45
Table 3. Average measurement accuracies with %RSD from saliva samples
Figure 9. Mass spectra for blank saliva (red) and blank water (blue) after extraction
Limits of detection (LOD) and limits of quantitation (LOQ) were estimated by calculating the standard deviation of the response at 100 ng/mL and using 3x the value for LOD and 10x the value for LOQ. Estimated limits of detection and quantitation for the analytes in saliva are given in Table 4. These detection limits in saliva show the potential for this technique to be a quick and easy way to screen many samples, prior to using more extensive confirmatory methods on positive samples.
LOD (ng/mL)
Fentanyl Alfentanil Sufenatnil
Butyryl fentanyl
5
20 15 15
Acetyl fentanyl 10 LOQ
(ng/mL) 20 70 50 50
40 Table 4. Estimated LOD and LOQ’s for saliva
Typical mass spectra obtained from the blank saliva sample, blank water sample and fortified saliva samples are given in Figures 9-10. Protonated molecular ions (M+H) (see Table 2) can be identified in the spectra in Figure 10. Additional m/z peaks at 116.0, 195.1, 271.2, and 430.3 are also present. These masses are present in the blank saliva sample but not in the blank water sample; indicating that they are small molecular weight compounds derived from the saliva matrix. The identity of these interferences was not determined as part of this study. However, the intensity of these masses was significantly higher in the blank saliva sample compared to the fortified saliva sample. The source of this enhancement effect has not been determined, but one possible cause could be that the target analytes have a higher affinity for the fibre than the matrix constituents and therefore take up the binding sites, preventing the matrix interferences from binding to the fibre.
In addition to the mass spectra, analyte responses from fortified saliva samples were compared to fortified water samples (Figure 11). The analyte responses in the saliva samples were found to be significantly higher than the responses in water. The increases in signal in the saliva samples could have several possible causes.
The presence of some of the matrix constituents could possibly be increasing the ionisation of the analytes, which would increase their MS signal compared to water, which has none of these constituents present. Another potential explanation is that the saliva matrix could be shifting the extraction equilibrium, which would cause the analytes to have higher affinities to the C18 phase on the fibre resulting in higher analyte concentrations on the fibre. A third proposed scenario is that, in the absence of matrix, the analytes in the water samples are binding more tightly to the phase on the fibre; and thus are less readily desorbed into the MS from the DART ionisation process. To determine if one or more of these scenarios are contributing to the results observed, further investigation is warranted.
Figure 10. Mass spectra obtained from 50 ng/mL fortified saliva sample after extraction
Figure 11. Analyte responses from fortified saliva and water samples
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