Evaluation of an alternative fluorinated sorbent for dispersive solid-phase extraction clean-up of the quick, easy, cheap, effective, rugged, and safe method for pesticide residues analysis.

In this study, the efficiency of a new fluorinated sorbent for dispersive solid-phase extraction (d-SPE) clean-up in extracts provided by the QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) acetate method from tomato and sweet pepper samples was evaluated by ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Clean-up using d-SPE technique has been widely used associated with the QuEChERS method. The most commonly sorbents used in d-SPE are primary secondary amine (PSA), octadecylsilane (C18) and graphitized carbon black (GCB), which are indicated to remove sugars, fatty acids, pigments, among others. The performance of an alternative fluorinated sorbent was compared with PSA and C18 sorbents for representative pesticides and better results were obtained when the fluorinated sorbent was used. Validation presented acceptable results for trueness and precision, with method limit of detection between 0.9 and 1.8µgkg-1 and limit of quantification from 2.6 to 5.4µgkg-1. Most of the compounds presented low matrix effect. Results showed that the fluorinated sorbent contribute to the clean-up of the tomato extract and is an effective alternative, with lower costs and greater efficiency. Commercial tomato samples were analyzed using the proposed method and residues of dimethoate, tetraconazole and thiamethoxam were detected.

Selective molecularly imprinted polymer combined with restricted access material for in-tube SPME/UHPLC-MS/MS of parabens in breast milk samples.

A new molecularly imprinted polymer modified with restricted access material (a hydrophilic external layer), (MIP-RAM) was synthesized via polymerization in situ in an open fused silica capillary. This stationary phase was used as sorbent for in-tube solid phase microextraction (in-tube SPME) to determine parabens in breast milk samples by ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Scanning electron micrographs (SEM) illustrate MIP surface modification after glycerol dimethacrylate (hydrophilic monomer) incorporation. The interaction between parabens and MIP-RAM was investigated by Fourier-transform infrared (FTIR) spectroscopy. The Scatchard plot for MIP-RAM presented two linear parts with different slopes, illustrating binding sites with high- and low-affinity. Endogenous compounds exclusion from the MIP-RAM capillary was demonstrated by in-tube SPME/LC-UV assays carried out with blank milk samples. The in-tube SPME/UHPLC-MS/MS method presented linear range from 10 ng mL(-1) (LLOQ) to 400 ng mL(-1) with coefficients of determination higher than 0.99, inter-assay precision with coefficient of variation (CV) values ranging from 2 to 15%, and inter-assay accuracy with relative standard deviation (RSD) values ranging from -1% to 19%. Analytical validation parameters attested that in-tube SPME/UHPLC-MS/MS is an appropriate method to determine parabens in human milk samples to assess human exposure to these compounds. Analysis of breast milk samples from lactating women demonstrated that the proposed method is effective.

Preparation and characterization of a new microwave immobilized poly(2-phenylpropyl)methylsiloxane stationary phase for reversed phase high-performance liquid chromatography.

A new reversed phase high-performance liquid chromatography (RP-HPLC) stationary phase was prepared and its chromatographic and physical-chemical properties were evaluated. The new stationary phase was prepared with a silica support and poly(2-phenylpropyl)methylsiloxane (PPPMS), a phenyl type polysiloxane copolymer. Since this is a new copolymer and there is little information in the literature, it was submitted to physical-chemical characterization by infrared spectroscopy and thermogravimetry. The chromatographic phase was prepared through sorption and microwave immobilization of the copolymer onto a silica support. The chromatographic performance was evaluated by employing test procedures suggested by Engelhardt and Jungheim, Tanaka and co-workers, Neue, and Szabó and Csató. These test mixtures provide information about the hydrophobic selectivity, silanophilic activity, ion-exchange capacity, shape selectivity and interaction with polar analytes of the new Si-PPPMS reversed phase. Stability tests were developed using accelerated aging tests under both basic and acidic conditions to provide information about the lifetime of the packed columns.

Determination of some organic contaminants in water samples by solid-phase extraction and liquid chromatography-tandem mass spectrometry.

