Summary
Optimization of signal-to-noise ratios (S/N) by optimizing electron multiplier (EM) voltage and resolution of the first and second mass analyser in a thermospray (TSP), tandem mass spectrometer system is studied. Using flow injection analysis (FIA) of samples containing eight chlorophenoxy carboxylic acid herbicides and bentazone, and a FIA system, the signal and background (noise) intensity i.e. S/N are studied with selected reaction monitoring (SRM) at different EM voltages. An EM voltage of 2500 V improves the S/N ratios 5.5–13 fold compared to the usual 1700 V. Applying additional resolution voltages of +3 to +4 V to the first and second mass analyser decreases resolution in each mass analyser, but there is no overall loss in selectivity, while the S/N ratios further increase 3–4 fold. The selectivity of measurements was studied using 2,4,5-T ((2,4,5-trichlorophenoxy)acetic acid) and triclopyr, which differ only one mass unit in the selection of the parent and daughter ion mass in the applied SRM method. Resolution could be decreased to 36–54% valley definition, while still ensuring the selectivity. With the herbicides studied, screening of surface water samples spiked at the 1 μg l−1 level, corresponding to 25 pg component s−1 into the MS, is easily achieved under optimum conditions without analyte concentration. Some sample clean-up is recommended, however, because ionization efficiencies tend to diminish with some of the raw sample studied.
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Abbreviations
- COFF:
-
Collision offset voltage
- CPCA:
-
Chlorophenoxy carboxylic acid herbicides
- dalton:
-
Atomic mass unit (12C=12 daltons), symbol “u”
- EM:
-
Electron multiplier
- FIA:
-
Flow injection analysis
- LC:
-
Liquid chromatography
- LC-MS:
-
Liquid chromatography — mass spectrometry
- m:
-
Mass
- M/ΔM:
-
Resolution defined as valley definition
- MRM:
-
Multi reaction monitoring
- MS-MS:
-
Technique utilizing mass analysers in tandem.
- MS:
-
Mass spectromet(er)ry
- MSMSC:
-
Empirical correction factor compensating for loss of energy by ions in collision cell
- m/z:
-
Mass number-to-charge number ratio
- NEU:
-
Neutral loss scan
- Q1:
-
First quadrupole analyser of triple quadrupole MS
- Q3:
-
Second quadrupole analyser of triple quadrupole MS
- Q1MS:
-
MS with tandem mass spectrometer; first mass analyser scanning.
- Q3MS:
-
MS with tandem mass spectrometer; second mass analyser scanning
- RIC:
-
Reconstructed ion chromatogram
- S/N:
-
Signal-to-noise ratio
- SRM:
-
Selected reaction monitoring
- Tandem:
-
MS-MS
- TSP:
-
Thermospray
- z:
-
Charge
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Geerdink, R.B., Kienhuis, P.G.M. & Brinkman, U.A.T. Optimization of instrumental parameters for flow injection analysis-thermospray tandem mass spectrometry. Chromatographia 39, 311–319 (1994). https://doi.org/10.1007/BF02274519
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DOI: https://doi.org/10.1007/BF02274519