Measurement of bisphenol A in human serum by gas chromatography/mass spectrometry

The purpose of this study is to establish an easy and accurate method for the determination of bisphenol A (BPA) in the human serum. The samples were applied to the C₁₈ solid phase extraction (SPE) column for clean up of samples. The BPA is conjugated with tetrabutylammonium hydrogen sulfate as the counter ion in alkali solution. The ion paired BPA is moves from the aqueous phase to the organic phase as an ion paired extraction. BPA extracted from human serum were derivatized with pentafluorobenzyl bromide (PFBBr). The derivative was analyzed by gas chromatography (GC)/mass spectrometry (MS) using negative chemical ionization (NCI). The instrumental detection limit of BPA was 5 pg/ml (10 fg). The instrumental response between 0.01 and 100 pg/ml of BPA standards was linear (r²=0.998). The recovery of BPA spiked into human serum was 101.0±4.63 (1 pg/ml) and 100.9±3.75 (10 pg/ml), respectively. The concentration of BPA in the human serum from 20 individuals was 0.54 pg/ml.     

Determination of drugs of abuse in water by solid-phase extraction,derivatisation and gas chromatography–ion trap-tandem mass spectrometry

An alternative method for the sensitive determination of several drugs of abuse and some of their metabolites in surface and sewage water samples is proposed. Analytes are concentrated using a solid-phase extraction (SPE) sorbent, converted into the corresponding trimethylsilyl derivatives and selectively determined by gas chromatography (GC) with tandem mass spectrometry (MS/MS) detection. Parameters affecting the performance of extraction, derivatisation and determination steps are systematically investigated. Moreover, the stability of target analytes in sewage water samples is discussed. Under final working conditions, water samples were adjusted at pH 8.5 and concentrated using a 200 mg OASIS HLB SPE cartridge. Analytes were sequentially eluted with ethyl acetate followed by acetone and silylated using N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA). The reaction was completed in 60 min at 80 °C and the mixture injected directly in the GC–MS/MS system without further purification. In most cases, analytes presented a poor stability in sewage water samples; however, once they are submitted to the SPE process, cartridges can be stored at −20 °C for at least 3 months without significant degradation and/or inter-conversion reactions of illicit drugs. The proposed method provided recoveries over 74% and LODs between 0.8 and 15 ng/L for river and treated wastewater samples. In the case of raw wastewater slightly worse recoveries, between 63 and 137%, and similar LODs were attained. Analysis of a limited number of waste and surface water samples confirmed the presence of several illicit drugs in the aquatic environment, with the highest levels and frequency corresponding to benzoylecgonine, the main metabolite of cocaine.     

Determination of various estradiol mimicking-compounds in sewage sludge by the combination of microwave-assisted extraction and LC-MS/MS

In this work, we present the development and application of a microwave assisted extraction followed by liquid chromatography-tandem mass spectrometry methodology (MAE-LC-MS/MS) for the determination of various estradiol-mimicking compounds in sewage sludge samples. For the purification of the MAE extracts, we have employed a solid phase extraction (SPE) clean-up procedure, previously optimised. The entire method provides recoveries between 71.7% and 103.1%, with relative standard deviation lower than 11.1% and limits of detection ranging from 0.6 to 3.5 ng g⁻¹. The developed method was applied to samples from three wastewater treatment plants (WWTPs) located in Las Palmas of Gran Canaria (Spain), two of which had a conventional activated sludge treatment (AST), whereas the third treatment plant had an advanced membrane bioreactor treatment (MBR). All of the analytes in the study, including (nonylphenol (NP), octylphenol (OP), and some of their ethoxylated chains AP_nEOs (n ≤ 7), 17β-estradiol (E2), estriol (E3), 17α-ethynylestradiol (EE) and bisphenol-A (BPA)), were found in almost all samples in concentrations ranging from 0.9 to 710.2 ng g⁻¹.     

