What is the calibration curve?
Calibration curve is a method used in analytical chemistry to determine the concentration of an unknown sample solution. It is a graph generated by experimental means, with a concentration of a solution on the X-axis and an observable variable-for example, the absorbance of the solution-appointed on the Y-axis. The curve is designed by measuring the concentration and absorbance of several prepared solutions called calibration standards. Once the curve is plotted, the concentration of the unknown solution may be determined by placing on the curve based on its absorbance or other observable variables.
Chemical solutions absorb different amounts of light based on their concentration. This is quantified in an equation known as a beer law that shows a linear relationship between light absorption and its concentration. Scientists can measure the absorption of the solution using a laboratory tool called spectrophotometer. The process as a whole is called spectrophotometry. For example, if the researcher has a sample of river water and CHTE know your lead content, it can determine it using a spectrophotometer to render the calibration curve. First, the researcher creates several standard lead solutions, from less concentrated. These samples are placed in a spectrophotometer that records a different absorbance for each of them.
Experimentally determined absorbance values are brought into the graph against the known concentration of each calibration standard. A set of points is created that should be roughly linear due to the absorbance law. A line is drawn to connect these data points and creates a calibration curve. In almost any case, the data points will not be accurate, so the line should be drawn to capture the maximum number of points - this is the best line. Although the relationship of absorbance to concentration is linear, it is not always true for other experimentally determined variables and occasionally must be usedcurves to describe the relationship.
At this stage, an unknown solution can be analyzed. The sample is inserted into the spectrophotometer and its absorbance is measured. Because this sample is measured according to several standards containing the same compound, its absorbance and concentrations somewhere along the calibration curve for this compound. This means that once the solution is known, its concentration may be derived mathematically or graphically.
The horizontal line can be drawn from the value of an unknown solution-is absorbance that has just been measured. The point in which the line passes through the calibration curve will indicate-evaluation-concentration. The vertical line, drawn down from this point, gives the concentration of an unknown solution. The equation for the calibration curve line can also be used to mathematical determination of the concentration of the solution.