Headspace single-drop microextraction with in-drop derivatization for aldehyde analysis

A new technique, headspace single-drop microextraction (HS-SDME) with in-drop derivatization, was developed. Its feasibility was demonstrated by analysis of the model compounds, aldehydes in water. A hanging microliter drop of solvent containing the derivatization agent of O-2,3,4,5,6-(pentaflurobenzyl)hydroxylamine hydrochloride (PFBHA) was shown to be an excellent extraction, concentration, and derivatization medium for headspace analysis of aldehydes by GC-MS. Using the microdrop solvent with PFBHA, acetaldehyde, propanal, butanal, hexanal, and heptanal in water were headspace extracted and simultaneously derivatized. The formed oximes in the microdrop were analyzed by GC-MS. HS-SDME and in-drop derivatization parameters (extraction solvent, extraction temperature, extraction time, stirring rate microdrop volume, and the headspace volume) and the method validations (linearity, precision, detection limit, and recovery) were studied. Compared to liquid-liquid extraction and solid-phase microextraction, HS-SDME with in-drop derivatization is a simple, rapid, convenient, and inexpensive sample technique.     

Rapid determination of acetone in human blood by derivatization with pentafluorobenzyl hydroxylamine followed by headspace liquid-phase microextraction and gas chromatography/mass spectrometry

In the current work, a simple, rapid, accurate and inexpensive method was developed for the determination of acetone in human blood. The proposed method is based on derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA), followed by headspace liquid-phase microextraction (HS-LPME) and gas chromatography/mass spectrometry (GC/MS). In the present method, acetone in blood samples was derivatized with PFBHA and acetone oxime formed in several seconds. The formed oxime was enriched by HS-LPME using the organic solvent film (OSF) formed in a microsyringe barrel as extraction interface. Finally, the enriched oxime was analyzed by GC/MS in electron ionization (EI) mode. HS-LPME parameters including solvent, syringe plunger withdrawal rate, sampling volume, and extraction cycle were optimized and the method reproducibility, linearity, recovery and detection limit were studied. The proposed method was applied to determination of acetone in diabetes blood and normal blood. It has been shown that derivatization with HS-LPME and GC/MS is an alternative method for determination of the diabetes biomarker, acetone, in blood samples.     

A simple, rapid and sensitive method for determination of aldehydes in human blood by gas chromatography/mass spectrometry and solid-phase microextraction with on-fiber derivatization

Aldehydes are considered potential markers for enhanced oxidative stress and have been proposed as a diagnostic measure of cancer status. Do to their volatility and activity, it is very difficult to accurately measure aldehydes in human blood. In the present work, gas chromatography/mass spectrometry (GC/MS) and solid-phase microextraction (SPME) with on-fiber derivatization was developed for determination of aldehydes in human blood. O-(2,3,4,5,6-Pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) in aqueous solution was first adsorbed by a SPME fiber, and then the aldehydes in blood samples were headspace extracted by the SPME fiber and rapidly derivatized with PFBHA on the SPME fiber. Finally, the oximes formed were desorbed and detected by GC/MS in electron ionization (EI) mode. Validation of the present method was carried out, and the method was applied to quantitative analysis of the aldehydes in lung cancer blood. The results demonstrated that GC/MS and SPME with on-fiber derivatization is a simple, rapid, sensitive and solvent-free method for the determination of aldehydes in human blood.     

Analysis of Hexanal and Heptanal in Human Blood by Simultaneous Derivatization and Dispersive Liquid–Liquid Microextraction then LC–APCI–MS–MS