Independent methods for determination of organic contaminants such as pharmaceuticals and pesticides in drinking water samples, using SPE as the extraction technique and LC-MS/MS in the MRM mode with electrospray ionization, were developed and validated. Different SPE sorbents were evaluated, including lab-made fluorinated and phenyl and commercial Oasis HLB and C18, with the commercial phases being more suitable for the target compounds. Recoveries in the range of 70-120% were obtained for all target compounds, with the exception for paracetamol (acetaminophen), and precision values (inter-day and intra-day), expressed in terms of relative standard deviations (RSD), lower than 20% were obtained for all target compounds. Quantification limits were in the range of 0.006-0.208 µg L(-1) and the methods developed were successfully applied for the analysis of drinking water samples, detecting some pharmaceuticals and pesticides, but at concentration levels lower than the MRL.

Some new selective stationary phases for RP-HPLC.

At the present time, more complex analyses of apolar compounds with similar chemical structures or of polar compounds, especially basic ones, having diverse properties require more selective stationary phases having better stabilities. This paper describes several new stationary phases with directed selectivities that were prepared by immobilizing two different phenyl group-containing siloxanes and a trifluoropropyl-containing siloxane onto chromatographic silica and, in the case of the fluorinated siloxane, onto zirconized silica, using thermal treatment or microware radiation. The chromatographic properties and stabilities of these new phases were determined and several applications were evaluated. The phenyl-containing phases showed excellent characteristics related to the separation of several different types of aromatic compounds while the fluorinated phases, which present a more polar character, revealed selectivity for the separation of positional isomers as well as for a mixture of basic pharmaceuticals. Stability tests indicate that immobilization of the polysiloxanes increases column lifetimes by making the stationary phases less susceptible to dissolution, while the phases immobilized with microwave radiation were somewhat more stable than those immobilized by thermal treatments.

Determination of beta-artemether and its main metabolite dihydroartemisinin in plasma employing liquid-phase microextraction prior to liquid chromatographic-tandem mass spectrometric analysis.

A method for the determination of artemether (ART) and its main metabolite dihydroartemisinin (DHA) in plasma employing liquid-phase microextraction (LPME) for sample preparation prior to liquid chromatography-tandem mass spectrometry (LC-MS-MS) was developed. The analytes were extracted from 1mL of plasma utilizing a two-phase LPME procedure with artemisinin as internal standard. Using the optimized LPME conditions, mean absolute recovery rates of 25 and 32% for DHA and ART, respectively, were achieved using toluene-n-octanol (1:1, v/v) as organic phase with an extraction time of 30min. After extraction, the analytes were resolved within 5min using a mobile phase consisting of methanol-ammonium acetate (10mmolL(-1), pH 5.0, 80:20, v/v) on a laboratory-made column based on poly(methyltetradecylsiloxane) attached to a zirconized-silica support. MS-MS detection was employed using an electrospray interface in the positive ion mode. The method developed was linear over the range of 5-1000ngmL(-1) for both analytes. Precision and accuracy were within acceptable levels of confidence (<15%). The assay was applied to the determination of these analytes in plasma from rats treated with ART. The two-phase LPME procedure is affordable and the solvent consumption was very low compared to the traditional methods of sample preparation.

A new thermally immobilized fluorinated stationary phase for RP-HPLC.

A new fluorinated stationary phase was prepared through thermal immobilization of poly(methyl-3,3,3-trifluoropropylsiloxane) onto 5 microm Kromasil silica particles. The best conditions of immobilization time and temperature were determined through a central composite design and response surface methodologies. Physical-chemical characterization using solid-state (29)Si NMR measurements, infrared spectroscopy and elemental analysis showed that the immobilization process was effective to promote a coating of the support that corresponds to a monolayer of polymer. The stationary phase presents selectivity for positional isomers and good peak shape for basic compounds.

Effects of different high pH solutions on the chemical stability of immobilized-polymer stationary phases.

