Basic requirements

Basic requirements

The general requirements and ideas in developing a new HPLC/TOFMS for example are:

1. Drug discovery--this is the most focused market especially target oriented compound assays.
2. Sample throughput --1000 samples per day, 24 hours per week operation.
3. Chromatography retention time reproducibility--CV = 0.1%
4. Compatible to FAST-LC technology (one minute separation)
5. MTBF = one year or better
6. Mass accuracy of 3 ppm at ''m/z''=609

The above are very common requirements but they are more complex then they seem. For example, how many target compounds should be determined from a single injection of chromatography? If the purpose is to confirm an organic compound then a total of three target compounds per chromatogram may be a practical number. If the purpose is to analyze a metabolite analysis assay from an in vivo sample, then the total number of target compounds must be more than three. In order to make correctly design the instrument both the practical and maximum number of targets should be estimated.

Another consideration is the ''m/z'' difference of each target compound that the customer wants to indentify within a single sample. For example, when analyzed with in-source CID, 1-hydroxytacrine (m/z=215.1184) forms two fragment peaks, one by the loss of -OH and another by the loss of -NH₂. The mass difference between these two fragments is 23.8mDa. Therefore, the instrument should have a resolving power higher than 8500 and the mass accuracy for this compound should be 2.3mDa (12ppm).

Expecting the user to use UHPLC separation the average chromatographic peak width should be less than half a second. In order to assay the target compound it has to have more than ten sampling points per peak with a practical sampling interval around 50ms (20Hz) to avoid loosing sensitivity.