1.

In Chapters 1 and 2, several examples from a Public Analyst's laboratory of the analysis by HPLC of sugars in orange juice were presented. Exercise 2.2, p 49, gave 50 values of the recoveries of glucose from control samples using in monitoring the stability of the analytical system. The controls were either soft drinks or clarified orange juice, spiked with glucose.

The summary statistics for the 50 results are: mean = 98.443 and SD = 2.451. Carry out a t-test, using a significance level of 0.05, of the hypothesis that the method is unbiased, i.e., that the long-run average recovery rate is 100%.

2.

The Public Analyst's laboratory referred to above, routinely measures total oxidized nitrogen in water by continuous flow analysis (an automated colorimetric method). The internal QC system involves making duplicate measurements on water spiked with 5.05 mg L ^-1 of nitrogen. The 35 most recent in-control points (averages of two replicates) on the X-bar chart gave a mean of 5.066 and a SD of 0.051. If we can assume that before spiking the water is free of nitrogen, do the summary statistics suggest that the analytical system is biased or unbiased, i.e., does the long-run mean equal 5.05 mg L ^-1 of nitrogen? Use a significance level of 0.05.

Note that the duplicates were averaged before the summary statistics were calculated. Accordingly the fact that the 35 values are averages is irrelevant-they are treated as 35 final results. No...