Increasing Sample Throughput using a Dual Ion Source on a Triple Quadrupole Mass Spectrometer Sha Joshua Ye, Ellie Majdi, and George Scott, IONICS Mass Spectrometry Group, 32 Nixon Rd, Bolton, Ontario L7E 1W2, Canada PARAMETRIC STUDY RESULTS In order to take advantage of the dual probe ion source for increased sample throughput, there should be little interference between the probes. Therefore studies are undertaken to verify the absence of interference or potential carryover (for example, due to mixing or contamination) between source probes. Such investigations are performed on an IONICS 3Q Molecular Analyzer Series A triple quadrupole MS equipped with an ESI/ESI coaxial flow TorrentTM dual ion source[1] connected to two Shimadzu Prominence XR LC’s. The experimental setup is shown in Fig. 1. A parametric study of the source probe physical parameters is first carried out to evaluate the effect of one source on the other. Quantitative studies are then carried out to verify the results using the optimal source conditions of a coaxial flow ion source obtained from the parametric evaluation. A switching valve is used to divert the Analysis 1 solvent from the source when the Analysis 2 is running, and vice versa. 0.9 0.8 Vitamin D3 Nebulizer gas of non- Nebulizer gas of nonconcentration analytical probe OFF analytical probe ON (pg/ul) Area Area 0.7 0.6 Two separate LC analyses of Vitamin D3 at low pg/ul level are run sequentially using optimal condition from previous analysis, one on each probe, creating two separate calibration curves. A low nebulizer gas flow was used on the non-analysis probe. The results without and with internal standard (Vitamin D2) are shown in Figs. 4 and 5, respectively. The results show good linearity (R=0.9995) and correlation of variant (CV) values of less than 5% for each quantitation curve, shown in Fig. 4. The single calibration curve created by combining the data from both probes agree reasonably well with an average CV value of 7% when an internal standard is used, shown in Fig. 5. 0.5 0.4 50 Nebulizer Gas 5516 5482 12000 2911 2956 3.5 probe 1 10000 0.3 probe 2 Heating Gas 0.2 100 Probe Temperature 0.1 9952 9981 5432 5396 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Normalized Non-analytical Probe Parameter Value Figure 2. Probe 1 performance with respect to probe 2 parameter Table 1. Effect of nebulizer gas of the non-analytical probe on the analytical probe signal Area (Analyte) APPROACH 1 Relative Intensity of Analytical Probe Single ionization sources are standard for quantitative analysis on triple quadrupole systems combined with liquid chromatography (LC/MS/MS). The total analysis time per sample consists of the MS/MS analysis time plus the LC system conditioning time. One way to increase the throughput is to minimize the LC conditioning time by employing two LCs, and analyzing the electrospray output sequentially. Traditionally, coordination of multiple LCs is handled by use of switching valves. Running two LCs using two separate ion source inlets could accomplish the same goal without possible carryover and contamination problems seen in the single source dual analysis. This concept is tested by optimizing the physical parameters of the dual ion source, and evaluating the sample calibration curves generated from the source probes. CALIBRATION CURVES Area Ratio (Analyte/Internal Standard) INTRODUCTION 8000 6000 4000 2000 Probe 2 2.5 2 1.5 1 0.5 0 0 0 (b) blank Probe 1 3 20 40 60 80 100 Concentration (pg/ul) 0 20 40 60 80 100 Concentration (pg/ul) (a) analyte Figure 4. Calibration curves from sequential run on the dual source Figure 1. Dual probe coaxial flow ion source operated in ESI mode Similar results are also obtained running testosterone in the dual source mode. The results (not shown) show good linearity and CV values for each quantitation curve. The stability of the instrument running in dual source mode is also evaluated by injecting the same concentration sample 20 times. The relative standard deviation (RSD) of the peak area obtained from these injections is less than 4%. Figure 3. (a). An injection of high concentration Vitamin D3 from Probe 1, (b) followed by an injection of blank from Probe 2 EXPERIMENTAL CONDITIONS A parametric study of the source probe physical parameters is accomplished by split flow infusion of 10ul/min of the compound of interest into 500ul/min of mobile phase (30/70 of water/methanol, 2mM ammonium acetate, 0.1% formic acid) for each probe. The physical source parameters investigated to determine the effect of operating parameters of one probe on the other probe include: nebulizer and heating gas flow; probe position; and temperature. The signal intensity from one probe is monitored while varying the parameters on the other probe. The quantitative studies are carried out by choosing the optimal source conditions of a TorrentTM ion source obtained from the parametric evaluation. Testosterone and Vitamin D3 are chosen as the compound of interest to evaluate the dual source performance in real application. The possibility of compound carryover or mixing between probes is investigated by injecting a high concentration analyte from one probe, and a low concentration or blank from the other probe. The LC columns used in this study are Fortis C18 50x2.1mm and Genesis C18 30x2.1mm, and the mobile phases used are 30/70 of water/methanol, 2mM ammonium acetate, 0.1% formic acid. Figure 5. Calibration curves from sequential run on the dual source with internal standards Various source parameters are investigated to determine the effect of operating parameters of one probe on the other probe. In general, the signal from one ESI probe is found to be most susceptible to the nebulizer flow of the other non-analysis probe, whereas the effect of all other parameters combined is minimal, as shown in Figure 2. Therefore, in practice, the interaction of the non-analyzing probe nebulizer gas flow on the analysis probe can be minimized by reducing the non-analysis nebulizer gas flow. Duplicate injections of two concentrations of Vitamin D3, with and without using the maximum nebulizer gas from the non-analysis probe, were performed to verify the parametric study mentioned above. The results are summarized in a Table 1. Possible compound carryover between probes is examined by alternatively injecting a high concentration (1000 pg/ul) analyte Vitamin D3 from one probe and a blank from the other probe in triplicate. Examples of high concentration and blank sample raw data chromatogram are shown in Figure 3. The chromatograms indicate the signals of blank sample are the background from the matrix and the carryover between injections is very small. CONCLUSIONS Experimental study of ESI/ESI dual probe ion source application for increasing sample analysis throughput was performed on IONICS 3Q Molecular Analyzer Series A triple quadrupole MS equipped with a dual probe ion source. The results indicate: The critical parameter of the non-analytical probe is the nebulizer gas, which reduces the analyzing probe’s intensity by ~50% at most. The carryover issue is not present in current setup. The results show good linearity (R2=0.9995) and CV values (<5% ) for each quantitation curve. The calibration curve by combining the data from both probes agree very well when internal standard is used. All the results indicate that this configuration can increase sample throughput without sacrificing quantitation quality. 1. Charles Jolliffe, Lisa Cousins, Sergeui Savtchenko, Theoretical Study of the Effect of the Swirling Flow in Ion Focusing in a Coaxial Flow Ion Source, 2009 ASMS meeting poster.
© Copyright 2024