Why do Elvatech XRF spectrometers have record stability and never require calibration

The high stability of an x-ray fluorescence analyzer ensures that you get the same sample results whether you take several measurements in a row (short-term stability) or in the long term, when you analyze that sample the next day, month, year, or 10 years later (long-term stability).

Let’s understand what factors affect stability.

Short-term stability is responsible for the convergence of parallel measurements (i.e. several consecutive measurements of the same sample by the same analyzer under unchanged conditions) and is quantified by the standard deviation of the analytical results. It is assumed that the analyzer does not change its properties or parameters during the series of parallel measurements. Thus, only the statistics of the measured spectra, which, in turn, is determined by the speed of the spectrometer – the number of X-ray quanta recorded per unit time – influences the dispersion of the results.

Elvatech spectrometers have the highest speed, over 500 000 counts per second, which is several times higher than other similar analyzers. This gives them the highest short-term stability in the industry.

Long-term stability is responsible for the repeatability of your sample results over the long term, e.g., an entire work day or over any other extended period of time. In contrast to short-term stability, long-term stability is affected by a wide variety of factors related both to the analyzer itself and to changes in environmental conditions such as temperature, pressure, etc.

One of the main factors affecting long-term stability is the drift of the energy scale of the spectrometer, which causes the element peaks in the X-ray fluorescence spectrum to shift from their ideal position. The main reason for this drift is the heating of the electronic components of the detector preamplifier and the digital pulse processor. Basically, to correct the energy scale the spectrometer is periodically calibrated using a special calibration sample, which is supplied with the spectrometer, or is built into. This approach has two significant drawbacks. First, drift does occur between calibrations and the results of the sample immediately after calibration and at the end of the cycle before the next calibration can differ significantly. The second is that calibration requires some time, and for this it is necessary to stop performing work on solving analytical tasks, which reduces the productivity of using the analyzer.

Elvatech spectrometers solve this problem differently. Temperature sensors installed at critical locations in the spectrometer continuously monitor temperature drifts and the firmware automatically corrects the energy calibration coefficients accordingly. This is usually sufficient to ensure the stability of the energy scale for the life of the analyzer. However, the analytical software of the spectrometer still additionally checks at each measurement whether the element peaks have shifted. In the event that such a shift is detected, the software automatically corrects the energy scale directly from the spectrum of the sample being analyzed without the need for a special calibration sample.

Another cause of energy scale drift and spectral peak width variations is the dependence of the energy calibration and resolution of the spectrometer on its statistical loading (the intensity of X-rays reaching the detector, measured in pulses per second, cps). The loading can vary depending on the size of the sample (the larger the sample, the more secondary X-rays it produces at the same intensity of the X-ray tube) and also depending on its composition. To eliminate the influence of this effect, the Elvatech spectrometers use a loading stabilization mode before each measurement. When the X-ray tube is turned on, the spectrometer measures the loading and automatically corrects the tube current so that when analyzing any object, the spectrometer’s loading is fixed. This solution guarantees the highest stability of peak positions and widths on the spectrometer’s energy scale, further enhancing long-term stability.

However, even with a stable energy calibration, the analysis results may not be stable due to variations in the X-ray excitation source parameters. The actual voltage at the X-ray tube anode can vary depending on the temperature of the X-ray generator, which will affect the excitation efficiency of different elements and, accordingly, lead to changes in the analysis results. To exclude this effect the unique digiX digital X-ray generators of our own development, which automatically correct the high voltage at the anode of the tube, depending on the temperature, are used in the Elvatech spectrometers.

Intensity of peaks of light elements as Na, Mg, Al, Si, P and S is significantly affected by atmospheric air pressure which can also decrease long-term stability of analytical results of these elements. To exclude influence of atmospheric pressure variation Elvatech analyzers use automatic barometric correction of light elements peaks intensity.

The combination of the above measures provides Elvatech XRF spectrometers with unsurpassed short- and long-term stability of analytical results without the need for additional calibrations, and provides users with a guarantee of getting accurate analytical results during the entire analyzer’s service life.