Development of a slurry-extraction procedure for direct determination of cobalt by electrothermal atomic absorption spectrometry in complex environmental samples

A new procedure for Co determination in a complex matrix (coal fly ash) by slurry extraction-electrothermal atomic absorption spectrometry (ETAAS) is presented. Fractional experimental designs were applied to find the most important variables affecting Co extraction. Two liquid media (HCl + HNO₃ and HF) and three agitation modes (ultrasonic probe, ultrasonic bath and manual shaking) were assayed. HF revealed as the most suitable medium for Co extraction, being its concentration and time of contact the most significant variables. Quantitative extraction was obtained after their optimisation (16%, v/v HF; 5 min), with good accuracy (coal fly ash SRM 1633a and SRM 1633b) and precision (R.S.D. < 11.5%). The limit of detection of the method was 0.02 μg g⁻¹ (100 mg mL⁻¹ slurry), and the characteristic mass was 15 ± 1 pg. The ‘slurry-extraction procedure’ established is simple, fast, cheap and was also validated for soil and sediment analysis. As far as we know, a slurry-extraction procedure has not yet been applied to quantify cobalt by ETAAS in such matrices. Moreover, nine coal fly ashes, 12 sediments and 18 soils were analysed by the proposed method and also by a direct slurry sampling-ETAAS procedure in order to compare their performance. In general, the HF-extraction slurry procedure revealed superior.     

High-precision measurements of seawater Pb isotope compositions by double spike thermal ionization mass spectrometry

A new method for the determination of seawater Pb isotope compositions and concentrations was developed, which combines and optimizes previously published protocols for the separation and isotopic analysis of this element. For isotopic analysis, the procedure involves initial separation of Pb from 1 to 2 L of seawater by co-precipitation with Mg hydroxide and further purification by a two stage anion exchange procedure. The Pb isotope measurements are subsequently carried out by thermal ionization mass spectrometry using a ²⁰⁷Pb–²⁰⁴Pb double spike for correction of instrumental mass fractionation. These methods are associated with a total procedural Pb blank of 28 ± 21 pg (1sd) and typical Pb recoveries of 40–60%. The Pb concentrations are determined by isotope dilution (ID) on 50 mL of seawater, using a simplified version of above methods. Analyses of multiple aliquots of six seawater samples yield a reproducibility of about ±1 to ±10% (1sd) for Pb concentrations of between 7 and 50 pmol/kg, where precision was primarily limited by the uncertainty of the blank correction (12 ± 4 pg; 1sd). For the Pb isotope analyses, typical reproducibilities (±2sd) of 700–1500 ppm and 1000–2000 ppm were achieved for ²⁰⁷Pb/²⁰⁶Pb, ²⁰⁸Pb/²⁰⁶Pb and ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁴Pb, respectively. These results are superior to literature data that were obtained using plasma source mass spectrometry and they are at least a factor of five more precise for ratios involving the minor ²⁰⁴Pb isotope. Both Pb concentration and isotope data, furthermore, show good agreement with published results for two seawater intercomparison samples of the GEOTRACES program. Finally, the new methods were applied to a seawater depth profile from the eastern South Atlantic. Both Pb contents and isotope compositions display a smooth evolution with depth, and no obvious outliers. Compared to previous Pb isotope data for seawater, the ²⁰⁶Pb/²⁰⁴Pb ratios are well correlated with ²⁰⁷Pb/²⁰⁶Pb, underlining the significant improvement achieved in the measurement of the minor ²⁰⁴Pb isotope.     

