Off-line solid-phase microextraction and capillary electrophoresis mass spectrometry to determine acidic pesticides in fruits

A method based on solid-phase microextraction (SPME) and capillary electrophoresis/mass spectrometry (CE/ MS) is described for determining simultaneously five acidic pesticides (o-phenylphenol, ioxynil, haloxyfop, acifluorfen, picloram) in fruits. The CE device is coupled to an electrospray interface by a commercial sheath-flow adapter. Emphasis is placed on fulfillment of the speed and sensitivity requirements. The best separation is achieved using 32 mM ammonium formate/acid formic buffer at pH 3.1, with a working voltage of 25 kV. The MS detection of the five pesticides was performed in negative ionization mode. Full-scan spectra with base peaks corresponding to [M-H]- were obtained except for acifluorfen, which gives [M-H-CO2]- as most abundant ion. Compared with the conventional EC-UV, the limits of detection were lower for acifluorfen, haloxyfop, ioxynil, and picloram, by a factor of 20, 20, 50, and 2, respectively. Extraction involved fruit sample homogenization with an acetone-water solution (5:1), filtration, and acetone evaporation prior to fiber extraction. SPME conditions such as time, pH, ion strength, stationary phase of the fiber, sample matrix, and desorption solvents were examined. The recovery of the analytes ranged from 7 to 94%, and the relative standard deviation was between 3 and, 13%. The method was found to be linear between 0.02 and 500 mg kg(-1) with correlation coefficients ranging from 0.992 to 0.997. The limits of quantification were from 0.02 to 5 mg kg(-1). The optimized method was successfully applied to the analysis of acid pesticides in fruit samples.     

Thermal desorption solid-phase microextraction inlet for differential mobility spectrometry

A splitless thermal desorber unit that interfaces a differential mobility spectrometry (DMS) sensor has been devised. This device was characterized by the detection of benzene, toluene, and xylene (BTX) in water. The detection of BTX in water is important for environmental monitoring, and ion mobility measurements are traditionally difficult for hydrocarbons in water because water competes for charge and quenches the hydrocarbon signals. This paper reports the use of a DMS with a photoionization source that is directly coupled to a solid-phase microextraction (SPME) desorber. The separation and detection capabilities of the DMS were demonstrated using BTX components. Detection limits for benzene, toluene, and m-xylene were 75, 50, and 5 microg mL(-1), respectively.     

A solid-phase microextraction device for the analysis of electrochemical reaction products by gas chromatography/mass spectrometry

Presented is a solid-phase microextraction syringe-electrode assembly that may be used to identify electrode reaction products. After an electrochemical experiment, the electrode within this syringe-electrode assembly can be introduced into the injection port of a gas chromatograph. Electrochemical reaction products can be analyzed, provided they adhere to the electrode surface and are amenable to gas chromatographic/mass spectrometric analysis. We highlight the potential usefulness of this device using well-known electrochemical reaction of quinones.     

Laser desorption-membrane introduction mass spectrometry

In this paper we describe the first use of laser desorption in conjunction with membrane introduction mass spectrometry (MIMS). In this technique, a low-powered carbon dioxide laser is used to irradiate the low-pressure (vacuum) side of a silicone membrane during a typical MIMS analysis of an aqueous solution. The absorption of laser energy results in direct membrane heating and rapid desorption of permeate molecules. This improves both the sensitivity and response times of MIMS when analyzing compounds having high molecular weight and low volatility. Two simple interfaces are described for performing laser desorption inside and outside the vacuum manifold of a GCQ ion trap mass spectrometer. Together with flow injection (FI) sample introduction, we demonstrate direct on-line monitoring of aqueous solutions of high boiling point (200-530 °C) polynuclear aromatic hydrocarbons such as naphthalene, anthracene, pyrene, benzo[b]fluoranthene, and indeno[123-cd]pyrene.     

