Selection of the optimum concentration range for reflectance spectrophotometric analysis

Two graphical methods for selecting the optimum range and determining the maximum accuracy of reflectance spectrophotometric analysis are discussed. Results obtained with the use of two systems (Rhodamine B, which absorbs in the visible region of the spectrum, and aspirin, which absorbs in the ultraviolet region, both adsorbed on silica gel) are employed to illustrate how the methods might be employed in practice. Experimental results are contrasted with those expected by application of the Kubelka-Munk equation. The results indicate that the minimum relative error in concentration to be expected in reflectance spectrophotometric analysis is about 6% per 1 % reading error, and that the optimum range for analysis can be arrived at after plotting the reflectance data for either of the two systems discussed, whether the system conforms to the Kubelka-Munk equation or not.