How to use a Spectrophotometer to Answer Biological Questions Standard Concentration Curve and Determining the Concentration of a Characterized Substance What does the concentration curve for neutral red look like?
How do we use this concentration curve to determine the concentration of an unknown concentration of neutral red? Standard concentration curve of a solution is constructed by measuring the absorbance of several different known concentrations of the solution and graphing the results by plotting absorbance on the Y-axis and concentration on the X-axis. Spectrophotometry can be used to measure the absolute or relative concentration of a characterized substance in solution. To determine the absolute concentration of a pure substance, one first constructs a standard concentration curve from known concentrations and then takes the absorbance reading of the unknown concentration. The unknown concentration can be determined from the standard curve by drawing a horizontal line on the graph parallel to the X-axis and through the point on the Y-axis which corresponds to the absorbance (Figure 2). This line will intersect the standard curve; at this intersection, a vertical line is dropped to the