Many chromatographic separations require high pH mobile phases for the elution of basic compounds with symmetrical peaks appropriate for quantitation. Phosphate and carbonate salts are the most common additives used to achieve these conditions. However, they act in different ways on the stability of silica-based stationary phases. To provide a faster evaluation of the effects of these high pH solutions on the column lifetime of new immobilized-polymer metalized-silica-based phases prepared in our laboratory, an accelerated stability test at a nominal pH of 10 and at 50 degrees C was developed and applied with monitoring of the retention factor, column efficiency, and asymmetry as functions of the volume of high pH mobile phase. The laboratory-made stationary phases presented chemical stabilities in phosphate solution more than three times better their chemical stabilities in carbonate buffer.

Combined column-mobile phase mixture statistical design optimization of high-performance liquid chromatographic analysis of multicomponent systems.

A statistical approach for the simultaneous optimization of the mobile and stationary phases used in reversed-phase liquid chromatography is presented. Mixture designs using aqueous mixtures of acetonitrile (ACN), methanol (MeOH) and tetrahydrofuran (THF) organic modifiers were performed simultaneously with column type optimization, according to a split-plot design, to achieve the best separation of compounds in two sample sets: one containing 10 neutral compounds with similar retention factors and another containing 11 pesticides. Combined models were obtained by multiplying a linear model for column type, C8 or C18, by quadratic or special cubic mixture models. Instead of using an objective response function, combined models were built for elementary chromatographic criteria (retention factors, resolution and relative retention) of each solute or pair of solutes and, after their validation, the global separation was accomplished by means of Derringer's desirability functions. For neutral compounds a 37:12:8:43 (v/v/v/v) percentage mixture of ACN:MeOH:THF:H2O with the C18 column and for pesticides a 15:15:70 (v/v/v) ACN:THF:H2O mixture with the C8 column provide excellent resolution of all peaks.

Development of a polymer-coated stationary phase with improved chemical stability in alkaline mobile phases.

An endcapped stationary phase is prepared by thermal immobilization of poly(methyltetradecylsiloxane) (PMTDS) onto a doubly zirconized silica support followed by endcapping using a mixture of hexamethyldisilazane and trimethylchlorosilane. The preparation of the Si-Zr(PMTDS)ec phase shows good repeatability with RSD <3.0% for carbon loadings and column efficiency. This new stationary phase has a lower density of residual hydroxyl groups, according to spectroscopic methods while basic compounds from the Tanaka and Engelhardt test mixtures are eluted with essentially symmetric peaks. Furthermore, the stability of the Si-Zr(PMTDS)ec stationary phase, measured using an accelerated aging test, is twice as great as the stability of a similar nonendcapped phase. The new phase shows promise for the separation of basic pharmaceuticals.

Determination of pesticides and metabolites in wine by high performance liquid chromatography and second-order calibration methods.

The models parallel factor analysis (PARAFAC) and the recently introduced bilinear least squares (BLLS) were applied to develop second-order calibration methods to high performance liquid chromatography with diode array detection (HPLC-DAD) data, where overlap of interferences with the compounds of interest was observed, making the determination and resolution of the analytes possible. In this work, the simultaneous determination of five pesticides and two metabolites in wine samples by HPLC-DAD was performed, using the second-order advantage. The results of two chromatographic methods were compared, involving either isocratic or gradient elution. An appropriate preprocessing method was necessary to correct the effects of time shifts, baseline variations and background. BLLS presented results that were of the same quality as PARAFAC in five cases, but in two other situations only PARAFAC enabled analyte quantitation. Relative errors of prediction lower than 10% for all compounds were obtained, indicating that the methodology employing HLPC-DAD and second-order calibration can handle complex analytical systems.

Poly(methyltetradecylsiloxane) immobilized onto silica for extraction of multiclass pesticides from surface waters.

