Preconcentration and Instrumental Methods for Trace Elements in Marine Samples by Neutron Activation

Abstract

Neutron activation analysis (NAA) methods have been developed in this study for the determination of trace elements in marine samples. An instrumental NAA (INAA) method has been used for measuring concentrations of up to 21 elements in microgram quantities of marine suspended particulate matter (SPM) while preconcentration methods followed by NM have been developed for determining Mo, Co, Zn, Mn and V in sea water.

The INAA method for marine SPM consists of two irradiation and four decay periods. Concentrations of Al, Ba, Br, Ca, Cl, I, Mg, Mn, Na, Sr, Ti and V have been measured using their short-lived thermal neutron activation products while long-lived nuclides have been utilized for determining Au, Ce, Fe, Hg, K, La, Sc, Sm and Zn content. The major problems associated with multielement analysis in microgram amounts of marine SPM and procedures developed to minimize their effects are described here. The precision of the INAA method varied between 3 and 22%. The accuracy of measurements has been observed to be - 10% in general. The limits of detection and determination are also reported here. The nature and origin of SPM have been studied using inter-element concentration correlationships.

Molybdenum has been selectively and quantitatively pre-concentrated from sea water by cocrystallization with ß-naphthoin oxime. Factors affecting the recovery of Mo have been investigated in detail using a radioactive tracer and reported here. The method developed has been applied to determine Mo concentrations in marine and estuarine water samples. The precision and the accuracy (better than +- 10%) of the method and the limits of detection (0.30 µg Mo L-1) and determination (1.00 µg Mo L-1) have been evaluated.

Cobalt, Zinc and Manganese have been preconcentrated using chitosan. Conditions have first been established using radioactive tracers to obtain maximum possible recoveries for each element. Details of the methods developed are reported here. The applicability of the methods have been evaluated by analyzing a few sea water samples. Detection limits of 0.034 µg Co L-1, 1.22 µg Zn L-1 and 0.22 µg Mn L-1, and determination limits of 0.11 µg Co L-1, 4.13 µg Zn L-1 and -1 1.17 µg Mn L-1 have been obtained.

An analytical method has been developed for preconcentrating vanadium from sea water with Mg(OH)2 which is formed by adding ammonium hydroxide to sea water. The method has been found to be quantitative and specific for concentrating V under the experimental conditions used. The method has been applied to determine V concentrations in a few sea water samples. A detection limit of 0.38 µg V L-1 and a determination limit of 1.50 µg V L-1 have been achieved.