Kinetic electro membrane extraction under stagnant conditions—Fast isolation of drugs from untreated human plasma

Amitriptyline, citalopram, fluoxetine, and fluvoxamine were isolated by electro membrane extraction (EME) from 70 μl of untreated plasma (pH 7.4), through a supported liquid membrane (SLM) of 1-ethyl-2-nitrobenzene immobilized in the pores of a porous polypropylene hollow fiber, and into 30 μl of 10 mM HCOOH as acceptor solution inside the lumen of the hollow fiber. The driving force of the extraction was a 9 V potential sustained over the SLM with a common battery, with the positive electrode placed in the plasma sample and the negative electrode placed in the acceptor solution. Extractions were performed under totally stagnant conditions with a very simple device for 1 min (kinetic regime), and subsequently the acceptor solution was analyzed directly by liquid chromatography–mass spectrometry (LC–MS). Recoveries were 12, 13, 22, and 17% for fluoxetine, amitriptyline, citalopram, and fluvoxamine, respectively. Sample clean-up was comparable to reversed-phase solid-phase extraction (SPE), but EME required substantially less time than SPE. The time advantage of EME was further improved by parallel extraction of three samples (for 1 min) with the same 9 V battery. EME from plasma combined with LC–MS provided limits of quantification (S/N = 10) in the range 0.4–2.3 ng/ml, linearity in the range 1–1000 ng/ml with r²-values of 0.998–0.999, and repeatability in the range 3.2–8.9% RSD in the mid-therapeutic window (100 ng/ml).     

Quantification of the xenoestrogens 4-tert.-octylphenol and bisphenol A in water and in fish tissue based on microwave assisted extraction, solid-phase extraction and liquid chromatography-mass spectrometry

Extraction methods were developed for quantification of the xenoestrogens 4-tert.-octylphenol (tOP) and bisphenol A (BPA) in water and in liver and muscle tissue from the rainbow trout (Oncorhynchus mykiss). The extraction of tOP and BPA from tissue samples was carried out using microwave-assisted solvent extraction (MASE) followed by solid-phase extraction (SPE). Water samples were extracted using only SPE. For the quantification of tOP and BPA, liquid chromatography mass spectrometry (LC-MS) equipped with an atmospheric pressure chemical ionisation interface (APCI) was applied. The combined methods for tissue extraction allow the use of small sample amounts of liver or muscle (typically 1 g), low volumes of solvent (20 ml), and short extraction times (25 min). Limits of quantification of tOP in tissue samples were found to be approximately 10 ng/g in muscle and 50 ng/g in liver (both based on 1 g of fresh tissue). The corresponding values for BPA were approximately 50 ng/g in both muscle and liver tissue. In water, the limit of quantification for tOP and BPA was approximately 0.1 microg/l (based on 100 ml sample size).     

Capillary electrophoresis-mass spectrometry using an in-line sol-gel concentrator for the determination of methionine enkephalin in cerebrospinal fluid

In this study, a CE-MS method using a monolithic sol-gel concentrator for in-line solid-phase extraction (SPE) is evaluated for the analysis of methionine enkephalin in biological samples. Operational SPE parameters such as sample pH, loading volume, elution volume and composition have been studied. After optimization of the in-line preconcentration methodology, a 40-fold preconcentration was demonstrated for a methionine enkephalin test solution using a loading volume of 3200 nL. The method was linear in the range from 62.5 to 1000 ng/mL (R² > 0.99). R.S.D. values for migration times and peak areas were 1.2% and 8.4%, respectively. Finally, the analysis of cerebrospinal fluid samples spiked with methionine enkephalin and deproteinized with perchloric acid (1:1, v/v) showed a detection limit (S/N = 3) of approximately 1 ng/mL (ca. 5 nM). The recoveries of methionine enkephalin for three concentration levels (100, 10 and 1 ng/mL) were in the range of 74-91%, demonstrating the promising potential of the methodology for the analysis of biological samples.     