Direct determination of Ge in hot spring waters and coal fly ash samples by hydride generation-ETAAS

A method for Ge determination in hot spring water and acid extracts from coal fly ash samples involving hydride generation, trapping and atomisation of the hydride generated from Ir-treated graphite tubes (GTs) has been developed. Hydride was generated from hydrochloric acid medium using sodium tetrahydroborate. Several factors affecting the hydride generation, transport, trapping and atomisation efficiency were studied by using a Plackett-Burman design. Results obtained from Plackett-Burman designs suggest that trapping and atomisation temperatures are the significant factors involved on the procedure. The accuracy was studied using NIST-1633a (coal fly ash) reference material. The detection limit of the proposed method was 2.4 μg l⁻¹ and the characteristic mass of 233 pg was achieved. The Ge concentrations in fly ash and hot spring samples were between 6.25-132 μg g⁻¹ and 12.84-36.2 μg l⁻¹.     

Determination of cadmium,mercury and lead in coal fly ash by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry

Ultrasonic slurry sampling electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry (USS-ETV-ID-ICP-MS) has been applied to the determination of Cd, Hg and Pb in coal fly ash samples. Thioacetamide (TAC) was used as the modifier. Since the sensitivities of the elements studied in coal fly ash slurry and aqueous solution were quite different, isotope dilution method was used for the determination of Cd, Hg and Pb in these coal fly ash samples. The isotope ratios of each element were calculated from the peak areas of each injection peak. This method has been applied to the determination of Cd, Hg and Pb in NIST SRM 1633a coal fly ash reference material and a coal fly ash sample collected from Kaohsiung area. Analysis results of reference sample NIST SRM 1633a coal fly ash agreed satisfactorily with the certified values. The other sample determined by isotope dilution and method of standard additions was agreed satisfactorily. Precision was better than 6% for most of the determinations and accuracy was better than 4% with the USS-ETV-ID-ICP-MS method. Detection limits estimated from standard addition curves were in the range of 24–58, 6–28 and 108–110 ng g⁻¹ for Cd, Hg and Pb, respectively.     

Isotopic Analysis of tungsten using multiple collector-inductively coupled plasma-mass spectrometer coupled with electrothermal vaporization technique

We have developed a micro-electrothermal vaporization (μETV) device for the multiple collector-ICP-mass spectrometry (μETV-MC-ICPMS) to improve analytical precision in the ¹⁸²W/¹⁸³W and ¹⁸⁴W/¹⁸³W ratio measurements from nanogram quantities of W. The W solution was loaded onto the Re-filament, and the gradual evaporation of W was achieved by controlling the incident current onto the Re filament and D-Glucose. With the W evaporation under the Ar atmosphere, the measured W isotope ratios became erroneous mainly due to the contribution of signal spikes Ala-Arg-Gly-Phy-Tyr. In strike contrast, signal intensity profile became smooth when the He ambient/carrier gas was employed, and this resulted in better precision in the isotope ratio measurements. The measured UV–vis isotope ratio data obtained with present μETV technique were significantly deviated from the ratio data obtained with solution nebulization technique, mainly due to the contribution of the isotope fractionation effect through the evaporation process. Rigorous testing for the correction of the isotope fractionation processes pH–activity curve revealed that the Rayleigh fractionation law, rather than the conventional exponential law, provided the most reliable ratio data (1.851720 ± 0.000018 for ¹⁸²W/¹⁸³W and 2.141248 ± 0.000028 for ¹⁸⁴W/¹⁸³W ratios), which agreed well with the ratio data obtained through the conventional solution nebulization technique (1.851718 ± 0.000039 for ¹⁸²W/¹⁸³W and 2.141248 ± 0.000022 for ¹⁸⁴W/¹⁸³W). Moreover, mass dependency for the mass fractionation law suggested that W was evaporated as oxides (WO₃), rather than the metallic form (W), from the Re filament, and therefore, information concerning the chemical form of the analytes could also be derived by the ETV technique developed in this study. The data presented here demonstrate clearly that the ETV sample introduction technique has a potential to become a sensitive tool for the precise isotope analysis for the MC-ICPMS technique.     

