Derivatisation and gas chromatography-chemical ionisation mass spectrometry of selected synthetic and natural endocrine disruptive chemicals

Derivatization gas chromatography negative chemical ionization mass spectrometry for the analysis of trace organic pollutants and their metabolites in human biological samples

Gas chromatography negative chemical ionization mass spectrometry (GC-NCI-MS) is a preferred instrumental approach for the trace and ultra-trace analysis of various toxic organics and their metabolites in human biological fluids. Specifically, the method has played an important role in the highly sensitive and specific quantitative detection of persistent highly halogenated compounds in environmental matrices and biota during the past few decades. However, for the analysis of toxic metabolites with active hydrogen atoms, such as acids, alcohols, and phenolic compounds, from biological matrixes or organics without electronegative atoms or groups, a derivatization step is often needed prior to GC analysis. Such derivatization aims to change the properties of targets to improve their separation, increase their volatility, and enhance the sensitivity of instrumental detection. This review summarizes three derivatization strategies commonly used for GC methods, i.e., alkylation, silylation, and acylation, together with their application combined with GC-NCI-MS for the high sensitivity analysis of toxic organic metabolites in the human body. The advantages and disadvantages of each derivatization method and potential directions for future applications are discussed. Given the broad variety of applications as well as the compound-specific sensitivity for the ultra-trace analysis of target xenobiotics in human biological fluids, subsequent studies are required to develop convenient, faster derivatization procedures and reagents better suited for routine analysis. Graphical abstract.

The impact of variations of influent loading on the efficacy of an advanced tertiary sewage treatment plant to remove endocrine disrupting chemicals

The impact of changes in influent load on the removal of endocrine disrupting chemicals (EDCs) by sewage treatment has not been fully characterised. This study assessed the efficacy of an advanced tertiary sewage treatment plant (STP) to remove EDCs during normal and peak flow events of sewage influent using trace chemical analysis of selected EDCs and four estrogenic in vitro bioassays. During the summer holiday season, influent volume increased by 68%, nutrient concentrations by at least 26% and hydraulic retention time was reduced by 40% compared with base flow conditions. Despite these pressures on the treatment system the concentrations and mass loading of estrone, 17β-estradiol, estriol, Bisphenol A, 4-t-octylphenol and technical nonylphenol were not significantly higher (p>0.05) during the peak flow conditions compared with base flow conditions. Chemical analysis and in vitro bioassays showed that the efficacy of the STP in removing EDCs was not affected by the different loadings between baseline and peak flow regimes. This study demonstrates that large flow variations within the design capacity of advanced multi-stage STPs should not reduce the removal efficacy of EDCs.

Evaluation of four mathematical models to describe dissipation kinetics of 4-n-nonylphenol and bisphenol-A in groundwater-aquifer material slurry

The performance of four mathematical models (hockey stick, biexponential, first-order double exponential decay, and first-order two-compartment) was evaluated to describe the dissipation kinetics for 4-n-nonylphenol (4-n-NP) and bisphenol-A (BPA) in groundwater-aquifer material slurry under aerobic and anaerobic conditions conducted under controlled laboratory conditions. The fit of each model to the measured values under both conditions was tested using an array of statistical indices to judge the model's ability to fit the measured datasets. Corresponding 50% (DT(50)) and 90% (DT(90)) dissipation values for each compound were numerically obtained and compared against each model. The model derived DT(50) values in groundwater-aquifer material ranged from 1.06 to 1.24 (4-n-NP) and 0.341 to 0.568 days (BPA) under aerobic condition, while they were 2- to 4-fold higher under anoxic condition. DT(90) values for 4-n-NP ranged anywhere between 2.3 and 4.45 days under both conditions, while DT(90) values for BPA ranged from around 1 day to as high as 12 days under both conditions tested. A visual examination of the measured and fitted plots as well as the statistical indices showed that, with the exception of the hockey stick model, the models performed satisfactorily. Despite having only 3 parameters, the biexponential model could describe the dissipation kinetics very well and this was supported by the statistical indices generated for each case.

