How to Use Our Certified Reference Materials

Insertion of CRMs into the Sample Stream

Clients of Laboratories

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.

Laboratories

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.

Assessment of Results

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).

• The mean value is the target grade for the material.
• The standard deviation is the variation expected in the resutls. 68% of results should be within 1 standard deviation of the mean, 95.5% should be within 2, and 99.7% should be within 3.
• The count of analyses is the number of results used to calculate the mean and standard deviation.
• The 95% confidence interval (95% CI) is an indication of the quality of the material and the certification testwork. We are 95% confident that the true mean of the material lies within this interval of the mean.

We recommend the use of 3 standard deviations as the control limits when monitoring analyses on our CRMs.