovery, LOD and precision. Therefore, nylon6 nanofibers mat has great potential as a novel material for solid phase extraction.     

Evaluation of different extraction approaches for the determination of phenolic compounds and their metabolites in plasma by nanoLC-ESI-TOF-MS

Sample preparation is an important step for the determination of phenolic compounds in biological samples. Different extraction methods have been tested to determine phenolic compounds and their metabolites in plasma by nano-liquid chromatography coupled to electrospray ionisation-time-of-flight mass spectrometry (nanoLC-ESI-TOF-MS). The sample treatment optimisation was performed using commercial foetal bovine serum spiked with representative phenolic standards, namely naringenin, luteolin, verbascoside, apigenin, rutin, syringic acid and catechin. Different protein-precipitation conditions were evaluated as well as enzymatic digestion with trypsin and solid-phase extraction using different phases such as C-18, ABN and ENV+, working at different pH values. The optimum extraction procedure consisted of a previous protein-precipitation step using HCl 200?mmol/L in methanol for 2.5?h at 50?°C followed by a solid-phase extraction using C-18 cartridges at pH?2.5. This procedure was finally applied to the plasma of rats overfed with a phenolic-rich Lippia citriodora extract. These samples were analysed by nanoLC-ESI-TOF-MS, enabling the identification of five compounds previously found in the administered L. citriodora extract and one metabolite.     

Determination of Dydrogesterone in Human Plasma by Tandem Mass Spectrometry: Application to Therapeutic Drug Monitoring of Dydrogesterone in Gynecological Disorders

A sensitive and specific tandem mass spectrometric (MS–MS) method was developed and validated for the determination of dydrogesterone (Duphaston^®), an orally active synthetic progestogen, in human plasma. Multiple reaction monitoring (MRM) scans at m/z 313.1 > 105.5 (dydrogesterone) and m/z 393 > 147 (dexamethasone, internal standard) were selected to determine dydrogesterone by the internal standard method. Linear correlations (r: ～0.99 ± 0.05) of the calibration curves were established over the concentration range 10–60 ng mL^?1 with a lower limit of quantification (LLQ) of 10 ng mL^?1 (RSD% 14.9 and %DEVs ?10.5 to +15.6). Solid-phase extraction (SPE) technique was used for extraction of dydrogesterone and internal standard from patient plasma samples using Oasis^® Max C18 cartridges. Ion suppression studies indicated negligible effects of plasma matrix on the mass ions detection of dydrogesterone and IS, when measured in MRM mode. Validation data showed that RSD% values were <22.0%, whereas %DEV values were in the range of ?20.2 to +13.3 for intra- and inter-day precision and accuracy, respectively. Analytical recoveries of dydrogesterone from supplemented plasma samples with the drug were in the range of 100.7–112%, indicating the efficiency of the SPE for separation of dydrogesterone from human plasma. Stability studies conducted at ?20 °C, showed that dydrogesterone was stable in plasma as indicated from the measured degradation kinetic parameters. The developed method was applied for monitoring plasma levels of dydrogesterone in 25 patients treated with Duphaston^® tablets at a dose of 10 mg three times daily. Mean plasma concentration of 16.1 ± 3.5 ng mL^?1 of dydrogesterone were measured at the steady state. The data suggest the utility of tandem mass method in therapeutic drug monitoring of plasma levels of dydrogesterone in gynecological disorders treated with Duphaston^® tablets.     

