Isotope titration

The Isotopentitration is a 1960 developed by A. Fuchs micro method for the quantitative determination of nanogram amounts of lead, mercury and other heavy metals. This method has high sensitivity and accuracy. Isotope titration is a complexometric determination using cobalt-60 as a non- isotopic radioactive indicator . This procedure is used in toxicology and pathology .

Procedure

If there are several elements in a solution that can react with a complexing agent, if there is a deficit of complexing agent, it is predominantly the elements that form the most stable complexes that react. When lead and cobalt are present in a solution, the lead forms a much more stable complex with ethylenediaminetetraacetic acid (EDTA) than cobalt. The cobalt will only form an EDTA complex when all the lead ions have already formed a complex with EDTA. The formation of the EDTA-cobalt complex can then be followed by using labeled cobalt and electrophoretically separating the negatively charged complexes from the positively charged free cobalt ions .

This process is suitable for all metals whose complex formation constant is 10 ¹⁶ greater than that of cobalt. If there are different metals in the solution, they must first be separated from the metal to be analyzed.

technology

An aqueous solution containing the element to be determined and a known amount of cobalt marked with Cobalt-60 is applied to the center of a strip of filter paper. The two ends of the test strip are wetted with a neutral salt solution. The conductivity of the saline solution must be greater than that of the solution to be analyzed. The entire strip is then immersed in a bath of carbon tetrachloride for cooling and a voltage of approx. 1.8 kV is applied to the ends. A sharp separation of cobalt and cobalt-EDTA complex is achieved after at least three minutes. After the strip has subsequently been dried and cut, the counting rate of the sections is measured with a scintillation counter. Then, from the quotient of the counting rate of the complex and the free cobalt ions together with the amount of EDTA and cobalt used, the amount of heavy metal in the solution can be calculated. When determining lead in the nanogram range, a standard deviation of less than one nanogram is possible with this method.

Comparison with isotope dilution analysis.

An advantage of isotope titration compared to isotope dilution analysis is that elements can also be determined which themselves do not have an isotope which is suitable for isotope dilution analysis in terms of half-life and specific activity. A disadvantage is that the isotope titration requires a quantitative work-up.

Individual evidence

↑ ^a ^b ^c ^d A. Fuchs: Detection of heavy metals by isotope titration . In: German journal for all forensic medicine . tape 57 , no. 1-2 , March 1, 1966, ISSN 1437-1596 , pp. 310-312 , doi : 10.1007 / BF00576178 ( springer.com [accessed January 13, 2019]).

[:0-1] A. Fuchs: Detection of heavy metals by isotope titration . In: German journal for all forensic medicine . tape 57 , no. 1-2 , March 1, 1966, ISSN 1437-1596 , pp. 310-312 , doi : 10.1007 / BF00576178 ( springer.com [accessed January 13, 2019]).