DR-CALUX((R)) screening of food samples: evaluation of the quantitative approach to measure dioxin, furans and dioxin-like PCBs

European legislation laid down maximum tolerable levels of dioxin in feed and food as well as analytical method requirements. In order to face with large monitoring programs, it was foreseen in the EU strategy to integrate screening methods, using either a qualitative (screening) approach, or a quantitative approach. In this study, dioxin results obtained using the Dioxin Responsive Chemical-Activated LUciferase gene eXpression (DR-CALUX^®) cell-based assay (quantitative approach), were compared with gas chromatography–high resolution mass spectrometry (GC–HRMS) analyses data. Instead of using World Health Organization–toxic equivalent factor (WHO–TEF), the comparison was based on the assessment of relative effective potencies (REPs) for each congener of the 17 toxic 2,3,7,8-polychlorodibenzo-p-dioxins/furans (PCDD/Fs) and 12 dioxin-like polychlorobiphenyls (DL-PCBs). According to published data, DR-CALUX^®-REP evaluated here appear similar to WHO–TEF for PCDD/Fs while lower values were observed for DL-PCBs.

We analyzed two “home made” contaminated fat samples, displaying both the same WHO–toxic equivalent quantities (WHO–TEQ) concentration (12 pg WHO–TEQ g⁻¹). They were spiked with either a low or a high amount of DL-PCBs. In both cases, the DR-CALUX^® measured concentration (picogram 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) eq. g⁻¹) corresponded to the PCDD/Fs WHO–TEQ concentration only. A good agreement was nevertheless found between the DR-CALUX^® measurements and the recalculated DR-CALUX^®-TEQ contents (using DR-CALUX^®-REP instead of WHO–TEF), demonstrating that the observed response was due, in both cases, to the addition of the responses of the standards added to the fat. By contrast, in real contaminated samples (feed or cod liver samples), DR-CALUX^® measured concentrations were similar to WHO–TEQ GC–HRMS measured concentrations. But, depending on the PCDD/Fs and DL-PCBs congener content, the DR-CALUX^® measured concentrations were either lower or higher than calculated DR-CALUX^®-TEQ contents, demonstrating that possible co-extracted contaminants contributed to the CALUX response.

Owing to these divergences, the quantitative determination of dioxin-like content in food and feed using CALUX as screening method is questionable, except for samples displaying constant congener patterns, in which cases, correction factors could be applied.     

PTV-LV-GC/MS/MS as screening and complementary method to HRMS for the monitoring of dioxin levels in food and feed

Recent developments in trapping efficiency inside ion trap mass spectrometer permitted to lower instrument detection limit (IDL). An IDL of 200 fg μl⁻¹ injected with a signal-to-noise ratio of 5:1 for tetrachlorodibenzo-p-dioxin (TCDD) was obtained by gas chromatography coupled to a quadrupole ion storage mass spectrometer in tandem mode (GC/MS/MS). Coupling large volume programmable temperature vaporizer (PTV-LV) injection to GC/MS/MS provides an alternative and complementary method to classical splitless-GC injection connected to high-resolution mass spectrometry (splitless-GC/HRMS) method for dioxin monitoring in food and feed.

An injection volume of 10 μl was found to be the best compromise between the sensitivity requirements and the robustness required for a high throughput method. PTV-LV-GC/MS/MS and Splitless-GC/HRMS were compared by performing analysis on five different matrices such as beef fat, yolk eggs, milk powder, animal feed and serum samples covering a concentration range of two orders of magnitude (i.e. 0.2–25 ng WHO-TEQ kg⁻¹). An analysis of variance (ANOVA) was carried out. Fisher tests pointed out that the method effect for all the 2,3,7,8 congeners was not significant, indicating that the null hypothesis (H₀: μ₁=μ₂=…=μ_n) was not rejected. Moreover, the interaction effects between methods and matrices were not significant for most of the 2,3,7,8 congeners. However, three congeners (2,3,7,8-TCDF; 1,2,3,4,7,8-HxCDD and 1,2,3,4,6,7,8-HpCDD) were characterized by P-values lower than the significance level (=0.05). In toxic equivalence (TEQ), the study showed that no significant bias was observed between the two methods. Consequently, PTV-LV-GC/MS/MS is an attractive technique and can be used as a cost effective complementary method to HRMS for dioxin levels monitoring in food and feed.     

