Determination of methylmercury in environmental samples using static headspace gas chromatography and atomic fluorescence detection after aqueous phase ethylation

A rapid and automated method for the determination of monomethylmercury (MMHg) in environmental samples was developed using headspace gas chromatography with atomic fluorescence detection in combination with aqueous phase ethylation. Sample preparation steps were optimized for sediments, biological samples, and water samples using certified reference materials and real samples with a broad range of MMHg concentrations. Different extraction procedures were compared for both sediments and biological samples. The methods were applied in the intercomparison exercises for the certification of MMHg in sediments (IAEA 405) and in Oyster tissue (BCR 710) and the results were accepted for certification. The detection limits for MMHg are 0.002 ng Hg/g for sediments and biological samples and 0.01 ng Hg/L for water samples. The method was tested for methylation artifacts; no artifact was observed in the sediment samples and CRMs tested.     

Validation and application of an analytical method for monomethylmercury quantification in aquatic plant tissues

An analytical methodology for monomethylmercury (MMHg) determination in aquatic plant tissues with low detection limit (346 pg g⁻¹) is proposed. It consists of acid digestion (HBr/CuSO₄), cleanup step with a Na₂S solution, pre-concentration procedure using a dithizone solution in toluene and quantification by GC–ECD. The performance of the methodology has been tested by determining the MMHg concentrations in the certified reference material Fucus Sea Plant Homogenate—IAEA-140/TM (CRM) and in leaves, stems and roots of the salt marsh plants Sarcocornia fruticosa and Halimione portulacoides. The results obtained for CRM were not statistically different ( = 0.056) from the certified value and repeatability was lower than 2.5% for the plant samples analyzed. This coefficient of variation was similar to those obtained in the externally quality control using within-batch and between-batch (<1.4%).     

Determination of total mercury in environmental and biological samples by flow injection cold vapour atomic absorption spectrometry

A simple and accurate method has been developed for the determination of total mercury in environmental and biological samples. The method utilises an off-line microwave digestion stage followed by analysis using a flow injection system with detection by cold vapour atomic absorption spectrometry.

The method has been validated using two certified reference materials (DORM-1 dogfish and MESS-2 estuarine sediment) and the results agreed well with the certified values. A detection limit of 0.2 ng g⁻¹ Hg was obtained and no significant interference was observed. The method was finally applied to the determination of mercury in river sediments and canned tuna fish, and gave results in the range 0.1–3.0 mg kg⁻¹.     

Application of multivariate techniques in the optimization of a procedure for the determination of bioavailable concentrations of Se and As in estuarine sediments by ICP OES using a concomitant metals analyzer as a hydride generator

A procedure has been developed for the determination of bioavailable concentrations of selenium and arsenic in estuarine sediments employing inductively coupled plasma optical emission spectrometry (ICP OES) using a concomitant metals analyzer device to perform hydride generation. The optimization of hydride generation was done in two steps: using a two-level factorial design for preliminary evaluation of studied factors and a Doehlert design to assess the optimal experimental conditions for analysis. Interferences of transition metallic ions (Cd²⁺, Co²⁺, Cu²⁺, Fe³⁺ and Ni²⁺) to selenium and arsenic signals were minimized by using higher hydrochloric acid concentrations. In this way, the procedure allowed the determination of selenium and arsenic in sediments with a detection limit of 25 and 30 μg kg⁻¹, respectively, assuming a 50-fold sample dilution (0.5 g sample extraction to 25 mL sample final volume). The precision, expressed as a relative standard deviation (% RSD, n = 10), was 0.2% for both selenium and arsenic in 200 μg L⁻¹ solutions, which corresponds to 10 μg g⁻¹ in sediment samples after acid extraction. Applying the proposed procedure, a linear range of 0.08-10 and 0.10-10 μg g⁻¹ was obtained for selenium and arsenic, respectively. The developed procedure was validated by the analysis of two certified reference materials: industrial sludge (NIST 2782) and river sediment (NIST 8704). The results were in agreement with the certified values. The developed procedure was applied to evaluate the bioavailability of both elements in four sediment certified reference materials, in which there are not certified values for bioavailable fractions, and also in estuarine sediment samples collected in several sites of Guanabara Bay, an impacted environment in Rio de Janeiro, Brazil.     

