Volatile Cd Species Research Articles

Sensitive Determination of Arsenic by Photochemical Vapor Generation with Inductively Coupled Plasma Mass Spectrometry: Synergistic Effect from Antimony and Cadmium.

A novel method for the determination of trace arsenic (As) by photochemical vapor generation (PVG) with inductively coupled plasma mass spectrometry measurement was developed in this study. The synergistic effect from antimony (Sb) and cadmium (Cd) was found for the photochemical reduction of As for the first time. Effective photochemical reduction of As was obtained in the system containing 10% (v/v) acetic acid, 5.0 mg L-1 Sb(III), and 20.0 mg L-1 Cd(II) with 100 s UV irradiation. Analytical sensitivity of As(III) was comparable with that of As(V) under the tested conditions, making direct determination of total As feasible. Compared to the pneumatic nebulization method, analytical sensitivity of the developed method was enhanced about 50 folds. The PVG efficiency was estimated up to be 99 ± 3%. The limit of detection (LOD) (3σ) was found to be 2.1 ng L-1 for As, which was improved about 30-fold compared to that using direct sample introduction solution nebulization. Considering the sample dilution prior to analysis (usually one-fold), the LOD was actually enhanced about 15 folds. The relative standard deviations of seven replicate measurements of 1.0 μg L-1 As(III) and As (V) standard solutions were 2.3 and 2.9% for As(III) and As(V), respectively. The proposed method was successfully applied for the detection of As in certified reference materials of sediments (GBW07303a and GBW07305a), as well as three water samples. The mechanism of the PVG system was investigated by using gas chromatography mass spectrometry, electron paramagnetic resonance, and X-ray photoelectron spectroscopy. (CH3)3As along with (CH3)3Sb were synthesized under UV irradiation. Besides, volatile species of Cd were also found. The result obtained in this study is useful for developing efficient "sensitizers" in PVG and understanding the transformation of As in the presence of hydride/cold vapor forming elements in the photochemical process.

Efficient generation of volatile cadmium species using Ti(III) and Ti(IV) and application to determination of cadmium by cold vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS)

In this study, a highly efficient chemical vapor generation (CVG) approach is reported for determination of cadmium (Cd). Titanium (III) and titanium (IV) were investigated for the first time as catalytic additives along with thiourea, L-cysteine and potassium cyanide (KCN) for generation of volatile Cd species. Both Ti(III) and Ti(IV) provided the highest enhancement with KCN. The improvement with thiourea was marginal (ca. 2-fold), while L-cysteine enhanced signal slightly only with Ti(III) in H2SO4. Optimum CVG conditions were 4% (v/v) HCl+0.03M Ti(III)+0.16M KCN and 2% (v/v) HNO3+0.03M Ti(IV)+0.16M KCN with a 3% (m/v) NaBH4 solution. The sensitivity was improved about 40-fold with Ti(III) and 35-fold with Ti(IV). A limit of detection (LOD) of 3.2ngL−1 was achieved with Ti(III) by CVG-ICP-MS. The LOD with Ti(IV) was 6.4ngL−1 which was limited by the blank signals in Ti(IV) solution. Experimental evidence indicated that Ti(III) and Ti(IV) enhanced Cd vapor generation catalytically; for best efficiency mixing prior to reaction with NaBH4 was critical. The method was highly robust against the effects of transition metal ions. No significant suppression was observed in the presence of Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Ni(II) and Zn(II) up to 1.0μgmL−1. Among the hydride forming elements, no interference was observed from As(III) and Se(IV) at 0.5μgmL−1 level. The depressive effects from Pb(II) and Sb(III) were not significant at 0.1μgmL−1 while those from Bi(III) and Sn(II) were marginal. The procedures were validated with determination of Cd by CVG-ICP-MS in a number certified reference materials, including Nearshore seawater (CASS-4), Bone ash (SRM 1400), Dogfish liver (DOLT-4), Mussel tissue (SRM 2976) and Domestic Sludge (SRM 2781).

