Stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry for the measurement of 4-nonylphenol and 4-tert-octylphenol in human biological samples

Stir bar sorptive extraction for trace analysis

Stir bar sorptive extraction (SBSE) was introduced in 1999 as a solventless sample preparation method for the extraction and enrichment of organic compounds from aqueous matrices. The method is based on sorptive extraction, whereby the solutes are extracted into a polymer coating on a magnetic stirring rod. The extraction is controlled by the partitioning coefficient of the solutes between the polymer coating and the sample matrix and by the phase ratio between the polymer coating and the sample volume. For a polydimethylsiloxane coating and aqueous samples, this partitioning coefficient resembles the octanol-water partitioning coefficient. In comparison to solid phase micro-extraction, a larger amount of sorptive extraction phase is used and consequently extremely high sensitivities can be obtained as illustrated by several successful applications in trace analysis in environmental, food and biomedical fields. Initially SBSE was mostly used for the extraction of compounds from aqueous matrices. The technique has also been applied in headspace mode for liquid and solid samples and in passive air sampling mode. In this review article, the principles of stir bar sorptive extraction are described and an overview of SBSE applications is given.

Development of stable isotope dilution quantification liquid chromatography-mass spectrometry method for estimation of exposure levels of bisphenol A, 4-tert-octylphenol, 4-nonylphenol, tetrabromobisphenol A, and pentachlorophenol in indoor air

The potential risks to human health and reproduction of phenolic xenoestrogens, such as bisphenol A (BPA), 4-tert-octylphenol (OP), 4-nonylphenol (NP), tetrabromobisphenol A (TBBPA), and pentachlorophenol (PCP), have not been fully elucidated. It is possible that healthy humans are exposed to phenolic xenoestrogens in their daily lives. It is also possible that the source of human exposure to trace amounts of phenolic xenoestrogens is indoor air. Therefore, we have established an accurate, sensitive, and selective method for determining BPA, OP, NP, TBBPA, and PCP in air samples by using stable isotope dilution techniques using 13C12-BPA, 4-(1-methyl) octylphenol-d5 (m-OP-d5), 13C12-TBBPA, 13C6-PCP, and liquid chromatography-mass spectrometry (LC-MS). Air sampling (71/min, 24 hours), using glass filters (GB-100R, 47 mm) and Empore SDB-XD filters (47 mm/0.5 mm, 3M, Tokyo, Japan) and subsequent extraction by washing were carried out. Then the extracted sample solution was subjected to LC-MS. The percentage recovery of these analytes ranged from 87.0% to 101.9% (SD 0.2% to 4.6%, n=3) with correction using the stable isotope dilution quantification method. The quantification limit (signal-to-noise ratio, S/N>10) in the air samples was 0.1 ng/m3. Our findings suggest that the LC-MS method can detect low levels of phenolic xenoestrogens in air samples and that these trace levels of analytes exist in indoor air.

Estrogen-Like Response to p-Nonylphenol in Human First Trimester Placenta and BeWo Choriocarcinoma Cells

p-Nonylphenol (p-NP) is a metabolite of alkylphenol ethoxylates used as surfactants in the manufacturing industry. Although it is reported to have estrogenic activity and to be transferred from the mother to the embryo, no data are available on its effects on the development of the human placenta. In the present study, we investigated estrogen receptors' (ERs) expression in the first trimester human placenta. Using an in vitro model of chorionic villous explants, we then compared the effects of p-NP and 17beta-estradiol (17beta-E2). Finally, a trophoblast-derived choriocarcinoma cell line, BeWo, was used as a model of trophoblast cell differentiation. Our results showed that the first trimester placenta expresses three ER-alpha isoforms of 67, 46, and 39 kDa and one ER-beta isoform of 55 kDa. Immunohistochemistry revealed the expression of ER-alpha in the villous cytotrophoblast, whereas ER-beta was mainly expressed by the syncytiotrophoblast. Treatment of explant cultures with p-NP (10(-9)M) and 17beta-E2 (10(-9)M) significantly increased beta-hCG secretion and cell apoptosis but did not modify ER expression. After 72 h of exposure, hormone release was significantly higher in p-NP- than 17beta-E2-treated explant cultures. By this time, cleavage of caspase-3 was evident in cultures treated with 17beta-E2 and p-NP. In BeWo cells, a caspase-3 band of 20-16 kDa was evident after 1 h of treatment with p-NP and after 24 h of treatment with 17beta-E2 or forskolin. These findings suggest that the human trophoblast may be highly responsive to p-NP and raise concern about maternal exposure in early gestation.

