Abstract
Sensitivity is one of the main specification parameters of a Single Quadrupole GC-MS Instrument. Sensitivity can be defined as ability of the instrument to detect the lowest amount of analyte present in the sample matrix. Signal to Noise ratio (S/N) is the ratio of signal height to average noise in chromatographic system, which is used to estimate the lowest limit of detection (LOD) and limit of quantification (LOQ).
Standards & solution
The GC/MS Sensitivity test standard Octafluoronaphtalene 1 pg/ul is directly purchased from Restek #573251
Procedure:
The instrument is tuned and calibrated as following:
Tab. 1. GC-MS Parameters
| GC conditions | |
| GC-MS system | Q-Tek GC-MS |
| Injector | Split/Splitless (liner: Restek 4 mm x 6.3 x 78.5) |
| GC column | (15m x 0.25mm; 250um) |
| Injection volume | 1 ul |
| Injector mode | Splitless; Purge 75 ml/min after 0.75 min |
| Injector temp. | 250°C |
| Carrier mode | Constant flow |
| Oven program | 45°C 2min;
40.0°C/min 200°C, 0.0min; Total run time: 5.58 |
| Carrier flow | (He) 1.0 ml/min |
| МС interface temp | 230°C |
| Detection parameters | |
| Ionization source | (EI) |
| T° Source | 230°C |
| Solvent delay | 3.0 min |
| Scan mode | SCAN 50 – 300 Da / Scan |
| Multiplier(SEM) | Atune+200v |
Analytical results and discussions
The Total Ion Chromatograms (TIC) was collected by injecting replicate injections of 1pg/μL of Octafluoronaphthalene (#573251) in GCMS as per the instrument conditions described above. The extracted ion chromatogram (EIC) of Octafluoronaphthalene was obtained by extracting the m/z 272 +/-0.1 Da. The Signal to Noise ratio for all the EIC chromatogram was calculated by using Q-tek Analytic v1.016® software. EIC showing signal to noise ratio achieved on Octafluoronaphthalene are annotated in the following figures:
Pic.1. EIC Chromatograms of 272 m/z +/- 0.1 Da Octafluoronaphthalene
Tab. 2. Signal-to-noise ratio RMS
| # Injection | S/N rms | Average value |
| 1 | 2478 | 2611.17 |
| 2 | 2852 | |
| 3 | 3572 | |
| 4 | 2157 | |
| 5 | 2357 | |
| 6 | 2251 |
Conclusions
The average Signal to Noise ratio (S/N) were found to be 2611.17 after injecting 1.0 μL of 1pg/μL of Octafluoronaphthalene successively for 6 times. Consequently, based on the results obtained in the current studies, it can be concluded that the GC-MS instrument shows high sensitivity in term of S/N ratio in scan mode.
