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PubMed2004

Highly sensitive analysis of multiple pesticides in foods combining solid-phase microextraction, capillary electrophoresis-mass spectrometry, and chemometrics.

A highly sensitive procedure to detect multiple pesticides at trace levels in foods is presented. Initially a comparative study between capillary electrophoresis (CE)-UV and CE-mass spectrometry (MS) is carried out analyzing five pesticides not studied up to now (pyrimethanil, pyrifenox, cyprodinil, cyromazine, and pirimicarb). The comparison between CE-UV and CE-MS is established in terms of separation efficiency, speed of analysis, reproducibility, and sensitivity. A good separation of these compounds is achieved by both techniques using a volatile aqueous buffer containing 0.3 M ammonium acetate/acetic acid at pH 4. Time analysis reproducibility is studied for the same day (n = 5) and three different days (n = 15), showing no significant differences between CE-UV and CE-MS. The study on peak areas reproducibility shows a slightly worse reproducibility for CE-MS compared with CE-UV. The best limit of detection (LOD) that can be achieved for these pesticides using CE-UV was 0.6 microg/mL. CE-MS provides LODs one order of magnitude better than CE-UV. Chemometrics are used to optimize the multiple parameters that play a role in solid-phase microextraction (SPME) and CE-MS analysis (e.g., extraction and desorption times, nebulizer pressure, dry gas flow, dry gas temperature, percentage of organic solvent and acid in the sheath liquid, etc.). The combined use of chemometrics and SPME-CE-MS clearly improves the LODs that can be achieved allowing the detection of pesticides at concentrations down to 15 ng/mL. The usefulness of this approach is demonstrated detecting multiple pesticides in different food samples as grapes and orange juice in a single run. The concentrations detected are below the maximum residue limits (MRLs) permitted for these pesticides in foods corroborating the value of our approach. This work demonstrates, to our knowledge for the first time, the good possibilities of the combined use of SPME-CE-MS and chemometrics.

Absorption↗
PubMedDate not supplied

Traditional sampling with laboratory analysis and solid phase microextraction sampling with field gas chromatography/mass spectrometry by military industrial hygienists.

The opinions or assertions contained herein are the private ones of the authors and are not to be construed as official or reflecting the views of the United States Department of Defense or the Uniformed Services University of the Health Sciences. Rapid on-site detection and identification of environmental contaminants to which personnel may be exposed is often needed during military deployment situations. The availability of military industrial hygienists with capabilities for "complete" on-site exposure assessment of chemical species should allow detection and identification of a number of important stressors almost immediately following sample collection. Portable gas chromatography/mass spectrometry (GC/MS) provides a rapid and efficient separation of volatile and semivolatile organic analytes, accompanied by sensitive electron impact ionization-mass spectrometry (EI-MS) detection. The use of GC/MS in the field is limited, however, by equipment cost, complexity of the equipment, and the analytical process. Additionally, a skilled operator is needed to obtain useful separations and to interpret mass spectral data. To demonstrate benefits and limitations of "complete" exposure assessment capabilities, a previously unidentified complex mixture, produced by thermal dispersion of riot control agents, was examined. Established active sampling methods were used with laboratory analyses. Solid phase microextraction, a passive sampling method that simplifies preparation for GC/MS analysis, also was used with a field-portable GC/MS system. Both sampling/analysis methods were used to detect CS riot control agent-derived air contaminants dispersed from riot control type canisters through oxidizer-supported combustion of a chemical fuel.

Chemistry Techniques, Analytical↗
PubMed2001

Analysis of fatty acid ethyl esters in hair as possible markers of chronically elevated alcohol consumption by headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS).

