Potentialities of polyurethane foams for trace level analysis of triazinic metabolites in water matrices by stir bar sorptive extraction

Polyurethane (PU) foams were applied for stir bar sorptive extraction of five triazinic metabolites (desethyl-2-hydroxyatrazine, desisopropylatrazine, desethylatrazine, 2-hydroxyatrazine and desethylterbuthylazine) in water matrices, followed by liquid desorption and high performance liquid chromatography with diode array detection (SBSE(PU)-LD/HPLC-DAD). The optimum conditions for SBSE(PU)-LD were 5 h of extraction (1000 rpm) and 5% (v/v) of methanol for the analysis of desethyl-2-hydroxyatrazine and 2-hydroxyatrazine, 15% (w/v) of sodium chloride for the remaining compounds and acetonitrile as back-extraction solvent (5 mL) under ultrasonic treatment (60 min). The methodology provided recoveries up to 26.3%, remarkable precision (RSD < 2.4%), excellent linear dynamic ranges between 5.0 and 122.1 μg/L (r² > 0.9993) and convenient detection limits (0.4-1.3 μg/L). The proposed method was applied in the analysis of triazinic metabolites in tap, river and ground waters, with remarkable performance and negligible matrix effects. The comparison of the recoveries obtained by PU and commercial stir bars was also performed, where the yields achieved with the former were up to ten times higher proving that PU is appropriate for analysis at trace level of this type of polar compounds in water matrices.     

Polydimethylsiloxane/polypyrrole stir bar sorptive extraction and liquid chromatography (SBSE/LC-UV) analysis of antidepressants in plasma samples

A new polymeric coating consisting of a dual-phase, polydimethylsiloxane (PDMS) and polypyrrole (PPY) was developed for the stir bar sorptive extraction (SBSE) of antidepressants (mirtazapine, citalopram, paroxetine, duloxetine, fluoxetine and sertraline) from plasma samples, followed by liquid chromatography analysis (SBSE/LC-UV). The extractions were based on both adsorption (PPY) and sorption (PDMS) mechanisms. SBSE variables, such as extraction time, temperature, pH of the matrix, and desorption time were optimized, in order to achieve suitable analytical sensitivity in a short time period. The PDMS/PPY coated stir bar showed high extraction efficiency (sensitivity and selectivity) toward the target analytes. The quantification limits (LOQ) of the SBSE/LC-UV method ranged from 20 ng mL⁻¹ to 50 ng mL⁻¹, and the linear range was from LOQ to 500 ng mL⁻¹, with a determination coefficient higher than 0.99. The inter-day precision of the SBSE/LC-UV method presented a variation coefficient lower than 15%. The efficiency of the SBSE/LC-UV method was proved by analysis of plasma samples from elderly depressed patients.     

Quantitative analysis of phosphoric acid esters in aqueous samples by isotope dilution stir-bar sorptive extraction combined with direct analysis in real time (DART)-Orbitrap mass spectrometry

A novel hyphenated technique, namely the combination of stir bar sorptive extraction (SBSE) with isotope dilution direct analysis in real time (DART) Orbitrap™ mass spectrometry (OT-MS) is presented for the extraction of phosphoric acid alkyl esters (tri- (TnBP), di- (HDBP), and mono-butyl phosphate (H2MBP)) from aqueous samples. First, SBSE of phosphate esters was performed using a Twister™ coated with 24 μL of polydimethylsiloxane (PDMS) as the extracting phase. SBSE was optimized for extraction pH, phase ratio (PDMS volume/aqueous phase volume), stirring speed, extraction time and temperature. Then, coupling of SBSE to DART/Orbitrap-MS was achieved by placing the Twister™ in the middle of an open-ended glass tube between the DART and the Orbitrap™. The DART mass spectrometric response of phosphate esters was probed using commercially available and synthesized alkyl phosphate ester standards. The positive ion full scan spectra of alkyl phosphate triesters (TnBP) was characterized by the product of self-protonation [M + H]⁺ and, during collision-induced dissociation (CID), the major fragmentation ions corresponded to consecutive loss of alkyl chains. Negative ionization gave abundant [M − H]⁻ ions for both HDnBP and H2MnBP. Twisters™ coated with PDMS successfully extracted phosphate acid esters (tri-, di- and mono-esters) granted that the analytes are present in the aqueous solution in the neutral form. SBSE/DART/Orbitrap-MS results show a good linearity between the concentrations and relative peak areas for the analytes in the concentration range studied (0.1–750 ng mL⁻¹). Reproducibility of this SBSE/DART/Orbitrap-MS method was evaluated in terms of %RSD by extracting a sample of water fortified with the analytes. The %RSDs for TnBP, HDnBP and H₂MnBP were 4, 3 and 3% (n = 5) using the respective perdeuterated internal standards. Matrix effects were investigated by matrix matched calibration standards using underground water samples (UWS) and river water samples (RWS). Matrix effects were effectively compensated by the addition of the perdeuterated internal standards. The application of this new SBSE/DART/Orbitrap-MS method should be very valuable for on-site sampling/monitoring, limiting the transport of large volumes of water samples from the sampling site to the laboratory.     

