Integration of Flow Injection Capillary Liquid Electrode Discharge Optical Emission Spectrometry and Microplasma-Induced Vapor Generation: A System for Detection of Ultratrace Hg and Cd in a Single Drop of Human Whole Blood

Abstract

A simple and miniature analytical system was developed to determine Hg and Cd in small amounts of samples by integrating flow injection capillary liquid electrode discharge (CLED) optical emission spectrometry (OES) and microplasma-induced vapor generation (PIVG) atomic fluorescence spectrometry (AFS). With the assistance of the inherent capillary driving force and the force arising from the solution vaporization in the microplasma, the sample solution was automatically transported into the discharge chamber wherein analytes were simultaneously excited to generate their atomic emission lines and converted to their volatile species. Subsequently, the volatile species were further swept into AFS for their further determination. Therefore, the same sample could be successively analyzed by OES and AFS. Owing to the unique independent linear-range and sensitivity of CLED-OES and PIVG-AFS, the developed system not only significantly extended its linear range to 6 orders of magnitude but also remarkably reduced the sample consumption to several microliters. Thus, wide linear-range and ultrasensitive determination of Hg and Cd in limited amounts of samples were accomplished simply by sharing one single capillary liquid electrode discharge source. Under the optimized conditions, limits of detection (LODs) of 10 μg L −1 were obtained for both Hg and Cd when CLED-OES was used as a detector, whereas the LODs for Hg and Cd were improved to 0.03 μg L −1 and 0.04 μg L −1 with AFS detector, respectively. In addition, the extremely wide linear-range of 0.001−100 mg L −1 and 0.001−40 mg L −1 were obtained for Hg and Cd, respectively. The potential application of this method was validated by successfully analyzing three Certified Reference Materials (ZK021-1, GBW(E)090033, and GBW(E)090034) and six human blood samples.

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

“…The results show that the obvious responses of Zn and Cd were detected as their concentrations beyond 5 mg L −1 . These results imply that most of the volatile species of Cd and Zn are molecular substances, which is different from those reported by the μPIVG using H 2 , 18,20,21,24,30 thus suggesting that μPIVG using methanol presents a different behavior compared to that using H 2 .…”

“…The analytical performance of Hg obtained by the proposed system is comparable or superior to the other reported systems. 16,20,53,54 On the other hand, the LODs for Cd and Zn are comparable to those obtained by DBD-plasma CVG but worse than those obtained by solution anode glow discharge (SAGD) and nonionic surfactant-enhanced thin-film dielectric barrier discharge plasma (NIS-enhanced TFDBD). 24,27,30,33,53 However, highly flammable, explosive, and colorless hydrogen gas is not required in the proposed method, which not only simplifies the experimental setup but also eliminates the danger of hydrogen storage and transport.…”

“…These results indicate that the generated volatile species of Hg is mercury cold vapor (Hg 0 ), which agreed well with a previous report. 20 For Cd and Zn, typical atomic fluorescence signals were obtained with the Ar−H 2 flame, whereas no obvious signal was observed without the Ar−H 2 flame. Since previous works reported that free atoms of Cd and Zn could be easily detected by hydrogenassisted μPIVG-AFS under the flameless conditions, 18,20,21,24,27,30 we speculated that the free atoms of Cd and Zn could be also generated by the proposed method but their concentrations were too low to be detected.…”

“…20 For Cd and Zn, typical atomic fluorescence signals were obtained with the Ar−H 2 flame, whereas no obvious signal was observed without the Ar−H 2 flame. Since previous works reported that free atoms of Cd and Zn could be easily detected by hydrogenassisted μPIVG-AFS under the flameless conditions, 18,20,21,24,27,30 we speculated that the free atoms of Cd and Zn could be also generated by the proposed method but their concentrations were too low to be detected. To prove this speculation, various concentrations of Cd and Zn were tested under flameless conditions, as shown in Figure S4.…”

Headspace Solid-Phase Microextraction Following Chemical Vapor Generation for Ultrasensitive, Matrix Effect-Free Detection of Nitrite by Microplasma Optical Emission Spectrometry

“…Recently, the application scope of microplasma optical emission spectrometry (MP-OES) has been significantly extended from metal ions (Hg, Cd, As, Pb, etc. ) − to nonmetallic analytes (total organic carbon, NH 3 , NO 3 – , NO 2 – , and carboxyl group) − when chemical vapor generation (CVG) was used as a sample introduction means. Although CVG coupling to MP has been successfully used to determine nitrite via monitoring the molecular emission of NO, the nitrogen contained in discharge gas resulted in a high blank, thus deteriorating the analytical performance. , …”