Application of solvent extraction method to the determination of magnesium in hard tissues of shellfish by ICP-AES

Abstract

The magnesium in hard tissues (shell and pearl) of shellfish inhabiting freshwater and sea water was determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES) after solvent extraction separation. We examined whether ICP-AES signals for magnesium were highly suppressed, or increased by large amounts of calcium ions. Two interferences, spectral and physics, were generated by the macro-component calcium for the emission intensity of magnesium. These interferences occurred simultaneously for magnesium. In addition, the calcium of the large excess adhered to a quartz torch, and the tip minute of the torch was damaged. From these results, it became cleare that it is necessary to separate magnesium from calcium prior to a measurement by ICP-AES. To eliminate this problem, we applied the solvent extraction method to separate magnesium from the interfering element, calcium. The chelating agent was easy to form the chelate with magnesium, and then a reagent that could extract the chelate from the acid solution was chosen. 1-phenyl-3-methyl-4-trifluoroacetyl-5-pyrazolone (HPMTFP) having a pKa value of 2.56 was chosen as the extraction reagent. Also, we selected some organic solvents in which the carbon did not adhere to torch without extinguishing plasma on the extractant. The sample solutions of shell and pearl used in the present work were treated with hot concentrated nitric acid, hydrochloric acid and perchloric acid. Magnesium was extracted with 0.01 mol/l-HPMTFP in dibutyl ether at pH 4.5 in order to separate it from the interfering calcium. Magnesium was determined by ICP-AES, and direct injection of the dibutyl ether. The magnesium content in the shell and pearl was found to be 16.4∼2627 μg/g.