Fatty acid ethyl esters (FAEE) are products of the nonoxidative ethanol metabolism, which are known to be detectable in blood only about 24h after the last alcohol intake. After deposition in hair they should be suitable long-term markers of chronically elevated alcohol consumption. Therefore, a method for the analysis of ethyl myristate, ethyl palmitate, ethyl oleate and ethyl stearate from hair was developed based on the extraction of the hair sample by a dimethylsulphoxide (DMSO)/n-hexane mixture, separation and evaporation of the n-hexane phase and application of headspace solid-phase microextraction (HS-SPME) in combination with gas chromatography-mass spectrometry (GC-MS) to the extract. For use as internal standards, the corresponding D(5)-ethyl esters were prepared. The HS-SPME/GC-MS measurements were automatically performed using a multi-purpose sampler. The detection limits of the FAEE were between 0.01 and 0.04ng/mg and the reproducibility was between 3.5 and 16%. By application of the method to hair samples of 21 fatalities with known heavy alcohol abuse 0.045-2.4ng/mg ethyl myristate, 0.35-13.5ng/mg ethyl palmitate, 0.25-7.7ng/mg ethyl oleate and 0.05-3.85ng/mg ethyl stearate were measured. For social drinkers (30-60g ethanol per week), the concentrations were about one order of magnitude smaller. For 10 teetotalers negative results or traces of ethyl palmitate were found. It was shown by supplementary investigations in single cases that FAEE are also present in sebum, that there is no strong difference in their concentrations between pubic, chest and scalp hair, and that they are detectable in hair segments after a 2 months period of abstinence. From the results follows that the measurement of FAEE concentrations in hair is a useful way for a retrospective detection of alcohol abuse.

Adolescent↗
PubMed2000

Time-weighted average sampling of volatile and semi-volatile airborne organic compounds by the solid-phase microextraction device.

The ultimate goal of the chemist is to perform sample preparation, and analysis, if possible at the place where a sample is located rather than moving the sample to laboratory, as is common practice in many cases at the present time. This approach eliminates errors and time associated with sample transport and storage and therefore it would result in more accurate, precise and faster analytical data. In addition to portability, two other important features of ideal field sample preparation technique are elimination of solvent use and integration with a sampling step. A method is developed which addresses these requirements for the determination of time-weighted average concentration of gas phase compounds using a solid-phase microextraction device. Quantification of target analytes in air using this method can be carried out without external calibration. The volatile and semi-volatile organic compounds in air diffuse into the fiber coating which is retracted a known distance into its needle housing during the sampling period. The coatings used are poly(dimethylsiloxane) and poly(dimethylsiloxane)-divinylbenzene. The sampling rate at which gas phase analytes load onto the fiber is determined for a wide range of hydrocarbons. There is a good agreement between the theoretical and experimental sampling rates. Sampling time ranges from 1 min to 24 h depending on the coating used and its retraction distance. Effect of the flow-rate on the uptake rate by the fiber is studied. The method is tested in the field and compared with National Institute of Occupational Health and Safety Method 1550. Good agreement between the results is obtained.

Chromatography↗
PubMed2004

Sensitive method for the determination of roxarsone using solid-phase microextraction with multi-detector gas chromatography.

We describe the development, optimization, and application of a novel method for the unequivocal identification and quantification of roxarsone (3-nitro-4-hydroxyphenylarsonic acid, 3-NHPAA) at low microg L(-1) levels. The method is based on capillary gas-liquid chromatography with parallel quadrupole ion-trap mass spectrometric (QIT-MS) and pulsed flame photometric detection (PFPD). The sensitive method couples the arsenic specificity of PFPD with the high selectivity of molecular MS for the determination of roxarsone, dimethylarsenic acid (DMAA), and monomethylarsonic acid (MMAA) in complex matrices. Analytes were derivatized based on the approach we previously reported [B. Szostek, J.H. Aldstadt, J. Chromatogr. A 807 (1998) 253 and D.R. Killelea, J.H. Aldstadt, J. Chromatogr. A 918 (2001) 169] for the reaction of organoarsenicals with 1,3-propanedithiol (PDT). The cyclic dithiaarsenolines formed were extracted from the sample matrix in the liquid phase by solid-phase microextraction (SPME). The optimized SPME conditions employed a 65 microm polydimethlysiloxane-divinylbenzene (PDMS-DVB) fiber, extraction temperature of 70 degrees C and fiber equilibration time of 15.0 min. The mass spectrum of the dithiaarsenoline of roxarsone showed a base peak that corresponded to the predicted structure at m/z 319 and the tell-tale peak of an arsenic compound derivatized with PDT at m/z 181. Further peaks at m/z 149 and 228 were observed and found to be unique to roxarsone, formed by an interesting internal rearrangement of the ONOH functionality. A linear calibration model was prepared for roxarsone over an environmentally relevant range (0.0-100 microg L(-1)) and a detection limit of 2.69 microg L(-1) (3sigma) was observed. The method was applied to several fortified environmental surface water samples (50 microg L(-1)) where the average recovery for roxarsone was 103+/-10.9%.