Interpretation of CALUX results in view of the EU maximal TEQ level in milk

Analyses of dioxins in food have become increasingly important since the European Commission has enforced maximal toxic equivalent concentration (TEQ) levels in various food and feed products. Screening methodologies are usually used to exempt those samples that are below the maximum permitted limit and that can, therefore, be released to the market. In addition, one needs to select those samples that require confirmation of their dioxin TEQ level. When bioassays are used as screening tools, the interpretation of the obtained results should consider the higher variability and uncertainty associated with them. This paper explores the use of CALUX data as quantitative screening results. The validation of the method for the polychlorinated dibenzo-p-dioxins (PCDD)/F TEQ determination in milk samples is described with emphasis on the decision limit (CC) and the precision of the method. The decision limit amounts to 4.53 pg TEQ/g fat. Repeatability and within-lab reproducibility coefficients of variation are below 30%. The newly introduced parameter CC^* of 1.47 pg TEQ/g fat delimits with CC a range of suspicious results. These data are not significantly different from the maximum limit of 3 pg TEQ/g fat and should be confirmed by a confirmatory analytical method such as HRGC–HRMS.     

TEQ-value determinations of animal feed; emphasis on the CALUX bioassay validation

Polyhalogenated aromatic hydrocarbons, such as polychlorinated dibenzo-p-dioxins are a large and diverse group of environmental pollutants. Their tendency to accumulate in the food chain and their toxicity make monitoring necessary. The reference analysis method is laborious and very expensive, therefore cheap and rapid bioassays have been developed. The chemical-activated luciferase bioassay (CALUX) bioassay uses a recombinant cell line, which responds to dioxins and dioxin-like molecules with Ah receptor (AhR)-dependent induction of firefly luciferase in a dose related response. The CALUX was tested for its use in the screening of feed. Aliquots of 20 g of enriched feed were extracted with a toluene:methanol mixture (20:4 v/v) and extracts were defatted on 33% H₂SO₄ silica columns and purified on carbon columns. Only the dioxin and furan fraction was analysed, the PCB fraction was discarded. The precision of the method is acceptable and in compliance with an R.S.D. <30% as suggested for cell-based bioassays in the Commission Directive 2002/70/EC of July 2002. The results evidence good agreement between TEQ-values obtained by either CALUX or GC–HRMS. The method is now routinely in use for a feed screening programme designed by the Federal Agency for the Safety of the Food chain. Approximately, 25 samples are analysed weekly. From the obtained results approximately 10% was confirmed by GC–HRMS. The false positive ratio is 1% and no false negatives were found, making the use of the CALUX technology advantageous.     

Evaluation of triclosan and biphenylol in marine sediments and urban wastewaters by pressurized liquid extraction and solid phase extraction followed by gas chromatography mass spectrometry and liquid chromatography mass spectrometry

Analytical methods, based on GC–MS and LC–MS, for the determination of traces of 2,4,4′-trichloro-2′-hydroxydiphenyl ether (triclosan) and biphenylol in urban wastewater and marine sediments were developed. These methods involve the use of diverse analytical techniques, such as solid phase extraction (SPE) and pressurized liquid extraction for sample preparation, and GC–negative chemical ionization MS and LC–electrospray ionization (ESI) MS–MS for identification and quantification. The recoveries of triclosan and biphenylol were 84 and 80% in wastewater and 100 and 73% in sediments, respectively. Detection limits obtained were in the range of ppb and ppt. To prove their applicability to real samples and as part of a more extensive monitoring program, the developed methods were applied to the analysis of wastewater samples, coming from an urban wastewater treatment plant (UWWTP), and of marine sediment samples collected at the outflow of two UWWTPs to the sea. Results obtained reveal the presence of triclosan in all the samples at concentrations that ranged from 0.8 to 37.8 μg/l in wastewater and from 0.27 to 130.7 μg/kg in sediments. These preliminary data reinforce the interest for further research on this topic.     