A new material based on poly(methyltetradecylsiloxane) (PMTDS) thermally immobilized onto a silica support has been tested as a sorbent for the solid-phase extraction (SPE) from water of several pesticides used in soybean cultivation. The SPE methodology was developed and validated for six of these pesticides (imazethapyr, imazaquin, metsulfuron-methyl, bentazone, chlorimuron-ethyl and tebuconazole) according to the International Conference on Harmonization directives and the results were compared with those obtained with a commercial C18 SPE cartridge. The PMTDS-based sorbent gives results similar to the commercial sorbent with recoveries and precisions in agreement with directives for residue analysis. The quantification limits, after concentration, of all the pesticides evaluated were 1.0 microg L(-1), below the levels imposed by the principal regulatory agencies. The PMTDS-based sorbent preparation is fast, easy and reproducible and the cartridges are less expensive than similar commercial SPE materials.

Immobilized polymeric stationary phases using metalized silica supports.

Immobilized presynthesized polymers on porous metalized (zirconized or titanized) silica particles as new stationary phases with improved chemical stability for RP-HPLC are reviewed. The preparations using different polymers, such as poly(methyloctylsiloxane), poly(methyltetradecylsiloxane), and poly(butadiene), different immobilization steps (gamma radiation, thermal treatment, and microwave radiation), and the chromatographic performances of these phases for polar, apolar, acidic, and basic compounds are discussed. The stability of some of these stationary phases using alkaline mobile phases is also presented.

Use of near infrared emission spectroscopy in the study of supporting materials and stationary phases for liquid chromatography.

Near infrared emission spectroscopy (NIRES) has been investigated in the study of different materials employed in liquid chromatography. The samples were heated in a nitrogen atmosphere and the emission spectra were obtained using a lab-made NIRES instrument. Through principal component analysis (PCA) using the raw emission spectra, it was possible to distinguish different materials according to their physical and/or chemical characteristics. Linear relationships between emissivity spectra and the contents of the coating material or the specific surface areas was observed for stationary phases or bare silicas, respectively. Furthermore, the thermal stability of stationary phases could be followed in real time.

Poly(methyloctylsiloxane) immobilized on silica as a sorbent for solid-phase extraction of some pesticides.

A laboratory-made sorbent for solid-phase extraction (SPE) was obtained by thermal immobilization of poly(methyloctylsiloxane) (PMOS) onto silica. Cartridges packed with the new sorbent were used for the simultaneous determination of imazethapyr, nicosulfuron, diuron, linuron and chlorimuron-ethyl in water. These pesticides were separated and quantified using high-performance liquid chromatography with diode array detection (HPLC-DAD). The recoveries achieved with the laboratory-made PMOS cartridges were compared with those of some commercially available silica-based and polymer-based cartridges having C18, C8 and NH(2) pendant groups. Method validation using the laboratory-made sorbent was performed for the five pesticides at three fortifications levels (1x, 2x and 10x the limit of quantification of each pesticide). The laboratory-made PMOS cartridge has low cost preparation and showed good recoveries (72-111%) for all pesticides. Repeatability and intermediate precision were lower than 15%. Its performance was similar or even better, in some cases, than those of the commercial cartridges.

High-performance liquid chromatographic determination of pesticides in tomatoes using laboratory-made NH2 and C18 solid-phase extraction materials.

A method for high-performance liquid chromatographic (HPLC) multiresidue determination of six pesticides in tomatoes was developed and validated. Silica-based C18 (octadecyl) and NH2 (aminopropyl) solid-phase extraction (SPE) sorbents, made in our laboratory, were used for sample preparation. The SPE materials were obtained by thermal immobilization of appropriate polysiloxanes onto 40 microm silica surfaces and were used in sample preparation for multiresidue analysis of the following pesticides: tebuthiuron and diuron (urea herbicides), simazine, atrazine and ametryn (triazines herbicides) and benomyl (benzimidazol fungicide). The results were compared with similar commercial materials. Reversed-phase high-performance liquid chromatography (RP-HPLC) using a Purospher RP-18 5 microm column and ACN: 0.01% aqueous NH4OH, pH 8.4 (35:65, v/v) as mobile phase, at 0.7 mlmin(-1), with 235 nm UV detection, was used for separation and quantification of the pesticides. Method validation was performed at three fortification levels (100, 200, 1000 microg l(-1)). Limits of detection and quantification show that the methods developed can be used to detect the pesticides in concentrations below the maximum residue levels (MRL) established by the Codex Alimentarius, USA, European Union and Brazilian legislations. The results showed that aminopropyl materials have a better performance than the octadecyl sorbents. Laboratory-made materials give results similar to commercial sorbents, with recoveries and precisions in agreement with directives for method validation in residue analysis.