Calibration↗
PubMed2006

Ochratoxin a determination in beer by solid-phase microextraction coupled to liquid chromatography with fluorescence detection: a fast and sensitive method for assessment of noncompliance to legal limits.

A solid-phase microextraction-liquid chromatography-fluorescence detection (SPME-LC-FD) method for the determination of ochratoxin A (OTA) in commercial beer samples was developed for the first time using a 60 microm thick poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber. The procedure required a very simple sample pretreatment, an isocratic elution, and provides a selective extraction. All of the factors influencing fiber adsorption (extraction time, temperature, pH, and salt addition) and desorption of the analyte (desorption and injection time and desorption solvent mixture composition) have been investigated. The linear range investigated in beer was 0.03-2 ng/mL; within-day and between-days relative standard deviation in beer were 4.3 and 5.9%, respectively. The limit of quantification in spiked beer was 53 pg mL(-)(1), well below all European regulatory levels.

Beer↗
PubMed2002

Headspace sorptive extraction (HSSE), stir bar sorptive extraction (SBSE), and solid phase microextraction (SPME) applied to the analysis of roasted Arabica coffee and coffee brew.

Headspace sorptive extraction (HSSE) and stir bar sorptive extraction (SBSE), two recently introduced solventless enrichment techniques, have been applied to the analysis of the headspace of Arabica roasted coffee and of the headspace of the brew and of the brew itself. In both HSSE and SBSE enrichment is performed on a thick film of poly(dimethylsiloxane) (PDMS) coated onto a magnet incorporated in a glass jacket. Sampling is done by placing the PDMS stir bar in the headspace (gas phase extraction or HSSE) or by immersing it in the liquid (liquid phase extraction or SBSE). The stir bar is then thermally desorbed on-line with capillary GC-MS. The performance of HSSE and SBSE have been compared through the determination of the recoveries and relative abundances of 16 components of the coffee volatile fraction to classical static headspace (S-HS) and to headspace and in-sample solid phase microextraction (HS-SPME and IS-SPME, respectively) applying the fibers PDMS 100 microm, Carbowax/divinylbenzene 65 microm (CW/DVB), Carboxen/PDMS 75 microm(CAR/PDMS), polyacrylate 85 microm(PA), PDMS/divinylbenzene 65 microm(PDMS/DVB), and Carboxen/divinylbenzene/PDMS 50-30 microm(CAR/PDMS/DVB). In all cases, HSSE and SBSE gave higher recoveries, and this is entirely due to the high amount of PDMS applied.

Chromatography, Gas↗
PubMed2001

Determination of fipronil by solid-phase microextraction and gas chromatography-mass spectrometry.