Tin determination in marine sediment, soil, coal fly ash and coal slurried samples by hydride generation-electrothermal atomic absorption spectrometry

Different procedures of tin hydride generation from aqueous and acidified slurries of marine sediment, soil, coal fly ash and coal samples, coupled to electrothermal atomic absorption spectrometry were optimised by using factorial designs. A batch mode generation system and Ir-treated graphite tubes were used for the hydride generation and atomisation, respectively. Eight variables, affecting the hydride generation and hydride transport efficiency (hydrochloric acid and sodium tetrahydroborate concentrations, particle size, acid volume and argon flow rate), the hydride trapping efficiency (trapping temperature and trapping time) and the atomisation efficiency (atomisation temperature) were studied and optimised. In addition, acid pre-treatment procedures assisted by ultrasonic energy were used for soil and coal matrices, to obtain acidified slurries and acid leachates. The involved variables were hydrochloric and nitric acid concentrations, exposure time to ultrasound, particle size and leaching solution volume. Adequate accuracy (41.5±0.8 and 1.4±0.2 mg kg⁻¹, for PACS-1 (sediment marine) and NIST-1633b (coal fly ash), respectively) were obtained by using aqueous slurry reference materials. In addition, values of 6.2±0.6 and 1.2±0.1 mg kg⁻¹ were assessed by analysing GBW-07401 (soil) and NIST-1632c (coal) certified reference materials.     

Speciation of chromium in Australian fly ash

The concentrations of chromium (III) and (VI) in fly ash from nine Australian coal fired power stations were determined. Cr(VI) was completely leached by extraction with 0.01 M NaOH solution and the concentration was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). This was confirmed by determining Cr(III) and Cr(VI) in the extracts of fly ash that had been spiked with chromium salts. These analytical measurements were done using a combination of ion-exchange chromatography and ICP-AES. The elutant was 0.05 M HNO₃ containing 0.5%-CH₃OH. When the column was operated at a flow rate of 1.2 ml min⁻¹ and samples were injected by use of a sample loop with a volume of 100 μl, Cr(III) and Cr(VI) in sample solution was exclusively separated within approximately 10 min. The detection limits (3σ) were 5 ng for Cr(III) (0.050 mg l⁻¹) and 9 ng for Cr(VI) (0.090 mg l⁻¹), respectively. A relative standard deviation of 1.9% (n = 6) was obtained for the determination by IC-ICP-AES of 0.25 mg l⁻¹ Cr(III) and Cr(VI).     

Retention of arsenate using genetically modified coryneform bacteria and determination of arsenic in solid samples by ICP-MS

A novel method for the retention of arsenate [As(V)] combining time-controlled solid-phase extraction with living bacterial biomass is presented. As(V) retention was carried out by exposing the extractant, consisting of a living double-mutant of Corynebacterium glutamicum strain ArsC1-C2, to the sample for a retention time of 1-7 min, before the arsenic distribution equilibrium between the sample solution and the extractant was established. The amount of As(V) retained in the biomass was measured by inductively coupled plasma-mass spectrometry (ICP-MS) after the sample had been treated with nitric acid. A theoretical model of the retention process was developed to describe the experimental retention-time profiles obtained with the bacterial cells. This relationship provided a feasible quantification of the retention process before steady-state was reached, providing that the agitation conditions and the retention time had been controlled. An analytical procedure for the retention/quantification of As(V) was then developed; the detection limit was 0.1 ng As(V) mL⁻¹ and the relative standard deviation 2.4-3.0%. The maximum effective retention capacity for As(V) was about 12.5 mg As (g biomass)⁻¹. The developed procedure was applied to the determination of total arsenic in coal fly ash, using a sample that had undergone oxidative pre-treatment.     