Recent advances in mass spectrometry analysis of phenolic endocrine disruptors and related compounds

This article reviews recent literature on current methodologies based on chromatography coupled to mass spectrometry to analyze phenolic compounds with endocrine-disrupting capabilities. For this review we chose alkylphenol ethoxylates, bisphenol A, bisphenol F, and their degradation products and halogenated derivatives, which are considered important environmental contaminants. Additionally, some related compounds such as bisphenol diglycidylethers were included. Growing attention has been paid to the mass spectrometric characterization of these compounds and the instrumentation and strategies used for their quantification and confirmation. The current use of gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) methodologies with different mass spectrometers and ionization and monitoring modes is discussed. Practical aspects with regards to the use of these analytical techniques, such as derivatizing reagents in GC-MS, ion suppression in LC-MS, and the most problematic aspects of quantification, are included in the discussion.

Steroid estrogens, conjugated estrogens and estrogenic activity in farm dairy shed effluents

Agricultural wastes are a source of steroid estrogens and, if present, conjugated estrogens may add to the estrogen load released to soil and aquatic environments. Dairy shed effluent samples were collected from 18 farms for analysis of steroid estrogens by GC-MS, conjugated estrogens by LC-MS-MS, and estrogenic activity by E-screen in vitro bioassay. 17alpha-estradiol was found at highest concentrations (median 730 ng l(-1)), followed by estrone (100 ng l(-1)) and 17beta-estradiol (24 ng l(-1)). Conjugated estrogens (estrone-3-sulfate, 17alpha-estradiol-3-sulfate and 17beta-estradiol-3,17-disulfate) were measured in most samples (12-320 ng l(-1)). Median estrogenic activity was 46 ng l(-1) 17beta-estradiol equivalents. Conjugated estrogens contributed up to 22% of the total estrogen load from dairy farming, demonstrating their significance. Steroid estrogens dominated overall estrogenic activity measured in the samples. Significantly, 17alpha-estradiol contributed 25% of overall activity, despite potency 2% that of 17beta-estradiol, highlighting the importance in environmental risk assessments of this previously neglected compound.

Analysis for estrogens as environmental pollutants--a review

The approaches to the analysis for estrogen compounds as environmental pollutants are critically reviewed and evaluated on the basis of significant, recent original publications. The importance of sample pretreatment and analyte preconcentration techniques is pointed out, with an emphasis on SPE and on the use of highly selective interactions such as molecular recognition. The hyphenated systems of high-performance gas or liquid chromatography and mass spectrometric techniques are discussed as the basic methods of determination of estrogens in environmental samples. Immunochemical procedures are shown to be useful in semiquantitative screening of estrogen pollutants (e.g. ELISA kits). Classical HPLC and GC with common UV/Vis, fluorescence and electrochemical detection are useful in routine checking on higher pollutant concentrations.

Analysis of steroid hormones in a typical dairy waste disposal system

The environmental loading of steroid hormones contained in dairy wastes may cause an adverse effect on aquatic species. To better assess the potential risks of hormone contamination resulting from land application of dairy wastes, various steroid hormones were determined in a typical dairy waste disposal system. Quantitative methods using gas chromatography/mass spectrometry (GC/MS) were developed to monitor low levels of steroid hormones in complex solid and liquid samples contaminated with dairy manure. The preparation method for wastewater analysis consisted of solid-phase extraction and purification steps, which minimized interference from the sample matrices and achieved low detection limits for the studied hormones. In the dairy wastewater and lagoon water, three endogenous hormones-17alpha-estradiol, 17beta-estradiol, and estrone-were detected. The concentration of 17alpha-estradiol in fresh milk parlor effluent rapidly decreased along the wastewater disposal route, whereas the concentration of estrone increased along this same pathway. This suggests that 17alpha-estradiol was readily oxidized to the metabolite estrone. Levels of total steroid hormones in the sequencing lagoon water were approximately 1-3 orders of magnitude lower than those in the fresh dairy wastewaters, indicating significant removal of these hormones during the transport of dairy wastewater from source to field. In solid dairy waste samples, four steroid hormones were identified and quantified. Increasing the piling time of solid wastes and increasing the residence time of wastewater in sequencing lagoons are suggested to be economical and efficient agriculture practices to extend the degradation time of hormone contaminants and thereby reduce the hormone load to the environment.

Porcine follicular fluids: Comparison of solid-phase extraction and matrix solid-phase dispersion for the GC–MS determination of hormones during follicular growth

The capabilities of solid-phase extraction (SPE) and matrix solid-phase dispersion (MSPD) for the determination of the hormones 17beta-estradiol, 2-hydroxyestradiol, 4-hydroxyestradiol and 2-methoxyestradiol by gas chromatography-mass spectrometry (GC-MS) in a very complex matrix like porcine follicular fluids were compared, thus proving the highest effectiveness of the SPE technique. Validation was carried out in terms of limit of quantitation (LOQ), precision, accuracy, recovery and stability. LOQ values in the low microg kg(-1) were achieved, with all the other parameters satisfying the acceptance criteria for the validation of bioanalytical methods. The applicability of the method to the determination of the hormones in porcine follicular fluids was demonstrated, thus allowing to observe an increase of the concentration of the hormones during the follicular growth.