Performances and limitations of the HRMS method for dioxins, furans and dioxin-like PCBs analysis in animal feedingstuffs: Part I: Results of an inter-laboratory study

The European strategy for dioxin monitoring of the food chain has defined high-resolution gas chromatography coupled to high-resolution mass spectrometry (HRGC/HRMS) method as the confirmatory method that can provide reliable and comparable results at sub-parts per trillion (ppt) level. This paper describes the first inter-laboratory study on dioxins, furans and dioxin-like PCBs by HRGC/HRMS method in animal feedingstuffs. Two different statistical approaches (ISO 5725 and Cofino’s statistics) were used for the statistical evaluation. For this particular study, the performances of the HRGC/HRMS method seem to be congener-independent in repeatability and reproducibility conditions over a concentration range covering more than four orders of magnitude. Results clearly show the effect of precision loss below 0.1 ppt level per congener in repeatability conditions and below 0.2 ppt level per congener in reproducibility conditions. LODs reported by the laboratories give median values of 0.02 ng/kg for most of the toxic congeners. Relative standard deviation between the laboratories’ mean values using upper-bound approach for TEQ calculation is 6.2%, more than twice the maximum level set at 0.75 ng TEQ/kg of product.     

Validation of the CALUX bioassay for PCDD/F analyses in human blood plasma and comparison with GC-HRMS

Following the dioxin crisis of 1999, several studies were conducted to assess the impact of this crisis on the dioxin body burden in the Belgian population. The Scientific Institute of Public Health identified a population from whom plasma samples were available and from whom, during the follow up survey, plasma samples were obtained in 2000. In total, 496 samples were collected for GC-HRMS and CALUX analyses to verify statistical assessment conclusions. This study was seen as an opportunity to validate the CALUX bioassay for biological sample analysis and to compare toxic equivalency (TEQ) values obtained by the reference GC-HRMS technique and by the screening method. This article focuses on the validation results of the CALUX bioassay for the analyses of the dioxin fractions of blood plasma. The sample preparation is based on a liquid–liquid extraction, followed by an acid silica in series with an activated carbon clean-up. A good recovery (82%) and reproducibility (coefficient of variation less than 25%) were found for this method. Based on 341 plasma samples, a significant correlation was established between the bioassay and chemical method (R = 0.64). However, a proportional systematic error was observed when the results obtained with the CALUX bioassay were regressed with the results from the GC-HRMS analyses. The limit of quantification (LOQ) used to calculate TEQ values from the GC-HRMS determinations, the use of the relative potency values instead of the toxic equivalent factor and the potential of CALUX bioassay to measure all compounds with affinity for the AhR may partly explain this proportional systematic error. Nevertheless, the present results suggest that the CALUX bioassay could be a promising valid screening method for human blood plasma analyses.     

Rapid screening of dioxin-contaminated soil by accelerated solvent extraction/purification followed by immunochemical detection

Since soils at industrial sites might be heavily contaminated with polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), there is a need for large-scale soil pollution surveys and, thus, for cost-efficient, high-throughput dioxin analyses. However, trace analysis of dioxins in complex matrices requires exhaustive extraction, extensive cleanup, and very sensitive detection methods. Traditionally, this has involved the use of Soxhlet extraction and multistep column cleanup, followed by gas chromatography—high-resolution mass spectrometry (GC/HRMS), but bioanalytical techniques may allow much more rapid, cost-effective screening. The study presented here explores the possibility of replacing the conventional method with a novel approach based on simultaneous accelerated solvent extraction (ASE) and purification, followed by an enzyme-linked immunosorbent assay (ELISA). Both the traditional and the novel cleanup and detection approaches were applied to contaminated soil samples, and the results were compared. ELISA and GC/HRMS results for Soxhlet-extracted samples were linearly correlated, although the ELISA method slightly underestimated the dioxin levels. To avoid an unacceptable rate of false-negative results, the use of a safety factor is recommended. It was also noted that the relative abundance of the PCDDs/PCDFs, evaluated by principal component analysis, had an impact on the ELISA performance. To minimize this effect, the results may be corrected for differences between the ELISA cross-reactivities and the corresponding toxic equivalency factor values. Finally, the GC/HRMS and ELISA results obtained following the two sample preparation methods agreed well; and the ELISA and GC/HRMS results for ASE extracts were strongly correlated (correlation coefficient, 0.90). Hence, the ASE procedure combined with ELISA analysis appears to be an efficient approach for high-throughput screening of PCDD-/PCDF-contaminated soil samples.      