A new analytical approach, simultaneous derivatization and dispersive liquid–liquid microextraction followed by liquid chromatography–atmospheric-pressure chemical ionization tandem mass spectrometry, has been developed for analysis of hexanal and heptanal in human blood. In the derivatization and extraction procedure a solution of 2,4-dinitrophenylhydrazine (derivatization reagent) in 85 μL acetonitrile (dispersive solvent) and 50 μL tetrachloromethane (extraction solvent) was rapidly injected into the aqueous sample containing hexanal and heptanal. Within a few seconds the aldehydes were derivatized and simultaneously extracted. After centrifugation, the hydrazones in the sediment phase were analyzed by LC–APCI–MS–MS. Derivatization and extraction conditions were investigated systematically. Under the optimum conditions enrichment factors for hexanal and heptanal in a 1-mL sample were 63 and 73, respectively. The calibration plots were linear in the ranges 0.5–100 and 100–1,000 nmol L^?1, respectively, and the respective limits of detection (LOD) were 0.17 and 0.076 nmol L^?1. Reproducibility and recovery were good. The experimental results were compared with those obtained by use of solid-phase extraction and polymer monolithic microextraction. Because sample derivatization, extraction, and concentration were combined in a single step, the proposed method enabled simple, rapid, inexpensive, and efficient analysis of aldehydes in blood. The method has great potential for clinical analysis of biologically relevant aldehydes.     

High-performance liquid chromatographic determination of hexanal and heptanal in human blood by ultrasound-assisted headspace liquid-phase microextraction with in-drop derivatization

In this paper, an ultrasound-assisted headspace liquid-phase microextraction with in-drop derivatization was developed for the extraction and determination of hexanal and heptanal as the biomarkers in human blood. In the method, a polychloroprene rubber (PCR) tube was utilized as container to load extraction solvent (methyl cyanide) and derivatization reagent (2,4-dinitrophenylhydrazine, 2,4-DNPH). Volatile aldehydes were headspace extracted and simultaneously derivatized in the droplet, followed by LC-UV detection of the formed hydrazones. The stability of organic solvent and the sensitivity of the method enhanced greatly. Under the optimal conditions, good linearity was obtained in the concentration range of 0.01–10 μmol L⁻¹ (r > 0.997) and the limits of detection (LOD) for hexanal and heptanal were 0.79 and 0.80 nmol L⁻¹, respectively. The recoveries in blood sample ranged from 75.2% to 101.1% with the inter- and intra-day precisions less than 9.8%. The method possesses the advantages such as simplicity, sensitivity, efficiency, low consumption of solvent, and little interference from sample matrix. It provides great potential for the investigation of volatile disease biomarkers (aldehydes) in complex biological samples.     

Rapid determination of C6-aldehydes in tomato plant emission by gas chromatography-mass spectrometry and solid-phase microextraction with on-fiber derivatization

A simple, rapid, sensitive, and solvent-free method was developed for determination of plant-signalling compounds, the three C6-aldehydes hexanal, (Z)-3-hexenal, and (E)-2-hexenal, in tomato plant emission by gas chromatography-mass spectrometry (GC-MS) and solid-phase microextraction (SPME) with on-fiber derivatization. In this method, O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine (PFBHA) in aqueous solution was first headspace adsorbed onto a 65 microm poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber at 25 degrees C for 5 min, and then the fiber with adsorbed PFBHA was used for headspace extraction of tomato plant emission at 25 degrees C for 6 min. Finally, the resulting oximes adsorbed on the fiber were desorbed and analyzed by GC-MS. Extraction conditions and method validation were studied. The proposed method had low detection limit values for the three aldehydes from 0.1 to 0.5 ng/L and good precision (RSD less than 10%). In this work, the method was applied to investigation of tomato plant defense response to Helicoverpa armigera.     

Pyrolysis–GC–MS to trace terrigenous organic matter in marine sediments: a comparison between pyrolytic and lipid markers in the Adriatic Sea

The effectiveness of semiquantitative pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) as a rapid analytical technique for sourcing continental organic matter (OM) in marine sediments was examined by comparison with classical GC–MS analyses of solvent extractable lipid markers. Py–GC–MS was directly applied to HCl/HF de-ashed surface sediment samples collected in five stations located in north western Adriatic Sea. The resulting pyrolysates were characterised by compounds indicative of different biological precursors (e.g. proteins, carbohydrates, chlorophylls), including lignin methoxyphenols diagnostic for continental inputs. The relative abundance of pyrolytic markers was compared to the distribution of n-alkanes, n-alkanols and sterols extracted from the same sediments and determined by GC–MS analyses. For each class of molecular indicators, the terrigenous to aquatic ratio (TAR) was determined as follows: relative abundance of methoxyphenol/protein markers (TAR_PY), concentration ratios of (C27 + C29 + C31)/(C15 + C17 + C19) n-alkanes (TAR_HC), (C26 + C28+ C30)/(C14 + C16) n-alkanols (TAR_AL) and sitosterol/cholesterol (TAR_ST). A positive correlation was found between TAR_PY and both TAR_HC and TAR_AL indicating a decreasing contribution of land-plant-derived materials seaward in two investigated transects. TAR_ST values displayed a different trend suggesting a mixed origin for sitosterol. The distribution of TAR_PY values was also in good agreement with that of atomic C/N ratios. Considering the complexity of environmental systems (diagenetic alteration, different fractions of OM analysed) the obtained results indicate that the pyrolytic marker approach by Py–GC–MS is valuable for sourcing marine OM on a semiquantitative base, providing data consistent with GC–MS determinations of lipid markers and elemental bulk analyses.     

