The Effect of Filter Pore-Size on Analytical Concentrations of Some Trace Elements in Filtrates of Natural Water

Abstract

Silver metal (Flotronics) membrane filters (pore-sizes 5-0.2 pm) and cellulose ester (MF-Millipore) membrane filters (poresizes 5-0.025 μm) are used to elucidate the relationship between filter poresize and analytically determined concentration of total “dissolved” iron, aluminium, silicon, and magnesium in the resulting filtrates. Iron and aluminium concentrations in the filtrate decrease with decreasing filter pore-size, but silicon and magnesium remain constant with changing filter pore-size. Filtration with two different types of membrane filter under the same conditions and having the same nominal pore-size produces differences in analytical concentrations of iron, aluminium, and silicon in the respective filtrates. This reduction is due very likely to a more complete removal of particulate matter by metal membrane filters compared to Millipore filters of the same nominal pore-size.

Acidification of filtrate with hydrochloric acid produces some reduction in determinable iron and aluminium by flameless atomic absorption. The cause does not appear to be the volatilization of metal chlorides during the charring of the sample, but this remains to be investigated further.

A large sample of water, unpolluted by man, from the Arctic Red River, NWT, Canada, was used for these experiments.

Key Words:

• Membrane filters
• natural water
• trace analysis
• iron
• aluminium