Postcolumn Infusion as a Quality Control Tool for LC-MS-Based Analysis

Abstract

Postcolumn infusion has been widely used to study the matrix effect of analytical methods based on liquid chromatography coupled to mass spectrometry (LC-MS). Nevertheless, this methodology is usually only applied during a method development or validation. With this application note, we aim to demonstrate that the continuous use of postcolumn infusion can be also a very useful tool to monitor the quality of LC-MS analyses and easily detect flaws in the analytical method performance. Here we propose a protocol that can be transferred to other LC-MS platforms, and we show some real situations in bioanalysis in which postcolumn infusion proved to be extremely helpful in, for example, the evaluation of a sample treatment or the detection of unexpected sources of the matrix effect.

Figure 1

(above) Matrix effect profile for atenolol-d₇ on a sample that was treated only with protein precipitation (red) or with phospholipid removal (blue). (below) Chromatogram of the phosphocholine fragment (184.075 m/z) extracted from the same samples.

Figure 2

Matrix effect profile for simvastatin-d₆ in a sample where a low response for simvastatin was observed (red) and in a sample where the expected response was observed (blue). Dotted line indicates the retention time of simvastatin. (inset) Response of simvastatin for urine samples (circles, triangles, and diamonds) or standard solutions (squares) spiked at 0.05 mg/L.

Figure 3

Matrix effect profile for atenolol-d₇ in plasma samples stored in citrate (blue) and heparin (red) tubes. The box indicates the suppression area in heparin tubes. Below, the spectra extracted from that area show the characteristic 44 Da fragmentation of poly(ethylene glycol).