The same SQT device was used for whole optimizations and calibrations; its sensitivity was still the same at the end of the study; this corresponds to at least 400 uses of the same SQT. However; Ta-coated-SQT was used for about 100 measurements before there was a significant reduction in sensitivity. Coated or uncoated SQT device was replaced when its sensitivity was about 50% of the initial or the precision was lower than 10% RSD.