chemistry

The issues an analyst needs to consider when a calibration is performed are as follows: The number of calibration standards – For an initial assessment of the calibration function at least seven different concentrations (including a blank) should be prepared. A calibration standard is a solution prepared from a substance or reference material used to calibrate an instrument.   The concentration of each of the calibration standards - The standard concentrations should cover, at least, the range of concentrations encountered during the analysis of test samples and be evenly spaced across the range. The number of replicates at each concentration   -   At least duplicate measurements at each concentration level. The preparation of the calibration standards -   Calibration solutions are prepared from a pure substance with a known purity value or a solution of a substance with a known concentration. The uncertainty associated with the concentration of the standard solution

Why calibration is such a common and important step in analytical methods? How is defined? Calibration is the process of assigning a value, usually in concentration units, to an instrument response. For example, you might calibrate the response of an analytical device – such as a spectrophotometer - by analyzing different “known” concentrations of an analyte (i.e. solution of a metal ion such as Zn +2 ) and establish the instrument’s response per unit concentration of the metal (Fig. 1). Then, an unknown concentration of a test sample of the same analyte can be estimated from the graph by extrapolating the observed absorbance (y-axis) over to the analyte concentration (x-axis) (yellow line in Fig. 1). In the graph shown in Fig. 1, the calibration function is established based on points in Table I.1:                       Table I.1: Instrument Response for different analyte A   concentrations   Analyte Concentration ( μ g/l) Instrument Response (Absorbance) 0 0 2 0