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All laboratories use modifications of the Kjeldahl method. These modifications differ with respect to choice of catalyst procedures for digestion, distillation and determination of the ammonia.

It is not only important to know which methods can be used to measure nitrogen or protein values, but it is also important to have insight in the reliability and precision of these data. To obtain that insight you will study the results of an interlaboratory trial in which protein content s of several products is determined by various experienced food labs. Study the results and answer the following questions.

To know whether the measurements are sufficient precise you have to know which CV between is reasonable achievable.

This can be calculated using the Horwitz equation.

C is the concentration of the component that was measured (here protein)

C has to be expressed as a fraction (e.g. 52.98g / 100g = 0.5298 g/g)

Please fill in a number in both boxes (last row of table above).

You are not right, try to correct your answer. Maybe it is most easy to calculate the CV in steps. (1) Calculate the logarithm of the concentration (2) Multiply this by 0.5 and so on. Remember that the C in the equation represent a fraction,

so 52,98g protein /100 g equals C=0.5298

Not right, now the right answers are shown in the table.

Right!

Calculate the achievable CV between for egg and milk using this equation. Add the results to the table above.
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