Simultaneous multi-species determination of trimethyllead,monomethylmercury and three butyltin compounds by species-specific isotope dilution GC–ICP–MS in biological samples

An accurate and sensitive multi-species species-specific isotope dilution GC–ICP–MS method was developed for the simultaneous determination of trimethyllead (Me₃Pb⁺), monomethylmercury (MeHg⁺) and the three butyltin species Bu₃Sn⁺, Bu₂Sn²⁺, and BuSn³⁺ in biological samples. The method was validated by three biological reference materials (CRM 477, mussel tissue certified for butyltins; CRM 463, tuna fish certified for MeHg⁺; DORM 2, dogfish muscle certified for MeHg⁺). Under certain conditions, and with minor modifications of the sample pretreatment procedure, this method could also be transferred to environmental samples such as sediments, as demonstrated by analyzing sediment reference material BCR 646 (freshwater sediment, certified for butyltins). The detection limits of the multi-species GC–ICP–IDMS method for biological samples were 1.4 ng g⁻¹ for MeHg⁺, 0.06 ng g⁻¹ for Me₃Pb⁺, 0.3 ng g⁻¹ for BuSn³⁺ and Bu₃Sn⁺, and 1.2 ng g⁻¹ for Bu₂Sn²⁺. Because of the high relevance of these heavy metal alkyl species to the quality assurance of seafood, the method was also applied to corresponding samples purchased from a supermarket. The methylated lead fraction in these samples, correlated to total lead, varied over a broad range (from 0.01% to 7.6%). On the other hand, the MeHg⁺ fraction was much higher, normally in the range of 80–100%. Considering that we may expect tighter legislative limitations on MeHg⁺ levels in seafood in the future, we found the highest methylmercury contents (up to 10.6 μg g⁻¹) in two shark samples, an animal which is at the end of the marine food chain, whereas MeHg⁺ contents of less than 0.2 μg g⁻¹ were found in most other seafood samples; these results correlate with the idea that MeHg⁺ is usually of biological origin in the marine environment. The concentration of butyltins and the fraction of the total tin content that is from butyltins strongly depend on possible contamination, due to the exclusively anthropogenic character of these compounds. A broad variation in the butylated tin fraction (in the range of <0.3–49%) was therefore observed in different seafood samples. Corresponding isotope-labeled spike compounds (except for trimethyllead) are commercially available for all of these compounds, and since these can be used in the multi-species species-specific GC-ICP-IDMS method developed here, this technique shows great potential for routine analysis in the future.     

Determination of phosphorus in small amounts of protein samples by ICP–MS

Inductively coupled plasma mass spectrometry (ICP-MS) is used for phosphorus determination in protein samples. A small amount of solid protein sample (down to 1 micro g) or digest (1-10 micro L) protein solution was denatured in nitric acid and hydrogen peroxide by closed-microvessel microwave digestion. Phosphorus determination was performed with an optimized analytical method using a double-focusing sector field inductively coupled plasma mass spectrometer (ICP-SFMS) and quadrupole-based ICP-MS (ICP-QMS). For quality control of phosphorus determination a certified reference material (CRM), single cell proteins (BCR 273) with a high phosphorus content of 26.8+/-0.4 mg g(-1), was analyzed. For studies on phosphorus determination in proteins while reducing the sample amount as low as possible the homogeneity of CRM BCR 273 was investigated. Relative standard deviation and measurement accuracy in ICP-QMS was within 2%, 3.5%, 11% and 12% when using CRM BCR 273 sample weights of 40 mg, 5 mg, 1 mg and 0.3 mg, respectively. The lowest possible sample weight for an accurate phosphorus analysis in protein samples by ICP-MS is discussed. The analytical method developed was applied for the analysis of homogeneous protein samples in very low amounts [1-100 micro g of solid protein sample, e.g. beta-casein or down to 1 micro L of protein or digest in solution (e.g., tau protein)]. A further reduction of the diluted protein solution volume was achieved by the application of flow injection in ICP-SFMS, which is discussed with reference to real protein digests after protein separation using 2D gel electrophoresis.The detection limits for phosphorus in biological samples were determined by ICP-SFMS down to the ng g(-1) level. The present work discusses the figure of merit for the determination of phosphorus in a small amount of protein sample with ICP-SFMS in comparison to ICP-QMS.     