Determination of As, Sb, Se, Te and Bi in milk by slurry sampling hydride generation atomic fluorescence spectrometry

A simple and fast analytical procedure has been developed for the determination of As, Sb, Se, Te and Bi in milk samples by hydride generation atomic fluorescence spectrometry (HG-AFS). Samples were treated with aqua regia for 10 min in an ultrasound water bath and pre-reduced with KBr for total Se and Te determination or with KI and ascorbic acid for total As and Sb, the determination of Bi being possible in all with or without pre-reduction. Slurries of samples, in the presence of antifoam A, were treated with NaBH₄ in HCl medium to obtain the corresponding hydrides, and AFS measurements were processed in front of external calibrations prepared and measured in the same way as samples. Results obtained by the developed procedure compare well with those found after microwave-assisted complete digestion of samples. The proposed method is simple and fast, and only 1 ml of milk is needed. The values obtained for detection limit are 2.5, 1.6, 3, 6 and 7 ng l⁻¹ for As, Sb, Se, Te and Bi respectively in the diluted samples, with average relative standard deviation values of 3.8, 3.1, 1.9, 6.4 and 1.2% for three independent analysis of a series of commercially available samples of different origin. Data found in Spanish market samples varied from 3.2±0.3 to 11.3±0.2 ng g⁻¹ As, from 3.1±0.2 to 11.6±0.4 ng g⁻¹ Sb, from 10.7±0.5 to 25.5±0.4 ng g⁻¹ Se, from 0.9±0.2 to 9.4±0.6 ng g⁻¹ Te and from 11.5±0.1 to 27.7±0.4 ng g⁻¹ Bi.     

Optimization and comparison of chemical and electrochemical hydride generation for optical emission spectrometric determination of arsenic and antimony using a novel miniaturized microwave induced argon plasma exiting the microstrip wafer

Continuous flow (CF) chemical hydride generation (CHG) and electrochemical hydride generation (ECHG) directly coupled to a novel 40 W, atmospheric pressure, 2.45 GHz microwave microstrip Ar plasma exiting a microstrip wafer has been developed for the emission spectrometric determination of As and Sb using a miniaturized optical fiber spectrometer and a CCD-array detector. The experimental conditions for both procedures were optimized with respect to the relative net intensities of the As I 228.8 nm and Sb I 252.8 nm lines and their signal-to-background intensity ratios. Additionally, the susceptibility to interferences from Cd, Co, Cr, Cu, Fe, Ni, Pb and Zn and other hydride-forming elements in the determination of As and Sb using the CHG and ECHG techniques was investigated in detail. Under the optimized conditions, it was found that ECHG is more prone to interferences compared to CHG. The detection limits (3σ) of As (6 ng mL⁻¹) and Sb (7 ng mL⁻¹) obtained for the ECHG-MSP-OES method are about three times lower than in the case of the CHG-MSP-OES method due to a two-fold lower amount of H₂ introduced into the MSP in case of the ECHG, resulting in a better plasma stability and reduced background level. The linearity ranges for both calibration curves to a concentration of up to 5 μg mL⁻¹ and a precision between 2% and 7% (2 μg mL⁻¹ and 0.050 μg mL⁻¹ of As and Sb, respectively) were found for both methods. The developed ECHG-MSP-OES method was validated for As through the analysis of a certified coal fly ash standard reference material (NIST SRM 1633a) after sample dissolution. The derived concentration (140 ± 8 μg g⁻¹) was found to agree well with the certified data (145 ± 15 μg g⁻¹). The method was also successfully applied to the analysis of both a galvanic bath sample, which contained Sb and was spiked with As, and a tap water sample spiked with both analytes. Recovery rates of 99-101% and a Sb concentration of 6.6 μg mL⁻¹ in the galvanic bath sample were revealed. The latter value showed a good agreement with the data obtained from ICP-OES analysis, which was also used for validation purpose.     