Single-step extraction and cleanup of bisphenol A in soft drinks by hemimicellar magnetic solid phase extraction prior to liquid chromatography/tandem mass spectrometry

Hemimicelles of tetradecanoate chemisorbed onto magnetic nanoparticles (MNPs) are here proposed as a sorbent for the single-step extraction and cleanup of bisphenol A (BPA) in soft drinks. The purpose of this work was to develop a simple, rapid and low-cost sample treatment suitable to assess the human exposure to BPA from this type of high consumption food. The nanoparticles were easily coated by mixing commercially available magnetite of 20–30 nm mean particle diameter with tetradecanoate at 85 °C for 30 min. The extraction/cleanup procedure involved stirring the samples (3 mL) with 200 mg of tetradecanoate-coated MNPs for 20 min, isolating the sorbent with a Nd–Fe–B magnet and eluting BPA with methanol. The extraction efficiency was not influenced by salt concentrations up to 1 M and pH values over the range 4–9. No cleanup of the extracts was needed, and the method proved matrix-independent. The extracts were analyzed by liquid chromatography, electrospray ionization tandem mass spectrometry. Quantitation was performed by internal standard calibration using BPA-¹³C₁₂. The limit of quantitation obtained for the method, 0.03 ng mL⁻¹, was below the usual range of concentrations reported for BPA in soft drinks (0.1–3.4 ng mL⁻¹). The proposed method was successfully applied to the determination of BPA in different samples acquired from various supermarkets in southern Spain; the concentrations found ranged from 0.066 to 1.08 ng mL⁻¹. Recoveries from samples spiked with 0.33 ng mL⁻¹ of BPA ranged from 91% to 105% with relative standard deviations from 3% to 8%.     

A systematic investigation to optimize simultaneous extraction and liquid chromatography tandem mass spectrometry analysis of estrogens and their conjugated metabolites in milk

In this study, the simultaneous extraction of estrone (E1), 17β-estradiol (E2), estriol (E3), ethinylestradiol (EE2), and their glucuronated and sulfated metabolites in milk was optimized using solid-phase extraction (SPE). The aim of this research was to analyze estrogens and their conjugated metabolites by liquid chromatography with tandem mass spectrometry (LC–MS/MS) in a single run, without the need to perform enzymatic cleavage and derivatization. Two SPE cartridges in tandem were used, consisting of sorbents based on the hydrophilic–lipophilic balance and amine-functionalized packing materials. To monitor analyte loss at every step of the SPE procedure ¹⁴C-labeled E2 was spiked into the milk sample and the radioactivity was monitored at all stages of the SPE. In addition, non-radiolabeled standards of estrogens and metabolites were used to optimize solvent systems for the SPE and LC–MS/MS. The optimized method described in this paper can achieve recoveries ranging from 72% to 117% for the free estrogens (E1, E2, E3, and EE2), and 62% to 112% for seven conjugated metabolites. The three doubly conjugated, highly polar metabolites included in this study gave lower recoveries (≤43%) due to poor retention in SPE. Finally, commercial milk samples were analyzed for the presence of estrogens and their conjugated metabolites. Estrone (concentration range: 23–67 ng/L) was found to be the major free estrogen present in all milk samples. Estradiol was consistently observed in milk, but the concentrations were below the limit of detection (LOD of 10 ng/L), and no estriol and ethinylestradiol were detected. Several conjugated estrogen metabolites were identified, 17β-estradiol-3-glucuronide (71–289 ng/L), estrone-3-sulfate (60–240 ng/L), 17β-estradiol-3,17β-sulfate (<LOD to 30 ng/L), and estrone-3-glucuronide (<LOQ of 25 ng/L). This method proved efficient in the simultaneous analysis of estrogens and their metabolites in milk.     

A novel superparamagnetic surface molecularly imprinted nanoparticle adopting dummy template: An efficient solid-phase extraction adsorbent for bisphenol A

Leakage of the residual template molecules is one of the biggest challenges for application of molecularly imprinted polymer (MIP) in solid-phase extraction (SPE). In this study, bisphenol F (BPF) was adopted as a dummy template to prepare MIP of bisphenol A (BPA) with a superparamagnetic core–shell nanoparticle as the supporter, aiming to avoid residual template leakage and to increase the efficiency of SPE. Characterization and test of the obtained products (called mag-DMIP beads) revealed that these novel nanoparticles not only had excellent magnetic property but also displayed high selectivity to the target molecule BPA. As mag-DMIP beads were adopted as the adsorbents of solid-phase extraction for detecting BPA in real water samples, the recoveries of spiked samples ranged from 84.7% to 93.8% with the limit of detection of 2.50 pg mL⁻¹, revealing that mag-DMIP beads were efficient SPE adsorbents.     

