Titrimetry is one of the few classical analytical methods that are still used for many applications. In this tutorial review, approaches to automatic titration based on flow analysis are briefly described. These include flow injection titration, sequential injection titration, flow ratiometric titration, gradient flow titration, triangular programmed coulometric titration and monosegmented flow titration.
Since the introduction of the catalytic cleaning of vehicle exhaust gases, platinum is discussed as environmentally relevant element. Increasing Pt concentrations have been reported from a number of countries. The determination of platinum in biological and environmental materials at the "natural" level was made possible by the development of extremely sensitive analytical methods. Two different sorbents for platinum preconcentration in catalyst, water, soil and vegetation were investigated: silica gel hnctionalized with 1,s-bis(di-2-pyridyl)methylene thiocarbohydrazide (DPTH-gel) and [1 ,5-Bis(2-pyridyl)-3-sulphophenyl methylene thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex 1 x 8-2OO)]. The sorbents were tested in a microcolumn, placed in the autosampler arm, at the flow rate 2.4 ml min-1. Elution was performed with 2 M nitric acid. Satisfactory results were obtained for two sorbents.
An accurate, precise and simple flow injection quantitative method for the determination of a-methyldopa in pharmaceutical formulations is proposed. The method is based on the reaction between a-methyldopa and p-aminophenol in strong alkaline medium. The reaction product is determined spectrophotometrically at 608 nm. Five pharmaceutical preparations purchased in the local market were analyzed. The results were compared with those obtained with the spectrophotometric United States Pharmacopoeia method. The statistical Student's t-test was applied to compare the results obtained with the two independent methods. In all cases complete agreement was observed, in a confidence level of 95% (α=0.05). Considering five samples analyzed using the proposed method and three determinations for each sample, the observed mean relative standard deviation, RSD, is about 1.7 %. The working analytical range, considering the final solution, is between 2×10-4 mol L-1 and 3×10-3 mol L-1. The correlation coefficient R of the analytical quadratic curve is 0.99998. The detection limit is about 0.3×10-4 mol L-1 in the final solution introduced in the flow system (3×SD of the blank) and 48 determinations can be performed per hour.
This review summarizes a potentiometric flow injection method for the determination of several redox species by using both a redox potential buffer solution consisting of a redox couple such as Fe(III)-Fe(II), Fe(CN)63--Fe(CN)64- and bromide-bromine, and a platinum electrode or a combined platinum-bromide ion selective electrode. The analytical principle and advantages of the proposed method are described and several examples of its application are demonstrated.