A method for the determination of trace amounts of the insecticide fipronil was developed using solid-phase microextraction-gas chromatography-mass spectrometry and selected ion monitoring. Fipronil was extracted with a fused-silica fiber coated with 85 microm polyacrylate. The effects of pH, ionic strength, sample volume, extraction and desorption times as well as the extraction temperature were studied. Lindane was used as an internal standard. The linear concentration range of application was 0.3-100 ng ml(-1) of fipronil, with a relative standard deviation of 9.5% (for a level of 50 ng ml(-1)) and a detection limit of 0.08 ng ml(-1). The method was applied to check the eventual existence of fipronil above this limit in water and soil samples from Granada (Spain) as well as in human urine samples. The method validation was completed with spiked matrix samples. The method can be applied as a monitoring tool for water, soil and urine, in the investigation of environmental and occupational exposure to fipronil.

Gas Chromatography-Mass Spectrometry↗
PubMed2000

Using microwave distillation-solid-phase microextraction--gas chromatography--mass spectrometry for analyzing fish tissue.

A technique for the analysis of the volatile compounds from fish tissue employing microwave distillation-solid-phase microextraction-gas chromatography-mass spectrometry is described. A qualitative listing of 174 compounds observed in the headspace is given, and a quantitative method for the determination of the off-flavor contaminants (2-methylisoborneol and geosmin) is presented. Borneol and decahydro-1-naphthol are used as the surrogate and internal standards, respectively. A linear calibration curve is obtained for 0.1 to 5 ppb with a recovery level of 60% at 2.5 ppb. Comparison of the instrumental method with a human flavor checker showed good agreement.

Animals↗
PubMed2004

[Determining mole ratio of monomers in new adsorbent of solid-phase microextraction by infrared spectroscopy].

In the present paper, butyl acrylate and phenylethylene were used as monomers, benzoyl peroxide as evocator, n-butyl acetate and methylbenzene as solvent, a new type of solid-phase micro extraction adsorbent that is phenylethylene-butyl acrylate copolymer was synthesized by solution polymerization. The polymer has good behaviour for adsorbing arenas. According to Lambert-Beer law and some calculation process, the linear relation between the absorptance (y) of the two functional groups, which are benzene and ester, and the two monomers' mole ratio (x) was obtained. The absorptances were determined by IR. The standard curve was obtained by external standard method. The linear regression equation is y = 0.1362 + 0.0841x. The precisions and recoveries were investigated. RSD is 2.464%, and recoveries are 92.89%-103.94%. The results are satisfactory. This method is rapid and accurate.

Acrylates↗
PubMed2004

Optimization of a solid-phase microextraction procedure for the determination of herbicides by micellar electrokinetic chromatography.

The use of a different optimization procedure that involves Experimental Design (ED) and Artificial Neural Networks (ANN) for the off-line coupling solid-phase microextraction-micellar electokinetic chomatography (SPME-MEKC) is presented. This combination of ED and ANN, mathematical tools not previously used in SPME-MEKC optimization, allowed us to obtain good extraction efficiencies in the SPME procedure for the determination of a group of eleven triazine herbicides in groundwater samples. Both extraction and desorption steps were carried out by solution stirring at 900 rpm. Optimal conditions for the off-line SPME procedure were: extraction with a poly(dimethylsiloxane)/divinylbenzene SPME fiber for 120 min, 10% (w/v) NaCl, desorption time 40 min, and 70% (v/v) of methanol/buffer as desorption mixture. Detection limits lay between 0.80 microg L(-1) and 4.89 microg L(-1). Finally, the optimized method was applied to the determination of these compounds in spiked and non-spiked groundwater samples using a previously optimized MEKC separation.

Chromatography↗
PubMed2005

Bronchoalveolar lavage examined by solid phase microextraction, gas chromatography--mass spectrometry and selected ion flow tube mass spectrometry.