Rapid and sensitive liquid chromatography-tandem mass spectrometry for the quantitation of epirubicin and identification of metabolites in biological samples

A highly sensitive and selective liquid chromatography-mass spectrometry (LC-MS) method has been developed for the determination of epirubicin in serum and cell specimens using daunorubicin as an internal standard. Using atmospheric pressure chemical ionisation (APCI), the epirubicin metabolites were readily distinguishable by their fragmentation pattern in the mass spectrometer. Selected reaction monitoring (SRM) mode was employed for quantitation of epirubicin and the metabolites. Following extraction, chromatography was performed on a C18 column with a mobile phase consisting of water-acetonitrile-formic acid, pH 3.2, with a flow rate of 200 μl/min. The limit of detection (LOD) and the limit of quantitation (LOQ) of this method in serum were determined to be 1.0 and 2.5 ng/ml, respectively. Linearity of the method was verified over the concentration range of 2.5-2000 ng/ml, with a high correlation coefficient (R² ≥ 0.998). For the extraction procedure, an aliquot of 500 μl serum, spiked with internal standard, was extracted using a chloroform-2-isopropanol (2:1, v/v) mixture. The method has been applied to the analysis of epirubicin in cancer cell samples and the identification of known and unknown metabolites in clinical trial patient serum samples.     

Determination of fecal sterols by gas chromatography–mass spectrometry with solid-phase extraction and injection-port derivatization

Injection-port derivatization combined with solid-phase extraction (SPE) was developed and applied for the first time to determine five types of fecal sterols (coprostanol, cholestanol, epicholestanol, epicoprostanol and cholesterol) with gas chromatography–mass spectrometry (GC–MS). In this method, silylation of fecal sterols was performed with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) at GC injection-port. The factors influential to this technique such as injection-port temperature, purge-off time, derivatization reagent (BSTFA) volume, and the type of organic solvent were investigated. In addition, the conditions of SPE (including the type of SPE cartridge, the type of elution organic solvent) were also studied. After SPE followed by injection-port silylation by GC–MS, good linearity of analytes was achieved in the range of 0.02–10 ng/mL with coefficients of determination, R² > 0.995. Good reproducibility was obtained with relative standard deviation less than 19.6%. The limits of detection ranged from 1.3 ng/mL to 15 ng/mL (S/N = 3) in environmental water samples. Compared with traditional off-line silylation of fecal sterols performed with water bath (60 °C, 30 min), this injection-port silylation method is much simpler and convenient. The developed method has been successfully applied for the analysis of fecal sterols from real environmental water samples.     

Preparation of functionalized magnetic nanoparticulate sorbents for rapid extraction of biphenolic pollutants from environmental samples

A new solid-phase extraction coupled with magnetic carrier technology was developed for extraction of bisphenol A (BPA) and diethylstilbestrol (DES) from water samples. The SPE sorbents, functionalized magnetic nanoparticles (Fe₃O₄@SiO₂/β-CD, core/shell), were synthesized in a two-stage system. The material was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, and a vibrating sample magnetometer. SPE extraction parameters, such as volume and pH of sample, adsorption time, and desorption conditions were optimized. Under selected conditions: 250 mL of water sample, 0.1 g of sorbents and elution with methanol (3 mL with 1% acetic acid), the extraction was completed in 25 min. SPE followed by HPLC was employed to determine BPA and DES in environmental samples. The developed method provided spiked recoveries of 80–105%, relative standard deviations of less than 7%, and LOD of BPA (20.0 ng/L) and DES (23.0 ng/L), respectively. The proposed method offered easy preparation of sorbents, rapid analysis, high enrichment yields, and reliable quantitative assay.     

