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Calibration of gas chromatography (G.C.)

Calibration of gas chromatography (G.C.)

G.C.Calibration: 

Calibration of oven: This test verifies the G.C. oven temperature accuracy using two set points 50°C, 100°C  and 230°C.Fix the temperature probe on the column hanger so that the end of the probe is aligned with the instrument's oven sensor.Secure the probe by looping the cable around the column hanger or fastening it to the column hanger with high-temperature tape.
Set point  of 50°C: Set the oven temperature to 50°C .Turn on the oven and wait for 5 minutes after the oven is ready.Observe the temperature on the calibrated thermometer's display and when the temperature stabilizes, record the reading.
Set point  of 100°C: Set the oven temperature to 100°C .Turn on the oven and wait for 5 minutes after the oven is ready.Observe the temperature on the calibrated thermometer's display and when the temperature stabilizes, record the reading.
Set point  of 230°C: Set the oven temperature to 230°C .Turn on the oven and wait for 5 minutes after the oven is ready.Observe the temperature on the calibrated thermometer's display and when the temperature stabilizes, record the reading.

 Flow test calibration: G.C. flows are achieved by maintaining a constant pressure against a known and well characterized restriction (E.P.C.). G.C. flow accuracy is determined by measuring the flows with a flow meter and comparing these measurement to the value set in gas chromatography.
Test of hydrogen gas: Hydrogen gas used as fuel.Close the detector inlet completely with an appropriate fitting.Turn off all gas flows except Hydrogen as fuel.Set the flow parameters specified as per method.Connect the flow meter to the detector exit.Record the measured value of hydrogen gas with the help of digital calibrated flow meter.
Test of air gas: Turn off all gas flows except air as support gas.Set the flow parameters specified as per method.Connect the flow meter to the detector exit.Record the measured value of hydrogen gas with the help of digital calibrated flow meter.
Test of carrier gas (Helium or nitrogen): Remove the blind plug fitting from the detector inlet and fix the column in the G.C.Turn off all gas flows except carrier gas flow.Set the flow parameters specified as per method.Connect the flow meter to the detector exit.Record the measured value of hydrogen gas with the help of digital calibrated flow meter.

Calibration of Detector response: 
Inlet Heater= 250°C 
Column=HP/BP-5, 30 m x 0.32 mm x 0.25 ┬Ám 
Oven Temperature= 50°C (Set parameter as calibration method)
Detector=FID
Detector heater=300°C
H2 Flow=30 ml/minute
Air Flow=300 ml/minute
Makeup Flow (He or N2)=25 ml/minute
Sample preparation: Sample preparation for repeatability and Linearity of detector response and flow rate : 
For Linearity: Make five different solutions for measurement of linearity of detector.
Solution-A       Take 0.2 gram Toluene and 19.8 gram IPA in 20 ml volumetric flask
Solution-B       Take 0.4 gram Toluene and 19.6 gram IPA in 20 ml volumetric flask.
Solution-C       Take 0.6 gram Toluene and 19.4 gram IPA in 20 ml volumetric flask.
Solution-D       Take 0.8 gram Toluene and 19.2 gram IPA in 20 ml volumetric flask
Solution-E        Take 1.0 gram Toluene and 19.0 gram IPA in 20 ml volumetric flask.
Plot the graph between concentration of toluene against area % of toluene
 (R2 value not less then 0.99) 
For Example:


Sol-A
Sol-B
Sol-C
Sol-D
Sol-E
Wt of Toluene
0.2011
0.4240
0.6143
0.8099
1.0082
Wt.of IPA
19.8063
19.6218
19.4187
19.2081
19.0188
% Toluene
1.0051
2.1152
3.0664
4.0459
5.0342
Injection-1
6.91
14.54
19.16
24.54
29.45
Injection-2
6.91
14.58
18.76
23.76
29.42
Mean
6.91
14.56
18.96
24.15
29.44

calibration of gas chromatography
For Repeatability: Inject Solution-2 six times and calculate RSD (Limit < 2.0%)

For Example:


Retention Time
Concentration
Calculated value from RF
Sol-B
IPA
Toluene
IPA
Toluene
IPA
Toluene
Injection 1
7.454
10.638
50.01
49.99
87.86
10.89
Injection 2
7.405
10.613
51.32
48.68
90.17
10.60
Injection 3
7.427
10.641
50.51
49.49
88.75
10.78
Injection 4
7.417
10.629
50.62
49.38
88.94
10.76
Injection 5
7.420
10.632
51.63
48.37
90.72
10.79 
Injection 6
7.455
10.651
51.46
48.54
90.41
 10.81
Avg.
7.430
10.634
50.925
49.075
89.475
10.758
STD
0.021
0.013
0.639
0.639
1.12493
0.11955
Rel. Std.
0.276%
0.121%
1.255%
1.302%
1.257%
1.111%

Calculation for RSD: Calculate the average ( x ) of all six injection area for  Impurity and purity both.Calculate the standard deviation (s) using the equation :

                                                     ∑ (x - x1 )2
                                               s =---------------
                                                         n - 1
Where x is a single measurement and x1 is the average measurement. The symbol  ∑  means 'sum of'. And n means nos of injections of the sample.
Calculate the relative standard deviation (%RSD), using the equation :

                                                          100 X s
                                          % RSD =-----------
                                                               x1







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