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An SPME method was developed for sampling gaseous 2,4-toluene diisocyanate (2,4-TDI) involving derivatisation of the isocyanate by reacting with dibutylamine (DBA). The TDI-DBA derivative thus formed was determined by LC-MS-MS utilising atmospheric pressure chemical ionisation (APCI). As a first step, DBA was loaded onto a poly(dimethylsiloxane)/divinylbenzene (PDMS-DVB) fibre coating by direct vapour-phase extraction of a highly concentrated diethyl ether solution of DBA. The DBA-loaded fibre was then exposed to an artificially generated atmosphere of gaseous 2,4-TDI. The linearity of the method ranged from 52.8 to 3100 microg m(-3) (6.8 to 400 ppbv) with a sampling time of 60 min. The proposed method has been applied to 2,4-TDI determination in an artificially generated dynamic standard atmosphere, yielding an approximate method detection limit (MDL) of 2 microg m(-3) (0.25 ppbv). This concentration is one twentieth of the Occupational Safety and Health Administration (OSHA) 8-hour time-weighted average (TWA) exposure limit. The sampler with the PDMS-DVB-DBA coating was found to be stable and retains the required amount of DBA for at least 10 days, an important feature for sampling systems with potential in-situ applications.
Caffeine concentrations in beverages were determined using a simple and rapid method based on microextraction of caffeine onto the surface of a fused-silica fiber. The uncoated fiber was dipped into the beverage sample for 5 min after the addition of isotopically labeled (trimethyl 13C)caffeine. The adsorbed caffeine was then thermally desorbed in a conventional split/splitless injection port, and the concentration of caffeine was determined using gas chromatography with mass spectrometric detection. Quantitative reproducibilities were ca. 5% (relative standard deviation) and the entire scheme including sample preparation and gas chromatographic analysis was completed in ca. 15 min per sample. The potential of the microextraction technique for the analysis of flavor and fragrance compounds in non-caffeinated beverages is also demonstrated. Since no solvents or class-fractionation steps are required, the method has good potential for automation.
In this work the photochemical behaviour of a technical mixture of polybrominated diphenyl ethers (PBDEs) (BDE-47, BDE-99, BDE-100, BDE-153 and BDE-154) has been studied. The mixture of BDEs was extracted from aqueous solutions using SPME fibers that were subsequently exposed to different UV irradiation times, procedure so-called Photo-SPME. PBDEs photochemical studies in such medium have been accomplished for the first time. Twenty one different photoproducts, all of them generated by successive bromine atoms losses, have been identified, being their photoformation-photodegradation curves easily determined by the Photo-SPME technique.
The aim of this study was the optimization of headspace SPME conditions for trapping diterpenes present in frankincense (olibanum). Diterpenes like cembrenes or incensole and its derivatives are characteristic of olibanum. So in order to detect by SPME the occurrence of olibanum in archeological objects, it appears essential to have the best extraction conditions for these diterpenes that will be in very small quantities. Both sampling time and extraction temperature were studied and five fiber coatings were tested: polydimethylsiloxane (PDMS), polydimethylsiloxane/divinylbenzene (PDMS/DVB), carboxen/polydimethylsiloxane (CAR/PDMS), divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) and carbowax/divinylbenzene (CW/DVB). The PDMS/DVB fiber was found to be the most efficient for trapping olibanum characteristic diterpenes, with a sampling time of 1 h and a sampling temperature of 80 degrees C.
Allyloxy bisbenzo 16-crown-5 trimethoxysilane was first used as precursor to prepare the sol-gel-derived bisbenzo crown ether/hydroxyl-terminated silicone oil (OH-TSO) SPME coating. The coating procedure involving sol solution composition and conditioning process was presented. Compared with commercial SPME stationary phases, the new coatings showed higher extraction efficiency and therefore could provide higher sensitivity for organphosphorous pesticides (OPs). Limits of detection (LODs) were in the range of 0.003-1.0 ng/g for these OPs in food samples (honey, juice, orange and pakchoi). The optimal extraction conditions of the new coatings to OPs in these samples were investigated by adjusting extraction time, salt addition, extraction temperature, and dilution ratios of samples with distilled water by using SPME coupled with gas chromatography (GC)-flame photometric detection (FPD). The method was applied to determine the concentrations of OPs in real samples.