Determination of nanomolar levels of formate in natural waters based on a luminescence enzymatic assay

A light-producing reaction utilizing three enzymes, bacterial luciferase, dehydrogenase and diaphorase, can be used to determine formic acid in natural waters at nanomolar concentrations. The method is rapid and convenient, requiring no preconcentration, desalting or derivatization procedures. Determinations can be done on small sample volumes (25 μl) at room temperature and pH 7. The precision (relative standard deviation for sea water samples containing 1.0 μM formate was 9.0% (n = 15). The reaction is specific for formate with a detection limit of 20 nM (signal-to-noise ratio = 3). Results for applications of the method to sea, estuarine and rain water are given.     

Simplified procedures for the analysis of polycyclic aromatic hydrocarbons in water, sediments and mussels

We describe in this paper simple and robust analytical protocols to determine the 16 polycyclic aromatic hydrocarbons (PAHs) of the US Environmental Protection Agency priority list in water, sediment and mussels. For water samples, eight different solid-phase extraction (SPE) sorbents have been compared and among them, C18 provided highest recoveries and limits of detection of 0.3-15 ng/L. For lyophilized sediments, Soxhlet and ultrasonic extraction were compared, and the last one permitted to recover all analytes with highest repetitivity and was validated by analysing a certified reference material. Finally, the analysis of mussels was undertaken using Soxhlet, ultrasonic and pressurized liquid extraction (PLE) and the performance of several clean-up steps are compared. Whereas for the former two, incomplete recovery or losses of some analytes were evidenced, PLE permitted a more efficient extraction and although alkaline digestion was necessary to remove coextracted compounds, the method gave acceptable recoveries and limits of detection of 0.5-7.7 microg/kg dry mass, as for sediments. In all cases, analysis was performed by gas chromatography coupled to mass spectrometry and internal standard quantification was performed using five deuterated PAHs. Each method performance is discussed for the three matrices analysed and the paper reports advantages and disadvantages of each for their routine application in monitoring programs.     

Determination of Lead in Lipstick by Direct Solid Sampling High-Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry: Comparison of Two Digestion Methods

A new analytical procedure for the determination of lead in lipstick has been developed using direct solid sampling high resolution continuum source graphite furnace atomic absorption spectrometry (SS HR CS GFAAS). The performance of this method has been compared to acid digestion methods for sample preparation, with or without hydrofluoric acid (HF) with inductively coupled plasma mass spectrometry (ICP-MS) detection. Good reliability was obtained for all three methods; the results obtained for certified reference materials with concentrations between 1 and 20 ppm were in agreement with the certified values. However, for materials with complex matrices, such as pearl or Ca-Na borosilicate, only ICP-MS with HF sample digestion or AAS with direct solid sampling allowed complete recovery of lead. To avoid the use of hazardous acids, the development of SS HR CS GFAAS is an interesting alternative. With the AAS method, a characteristic mass of 13.2 pg of lead was obtained, and the limit of detection was 0.005 µg/g. The performance of the method was evaluated by determining lead in lipstick. The use of the solid sampling technique constitutes a good alternative for accurate and rapid determination of lead content in lipstick and cosmetic raw materials, with a suitable limit of detection and a reduced risk of contamination or of analyte loss. Another alternative would be to use ICP-MS determination in conjunction with microwave-assisted acid digestion without the use of HF, which implies accepting a quantification of “nearly total” lead, closer to a “bio-extractible” fraction.     

