Table 4 Main considerations for the selection of LC method parameters for NTS
From: NORMAN guidance on suspect and non-target screening in environmental monitoring
Selection | Consideration |
|---|---|
Separation approach(es) | Compound domains “One fits all” compromise or different complementary methods Same or different methods for positive and negative mode ionisation |
Stationary phase chemistry | Compound domains of interest Compatibility with mobile phase (pH, high aqueous fraction) |
Column dimensions / particle size & flow rate | Peak width to match temporal resolution of MS (Sect. “Choice of mass spectrometry settings”) Flow rate compatible with ionisation source (Sect. “Choice of ionisation technique”) Overall analysis time Robustness of analysis |
Gradient time | Peak capacity vs. overall analysis time |
Use of inline-filter and pre-column | Protection of (more expensive) main column and robustness vs. increased dead volumes |
Eluents: Methanol or acetonitrile, additional solvents | Cost (acetonitrile is more expensive) Preferred (or only possible) choice for particular stationary phase Lower viscosity of acetonitrile Protic or aprotic eluent Matrix load of samples |
Eluent additives / eluent pH | Retention and peak shape of ionisable compounds Compatibility with stationary phase Compatibility with ion source MS ionisation behaviour (see Sect. “Choice of ionisation technique”) |
Column oven temperature | Decreased viscosity and back pressure vs. column stability (dissolution of silica gel at higher temperature) |
Purity of eluents and additives | Cost vs. background noise/contamination |
Injections solvent and volume | Solubility of compounds and matrix constituents vs. peak shape deterioration for high solvent fractions |