Method of making a standard
A measurement standard suitable for measuring amounts of certain elements in pharmaceutical excipients is described. A reference standard is dissolved in a solvent, for example acetone, and mixed with a pharmaceutical excipient such as cellulose, lactose or calcium carbonate. The solvent is then evaporated to provide a dry standard.
1. A method of manufacturing a dry reference standard for X-ray fluorescence measurements, comprising:
providing a reference sample having a known concentration of a predetermined element;
transferring the reference sample volumetrically into acetone to prepare a diluted reference standard having a concentration of 10 to 500 ppm of the predetermined element;
mixing the diluted reference standard with an excipient material in powder form;
evaporating the acetone to form a dry reference standard with the known concentration of the predetermined element homogeneously dispersed in the excipient material.
2. The method according to claim 1 wherein evaporating the acetone includes carrying out a first evaporation step at room temperature followed by a second evaporation step in an oven at an elevated temperature above 35° C.
3. The method according to claim 2 wherein the second evaporation step is carried out for a period of at least 24 hours.
4. The method according to claim 1 , wherein the excipient material is lactose, cellulose or calcium carbonate or any mixture thereof.
5. The method according to claim 1 , wherein providing a reference sample includes providing at least one reference sample having a known concentration of each of a plurality of elements and transferring the at least one reference sample volumetrically into a solvent to obtain a diluted reference sample having a known concentration of each of the said plurality of elements.
6. A method of providing a plurality of dry reference standards,
the method comprising providing a reference sample having a known concentration of a predetermined element;
transferring a different concentration of the reference sample volumetrically into acetone for each of the plurality of dry reference standards to prepare a plurality of diluted reference standards having a concentration of 10 to 500 ppm of the predetermined element;
mixing the diluted reference standards with an excipient material in powder form;
evaporating the acetone to form the plurality of dry reference standards with different known concentrations of the predetermined element homogeneously dispersed in the excipient material.
7. A method of calibrating X-ray fluorescence apparatus, comprising:
preparing a plurality of dry reference standards having different concentrations of a predetermined element providing a reference sample having a known concentration of the predetermined element by, for each dry reference standard, transferring the reference sample volumetrically into acetone to prepare a plurality of diluted reference standards having a concentration of 10 to 500 ppm of the predetermined element; mixing the diluted reference standards with an excipient material in powder form; and evaporating the acetone to form a dry reference standard with the known concentration of the predetermined element homogeneously dispersed in the excipient material;
measuring the X-ray fluorescence of each of the dry reference standards; and
calculating a calibration line from the measured X-ray fluorescence and the known concentrations of the predetermined element.