A series of experiments was designed to test the long-term performance of the Q-Tof Premier. The tests utilized temazepam in plasma in order to generate representative “real world” results. The results obtained indicate the typical mass accuracy and dynamic range values that can be obtained with the Q-Tof Premier. Using temazepam (500 pg/μL), the mass measurement performance of the Q-Tof Premier was tested over extended, continuous periods in both V-and W-mode resolution geometries. In addition, temazepam was used to test the linear dynamic range in both MS and MS/MS modes.
An example of the data acquired for temazepam in plasma are presented in Figure 2, where the total ion chromatogram and the m/z 301.074 extracted exact mass chromatogram are shown. For the corresponding exact mass spectrum in Figure 3, the data were generated by simply combining the data across the extracted ion chromatogram at half-height to generate an accurate mass spectrum with only a –0.7 ppm error. With pDRE, it is no longer necessary to be selective in the choice of data in order to generate an accurate mass spectrum.
Isocratic conditions were chosen to deliberately increase the retention of temazepam on-column, so that Q-Tof Premier performance could be tested over an extended period of time. Initially, the mass measurement performance was tested in V-mode, where 95% of the mass measurements made were within a 5 ppm error. After 500 consecutive injections in V-mode, an overall RMS error of 2.45 ppm was obtained (Figure 4).
The mass measurement performance test was continued with W-mode geometry and another 500 consecutive injections were made. The resulting data was automatically processed with MetaboLynx. Overall, 100% of the mass measurements made in W-mode were obtained within a <5 ppm error and 95% were obtained at <3 ppm. An RMS error of 1.47 ppm was obtained for the 500 consecutive injections in W-mode (Figure 5). The Q-Tof Premier was calibrated once in V-mode and W-mode, and operated continuously 24 hours a day for eight days before the experiment was completed. The results obtained were acquired using leucineenkephalin as a reference mass, with the Q-Tof Premier’s LockSpray interface. As can be seen from the mass measurement errors obtained, LockSpray “on-the-fly” mass correction is an extremely robust technique and clearly compensates for the environmental fluctuations in a typical laboratory.
pDRE extends the operating range of the Q-Tof Premier to four orders of magnitude. As a result, both quantitative and qualitative studies can be performed, with the benefits of full-spectrum acquisition and accurate mass measurement. In MS mode, a correlation coefficient of r=0.999851 was obtained for temazepam in plasma from 0.5 to 5000 pg/μL (Figure 6). For the corresponding MS/MS linearity plot, a correlation coefficient of r=0.9997 was obtained (Figure 7).
In MS/MS mode, the combined peak areas of the product ions m/z 283.062 and 255.067 and the remaining parent m/z 301.074 were used to determine the response obtained. An example of the MS/MS exact mass spectrum acquired for temazepam at 500 pg/μL is shown, where all of the mass measurements were determined with a <5 ppm error. From the exact mass spectrum shown in Figure 8, it can be seen that accurate mass measurement enables the elemental composition of the product ions to be determined along with the full isotope pattern, which in itself helps to facilitate rapid structural elucidation. The results illustrate that excellent accurate mass measurement was obtained.
As displayed in Figure 9, a typical monthly 1-minute calibration has residuals of just 0.042 mDa – a result of the latest innovations in electronics, power supply design and ion optics enhancements incorporated into the Q-Tof Premier instrument design. This, in turn, facilitates the routine acquisition of data with <3 ppm error as standard for busy laboratory environments.
