Design qualification

Design Qualification

Once we determine an SST method, we have to verify that instrument appropriately meets the design qualifications.

Absolute mass accuracy

Mass accuracy is dependent on calculation accuracy of the centroid calculation. The centroid calculation is dependent on the sampling point. Assuming that the profile mass peak follows the Gauss function and the sampled data point is exactly symmetrical along the Gauss function peak apex, the estimates result has zero error. The more the sampling point moves away from a symmetrical position, the more the theoretical calculation error increasings. This theoretical error will follow a sin curve.

Before a discussion of instrument mass accuracy takes place a centroid calculation performance should be qualified by using a theoretical (mathematically generated) spectrum with and without simulated noise.

Retention time accuracy and reproducibility

In the same way as mass accuracy, the retention time calculation accuracy needs to be validated using a mathematically generated signal. In addition to calculation algorithm validation, absolute accuracy for chromatographic time has to be validated.

If the chromatographic sampling interval is 100ms (10Hz) and if the injection timing signal is flagged on a data (spectrum), injection timing may have a delay of a maximum of 100ms. Observed retention time may be vary between 0 and 100ms injection to injection. One hundred milliseconds of error is corresponding to 0.16% peak to peak error at time 1.0min is roughly 0.05% RSD. According to the user requirements of 0.1% CV for retention time reproducibility, this hardware configuration is critical and difficult to realize.

If the requirement does not require UHPLC separation, practical chromatography run time is five to ten minutes since 100ms error is small and can be ignored to meet the 0.1% retention time reproducibility requirement. However less than one minute chromatographic separation is expected on UHPLC, practically less than 45 seconds of chromatogram, and so traditional injection signal handling hardware configuration causes serious problems.

When using gradient elution for chromatography, keeping a constant injection interval is important for retention time reproducibility. Because the next sample injection will occur before a complete re-equilibration from the previous injection, keeping a constant interval (timing) of the gradient run will make the chromatogram reproducible.

The customer requires “high throughput” chromatography so keeping a constant interval injection to reduce the total analysis time is an essential requirement.

Planning Performance Verification

Detection sensitivity and resolving power of the mass spectrometer depends on the tuning. If the tuning procedure is not well determined the acquired data may not be able to be analyzed properly. We determined a standard procedure for tuning the instrument and verified the tuning and the condition of the entire instrument by running our SST before acquiring any data.