Development of an on-line isotope dilution laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method for determination of boron in silicon wafers

A method has been developed based on an on-line isotope dilution technique couple with laser ablation/inductively coupled plasma mass spectrometry (LA-ICP-MS), for the determination of boron in p-type silicon wafers. The laser-ablated sample aerosol was mixed on-line with an enriched boron aerosol supplied continuously using a conventional nebulization system. Upon mixing the two aerosol streams, the isotope ratio of boron changed rapidly and was then recorded by the ICP-MS system for subsequent quantification based on the isotope dilution principle. As an on-line solid analysis method, this system accurately quantifies boron concentrations in silicon wafers without the need for an internal or external solid reference standard material. Using this on-line isotope dilution technique, the limit of detection for boron in silicon wafers is 2.8 × 10¹⁵ atoms cm⁻³. The analytical results obtained using this on-line methodology agree well with those obtained using wet chemical digestion methods for the analysis of p-type silicon wafers containing boron concentrations ranging from 1.0 × 10¹⁶ to 9.6 × 10¹⁸ atoms cm⁻³.     

Cold vapour atomic fluorescence determination of mercury in milk by slurry sampling using multicommutation

A highly sensitive mechanized method has been developed for the determination of mercury in milk by atomic fluorescence spectrometry (AFS). Samples were sonicated for 10 min in an ultrasound water bath in the presence of 8% (v/v) aqua regia, 2% (v/v) antifoam A and 1% (m/v) hydroxilamine hydrochloride, and after that, they were treated with 8 mmol l⁻¹ KBr and 1.6 mmol l⁻¹ KBrO₃ in an hydrochloric medium. Atomic fluorescence measurements were made by multicommutation, which provides a fast alternative in quality control analysis, due to the easy treatment of a large number of samples (approximately 70 h⁻¹), and is an environmentally friendly procedure, which involves a waste generation of only 94.5 ml h⁻¹ as compared with the 605 ml h⁻¹ obtained by using continuous AFS measurements. The limit of detection found was 0.011 ng g⁻¹ Hg in the original sample. The method provided a relative standard deviation of 3.4% for five independent analysis of a sample containing 0.30 ng g⁻¹ Hg. To validate the accuracy of the method, a certified reference material NIST-1459 (non-fat milk powder) containing 0.3±0.2 ng g⁻¹ Hg was analysed and a value of 0.27±0.06 ng g⁻¹ Hg was found. A comparison made between data found by the developed procedure and those obtained by microwave-assisted digestion and continuous AFS measurements evidenced a good comparability between these two strategies. Results obtained for commercially available milk samples varied between 0.09 and 0.61 ng g⁻¹ Hg depending on the type of sample and its origin. The confluence of the analytical waste with a 6 mol l⁻¹ NaOH allowed us to reduce the waste generation in a working session from 1 l to 5 g solid residue with a matrix of Fe(OH)₃ which contributes to the deactivation of traces of heavy metals presents in the samples that does not form volatile hydrides.     

Determination of thallium in environmental samples by activation analysis with fast reactors neutrons

A procedure is described for the determination of thallium in coal fly ash by fast neutron activation analysis using the reaction²⁰³Tl/n, 2n/²⁰²Tl. A 31 h reactor irradiatioon under cadmium cover at a fast neutron flux of 3.05×10¹² n.cm^–2.s^–1 is applied. The simple radiochemical separation involves a wet attack in acids followed by an extraction of Tl/III/into diisopropylether from 0.5M HBr. The radiochemical purity is sufficient for immediate -spectrometry. A value of 5.7±0.7 ppm is found in the NBS 1633a coal fly ash.     

Determination of Cd and Zn by isotope dilution-thermal ionisation mass spectrometry using a sequential analysis procedure

Isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) was used to examine the certified Cd and Zn content of 4 Certified Reference Materials (CRMs); 2 soils: GBW07401 and GBW07405, 1 plant CRM060 and an animal tissue SRM1566a. The CRMs were chosen to be of contrasting origin and Cd:Zn content. Three digestion procedures were compared: (i) an open tube aqua regia procedure (ii) microwave digestion using Teflon bombs and (iii) hydrofluoric acid (HF) digestion using PTFE bombs. The Cd and Zn levels obtained using ID-TIMS all fell within the published certified range for the CRMs. This was the case regardless of the digestion procedure used, although HF digestion tended to yield marginally higher levels than the other procedures and in one instance, Cd in GBW07401, was significantly different (P<0.05) from the certified range. A filament loading procedure was developed, to allow sequential analysis of Cd and Zn on the same single filament during thermal ionisation mass spectrometry analysis. The sequential analysis technique was evaluated to ensure that Zn did not fractionate during Cd analysis and there was no inter-element interference. No marked difference in the precision and accuracy of the isotope ratio measurements were obtained from sequential element analyses on the same filament when compared to individual element analyses for a range of standard solutions or for sample digests. The most efficient procedure in terms of costs and productivity for future work of this kind would be a combination of microwave digestion and sequential analysis of Cd and Zn on the same filament.     