Quantitative determination of wine polyfunctional mercaptans at nanogram per liter level by gas chromatography–negative ion mass spectrometric analysis of their pentafluorobenzyl derivatives

A fast method for the determination of aroma-powerful polyfunctional thiols at nanogram per liter level has been developed and applied to wine. A small volume of wine (6 mL) was extracted with 1.5 mL of benzene containing four internal standards. Pentafluorobenzyl derivatives of mercaptans were formed in the extract by adding small amounts (100 mg L(-1)) of pentafluorobenzyl bromide and a strong alkali: 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). After washing with a water:methanol (5:1) solution 0.5M in HCl, 20 microL of the extract was directly injected into a gas chromatograph. Derivatives were detected by negative ion mass spectrometry. The method makes it possible to simultaneously determine 2-furfurylthiol (2-furanmethanethiol) (FFT), 4-mercapto-4-methyl-2-pentanone (MP), 3-mercaptohexylacetate (MHA) and 3-mercaptohexanol (MH). Inconsistent results were obtained for 2-methyl-3-furanthiol (MF). Detection limits were 0.5 ng L(-1) (FFT), 0.1 ng L(-1) (MP), 0.6 ng L(-1) (MHA) and 7 ng L(-1) (MH), well below the corresponding odor detection thresholds. Method repeatability (10%<RSD<17%) and linearity (0.98<R(2)<0.999) were satisfactory. The linear range was more than 2 orders of magnitude wide, covering the natural range of occurrence of these compounds in wine, and the slopes of the standard addition plots from different wines were very similar. The different aspects of the method optimization are discussed.

Optimizing gas chromatographic–mass spectrometric analysis of selected pharmaceuticals and endocrine-disrupting substances in water using factorial experimental design

An analytical method based on gas chromatography-mass spectrometry (GC-MS) has been developed to simultaneously determine selected acidic and neutral pharmaceuticals and endocrine-disrupting substances in surface and tap water. Solid-phase extraction (SPE) with Oasis HLB cartridges is followed by derivatization of the target analytes in the eluted extract. Derivatization was systematically optimized by employing a factorial experimental design. More specifically a central composite design was applied to search for the optimal conditions of the derivatization process and it was demonstrated that N-methyl-N-tert-butyl-dimethysilyl-trifluoroacetamide (MTBSTFA) had a better overall performance compared to N,O-bis(trimethylsilyl) trifluoroacetamide (BSTFA). The influence of solvent ratios and elution volumes while using SPE were also studied using a factorial design. The method was developed successfully for most of the selected compounds [i.e. ibuprofen, salicylic acid, gemfibrozil, naproxen, triclosan, propranolol, diclofenac, carbamazepine, 4-octylphenol (OP), 4-nonylphenol (NP), nonylphenol-monoethoxylate (NP1EO), nonylphenoxyacetic acid (NP1EC), estrone (E1), and 17alpha-ethinyloestradiol (EE2)]. Relative recoveries for spiked river and tap water ranged from 47 to 130% and 60-109%, respectively. Typical limits of detection were less than 5 ng/L in tap water and less than 10 ng/L in river water. Twelve target compounds were detected in river and tap water samples using the developed method. This method is currently used in bench-scale drinking water treatment studies.

Automated on-line column-switching HPLC-MS/MS method with peak focusing for the determination of nine environmental phenols in urine

