An electrochemical method for the simultaneous determinations of Hg" concentration and total As"' and AsV concentration has been developed. The method does not require the additional preliminary step of the chemical reduction of AsV to As"', or oxidation of As"' to AsV before stripping analysis takes place. Also, the method for the simultaneous determination of Hg" concentration and As"' concentration is described. Measurements were performed in 0.1 M HCI using a gold-plated graphite electrode as sensor. Detection limits for both methods are below 0.4ppb. Relative standard deviation did not exceed 15 70. The possible interference by other trace metals was investigated. Analyses of natural water and industrial solutions were made using proposed methods and AAS. The t-test demonstrates that there was no significant difference between the results obtained with these methods. Proposed methods decrease the time of analysis because concentrations of the Hg" and arsenic ions were measured simultaneously. Also, the removal of the additional step of chemical reduction of AsV to AsIn or oxidation of As"' to AsV decreases analysis time, and also reduces the chance of contamination due to the use of additional reagents.
Use of optimized instrument parameters that result from statistical experimentation revealed that the sensitivity of atmospheric pressure chemical ionization (APCI) liquid chromatography-mass spectrometry (LC/MS) is greater than the sensitivity of an optimized Thermabeam™ LC/MS interface by about 3 orders of magnitude, when tested on aromatic compounds. APCI is one of the few LC/MS techniques in which the chromatogram is directly comparable with liquid chromatographs that use ultraviolet detection. The optimum instrument parameters for a Finnigan SSQ-7000 APCI LC/MS interface were found at low flow rates (e. g., 0. 1 mL/min), relatively low capillary heat (e. g., 225 °C), and high sheath-gas pressure (e. g., 60 lb/in(2)). The optimization was achieved by monitoring the responses of sensitivity, fragmentation, and cluster ion formation. The fine tuning for high sensitivity calls for a high percentage of water in the mobile phase. In contrast, a high percentage of organic content in the mobile phase is required to obtain abundant protonated molecular ions with respect to fragmentation and clustering. This is an important consideration for analyses of unknowns.
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