Liquid chromatographic method for determination of water in soils

Abstract

A simple, rapid, and sensitive liquid Chromatographic (LC) method for the determination of water in soils was developed. In this method, water is extracted from soil with anhydrous methanol and injected into an LC system including a cation-exchange column in the H form. The eluent is 1.0 mM transcinnamaldehyde in acetonitrile-methanol (40:60). The detection scheme is based on the effect of water on the equilibrium established when trans-cinnamaldehyde and methanol react in the H + column to form cinnamaldehyde dimethylacetal and water. The equilibrium of the reaction is shifted towards the trans-cinnamaldehyde (absorbs strongly at the detection wavelength, 300 nm) when water is introduced into the column. The extent of the shift and the resulting change in absorbance at 300 nm are proportional to the amount of water present.Application of the method to a wide range of soils and of clay minerals containing from 0.7 to 25% water showed that the results of the LC method 1849 1850 BENZ, TAB ATABAI, AND FRITZ agreed closely with those of the gravimetric method. The LC method is accurate, precise, relatively free from interference, requires a small sample size, and gives a linear calibration graph over approximately three orders of magnitude of water concentrations. A single operator can perform approximately 80 analyses in a normal working day.