Determination of Cd in biological samples by flame AAS following on-line preconcentration by complexation with O,O-diethyldithiophosphate and solid phase extraction with Amberlite XAD-4

A method for the on-line preconcentration of Cd based on its complex formation with the ammonium salt of O,O-diethylditiophosphate (DDTP) and using the Amberlite XAD-4 resin as a solid support in a column is proposed. Cadmium was detected by flame atomic absorption spectrometry. Different conditions, such as complexing agent concentration, preconcentration time, solutions flow rates and nature and concentration of the eluent were optimized. Different detection limits (LODs) could be established by using different preconcentration times, between 30 s and 5 min, with corresponding LODs from 5 to 1 μg L⁻¹, respectively. The method was validated by analyzing five biological certified samples. The relative standard deviation was usually around 3%, indicating a very good precision. The found concentrations values are in agreement with the certified ones, according to the t-test, for a confidence level of 95%. Enriched seawaters were also analyzed, and the recoveries were between 93 and 108%. The FI method is very simple and probably can be coupled to other measuring analytical techniques.     

Mercury speciation in hair by headspace injection-gas chromatography-atomic fluorescence spectrometry (methylmercury) and combustion-atomic absorption spectrometry (total Hg)

The speciation of Hg in human hair was carried out with combustion-atomic absorption spectrometry for total Hg (THg) and headspace-gas chromatography-atomic fluorescence spectrometry (HS-GC-AFS) for methylmercury (MMHg).The determination of total Hg in hair was carried out with the AMA analyzer (Advanced Mercury Analyser 254). Accuracy and reproducibility were assessed on a Certified Reference hair sample (IAEA-086 CRM), yielding, respectively, a recovery of 97.5% and a RSD of 3.2%. Analyses of 10 blank measurements resulted in a detection limit of 1.5 ng g⁻¹ of THg for a 20 mg sample of human hair.MMHg concentrations in hair were assessed with HS-GC-AFS in a single analysis step. Either acid or alkaline extraction can be applied because they yielded very similar results on a IAEA-086 CRM: we observed a recovery of 103% and a RSD of 7% with acid extraction and a recovery of 110% and a RSD of 9% with alkaline extraction. Optimization of the headspace vial, injection and GC parameters is described. The detection limit of the MMHg determination in human hair, which amounts to 0.04 ng g⁻¹ for a 20 mg sample, is far below the concentrations observed in natural samples.The number of samples that can be analyzed per hour, respectively, amounts to 8 for THg and 4 for MMHg. Finally, Hg speciation in natural human hair samples was carried out by combining both AMA and HS-GC-AFS analysis methods. THg levels were at the μg g⁻¹, level, with an average MMHg fraction of about 70%.     

Rapid Ultrasound-Assisted Emulsification Microextraction Combined with COU-2 Dispersive Micro-solid Phase Extraction for the Determination of Azole Antifungals in Milk Samples by HPLC-DAD

A rapid, simple, and efficient method using ultrasound-assisted emulsification microextraction combined with dispersive micro-solid phase extraction (USAE-D-µ-SPE) was developed for detection and quantification of three azole antifungals in milk samples by high-performance liquid chromatography diode array detector. In this study, mesoporous carbon, COU-2, was used as sorbent in USAE-D-µ-SPE for the extraction and preconcentration of analytes. Several important experimental parameters, including type of deproteinized solvents, desorption time, type of extraction solvents, volume of extraction solvent, extraction time, emulsification time, sample pH, salt addition, and mass of COU-2 sorbent, were optimized using spiked milk samples. Under the optimum extraction and detection conditions, three azole antifungals, namely ketoconazole, clotrimazole, and miconazole, were determined within 20 min, with good linearity of matrix-matched calibration in the range of 0.5–5000.0 µg L^?1 with coefficient of determination, r ² ≥ 0.9943. The method showed limits of detection and limits of quantification of all analytes in the range of 0.15–3.0 and 0.5–10.0 µg L^?1, respectively. Good repeatability with RSDs <15% (n = 3) and satisfactory relative recoveries (83.3–111.1%) were obtained for spiked azole antifungal drugs in milk. The results reveal that the developed USAE-D-µ-SPE method was a simple, rapid, efficient, environmentally friendly, and practicable method for the determination of azole antifungals in milk samples.     

