Clients of laboratories should try to submit samples of CRMs into their normal sample stream, blind to the laboratory. This is especially important for coarse blanks, "dosed" samples and coarse CRMs.
When this is not possible (particularly with pulp CRMs), it is best to provide the laboratory with pre-numbered sets of samples (of at least three samples) and instruct the laboratory to insert one set per batch, evenly distributed throughout.
The majority of our laboratory clients purchase our CRMs in bulk (1kg containers, 200g jars etc). This allows the CRMs to be sampled and inserted into batches at the weighing stage.
The results on our CRMs should be assessed using control charts. These plot the results against the target grade, and show control limits corresponding to the material.
The certificates for our materials present a mean value, a standard deviation, count of analyses and a 95% Confidence Interval (95% CI).
We recommend the use of 3 standard deviations as the control limits when monitoring analyses on our CRMs.