Pyrolysis–GC–MS to trace terrigenous organic matter in marine sediments: a comparison between pyrolytic and lipid markers in the Adriatic Sea

The effectiveness of semiquantitative pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) as a rapid analytical technique for sourcing continental organic matter (OM) in marine sediments was examined by comparison with classical GC–MS analyses of solvent extractable lipid markers. Py–GC–MS was directly applied to HCl/HF de-ashed surface sediment samples collected in five stations located in north western Adriatic Sea. The resulting pyrolysates were characterised by compounds indicative of different biological precursors (e.g. proteins, carbohydrates, chlorophylls), including lignin methoxyphenols diagnostic for continental inputs. The relative abundance of pyrolytic markers was compared to the distribution of n-alkanes, n-alkanols and sterols extracted from the same sediments and determined by GC–MS analyses. For each class of molecular indicators, the terrigenous to aquatic ratio (TAR) was determined as follows: relative abundance of methoxyphenol/protein markers (TAR_PY), concentration ratios of (C27 + C29 + C31)/(C15 + C17 + C19) n-alkanes (TAR_HC), (C26 + C28+ C30)/(C14 + C16) n-alkanols (TAR_AL) and sitosterol/cholesterol (TAR_ST). A positive correlation was found between TAR_PY and both TAR_HC and TAR_AL indicating a decreasing contribution of land-plant-derived materials seaward in two investigated transects. TAR_ST values displayed a different trend suggesting a mixed origin for sitosterol. The distribution of TAR_PY values was also in good agreement with that of atomic C/N ratios. Considering the complexity of environmental systems (diagenetic alteration, different fractions of OM analysed) the obtained results indicate that the pyrolytic marker approach by Py–GC–MS is valuable for sourcing marine OM on a semiquantitative base, providing data consistent with GC–MS determinations of lipid markers and elemental bulk analyses.     

The international validation of bio- and chemical-analytical screening methods for dioxins and dioxin-like PCBs: the DIFFERENCE project rounds 1 and 2

The European research project DIFFERENCE is focussed on the development, optimisation and validation of screening methods for dioxin analysis, including bio-analytical and chemical techniques (CALUX, GC-LRMS/MS, GC×GC-ECD) and on the optimisation and validation of new extraction and clean-up procedures. The performance of these techniques is assessed in an international validation study and the results are compared with the reference technique GC-HRMS. This study is set up in three rounds and is in accordance with the International Harmonized Protocol for Proficiency Studies and the ISO 5725 standard. The results of the first two rounds are very promising in particular for GC-LRMS/MS. The results obtained with this technique were as accurate as the results reported by the labs using the GC-HRMS. The initial results reported for GC×GC-ECD overestimate the dioxin concentration in the samples. The results reported by the labs using the CALUX technique underestimate the total TEQ concentrations in the samples, compared to the GC-HRMS reference method. The repeatability of the CALUX is significantly higher than the other screening techniques. It was shown that accelerated solvent extraction (ASE) is a valid alternative extraction and clean-up procedure for fish oil and vegetable oil. The results obtained with CALUX and GC-HRMS after ASE are equivalent to the results obtained with the classical extraction and purification procedures.     

Multi-residue screening of pesticides in vegetables,fruits and baby food by stir bar sorptive extraction-thermal desorption-capillary gas chromatography-mass spectrometry

The performance of stir bar sorptive extraction (SBSE) for the enrichment of pesticides from vegetables, fruits and baby food samples is discussed. After extraction with methanol, an aliquot is diluted with water and SBSE is performed for 60 min. By applying a new thermal desorption unit (TDU), fully automated and unattended desorption of 98 stir bars is feasible, making SBSE very cost-effective. The presence of pesticide residues is elucidated with the retention time locked gas chromatography–mass spectroscopy method (RTL-capillary GC–MS). With SBSE–RTL-capillary GC–MS operated in the scan mode, more than 300 pesticides can be monitored in vegetables, fruits and baby food. The multi-residue method (MRM) described provides detectabilities from the mg/kg (ppm) to the sub-μg/kg (ppb) level, thereby complying with the maximum residue levels (MRLs) set by regulatory organizations for pesticides in different matrices. Several examples, i.e. pesticide residues in lettuce, pears, grapes and baby food, illustrate the potential of SBSE–RTL-capillary GC–MS.     