Accuracy in the Isotope Dilution Mass Spectrometry of Uranium in Rubidium Uranium Sulphate Rb2U(SO4)3

Abstract

Problems encountered in the determination of uranium in rubidium uranium sulphate (Rb₂U(SO₄)₃) employing isotope dilution thermal ionisation mass spectrometry (ID-TIMS) are discussed. The positive bias of 0.2 to 0.3% in the determination of uranium in Rb₂U(SO₄)₃ by ID-TIMS with respect to the stoichiometric composition has been resolved by modifying the chemical exchange procedures. The concentration of uranium in Rb₂U(SO₄)₃ could be determined with an accuracy better than 0.1% employing the HClO₄ treatment for proper isotopic exchange between the spike and sample isotopes.     

Factorial design for Fe, Cu, Zn, Se and Pb preconcentration optimization with APDC and analysis with a portable X-ray fluorescence system

Preconcentration of heavy metals in water with ammonium pyrrolydine dithiocarbamate (APDC) is a common practice in analytical chemistry. A literature review on this topic showed that several authors use this precipitation agent, but in different preconcentration conditions, conducting to divergent results. The objective of this work is to use factorial design to optimize the factors involved in the preconcentration process of heavy metals using APDC. Five factors were studied: sample volume, solution pH, APDC concentration, APDC volume and stirring time. The assays were performed by energy dispersive X-ray fluorescence (EDXRF). The values for detection limits within 95% confidence level, in μg L⁻¹, were: Fe (6.0 ± 0.1), Cu (4.0 ± 0.1), Zn (2.0 ± 0.1), Se (4.0 ± 0.1) and Pb (5.0 ± 0.1). The value for quantification limit for the five elements was 20 μg L⁻¹, with 3% deviation. Multi-element standard solutions were prepared. Precipitation procedure was applied in the spiked solutions and the samples were filtered in cellulose ester membrane for quantification measurements. The optimum values obtained were 300 mL of sample solution, pH 4, 1 mL of 2% APDC and 10 min of stirring time. The concentration results obtained for the validation measurements were satisfactory for in situ survey employing a portable instrument.     

On-line solid phase extraction-liquid chromatography–mass spectrometry for trace determination of nerve agent degradation products in water samples

Three primary nerve agent degradation products (ethyl-, isopropyl- and pinacolyl methylphosphonic acid) have been determined in water samples using on-line solid phase extraction-liquid chromatography and mass spectrometry (SPE-LC–MS) with electrospray ionisation. Porous graphitic carbon was employed for analyte enrichment followed by hydrophilic interaction chromatography. Diethylphosphate was applied as internal standard for quantitative determination of the alkyl methylphosphonic acids (AMPAs). By treating the samples with strong cation-exhange columns on Ba, Ag and H form, the major inorganic anions in water were removed by precipitation prior to the SPE-LC–MS determination. The AMPAs could be determined in tap water with limits of detection of 0.01–0.07 μg L⁻¹ with the [M−H]⁻ ions extracted at an accuracy of ±5 mDa. The within and between assay precisions at analyte concentrations of 5 μg L⁻¹ were 2–3%, and 5–9% relative standard deviation, respectively. The developed method was employed for determination of the AMPAs in three natural waters and a simulated waste water sample, spiked at 5 μg L⁻¹. Recoveries of ethyl-, isopropyl- and pinacolyl methylphosphonic acid were 80–91%, 92–103% and 99–106%, respectively, proving the applicability of the technique for natural waters of various origins.     

