Can TargetLynx calculate Signal/Noise as stipulated by the US Pharmacopeia standard? - WKB271167

ENVIRONMENT

• MassLynx 4.1
• MassLynx 4.2
• TargetLynx

ANSWER

TargetLynx is not able to calculate S/N using the USP formula. It would require two separate injections, one for the blank and one for the reference. Custom calculations in TargetLynx can only be based on a single injection.

Part of the reason for this is that the nature of a mass spectrometry trace is different than that of a trace on other types of detectors. TargetLynx is able to calculate S/N based on a single trace that is being measured. Most other types of detectors (such as UV) are not able to do this.

For a UV analytical sample, it is not usually possible to accurately measure signal-to-noise in the same injection.There are other things eluting that prevent you from doing this, so there is no reliable background that is just the noise. Instead, you use a calculation method based on both a reference injection and a blank.

The USP monographs are based on specific detector technology that is almost never mass spectrometry.

However, the USP accepts alternative metrics to prove analytical quality, so this is not a problem.

The S/N method in TargetLynx is the preferred method and will not be changed; nor is there any requirement to calculate S/N based on the USP formula.

ADDITIONAL INFORMATION

This is what the USP states:

The signal-to-noise ratio is calculated using the following equation:

S/N = 2H/h

H = height of the peak corresponding to the component concerned, in the chromatogram obtained with the prescribed reference solution, measured from the maximum of the peak to the extrapolated baseline of the signal observed over a distance equal to 20 times the width at half-height

h = range of the noise in a chromatogram obtained after injection of a blank, observed over a distance equal to 20 times the width at half-height of the peak in the chromatogram obtained with the prescribed reference solution and, if possible, situated equally around the place where this peak would be found.