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)

Abstract

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 + 0.03 M Ti(III) + 0.16 M KCN and 2% (v/v) HNO3 + 0.03 M Ti(IV) + 0.16 M 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 3.2 ng L−1 was achieved with Ti(III) by CVG-ICP-MS. The LOD with Ti(IV) was 6.4 ng L−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 1.0 μg mL−1. Among the hydride forming elements, no interference was observed from As(III) and Se(IV) at 0.5 μg mL−1 level. The depressive effects from Pb(II) and Sb(III) were not significant at 0.1 μg mL−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).

Chemical vapour generation assisted by Cr3+/KCN coupled to atomic fluorescence spectrometry for ultrasensitive determination of cadmium in water and rice samples

“…Such sensitivity brings additional issues to be dealt with, especially signicant contribution of analyte contamination in the reagents to the background intensity unless high purity reagents are used. Regarding the reagents, it should be mentioned that despite the signicant reduction of KCN modier consumption in comparison with previous studies, 22,23,35,36 the use of this modier still poses some risk and proper handling of the waste is advised. The methodology was validated by Cd determination in various certied reference materials of water and it was even found suitable for direct determination of low concentrations of Cd (without any dilution) in samples with a matrix as complex as seawater.…”

“…CVG of Cd has been thoroughly studied throughout recent years employing different approaches. 15–35 A mixture of atomic and molecular volatile species is supposedly formed during CVG. 15–18 It seems that their fraction, as well as CVG efficiency, depends profoundly on the experimental conditions, especially the BH 4 − /acid ratio (pH), but also the oxygen dissolved in the reagents has shown to play a significant role.…”

Atomic spectrometry update: review of advances in atomic spectrometry and related techniques

“…Interference free determinations were possible using ICP-MS when by the methods of standard additions and ID-MS. An identical design of photoreactor was used by Duan et al 36 for the PVG of Sn in the presence of 0.8% acetic acid, with LOQ of 0.02 mg L À1 using ICP-MS. Research in this area suggests that PVG is a highly efficient method of vapour generation for certain analytes, though matrix effects have yet to be fully evaluated to test the analytical utility of the technique for real samples. Catalytic additives to enhance CVG were utilised by Arslan et al 37 to enhance the CVG of Cd. They optimised the CVG process to achieve enhancement in Cd signal by 40-fold, with 3% (m/v) NaBH 4 and {4% (v/v) HCl + 0.03 M Ti III + 0.16 M KCN}, and 35-fold using 3% (m/v) NaBH 4 and {2% (v/v) HNO 3 + 0.03 M Ti IV + 0.16 M KCN}.…”

Determination of sub-ng g−1 Au in geological samples by ion molecule reaction ICP-MS and CH4 plasma modifier

“…Au, 9.225 eV) in the central channel of the plasma. 7,30,31,36 On the other hand, addition of carbon to the plasma can alleviate the interference (oxide or hydroxide ions) on Au at m/z 197, which due to the conversion of MO + species into M + by reaction with C. 27,30,45 Fig. 3b illustrates the signals of oxide and hydroxide ions (TaO + and HfOH + ) in CH 4 -Ar mixed gas (2 mL min À1 CH 4 ) plasma DRC-ICP-MS (normalised to the pure Ar-plasma DRC-ICP-MS) as a function of nebulizer gas ow rates.…”

“…20,24,27,29 The signal enhancement of elements with high ionisation potential (9-11 eV) is mainly due to the increased degree of ionisation in carbon-modied plasma, which due to the charges transfers from C + -species to analyte atoms in the central channel of the plasma discharge. [30][31][32][33][34][35][36] The aim of this work was to develop a reliable method for direct determination of sub-ng g À1 Au in geological samples using ion molecule reaction ICP-MS with a CH 4 plasma modier. The elimination of the interfering 181 Ta 16 O + and 180 Hf 16 OH + on 197 Au was evaluated through the reaction with CH 4 gas in a DRC in combination with the addition of CH 4 gas to the ICP plasma to improve SBR by increasing the poor sensitivity of Au + and decreasing the background signal.…”