Development of gas chromatography-mass spectrometry following headspace single-drop microextraction and simultaneous derivatization for fast determination of short-chain aliphatic amines in water samples

In this work, for the first time, gas chromatography-mass spectrometry (GC-MS) following headspace single-drop microextraction (HS-SDME) and simultaneous derivatization was developed for fast determination of short-chain aliphatic amines (SCAAs) in water samples. In the proposed method, SCAAs in water samples were headspace extracted and concentrated by suspending a microdrop of solvent, and SCAAs extracted in the microdrop of solvent were simultaneously and rapidly reacted with pentafluorobenzaldehyde (PFBAY). The formed SCAA derivatives were analyzed by GC-MS. The HS-SDME parameters of solvent selection, solvent volume, sample temperature, extraction time and stirring rate were studied, and the method linearity, precision and detection limits, were also studied. The results show that the proposed method provided good linearity (R(2)>0.99, 5.0-500 ng/ml), low detection limit (0.6-1.1 ng/ml), and good precision (RSD value less than 10%). The proposed method was further tested by its application to quantitative analysis of SCAAs in four wastewater samples. The experiment results have demonstrated that GC-MS following HS-SDME and simultaneous derivatization is a simple, rapid and low-cost method for the determination of SCAAs in water samples.     

Development of a multiresidue method for analyzing herbicide and fungicide residues in bovine milk based on solid-phase extraction and liquid chromatography-tandem mass spectrometry

The adverse effect of reactive chemical residues on the quality of drug products has necessitated the determination of low-molecular-weight aldehydes in pharmaceutical excipients. An analytical methodology for the detection of trace amounts of C1-C8 aliphatic aldehydes and benzaldehyde in excipients is described. The proposed procedure is based on the derivatization of aldehydes in aqueous solution with O-2,3,4,5,6-(pentafluorobenzyl) hydroxylamine hydrochloride (PFBHA), followed by static headspace gas chromatographic (SHS-GC) analysis of PFBHA aldehyde oximes with negative chemical ionization (NCI) MS detection. The method developed was demonstrated to be simple, selective, sensitive, and was successfully applied to the screening of aldehydes at sub-microg/g levels in over 30 typical excipients. The most abundant aldehydes found in the samples were formaldehyde and acetaldehyde, for which a rapid and reliable routine quantification method by readily available SHS-GC instrumentation coupled with flame-ionization detection was also developed and validated.     

Headspace single-drop microextraction coupled with gas chromatography electron capture detection of butanone derivative for determination of iodine in milk powder and urine

A new detection method using headspace single-drop microextraction (HS-SDME) coupled to gas chromatography (GC) was established to determine the iodine in milk powder and urine. The derivative from the reaction between iodine and butanone in the acidic media was extracted into a micro-drop then determined by GC-ECD. With the optimisation of HS-SDME and derivatisation, the calibration curve showed good linearity within the range of 0.004–0.1 μg mL^?1 (0.004–0.1 μg g^?1) (R ² = 0.9991), and the limits of detection for milk powder and urine were 0.0018 μg g^?1 and 0.36 μg L^?1, respectively. The mean recoveries of milk powder and urine were 90.0–107 % and 89.4–101 % with mean RSD of 1.7–3.4 % and 2.7–3.3 %, respectively. This detection method affords a number of advantages, such as being simple, rapid, and inexpensive, with low organic solvent consumption, and is remarkably free from interference effects, rendering it an efficient method for the determination of iodine in milk powder and urine samples.     