The applicability of a composite composed of polydimethylsiloxane (PDMS) and poly(vinyl alcohol) (PDMS/PVA) as coating sorbent for SPME fibers is demonstrated here. Fused silica (FS) fibers were coated with PDMS/PVA composite through a sol-gel process, using methyltrimethoxysilane as reticulating agent. The chemical and physical properties of the sol-gel PDMS/PVA composite were determined by infrared spectroscopy and thermogravimetric analysis. Electron scanning microscopy of the prepared fibers, showed that the coating obtained was highly microporous, having a thickness of approximately 5 microm. The fibers were tested for the headspace extraction of several organic compounds (o-xylene, naphthalene, ethyl caprate, p-chlorotoluene and PCB) prior to gas chromatographic analysis. The extractive capacity of the PDMS/PVA coating was found to be superior to that of pure conventional PDMS fibers.
Virgin females of the minute parasitoid wasp Trichogramma turkestanica produce about 2 pg/h of two putative sex pheromonal compounds. These compounds could be successfully sampled during 20-50 h with SPME from 1.8 mL vials, containing 50-110 wasps and analysed by GC-MS. Accurate mass measurements at the 1 ng scale were possible with an internal standard of sulphur. One compound with MW 236 was identified as a C17H32 hydrocarbon while the other compound was the corresponding allylic alcohol with composition C17H32O. The alcohol could be silylated on-fibre and its mass spectrum suggested the presence of a conjugated 2,4-diene moiety. A miniaturised solvent extraction system for SPME needles, using 5 microL of acetone in a microtube was developed. After reaction of the extracted volatiles with the dienophile 4-methyl-1,2,4-triazoline-3,5-dione (MTAD), GC-MS of the MTAD adducts confirmed the presence of a diene. Interpretation of the combined mass spectral data, in combination with retention indexes of both compounds on non-polar and polar columns, suggested 2,6,8,12-tetramethyltrideca-2,4-diene and 2,6,8,12-tetramethyltrideca-2,4-dien-1-ol as most probable structures. These compounds have not been described previously. Biogenetically, they are most likely polyketides made up of a C4 starter unit that has been elongated with C2 and C3 units. Further biological and synthetic studies are necessary to prove their role as sex pheromone, confirm the proposed structures and determine the correct stereochemistry of the double bonds and the methyl groups.
A new sol-gel application for the development of SPME fibers is described. Phenyltrimethoxysilane (PTMOS) and methyltrimethoxysilane (MTMOS) were the sol-gel precursors used at different proportions, together with different water contents, catalyst and reaction time. It was observed that obtaining a good film quality was determinant for a good extracting fiber performance. The film thickness ranged 0.2-1 microm and could not be increased by multi-coating processes. Apparently, a dense, non-porous microstructure was obtained. These coatings exhibited a strong hydrophobic character, as shown by the capability of extraction of long chain and apolar aromatic compounds, which, was comparable to that of the 100 microm polydimethylsiloxane (PDMS) and 65 microm carbowax-divinylbenzene (CW-DVB). The developed fiber has shown high thermal (350 degrees C) and organic solvent stability (ethanol, toluene and dichloromethane), thus bearing adequate characteristics to be associated to GC and potentialities that may also envisage suitability for HPLC. The new fibers may be useful for the microextraction of non-polar compounds, although at trace levels and in simple matrixes only, due to the susceptibility to competition.
The reliability of SPME combined with a chemical reaction for the analysis of short-chain aliphatic amines by liquid chromatography has been investigated. Different options to couple SPME and derivatization have been tested and compared: (i) derivatization of the analytes in solution followed by the extraction of the derivatives, (ii) extraction of the analytes and subsequent derivatization by immersing the SPME fibre onto a solution of the reagent, and (iii) extraction/derivatization of the analytes using fibres previously coated with the reagent. Methylamine (MA), dimethylamine (DMA) and trimethylamine (TMA) have been selected as a model of primary, secondary and tertiary amines, respectively. The analytes have been derivatized with the fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC), and the fibre coating was Carbowax-templated resin (CW-TR). The employment of fibres coated with FMOC to extract and derivatize the analytes was the best option, as compared with the other approaches tested the sensitivity was considerably improved. On the basis of these studies, a new procedure for the determination of MA, DMA and TMA in water is presented. To demonstrate the utility of the proposed conditions data on linearity, accuracy, repeatability and sensitivity are given. Results of the determination of the amines in tap, river and waste water are also presented.
