Determination of As, Hg and Pb in herbs using slurry sampling flow injection chemical vapor generation inductively coupled plasma mass spectrometry.
Analysis of herbs for As, Hg and Pb has been carried out using slurry sampling inductively coupled plasma mass spectrometry (ICP-MS) with flow injection vapor generation. Slurry containing 0.5% m/v herbal powder, 0.1% m/v citric acid and 2% v/v HCl was injected into the VG-ICP-MS system for the determination of As, Hg and Pb that obviate dissolution and mineralization. Standard addition and isotope dilution methods were used for quantifications in selected herbal powders. This method has been validated by the determination of As, Hg and Pb in NIST standard reference materials SRM 1547 Peach Leaves and SRM 1573a Tomato Leaves. The As, Hg and Pb analysis results of the reference materials agreed with the certified values. The precision obtained by the reported procedure was better than 7% for all determinations. The detection limit estimated from standard addition curve was 0.008, 0.003, and 0.007 ng mL(-1) for As, Hg and Pb, respectively.
Flexible liquid crystal polymer-based electrochemical sensor for in-situ detection of zinc(II) in seawater
AbstractThe authors describe a liquid crystal polymer (LCP) based bismuth (Bi) film electrode that can be directly deployed for in-situ determination of zinc(II) ions. The use of an LCP warrants improved operational reliability, high durability, and flexibility of the sensor, allowing it to be mounted on any flat or shaped surface. Square wave anodic stripping voltammetry shows the sensor to be able to detect Zn(II) (−1.64 V vs. thin-film Ag/AgCl reference electrode) in concentrations as low as 1.22 nM at a deposition time of 180 s. Other figures of merit include (a) an analytical sensitivity of 1.55 nA∙nM−1∙mm−2, (b) a linear detection range extending from 4.59 to 1071 nM, (c) a repeatability with a relative standard deviation of 3.35% (for n = 10), (d) a reproducibility with a relative standard deviation of 1.64% (for n = 6). Real-time applicability of the sensor for in-situ detection was demonstrated by determination of Zn(II) in seawater. In an extension of the method, a flexible sensor array consisting of four LCP-based sensors was attached to the hull of an autonomous kayak, which was remotely operated. The response of the sensor array indicated a clear trace of Zn(II) concentrations in seawater. This was confirmed by ICP-MS analysis. The results suggest the potential usage of the flexible LCP electrochemical sensor for in-situ monitoring.
 Graphical abstractSchematic presentation of a flexible liquid crystal polymer based electrochemical sensor. Real-time application of the sensor for in-situ Zn(II) detection is demonstrated by performing sea trial testing with a sensor array attached to an autonomous kayak.
New method for analysis of enzymatic reactions: Thermolysin-catalyzed synthesis of aspartame precursor
Aspartame is an artificial sweetener which is 200 times sweeter than sucrose. A precursor of aspartame, N-(benzyloxycarbonyl)-l-aspartyl-l-phenylalanine methyl ester (Z-APM) was synthesized and hydrolyzed with thermolysin in an aqueous monophasic system. Graphical plotting methods and/or nonlinear regression have been used to analyze enzymatic reactions because of the nonlinearity of enzymatic rate equations. There are, however, problems: the former require accurate measurement of the initial reaction rate and the latter gives no analytical information. The authors proposed a method to solve the nonlinear enzymatic rate equations with respect to the concentration of a product with the Taylor expansion, especially for the reversible Theorell-Chance mechanism (Murakami, Y., Hirata, M., and Hirata, A., J. Ferment. Bioeng., 82, 246–252, 1996). This solution, however, is complex for practical use. In this paper, a simpler solution to explain the thermolysin-catalyzed synthesis of Z-APM is obtained. New methods to determine the kinetic parameters, especially for the reversible Theorell-Chance mechanism, based on the approximated solution are proposed. The results calculated using the obtained kinetic parameters can satisfactorily explain the experimental results, which demonstrates the effectiveness of the proposed analysis. We must know the relation between the concentrations of substrates and a product, and accurately evaluate of the result obtained using Taylor expansion when we determine the kinetic parameters using our newly developed methods. The methods to determine the kinetic parameters of the reversible Theorell-Chance mechanism described in this paper is, however, expected to be applied to general enzymatic reactions.