Rotating-disk sorptive extraction of nonylphenol from water samples

In this study the sorption of nonylphenol was implemented on a rotating Teflon disk coated with a PDMS film on one of its surfaces. In this way, the disk, which has a high surface area, contacts only the liquid sample, which can be stirred at higher velocity than with the stir bar used in stir-bar sorptive extraction (SBSE), without damaging the phase while at the same time facilitating analyte mass transfer to the PDMS surface. We refer to the procedure as rotating-disk sorptive extraction (RDSE). Extraction variables such as disk rotational velocity, extraction time, and surface area of PDMS film were studied to establish the best conditions for extraction. With increasing rotational velocity, the amount of extracted analyte significantly increases because the stagnant layer concomitantly decreases. On the other hand, the extracted amount concomitantly increases with extraction time, reaching equilibrium at approximately 20 min, which can be reduced to 10 min when the surface area of PDMS increases from 1.74 to 6.97 cm². Precision of the method was determined by using the same disk (n = 6) and different disks (n = 3), showing relative standard deviations for the analyte of 3.7% and 10%, respectively. The detection limit of the method was 0.09 μg/L NP, defined at a signal to noise ratio of 3. The method was applied to a real sample, achieving quantitative recovery. The PDMS phase on the disk could be used for at least 50 experiments. In any case, replacement of the PDMS film on the disk is very easy and inexpensive, as compared to the commercial alternative SBSE.     

Powdered activated carbons as effective phases for bar adsorptive micro-extraction (BAμE) to monitor levels of triazinic herbicides in environmental water matrices

Bar adsorptive micro-extraction using three powdered activated carbons (ACs) as adsorbent phases followed by liquid desorption and high performance liquid chromatography with diode array detection (BAμE(ACs)-LD/HPLC-DAD), was developed to monitor triazinic herbicides (atrazine, simazine and terbutylazine) in environmental water matrices. ACs used present apparent surface areas around 1000 m² g⁻¹ with an important mesoporous volume and distinct surface chemistry characteristics (pH_PZC ranging from 6.5 to 10.4). The textural and surface chemistry properties of the ACs adsorbent phases were correlated with the analytical data for a better understanding of the overall enrichment process. Assays performed on 10 mL water samples spiked at the 10.0 μg L⁻¹ levels under optimized experimental conditions yielded recoveries around 100% for the three herbicides under study. The analytical performance showed good precision (RSD < 15.0%), convenient detection limits (≈0.1 μg L⁻¹) and suitable linearity (1.0-12.0 μg L⁻¹) with good correlation coefficients (r² > 0.9914). By using the standard addition method, the application of the present method on real water matrices, such as surface water and wastewater, allowed very good performances at the trace level. The proposed methodology proved to be a suitable sorptive extraction alternative for the analysis of priority pollutants with polar characteristics, showing to be easy to implement, reliable, sensitive and requiring a low sample volume to monitor triazinic compounds in water matrices.     