Headspace Single-Drop Microextraction with Gas Chromatography for Determination of Volatile Halocarbons in Water Samples

A simple, rapid and inexpensive procedure for extraction and analysis of volatile halocarbons in water samples was presented using the headspace single-drop microextraction (HS-SDME) technique and gas chromatography with microcell electron capture detector (GC-μECD). Operation parameters. such as extraction solvent. headspace volume. organic drop volume. salt concentration. temperature and sampling time, were studied and optimized. Extraction of 10 volatile halocarbon compounds was achieved using the optimized method. Calibration curves of 10 target compounds yielded good linearity in the respective range of concentration (R ² ≥ 0.9968, chlorodibromomethane in the concentration range of 0.05–50 μg/L). The limits of detection were found between 0.002 (tetrachloroethene) and 0.374μg/L (1,1,2-trichloroethane). and relative standard deviations (RSD%) ranged between 4.3 (chloroform) and 9.7% (1,1,2,2-tetrachloroethane). Spiked recoveries of tap water and ground water agreed well with the known values between 118.97 (20.0μg/L of 1,1,2-trichloroethane) and 82.61% (10.0μg/L of tetrachloroethene), demonstrating that the HS-SDME combined GC-μECD was a useful and reliable technique for the rapid determination of volatile halocarbon compounds in water samples.     

Analysis of volatile compounds in Herba Asari by single-drop micro-extraction gas chromatography mass spectrometry

A rapid headspace single-drop micro-extraction(mix) gas chromatography mass spectrometry(SDMEGC -MS) for the analysis of the volatile compounds in Herba Asari was developed in this study.A mixed solvent of n-tridecane and butyl acetate(1:1) was finally used for the extraction at 70 C for 15 min with sample amount of 0.750 g and 100 mesh particle size.Under the determined conditions,the pound samples of Herba Asari were directly applied for the analysis.SDME-GC-MS,SPME-GC-MS and SD-GCMS methods were compared and the results showed that SDME-GC-MS method was a simple, inexpensive and effective way to measure the volatile compounds in Herba Asari and could be used for the analysis of volatile compounds in complex samples.     

Analysis of aldehydes in water by solid-phase microextraction with on-fiber derivatization

The solid-phase microextraction (SPME) technique with on-fiber derivatization was evaluated for the analysis of aldehydes in water. The poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber was used and O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) were first loaded onto the fiber. The aldehydes in water sample were agitated into headspace and extracted by SPME with on-fiber derivatization. Gas chromatography/mass spectrometry (GC/MS) was used for the analysis of oximes formed and the adsorption-time profiles were examined. The precision, recovery and method detection limits (MDLs) were evaluated with spiked bidistilled water, chlorinated tap water as well as well water. The relative standard deviations from different spiked water sample were all less than 10% and the recoveries were 100 +/- 15%. With 2 ml of water sample, MDLs were in the range of 0.12-0.34 microg/l. Compared with other techniques, the study shown here provided a simple, fast and reliable method for the analysis of aldehydes in water.     

Headspace Single Drop Microextraction for the Analysis of Fire Accelerants in Fire Debris Samples

Fire accelerants such as gasoline, kerosene, and diesel have commonly been used in arson cases. Improved analytical methods involving the extraction of fire accelerants are necessary to increase sample yield and to reduce the number of uncertain findings. In this study, an analytical method based on headspace single drop microextraction (HS-SDME) followed by gas chromatography–flame ionization detection (GC-FID) has been developed for the analysis of simulated fire debris samples. Curtain fabric was used as the sample matrix. The optimized conditions were 2.5 μL benzyl alcohol microdrop exposed for 20 min to the headspace of a 10 mL aqueous sample containing accelerants placed in 15-mL sample vial and stirred at 1500 rpm. The extraction method was compared with the solvent extraction method using n-hexane for the determination of fire accelerants. The HS-SDME process is driven by the concentration difference of analytes between the aqueous phases containing the analyte and the organic phase constituting the microdrop of a solvent. The limit of detection of HS-SDME for kerosene was 1.5 μL. Overall, the HS-SDME coupled with GC-FID proved to be rapid, simple and sensitive and a good alternative method for the analysis of accelerants in fire debris samples.     