Dual derivatization–stir bar sorptive extraction–thermal desorption–gas chromatography–mass spectrometry for determination of 17β-estradiol in water sample

A novel method for the trace analysis of 17beta-estradiol (E2) in river water sample was developed, which involved stir bar sorptive extraction (SBSE) with in situ acylation (first derivatization) and thermal desorption (TD) with quartz wool assisted (QWA) in tube silylation (second derivatization), followed by gas chromatography-mass spectrometry (GC-MS), and is called the "dual derivatization method." The optimum conditions for SBSE with in situ acylation, such as the volume of acetic acid anhydride and the extraction time, were investigated. In addition, the optimum conditions for TD with QWA in tube silylation, such as the volume of N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and the TD temperature and hold time, were investigated as well. The detection limit (S/N = 3) and the quantitation limit (S/N>10) of E2 in the river water sample were 0.5 and 2 pg ml(-1) (ppt), respectively, by the dual derivatization method. In addition, the detection limit was 0.1 pg ml(-1) by using dual derivatization method with multi-shot mode. The calibration curve for E2 was linear in the range of 0.002-10 ng ml(-1) with correlation coefficients >0.999. The average recoveries of E2 (n = 6) at the concentrations of 0.05 and 1.0 ng ml(-1) from the river water sample were 93.1 (RSD: 1.4%) and 98.4% (RSD: 0.8%), respectively, with correction using the added surrogate standard, 17beta-estradiol-(13)C(4). This simple, accurate, sensitive and selective analytical method may be applicable to the determination of trace amounts of E2 in water samples.

Novel stir bar sorptive extraction methods for environmental and biomedical analysis

Stir bar sorptive extraction (SBSE) is sample preparation technique that involves the extraction and enrichment of organic compounds from a liquid sample. The technique is based on the principle of sorptive extraction. A large amount of extraction phase is coated on a stir bar. An analyte is extracted into the extraction phase, based on its octanol-water partitioning coefficient and the phase ratio. Recently, various methods involving SBSE were developed in order to further facilitate analysis and improve sensitivity. In this review, we focused on the novel methods that involve SBSE with in situ derivatization, SBSE with in situ de-conjugation, thermal desorption (TD) in the multi-shot mode and TD with in tube derivatization method. Those methods were applied successfully to the trace analysis of environmental and biological samples and extremely low detection limits were achieved.

Stir bar sorptive extraction with in situ de-conjugation and thermal desorption gas chromatography-mass spectrometry for measurement of 4-nonylphenol glucuronide in human urine sample

4-Nonylphenol glucuronide (NP-G) in human urine samples was analyzed using stir bar sorptive extraction (SBSE) with in situ de-conjugation by beta-glucuronidase and thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS). Distilled water (1 ml), 1.0 M ammonium acetate solution (100 microl) and beta-glucuronidase (10,000 units ml(-1), 10 microl) were added to human urine sample (1 ml), and extraction was commenced for 90 min at 37 degrees C while stirring at 250 rpm with a stir bar coated with a 500-microm-thick polydimethylsiloxane (PDMS) layer. Then, the stir bar was subjected to TD-GC-MS in the selected ion monitoring (SIM) mode. The calibration curve was made by SBSE method using 4-nonylphenol (NP) as the standard solution. The method showed good linearity and the correlation coefficients were 0.999 over the concentration range of 5-500 nM. Moreover, to optimize the conditions for SBSE with in situ de-conjugation and the recovery test, NP-G was synthesized by a biochemical technique in our laboratory. The limits of detection (S/N = 3) and quantitation (S/N > 10) for NP were 0.2 ng ml(-1) (1.0 nM) and 1.1 ng ml(-1) (5.0 nM), respectively. The average recoveries in the human urine samples (n = 6) spiked with NP-G at levels of 20 and 100 nM were 104.1 (R.S.D. 7.1%) and 100.6% (R.S.D. 9.2%), respectively, with correction using the added internal standard, 4-(1-methyl) octylphenol-d(5). The method enabled the precise determination of the standard and was applicable to the detection of trace amounts of NP-G in human urine samples.

