Counter-current gas

{
  "id": "MLC-T-CHM-002638",
  "term": "Counter-current gas",
  "field": "Chemistry",
  "definition": "A flow of gas directed opposite to the path of ions entering a mass spectrometer from an atmospheric pressure ionization source. This gas, typically nitrogen, serves to desolvate ions further and to prevent neutral molecules and solvent vapor from entering the higher vacuum stages of the instrument. The pressure of the counter-current gas is carefully controlled, as excessive flow can reduce the ion signal by deflecting ions away from the inlet capillary.",
  "subject": "Analytical Chemistry",
  "see_also": [
    "drying gas",
    "spray ionization"
  ],
  "references": [
    "PAC, 2013, 85, 1515. 'Definitions of terms relating to mass spectrometry (IUPAC Recommendations 2013)' on page 1534 (https://doi.org/10.1351/PAC-REC-06-04-06)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/counter-current-gas/"
}