Efficient generation of volatile species for cadmium analysis in seafood and rice samples by a modified chemical vapor generation system coupled with atomic fluorescence spectrometry

A vapor generation procedure to determine Cd by atomic fluorescence spectrometry (AFS) has been established. Volatile species of Cd are generated by following reaction of acidified sample containing Fe(II) and l-cysteine (Cys) with sodium tetrahydroborate (NaBH4). The presence of 5mgL−1 Fe(II) and 0.05% m/v Cys improves the efficiency of Cd vapor generation substantially about four-fold compared with conventional thiourea and Co(II) system. Three experiments with different mixing sequences and reaction times are designed to study the reaction mechanism. The results document that the stability of Cd(II)–Cys complexes is better than Cys–THB complexes (THB means NaBH4) while the Cys–THB complexes have more contribution to improve the Cd vapor generation efficiency than Cd(II)–Cys complexes. Meanwhile, the adding of Fe(II) can catalyze the Cd vapor generation. Under the optimized conditions, the detection limit of Cd is 0.012μgL−1; relative standard deviations vary between 0.8% and 5.5% for replicate measurements of the standard solution. In the presence of 0.01% DDTC, Cu(II), Pb(II) and Zn(II) have no significant influence up to 5mgL−1, 10mgL−1and 10mgL−1, respectively. The accuracy of the method is verified through analysis of the certificated reference materials and the proposed method has been applied in the determination of Cd in seafood and rice samples.

Cyanovanadate(III) complexes as novel additives for efficient generation of volatile cadmium species in complex samples prior to determinations by inductively coupled plasma mass spectrometry (ICP-MS)

A new method has been described for generation of volatile species of Cd using vanadium(III) cyanide complex. Aqueous solutions of 0.04molL−1 vanadium chloride (VCl3) and 0.12molL−1 potassium cyanide (KCN) were reacted on-line yielding a suspension of vanadium hydroxide, V(OH)3. This suspension was dissolved along the stream of sample solution in dilute HCl to form heptacyanovanadate(III) complex, [V(CN)7]4−. Volatile Cd species were generated by reacting the stream of sample solution and cyanovanadate(III) complex with sodium borohydride (NaBH4). Feasibility of off-line and on-online approaches was investigated for quantitative determinations. Better precision and daily stability were achieved with on-line settings. Optimum signals were obtained from sample solutions within a range of 3 to 5% v/v HCl. A concentration of 2% m/v NaBH4 was adequate to achieve an enhancement of 20-fold in the presence of cyanovanadate(III) complex. The limits of detection were 5.0 and 4.5ngL−1 for 110Cd and 111Cd isotopes, respectively. Precision (%RSD) was better than 4.7% for six replicate measurements. The interferences of Cu(II) and Ni(II) were marginal (<10%) at 1.0µgmL−1. Depressive effects from Bi, Se and Sn were not significant below 0.1µgmL−1. The method was validated by determination of Cd using ICP-MS in certified reference materials of Nearshore seawater (CASS-4), Bone ash (SRM 1400), Dogfish liver (DOLT-4) and Mussel tissue (SRM 2976).

Application of the high-speed self-reversal background corrector to the determination of cadmium by chemical vapor generation atomic absorption spectrometry