Target and nontarget screening of organic micropollutants in water by solid-phase microextraction combined with gas chromatography/high-resolution time-of-flight mass spectrometry

The potential of gas chromatography coupled to high-resolution time-of-flight mass spectrometry (GC/TOF-MS) for screening of organic pollutants in water has been explored. After optimization of the solid-phase microextraction (SPME) step, where parameters such as fiber selection and addition of salt were studied, this extraction technique was applied to the analysis of different types of water samples. Investigation of 60 target organic pollutants, including pesticides, octyl/nonyl phenols, pentachlorobenzene, and polycyclic aromatic hydrocarbons (PAHs) was carried out by evaluating the presence of up to five representative m/z ions per analyte, measured at high mass accuracy, and the attainment of their Q/q (Q, quantitative ion; q, confirmative ion) intensity ratio. This strategy led to the detection of 4-t-octylphenol, simazine, terbuthylazine, chlorpyrifos, terbumeton, and terbutryn in several water samples at low part-per-billion levels. Full spectrum acquisition data generated by the TOF-MS analyzer also allowed subsequent investigation of the presence of polybrominated diphenyl ethers and several fungicides in samples after MS data acquisition, without the need to reanalyze the water samples. In addition, nontarget analysis was also tested by application of a deconvolution software. Several organic pollutants that did not form a part of the list of contaminants investigated were identified in the water samples, thanks to the excellent sensitivity of TOF-MS in full spectrum acquisition mode and the valuable accurate mass information provided by instrument. Bisphenol A, the antioxidant 3,5-di-tert-butyl-4-hydroxy-toluene (BHT), its metabolite 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO), the polycyclic musk galaxolide, and the UV filter benzophenone were some of the compounds present in the water samples analyzed. SPME in combination with GC/TOF-MS has been proved to be an attractive and powerful approach for the rapid screening of multiclass organic pollutants in water, with very little sample manipulation and no solvent consumption. This combination provides to the analyst with information-rich MS data that facilitates the reliable identification of many different organic compounds in samples.     

Determination of nicotine and other minor alkaloids in international cigarettes by solid-phase microextraction and gas chromatography/mass spectrometry

Nicotine, nornicotine, anabasine, and anatabine are the most abundant alkaloids in tobacco. Along with the addictiveness of nicotine, other properties, including their occurrence in tobacco at relatively high concentrations, and as the primary precursors for the highly carcinogenic tobacco-specific nitrosoamines, make these chemicals important from a public health standpoint Therefore, developing a fast and accurate quantitative method to screen large numbers of cigarette samples for these alkaloids was important. This report describes the first use of headspace analysis using solid-phase microextraction combined with gas chromatography/mass spectrometry for the unambiguous detection of tobacco alkaloids. Detection and confirmation of each analyte isestablished by both chromatographic retention times and the ratio of reconstructed ion chromatogram peak areas from characteristic quantitation ion and confirmation ion. Twenty-eight cigarette brands from 14 countries were analyzed. Surprisingly, the minor alkaloids' response factors varied considerably among different styles of cigarettes. Accurate quantification was achieved using a three-point standard addition protocol. The standard addition approach was essential to obtain accurate measurements by minimizing matrix effects that would otherwise have contributed to quantitation bias. Significant differences in the alkaloid profiles were measured in the different cigarette brands. These results strongly suggest that such differences reflect variations associated with blend compositions, tobacco quality, and manufacturing practices.     

Identification of proteins in complexes by solid-phase microextraction/multistep elution/capillary electrophoresis/tandem mass spectrometry.

A method to directly identify proteins in complex mixtures by solid-phase microextraction (micro-SPE)/multistep elution/capillary electrophoresis (CE)/tandem mass spectrometry (MS/MS) is described. A sheathless liquid-metal junction interface is used to interface CE and electrospray ionization MS/MS. A subfemtomole detection limit is achieved for protein identification through database searching using MS/MS data. The SPE serves as a semiseparation dimension using an organic-phase step-elution gradient in combination with the second separation dimension for increased resolving power of complex peptide mixtures. This approach improves the concentration detection limit for CE and allows more proteins in complex mixtures to be identified. A 75-protein complex from yeast ribosome is analyzed using this method and 80-90% of the proteins in the complex can be identified by searching the database using the MS/MS data from a complete analysis. This multidimensional CE/MS/MS methodology provides an alternative to multidimensional liquid chromatography/MS/MS for direct identification of small amounts of protein in mixtures.     