Stir bar sorptive extraction with in situ derivatization and thermal desorption-gas chromatography–mass spectrometry for measurement of phenolic xenoestrogens in human urine samples

A high-sensitivity analytical method that uses stir bar sorptive extraction (SBSE) with in situ derivatization and thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS) for the simultaneous measurement of trace amounts of phenolic xenoestrogens (PXs), such as 2,4-dichlorophenol (DCP), 4-tert-butylphenol (BP), 4-tert-octylphenol (OP), 4-nonylphenol technical isomers (NP), pentachlorophenol (PCP) and bisphenol A (BPA), in human urine samples was developed. The urine sample (1 ml) was de-conjugated by adding beta-glucuronidase and sulfatase. Then, protein precipitation was performed by the addition of acetonitrile. After centrifugation, the supernatant was diluted with purified water and subjected to SBSE with in situ derivatization and TD-GC-MS. The detection limits of DCP, BP, OP, NP, PCP and BPA in the urine samples were 20, 10, 10, 50, 20 and 20 pg ml-1 (ppt), respectively. The calibration curves for PXs were linear and had correlation coefficients higher than 0.99. The average recoveries of those analytes in the urine samples were higher than 95% (RSD: <10%, n=6) with correction using the added surrogate standards. This simple, accurate, sensitive and selective method can be used in the determination of PXs in human urine samples.

Stir bar sorptive extraction based on restricted access material for the direct extraction of caffeine and metabolites in biological fluids

A biocompatible stir bar sorptive extraction (SBSE) device was prepared using an alkyl-diol-silica (ADS) restricted access material (RAM) as the SBSE coating. The RAM-SBSE bar was able to simultaneously fractionate the protein component from a biological sample, while directly extracting caffeine and its metabolites, overcoming the present disadvantages of direct sampling in biological matrices by SBSE, such as fouling of the extraction coating by proteins. Desorption of the analytes was performed by stirring the bar in a water/ACN mixture (3/1, v/v) and subsequently reconcentrating the sample solution in water to enable HPLC-UV analysis to be performed. The limit of detection, based on a signal to noise ratio of 3, for caffeine was 25 ng/mL in plasma. The method was confirmed to be linear over the range of 0.5-100 microg/mL of caffeine with an average linear coefficient (R2) value of 0.9981. The injection repeatability and intra-assay precision of the method were evaluated over ten injections, resulting in a %RSD of approximately 8%. The RAM-SBSE device was robust (>50 extraction in plasma without significant signal loss) and simple to use, providing many direct extractions and subsequent determination of caffeine and its metabolites in biological fluids. In contrast to existing sample preparation methods for the analysis of caffeine and selected metabolites in biological fluids, this feasibility study using a biocompatible SBSE approach was advantageous in terms of simplifying the sample preparation procedures.

Urinary concentrations of bisphenol A and 4-nonylphenol in a human reference population

Bisphenol A (BPA) is used to manufacture polycarbonate plastic and epoxy resins, which are used in baby bottles, as protective coatings on food containers, and for composites and sealants in dentistry. 4-Nonylphenol (NP) is used to make nonylphenol ethoxylates, nonionic surfactants applied as emulsifying, wetting, dispersing, or stabilizing agents in industrial, agricultural, and domestic consumer products. The potential for human exposure to BPA and NP is high because of their widespread use. We measured BPA and NP in archived urine samples from a reference population of 394 adults in the United States using isotope-dilution gas chromatography/mass spectrometry. The concentration ranges of BPA and NP were similar to those observed in other human populations. BPA was detected in 95% of the samples examined at concentrations > or = 0.1 microg/L urine; the geometric mean and median concentrations were 1.33 microg/L (1.36 microg/g creatinine) and 1.28 microg/L (1.32 microg/g creatinine), respectively; the 95th percentile concentration was 5.18 microg/L (7.95 microg/g creatinine). NP was detected in 51% of the samples examined > or = 0.1 microg/L. The median and 95th percentile concentrations were < 0.1 microg/L and 1.57 microg/L (1.39 microg/g creatinine), respectively. The frequent detection of BPA suggests widespread exposure to this compound in residents of the United States. The lower frequency of detection of NP than of BPA could be explained by a lower exposure of humans to NP, by different pharmacokinetic factors (i.e., absorption, distribution, metabolism, elimination), by the fact that 4-n-nonylphenol--the measured NP isomer--represents a small percentage of the NP used in commercial mixtures, or a combination of all of the above. Additional research is needed to determine the best urinary biomarker(s) to assess exposure to NP. Despite the sample population's nonrepresentativeness of the U.S. population (although sample weights were used to improve the extent to which the results represent the U.S. population) and relatively small size, this study provides the first reference range of human internal dose levels of BPA and NP in a demographically diverse human population.

