Laboratory 1 Laboratory 2
34.97 35.02
34.85 34.96
34.94 34.99
34.88 35.0734.85Comment upon the precisions attained in the two laboratories.
(7) On the basis of extensive past analysis the iron content of an homogeneous ore sample is accepted to
be 19.85%. An analysis of seven samples gave an average of 20.06% Fe. Within what probability levels
is a determinate error indicated in the analysis if the absolute standard deviation of the results is 0.14%?
(8) The efficiency of mixing of powdered solids in a process stream is being investigated. Two samples
of the mixture, each of about 1 kg, are taken from different parts of the same hopper. After grinding to a
fine powder, analytical samples were obtained using the coning and quartering technique. Subsequent
analysis gave the following results for one component:
The precisions were found to be similar and the pooled standard deviation (absolute) computed to be
0.071%. Comment upon the efficiency of the mixing.
(9) Replicate analysis by a new method for a constituent of a standard sample gave the following results
(%):
The content of the standard is accepted to be 0.47%.
Assess these data and draw conclusions concerning the suitability of the method of analysis for routine
use.
(10) A standard reference material with an accepted analyte content of 5.85 ppm was used to compare
the performance of two alternative methods of analysis. Solutions were prepared using a range of
sample weights. Each solution was analysed by the two methods. Use the results obtained to assess any
determinate errors exhibited by the methods.
Sample weight/g Result, Method 1/ppm Result, Method 2/ppm0.125 6.37 5.720.612 5.97 5.690.334 6.10 5.700.781 5.93 5.71