Signal-to-noise calculation (Data Analysis)
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Signal-to-noise calculation

OpenLab CDS has different options for the signal-to-noise calculation. You can choose both the algorithm and the noise range.

6 sigma or RMS method

The signal-to-noise is calculated using the formula:

 

Signal-to-noise ratio

Peak to peak or ASTM method

The signal-to-noise is calculated using the formula:

S/N = 2H/h

where

H

Height of the peak corresponding to the component concerned in the chromatogram obtained with the prescribed reference solution.

h

Absolute value of the largest noise fluctuation from the baseline in a chromatogram obtained after injection or application of a blank and observed over a distance equal to twenty times the width at half- height of the peak in the chromatogram obtained with the prescribed reference solution, and situated equally around the place where this peak would be found.

According to the definition of the European Pharmacopoeia, signal-to-noise is calculated against a blank reference signal and a noise calculated over the time range which contains the peak the S/N ratio is being calculated for.

Noise range

Noise can be calculated against the following time regions and signals:

  • Automatically determined time region on a blank reference signal. The noise range that equals 20 times the peak width at half-height.

  • Automatically determined time region on the same signal or on a blank reference signal. The noise range that equals n times the peak width at half-height.

  • Fixed time region, on the same signal or on a blank reference signal

  • Time region relative to the peak start or end, on the same signal or on a blank reference signal

An automatically determined time region is calculated according to one of the following algorithms:

  • If the reference signal is not long enough

    (EndTime - StartTime < N*W50)

    • StartTime = starttime of the signal, and

    • EndTime = endtime of the signal

      N = number of times the width at half height of the peak (between 5 and 20, depending on the Pharmacopeia)

  • If the reference signal is long enough, but the peak is situated too close to the starttime

    (tR-(N/2)*W50 < starttime of the reference signal)

    • StartTime = starttime (of reference signal), and

    • EndTime = StartTime + 20*W50

  • If the reference signal is long enough, but the peak is situated too close to the endtime

    (tR+(N/2)*W50 > endtime of the reference signal)

    • EndTime = endtime (of the reference signal), and

    • StartTime = EndTime - N*W50

  • If the reference signal is long enough, and the peak is situated far enough away from starttime and endtime of the reference signal

    (tR-(N/2)*W50 > starttime, tR+(N/2)*W50 < endtime)

    • StartTime = tR - (N/2)*W50, and

    • EndTime = tR + (N/2)*W50

where

tR is the retention time,

W50 is the peak width at half height, and

N is the number of times the width at half height of the peak (between 5 and 20, depending on the Pharmacopeia).