Characterization of a new stationary phase based on microwave immobilized polybutadiene on titanium oxide-modified silica.

Titanium oxide-modified silica was prepared by reaction of silica with titanium tetrabutoxide and then was used as support in the preparation of stationary phases with self-immobilized polybutadiene (PBD) and PBD immobilized through microwave radiation. Chromatographic performance of the stationary phases was evaluated in terms of the efficiency (plates/m), asymmetry (A(s)), retention factor (k) and resolution (R(s)) of two standard sample mixtures, one of then containing the basic compound N,N-dimethylaniline. A microwave irradiation of 30 min at 520 W gave the best efficiency (86,500 N m(-1)), greater than that of a 6-day self immobilized phase (69,500 N m(-1)). Self-immobilized stationary phases prepared with bare silica were also studied for comparison. These resulted in lower chromatographic performance, 43,800 N m(-1), when compared to the self-immobilized phase prepared with titanized silica.

New materials for solid-phase extraction and multiclass high-performance liquid chromatographic analysis of pesticides in grapes.

Sample preparation procedures which included the use of new aminopropyl (NH2) and octadecyl (C18) solid-phase extraction (SPE) sorbents are proposed for the simultaneous multiclass determination of the fungicide benomyl and of the herbicides tebuthiuron, diuron, simazine, atrazine, and ametryn in grapes, using single wavelength high-performance liquid chromatography. Sorbent preparation uses a fast, easy, and effective procedure to obtain silica-based materials, made by depositing polysiloxanes on a silica support followed by thermal immobilization. Recovery results of the compounds, after elution from the SPE cartridges, indicate that the most efficient system employed silica loaded with 40% of an aminofunctional polydimethylsiloxane as sorbent, using dichloromethane:methanol (95:5, v/v) as eluent. Method validation, carried out in agreement with International Conference on Harmonization directives, was performed at three fortification levels (100, 200, and 1000 microg kg(-1)). Limits of detection and quantification show that the method developed can be used to detect the pesticides at concentrations below the maximum residue levels established by Codex Alimentarius, the US Environmental Protection Agency, the European Union, and Brazilian legislation.

Microwave-immobilized polybutadiene stationary phase for reversed-phase high-performance liquid chromatography.

Polybutadiene (PBD) has been immobilized on high-performance liquid chromatography (HPLC) silica by microwave radiation at various power levels (52-663 W) and actuation times (3-60 min). Columns prepared from these reversed-phase HPLC materials, as well as from similar non-irradiated materials, were tested with standard sample mixtures and characterized by elemental analysis (%C) and infrared spectroscopy. A microwave irradiation of 20 min at 663 W gives a layer of immobilized PBD that presented good performance. Longer irradiation times give thicker immobilized layers having less favorable chromatographic properties.

Influence of air on polybutadiene used in the preparation of stationary phases for high-performance liquid chromatography.

A 100 ml bottle of polybutadiene, PBD, was repeatedly exposed to air over a period of 6 months. Samples were taken at time zero (PBD-0), after 3 months (PBD-3) and 6 months (PBD-6). These samples were sorbed onto HPLC silica by an open-air solution-evaporation procedure, which involved exposure to the atmosphere for 6 days. Portions of the three sets of samples were used to compare self-immobilization and the effects of 100 degrees C thermal treatments in air or nitrogen on HPLC performance of the resulting phases. It is concluded that self-immobilization is enhanced by prior exposure of sorbed PBD to air and subsequent heating at 100 degrees C further enhances column performance. The best performance (10(5) plates m(-1)) resulted from 4 h heating of PBD-6 material in nitrogen.