LC-MS Column and Solvent Guide

When purchasing a column, an appropriate guard column should be purchased to extend the life of the column.

The LC-MS will give the best results when using a 2.1mm ID column with 3um particle size.

Common Reverse Phase Columns:

C-18: Highest Retention, low selectivity (most common, good starting point)
C-8: High Retention, low selectivity
Phenyl: Moderate Retention, Unique selectivity

Common Reverse Phase Solvents:

Decreasing Polarity, Water Mathanol Acetonitrile THF, Increasing Solvent Strength

Solvents should be LC-MS grade. HPLC grade may not be sufficient, especially when dealing with acetonitrile.

Solution Chemistry

The pH of the solvent has a major effect on analytes in solution:

Acidic pH (<7.0; 5 preferred) for positive ions
Basic pH (>7.0; 9 preferred) for negative ions

*See column manual, for pH tolerance of column*

Manipulation of the pH can enhance the performance for analytes that are weak bases or acids. Only volatile additives should be used for pH adjustment.

Acidic additives for positive ion mode:

Formic acid, 0.1-1.0%
Acetic acid, 0.1-1.0%

Basic additives for negative ion mode:

Ammonium hydroxide (pH10-11)