Statistical mixture design development of digestion methods for Oyster tissue using inductively coupled plasma optical emission spectrometry for the determination of metallic ions.

The quantitative determination of chemical elements in organic or biological samples is an important analytical problem. Normally the elements to be determined in the organic matrix must be transformed into a simple inorganic form. A digestion method by heating on a block digestor has been developed for the determination of Al, As, Ba, Ca, Cd, Co, Cu, Fe, Mg, Mn, V and Zn in Oyster tissue by ICP OES. A simplex centroid statistical mixture design has been used to study the effects of changing HNO(3), HCl and H(2)O(2) reagent proportions on the digestion of these samples. Response surface and principal component analyses show that the species Ca, Cd, Cu, Fe, Mg, Mn and Zn have very similar analytical tendencies under this experiment. By means of mixture modeling maximum recoveries for these ions were predicted using 19%, 18% and 63% of the HCl, HNO(3) and H(2)O(2) pseudocomponent mixtures, respectively. This corresponds to 21.4%, 30.8% and 47.8% of the HCl, HNO(3) and H(2)O(2) commercial solutions. Furthermore the As, Co and V ions present large recoveries for these mixtures as well. The Al and Ba ion recoveries are seen to be independent of the mixture proportions. The analysis of Oyster tissue reference material (SRM 1566b - NIST) under optimized conditions at the selected wavelengths resulted in ion recoveries between 90% and 100%.

Use of silica gel chemically modified with zirconium phosphate for preconcentration and determination of lead and copper by flame atomic absorption spectrometry.

An analytical method using silica gel chemically modified with zirconium (IV) phosphate for preconcentration of lead and copper, in a column system, and their sequential determination by flame atomic absorption spectrometry (FAAS), was developed. Sample solutions are passed through a glass column packed with 100 mg of the sorbent material, at pH 4.5, and lead and copper are eluted with 1.0 mol l(-1) HNO(3) at a flow rate of 2.0 ml min(-1). The extraction of copper is affected by Fe(II), Mn(II), Zn(II), Ni(II) and Co(II) while only Fe(II) interferes in the lead determination. These interferences may be overcome with an appropriate addition of a KI or NaF solution. An enrichment factor of 30 was obtained for both metals. While the limits of detection (3sigma) were 6.1 and 1.1 microg l(-1), for Pb and Cu, respectively, the limits of determination were 16.7 and 3.3 microg l(-1). The precision expressed as relative standard deviation (R.S.D.) obtained for 3.3 microg l(-1) of Cu and 16.7 microg l(-1) of Pb were 4.3 and 4.7%, respectively, calculated from ten measurements. The proposed method was evaluated with reference material and was applied for the determination of lead and copper in industrial and river waters.

Determination of bismuth in urine and prescription medicines using atomic absorption with an on-line hydride generation system.

The bismuth contents of various digested urine samples and prescription medicines were determined by atomic absorption spectrometry combined with hydride generation. The procedure followed was a standard addition method for urine and direct calibration for the prescription medicines. The detection limit of the method was determined to be 320 pg ml-1 Bi with an analytical frequency of 150 h-1. A relative standard deviation of 4.7% was found for Bi in urine at the level of 4.3 ng ml-1 Bi. Interference caused by NiII, CoII, CuII, AgI, SeIV, SbIII and HgII could be controlled with a masking solution of thiourea (0.2%)-KI (10%).