Determination of diclofenac from paediatric urine samples by stir bar sorptive extraction (SBSE)-HPLC-UV technique

A novel stir bar sorptive extraction (SBSE) method coupled with high performance liquid chromatography (HPLC) and UV detection for the extraction of diclofenac (DIC) from paediatric urine samples has been developed and validated. Selectivity and sensitivity being the prime objectives of the bioanalytical method for clinical samples, an optimised SBSE protocol was developed that selectively extracted DIC from various concurrently administered drugs. The validated assay was found to be linear (r = 0.9999) over a concentration range of 100-2000 ng mL⁻¹. SBSE showed consistent recoveries (∼70%) of DIC across the validated linearity range. Overall, the method exhibited excellent accuracy and precision across all QC concentrations, tested over three days. Calculated LOD and LOQ were found to be 12.03 ng mL⁻¹ and 36.37 ng mL⁻¹, respectively, however, for the experimental purposes, 100 ng mL⁻¹ was considered as the validated LOQ (accuracy and precision at this LQC was <20%). Further, studies on various attributes of the stir bar/SBSE, showed no significant inter- and intra-stir bar variability for DIC extraction. There was no carryover effect with re-use of conditioned stir bars and for the first time, a systematic investigation on the effect of ageing of stir bars on their extraction efficiency was carried out. Results showed that, for the present study, stir bars which were used 150 times were still functional based on in-house acceptance criteria and extraction efficiency. The validated method was successfully applied to the analysis of DIC in paediatric clinical trial samples.     

On-tap passive enrichment,a new way to investigate off-flavor episodes in drinking water

Because taste and odor events in drinking water are often fleeting and unpredictable phenomena, an innovative enrichment sampler has been developed to trap off-flavor compounds directly at the consumer's tap. The ARISTOT (Advanced Relevant Investigation Sampler for Taste & Odor at Tap) consists of a tap adapter in which seven polydimethylsiloxane (PDMS) coated stir bars are placed, allowing the stir bar sorptive extraction (SBSE) of organic compounds during each tap opening. In order to study the efficiency of ARISTOT, a private network pilot unit has been constructed in our laboratory, equipped with four faucets in parallel, solenoid valves for an automation of the system and a mixing chamber to spike drinking water with odorous compounds in order to have homogenously smelling water at each tap. After enrichment, the stir bars are taken out, in-line thermo-desorbed and analyzed by gas chromatography coupled with a mass spectrometer. The results showed the high sensitivity of ARISTOT, which was able to quickly monitor odorous compounds at the sub ng/L level. A “multishot” method was developed to analyze chemicals concentrated on the seven stir bars in only one chromatographic run, thereby increasing the sensitivity of the system. Higher enrichment factors were obtained under low water flow rates or by using longer stir bars and/or stir bars with a higher PDMS film thickness. No significant loss of extracted compounds was reported for flow rates between 2 and 4 L/min. This allowed us to spike the stir bars with an internal standard prior to sampling in order to monitor the analytical variations. It was also observed that hot water increases the loss of enriched solutes but the quantification can be corrected by internal standard addition.     

Cadmium (II) imprinted 3-mercaptopropyltrimethoxysilane coated stir bar for selective extraction of trace cadmium from environmental water samples followed by inductively coupled plasma mass spectrometry detection

Cd(II) imprinted 3-mercaptopropyltrimethoxysilane (MPTS)-silica coated stir bar was prepared by sol–gel technique combining with a double-imprinting concept for the first time and was employed for stir bar sorptive extraction (SBSE) of trace Cd(II) from water samples followed by inductively coupled plasma mass spectrometry (ICP-MS) detection. A tetramethoxysilane (TMOS) coating was first in situ created on the glass bar surface. Afterward, a sol solution containing MPTS as the functional precursor, ethanol as the solvent and both Cd(II) and surfactant micelles (cetyltrimethylammonium bromide, CTAB) as the template was again coated on the TMOS bar. The structures of the stir bar coating were characterized by FT-IR spectroscopy. Round-bottom vial was used for the extraction of Cd(II) by SBSE to avoid abrasion of stir bar coatings. The factors affecting the extraction of Cd(II) by SBSE such as pH, stirring rate and time, sample/elution volume and interfering ions have been investigated in detail, and the optimized experimental parameters were obtained. Under the optimized conditions, the adsorption capacities of non-imprinted and imprinted coating stir bars were found to be 0.5 μg and 0.8 μg bar⁻¹. The detection limit (3σ) based on three times standard deviations of the method blanks by 7 replicates was 4.40 ng L⁻¹ and the relative standard deviation (RSD) was 3.38% (c = 1 μg L⁻¹, n = 7). The proposed method was successfully applied for the analysis of trace Cd(II) in rain water, East Lake and Yangtze River water. To validate the proposed method, certified reference material of GSBZ 50009-88 environmental water was analyzed and the determined value is in a good agreement with the certified value. The developed method is rapid, selective, sensitive and applicable for the analysis of trace Cd(II) in environmental water samples.     

