Abstract
A simple and rapid spectrometric determination of micro amounts of palladium using 4-(2-pyridylazo)-resorcinol(PAR) and EDTA was described. It has been known that Pd(II) reacts with PAR to form four kinds of stable 1 : 1 chelates, one of them was green at pH below 4 and the others were red at pH above 4. The water soluble red complex at pH 10.311 had an absorption maximum at 520 nm in 0.01 M EDTA. EDTA (0.1 M) the pH of which was adjusted at 10.5 with sodium hydroxide had rather strong buffer action, and 5 ml of the solution was used to the test solution before the addition of 0.5 ml of 0.1% PAR per 50 ml of each solution to be measured; i.e. by the use of the EDTA solution, not only a masking of diverse ions also a buffer action at pH 10.5 had been achieved. It was necessary to warm the test solution after addition of PAR, because in the presence of some elements such as V or As, the formation of Pd-PAR chelates was very slow and gave low values for palladium contents. Beer's law was confirmed over the range of 0100 μg Pd(II) in 50 ml and sensitivity which gave the absorbance of 0.001 was 0.0043 μg Pd(II)/cm2. In the above method, when a large amount of diverse ions such as cobalt(II) or iron(II) etc. are present, the solvent extraction separation was employed. To the sample solution, 2 ml of 0.1 M EDTA, 0.5 ml of PAR and 5 ml of 0.1 M NaH2PO4 were added. The solution was adjusted to pH 2 with 0.1 M H3PO4 and was warmed in a water bath at 80 °C for 10 min. and was cooled.
The green chelate formed was extracted twice by 5 ml each of the methylisobutyl-ketone (MIBK) and this chelate in organic phase was back-extracted rapidly into an aqueous alkaline solution. Five ml of 0.1 M EDTA (pH 10.5) could be used for this alkaline solution and then the aqueous phase was separated after back-extraction and was diluted to 50 ml with water to provide the solution for measurement. The calibration curve almost agreed with that obtained when the extraction separation had not been employed.