Determination of flunitrazepam and 7-aminoflunitrazepam in human urine by on-line solid phase extraction liquid chromatography-electrospray-tandem mass spectrometry

A method using an on-line solid phase extraction (SPE) and liquid chromatography with electrospray-tandem mass spectrometry (LC-ES-MS/MS) for the determination of flunitrazepam (FM2) and 7-aminoflunitrazepam (7-aminoFM2) in urine was developed. A mixed mode Oasis HLB SPE cartridge column was utilized for on-line extraction. A reversed phase C₁₈ LC column was employed for LC separation and MS/MS was used for detection. Sample extraction, clean-up and elution were performed automatically and controlled by a six-port valve. Recoveries ranging from 94.8 to 101.3% were measured. For both 7-aminoFM2 and FM2, dual linear ranges were determined from 20 to 200 and 200-2000 ng/ml, respectively. The detection limit for each analyte based on a signal-to-noise ratio of 3 ranged from 1 to 3 ng/ml. The intra-day and inter-day precision showed coefficients of variance (CV) ranging from 4.6 to 8.5 and 2.6-9.2%, respectively. The applicability of this newly developed method was examined by analyzing several urine samples.     

Determination of trace bisphenol A in complex samples using selective molecularly imprinted solid-phase extraction coupled with capillary electrophoresis

The highly selective, fast and effective sample pretreatment technique molecularly imprinted solid-phase extraction (MISPE) can overcome the low sensitivity of the highly efficient capillary electrophoresis-UV method (CE-UV). In this work, narrowly dispersible bisphenol A (BPA)-imprinted polymeric microspheres with a high capacity factor of k′ = 6.8 and an imprinted factor of I = 6.53 were investigated as selective solid-phase extraction (SPE) sorbents for use in extraction of BPA from different sample matrices (tap water, wastewater, Yangtze River water, soil from the Yangtze River, shrimp and human urine). Washing and eluting protocols of MISPE were optimized. Under optimal conditions, recoveries of MISPE were investigated. Recoveries were basically constant and the relative standard deviation (RSD) was lower than 5.8% when loading volumes changed from 1 to 50 mL. Recoveries ranged from 71.20% to 86.23% for different sample matrices. Compared with C18 SPE, MISPE had higher selectivity and recovery for BPA. BPA was determined with good accuracy and precision in different complex samples using CE-UV coupled with MISPE. Spiked recoveries ranged from 95.20% to 105.40%, and the RSD was less than 7.2%. Because a large loading volume was achieved, the enrichment efficiency of pretreatment and the sensitivity of this method were improved. The limits of detection of this MISPE-CE-UV method for BPA in tap water, wastewater, Yangtze River water, soil from the Yangtze River, shrimp and human urine were 3.0 μg L^− 1, 5.4 μg L^− 1, 6.9 μg L^− 1, 2.1 μg L^− 1, 1.8 μg L^− 1 and 84 μg L^− 1, respectively.     

Combination of solid phase extraction and in vial solid phase derivatization using a strong anion exchange disk for the determination of nerve agent markers

Alkylphosphonic acids (APAs) are degradation products and chemical markers of organophosphorous (OP) nerve agents (chemical warfare agents). Anion exchange disk-based solid phase extraction (SPE) has been combined with in vial solid phase derivatization (SPD) and GC–MS analysis for the determination of APAs in aqueous samples. The optimization of critical method parameters, such as the SPD reaction, was achieved using statistical experimental design and multivariate data analysis. The optimized method achieved quantitative recoveries in the range from 83% to 101% (n = 13, RSD from 4% to 10%). The method was sensitive, with LODs in SIM mode of 0.14 ppb, and demonstrated excellent linearity with an average R² ≥ 0.99 over the concentration range of 0.07–1.4 ppm in full scan mode and from 0.14 ppb to 14 ppb in SIM mode. For forensic applications, aqueous samples containing APAs at concentrations exceeding 14 ppb were concentrated and target analytes were successfully identified by spectral library and retention index matching. Method robustness was evaluated using aqueous samples from the official OPCW Proficiency Test (round 19) and all APAs present in the sample were conclusively identified. The SPE disk retained the underivatized APAs in a stable condition for extended periods of time. No significant losses of APAs from the disk were observed over a 36-day period. Overall, the method is well suited to the qualitative and quantitative analysis of degradation markers of OP nerve agents in aqueous matrices with simplicity, a low risk of cross-contamination and trace level sensitivity.     