Development and application of stir bar sorptive extraction with polyurethane foams for the determination of testosterone and methenolone in urine matrices

This work describes the development, validation, and application of a novel methodology for the determination of testosterone and methenolone in urine matrices by stir bar sorptive extraction using polyurethane foams [SBSE(PU)] followed by liquid desorption and high-performance liquid chromatography with diode array detection. The methodology was optimized in terms of extraction time, agitation speed, pH, ionic strength and organic modifier, as well as back-extraction solvent and desorption time. Under optimized experimental conditions, convenient accuracy were achieved with average recoveries of 49.7 8.6% for testosterone and 54.2 ± 4.7% for methenolone. Additionally, the methodology showed good precision (<9%), excellent linear dynamic ranges (>0.9963) and convenient detection limits (0.2-0.3 μg/L). When comparing the efficiency obtained by SBSE(PU) and with the conventional polydimethylsiloxane phase [SBSE(PDMS)], yields up to four-fold higher are attained for the former, under the same experimental conditions. The application of the proposed methodology for the analysis of testosterone and methenolone in urine matrices showed negligible matrix effects and good analytical performance.     

Development of selective and chemically stable coating for stir bar sorptive extraction by molecularly imprinted technique

A novel stir bar coated with molecularly imprinted polymer (MIP) as selective extraction phase for sorptive extraction of triazine herbicides was developed. The stir bar was prepared by chemically bonding the MIP to the glass bar to improve its stability. A homogeneous and porous structure was observed on the stir bar surface. Extraction performance shows that the MIP-coated stir bar has stronger affinity to the template molecule terbuthylazine as compared with that of the reference stir bar without addition of template. Owning to the shape and structural compatibility, the obtained stir bar also demonstrated specific selectivity to the structural related-compounds of nine triazines, and thus can be applied to simultaneous determination of these compounds from complex samples coupled with high performance liquid chromatography. Four complex samples with different matrix, including rice, apple, lettuce and soil were used to evaluate this proposed method. The limits of detection obtained are in the range of 0.04-0.12 μg L⁻¹, and the recoveries for the spiked rice, apple, lettuce and soil samples were 80.8-107.7%, 80.6-107.8%, 72.0-109.8% and 89.0-114.8% with RSD from 1.2 to 7.9%, respectively. Moreover, this MIP-coated stir bar was firm, durable and can be prepared simply and reproducibly. The developed coating method would be useful to prepare a range of selective stir bars in order to extend the applicability of stir bar sorptive extraction (SBSE) in complex sample analysis.     

A comparison of solid-phase microextraction and stir bar sorptive extraction coupled to liquid chromatography for the rapid analysis of resveratrol isomers in wines, musts and fruit juices

A comparison of direct immersion solid-phase microextraction (DI-SPME) and stir bar sorptive extraction (SBSE) coupled to liquid chromatography (HPLC) with fluorimetric detection for the rapid analysis of resveratrol isomers is described. For DI-SPME, a polar Carbowax-template resin (CW/TPR) 50 μm fiber was the most efficient and optimum extraction conditions were 40 °C and an extraction time of 30 min, stirring in the presence of 5% (m/v) sodium chloride and 0.07 M acetate/acetic acid buffer (pH 6). Desorption was carried out using the static mode for 10 min. Linearity was obtained in the 5-150 and 2-150 ng mL⁻¹ ranges for trans- and cis-resveratrol, with detection limits of 2 and 0.5 ng mL⁻¹, respectively. When using SBSE, a polydimethylsiloxane (PDMS) twister provided best extraction by means of a derivatization reaction in the presence of acetic anhydride and potassium carbonate. The same time and temperature were used for the extraction step in the presence of 2.5% (m/v) sodium chloride, and liquid desorption was performed with 150 μL of a 50/50 (v/v) acetonitrile/1% (v/v) acetic acid solution in a desorption time of 15 min. Linearity was now between 0.5 and 50 ng mL⁻¹ for trans-resveratrol with a detection limit of 0.1 ng mL⁻¹, while cis-resveratrol could not be extracted. The proposed methods were successfully applied to determining the resveratrol isomer content of wine, must and fruit juices.     

