I performed a "related substances" test using HPLC on 1 sample. The 1st value for an impurity is 0% (not detected) and the 2nd value is 0.3%. THe passing limit is 4% for this test.

Are the results acceptable, i.e. to take the average of the 2 values to give 0.15%?

To determine if the results of the "related substances" test are acceptable and whether you can take the average of the two values, you need to compare them to the passing limit.

In this case, the passing limit is 4%.

The first value of the impurity is 0% (not detected), and the second value is 0.3%.

Since the first value is 0% (not detected), it is well below the passing limit of 4%. This indicates that the impurity is not present or is present at a very low concentration.

The second value is 0.3%, which is also below the passing limit of 4%.

Based on these results, both values are below the passing limit, suggesting that the impurity is within acceptable levels. However, it is important to note that the first value being 0% indicates that the impurity might not be present at all.

To calculate the average of the two values, you can sum them up and divide by the number of values (in this case, 2):

(0% + 0.3%) / 2 = 0.3% / 2 = 0.15%

So, the average of the two values is 0.15%.

Taking the average in this case indicates that the average impurity concentration is 0.15%.

In summary, based on the results of the "related substances" test, the impurity amounts are acceptable as both values are below the passing limit of 4%. However, it is important to consider that the first value of 0% indicates that the impurity might not be present at all. Taking the average of the two values gives a calculated average impurity concentration of 0.15%.