Comparison of silica gel modified with three different functional groups with C-18 and styrene-divinylbenzene adsorbents for the analysis of selected volatile flavor compounds

A comparison of SPE cartridges produced in authors laboratory containing silica modified by addition of three functional moieties with standard C-18 and SDVB cartridges was made in terms of their applicability for the isolation of flavor compounds. Compounds found in wine and grapes were used for model mixture, which was spiked into a grape juice. Functionalized phases for SPE were prepared modifying silica gel with alkoxysilanes with different functional groups: (3-(phenylamino)-propyltrimethoxysilane, octyltriethoxysilane and octadecyl-silane. The functionalization was carried out by the dry method, which resulted 5, 10 and 20 weight parts of initial support. Functionalized phases were characterized using FT-IR, elemental analysis and NMR.Performance for new phases compared to “standard” ones (C-18 and SDVB (styrene–divinylbenzene) varied, depending on the group or type of analyzed compound. They were more efficient in extraction of methyl anthranilate and vanilins. For extraction of terpenes, C-6 alcohols, isoprenoids, benzene derivatives and phenols their efficiency was comparable to that of C-18.Functionalized laboratory-made mixed phases are suitable for extraction of flavor compounds from grape juice. They are suitable for extraction of compounds belonging to different chemical classes with the efficiency comparable to C-18 and SDVB phases. The production of such functionalized phases can be easily performed in the laboratory, at a very low cost, comparing to C-18 or SDVB cartridges. This makes the proposed functionalized phases an interesting alternative, in sample preparation for analysis and particularly in preparative/flash chromatography.     

Trace analysis of triazines and organophosphorus pesticides in water

A method for the determination of trace levels of triazines and organophosphorus pesticides in water is presented. The extraction method is based on a solid-phase extraction on C-18 bound silica SPE cartridges. A precolumn filled with Merck C-18 bound silica and home-made C-18 bound silica have been tested at a flow-rate of 3 ml/min with comparable preconcentration yields. A SIM-MS method using a ¹⁵N labelled internal standard has been developed for the organophosphorus pesticides. Detection limits lower than 1 g/L have been obtained. Separations have been carried out on a conventional GC column OV 17 (1 m) and a capillary column OV 17 (25 m) with a temperature program from 150° C (2 min) to 300° C (rate of 6° C/min).     

Determination of Pyrethroid and Organophosphorus Insecticides in Indoor Air by Microwave-Assisted Extraction with Gas Chromatography/Mass Spectrometry

The goal of this study was to evaluate the efficiency of microwave-assisted extraction for the recovery of pyrethroid and organophosphorus insecticides adsorbed on quartz fiber filters and C18 disks used for indoor air sampling. The extraction solvent, temperature, and time were optimized by spiking tests. The recoveries for the insecticides obtained by microwave-assisted extraction with acetone at 50°C for 5 min were between 71.9% and 119.2% with relative standard deviations between 0.3% and 9.3% at two spike levels (0.1 µg and 1.0 µg). The results of the microwave-assisted extraction under the validation conditions were comparable to those obtained by Soxhlet extraction, which was used as a reference technique. In a preliminary analysis, resmethrin and tetramethrin were determined in the indoor air of an apartment unit at concentrations of 7.8 ng/m³ and 66.0 ng/m³, respectively, using the microwave-assisted extraction-based method with gas chromatography/mass spectrometry.     

Solid-Phase Extraction of Caffeine and Theophylline from Green Tea by a New Ionic Liquid-Modified Functional Polymer Sorbent

The new ionic liquid-modified polymer sorbent was developed by surface chemical modification of the synthesized polymer particles using ionic liquids. The obtained ionic liquid-modified polymer was successfully used as a special sorbent in a solid-phase extraction (SPE) process to isolate caffeine and theophylline from green tea. A comparison of different SPE cartridges using the blank polymer, C₁₈, and ionic liquid-modified polymer revealed that the highest recovery was obtained using ionic liquid-modified polymer sorbent. Quantitative analysis was carried out by using a C₁₈ column (5 µm, 150 × 4.6 mm) as an analytical column. Good linearity was obtained from 5 × 10^?4 to 0.5 mg/mL (r²>0.999) for the two analytes with relative standard deviations <4.5%.     

