Methanol-Enhanced Liquid Electrode Discharge Microplasma-Induced Vapor Generation of Hg, Cd, and Zn: The Possible Mechanism and Its Application

Abstract

Despite increased interest in microplasma-induced vapor generation (μPIVG) over the past several years, applications in real sample analyses remain limited due to their relatively low vapor generation efficiency and ambiguous mechanism. In this work, a novel method using methanol for significantly enhancing the liquid electrode discharge μPIVG efficiency was developed for the simultaneous and sensitive determination of Hg, Cd, and Zn by atomic fluorescence spectrometry (AFS). It is worth noting that the possible enhancement mechanism was investigated via the characterizations of volatile products by AFS, microplasma optical emission spectrometry, online gas chromatography, and gas chromatography–mass spectrometry, which involved the reductive species such as electrons, hydrogen radicals (·H), methyl radicals (·CH3), and other intermediates in the argon plasma adding methanol. Under the optimized conditions, the limits of detection of 0.007, 0.05, and 0.5 μg L–1 were obtained for Hg, Cd, and Zn, respectively, with relative standard deviations of 3.1, 3.7, and 5.2% for these elements, respectively. Vapor generation efficiencies of 90, 83, and 55% were achieved for Hg, Cd, and Zn, respectively, and improved 2.7-, 4.8-, and 7.9-fold, respectively, compared to those obtained in the absence of methanol. The accuracy and practicability of the proposed method were validated by the determination of Hg, Cd, and Zn in a certified reference material (CRM, Lobster hepatopancreas, TORT-3) and crayfish samples collected from three different provinces of China.

Direct and Sensitive Determination of Antimony in Water by Hydrogen-Doped Solution Anode Glow Discharge-Optical Emission Spectrometry Without Hydride Generation

“…The observed difference in the response between Sb­( iii ) and Sb­( v ) [Sb­( iii ) signal was about 13% higher than that of Sb­(V) at pH = 14, Figure S2] partly supports this hypothesis. It is worth noting that the optimized pH for Sb detection by hydrogen-doped SAGD-OES is quite different with other elements (e.g., Cd, Zn, Ag, Hg, In, Pb, Tl, and Bi), as in other previously reported SAGD-OES studies, of which the optimum pH value was typically under 7. − For instance, pH of 3.2 was employed for Cd and Zn detection by SAGD-OES . The results suggest that vapor generation of Sb is more readily affected by H 3 O + ions than other elements.…”

“…Previous studies reported that SAGD-OES typically suffered from the interference of the coexisting metal ions, especially transition metals (Mn, Ni, and Fe). − For instance, Greda et al reported that with the addition of 10 mg L –1 Na, K, Mg, and Ca, the recoveries of Ag, Cd, Hg, In, Pb, and Zn did not exceed 70% . Moreover, the presence of Fe and Mn at 10 mg L –1 depressed the signal of Bi (0.5 mg L –1 ) to less than 20% …”

“…For example, the reported LOD for the direct detection of Sb in liquid samples by SCGD-OES was as high as 2100 μg L –1 , which was insufficient for Sb detection in most cases . In contrast to SCGD, SAGD offers much better sensitivity for several elements, likely a result of simultaneous vapor generation and excitation in the same plasma. − Therefore, the performance of SAGD-OES for the direct detection of Sb was first evaluated and compared with SCGD-OES. As shown in Figure a, no Sb emission could be observed with the use of He-SCGD-OES even at a concentration of 2 mg L –1 Sb.…”

“…In recent years, OES-based microplasma sources have received increasing attention because of their potential to be developed into compact, low-cost, and portable instruments. Different microplasma sources, for example, microwave-induced plasma, solution cathode glow discharge (SCGD), − low-power capacitively coupled plasma (CCP), dielectric barrier discharge (DBD), − point discharge (PD), atmospheric pressure glow discharge (APGD), − and solution anode glow discharge (SAGD), − have been developed, and some of them have also been employed for Sb measurement. In 2014, Frentiu et al evaluated the use of hydride generation (HG)-CCP-OES for the sensitive determination of Sb in soil samples.…”

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

“…Plasma induced vapour generation (PIVG) has become popular over the last few years, but its application has been mostly limited to synthetic ‘samples’. Pan et al 32 aimed to address this by investigating methanol enhancement for liquid electrode PIVG. The VG manifold was constructed of a PMMA chip into which a tungsten rod (1.6 mm in diameter), and a stainless-steel tube (0.6 mm i.d.…”