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Calibration of Gas Chromatograph (GC): How to Perform
Description of Gas Chromatograph calibration
The following parameters are performed in the Gas chromatograph calibration:
- Column-oven temperature
- Flow rate of the gases
- Detector performance
- Detector precision
- Detector linearity
Frequency of the Gas Chromatograph calibration
Once in a six months ± 5 days or any failure
Reagents and instruments required for calibration
The following reagents and instruments are required with valid certificate of analysis:
- n-Hexane
- n-Tetradecane
- n-Pentadecane
- n-Hexadecane
- Calibrated temperature probe
- Capillary column, (30 meter x 0.32mm), fused silica column with 0.25µm film of cross linked methyl siloxane (HP1 or equivalent column can be used
Gas Chromatograph calibration
Column-oven temperature
- Set the column oven temperature for at least three point from 40oC to 300oC
- After about 10 minutes record the observed temperature using a calibrated temperature probe
- Ensure that temperature inside the oven is the same as that set, Also Injector and Detector temperature must equate with the temperature set for them
Acceptance criteria: The observed temperature should be within ± of the set temperature
The flow rate of the gases
Check whether the flow rate of the carrier gases (Nitrogen or Helium) is within the limit of 22.5 to 27.5 ml/minute, the Hydrogen gas flow rate is within limit of 36 to 44 ml/minute and the air flow rate is within the limit of 360 to 440 ml/minute.
Detector Performance
GC column: (30 meter x 0.32mm), fused silica column with 0.25µm film of cross linked methyl siloxane (HP1 or equivalent)
GC chromatographic conditions
| Oven temperature(1) | 40°C |
| Time(1) | 0 minute |
| Rate(1) | 25°C/minute |
| Oven temperature(2) | 90°C |
| Time(2) | 0 minute |
| Rate(2) | 15°C/minute |
| Oven temperature(3) | 170°C |
| Time(3) | 15 minutes |
| Injector temperature | 250°C |
| Detector FID temperatures | 270°C |
| Carrier gas (N2 or He) flow rate | 0.5ml/minute |
| Split ratio | 10:1 |
| Hydrogen flow | 40 ± 4 ml/minute |
| Zero Air flow | 400 ± 4 ml/minute |
| Axillary flow (N₂) | 25 ± 2.5 ml/minuteI |
| Injection volume | 1.0μl |
| Septum purge flow | 5 ml/minute |
| Syringed capacity | 10μl |
| Solvent wash pre-injection/Pre-clean with solvent | 5 |
| Preclean with sample | 3 |
| Sample pump/ filling strokes | 5 |
| Post clean with solvent | 5 |
1000mcg/ml of standard stock preparation
Weigh accurately 50 mg of each n-Tetradecane, n-Pentadecane and n-Hexadecane and transfer then in a 50 ml of volumetric flask containing 20 ml of n-Hexane and finally make up the volume upto mark with n-Hexane .
100 mcg/ml. 200 mcg/ml. 300 mcg/ml, 400 mcg/ml and 500 mcg/ml of standard mixture preparation
Take 5 five ml volumetric flasks of 10 ml capacity.
- 100 mcg/ml solution: Transfer 1 ml of standard stock solution in 10 volumetric flask and make up the volume up to the mark
- 200 mcg/ml solution: Transfer 2 ml of standard stock solution in 10 volumetric flask and make up the volume up to the mark
- 300 mcg/ml solution: Transfer 3 ml of standard stock solution in 10 volumetric flask and make up the volume up to the mark
- 400 mcg/ml solution: Transfer 4 ml of standard stock solution in 10 volumetric flask and make up the volume up to the mark
- 500 mcg/ml solution: Transfer 5 ml of standard stock solution in 10 volumetric flask and make up the volume up to the mark
Detector precision
Inject 1μl of 300 mcg/ml standard solution six times and calculate
- the ratio of the area response of n-Pentadecane and n-Tetradecane in all sex injection
- the ratio of the area response of n-hexadecane and n-Tetradecane in all six injections
Calculate the RSD of ratio of area response for both n-Pentadecane and n-hexadecane.
The retention time of n-Tetradecane is about 10.5 minutes. The following are the RRTs of the other peaks:
| Compound name | RRTs |
| n-Hexane | about 0.41 |
| n-Tetradecane | 1 |
| n-Pentadecane | about 1.16 |
| n-Hexadecane | about 1.39 |
Acceptance criteria:
Percentage RSD of the area response of the peaks corresponding to n-Pentadecane and n-Hexadecane to that of n-Tetradecane in the chromatograms of six replicatem injection should not be more than 2.0%.
Detector linearity
- Inject inject 1μl of each 100 mcg/ml. 200 mcg/ml. 300 mcg/ml, 400 mcg/ml and 500 mcg/ml of standard mixture in duplicate.
- Plot the linearity from the obtained data (in x-axis concentration and in y-axis area response).
- Acceptance criteria: The correlation coefficient (r2) should be more than 0.99
Abbreviation
- GC: Gas chromatograph
Reference
- IP
- IN-house