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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.

Not completely right. For some foods (e.g. eggs), the CV between is equal to the CV between achievable. For some other foods the CV between is higher than achievable, but not that much higher. In this laboratory trial foods were also analyzed for their fat contents. For fat, sometimes the CV between was 10 times higher than achievable. Compared to this, the differences between laboratories with respect for protein analysis are rather small, although higher than expected (based on the CV achievable).

Not right. Note that different laboratories use different conversion factors. This could result in differences between laboratories.

Not completely right. There are more right statements. Please realize that the different laboratories probably use different modifications of the Kjeldahl method. It is likely that this results in differences between laboratories.

Not completely right. There are more right statements. Sometimes laboratories use poorly validated methods. It is likely that this results in differences between laboratories.

Right!

a

Which statements are true? The differences between the laboratories….

b
c
d
e

are rather small, but for some foods still higher than expected.

are much higher than expected.

can be partly due to the use of different nitrogen - protein conversion factors.

can be partly due to methods modifications (e.g. the choice of catalyst in the Kjeldahl method).

can be partly due to poorly validated methods in one or more laboratories.