Deconvolution of liquid scintillation alpha spectra of mixtures of uranium and radium isotopes

A method for the determination of uranium and radium isotopes in water samples is proposed. Liquid scintillation techniques were used for collecting alpha spectra, which were then analyzed by fitting the alpha peaks with overlapping Gaussians. The analysis can quantify the observed isotopes with accuracy depending on the activity of each isotope.In order to simulate the peaks with Gaussian normal distribution functions, the centroid of each peak as well as the full width at half maximum (FWHM) are required, as they depend on the quenching of the sample. For this purpose, samples with known activities of ²²⁶Ra and its decay products and also of the uranium isotopes ²³⁸U and ²³⁴U, at various quenching levels, were used to establish the correlation of the peaks’ shift with the quench effect. In addition, the correlation of the FWHM with the centroid of a peak was determined, using the same procedure.Following the above analysis technique, an average of 97 ± 2% of detection efficiency and a lower limit of detection of 8.2 mBq kg⁻¹ for alpha isotopes were achieved.     

An ultra-clean technique for accurately analysing Pb isotopes and heavy metals at high spatial resolution in ice cores with sub-pg g Pb concentrations

Measurements of Pb isotope ratios in ice containing sub-pg g⁻¹ concentrations are easily compromised by contamination, particularly where limited sample is available. Improved techniques are essential if Antarctic ice cores are to be analysed with sufficient spatial resolution to reveal seasonal variations due to climate. This was achieved here by using stainless steel chisels and saws and strict protocols in an ultra-clean cold room to decontaminate and section ice cores. Artificial ice cores, prepared from high purity water were used to develop and refine the procedures and quantify blanks. Ba and In, two other important elements present at pg g⁻¹ and fg g⁻¹ concentrations in Polar ice, were also measured. The final blank amounted to 0.2 ± 0.2 pg of Pb with ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios of 1.16 ± 0.12 and 2.35 ± 0.16, respectively, 1.5 ± 0.4 pg of Ba and 0.6 ± 2.0 fg of In, most of which probably originates from abrasion of the steel saws by the ice. The procedure was demonstrated on a Holocene Antarctic ice core section and was shown to contribute blanks of only ∼5%, ∼14% and ∼0.8% to monthly resolved samples with respective Pb, Ba and In concentrations of 0.12 pg g⁻¹, 0.3 pg g⁻¹ and 2.3 fg g⁻¹. Uncertainties in the Pb isotopic ratio measurements were degraded by only ∼0.2%.     

Determination of the rate of production and dissolution of biosilica in marine waters by thermal ionisation mass spectrometry

A new method is described for a precise and simultaneous determination of the rate of production and dissolution of biosilica in marine waters, using isotopic dilution technique. No HF or F₂ is required for chemical preparations as the change in isotopic composition is measured on silica producing SiO₂⁻ ions. The seawater sample flask is spiked with ³⁰Si(OH)₄ (<10% of increase in situ concentration) and incubated in in situ conditions. At the end of incubation, changes of the ³⁰Si:²⁸Si ratios in particulate and liquid phases are measured by using a thermal ionisation mass spectrometer Finnigan THQ. The relative analytical precision of the isotopic ratio measurements is <0.5%. The limit of detection of the change in isotopic ratio during incubation is 0.02 atom%. The overall repeatability determined on eight subsamples (average production: 0.23 μM day⁻¹; average dissolution: 0.07 μM day⁻¹) is ±0.02 and ±0.01 μM day⁻¹ for production and dissolution, respectively. Using mass and isotopic balances of the particulate and dissolved phases in the incubation flask, the best estimates for production and dissolution rates are calculated iteratively. This method was applied to 112 samples of marine waters (production, range: 0.00-2.38 μM day⁻¹; dissolution, range: 0.00-1.18 μM day⁻¹).