Evaluation of multiple alternative instrument platforms for targeted and non‐targeted dioxin and furan analysis

The use of gas chromatography coupled to high‐resolution magnetic sector mass spectrometers (GC‐HRMS) is well established for dioxin and furan analysis. However, the use of gas chromatography coupled to triple quadrupole (MS/MS) and time of flight (TOF) mass spectrometers with atmospheric pressure ionization (API) and traditional electron ionization (EI) for dioxin and furan analysis is emerging as a viable alternative to GC‐HRMS screening. These instruments offer greater versatility in the lab for a wider range of compound identification and quantification as well as improved ease of operation. The instruments utilized in this study included 2 API‐MS/MS, 1 traditional EI‐MS/MS, an API‐quadrupole time of flight mass spectrometer (API‐QTOF), and a EI‐high‐resolution TOF (EI‐HRTOF). This study compared these 5 instruments to a GC‐HRMS using method detection limit (MDLs) samples for dioxin and furan analysis. Each instrument demonstrated acceptable MDL values for the 17 chlorinated dioxin and furans studied. The API‐MS/MS instruments provide the greatest overall improvement in MDL value over the GC‐HRMS with a 1.5 to 2‐fold improvement. The API‐QTOF and EI‐TOF demonstrate slight increases in MDL value as compared with the GC‐HRMS with a 1.5‐fold increase. The 5 instruments studied all demonstrate acceptable MDL values with no MDL for a single congener greater than 5 times that for the GC‐HRMS. All 5 instruments offer a viable alternative to GC‐HRMS for the analysis of dioxins and furans and should be considered when developing new validated methodologies.     

Rapid aryl hydrocarbon receptor based polymerase chain reaction screening assay for polychlorinated dibenzo-p-dioxins and furans in soil and sediment

A method for the estimation of polychlorinated dibenzo-p-dioxin and furan (PCCD/F) toxicity equivalent quotient (TEQ) of soil and sediment matrices is described. The method includes extraction, isolation of the PCDD/Fs from interfering compounds, such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), and measurement of PCDD/F using the PROCEPT aryl hydrocarbon (AhR) receptor based polymerase chain reaction (PCR) assay. The values obtained using the PROCEPT assay correlate well with reference TEQ values generated from gas chromatography-high resolution mass spectrometry (GC-HRMS), with a linearity coefficient (R(2)) of 0.94. Applied in a screening mode at 50pg/g PCDD/F TEQ, the PROCEPT assay yielded five false positive results (2.6%) and no false negative results for 196 analyses of spiked soils and environmental samples obtained from US EPA Superfund sites.     

Screening of urinary coproporphyrin using cloud point extraction and chemiluminescence detection

A simple screening test was developed for the sensitive and selective measurement of urinary coproporphyrin. In this screening test, efficient and selective extraction/pre-concentration of coproporphyrin from the aqueous medium(urine) into a much smaller volume phase containing a common non-ionic surfactant (Triton X-100) and ethyl acetate was accomplished by the addition of a relatively large amount of a cloud point depressing electrolyte (K(3)PO(4)) into the sample solution to effect cloud point separation. Sensitive and selective detection of coproporphyrin in the mixed Triton X-100 and ethyl acetate phase was performed via chemical excitation using the peroxyoxalate chemiluminescence reaction. The effects of surfactant and cations (from the cloud point depressing electrolyte) on the chemiluminescence intensity of coproporphyrin were briefly investigated. Furthermore, the spectrum of urinary coproporphyrin obtained using the present chemiluminescence method was briefly compared with that obtained from fluorescence method.     

Cloud point extraction and preconcentration for the gas chromatography of phenothiazine tranquilizers in spiked human serum.

Cloud point extraction was successfully applied to the preconcentration of phenothiazine derivatives, such as pericyazine (PC), chlorpromazine (CP) and fluphenazine (FUL), for gas chromatography (GC). Phenothiazine derivatives were separated from surfactants by passing the surfactant-rich phase through a cation exchange column after cloud point extraction, permitting the determination of the phenothiazine derivatives extracted in the surfactant-rich phase by GC. The optimal condition for the cloud point extraction of phenothiazine derivatives was also investigated using Triton X-100, Triton X-114, and PONPE10. Triton X-114 provided the most efficient recovery of phenothiazine derivatives among the surfactants used. The addition of sodium chloride and excess ammonia to the sample solution resulted in a decrement of the recovery of the phenothiazine derivatives. The proposed method was applied to the determination of phenothiazine derivatives in spiked human serum by GC. The recoveries of PC, CP, and FUL in spiked human serum were 95.1%, 87.1%, and 84.7%, respectively.     