Concentrations of cadmium (Cd) in extracting solutions (neutral salts) from contaminated soils are often too low to be determined by conventional flame atomic absorption spectrometry. For this reason, determination of Cd requires sensitive analytical methods free from interference problems generated by samples. In this context, vapor generation atomic absorption spectrometry (HGAAS) was combined with a high-speed self-reversal background corrector. This new approach was successfully applied after optimization of the analytical parameters to obtain a maximal absorbance signal of the volatile Cd species. The optimum condition was achieved with a 3% (m/v) NaBH4 in 1.5% (m/v) NaOH reducing solution and a solution containing 0.3 mol/L HNO3. The detection limit was 1 ng mL–1 under the previous conditions and the relative standard deviation was up to 5% for 10 replicate analyses of Cd at 0.2 and 1 ng mL–1, reflecting a very highly sensitive and reproducible method. Moreover, the results showed that the proposed combination was an efficient method to overcome the interference problems caused by different coexisting cations, As, Al, Ca, Cu, Fe, Mg, Mn, Ni, Pb, Se and Zn, up to 10 µg mL–1. The method was validated with analyses of two standard reference materials and was used for Cd determination in 0.01 mol/L CaCl2 extracts from contaminated kitchen garden soils. The data were compared with those obtained by two other more conventional methods, electrothermal atomic absorption spectrometry (ETAAS) and flame atomic absorption spectrometry (FAAS). The analytical results obtained by the ETAAS and HGAAS were in a good agreement, suggesting the suitability of the method for Cd determination in 0.01 mol/L CaCl2 extracting solution.

On-line chemical vapour generation of cadmium in the presence of hexacyanochromate(iii) for determination by inductively coupled plasma mass spectrometry (ICP-MS)

A vapour generation (VG) procedure has been described for determination of Cd by ICP-MS. Volatile species of Cd were generated on-line by interacting acidic sample solution containing potassium hexacyanochromate(III), K3Cr(CN)6, with sodium borohydride (NaBH4). The hexacyanochromate(III) complex was generated on-line by reacting 0.04 mol L-1 chromium(III) nitrate and 0.16 mol L-1 potassium cyanide (KCN) solutions in water. The resulting suspension of chromium(III) hydroxide, Cr(OH)3, was fed continuously to acidic stream of sample solution in the presence of excess KCN. The experimental conditions were optimized for effective generation of volatile species of Cd. Optimum signals were obtained from reaction of sample solutions in 4% v/v HCl with 2% m/v NaBH4 solution. Presence of K3Cr(CN)6 improved the efficiency of Cd vapour generation substantially affording 15-fold higher sensitivity. This phenomenon was thought to occur through formation of reactive intermediates evolved from interaction of [Cr(CN)6]3- with NaBH4 that react with Cd(II) to increase the yield volatile Cd species. Under the optimum conditions, no significant interferences were observed from the transition metals, including Cu and Ni, up to 1.0 μg mL-1 levels. Among the hydride forming elements, Bi, Pb, Sb and Sn depressed the signals above 0.1 μg mL-1. The detection limits (3s) were 6.2 and 5.2 ng L-1 for 110Cd and 111Cd isotopes, respectively. The method was successfully applied to determination of Cd by ICP-MS in several certified reference materials, including Nearshore seawater (CASS-4), Bone ash (SRM 1400), Dogfish liver (DOLT-4) and Mussel tissue (SRM 2976).

Simultaneous determination of trace cadmium and mercury in Chinese herbal medicine by non-dispersive atomic fluorescence spectrometry using intermittent flow vapor generator.

A method was proposed for the simultaneous determination of trace cadmium and mercury by vapor generation non-dispersive atomic fluorescence spectrometry using an intermittent flow system. The effects of the parameters on the performance were studied systematically. The parameters such as acid concentration of the reaction medium, flow rate of the carrier gas and shield gas, the observation height and the atomizer temperature, etc. which affected the sensitivity, were optimized. Ascorbic acid, cobalt ion and thiourea were used as enhancement reagents or masking agents to enhance the generation efficiency of the volatile species of Cd and Hg. The mechanisms of their effects on vapor generation were investigated. In the presence of thiourea and ascorbic acid, the influences of some coexisting elements on the determination of cadmium and mercury were investigated. The detection limits (3sigma) were 0.010 microg l(-1) for Cd and 0.019 microg l(-1) for Hg, respectively. The relative standard deviations for Cd and Hg at 1.00 microg l(-1) were 2.6% and 0.97% (n = 11), respectively. The proposed method has been satisfactorily applied to the determination of trace cadmium and mercury in Chinese herbal medicine.

