Co-crystallization with 1-(2-pyridylazo)-2-naphthol, and X-ray fluorescence, for trace metal analysis of water

Adding 20mg of 1-(2-pyridylazo)-2-naphthol (PAN) to a water sample at 70 degrees , and filtering off the precipitate after cooling, gives efficient preconcentration prior to X-ray fluorescence analysis of water. Up to the capacity of about 100 mueq of PAN used, the trace metal recoveries are around 90% or higher for Cr(3+), Mn(2+), Ni(2+), Cu(2+), Zn(2+), Hg(2+) and Eu(3+), and above 70% for many other ions. The recovery yields usually do not vary critically with pH in the neutral pH-range, and are practically independent of the sample salinity, sample volume and trace-metal concentration. Enrichment factors as high as 2 x 10(5) can be achieved. Counting statistics would then allow detection limits of 0.03 ppM. The blank levels in commercial PAN, however, lead to typical detection limits of about 1 ppm. The coefficient of variation is typically in the 5-10% range at the 10-ppM level. The accuracy and applicability of the procedure are illustrated by comparative analyses on samples of synthetic solutions, river and drinking water.