LIQUID-CHROMATOGRAPHIC METHOD FOR DETERMINATION OF WATER IN SOILS

A simple, rapid, and sensitive liquid chromatographic (LC) method for the determination of water in soils was developed. In this method, wat er is extracted from soil with anhydrous methanol and injected into an LC system including a cation-exchange column in the H+ form. The elue nt is 1.0 mM trans-cinnamaldehyde in acetonitrile-methanol (40:60). Th e detection scheme is based on the effect of water on the equilibrium established when trans-cinnamaldehyde and methanol react in the H+ col umn to form cinnamaldehyde dimethylacetal and water. The equilibrium o f the reaction is shifted towards the trans-cinnamaldehyde (absorbs st rongly at the detection wavelength, 300 nm) when water is introduced i nto the column. The extent of the shift and the resulting change in ab sorbance at 300 nm are proportional to the amount of water present. Ap plication 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 met hod agreed closely with those of the gravimetric method. The LC method is accurate, precise, relatively free from interference, requires a s mall sample size, and gives a linear calibration graph over approximat ely three orders of magnitude of water concentrations. A single operat or can perform approximately 80 analyses in a normal working day.