MSACL Conference Schedule

Improvement of Sample Clean-Up for Clinical Chemical LC-MS Analysis of Small Molecules in Biofluids
Mon 11:00 AM - Session: Small Molecule Analytes
Karl Boos
At present, main drawbacks of clinical-chemical LC-MS protocols are:
  1. time consuming and labour intensive nature of sample pretreatment,
  2. limited sample throughput, and
  3. 'matrix effects' i.e. varying suppression of the ionization yield.

Currently, Solid Phase Extraction (SPE) is the dominant clean-up technique for the extraction of drugs, xenobiotics or endogenous compounds by partitioning-, ion-exchange or affinity chromatography. In order to automate and to fully integrate SPE into a LC-MS platform the technique of column-switching (on-line SPE-LC) is applied. For that purpose a small SPE-column (e.g. 25 x 4 mm ID) is filled with tailor-made packings, i.e. Restricted Access Materials (RAM) allowing a size-selective fractionation of complex (bio)fluids and a simultaneous extraction of the target analyte(s). Such a SPE-column can be operated at flow-rates up to 4 mL/min thus reducing the clean-up time of e.g. a plasma sample to less than 60 sec.

In addition such a SPE-LC platform can be easily downsized in order to improve throughput and sensitivity. Towards the elimination of matrix effects in LC-ESI-MS we successfully extended such an on-line SPE-LC platform by a second SPE-column (multidimensional SPE) which possesses orthogonal chromatographic properties with respect to the fractionation of small molecules. This method is generic with regard to the extraction of basic drugs such as antidepressants directly from native human plasma [1].

Recently we developed a unique procedure for the direct injection, in-line processing and SPE-LC-MS/MS analysis of anticoagulated whole blood samples [2].

[1] Georgi K, Boos K-S (2006) Chromatographia 63:523-531
[2] Morello R, Milojkovic J, Boos K-S (2007) Therapeutic Drug Monitoring 29:5005