Development of a new multi-residue laser diode thermal desorption atmospheric pressure chemical ionization tandem mass spectrometry method for the detection and quantification of pesticides and pharmaceuticals in wastewater samples

A new solid phase extraction (SPE) method coupled to a high throughput sample analysis technique was developed for the simultaneous determination of nine selected emerging contaminants in wastewater (atrazine, desethylatrazine, 17β-estradiol, ethynylestradiol, norethindrone, caffeine, carbamazepine, diclofenac and sulfamethoxazole). We specifically included pharmaceutical compounds from multiple therapeutic classes, as well as pesticides. Sample pre-concentration and clean-up was performed using a mixed-mode SPE cartridge (Strata ABW) having both cation and anion exchange properties, followed by analysis by laser diode thermal desorption atmospheric pressure chemical ionization coupled to tandem mass spectrometry (LDTD-APCI-MS/MS). The LDTD interface is a new high-throughput sample introduction method, which reduces total analysis time to less than 15 s per sample as compared to minutes with traditional liquid-chromatography coupled to tandem mass spectrometry (LC–MS/MS). Several SPE parameters were evaluated in order to optimize recovery efficiencies when extracting analytes from wastewater, such as the nature of the stationary phase, the loading flow rate, the extraction pH, the volume and composition of the washing solution and the initial sample volume. The method was successfully applied to real wastewater samples from the primary sedimentation tank of a municipal wastewater treatment plant. Recoveries of target compounds from wastewater ranged from 78% to 106%, the limit of detection ranged from 30 to 122 ng L⁻¹ while the limit of quantification ranged from 90 to 370 ng L⁻¹. Calibration curves in the wastewater matrix showed good linearity (R² ≥ 0.991) for all target analytes and the intraday and interday coefficient of variation was below 15%, reflecting a good precision.     

On-line solid phase extraction LC-MS/MS analysis of pharmaceutical indicators in water: A green alternative to conventional methods

A method using automated on-line solid phase extraction (SPE) directly coupled to liquid chromatography/tandem mass spectrometry (LC-MS/MS) has been developed for the analysis of six pharmaceuticals by isotope dilution. These selected pharmaceuticals were chosen as representative indicator compounds and were used to evaluate the performance of the on-line SPE method in four distinct water matrices. Method reporting limits (MRLs) ranged from 10 to 25 ng/L, based on a 1 mL extraction volume. Matrix spike recoveries ranged from 88 to 118% for all matrices investigated, including finished drinking water, surface water, wastewater effluent and septic tank influent. Precision tests were performed at 50 and 1000 ng/L with relative standard deviations (RSDs) between 1.3 and 5.7%. A variety of samples were also extracted using a traditional off-line automated SPE method for comparison. Results for both extraction methods were in good agreement; however, on-line SPE used approximately 98% less solvent and less time. On-line SPE coupled to LC-MS/MS analysis for selected indicators offers an alternative, more environmentally friendly, method for pharmaceutical analysis in water by saving time and costs while reducing hazardous waste and potential environmental pollution as compared with off-line SPE methods.     

Hollow fiber supported ionic liquid membrane microextraction for determination of sulfonamides in environmental water samples by high-performance liquid chromatography