Development of a flow system for the determination of low concentrations of silver using Moringa oleifera seeds as biosorbent and flame atomic absorption spectrometry

In this study a method for the determination of low concentrations of silver in waters using solid-phase extraction with a flow injection analysis system and detection by flame atomic absorption spectrometry (FAAS) was developed. Moringa oleifera seeds were used as a biosorbent material. Chemical and flow variables of the on-line preconcentration system such as sample pH and flow rate, preconcentration time, eluent concentration and sorbent mass were studied. The optimum preconcentration conditions were obtained using sample pH in the range of 6.0-8.0, preconcentration time of 4 min at a flow rate of 3.5 mL min^− 1, 0.5 mol L^− 1 HNO₃ eluent at a flow rate of 4.5 mL min^− 1 and 35 mg of sorbent mass. With the optimized conditions, the preconcentration factor, precision, detection limit and sample throughput were estimated as 35 (for preconcentration of 14 mL sample), 3.8% (5.0 μg L^− 1, n = 7), 0.22 μg L^− 1 and 12 samples per hour, respectively. The developed method was successfully applied to mineral water and tap water, and accuracy was assessed through analysis of a certified reference material for water (APS-1071 NIST) and recovery tests, with recovery ranging from 94 to 101%.     

Development and validation of a gas chromatography mass spectrometry method for the analysis of phytoestrogens,phytosterols and mycotoxins in estuarine water samples

Many pollutants currently released into the environment may cause adverse effects on exposed organisms leading to disruption of the endocrine system. Among them are natural compounds such as phytoestrogens and phytosterols, found in various plants and mycotoxins produced by a wide range of fungal species. The presence of some classes of phytoestrogens and phytosterols has been demonstrated in environmental samples while little information can be found about the presence of mycotoxins. Due to the complexity of environmental matrices and the low concentrations normally found, sensitive and selective methods are required for an unequivocal quantification of this type of compounds. The aim of this study was to develop and validate an analytical method for the simultaneous quantification of seven phytoestrogens, two phytosterols and three mycotoxins in estuarine water samples. The method consisted of the preconcentration of estuarine water samples (1 L) on 200 mg OASIS HLB cartridges, followed by a clean-up step in 1 g silica cartridges and quantification by gas chromatography with mass spectrometry ion trap analyser. Validation parameters were evaluated and the method demonstrated to be selective and linear with correlations higher than 0.99. Method detection limits were in the ng L^?1 levels ranging from 18.0 to 90.0 ng L^?1, recovery rates ranged from 59.8% to 99.5% and precision (RSD) from 5.5% and 9.7%. The feasibility of the method was demonstrated in surface water samples from Douro River estuary, a polluted estuary, with reported incidence of endocrine-disrupting phenomena.     

HPLC-UV and HPLC-MSn multiresidue determination of amidosulfuron, azimsulfuron, nicosulfuron, rimsulfuron, thifensulfuron methyl, tribenuron methyl and azoxystrobin in surface waters

The paper presents a new HPLC method, with UV and MSⁿ detection, for the determination of seven pesticides, including the sulfonylurea herbicides amidosulfuron, azimsulfuron, nicosulfuron, rimsulfuron, thifensulfuron methyl, tribenuron methyl, and the fungicide azoxystrobin characterised by a methoxyacrilate structure. The methodology consists of a preconcentration/SPE (solid phase extraction) step and HPLC-UV (240 nm detection wavelength)-MSⁿ analysis. Under the optimised conditions and after a 1000/1 preconcentration factor, the limits of detection were lower than 14.5 ng L⁻¹ for UV detection and lower than 8.1 ng L⁻¹ for MS detection. The limits of quantification were lower than 48.3 ng L⁻¹ in UV detection and than 26.9 ng L⁻¹ in MSⁿ detection. The analysis of two samples, spiked with a mixture of the pesticides at threshold level concentrations, gave more than 60% recovery.     