Investigation of ractopamine molecularly imprinted stir bar sorptive extraction and its application for trace analysis of β2-agonists in complex samples

In this paper, a novel molecularly imprinted polymer (MIP) coated stir bar with ractopamine as template by glass capillary filling with magnetic core as substrate was prepared reproducibly. The ractopamine MIP coating was homogeneous and porous with the average thickness of 20.6 μm. The extraction apparatus for the stir bar was improved to avoid coating loss. The MIP-coated stir bar showed better extraction capacity and good selectivity than that of non-imprinted polymer (NIP) coated stir bar to ractopamine and its analogues. The extraction capacities of ractopamine, isoxsuprine, clenbuterol and fenoterol for MIP-coated stir bar were 3.3, 3.1, 2.8 and 2.4 times as much as that of the NIP coated stir bar, respectively. The MIP-coated stir bars could be used at least 40 times without apparent damage and kept in dried air for 8 months without reduce of extraction ability. A method for the determination of β₂-agonists in complex samples by MIP-coated stir bar sorptive extraction coupled with high-performance liquid chromatography (HPLC) was developed. The linear ranges were 0.5–40 μg/L for ractopamine and 1.0–40 μg/L for isoxsuprine and clenbuterol. The detection limits were within the range of 0.10–0.21 μg/L. The method was successfully applied to the analysis of β₂-agonists in spiked pork, liver and feed samples with the recoveries of 83.7–92.3%, 80.5–90.2% and 73.6–86.2%, respectively. The RSDs was within 2.9–8.1%. The method is very suitable for the determination of trace β₂-agonists in pork, liver and feed samples.     

Development, optimisation and application of polyurethane foams as new polymeric phases for stir bar sorptive extraction

In this contribution, polyurethane foams are proposed as new polymeric phases for stir bar sorptive extraction (SBSE). Assays performed for polyurethane synthesis demonstrated that four series of formulations (P(1), P(2), P(3) and P(4)) present remarkable stability and excellent mechanical resistance to organic solvents. For polymer clean-up treatment, acetonitrile proved to be the best solvent under sonification, ensuring the reduction of the contamination and interferences. SBSE assays performed on these polyurethane polymers followed by liquid desorption and high-performance liquid chromatography-diode array detection (LD-HPLC-DAD) or large volume injection-capillary gas chromatography-mass spectrometry (LD-LVI-GC-MS), showed that P(2) presents the best recovery yields for atrazine, 2,3,4,5-tetrachlorophenol and fluorene, used as model compounds in water samples at a trace level. SBSE(P(2)) assays performed on this polymer mixed up with several adsorbent materials, i.e. activated carbon, a mesoporous material and a calixarene, did not bring any advantages in relation with the polymeric matrix alone. The comparison between assays performed by SBSE(P(2)) and by the conventional SBSE(PDMS) showed much better performance for the former phase on aqueous samples spiked with atrazine, 2,3,4,5-tetrachlorophenol and fluorene, in which the foremost two analytes present recovery values 3- and 10-fold higher, respectively. The polyurethanes proposed as new polymeric phases for SBSE provided powerful capabilities for the enrichment of organic compounds from aqueous matrices, showing to be indicated mainly in the case of the more polar analytes.     

