Enrichment Procedures for Water Analysis by X-Ray Energy Spectrometry

Abstract

Energy-dispersive X-ray fluorescence might advantageously be used for the determination of trace metals in water. Suspended material can straightforwardly be collected on a 0.45 μm pore-size Nuclepore membrane by filtration. Dissolved ion analysis usually requires a physical or chemical enrichment step. Spotting a 1.5 ml water sample on a Whatman-41 filter within a 29 mm diameter hydrophobic ring and drying by a cold air stream from underneath yielded a 50 ppb sensitivity for many elements, and a 18% accuracy. Filtration of a 200 ml water sample at the natural pH through a pair of Chelest-100 chelating ion-exchange resin loaded filter papers allowed 1-5 ppb sensitivities but suffered from the combination of limited load capacity and significant uptake of usually abundant alkali earth metals.

Chelex-100 ion-exchange filter membranes for preconcentration in x-ray fluorescence spectrometric analysis of water

“…For natural waters, ammonia exerts a stress in several ways. Among these ways we can mention its contribution to blue-green algae growth (1) causing eutrophication, toxicity to fish and aquatic life, causing corrosion of certain metals of construction, reducing the amount of dissolved oxygen in receiving waters due to nitrification process, and inhibiting the water and food intake for both mammals (2) and plants (3) affecting their appetites. Excess amounts of ammonia and ammonium salts decrease the pH in human blood, causing acidosis which can be monitored by the increase of ammonia in urine (4).…”

“…The Nessler method is sensitive down to 20 ppb NHS-N. Among the other well-established techniques for ammonia determination are the Berthelot method which is based on the blue color formed 1 Present address, Department of Chemistry, Middle East Technical University, Ankara, Turkey.…”

“…Yet it is rarely applied to aqueous samples. Direct irradiation of aqueous samples in a measuring vial with a thin Mylar bottom leads to typical sensitivities for transition metals in the order of 0.3-5 ppm (1). When sensitivities in the ppb region are required, the trace metals must first be preconcentrated and the difficulty lies obviously in preparing targets containing all elements sufficiently enriched and distributed with sufficient uniformity to permit sensitive and reliable analysis.…”

Determination of light rare earth elements in apatite by x-ray fluorescence spectrometry after anion exchange extraction

“…This technique can also be extended to some trace elements in common silicate rocks. In order to enhance both sensitivity and accuracy, chemists have proposed different procedures for preliminary chemical enrichments and separations of the trace elements from the original sample for use with XRF analysis, e.g., precipitation (15), solvent extraction (21), and ion exchange [resins such as Amberlite and Chelex-100 or filters such as membranes or resin-loaded papers supplied by Whatman and Gelman-Hawksley (17, [21][22][23][24][25][26][27][28][29][30][31]].…”

Target preparation for x-ray emission analysis by anodic electrodeposition of cyano metalates from 2-propanol-water mixtures

“…Because of the low penetrating power of the excitation beam, optimal standard and sample targets should be thin and uniform films strongly adhering to a supporting material with low contribution to the background of the X-ray spectrum. These requirements are only partly fulfilled by sample preparation techniques so far reported, such as adsorption of dissolved metal traces directly on chelating resins (4)(5)(6)(7)(8)(9)(10)(11) or on silylated silica gel (12,13), or as 8-hydroxyquinolates on charcoal (14). These methods suffer from the inability of sorbents to discriminate between traces and bulk constituents.…”