Electrochemical thermospray mass spectrometry instrumentation for coupling electrochemistry to mass spectrometry

Reaction products in electrochemical processes can be identified by coupling an electrochemical thin-layer flow cell to a thermospray mass spectrometer. The performance of this analytical method, electrochemical thermospray mass spectrometry, is demonstrated. This includes the characterization of the improved electrochemical thin-layer flow cell. This cell offers the possibility to combine cyclic voltammograms with mass spectrometry. This goal was achieved, too, by the construction of a new thermospray ion source and a special vacuum recipient.     

Air sampling with porous solid-phase microextraction fibers

A new, rapid air sampling/sample preparation methodology was investigated using adsorptive solid-phase microextraction (SPME) fiber coatings and nonequilibrium conditions for volatile organic compounds (VOCs). This method is the fastest extraction technique for air sampling at typical airborne VOC concentrations. A theoretical model for the extraction was formulated based on the diffusion through the interface between the sampled (bulk) air and the SPME coating. Parameters that affect the extraction process including sampling time, air velocity, air temperature, and relative humidity were investigated with the porous (solid) PDMS/DVB and Carboxen/PDMS coatings. Very short sampling times from 5 s to 1 min were used to minimize the effects of competitive adsorption and to calibrate the extraction process in the initial linear extraction region. The predicted amounts of extracted mass compared well with the measured amounts of target VOCs. Findings presented in this study extend the existing fundamental knowledge related to sampling/sample preparation with SPME, thereby enabling the development of new sampling devices for the rapid sampling of air, headspace, water, and soil.     

Identification of peptides using gold nanoparticle-assisted single-drop microextraction coupled with AP-MALDI mass spectrometry

A novel technique, gold nanoparticle-assisted single-drop microextraction (SDME) combined with atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry (AP-MALDI-MS) for the identification of peptides has been described. The SDME of peptides from aqueous solution was achieved using gold nanoparticles prepared in toluene as the acceptor phase. A simple phenomenon of isoelectric point (pI) of the peptides has been utilized successfully to extract the peptides into a single drop of nanogold in toluene. After extraction, a single-drop nano gold solution was directly spotted onto the target plate with an equal volume of matrix, proportional, variant-cyanohydroxy cinnamic acid ( proportional, variant-CHCA) and analyzed in AP-MALDI-MS. The parameters, such as solvent selection, extraction time, agitation rate, and pH effect, were optimized for the SDME technique. Using this technique, in aqueous solution, the lowest concentration detected for Met- and Leu-enkephalin peptides was 0.2 and 0.17 microM, respectively. In addition, the application of this technique to obtain the signal for the selected peptides in a mass spectrum in the presence of matrix interferences such as 1% Triton X-100 and 6.5 M urea has been showed. The application was extended to identify the peptides spiked into urine.     

Valved sampling cell for membrane introduction mass spectrometry

Membrane extractors comprising a membrane house inside of a valve have been developed to separate compounds of interest from a sample matrix and introduce these compounds into a mass spectrometer. Experimental control over parameters that affect permeability or that may damage the membrane, such as the membrane temperature, is provided with the valve. The valve was tested for response and response times with the valve separated from the mass spectrometer by various interface tube lengths. Data for steady state response measurements showed no significant change with the valve at different distances from the ion source. Polar compounds show a strong response time dependency on the interface tube length. This adsorption phenomenon is minimized by simply heating the interface tube. Other factors affecting the performance of the device are discussed.     

A device for automated direct sampling and quantitation from solid-phase sorbent extraction cards by electrospray tandem mass spectrometry