Mercury speciation analysis in human hair by species-specific isotope-dilution using GC–ICP–MS

We optimized a mercury (Hg) speciation extraction method for human hair in combination with species-specific isotope-dilution analysis by gas chromatography–inductively coupled plasma–mass spectrometry (GC–ICP–MS). The method was validated on human hair reference material RM (IAEA-086), which is recommended for analysis of monomethylmercury (MMHg) and inorganic mercury (IHg). Three reagents, hydrochloric acid (HCl), nitric acid (HNO₃), and tetramethylammonium hydroxide (TMAH), and three extraction procedures, at ambient temperature for 12 h, microwave-assisted at 75 °C for 6 min, and oven heated at 80 °C for 2 h were tested. Extraction efficiency, recovery, and potential species transformations were evaluated for each method. The most efficient procedures, with recovery of ~90 % for each species with limited demethylation (<5 %) and methylation (0 %), were HNO₃ digestion, irrespective of temperature, and microwave-assisted TMAH extraction. Acidic extraction with HCl induces significant demethylation, with production of artifacts. To correct for potential demethylation artifacts we recommend spiking with isotopically enriched standards before the extraction step.     

Determination of arsenic species and arsenosugars in marine samples by HPLC–ICP–MS

Arsenic-speciation analysis in marine samples was performed by high-pressure liquid chromatography (HPLC) with ICP–MS detection. Separation of eight arsenic species—As^III, MMA, DMA, As^V, AB, TMAO, AC and TeMAs⁺—was achieved on a C₁₈ column with isocratic elution (pH 3.0), under which conditions As^III and MMA co-eluted. The entire separation was accomplished in 15 min. The HPLC–ICP–MS detection limits for the eight arsenic species were in the range 0.03–0.23 μg L⁻¹ based on 3σ for the blank response (n=5). The precision was calculated to be 2.4–8.0% (RSD) for the eight species. The method was successfully applied to several marine samples, e.g. oysters, fish, shrimps, and marine algae. Low-power microwave digestion was employed for extraction of arsenic from seafood products; ultrasonic extraction was employed for the extraction of arsenic from seaweeds. Separation of arsenosugars was achieved on an anion-exchange column. Concentrations of arsenosugars 2, 3, and 4 in marine algae were in the range 0.18–9.59 μg g⁻¹. This paper was presented at the European Winter Conference 2005     

Determination of flurbiprofen in pharmaceutical preparations by GC–MS

This article describes a gas chromatography–mass spectrometry (GC–MS) method for the determination of flurbiprofen in pharmaceutical preparations. The method is based on the derivatization of flurbiprofen with N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA). For GC–MS, electron ionization mode (EI = 70 eV) and selected ion monitoring (SIM) mode were used for quantitative analysis (m/z 180 for flurbiprofen). Calibration curve was linear between the concentration range of 0.25–5.0 μg/mL. Intra- and inter-day precision values for flurbiprofen were less than 3.64, and accuracy (relative error) was better than 2.67%. The mean recovery of flurbiprofen was 99.4% for pharmaceutical preparations. The limits of detection and quantification of flurbiprofen were 0.05 and 0.15 μg/mL, respectively. No interference was found from tablet excipients at the selected assay conditions. Also, the method was applied for the quality control of five commercial flurbiprofen dosage forms to quantify the drug and to check the formulation content uniformity.     

Determination of steroid hormones in blood by GC–MS/MS

This paper presents the development, optimization and validation of a methodology to determine nine key steroid hormones (viz. pregnenolone, progesterone, dehydroepiandrosterone, androstenedione, testosterone, dihydrotestosterone, estrone, 17α-estradiol and 17β-estradiol) expressed in the steroidogenesis in biological fluids. The analytical method allows for the determination of steroid hormones in blood plasma and serum down to 0.08–0.16 ng/mL for estrogens, 0.20–0.36 ng/mL for androgens and 0.36–0.43 ng/mL for progestagens. These limits of detection were obtainable using a two-step solid-phase clean-up for fractionation and elimination of interfering lipids (fatty acids, phospholipids, glycerides and sterols) from the steroid hormones. The accuracy of the method was 50–112% in the range 0.10 to 2.00 ng/mL.     

GC–MS Determination of Sucralose in Splenda

Sucralose (1,6-dichloro-1,6-dideoxy-β-d-fructofuranosyl-4-chloro-4-deoxy-α-d-galactopyranoside) is a high-intensity non-nutritive sweetener derived from sucrose. Determination of sucralose in food is important to ensure consistent product quality. The authors have developed a new method for determination of sucralose. The sucralose was converted into its trimethylsilyl (TMS) ether and qualitative and quantitative analysis were achieved by GC–MS and GC–FID, respectively, using myo-inositol ester as the internal standard. A good linear relationship between response and amount of sucralose TMS ether was obtained in the range 0.005–0.06 mg mL^?1 (r = 0.9994). The detection limit was 0.25 ng.     