Stir bar sorptive extraction and trace analysis of alkylphenols in water samples by thermal desorption with in tube silylation and gas chromatography–mass spectrometry

A novel method called thermal desorption (TD) with in tube silylation followed by gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of alkylphenols (APs) in river water samples, is described. APs are extracted from river water samples and concentrated by the stir bar sorptive extraction (SBSE) technique. The stir bar coated with polydimethylsiloxane (PDMS) is added to 2.0 ml water sample and stirring is carried out for 60 min at room temperature (25 degrees C) in the vial. Then, the PDMS stir bar is subjected to TD with in tube silylation followed by GC-MS. The detection limit is of the sub pg ml(-1) (ppt) level. The method shows good linearity and the correlation coefficients are higher than 0.99 for all analytes. The average recoveries of APs are higher than 90% (R.S.D.: 3.6-14.8%, n=6). This simple and sensitive analytical method may be used in the determination of trace amounts of APs in river water samples.

Preconcentration technique for nonylphenol using cellulose cotton with homogenous liquid?liquid extraction for liquid chromatographic analysis

A powerful preconcentration method for nonylphenol (NP) has been developed for liquid-chromatography by combining the use of cellulose cotton (solid-phase extraction) with homogeneous liquid-liquid extraction. A 100 ml of sample solution was preconcentrated using cotton, and the eluate obtained (acetonitrile; 5 ml) was further preconcentrated to 50 microl within 10 min using a homogeneous liquid-liquid extraction method (volume ratio, 2,000-fold; 100 ml--> 50 microl). The sample concentration increases from preconcentration was 1,599-fold, and NP was extracted into the sedimented phase at 80%. The proposed method was applied to high performance liquid chromatography with fluorescence detection (FL/HPLC); the lowest determination limit obtained was 1.0 x 10(-9) mol l(-1).

Trace analysis of phenolic xenoestrogens in water samples by stir bar sorptive extraction with in situ derivatization and thermal desorption–gas chromatography–mass spectrometry

A method for the simultaneous measurement of trace amounts of phenolic xenoestrogens, such as 2,4-dichlorophenol (2,4-DCP), 4-tert-butyl-phenol (BP), 4-tert-octylphenol (OP), 4-nonylphenol (NP), pentachlorophenol (PCP) and bisphenol A (BPA), in water samples was developed using stir bar sorptive extraction (SBSE) with in situ derivatization followed by thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS) analysis. The conditions for derivatization with acetic acid anhydride were investigated. A polydimethylsiloxane (PDMS)-coated stir bar and derivatization reagents were added to 10 ml of water sample and stirring was commenced for 10-180 min at room temperature (25 degrees C) in a headspace vial. Then, the extract was analyzed by TD-GC-MS. The optimum time for SBSE with in situ derivatization was 90 min. The detection limits of 2,4-DCP, BP, OP, NP, PCP and BPA were 2, 1, 0.5, 5, 2 and 2 pg ml(-1), respectively. The method showed good linearity over the concentration ranges of 10, 5, 2, 20, 10 and 10-1000 pg ml(-1) for 2,4-DCP, BP, OP, NP, PCP and BPA, respectively, and the correlation coefficients were higher than 0.99. The average recoveries of those compounds in river water samples were equal to or higher than 93.9% (R.S.D. <7.2%) with correction using the added surrogate standards. This simple, accurate, sensitive and selective method can be used in the determination of trace amounts of phenolic xenoestrogens in river water samples.

Simultaneous determination of alkylphenols and bisphenol A in river water by stir bar sorptive extraction with in situ acetylation and thermal desorption–gas chromatography–mass spectrometry

A method for the determination of seven alkylphenols and bisphenol A by stir bar sorptive extraction (SBSE) with in situ derivatization-thermal desorption (TD)-gas chromatography (GC)-mass spectrometry (MS) is described. SBSE was performed with in situ acetylation and without derivatization for comparison. For 4-tert-butylphenol and bisphenol A, in situ acetylation improved the responses in SBSE-TD-GC-MS. The method detection limits ranged from 0.1 to 3.2 ng/l. The recoveries of the analytes from a river water sample spiked with standards at 10 and 100 ng/l were 85.3-105.9% (R.S.D., 3.0-11.0%) and 88.3-105.8% (R.S.D., 1.6-8.3%), respectively.