A new solid-phase extraction (SPE) device in the 96-well format (SPE Card) has been employed for automated off-line sample preparation of low-volume urine samples. On-line automated analyte elution via SPE and direct quantitation by micro ion spray mass spectrometry is reported. This sample preparation device has the format of a microtiter plate and is molded in a plastic frame which houses 96 separate sandwiched 3M Empore sorbents (0.5-mm-thickness, 8-microm particles) covered on both sides by a microfiber support material. Ninety-six discrete SPE zones, each 7 mm in diameter, are imbedded into the sheet in the conventional 9-mm pitch (spacing) of a 96-well microtiter plate. In this study one-quarter of an SPE Card (24 individual zones) was used merely as a convenience. After automated off-line interference elution of applied human urine from 24 samples, a section of SPE Card is mounted vertically on a computer-controlled X, Y, Z positioner in front of a micro ion spray direct sampling tube equipped with a beveled tip. The beveled tip of this needle robotically penetrates each SPE elution zone (sorbent disk) or stationary phase in a serial fashion. The eluted analytes are sequentially transferred directly to a microelectrosprayer to obtain tandem mass spectrometric (MS/MS) analysis. This strategy precludes any HPLC separation and the associated method development. The quantitative determination of Ritalin (methylphenidate) from fortified human urine samples is demonstrated. A trideuterated internal standard of methylphenidate was used to obtain ion current response ratios between the parent drug and the internal standard. Human control urine samples fortified from 6.6 to 3300 ng/mL (normal therapeutic levels have been determined in other studies to be between 50 and 100 ng/mL urine) were analyzed and a linear calibration curve was obtained with a correlation coefficient of 0.9999, where the precision of the quality control (QC) samples ranged from 9.6% at the 24 ng/mL QC level to 1.2% at the 3000 ng/mL QC level, and the accuracy for the four levels of QC samples ranged from 98.1% to 100.3%. The QC samples were prepared at four concentrations which included 24, 240, 1200, and 3000 ng/mL, respectively. The run time per sample in this work was 1.5 min not including the sample preparation time.     

On-line coupling of in vivo microdialysis with tandem mass spectrometry.

The capability of interfacing in vivo microdialysis with mass spectrometry has been demonstrated. The goal of this research was to demonstrate the feasibility of real-time analysis in biological systems using microdialysis in combination with tandem mass spectrometry (MS/MS). Microdialysis sampling was accomplished by surgically implanting a small microdialysis probe into a tissue or area of interest. Molecules diffuse through the membrane of the microdialysis probe due to concentration differences. These molecules are collected in a sample loop and analyzed by tandem mass spectrometry. Sequential injections can be made in as little as 2 min. This capability is advantageous in the study of molecules with very rapid elimination rates. Tris(2-chloroethyl)phosphate (TRCP) was used as a model compound in the development of this analytical technique. As an example of an application of the microdialysis/MS/MS technique, plasma concentration vs time curves were obtained and compared with the plasma concentration profiles obtained using conventional studies. For the microdialysis/MS/MS studies, the average slope from three animals was -0.086 min-1. In comparison, the average slope from four animals from the conventional studies was -0.035 min-1.     

Development of a solid-phase microextraction gas chromatography/tandem mass spectrometry method for polybrominated diphenyl ethers and polybrominated biphenyls in water samples

Solid-phase microextraction has been applied for the first time to the determination of trace concentrations of some brominated flame-retardant compounds (BFRs) in water samples. For the development of the method, six polybrominated diphenyl ethers and two polybrominated biphenyls were considered as target analytes. The factors expected to influence the extraction process are fully discussed. Quantification has been performed by gas chromatography/tandem mass spectrometry using an ion trap mass analyzer. This is also the first time that tandem mass spectrometry is applied with these analytes. Unlike conventional methods for BFR analysis, which involve solvent extraction and several cleanup steps before gas chromatography, the proposed method uses headspace extraction and hard contamination of the chromatographic system is prevented. In addition, tandem mass spectrometry provides selectivity and sensitivity in the detection process. The method performs well achieving good linearity (R(2) > 0.997), precision, and detection limits (S/N = 3) ranging from 7.5 to 190 pg/L. The method has been applied to a variety of water samples.     

Peptide profiling of cells with multiple gene products: combining immunochemistry and MALDI mass spectrometry with on-plate microextraction

Due to the intracellular chemical complexity and a wide range of transmitter concentrations, the detection of the complete set of peptide transmitters in a single cell is problematic. In the current study, a multidisciplinary approach combining single-cell MALDI-MS peptide profiling, northern analysis, in situ hybridization, and immunocytochemistry allows characterization of a more complete set of neurotransmitters than individual approaches in the Aplysia californica B1 and B2 motor neurons. Because different results were obtained using both in situ and immunohistochemical techniques compared to previous reports, MALDI-MS assays have been used to examine CP1-related gene products in these cells. However, MALDI with standard sample preparation does not detect the presence of the CP1 gene products. A novel on-plate microextraction approach using concentrated MALDI matrix 2,5-dihydroxybenzoic acid with a mixture of acetone and water as the solvent has been developed to allow the detection of trace-level gene expression products. Both neuropeptide precursors in the B1 and B2 neurons-the SCP and CP1 prohormones-end with large peptides that have multiple cysteine residues. For SCP, MALDI-MS verifies the presence of a novel 9325 Da SCP-related peptide. In the case of CP1, a disulfide-bonded homodimer is detected and the disulfide bonding pattern elucidated using MALDI-MS coupled with on-plate enzymatic digestion.     

