Introduction to XRF Drift Monitors

An XRF monitor sample is mainly used for correcting instrumental drift over time. It can be used to correct any changes in the calibration due to difference in instrument performance even though it is not necessarily a Certified Reference Material (CRM) or calibration standard. It is necessary for the monitor to have good long term stability in order to use XRF instrument programs for long periods without recalibration.

The main requirement of a monitor is that the count rates for the elements it contains do not differ over time. The count rates of the elements need not be near those of the samples being analyzed, but specific potential errors are reduced if there is an order of magnitude correspondence between the count rates from the monitor and the samples being examined. This minimizes counting times apart from other considerations.

AUSMON monitors developed by XRF Scientific have exceptional long term stability and this allows them to be used for monitoring instrument performance and count rates over extensive periods. Where extremely low concentrations are being determined, the count rate of the monitor is set not to match the analytes, but it is set to attain a counting error, which is smaller than required for analysis in a short counting time. Where key elements are being determined, and where the spectrometer has a high sensitivity to those elements, the count rate from the monitor will have to be adjusted not to go beyond count rates that cannot be precisely handled by modern measuring equipment.

Instrument Maintenance

The data obtained from consistent analysis of the monitor can also be used to assess the laboratory environment and instrument performance. Intensity changes are indicative of some change in the instrument since these drift monitors do not change with time. A decrease in intensities may indicate the need for instrument maintenance. For instance, it is common for scintillation counters to decrease in efficiency due to moisture reacting with the NaI crystal. When this occurs, the shorter wavelengths (e.g. SnKa) are minimally affected while there is a huge decrease in intensity for longer wavelengths, (e.g. FeKa).

Checking Instrument Performance

Since the monitors vary very little, it is possible for different laboratories to compare intensities from the monitor in order to check that the instruments are giving acceptable performance.

AUSMON – “Silicates and General” comprises of 53 elements, hence it is possible to draw a comparison employing all the selectable parameters, that is, changing crystals, collimators and detectors, etc.

Composition: This monitor comprises of the following elements as majors:

Additionally, the sample comprises of approximately 0.2 – 0.5% of each of the following:

Sc, V, Cr, Co, Cu, Ni, Zn, Ga, Gd, Ge, Se, As, Rb, Sr, Br, Cl, Y, Zr, Nb, Mo, Ag, Cd, Sn, Sb, Te, Cs, Ba, La, Ce, Nd, Pr, Sm, Yb, Hf, Ta, W, Bi, Pb, Tl, Th and U.

The monitor comprises of 53 elements and its composition is such that reasonable counting precision can be attained for any element within a short time period, usually less than 20 seconds. It also contains extremely little flux and thus has good long term stability. In order to provide accurately repeatable surface presentations, the disk is polished optically flat so that it can be mounted consistently and precisely in the sample holder.

*Available in both 40 mm & 32 mm diameter size
Additional types & sizes available upon request

This information has been sourced, reviewed and adapted from materials provided by XRF Scientific.

For more information on this source, please visit XRF Scientific.