Cerate-Arsenite Measurement of Iodine in the Subnanogram Range

Abstract

A method for the measurement of subnanogram quantities of iodine is described. Procedural detail and precision of results are presented for application of the method to protein-bound or total iodine in duplicate on 12.3 µl serum. Following wet ashing with chloric reagent, the iodine-catalyzed cerate-arsenite reaction was carried out at temperatures between 23 and 27°, and the reaction rate coefficients were corrected to refer to 25.0° by an empirical equation. The recovery of iodine standards, added to the precipitated protein before ashing, ranged between 96 and 106%. One contributing cause of this variation is the formation of an inhibitor of unknown nature during heating. Samples were brought to a final volume of 180 µl prior to fading. The detection limit was of the order of 0.04 ng iodine. For 62 serum samples having a mean iodine content of 0.558 ng (range 0.15-1.31 ng), the standard deviation calculated from duplicates was 0.019 ng/180 µl. For 31 samples having a mean iodine content of 2.24 ng (range 1.61-2.96 ng), the standard deviation was 0.039 ng/180 µl. Expressed as micrograms of iodine per 100 ml of serum, the mean ± standard deviation for the group of 62 samples was 4.54 ± 0.15.

Fenton Digestion of Milk for Iodinalysis

“…This procedure was adopted for a variety of biosamples . Some other chloric acid procedures additionally use perchloric and chromic acids; , appropriate precautions must be taken. Pino et al developed a procedure in which ammonium persulfate (AP) is used to digest urine.…”

Methods for measuring iodine in urine and serum

“…Several methods are available for determining urinary iodine (May et al 1997;Sanz et al, 1958;Helwig et al, 1957;Hoch et al, 1969;Wayne et al, 1964 depends on the intended app!ication, the number of samples, the cost and the technical capability (Dunn et al, 1998). Having several different methods in one laboratory allows the user to se!ect the one best suited to specific needs.…”

“…-Cost -Many urine samples need to be run to monitor progress, and it is essential to keep the expense of each sample to the minimum level that is compatible with reliability. The most common techniques for measuring urinary iodine are the colorimetric ceric-arsenic assays (Hoch et al, 1969;Aumont et al, 1987;Garry et al, 1973;Wawschinek et al, 1985;Hellstem et al, 1980;Dunn et al:, 1993;Benotti et al, 1963;Benotti et al, 1965), which are based on the catalytic effect of iodide in the redox reaction between the yellow cerium (IV) and arsenic (III), which yields the colourless cerium (III) and arsenic (V) (Sandell and Kolthoff, 1934;Sandell and Kolthoff, 1937):…”