Trace analysis of ethanol, MTBE, and related oxygenate compounds in water using solid-phase microextraction and gas chromatography/mass spectrometry

Solid-phase microextraction (SPME) and gas chromatography/mass spectrometry have been combined for trace-level determination of very polar compounds in water, including the widely used gasoline oxygenates ethanol and methyl tert-butyl ether (MTBE). A relatively simple extraction method using a divinylbenzene/Carboxen/poly(dimethylsiloxane) SPME fiber was optimized for the routine analysis of ethanol and MTBE in groundwater and reagent water. A sodium chloride concentration of 25% (w/w) combined with an extraction time of 25 min provided the greatest sensitivity while maintaining analytical efficiency. Replicate analyses in fortified reagent and groundwater spiked with microgram per liter concentrations of ethanol and MTBE indicate quantitative and reproducible recovery of these and related oxygenate compounds. Method detection limits were 15 microg L(-1) for ethanol, 1.8 microg L(-1) for tert-butyl alcohol, 0.038 microg L(-1) for tert-amyl methyl ether, 0.025 microg L(-1) for ethyl-tert-butyl ether, and 0.008 microg L(-1) for MTBE.     

Artificial receptor-facilitated solid-phase microextraction of barbiturates

A receptor for barbiturates, N,N'-Bis-[6-(2-ethylhexanoylamino)-pyridin-2-yl]-isophthalamide, was designed to dissolve in plasticizers of poly(vinyl chloride) (PVC). Microextractions using receptor-doped films of PVC were carried out as a function of receptor concentration. The effect of the concentration of the receptor on extraction yield is considerable for barbiturates that have significant binding to the receptor but negligible for very similar molecules that do not bind to the receptor strongly. Thus, it is the receptor's ability in molecular recognition, not its generic ability as an H-bonding cosolvent, that is important. On the other hand, NMR data show that the receptor self-associates. A simple, approximate analysis is given to extract the amount of active receptor from the data. Receptor-enhanced extractions of barbiturates from urine are compared to extractions using a phosphate ester as solvent.     

Automated in-tube solid-phase microextraction coupled with liquid chromatography/electrospray ionization mass spectrometry for the determination of beta-blockers and metabolites in urine and serum samples.

The technique of automated in-tube solid-phase microextraction (SPME) coupled with liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) was evaluated for the determination of beta-blockers in urine and serum samples. In-tube SPME is an extraction technique for organic compounds in aqueous samples, in which analytes are extracted from the sample directly into an open tubular capillary by repeated draw/eject cycles of sample solution. LC/MS analyses of beta-blockers were initially performed by liquid injection onto a LC column. Nine beta-blockers tested in this study gave very simple ESI mass spectra, and strong signals corresponding to [M + H]+ were observed for all beta-blockers. The beta-blockers were separated with a Hypersil BDS C18 column using acetonitrile/methanol/water/acetic acid (15:15:70:1) as a mobile phase. To optimize the extraction of beta-blockers, several in-tube SPME parameters were examined. The optimum extraction conditions were 15 draw/eject cycles of 30 microL of sample in 100 mM Tris-HCl (pH 8.5) at a flow rate of 100 microL/min using an Omegawax 250 capillary (Supelco, Bellefonte, PA). The beta-blockers extracted by the capillary were easily desorbed by mobile-phase flow, and carryover of beta-blockers was not observed. Using in-tube SPME/LC/ESI-MS with selected ion monitoring, the calibration curves of beta-blockers were linear in the range from 2 to 100 ng/mL with correlation coefficients above 0.9982 (n = 18) and detection limits (S/N = 3) of 0.1-1.2 ng/mL. This method was successfully applied to the analysis of biological samples without interference peaks. The recoveries of beta-blockers spiked into human urine and serum samples were above 84 and 71%, respectively. A serum sample from a patient administrated propranolol was analyzed using this method and both propranolol and its metabolites were detected.