Standard procedure for the determination of P in cheese. An interactive lab experiment.
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A spectrophotometric method is used for the determination of P content in a sample of cheese. The procedure is based on the formation of molybdenum blue and measurement of the absorbance at 820 nm. The interactive experiment starts with the weighing of the cheese sample in the range 0.2-0.45 g (analytical balance, four significant figures). A random weight of cheese is obtained. Then, according to the procedure, the cheese is mineralized to convert P into phosphate which is treated with the molybdenum reagent to yield molybdenum blue. The absorbance of both samples and standards are measured at 820 nm. A calibration graph is constructed from the data of the P standard solutions and the least squares method is applied to obtain the corresponding equation. Finally, using this equation, the concentration of P (as mass percent) in the cheese is found. All data in the simulated experiment are randomly generated. In the calibration step, an outlier can appear that can be rejected by application of the Dixon’s test. The final result is expressed in terms of the mean value with the associated statistical treatment.