Nj. Benz et al., LIQUID-CHROMATOGRAPHIC METHOD FOR DETERMINATION OF WATER IN SOILS, Communications in soil science and plant analysis, 24(15-16), 1993, pp. 1849-1863
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.