How to calculate the minimum interscan delay times for SIR Voltage experiments carried out on the AutoSpec - WKB96691

OBJECTIVE or GOAL

How to calculate the minimum interscan delay times for SIR Voltage experiments carried out on the AutoSpec.

ENVIRONMENT

• AutoSpec Premier
• AutoSpec Ultima
• MassLynx

PROCEDURE

1. The SIR Voltage experiment has a mass value, channel time, and delay (interscan) time. The delay time occurs before the channel time.
2. The minimum delay time is calculate as 1% change in mass x 1 msec + 5 msec.

3. In the example above, the mass 334 goes to mass 317 = 17Da mass change. 17/317 = 5.4% change in mass. Multiplying this by 1 msec = 5.4 msec + 5 msec = 10.4 msec. I recommend that the value be rounded up to the nearest 5 msec, so the calculated delay time should be 15 msec.

ADDITIONAL INFORMATION

1. If the minimum delay time is not calculated correctly, the first mass can fall out of relative intensity limits with respect to its M+2 isotope for EPA dioxin methods. Lowest mass ions tend to be due to the polychlor furan compounds.
2. Do not assume that canned SIR Voltage experiments that come with MassLynx have the correct calculated delay times.
3. Channel times can be altered sometimes to as low as 10 msec. Note that there will be a √2 decrease in signal/noise as a result.
4. See WKB95321 on how an SIR Voltage experiment is carried out on the AutoSpec.