Samples (210 in total) of broncholaveolar lavages (BALs), obtained from patients hospitalized with pneumonia in various departments of two hospitals, were analysed using the method of solid phase microextraction-gas chromatography (SPME-GC) with FID detection. Up to 20% (9% unequivocally, 11% probably) of these samples was found to contain volatile fatty acids (VFAs) in the series from acetic acid to heptanoic acid. Importantly, the presence of these acids indicates the presence of fermenting anaerobic bacteria, which were not detected by the conventional microbiological examination. Other compounds, namely the heptanol and cyclohexanone, were also detected by this method in some samples. Cyclohexanone occurred almost exclusively in samples from patients receiving intensive care with mechanical ventilation, and is suspected to originate from plastic parts of ventilators. Selected representative samples were also analysed using further methods, namely gas chromatography-mass spectrometry (GC-MS) of native and silylated samples, and selected ion flow tube mass spectrometry (SIFT-MS). These methods confirmed the identities of above mentioned compounds, and detected numerous other compounds tentatively identified as various alcohols, aldehydes, ketones, esters and hydrogen cyanide, HCN. Most of these compounds occurred in small amounts and their origin and diagnostic significance remains uncertain, except, that is, for the HCN, which indicates the presence of Pseudomonas aeruginosa.

Bacteria, Anaerobic↗
PubMed2004

Solid-phase microextraction for flavor analysis in Harari Khat (Catha edulis) stimulant.

This research examined the typical flavor compounds in the commonest type of Khat called Harari Khat grown in the region of Ethiopia. Twenty-eight compounds, which includes 1,2-Propanedione, 1-Phenyl, Hexanol, Hexanal com-pounds, Limonene, Benzaldehyde with other flavors, were extracted by polydimethylsiloxane at room temperature for 30 min from Khat samples, and identified by solid-phase microextraction-gas chromatography-mass spectrometry (SPME- GC-MS). This method needs no organic solvents and required minimal sample.

Catha↗
PubMed2005

Selective extraction of trace levels of polychlorinated and polybrominated contaminants by supercritical fluid-solid-phase microextraction and determination by gas chromatography/mass spectrometry. Application to aquaculture fish feed and cultured marine species.

The persistence, ubiquity, and toxicity of polyhalogenated compounds, together with their presence in fish feed, make it necessary to monitor these organic pollutants in the routine quality assurance programs of aquaculture activities, as this food chain is a source of these toxic compounds for human consumers. A new approach based on simultaneous supercritical fluid extraction-sample cleanup, followed by solid-phase microextraction-gas chromatography/mass spectrometry (SFE-SPME-GC/MS/MS) has been developed as an advantageous analytical tool for the determination of 15 organohalogenated compounds (including pesticides, polychlorinated and polybrominated biphenyls, and polybrominated diphenyl ethers) in aquaculture feed at very low levels. The influence of several parameters in the efficiency of the SPE/SPME combination was systematically investigated by chemometric approaches. In the optimal conditions, the developed procedure provides an excellent linearity, detection, and quantification limits (below 10 pg/g) for most of the analytes investigated, being at the same time advantageous in terms of rapidity, convenience, and avoiding the need of toxic organic solvents. The procedure was applied to the analysis of aquaculture feed and cultured marine species and tested for accuracy against IAEA 406 reference material.

Animal Feed↗
PubMed1998

Optimization of solid phase microextraction - capillary zone electrophoresis - mass spectrometry for high sensitivity protein identification.

We have previously described the use of a solid phase extraction (SPE) - capillary zone electrophoresis (CZE) - tandem mass spectrometry (MS/MS) system for protein analysis at the low femtomole to subfemtomole level. Here we describe the systematic optimization of a number of parameters which facilitate the use of the SPE-CZE-MS/MS system and further enhance its performance. Specifically, we describe a robust SPE cartridge design which can be assembled without the use of glue, the evaluation of procedures to chemically modify the inner wall of the fused-silica capillaries used in the system to improve separation and reproducibility, and the comparison of different reverse-phase (RP) resins used for the SPE cartridge. We also explored the effects of transient isotachophoresis with respect to system performance and compatibility with different fused-silica surface coatings, the RP resins used, and MS/MS. The enhanced performance of the optimized system is demonstrated by the analysis of calibrated tryptic digests of bovine serum albumin (BSA).

Acetonitriles↗