Multi-residue determination of veterinary drugs in milk by ultra-high-pressure liquid chromatography-tandem mass spectrometry

Stir bar sorptive extraction with polyurethane (PU) and polydimethylsiloxane (PDMS) polymeric phases followed by high-performance liquid chromatography with diode array detection [SBSE(PU or PDMS)/HPLC-DAD] was studied for the determination of six acidic pharmaceuticals [o-acetylsalicylic acid (ACA), ibuprofen (IBU), diclofenac sodium (DIC), naproxen (NAP), mefenamic acid (MEF) and gemfibrozil (GEM)], selected as non-steroidal acidic anti-inflammatory drugs and lipid regulators model compounds in environmental water matrices. The main parameters affecting the efficiency of the proposed methodology are fully discussed. Assays performed on 25 mL of water samples spiked at the 10 microg L(-1) level under optimized experimental conditions, yielded recoveries ranging from 45.3+/-9.0% (ACA) to 90.6+/-7.2% (IBU) by SBSE(PU) and 9.8+/-1.6% (NAP) to 73.4+/-5.0% (GEM) by SBSE(PDMS), where the former polymeric phase presented a better affinity to extract these target analytes from water matrices at the trace level. The methodology showed also excellent linear dynamic ranges for the six acidic pharmaceuticals studied, with correlation coefficients higher than 0.9976, limits of detection and quantification between 0.40-1.7 microg L(-1) and 1.5-5.8 microg L(-1), respectively, and suitable precision (RSD <15%). Moreover, the developed methodology was applied for the determination of these target analytes in several environmental matrices, including river, sea and wastewater samples, having achieved good performance and moderate matrix effects. In short, the PU foams demonstrated to be an excellent alternative for the enrichment of the more polar metabolites from water matrices by SBSE, overcoming the limitations of the conventional PDMS phase.     

Impact of water/PDMS phase ratio,volume of PDMS,and sampling time on Stir Bar Sorptive Extraction (SBSE) recovery of some pesticides with different KO/W

In Stir Bar Sorptive Extraction (SBSE) organic analytes are enriched from aqueous samples by sorption onto a thick film of polydimethylsiloxane (PDMS) coated on a glass‐enveloped magnet. Sampled analytes are recovered by thermodesorption (TDS) and analysed on‐line by cGC‐MS. This study evaluates the SBSE recovery as a function of K_O/W, the phase ratio (β), PDMS volume (20, 40, and 110 μL), sample volumes (4, 10, 100, and 1000 mL), and sampling time (0.67, 1, 2, 4, 5, 6, and 24 h) for three pesticides with different K_O/W [parathion methyl (K_O/W: 7.24×10²), β‐endosulfan (K_O/W: 6.8×10³), and buprofezin (K_O/W: 2.0×10⁴)]. Experimental recoveries with SBSE in reasonable sampling times were found to be mainly conditioned by β, which must be as low as possible either by operating on small sample volumes or by using stir bars coated with high PDMS volume when samples of relatively large volume are analysed.     

Sol–gel polydimethylsiloxane/poly(vinylalcohol)‐coated stir bar sorptive extraction of organophosphorus pesticides in honey and their determination by large volume injection GC

A PDMS/poly(vinylalcohol) (PDMS/PVA) film prepared through a sol–gel process was coated on stir bars for sorptive extraction, followed by liquid desorption and large volume injection–GC–flame photometric detector (LVI–GC–FPD) for the determination of five organophosphorus pesticides (OPPs) (phorate, fenitrothion, malathion, parathion, and quinalphos) in honey. The preparation reproducibility of PDMS/PVA‐coated stir bar ranged from 4.3 to 13.4% (n = 4) in one batch, and from 6.0 to 12.6% (n = 4) in batch to batch. And one prepared stir bar can be used for more than 50 times without apparent coating loss. The significant parameters affecting stir bar sorptive extraction (SBSE) were investigated and optimized. The LODs for five OPPs ranged from 0.013 (parathion) to 0.081 μg/L (phorate) with the RSDs ranging from 5.3 to 14.2% (c = 1 μg/L, n = 6). The proposed method was successfully applied to the analysis of five OPPs in honey.     