SPE of Tanshinones from Salvia miltiorrhiza Bunge by using Imprinted Functionalized Ionic Liquid-Modified Silica

Ionic liquid-modified silica, with functional groups based on imidazole as the cation, was obtained. A molecular imprinting technique was introduced to form the order of functional groups. The selectivity of the obtained ionic liquid-modified silica was successfully used as a special imprinted sorbent in the solid-phase extraction to isolate cryptotanshinone, tanshinone I and tanshinone IIA from Salvia miltiorrhiza Bunge. Several washing and elution solvents with different polarities were evaluated. The ionic liquid-modified silica as the sorbent exhibited a higher selectivity than blank ionic liquid-modified silica, traditional silica and C₁₈ cartridges. A quantitative analysis was conducted by liquid chromatography with a C₁₈ column and methanol/water (75:25, v/v, containing 0.5% acetic acid) as the mobile phase. A good linearity was obtained from 0.5 × 10^?4 to 0.1 mg mL^?1 (r ²  > 0.99) with relative standard deviations that were less than 4.6%.     

Investigation of commercial sorbents for the analysis of opioid peptides in human plasma by on‐line SPE‐CE

In this study, we investigated the performance of several commercial sorbents (Sep‐pack^® C18, ^tC18, C8 and ^tC2, Oasis^® HLB, Isolute^® ENV+, Strata^?‐X and Oasis^® MCX) for the determination of opioid peptides by solid‐phase extraction coupled on‐line to capillary electrophoresis (SPE‐CE). First, standard solutions were analyzed in order to achieve the lowest LOD and the best electrophoretic separations using UV detection. The best results were obtained using C18, C8 and ^tC2 sorbents, which were examined for the analysis of spiked human plasma samples. A double‐step sample clean‐up pretreatment, which consisted of precipitation with acetonitrile and filtration, was needed to prevent saturation of the on‐line SPE microcartridge. The filtration step was critical to obtain optimum analyte recovery and to clean up the sample matrix. A range of centrifugal filters and filtration conditions were tested and the recoveries of the sample pretreatment were evaluated by CE‐ESI‐MS. The LODs attained through SPE‐CE‐UV were approximately ten‐fold better with C18 than with C8 and ^tC2. The 0.1 μg/mL LODs achieved by C18‐SPE‐CE‐UV were further improved until we could detect 1 ng/mL concentrations of opioid peptides in plasma samples by C18‐SPE‐CE‐ESI‐MS, due to the outstanding selectivity of the MS detection.     

Statistical suitability testing of the Aliquat-336, AnaLig® Pu-02 and TRU® Resin use for the 239,240Pu, 238Pu determination

In this paper three different methods were used for plutonium separation and statistical tested-molecular recognition technology products AnaLig^® Pu-02, liquid–liquid extraction with Aliquat-336 and extraction chromatography with TRU^® Resin. The methods performance was investigated by analysis of NPL (High Alpha–Beta 2005) intercomparison sample. Regression diagnostics procedures were used for examination of the regression triplet and pair t test were applied for comparison of methods for the separation of ^239,240Pu, ²³⁸Pu with Aliquat-336, TRU^® Resin and AnaLig^® Pu-02. The presented results were evaluated as correct for all experimental data.     

Purification of 4-hydroxybenzoic Acid and 4-hydroxybenzaldehyde from Laminaria japonica Aresch Using Commercial and Monolithic Sorbent in SPE Cartridge

Phenolic compounds are one of the major compounds in Laminaria japonica Aresch. Solid-phase extraction was used to separate the two phenolic compounds (4-hydroxybenzoic acid and 4-hydroxybenzaldehyde). A new monolithic sorbent was developed and used successfully as a special sorbent in a solid-phase extraction process. The effects on different SPE cartridges using silica, C₁₈, and monolithic were compared. Quantitative analysis was carried out using a C₁₈ analysis column (5 µm, 150 × 4.6 mm). Good linearity was obtained for the two targets, ranging from 0.5 to 100 µg mL^?1 (r ²  > 0.999), with relative standard deviations <4.7%.     

