User`s guide

Chapter 5 Optimizing Instrument Settings
5-80 PerSeptive Biosystems
5
When to use Turn on Low Mass Gate when:
• Analyzing masses greater than 2,000–3,000 Da
• Matrix signal is more intense than the sample signal
Optimum setting
for starting mass
You will need to experiment with the optimum setting for the
starting mass (threshold) for Low Mass Gate. As a general
guideline:
• If you are analyzing peptides in the 400 to 2,000 Da
range, set the Low Mass Gate ~350 Da
• If you are analyzing peptides in the 2,000 to 8,000 Da
range, set the Low Mass Gate ~500 Da
• If you are analyzing samples in the 10,000 to 30,000 Da
range, set the Low Mass Gate ~3,000 Da
When not to use Do not use Low Mass Gate if:
• You are analyzing peaks in the same mass range as
matrix peaks
• You are using a matrix peak to calibrate
NOTE: Low mass gate is automatically disabled when you
change the instrument mode to PSD.
Low Mass Gate
spike
When Low Mass Gate is turned on, a characteristic spike may
occur in the spectrum (Figure 5-20). This spike is typically only
seen in Reflector mode.
NOTE: Systems with high current detectors (Voyager-DE
systems with serial number 1128 and later; Voyager-DE
PRO systems with serial number 6007 and later;
Voyager-DE STR systems with serial numbers 4112, 4113,
and 4116 and later) do not typically exhibit this spike. Older
systems (with a dual channel plate detector in Linear mode)
may exhibit a 50 to 1,000 mV spike.