By using ionic liquid as membrane liquid and tri-n-octylphosphine oxide (TOPO) as additive, hollow fiber supported liquid phase microextraction (HF-LPME) was developed for the determination of five sulfonamides in environmental water samples by high-performance liquid chromatography with ultraviolet detection The extraction solvent and the parameters affecting the extraction enrichment factor such as the type and amount of carrier, pH and volume ratio of donor phase and acceptor phase, extraction time, salt-out effect and matrix effect were optimized. Under the optimal extraction conditions (organic liquid membrane phase: [C₈MIM][PF₆] with 14% TOPO (w/v); donor phase: 4 mL, pH 4.5 KH₂PO₄ with 2 M Na₂SO₄; acceptor phase: 25 μL, pH 13 NaOH; extraction time: 8 h), low detection limits (0.1–0.4 μg/L, RSD ≤ 5%) and good linear range (1–2000 ng/mL, R² ≥ 0.999) were obtained for all the analytes. The presence of humic acid (0–25 mg/L dissolved organic carbon) and bovine serum albumin (0–100 μg/mL) had no significant effect on the extraction efficiency. Good spike recoveries over the range of 82.2–103.2% were obtained when applying the proposed method on five real environmental water samples. These results indicated that this present method was very sensitive and reliable with good repeatabilities and excellent clean-up in water samples. The proposed method confirmed hollow fiber supported ionic liquid membrane based LPME to be robust to monitoring trace levels of sulfadiazine, sulfamerazine, sulfamethazine, sulfadimethoxine and sulfamethoxazole in aqueous samples.     

High performance liquid chromatography–tandem mass spectrometry for the analysis of 10 pesticides in water: A comparison between membrane-assisted solvent extraction and solid phase extraction

This work describes the application of two sample preparation methods: membrane-assisted solvent extraction (MASE) and solid phase extraction (SPE) in combination with high performance liquid chromatography–tandem mass spectrometry (HPLC–MS–MS) for the determination of 10 pesticides in surface and ground water. Optimal extraction conditions for MASE were 60 min extraction time at 30 °C with a solvent volume of 100 μL toluene. 5 μL of the toluene extract were directly injected in the HPLC–MS–MS system. Concerning SPE, two materials were tested and C18 was superior to Oasis HLB. Complete desorption was ensured by desorbing the SPE (C18) cartridge with 3 mL of an acetonitrile/methanol mixture (1:1). After evaporation, the extract was injected in the analytical system. Analyte breakthrough was not found for the investigated compounds. For both methods, high extraction yields were achieved, in detail 71% (metalaxyl) till 105% (linuron) for MASE and 52% (ethiofencarb) till 77% (prometryne) for SPE (C18). Detection limits were in the low ng/L range for both methods and precision, expressed as the relative standard deviation (RSD) of the peak areas was below 13%. Five real water samples were analyzed applying both extraction methods. The results were in good agreement and standard addition proved that no matrix effects (such as ion suppression) occurred. In this comparison SPE has the potential of larger sensitivity whereas faster analysis and slightly better recoveries were achieved with MASE. MASE shows potential to be a promising alternative to the conventional off-line SPE concerning low to medium polar compounds.     

A novel sol-gel-material prepared by a surface imprinting technique for the selective solid-phase extraction of bisphenol A

A novel and simple imprinted amino-functionalized silica gel material was synthesized by combining a surface molecular imprinting technique with a sol-gel process on the supporter of activated silica gel for solid-phase extraction-high performance liquid chromatography (SPE-HPLC) determination of bisphenol A (BPA). Non-imprinted silica sorbent was synthesized without the addition of BPA using the same procedure as that of BPA-imprinted silica sorbent. The BPA-imprinted silica sorbent and non-imprinted silica sorbent were characterized by FT-IR and the static adsorption experiments. The prepared BPA-imprinted silica sorbent showed high adsorption capacity, significant selectivity and good site accessibility for BPA. The maximum static adsorption capacity of the BPA-imprinted and non-imprinted silica sorbent for BPA was 68.9 and 34.0 mg g⁻¹, respectively. The relatively selective factor value of this BPA-imprinted silica sorbent was 4.5. Furthermore, the difference of the retention characteristics of BPA on the C₈ SPE column and BPA-imprinted silica SPE (MIP-SPE) was compared. The MIP-SPE-HPLC method showed higher selectivity to BPA than the traditional SPE-HPLC method. At last, the BPA-imprinted polymers were used as the sorbent in solid-phase extraction to determine BPA in water samples with satisfactory recovery higher than 99% (R.S.D. 3.7%).