An SPME-LC-UV method for the determination of the non-steroidal anti-inflammatory drug (NSAID) naproxen and, after hydrolysis, its glucuronide in human urine samples was developed for the first time using a carbowax/templated resin (CW/TPR-100)-coated fibre. The procedure required a very simple sample pre-treatment, an isocratic elution, and provides a highly selective extraction. All the aspects influencing adsorption (extraction time, temperature, pH and salt addition) and desorption (desorption and injection time and desorption solvent mixture composition) of the analyte on the fibre have been investigated. The linear range investigated in urine was 0.2-20 microg/ml (that covers the typical naproxen urinary concentration) and almost quantitative recoveries were obtained. Within-day and between-days R.S.D.% in urine were 4.5 and 6.0, respectively. The LOD and LOQ in spiked urine were 0.03 and 0.20 microg/ml, well below the usual naproxen urinary level.
The development, optimization, and application of a novel method for arsenic speciation based on capillary gas-liquid chromatography with simultaneous quadrupole ion-trap mass spectrometric (MS) detection and pulsed flame photometric detection (PFPD) is described. The method couples the sensitive arsenic-selectivity of PFPD with the structure elucidation capability of molecular MS detection for the determination of trace levels of unknown organoarsenicals in complex matrices. The conditions that affect the PFPD response in the presence of interfering species were optimized using the sequential Simplex algorithm for three key factors: gate delay (18.3 ms), gate width (9.1 ms), and combustion gas composition (16.6 ml/min H2). Complete discrimination in the PFPD of the arsenic signal from interfering S-, C-, and OH-emitting species that are problematic in existing methods was achieved. Additionally, a revised interpretation of our previously reported mechanism [J. Chromatogr. A 807 (1998) 253] for the dithiol derivatization and subsequent GC-MS determination of dimethylarsinic acid is presented.
The suitability of "capillary extractors" is demonstrated for the "negligible depletion" extraction of benzene, toluene, ethylbenzene and xylenes in a clean-water matrix. Extraction set-up and major extractor parameters (length, internal diameter, and film thickness) are chosen to allow rugged analysis by GC with flame ionization detection. With the selected negligible extraction conditions, the efficiency for every consecutive extraction is about 2-3% of the dissolved amount.
A new analytical procedure was developed for the extraction of degradation products of chemical warfare agents from water and for in-situ derivatisation prior to analysis by gas chromatography-mass spectrometry (GC-MS). With this new procedure, degradation products of the chemical warfare agents can be analysed and identified without going through laborious sample preparation. Parameters such as fiber selection, pH, salt content, derivatisation temperature, extraction and derivatisation periods, and sequence of adsorption/derivatisation were experimented with, to optimise the efficiency of this method. The detection limit is in the ppb to sub-ppb range with GC-MS in the full scan mode. Based on six injections of the devised procedure, a relative standard deviation from 10-35% can be achieved, depending on the compound. This method was demonstrated during the 4th International Interlaboratory Proficiency Test organised by the Organisation for the Prohibition of Chemical Weapons to be comparable to existing recommended operating procedures for verification of degradation products of chemical warfare agents.
A method for the qualitative analysis of various metabolites of naphthalene, phenanthrene and pyrene is presented. The method uses SPME with a 85-microm polyacrylate fibre for extraction, headspace silylation with BSTFA without any catalyst for on-fibre derivatisation and GC-MS in the SIR mode for separation and detection. The suitability of the method for profile analysis of PAH metabolites is shown by analysing a smokers urine after enzymatic cleavage (and additionally after spiking with the target analytes) and spiked water. The method exhibits satisfactory separation of all investigated metabolites and no interferences due to matrix peaks.
An SPME-HPLC-UV method for the determination of delorazepam, a representative benzodiazepine, in spiked human urine samples was developed for the first time. The performances of two commercially available fibers, a carbowax/templated resin (Carbowax/TPR-100) and a polydimethylsiloxane/divinylbenzene (PDMS/DVB), were compared, indicating the latter as the most suitable for urine samples analysis. All the aspects influencing adsorption (extraction time, pH, temperature, salt addition) and desorption (desorption and injection time, desorption solvent mixture composition) of the analyte on the fiber have been investigated. In particular, short extraction times were necessary to reach the equilibrium and very short desorption times were employed. The procedure required simple sample pre-treatment and was able to detect 5 ng/ml in spiked urine, regardless of the complexity of the matrix.