Validation of <Superscript>90</Superscript>Sr separation method using molecular recognition product AnaLig<Superscript>®</Superscript> Sr01 gel and extraction chromatography Sr<Superscript>®</Superscript> resin

Two separation techniques for strontium determination using AnaLig^® Sr01 molecular recognition technology and extraction chromatography Sr^®  resin were tested. The methods performance was investigated by analysis of NPL (High Alpha–Beta 2003) intercomparison sample. The results obtained for both procedures were compared in terms of activities and recoveries. Data analysis proved a good agreement with the reference values. The AnaLig^® Sr01 separation method for ⁹⁰Sr determination was successfully validated with the same performance as the Sr^® resin method.     

Solid phase versus solvent extraction of pesticides from water

The average recovery for 12 pesticides spiked into 100 ml of water at 0.1 ppb was 90% when cartridges containing 100 mg of C-18 bonded porous silica were used for adsorption. Flow rates of up to 200 bed volumes per minute were employed for the adsorption step. Quantitative desorption of the pesticides was accomplished with less than 100l of solvent, thus eliminating the need for a solvent reduction step. The pesticides from samples of surface waters were adsorbed onto C-18 bonded porous silica at the sampling site and the cartridges containing the bonded phase were returned to the laboratory for elution and analysis. The analytical results obtained from use of this procedure agreed with those obtained for duplicate samples of the water that were processed in the laboratory using standard solvent extraction procedures.     

Separation and Simultaneous Determination of Enantiomers of Tau-fluvalinate and Permethrin in Drinking Water

The chiral liquid chromatographic separation of two pyrethroid insecticides, tau-fluvalinate and permethrin, on different polysaccharide-based chiral stationary phases (CSPs) has been investigated. Complete separation of these compounds was achieved with Chiralcel OJ under normal phase mode and a mobile phase of n-hexane:ethanol (90:10, v/v). This method has been used for determining these compounds in drinking water at ppb levels after solid-phase extraction (SPE) with C-18 cartridges. Recoveries ranged between 103–113% and precision values (expressed as relative standard deviations) were lower than 10%.     

Determination of organotin compounds (OTC) at low levels in seawater by solid-phase extraction (SPE) and gas chromatography-pulsed flame photometric detection (GC-PFPD)

In this work, a simple, sensitive and affordable analytical method for the simultaneous determination of nine organotin compounds (butyltins, phenyltins and methyltins) in seawater using solid-phase extraction (SPE) and gas chromatography-pulsed flame photometric detection was developed and validated. The performance of three different SPE cartridges (Envi C₁₈, Oasis HLB and Oasis MCX) and three elution solvents of different polarity (hexane, methanol and acetonitrile) was evaluated. The extraction parameters, such as solvent volume, presence of complexing and ion-pairing reagents, sample volume and pH and breakthrough volume, were also investigated. Tributyltin, as the organotin compound of special interest, was efficiently extracted using any of the cartridges and solvents tested. However, the simultaneous extraction of all nine organotin compounds was the most efficient using reversed-phase Envi C₁₈ cartridge and 0.1% (w/v) tropolone in methanol as eluent. The optimised method resulted in good recovery, precision and linearity for all compounds, particularly for tri- and disubstituted species. Method detection limits ranged from 0.22 to 1.27 ng(Sn) L^?1 for butyltins, 0.37 to 4.91 ng(Sn) L^?1 for phenyltins and 0.45 to 1.16 ng(Sn) L^?1 for methyltins. The accuracy of butyltins determination was further verified by the comparison with purchased derivatised standards. The developed method was successfully applied to the environmental samples.     