Determination of Six Resorcylic Acid Lactones in Feed by GC–MS

A method was developed to simultaneously detect six resorcylic acid lactones in feed by GC–MS. Samples were extracted with methanol followed by a two step liquid–liquid extraction and an HLB SPE clean-up. The samples were derivatized with BSTFA + TMCS (99/1; v/v) and determined by GC–MS. For all analytes, the ranges of recoveries were 81.2–98.2%, with RSDs of 3.2–15.2%, and the LODs were 0.2–0.6 μg kg⁻¹.

     

Determination of aniline in environmental water samples by alternating-current oscillopolarographic titration

A new method for the determination of aniline in environmental water based on oscillopolarographic titration was presented in this paper. Several factors including the kind, concentration, and volume of acid, the dosage of potassium bromide, the temperature and concentration of concomitant substances were investigated in detail. The experimental results indicated that this method was simple, rapid, and sensitive. The linear range was 8.367×10-4 to 2.789×10-2 mol L-1, the relative standard deviation (R.S.D.) was lower than 0.96%, and the spiked recoveries of aniline in environmental water samples were in the range of 99.4-106.9% under the optimal conditions. The results indicated that the present method could be used as an alternative method for aniline determination in realworld water samples.     

Determination of Estragole in Fennel Herbal Teas by HS-SPME and GC–MS

Estragole, a volatile phenylpropanoid contained in a variety of edible herbs, has been demonstrated to be genotoxic and carcinogenic, and its addition as a flavoring substance to foodstuffs has been banned by the regulatory bodies of the European Union. Fast and accurate analytical methods for its determination in herbs are thus necessary to assess the dietary exposure of this substance in humans and, in particular, to sensitive groups. In the present study, headspace solid-phase microextraction (HS-SPME) combined with gas chromatography–mass spectrometry (GC–MS) was applied for determination of estragole in infusions from different widely used commercial herbal teas based on Foeniculum vulgare (fennel) seeds. The optimized HS-SPME extraction conditions involved the use of a polydimethylsiloxane fiber exposed to the herbal infusion for 20 min at 50°C followed by GC–MS analysis. The method was fully validated for linearity, sensitivity, accuracy, and precision and applied to real samples; the level of estragole in infusions of commercial fennel seed teas was found to be within 50–250 µ`^?1.     

Determination of fifteen priority phenolic compounds in environmental samples from Andalusia (Spain) by liquid chromatography–mass spectrometry

This work describes the optimisation of a method to determinate fifteen phenolic compounds in waters, sediments and biota (green marine algae) by liquid chromatography coupled to mass spectrometry (LC-MS) with atmospheric pressure chemical ionisation (APCI) in the negative mode. The LC separations of the studied compounds and their MS parameters were optimised in order to improve selectivity and sensitivity. Separation was carried out with a C₁₈ column using methanol and 0.005% acid acetic as mobile phase in gradient mode. The molecular ion was selected for the quantitation in selective ion monitoring (SIM) mode. A solid-phase extraction (SPE) method was applied in order to preconcentrate the target analytes from water samples. However, extraction of the compounds from sediment and biota samples was carried out by liquid–solid extraction with methanol/water after studying the influence of other organic solvents. In addition, a clean-up step by SPE with HLB Oasis cartridges was necessary for sediments and biota. The proposed analytical methodology was validated in the target environmental matrices by the analysis of spiked blank matrix samples. Detection limits were 10–50 ng L^–1 for water, 1–5 g kg^–1 for sediments and 2.5–5 g kg^–1 for biota samples. Good recoveries and precision values were obtained for all matrices. This methodology has been successfully applied to the analysis of incurred water, sediment and biota samples from Andalusia (Spain).     

Effects of γ-sterilization on butyltin homogeneity and content in sediments: a GC–ICP–MS study

A GC-ICP-MS method based on extraction and alkylation of butyltins with sodium tetraethylborate was used to quantitatively assess the fate of these analytes in solutions and sediments following exposure to gamma-irradiation. The effects of a 2.5 Mrad sterilization dose on three butyltin species in both methanolic calibration solutions and in sediment matrices were investigated. Although significant losses of tributyltin (TBT, 90%), dibutyltin (DBT, 100%) and monobutyltin (MBT, 80%) were detected in standard solutions prepared in methanol following gamma-irradiation, no species inter-conversion occurred. Some degradation of TBT (38%) and DBT (32%) but no significant change in MBT content was found using a spiked sediment CRM HISS-1. Conversion DBT to MBT in spiked HISS-1 was deduced. Much smaller degradation of TBT (16% loss) and 10% loss of DBT by conversion to MBT (14% gain) was registered using a sediment blend of PACS-2 and HISS-1 (SOPH). Despite some initial losses of TBT and DBT due to irradiation, better than 2% RSD in both TBT and DBT concentrations measured in twelve different bottles of blended sediment SOPH were obtained, indicating the material may be considered homogeneous for these analytes. Results from a long-term five-year stability study of PACS-2 show that all three butyltins are stable during storage at 4 degrees C followed with 2.5 Mrad minimum dose of gamma-irradiation sterilization treatment.     

