Construction of Absorption Filter for colorimetry and its performance characteristics

The aim of this study was to device in house a suitable absorption filter for colorimetric analyses. An absorption filter was so constructed using 40% CuSO4.5H2O solution in 8M HCl (w/v) in glass support of 2mm internal diameter. The filter was found to have a nominal wavelength of 540±0.92nm, spectral bandwidth of 41±0.82nm and a peak transmittance of 36±0.40%. The filter offered a sensitivity of 0.81±0.03 for a single beam colorimeter at 540nm. Its photometric linearity was through an absorbance unit of 0.52±0.02 while that of the manufacturer filter was through 0.92±0.03. The significantly lower photometric linearity (P < 0.05) of the filter notwithstanding, it offered a mean value for blood haemoglobin concentration of 122±20g/l which was not significantly different from 124±19g/l obtained with manufacturer filter (P > 0.05). The filter would be suitable for absorbance measurement at 540nm wavelength particularly for blood haemoglobin concentration determination in a developing economy.