Bioanalysis online sample preparation

The higher selectivity attainable due to the use of LC-MS/MS is frequently reduced by decreasing the quality of the sample pretreatment and/or the chromatography. The motivation of this is an increase in the sample throughput. However, this often puts serious demands on the sample pretreatment methods. Also, the off-line sample pretreatment appeared to be the rate-limiting step. Speeding up the sample preparation is one of the most important factors in bioanalysis. One of the most applied approaches is the use of SPE or LLE in a 96-well plate format. Online sample preparation in a 96-well plate format was described by different authors. " Off-line sample preparation seems to be preferred by many researchers. 

This chapter will review recent advances in mass spectrometry, liquid chromatography, and sample preparation techniques that aim at achieving high throughput. In particular, online solid phase extraction and multiplexed HPLC front ends for quantitative bioanalysis will be discussed in detail. 

Because the instability of the N-oxide metabolite, which was subjected to decomposition during sample preparation (solvent evaporation during offline SPE), online SPE LC/MS became the method of choice for the application. Hsieh et al. (2004) built a system with two TFC cartridges and one analytical column, and another system with two TFC cartridges and two analytical columns for GLP quantitative bioanalysis of drug candidates. A Turbo C18 (50 x 1.0 mm, 5 /.mi, Cohesive Technologies), an Xterra MS C18 (30 x 2.0 mm, 2.5 /mi), and a guard column were used. Protein precipitation preceded injection. The cycle times for the two systems were 0.8 and 0.4 min. 

The limiting step in achieving fast bioanalysis is off-line sample preparation. This indicates the clear need of online sample pretreatment for speeding up sample preparation. One of most widely applied approaches is the 96-well plate format. While off-Une sample pretreatment seems to be preferred by many researchers, onUne strategies are described as well. " ... 

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