GC capillary / packed gel column; helium flow / passive flow…
Short overview of current designs?
Detection of baseline shifts, i.e. baseline not at 0 for all cupsSlow hV scan: see both shift in baseline before and after a given peak. Peak jump: that is, switch gas definitions to one with same tune conditions but offset hV. Jump position: determine from slow hV scan, pick stable baseline region Other signs: drift in d47 vs D47 slopes for heated/equilibrated gases
Causes of baseline shiftsSecondary electrons. Ion beam can kick off electrons when it hits the cups (or walls, other detector components, etc.) This shows up as a negative baseline, especially in the very sensitive cups and wider cups. Scales with main ion beam intensity. Peak tailing. The main ion beam does scatter slightly in flight, and some of those ions can be picked up in other cups. This shows up as a positive baseline. Scales with main ion beam intensity. ''to be continued''