Molecularly imprinted conducting polymer based electrochemical sensor for detection of atrazine

An original electrochemical sensor based on molecularly imprinted conducting polymer (MICP) is developed, which enables the recognition of a small pesticide target molecule, atrazine. The conjugated MICP, poly(3,4-ethylenedioxythiophene-co-thiophene-acetic acid), has been electrochemically synthesized onto a platinum electrode following two steps: (i) polymerization of comonomers in the presence of atrazine, already associated to the acetic acid substituent through hydrogen bonding, and (ii) removal of atrazine from the resulting polymer, which leaves the acetic acid substituents open for association with atrazine. The obtained sensing MICP is highly specific towards newly added atrazine and the recognition can be quantitatively analyzed by the variation of the cyclic voltammogram of MICP. The developed sensor shows remarkable properties: selectivity towards triazinic family, large range of detection (10⁻⁹ mol L⁻¹ to 1.5 × 10⁻² mol L⁻¹ in atrazine) and low detection threshold (10⁻⁷ mol L⁻¹).     

Determination of 4-nonylphenol and 4-tert.-octylphenol in water samples by stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry

A simple and highly sensitive method called thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of 4-nonylphenol (NP) and 4-tert.-octylphenol (OP) in water samples, is described. NP and OP in samples are extracted from water samples and concentrated by the stir bar sorptive extraction (SBSE) technique. A stir bar coated with polydimethylsiloxane (PDMS) is added to a 2.0 ml water sample and stirring is carried out for 60 min at room temperature (25 °C) in a headspace vial. Then the extract is high sensitively analyzed by TD-GC-MS without any derivatization step. The optimum SBSE conditions are realized at an extraction time of 60 min. The detection limits are 0.02 ng ml⁻¹ for NP and 0.002 ng ml⁻¹ for OP. The method shows good linearity over the concentration range of 0.1-10 ng ml⁻¹ for NP and 0.01-10 ng ml⁻¹ for OP, and the correlation coefficients are higher than 0.999. The average recoveries of NP and OP are higher than 97% (R.S.D.: 3.6-6.2%) with correction using the added surrogate standards, 4-(1-methyl) octylphenol-d₅ and deuterium 4-tert.-octylphenol. This simple, accurate, sensitive and selective analytical method may be used in the determination of trace amounts of NP and OP in tap and river water samples.     

The use of stir bar sorptive extraction—A potential alternative method for the determination of furan, evaluated using two example food matrices

A comparison is made between static headspace analysis and stir bar sorptive extraction (SBSE) for the quantitative determination of furan. The SBSE technique was optimised and evaluated using two example food matrices (coffee and jarred baby food). The use of the SBSE technique in most cases, gave comparable results to the static headspace method, using the method of standard additions with d₄-labelled furan as an internal standard. Using the SBSE method, limits of detection down to 2 ng g⁻¹ were achieved, with only a 1 h extraction. The method was performed at ambient temperatures, thus eliminating the possibility of formation of furan during extraction.     

Determination of pesticides in river water using rotating disk sorptive extraction and gas chromatography-mass spectrometry

The rotating disk sorptive extraction (RDSE) technique was applied to the determination of pesticides in aqueous samples. Pesticides of different polarities were considered in this study: chlorpyrifos, diazinon, fenvalarate, cyhalothrin, cypermethrin, lindane and malathion. The sorptive/desorptive behavior of the pesticides was studied using a rotating disk containing a polydimethylsiloxane (PDMS) phase on one of its surfaces. The analyte polarity was a significant factor in the extraction time; shorter extraction times were required for the more apolar pesticides. The optimum variables for the extraction of all analytes were: extraction time of 3 h, sample volume of 25 mL, rotational velocity of the disk 1250 rpm, desorption time of 30 min using methanol. For pesticides with values of Log K_ow > 4, the extraction time can be reduced to 30 min for a quantitative extraction. Under these conditions, recoveries between 76% and 101% were obtained for the target pesticides, and the repeatability of the methodology, expressed as relative standard deviation, was determined to be between 10% and 20%. Additionally, the limits of detection of the analytes were lower than 3.1 μg L⁻¹. The extraction method developed using the RDSE was compared to a stir bar sorptive extraction (SBSE) under the same conditions. It can be observed that the extraction using the rotating disk offers higher recoveries because of its higher PDMS volume and its higher surface area to volume ratio that allows for improved mass transfer.