Session: Session 1
Unveiling the Mystery of Dual Peaks: How Acetonitrile Injection Solvent Impacts Drug Separation in RPLC-HRMS
Forensic analysis of unknown compounds with Liquid Chromatography- Mass Spectrometry (LC-MS) requires a flexible method for diverse analytes with a wide polarity range. Sample prep is key, and solvent choice is critical. The ideal solvent dissolves a wide range of molecules and works with LC-MS, potentially even Gas Chromatography-MS (GC-MS) for gathering further information and confirming analyte identity.
A study compared 4 solvents (A: water/acetonitrile (95:5) + 0.1% formic acid, acetonitrile (ACN), toluene, and chloroform) for drug analysis using RPLC-HRMS. Surprisingly, acetonitrile yielded double peaks for some drugs, unlike the other solvents (single peak at consistent time). One peak appeared at the principal RT, mirroring the behavior in other solvents, while the other emerged at a significantly shorter retention time, potentially even at the void volume.
We propose this is due to strong interactions between some drugs and acetonitrile, forming a stable solvation shell. This could prevent rapid equilibration with the mobile phase, separating two forms of the analyte: mobile phase-solvated drugs eluting normally, and ACN-solvated drugs eluting faster (weaker stationary phase affinity when complexed with ACN). The unique immiscibility of certain water/acetonitrile ratios supports this, explaining the different behavior compared to other solvents.
Unlike GC (evaporated solvent), initial solvent choice is crucial in LC. This study suggests acetonitrile might not be universally suitable for LC-MS due to potential peak splitting.
A study compared 4 solvents (A: water/acetonitrile (95:5) + 0.1% formic acid, acetonitrile (ACN), toluene, and chloroform) for drug analysis using RPLC-HRMS. Surprisingly, acetonitrile yielded double peaks for some drugs, unlike the other solvents (single peak at consistent time). One peak appeared at the principal RT, mirroring the behavior in other solvents, while the other emerged at a significantly shorter retention time, potentially even at the void volume.
We propose this is due to strong interactions between some drugs and acetonitrile, forming a stable solvation shell. This could prevent rapid equilibration with the mobile phase, separating two forms of the analyte: mobile phase-solvated drugs eluting normally, and ACN-solvated drugs eluting faster (weaker stationary phase affinity when complexed with ACN). The unique immiscibility of certain water/acetonitrile ratios supports this, explaining the different behavior compared to other solvents.
Unlike GC (evaporated solvent), initial solvent choice is crucial in LC. This study suggests acetonitrile might not be universally suitable for LC-MS due to potential peak splitting.