Determination of nitrate in water containing dissolved organic carbon by ultraviolet spectroscopy

Direct measurement of ultraviolet (UV) light absorption by nitrate in the 2 00-205 mn wavelength band offers a reliable, accurate and rapid method of n itrate determination in natural waters. However, UV light is also strongly absorbed by organic matter at these wavelengths. A two-wavelength approach was adopted and evaluated for the correction of absorbance that organic mat ter might have contributed. The measurements were made at 205 nm and 300 nm . The relationship between absorbance at 205 nm and 300 nm due to organic m atter was incorporated into traditional nitrate calibration curve to make a llowance for the organic matter contribution. The method developed has a detection limit of 0.04 mg NO3-N dm(-3) and is c apable of determining nitrate concentration in the range of 0.08-4.0 mg NO3 -N dm(-3). In terms of accuracy and reproducibility, the method compares we ll with the hydrazine-reduction method, with matching precision (1.14% over the concentration range) and accuracy (+/-2%). This two-wavelength approac h based method is rapid, low-cost and does not require any reagents or trea tment, and is suitable for waters with dissolved organic carbon (DOC) conce ntration of up to 20-mg dm(-3).