Determination of cadmium in environmental samples by hydride generation with in situ concentration and atomic absorption detection.

A volatile Cd species (presumed to be the hydride) was generated from aqueous solutions by merging sample and tetrahydroborate reductant in a continuous-flow system. The gaseous analyte was transferred onto the inner wall of a graphite tube furnace for in situ preconcentration at 200 degrees C. Calibration was achieved via the method of standard additions. An absolute detection limit (3 sigma blank) of 10 pg was obtained using KBH4 as reductant. The precision of the determination was 12% (RSD) for a Cd concentration of 0.2 ng ml-1 using KBH4. The method was successfully applied to the determination of Cd in several certified environmental reference materials (soil, sediment, sea-water, biological samples) following pressure digestion of the samples by microwave heating in a mixture of acids.

Sensitive inductively coupled plasma atomic emission spectrometric determination of cadmium by continuous alkylation with sodium tetraethylborate

Continuous flow generation of volatile Cd species using NaBEt4 as a means of gaseous sample introduction into an inductively coupled plasma atomic emission spectrometry (ICP-AES) instrument has been investigated in detail. The assumed generation of CdEt2 is discussed and critically evaluated in terms of the sensitivity, selectivity and accuracy of the corresponding ICP-AES determination of low levels of Cd. The proposed method for the determination of Cd by ICP-AES using NaBEt4 provided detection limits of 0.4 ng ml–1, which are ten times better than those of conventional nebulization ICP-AES. A precision of ± 1.4% at the 50 ng ml–1 level of Cd was observed. Interference studies have been carried out, which demonstrated high selectivity of the proposed method. This method has been applied to the determination of low levels of Cd by ICP-AES in samples of sea-water and tea infusions. Satisfactory validation of the results obtained has been provided by electrothermal atomic absorption spectrometric analysis of the same samples.

Surfactant-based ordered media in analytical atomic spectrometry

During the last 10 years or so we have witnessed an enormous growth of interest and applications of surfactant-based ordered media in analytical chemistry. However, their use in analytical atomic spectroscopy (AAS) has been rather scarce and often controversial. The utilization of surfactants in this latter field is discussed here along two main lines: one refers to the favourable manipulation of physical properties of the sample solutions (Part A) while the other, demonstrated very recently, refers to the adequate manipulation of chemical reactions and/or interactions of analytes in solution by resorting to surfactants use (Part B). The control of physical properties of sample solutions, e.g. manipulation of the surface tension, allows three main applications of surfactants in atomic methods: possible increases of nebulization/atomization efficiencies in flame-AAS, improvement of aqueous/organic solvent compatibility (emulsification applications) and enhancement of the wettability of graphitic solid surfaces. The facts and controversies existing today on this method of utilization of surfactants to enhance atomic methodologies is critically discussed. The ability of surfactant-based “ordered media” to organize reactants at the molecular level has also been applied to enhance chemical generation of volatile species ( e.g. hydride generation or cold Hg vapour generation) used in atomic methods. The analytical potential and usefulness of micelles and vesicles to improve the detection power of hydride generation ICP-AES methodologies are summarized for the determination of arsenic, lead and cadmium by plasma emission. Increases up to two-fold in the sensitivity of As and Pb have been observed by addition of organized media. A volatile Cd species is formed very easily in cationic vesicles with NaBH 4. This Cd species can be used to increase by five times the detectability of Cd by ICP-AES. Moreover, synergic combinations of liquid chromatography separations/atomic detection are possible by resorting to the use of micellar or vesicular mobile phases. The successful application of this principle to the modern problem of toxic arsenic HPLC speciation by using a vesicular solution [as mobile phase for the HPLC separation of As(III), As(V), monomethylarsonic and dimethylarsinic acids] and “on-line” surfactant-enhanced arsine generation is also described in detail and completes the whole picture of the present interface between analytical atomic spectroscopy and surfactant assemblies.