Supramolecular microextraction of cobalt from water samples before its microsampling flame atomic absorption spectrometric detection

The supramolecular solvent system consists of tetrahydrofuran (THF) and 1-decanol, that was used as an extraction solvent for a microextraction procedure for the preconcentration and separation of Co(II). The proposed supramolecular-based procedure was combined with microsampling flame atomic absorption spectrometry for the determination of cobalt at trace levels in water samples. N-Benzoyl-N,N-diisobutylthiourea was used to chelate Co(II) in an aqueous solution. Quantitative extraction efficiency was obtained at pH 6.5. The effects of analytical parameters including pH, amount of ligand, type, ratio and volume of supramolecular solvent, sample volume and interfering ions were investigated for optimisation of the procedure. The proposed supramolecular solvent-based microextraction procedure (Ss-ME) exhibits a limit of detection (LOD) of 1.29 µg L^?1 and a limit of quantification (LOQ) of 3.88 µg L^?1. The procedure was validated by addition/recovery tests and by applying TMDA 64.2 and TMDA 53.3 water certified reference materials. The microextraction method was successfully applied for the preconcentration and determination of cobalt in water samples.     

Activated carbon cloth filled pipette tip for solid phase extraction of nickel(II), lead(II), cadmium(II), copper(II) and cobalt(II) as 1,3,4-thiadiazole-2,5-dithiol chelates for ultra-trace detection by FAAS

A solid phase extraction method is established for preconcentration of nickel, lead, cadmium, copper and cobalt using pipette tip solid phase extraction. The presented process was dependent on chelation of analytes with 1,3,4-thiadiazole-2,5-dithiol, then allowing the solution to flow through an activated carbon cloth packed pipette tip. The adsorbed metal chelates on the surface of activated carbon cloth were eluted by 5 mL of 3 M HNO₃. The concentrations of nickel, lead, cadmium, copper and cobalt were detected using a flame atomic absorption spectrometer (FAAS). The pipette tip solid phase extraction exhibit a preconcentration factor of 120. The limit of detection values were 2.7, 1.7, 1.3, 2.0 and 2.9 µg L^?1 for Ni(II), Pb(II), Cd(II), Cu(II) and Co(II), respectively. Validation of the method was checked by the analysis of TMDA-53.3 and TMDA-64.2 certified reference materials. The method was successfully applied for water and fertiliser samples.     

Determination of organotin compounds by headspace solid-phase microextraction–gas chromatography–pulsed flame-photometric detection (HS-SPME–GC–PFPD)

A method based on Headspace solid-phase microextraction (HS-SPME, with a 100 μm PDMS-fiber) in combination with gas-chromatography and pulsed flame-photometric detection (GC-PFPD) has been investigated for simultaneous determination of eight organotin compounds. Monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), monophenyltin (MPhT), and the semi-volatile diphenyltin (DPhT), triphenyltin (TPhT), monooctyltin (MOcT), and dioctyltin (DOcT) were determined after derivatization with sodium tetraethylborate. The conditions used for the extraction and preconcentration step were optimised by experimental design methodology. Tripropyltin (TPrT) and diheptyltin (DHepT) were used as internal standards for quantification of volatile and semi-volatile organotin compounds, respectively. The analytical precision (RSD) for ten successive injections of a standard mixture containing all the organic tin compounds ranged between 2 and 11%. The limits of detection for all the organotin compounds were sub ng (Sn) L⁻¹ in water and close to ng (Sn) kg⁻¹ in sediments. The accuracy of the method was evaluated by analysis of two certified reference material (CRM) sediment samples. The HS-SPME–GC–PFPD was then applied to the analysis of three harbour sediment samples. The results showed that headspace SPME is an attractive tool for analysis of organotin compounds in solid environmental matrices.     

