No abstract

A determination method for lead in waste water and effluent was studied using flame atomic absorption spectrometry after preconcentration of lead by the rapid coprecipitation technique with gallium phosphate. Lead ranging from 0.5 to 50 microg was quantitatively coprecipitated with gallium phosphate from 100-150 mL sample solution (pH approximately 5). The presence of gallium phosphate did not affect the atomic absorbance of lead. Since the concentration of gallium in the final sample solution is also measurable by flame atomic absorption spectrometry at 250.0 nm without further dilution, the rapid coprecipitation technique, which does not require complete collection of the precipitate, becomes possible using a known amount of gallium and measuring the concentrations of both lead and gallium in the final sample solution by flame atomic absorption spectrometry. The 32 diverse ions tested gave no significant interferences in the lead determination. The method proposed here is rapid and has good reproducibility.

Experimental ApparatusA Hitachi 170-50 atomic absorption spectrometer with an iron, lead, or indium hollow-cathode lamp (Hitachi or By applying an internal standardization, we could use a rapid coprecipitation technique using lanthanum phosphate as a coprecipitant for preconcentration of iron(III) and lead in their flame atomic absorption spectrometric determination. Indium as an internal standard was added to the initial sample solution together with lanthanum and phosphoric acid; the coprecipitation of iron(III) and lead was then carried out at pH about 3. After measuring the atomic absorbances of iron, lead, and indium in the final sample solution, we determined the contents of iron(III) and lead in the original sample solution by using the internal standardization with indium. In this method, complete collection of the precipitate was not required after the coprecipitation of iron(III), lead, and indium, because the ratio of the recovery of iron(III) or lead to that of indium was almost constant regardless of the recovery of the precipitate. This method was simple and rapid, and was available for the determination of 2 -300 µg L -1 of iron(III) and 5 -400 µg L -1 of lead in some water samples.

The usefulness of coprecipitation with lanthanum phosphate for separation and preconcentration of some heavy metals has been investigated. Although lanthanum phosphate coprecipitates iron(III) and lead quantitatively at pH 2.3, iron(II) can barely be collected at this pH. This coprecipitation technique was applicable to the separation and preconcentration of iron(III) before inductively coupled plasma atomic-emission spectrometric (ICP-AES) determination; the recoveries of iron(III) and iron(II) from spiked water samples were 103-105% and 0.2-0.7%, respectively. The coprecipitation was also useful for separation of 20 microg lead from 100 mL of an aqueous solution that also contained 1-100 mg iron. Coprecipitation of iron was substantially suppressed by addition of ascorbic acid, which enabled recovery of 97-103% of lead added to the solution, bringing the recovery to within 1.6-5.0% of the relative standard deviations. Lanthanum phosphate can also coprecipitate cadmium and indium quantitatively, although chromium(III), cobalt, and nickel and large amounts of sodium, potassium, magnesium, and calcium are barely coprecipitated at pH approximately/= 3.

A novel method that combines inductively coupled plasma atomic emission spectrometry (ICP-AES) with a coprecipitation technique to determine trace and sub-trace elements in crude drugs is described herein. Yttrium phosphate quantitatively coprecipitated seven elements (Al, Cr, Fe, Zn, Cd, Pb and Bi) at pH 6 in a solution prepared from microwave-digested samples of crude drugs. Some matrix elements such as Na, K, Mg and Ca were effectively removed by this process. The thus coprecipitated elements were then determined by ICP-AES with yttrium as an internal standard element. The detection limits (3σ, n = 10) were 0.17 mg/kg for Al, 0.004 mg/kg for Cr, 0.03 mg/kg for Fe, 0.13 mg/kg for Zn, 0.004 mg/kg for Cd, 0.19 mg/kg for Pb and 0.06 mg/kg for Bi. The proposed method was successfully utilized to determine the concentration of the above-mentioned seven elements in standard reference materials [National Institute of Standards Technology (NIST) SRM1515, SRM1547 and SRM1575a] and seven kinds of crude drugs.