We developed a method using isotope dilution on-line solid-phase extraction (SPE) coupled to high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) for the determination in urine of nine environmental phenolic compounds: Bisphenol A; 4-tert-octylphenol; o-phenylphenol; 2,4-dichlorophenol; 2,5-dichlorophenol; 2,4,5-trichlorophenol; 2,4,6-trichlorophenol; benzophenone-3 (2-hydroxy-4-metoxybenzophenone); and triclosan (2,4,4'-trichloro-2'-hydroxyphenyl ether). A unique fully automated column-switching system, constructed using 1 autosampler, 2 HPLC pumps, and a 10-port switching valve, was designed to allow for concurrent SPE-HPLC operation with peak focusing. The phenols present in 100 microL of urine were retained and concentrated on a C18 reversed-phase size-exclusion SPE column. Then, the phenols were "back-eluted" from the SPE column and diluted through a mixing Tee before being separated from other urine matrix components using a pair of monolithic HPLC columns. The phenols were detected by negative ion-atmospheric pressure chemical ionization-MS/MS. The efficient preconcentration of the phenols by the SPE column, analyte peak focusing by the dilution, and minimal ion suppression in the LC/MS interface by the buffer-free mobile phases resulted in limits of detection as low as 0.1-0.4 ng/mL for most analytes. The method was validated on spiked pooled urine samples and on urine samples from 30 adults with no known occupational exposure to environmental phenols. The method can be used for quick and accurate analysis of large numbers of samples in epidemiologic studies for assessing the prevalence of human exposure to environmental phenols.

Determination of UV filters and antimicrobial agents in environmental water samples

Although there is increasing concern about residues from personal care products entering the aquatic environment and their potential to accumulate to levels that pose a health threat to humans and wildlife, we still know little about the extent and magnitude of their presence in the aquatic environment. In this study we describe a procedure for isolation, and subsequent determination, of compounds commonly added to personal care products. The compounds of interest include UV filters with the commercial name Eusolex (homosalate, 4-methylbenzylidenecamphor, benzophenone-3, octocrylene, butylmethoxydibenzoylmethane, ethylhexyl methoxycinnamate) and two common anti-microbial agents, clorophene and triclosan. Water samples were filtered, acidified, and extracted by use of solid-phase extraction. Extracted compounds were then derivatised before analysis by gas chromatography-mass spectroscopy. By use of our method we obtained limits of detection of 13-266 ng L(-1) for UV filters, and 10-186 ng L(-1) for triclosan and clorophene. Recoveries were 82-98% for deionised water and 50-98% for natural water (seawater, pool water, lake water, and river water). Samples collected in Slovenia included seventeen recreational waters (seawater, pool water, lake water, and river water; August 2004) and four wastewaters (January 2005). The most abundant UV filter was benzophenone-3 (11-400 ng L(-1)). Of the two anti-microbial agents studied, trace amounts, only, of triclosan were present in the river Kolpa (68 ng L(-1)) and in an hospital effluent (122 ng L(-1)).

Quantification of urinary conjugates of bisphenol A, 2,5-dichlorophenol, and 2-hydroxy-4-methoxybenzophenone in humans by online solid phase extraction-high performance liquid chromatography-tandem mass spectrometry

Urinary concentrations of phenols or their metabolites have been used as biomarkers to assess the prevalence of exposure to these compounds in the general population. Total urinary concentrations, which include both free and conjugated (glucuronide and sulfated) forms of the compounds, are usually reported. From a toxicologic standpoint, the relative concentrations of the free species compared with their conjugated analogs can be important because conjugation may reduce the potential biologic activity of the phenols. In this study, we determined the percentage of glucuronide and sulfate conjugates of three phenolic compounds, bisphenol A (BPA), 2,5-dichlorophenol (2,5-DCP), and 2-hydroxy-4-methoxybenzophenone (benzophenone-3, BP-3) in 30 urine samples collected between 2000 and 2004 from a demographically diverse group of anonymous adult volunteers. We used a sensitive on-line solid phase extraction-isotope dilution-high performance liquid chromatography-tandem mass spectrometry method. These three phenols were detected frequently in the urine samples tested. Only small percentages of the compounds (9.5% for BPA, and 3% for 2,5-DCP and BP-3) were excreted in their free form. The percentage of the sulfate conjugate was about twice that of the free compound. The glucuronide conjugate was the major metabolite, representing 69.5% (BPA), 89% (2,5-DCP), and 84.6% (BP-3) of the total amount excreted in urine. These results are in agreement with those reported before which suggested that BPA-glucuronide was an important BPA urinary metabolite in humans. To our knowledge, this is the first study describing the distribution of urinary conjugates of BP-3 and 2,5-DCP in humans.