Determination of Palmatine in Rabbit Plasma by RP-HPLC with Solid-Phase Extraction

A rapid and specific reversed-phase high performance liquid chromatography (RP-HPLC) method for the determination of palmatine in rabbit plasma has been developed and validated. The chromatographic separation was performed on a C₁₈ column at 40 °C. The mobile phase, delivered at 1.0 mL min^?1, consisted of acetonitrile/phosphate buffer (pH 3.0) 40:60 (v/v). The detection wavelength was set at 345 nm. Palmatine and internal standard (IS) berberine were extracted from plasma by solid-phase extraction using C18 cartridges. Linearity was confirmed in the concentration range of 0.01 to 5 μg mL^?1, the inter-day and intra-day RSDs were within 10.0, the recoveries of palmatine ranged from 93.1 to 110.3, and the limit of detection (LOD, S/N > 3) was 0.002 μg mL^?1. The method is applicable to the determination of palmatine in rabbit plasma after intravenous administration of palmatine.     

Determination of pesticides in sugarcane juice employing microextraction by packed sorbent followed by gas chromatography and mass spectrometry

This paper describes the development of a method for the determination of six pesticides (tebuthiuron, carbofuran, atrazine, metribuzine, ametryn, and bifenthrin) in sugarcane juice using microextraction by packed sorbent as the extraction technique. The extraction steps were optimized by factorial design, being the variables pH, ionic strength, desorption solvent and solvent volume optimized for comparisons among sorbent materials. Among the evaluated materials C18‐Chromabond ^® showed better extraction efficiency. A factorial design 2³ with central point was used for the extraction cycles optimization. Draw/eject and washes cycles showed significant improvements in the extraction efficiency when the number of cycles increased. The method was validated and showed a limit of quantification in the range of 2.0–10.0 μg.L^?1. The calibration curves were constructed by weighting models that reduced the sum of absolute residues values and improved determination coefficient. The matrix factor and extraction efficiency were 97.3–77.3% and 27.1–64.8%, respectively. The accuracy was 71.7–106.9%; precision evaluated as the coefficient of variance obtained in intra and inter day analysis was 4.5–15.9%. The method was applied to the determination of pesticide residues in four sugarcane juice samples commercially available in markets from different cities from São Paulo state, Brazil.     

A Fully Automatic HPLC–CAD–DAD Method Coupled with ASE and Online SPE for Simultaneous Determination of Seven Antibiotics in Bio-Matrices

It is a challenge to simultaneously determine the multiple-component targets in complex matrices when some of the targets bear chromophores but some contain no chromophores. A novel HPLC–CAD–DAD method coupled with accelerated solvent extraction and online solid phase extraction (SPE) was developed for simultaneous determination of seven antibiotics in solid bio-matrices. The online SPE operation parameters were optimized on a Acclaim^®120 C18 cartridge in terms of extraction efficiency with sample injection volume of 1 mL, and the online SPE operation yielded enhancement factors in the range of 29–77 for the different antibiotics. The proposed method showed good recoveries ranging between 79.2 and 104.7 % for different antibiotics and excellent inter-day and intra-day precision with relative standard deviation values ranging from 0.6 to 7.8 %. The detection limits were between 1.8 and 18.0 μg kg⁻¹.

     

Production of FAME and FAEE via Alcoholysis of Sunflower Oil by Eversa Lipases Immobilized on Hydrophobic Supports

The performance of two new commercial low-cost lipases Eversa® Transform and Eversa® Transform 2.0 immobilized in different supports was investigated. The two lipases were adsorbed on four different hydrophobic supports. Interesting results were obtained for both lipases and for the four supports. However, the most active derivative was prepared by immobilization of Eversa® Transform 2.0 on Sepabeads C-18. Ninety-nine percent of fatty acid ethyl ester was obtained, in 3 h at 40 °C, by using hexane as solvent, a molar ratio of 4:1 (ethanol/oil), and 10 wt% of immobilized biocatalyst. The final reaction mixture contained traces of monoacylglycerols but was completely free of diacylglycerols. After four reaction cycles, the immobilized biocatalyst preserved 75% of activity. Both lipases immobilized in Sepabeads C-18 were very active with ethanol and methanol as acceptors, but they were much more stable in the presence of ethanol.