Evaluation of solid-phase micro-extraction coupled to gas chromatography-mass spectrometry for the headspace analysis of volatile compounds in cocoa products

The aroma profile of cocoa products was investigated by headspace solid-phase micro-extraction (HS-SPME) combined with gas chromatography–mass spectrometry (GC–MS). SPME fibers coated with 100 μm polydimethylsiloxane coating (PDMS), 65 μm polydimethylsiloxane/divinylbenzene coating (PDMS-DVB), 75 μm carboxen/polydimethylsiloxane coating (CAR-PDMS) and 50/30 μm divinylbenzene/carboxen on polydimethylsiloxane on a StableFlex fiber (DVB/CAR-PDMS) were evaluated. Several extraction times and temperature conditions were also tested to achieve optimum recovery. Suspensions of the samples in distilled water or in brine (25% NaCl in distilled water) were investigated to examine their effect on the composition of the headspace. The SPME fiber coated with 50/30 μm DVB/CAR-PDMS afforded the highest extraction efficiency, particularly when the samples were extracted at 60 °C for 15 min under dry conditions with toluene as an internal standard. Forty-five compounds were extracted and tentatively identified, most of which have previously been reported as odor-active compounds. The method developed allows sensitive and representative analysis of cocoa products with high reproducibility. Further research is ongoing to study chocolate making processes using this method for the quantitative analysis of volatile compounds contributing to the flavor/odor profile.     

Separation and determination of amitriptyline and nortriptyline by dispersive liquid-liquid microextraction combined with gas chromatography flame ionization detection

Dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–flame ionization detection (GC–FID) was applied for the determination of two tricyclic antidepressant drugs (TCAs), amitriptyline and nortriptyline, from water samples. This method is a very simple and rapid method for the extraction and preconcentration of these drugs from environmental sample solutions. In this method, the appropriate mixture of extraction solvent (18 μL Carbon tetrachloride) and disperser solvent (1 mL methanol) are injected rapidly into the aqueous sample (5.0 mL) by syringe. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. The mixture was centrifuged and the extraction solvent is sedimented on the bottom of the conical test tube. 2.0 μL of the sedimented phase is injected into the GC for separation and determination of TCAs. Some important parameters, such as kind of extraction and disperser solvent and volume of them, extraction time, pH and ionic strength of the aqueous feed solution were optimized. Under the optimal conditions, the enrichment factors and extraction recoveries were between 740.04–1000.25 and 54.76–74.02%, respectively. The linear range was (0.005–16 μg mL⁻¹) and limits of detection were between 0.005 and 0.01 μg mL⁻¹ for each of the analytes. The relative standard deviations (R.S.D.) for 4 μg mL⁻¹ of TCAs in water were in the range of 5.6–6.4 (n = 6). The performance of the proposed technique was evaluated for determination of TCAs in blood plasma.     

Headspace solid-phase microextraction with novel sol–gel permethylated-β-cyclodextrin/hydroxyl-termination silicone oil fiber for determination of polybrominated diphenyl ethers by gas chromatography–mass spectrometry in soil

A simple, sensitive, and accurate method for determination of polybrominated diphenyl ethers (PBDEs) in soil has been developed based on headspace solid-phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC–MS). Permethylated-β-cyclodextrin/hydroxyl-termination silicone oil (PM-β-CD/OH-TSO) fiber was first prepared by sol–gel technology and employed in SPME procedure. By exploiting the superiorities of sol–gel coating technique and the advantages of the high hydrophobic doughnut-shaped cavity of PM-β-CD, the novel fiber showed desirable operational stability and extraction ability. After optimization on extraction conditions like water addition, extraction temperature, extraction time, salts effect, and solvents addition, the method was validated in soil samples, achieving good linearity (r > 0.999), precision (R.S.D. < 10%), accuracy (recovery > 78%), and detection limits (S/N = 3) raging from 13.0 to 78.3 pg/g.     

