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.