22 February / March 2021
OPI, solvent sweeps the droplet to the mass spectrometer. This built-in ‘dilute-and-shoot’ process minimises matrix suppression effects that would normally result from injecting straight plasma into the MS. The result is higher ionisation efficiency for analytes and excellent sensitivity - all without any sample preparation.
A further study involved the analysis of angiotensin in yeast fermentation broths (Figure 5) [5]. The samples were prepared by lysing the active broth with 4:1 v/v acetonitrile/water and adding angiotensin standard to represent 25, 30 and 50 mg/L angiotensin in broth. The samples were then diluted with 40:60 v/v acetonitrile/water to 1x, 10x and 100x dilutions and subsequently centrifuged for 15 mins at 14000 rpm.
Very high reproducibility with consistent and precise quantification was observed across all dilutions, even for the least dilute sample. Even with such a complex matrix, almost no sample preparation was required.
Overcoming Matrix Suppression Effects
Figure 3. Linearity of injection. Droplet ladder (bottom) showed a reproducible, linear response from 1 through 20 droplets. 10 replicates were collected for each point on the droplet ladder (top).
Reproducible Analytical Performance
Despite the elimination of LC, the rapid delivery of sample via ADE to the OPI provides reproducible performance, as demonstrated with the Echo® MS System (SCIEX, Redwood City, CA). When a 384-well plate containing 100 nM dextromethorphan in 10% v/v methanol/water solutions in every well was analysed, MRM peak areas of 1.98% were achieved across all 384 wells (Figure 2). Additionally, all 384 wells were analysed in just under 7 minutes [4].
Furthermore, when a ‘droplet ladder’ study of 1 to 20 droplets (10 replicates for each) was generated from one of the dextromethorphan sample wells, the %CV obtained for the 10 replicates across the droplet ladder was <3% with excellent linearity and R2
samples was observed by the Boehringer Ingelheim researchers. For solutions of fentanyl in protein precipitated plasma, 1:1 plasma in water and untreated plasma, the best performance in establishing concentration curves was obtained with the untreated plasma solution, unlike the results with conventional LC-MS (Figure 4) [4].
This result occurs because in AEMS, when the sample droplet from the ADE enters the
In addition to affording an acceptable level of sensitivity, reproducibility and linearity, the AEMS approach negates the matrix suppression effects commonly observed with LC-MS methods. This behaviour was demonstrated using the Echo® MS System by analysing standards prepared in plasma fortified with PEG400 that were treated as quality controls when the data was processed [6]. PEG400 is a common formulation agent used in pharmaceutical research that can have significant suppressive effects in electrospray mass spectrometry.
of 0.9997 (Figure 3) [3]. The
ability to specify the number of droplets is analogous to adjusting an injection volume in standard HPLC work.
Little Sample Preparation Needed
The ability to achieve this type of reproducibility even for complex or ‘dirty’
Figure 4. Example calibration curve for fentanyl in untreated plasma. Concentration curve from X to Y ng/ mL of fentanyl in untreated plasma was generated and run with n=5 ejections at each concentration level.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56