Simultaneous measurement of urinary bisphenol A and alkylphenols by automated solid-phase extractive derivatization gas chromatography/mass spectrometry

Bisphenol A (BPA) and alkylphenols (APs) are widely used industrial chemicals. BPA is used to manufacture polycarbonate plastic and epoxy resins; APs are used to make alkylphenol ethoxylates, common nonionic surfactants. BPA and APs can leach into the environment during industrial production and after degradation of the polycarbonate plastics and nonionic surfactants. Environmental exposure to these phenolic compounds has been associated with adverse reproductive and developmental effects in wildlife. We developed a sensitive and robust method for measuring BPA and six APs; 3-tert-butylphenol, 4-tert-butylphenol, 4-n-octylphenol, 4-tert-octylphenol, 4-n-nonylphenol, and technical-grade nonylphenol in urine. The method is based on the use of automated solid-phase extraction (SPE) coupled to isotope dilution-gas chromatography/mass spectrometry (GC/MS). During the automated SPE process, the phenols are both extracted from the urine matrix and derivatized, using pentafluorobenzyl bromide, on commercially available styrene-divinylbenzene copolymer-based SPE cartridges. After elution from the SPE column, the derivatized phenols in the SPE eluate are analyzed by GC/MS. The method, validated on spiked pooled urine samples and on urine samples from exposed persons, has limits of detection of approximately 0.1 ng in 1 mL of urine.

Comparing two analytical methods: minimal standards in forensic toxicology derived from information theory

Frequently, new instrumentation and techniques are being applied to casework without an adequate knowledge of how this new technology compares to acceptable analytical procedures. Information theory provides a mathematical method to estimate the identification power of various analytical procedures and predicts if the new method produces a better or poorer confidence in the analysis than an accepted method. This paper makes comparisons based on relative informational power and discusses methods to make those estimates. With the procedures outlined in this paper, an analyst can estimate if a novel technique has the opportunity of reaching the accepted analytical methodology and, if necessary, identify places where the greatest improvement can be made to reach this equilivalence. Even though relative information theory can dismiss some proposed techniques before any analysis starts, it cannot verify if a given technique is adequate for a particular task. For that purpose, a complete procedural verification must be undertaken.

Quantitation of estrogens in ground water and swine lagoon samples using solid-phase extraction, pentafluorobenzyl/trimethylsilyl derivatizations and gas chromatography-negative ion chemical ionization tandem mass spectrometry

A method was developed for the confirmed identification and quantitation of 17beta-estradiol, estrone, 17alpha-ethynylestradiol and 16alpha-hydroxy-17beta-estradiol (estriol) in ground water and swine lagoon samples. Centrifuged and filtered samples were extracted using solid-phase extraction (SPE), and extracts were derivatized using pentafluorobenzy] bromide (PFBBR) and N-trimethylsilylimidazole (TMSI). Analysis was done using negative ion chemical ionization (NICI) gas chromatography-mass spectrometry-mass spectrometry (GC-MS-MS). Deuterated analogs of each of the estrogens were used as isotope dilution standards (IDS) and were added to the samples before extraction. A limit of quantitation of 1 ng/l in ground water was obtained using 500 ml of ground water sample, 1.0 ml of extract volume and the lowest calibration standard of 0.5 pg/microl. For a 25 ml swine lagoon sample, the limit of quantitation was 40 ng/l. The average recovery of the four estrogens spiked into 500 ml of distilled water and ground water samples (n = 16) at 2 ng/l was 103% (S.D. 14%). For 25 ml of swine lagoon samples spiked at 500, 1000 and 10,000 ng/l, the average recovery for the four estrogens was 103% (S.D. 15%). The method detection limits (MDLs) of the four estrogens spiked at 2 ng/l in a 500 ml of ground water sample ranged from 0.2 to 0.6 ng/l. In swine lagoon samples from three different types of swine operations, estrone was found at levels up to 25,000 ng/l, followed by estriol and estradiol up to levels at 10,000 and 3000 ng/l, respectively. It was found that pretreatment of swine lagoon samples with formaldehyde was necessary to prevent conversion of estradiol to estrone.

Review: Derivatization in mass spectrometry--2. Acylation

The present review is devoted to acylation as a widely employed derivatization procedure for protection of OH (alcohols, polyols, phenols, enols), SH (thiols) and NH (amines, amides) groups in order to increase volatility, improve chromatographic properties and, if possible, improve mass spectral properties of derivatives. Chemical aspects of derivatization and various acylating agents are characterized. Mass spectral [electron ionization (EI), chemical ionization (CI) and negative-ion (NI) CI] properties of derivatives that are helpful in identification, structure elucidation and quantitative determination of the analyzed compounds are discussed. Some recent analytical applications of the procedure in synthetic organic chemistry, clinical chemistry, environmental chemistry etc. are summarized.