Cloud point extraction equilibrium of lanthanum(III), europium(III) and lutetium(III) using di(2-ethylhexyl)phosphoric acid and Triton X-100

The cloud point extraction behaviors of lanthanoids(III) (Ln(III) = La(III), Eu(III) and Lu(III)) with and without di(2-ethylhexyl)phosphoric acid (HDEHP) using Triton X-100 were investigated. It was suggested that the extraction of Ln(III) into the surfactant-rich phase without added chelating agent was caused by the impurities contained in Triton X-100. The extraction percentage more than 91% for all Ln(III) metals was obtained using 3.0 × 10⁻⁵ mol dm⁻³ HDEHP and 2.0% (v/v) Triton X-100. From the equilibrium analysis, it was clarified that Ln(III) was extracted as Ln(DEHP)₃ into the surfactant-rich phase. The extraction constant of Ln(III) with HDEHP and 2.0% (v/v) Triton X-100 were also obtained.     

Importance of REP values when comparing the CALUX bioassay results with chemoanalyses results: Example with spiked vegetable oils

Differences between chemical activated luciferase gene expression (CALUX) bioassay and chemoanalyses results are observed.

This paper shows that calculations of the TEQ values using REP values instead of WHO TEF values give different results. The REP values do affect the results obtained by the CALUX technique. These differences are more marked for the dioxin like PCB compounds (CALUX TEQ values are lower than WHO TEQ values) than for the dioxin compounds (CALUX TEQ values are higher than WHO TEQ values).

The CALUX results were compared with the concentrations of the congeners’ spiked into the oil.     

Critical comparison of automated purge and trap and solid-phase microextraction for routine determination of volatile organic compounds in drinking waters by GC-MS

The use of two automated sample preparation techniques, solid-phase microextraction (SPME) and purge and trap (P&T) systems are critically compared for the GC–MS determination of eight volatile organic compounds (VOCs), including trihalomethanes (THMs), in drinking water samples. Compounds chosen for the comparison are regulated by Spanish and European official guidelines for drinking waters. Experimental parameters investigated for the two sample preparation techniques included SPME type of fibers, SPME modality, P&T gas flow, extraction and desorption times and desorption temperatures. Thus, optimal experimental conditions have been worked out for the SPME and P&T techniques. Under such optimised conditions, detection limits, precision and accuracy were evaluated. Both methods fulfilled the values that the official guidelines establish. The P&T–GC–MS method offers LDs ranged from 0.004 to 0.2 ng mL⁻¹, repeatabilities below 6% and recoveries between 81 and 117%; while LDs ranging from 0.008 to 0.7 ng mL⁻¹, 1–12% R.S.D. and recoveries from 80 to 119% were achieved with the SPME–GC–MS method. Finally, we chose P&T–GC–MS method as the best for this determination and we validate this methodology by its application to the analysis of an Aquacheck Interlaboratory Exercise.     

A new and fast extraction method for the determination of priority phenols from marine sediments by liquid chromatography

A new and fast method for the determination of priority phenols in marine sediment samples by high-performance liquid chromatography using microwave-assisted micellar extraction is optimized. This study is carried out using the nonionic surfactants polyoxyethylene 9 lauryl ether (polidocanol) and genapol X-080 as extractants. Parameters studied include surfactant concentration, solution pH, extraction time, and power. Once the method is optimized, it is applied to different spiked marine sediments from of the Canary Islands coastlines (Spain). The results obtained indicate that a power irradiation of 500 W for 2 min achieved the best extraction efficiency (approximately 100% recovery) and less than 10% relative standard deviation. Detection limits are obtained in the 2-20 microg/g range for the phenols studied. Finally, the proposed method provides a simple, fast, and organic solvent-free procedure to analyze phenols from marine sediment samples.     

Preconcentration and Determination of Tin in Water Samples by Using Cloud Point Extraction and Graphite Furnace Atomic Absorption Spectrometry

A method based on cloud point extraction and graphite furnace atomic absorption spectrometry (GFAAS) was developed for the analysis of trace tin in water samples. After cloud point extraction, the tin in the water samples was preconcentrated and successfully separated from most interferents. During the procedure, 8-hydroxyquinoline (8-HQ) was used as chelating reagent, and Triton X-114 was added as surfactant. The parameters affecting the sensitivity and the extraction efficiency, such as solution pH, concentration of 8-HQ and Triton X-114, equilibration temperature and centrifuge time, were evaluated and optimized. Under the optimum conditions, a preconcentration factor of 96.2 was obtained for a 20 mL water sample. The detection limit (LOD) was as low as 0.012 ng mL⁻¹, and the analytical curve was linear in the range of 0.05–2.0 ng mL⁻¹ with satisfactory precision (RSD <4.1%). The proposed method was successfully applied to the determination of trace tin in water samples with recoveries in the range of 85.0–112.0%.