Fast determination of Z-ligustilide in plasma by gas chromatography/mass spectrometry following headspace single-drop microextraction

Angelica sinensis (danggui in Chinese) is a common traditional Chinese medicine (TCM), and its essential oil has been used for the treatment of many diseases such as hepatic fibrosis. Z-Ligustilide has been found to be an important active component in the TCM essential oil. In this work, for the first time, headspace single-drop microextraction (HS-SDME) followed by gas chromatography-mass spectrometry (GC-MS) was developed for the determination of Z-ligustilide in rabbit plasma after oral administration of essential oil of danggui. The extraction parameters of solvent selection, solvent volume, sample temperature, extraction time, stirring rate, and ion strength were systemically optimized. Furthermore, the method linearity, detection limit, and precision were also investigated. It was shown that the proposed method provided good linearity (0.02-20 microg/mL, R2 = 0.997), low detection limit (10 ng/mL), and good precision (RSD value less than 9%). Finally, HS-SDME followed by GC/MS was used for fast determination of Z-ligustilide in rabbit plasma at different time intervals after oral administration of danggui essential oil. The experimental results suggest that HS-SDME followed by GC/MS is a simple, sensitive, and low-cost method for the determination of Z-ligustilide in plasma, and a low-cost approach to pharmacokinetics studies of active components in TCMs.     

Analysis of acrylamide in different foodstuffs using liquid chromatography–tandem mass spectrometry and gas chromatography–tandem mass spectrometry

Acrylamide levels over a wide range of different food products were analysed using both liquid chromatography–tandem mass spectrometry (HPLC–MS–MS) and gas chromatography–tandem mass spectrometry (GC–MS–MS). Two different sample preparation methods for HPLC–MS–MS analysis were developed and optimised with respect to a high sample throughput on the one hand, and a robust and reliable analysis of difficult matrices on the other hand. The first method is applicable to various foods like potato chips, French fries, cereals, bread, and roasted coffee, allowing the analysis of up to 60 samples per technician and day. The second preparation method is not as simple and fast but enables analysis of difficult matrices like cacao, soluble coffee, molasses, or malt. In addition, this method produces extracts which are also well suited for GC–MS–MS analysis. GC–MS–MS has proven to be a sensitive and selective method offering two transitions for acrylamide even at low levels up to 1 μg kg⁻¹. For the respective methods the repeatability (n=10), given as coefficient of variation, ranged from 3% (acrylamide content of 550 μg kg⁻¹) to 12% (acrylamide content of 8 μg kg⁻¹) depending on the food matrix. The repeatability (n=3) for different food samples spiked with acrylamide (5–1500 μg kg⁻¹) ranged from 1 to 20% depending on the spiking level and the food matrix. The limit of quantification (referred to a signal-to-noise ratio of 9:1) was 30 μg kg⁻¹ for HPLC–MS–MS and 5 μg kg⁻¹ for GC–MS–MS. It could be demonstrated that measurement uncertainties were not only a result of analytical variability but also of inhomogeneity and stability of the acrylamide in food.     

Critical comparison of automated purge and trap and solid-phase microextraction for routine determination of volatile organic compounds in drinking waters by GC-MS

The use of two automated sample preparation techniques, solid-phase microextraction (SPME) and purge and trap (P&T) systems are critically compared for the GC–MS determination of eight volatile organic compounds (VOCs), including trihalomethanes (THMs), in drinking water samples. Compounds chosen for the comparison are regulated by Spanish and European official guidelines for drinking waters. Experimental parameters investigated for the two sample preparation techniques included SPME type of fibers, SPME modality, P&T gas flow, extraction and desorption times and desorption temperatures. Thus, optimal experimental conditions have been worked out for the SPME and P&T techniques. Under such optimised conditions, detection limits, precision and accuracy were evaluated. Both methods fulfilled the values that the official guidelines establish. The P&T–GC–MS method offers LDs ranged from 0.004 to 0.2 ng mL⁻¹, repeatabilities below 6% and recoveries between 81 and 117%; while LDs ranging from 0.008 to 0.7 ng mL⁻¹, 1–12% R.S.D. and recoveries from 80 to 119% were achieved with the SPME–GC–MS method. Finally, we chose P&T–GC–MS method as the best for this determination and we validate this methodology by its application to the analysis of an Aquacheck Interlaboratory Exercise.