Signal to Noise Guidance

Guidance for Determination of S/N for 1^st FID of 2D Experiment

For Sample # 2, U-¹⁵N, 20% ¹³C labeled NIST Fab System Suitability Standard (SSS):

1. Collect and Fourier Transform 1^st FID of gsHSQC experiment and calculate S/N using the regions defined in Table 9. The target for the ¹H-¹⁵N gsHSQC is 60:1 and for the ¹H-¹³C gsHSQC is 40:1.
2. Collect full 2D spectrum and calculate S/N from the average of peaks heights in the signal region (set threshold just above noise) by the RMS amplitude of noise peak heights in the noise region (set threshold so noise peaks cover most of noise region) to ensure a minimum S/N of 10:1.

For Sample #3, unlabeled NIST Fab

1. For ¹H-¹³C gsHSQC experiment we find the unlabeled NIST requires approximately 8x the number of scans as the SSS to achieve comparable S/N.
2. Collect and Fourier Transform 1^st FID of the ¹H-¹³C gsHSQC and calculate S/N using the regions defined in Table 9, the target is 40:1.
3. Collect full 2D spectrum and calculate S/N from the average of peaks heights in the signal region (set threshold just above noise) by the RMS amplitude of noise peak heights in the noise region (set threshold so noise peaks cover most of noise region) to ensure a minimum S/N of 10:1.

Table 8: Signal and Noise Regions¹

¹Guidance is for online calculations of S/N on the spectrometer console. Example calculations were performed in Topspin 3.0 using the ‘.sino’ (sino.pdf) and ‘pp’ commands for 1D and 2D calculations respectively. The documentation was taken from Topspin 3.2 "Commands."

²Two signals appeared between 6.0 and 8.0 ppm. The noise region therefore had to be shifted further downfield.

CALCULATION OF S/N ON AGILENT SYSTEMS

Use the command dsn. Click the link for a description of this command. This was taken from the "Agilent VnmrJ3.2 Command and Parameter Reference Guide."        dsn.pdf