Indirect quantification of trace levels cyanide in environmental waters through flame atomic absorption spectrometry coupled with cloud point extraction

Cloud point extraction (CPE) has been used for the preconcentration and indirect quantification of cyanide after the formation of a ion-associate complex with 3-amino-7-diethylamino-8,9-benzo-2-phenoxazine chloride (Nile blue, NB⁺) in the presence of copper (II) ions, and later analysis by flame atomic absorption spectrometry (FAAS) using polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) as extracting surfactant. The chemical variables affecting the separation phase and the viscosity affecting the detection process were optimized. At pH 5.5, preconcentration of only 50 mL of sample in the presence of 0.04 % (w/v) PONPE 7.5 and 5.64 × 10^?5 mol L^?1 Nile blue permitted the detection of 3.75 μg L^?1 cyanide. The enhancement factor was 64.7 for cyanide. The proposed method was successfully applied to the determination of free cyanide in environmental water samples. The method was compared with the pyridine–barbituric acid method and the paired t test was used to determine whether the results obtained by the two methods differ significantly.     

Rapid method for the analysis of plutonium isotopes in a soil sample within 60 min.

A rapid method for the determination of Pu isotopes in a soil sample within 60 min of starting sample pretreatment was developed. The large reduction in the analysis time was attained by the rapid and perfect digestion of the sample using an alkaline fusion method with an induction heating machine. Pu concentrations were then determined by flow injection/ICP-MS using a solid extraction resin after preconcentration by batch extraction with a chelate resin. The limits of detection for 239Pu and 240Pu were 9.2 fg and 4.3 fg, corresponding to 0.03 and 0.05 Bq kg(-1), respectively, under our analytical conditions, which satisfy the lower detection limits (0.5 Bq kg(-1) of 239Pu, and 2 Bq kg(-1) of 240Pu) required for rapid analysis techniques by the Ministry of Education, Culture, Sports, Science and Technology, Japan. This method provides a powerful and practical technique for emergency monitoring in and around nuclear facilities that handle large amounts of plutonium.     

Comparison of microwave-assisted acid leaching techniques for the determination of heavy metals in sediments, soils, and sludges

Microwave-assisted EPA method 3051 for nitric acid leaching of environmentally key elements from sediments, soils, and sludges was tested, and the influence of leaching temperature and time on element recovery for an estuarine sediment (CRM 277) was investigated. The extraction efficiencies for four certified reference materials applying EPA method 3051, an optimized nitric acid procedure, and an aqua regia (HCl/HNO₃ 3:1) procedure were compared. Digestions were carried out in a high-pressure microwave system offering simultaneous temperature and pressure control for all digestion vessels employed. Eight elements (Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn) were determined by ICP-AES and ICP-MS. Extraction efficiency strongly depended on the applied leaching parameters and varied for certain elements among different materials when a nitric acid procedure was applied. In general, element recoveries obtained from the aqua regia procedure were superior to those obtained from nitric acid procedures and showed good agreement with the 95% confidence interval of the certified value for most of the elements investigated. Received: 27 March 1998 / Revised: 29 June 1998 / Accepted: 3 July 1998     

Validation of method for determination of different classes of pesticides in aqueous samples by dispersive liquid-liquid microextraction with liquid chromatography-tandem mass spectrometric detection

In this study, a simple, rapid and efficient method has been developed for the extraction and preconcentration of different classes of pesticides, carbofuran (insecticide), clomazone (herbicide) and tebuconazole (fungicide) in aqueous samples by dispersive liquid-liquid microextraction (DLLME) coupled with liquid chromatography-tandem mass spectrometric detection. Some experimental parameters that influence the extraction efficiency, such as the type and volume of the disperser solvents and extraction solvents, extraction time, speed of centrifugation, pH and addition of salt were examined and optimized. Under the optimum conditions, the recoveries of pesticides in water at spiking levels between 0.02 and 2.0 μg L⁻¹ ranged from 62.7% to 120.0%. The relative standard deviations varied between 1.9% and 9.1% (n = 3). The limits of quantification of the method considering a 50-fold preconcentration step were 0.02 μg L⁻¹. The linearity of the method ranged from 1.0 to 1000 μg L⁻¹ for all compounds, with correlation coefficients varying from 0.9982 to 0.9992. Results show that the method we propose can meet the requirements for the determination of pesticides in water samples. The comparison of this method with solid-phase extraction indicates that DLLME is a simple, fast, and low-cost method for the determination of pesticides in natural waters.