Determination of <Superscript>90</Superscript>Sr in contaminated environmental samples by tuneable bandpass dynamic reaction cell ICP–MS

A rapid method for the extraction and determination of ⁹⁰Sr in natural water, plant and sediment samples was developed using extraction chromatography and dynamic reaction cell ICP–MS, with O₂ as a reaction gas. While isobaric interference from the stable isotope ⁹⁰Zr was efficiently removed by this method, interferences produced from in-cell reactions with Fe⁺ and Ni⁺ required suppression by tuneable bandpass, and in sediments, additional chromatographic separation. Method detection limits were 0.1 pg g⁻¹ (0.5 Bq g⁻¹), 0.04 pg g⁻¹(0.2 Bq g⁻¹), and 3 pg L⁻¹ (5 Bq L⁻¹) for sediments, plant and water samples, respectively, and ⁹⁰Sr concentrations determined by ICP–MS were in good agreement with activities determined by Cerenkov counting and with certified reference values. While mass spectrometric determination does not rival detection limits achievable by radiometric counting, radiometric determination of ⁹⁰Sr, a pure beta-emitter, is hindered by long analysis times (several weeks); the comparatively fast analysis achieved via ICP–MS enables same-day preparation and analysis of samples, making this an important technique for the environmental monitoring of areas contaminated by radioactivity.     

Determination of Milnacipran in Human Plasma Using GC–MS

A new, simple, and fully validated gas chromatography–mass spectrometry (GC–MS) method was presented for quantitative analysis of milnacipran (MNP) in human plasma. MNP was efficiently derivatized with N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA) before analysis. The role of catalyst, temperature, time, solvent on the trimethylsilylation reaction were evaluated. The proposed method was fully validated by assessment of the following parameters: limits of detection and quantitation, precision, accuracy, linearity, specificity, stability, extraction recovery and robustness/ruggedness. The limit of quantitation (LOQ) was 30 ng mL^?1. The calibration curve was linear (r ² > 0.9988) in the range 30–500 ng mL^?1. The method was found specific, precise, accurate, selective and reliable according to validation data. This developed method was successfully applied to determine the steady state concentration of MNP in patients.     

Determination of Antioxidants and Preservatives in Cosmetics by SPME Combined with GC–MS

A rapid and simple procedure for the determination of antioxidants and preservatives in cosmetics has been developed utilizing solid-phase microextraction combined with GC–MS. A silica fiber coated with polyacrylate provided the highest extraction efficiency. Detection limits in the range from 0.4 to 8.5 ng mL⁻¹ were obtained. Linearity is over a wide range from 1 to 2,000 ng mL⁻¹ with a relative standard deviation under 16%. Cosmetic from a local supermarket were analysed for antioxidants and preservatives to demonstrate the effectiveness of the proposed method. The concentration of antioxidants and preservatives determined was 20–1,218 μg g⁻¹ for methylparaben and 5–3,779 μg g⁻¹ for propylparaben.     

Simple Determination of 4-Methylimidazole in Soft Drinks by Headspace SPME GC–MS

A simple method to detect 4-methylimidazole in soft drinks is described. This method is based on headspace solid-phase micro-extraction and gas chromatography–mass spectrometry (HS-SPME GC–MS). The HS-SPME parameters (selection of fiber, extraction temperature, heating time, and pH) were optimized and selected. Under the established condition, the detection and the quantification limit were 1.9 and 6.0 μg L^?1 using 4 mL of the liquid sample, respectively. The relative standard deviation for five independent determinations at 100.0 and 500.0 μg L^?1 was less than 8 %. The calibration curve was y = 0.6027x–0.0033 with a linearity of r ² = 0.997. Using the proposed method, the levels of 4-MEI were detected in a range from 94.0 to 324.8 μg L^?1. The comparison of liquid chromatography tandem mass spectrometry (LC–MS/MS) with the proposed method was performed and the agreement with LC–MS/MS for all samples was acceptable.