Shorter signals for improved signal to noise ratio, the influence of Poisson distribution

Abstract

Signal to noise ratios of transient signals depend on the signal duration and are usually better for shorter signals. Poisson distribution is the dominating noise source for mass spectrometers at low count numbers. The IUPAC concept of ‘detection limit’ is used as a measure of the noise level and three different ways of detection limit calculations are compared and discussed. Assumption of Normal distribution leads to underestimation of the detection limit compared to exact Poisson based calculations. A simple formula given by IUPAC bases detection limit on the standard deviation of the blank but introduces a term to correct for the difference between Normal and Poisson distributions. Results of this formula are comparable to exact Poisson calculations. Signal to noise in transient signals was evaluated. It was found that an optimum duration for transient signals exists and that it depends on the level of the instrument background.