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How to calibrate a gas chromatograph?

Time:2018/08/12   Pageviews:29    Share:
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There are differences in the calibration of different models and different instruments. The following is for Agilent instruments for your reference:

Gas chromatograph calibration procedure

1. Purpose
In order to ensure the accuracy and reliability of the analytical data, the instrument must be calibrated, and this calibration procedure is specially formulated.
2. area
This procedure applies to the calibration of gas chromatograph using thermal conductivity cells (TCD) and flame ionization (FID) as detectors.
3. Management duties
3.1 This procedure is organized and implemented by the analytical engineers of the Quality Inspection Department.
3.2 The quality inspection supervisor is responsible for supervision and inspection.
4. Calibration items and technical requirements
4.4 Thermal Conduction Cell (TCD) Detector
4.2 Baseline noise ≤ 0.1mV; baseline drift (30min) ≤ 0.2 mV
4.3TCD sensitivity STCD≥800Mv0ml/mg
4.4 Flame Ionization (FID) Detector
4.5FID detection limit ≤ 5 × 10-10g / s
4.6FID baseline noise ≤1×10-12A; baseline drift (30min)≤1×10-11A
4.7 Quantitative repeatability of the instrument RSD ≤ 3%
5. Correction conditions
5.110μl micro-sampler
5.2 Chromatographic standard materials
5.3 benzene-toluene solution
5.4 n-hexadecane-isooctane solution
6. Correction method
6.1 Thermal conductivity cell (TCD) is the detector
6.1.1 Correction conditions Column: TDX-01 (or similar performance carrier) Stainless steel column with inner diameter 2-3mm and length 1-2m Carrier gas: helium (purity not less than 99.99%), flow rate 30-60ml/min Temperature: about 70 ° C in the oven, 100 ° C in the detection chamber, 120 ° C in the vaporization chamber Bridge flow or hot wire temperature: choose the best value
6.1.2 Determination of baseline noise and baseline drift in TCD According to the conditions of 6.1.1, the attenuation is placed in the most sensitive gear, and the zero adjuster is used to adjust the output signal to the middle of the recorder or the integrator. After the bridge current is stabilized, the baseline is recorded for half an hour. Measure and calculate baseline noise and baseline drift. The baseline noise and drift of the Agilent 7890 chromatograph are calculated and printed directly using the workstation software. In the OFFLINE, click Report→System Suitability→Edit Noise Ranges, and then enter the time range for calculating the baseline noise and drift. Select the Performance report form when viewing the report. Acceptable criteria: baseline noise ≤ 0.1mV Baseline drift (30min) ≤ 0.2mV
6.1.3TCD sensitivity AFC determination Under the condition of 6.1.1, after the baseline is stabilized, inject 2 μl of a benzene-toluene solution with a concentration of 5 mg/ml, and inject continuously for 6 times to record the area of ??the benzene peak.
STCD: TCD sensitivity (Mv. ml/mg); A: arithmetic mean of benzene peak area; W - benzene injection amount (mg);
Fc - corrected carrier gas flow rate (ml/min) Acceptable criteria: STCD≥
6.2 Flame Ionization (FID) Detector
6.2.1 Correction conditions The column is DB-5 or HP-5, the inner diameter is 0.25~0.32mm, the film thickness is 0.25~0.32μm, and the length is 30~50m. Carrier gas: helium (purity ≥99.99%), flow rate 1-2ml/min; hydrogen (purity ≥99.99%), flow rate 50ml/min; air, must not contain dust, moisture and corrosiveness that affect the normal operation of the instrument Substance, flow rate 450ml/min Diversion to 1:50 Temperature: about 150 ° C in the oven, 300 ° C in the detection chamber, 260 ° C in the gasification chamber Range: Select the best value Liquid reference material: 100 ng/μl n-hexadecane-isooctane solution
6.2.2 FID baseline noise and baseline drift correction measurements According to the calibration conditions of 6.2.1, after ignition and after the baseline is stable, record for half an hour, measure and calculate baseline noise and baseline drift Baseline noise and drift calculations for the Agilent 6890 chromatograph are the same as in 6.1.2. Acceptable criteria: baseline noise ≤ 1 × 10-12A Baseline drift (30min) ≤ 1 × 10-11A
6.2.3 Determination of FID detection limit Under the calibration conditions of 5.2.1, the instrument is in optimal operation. After the baseline is stabilized, inject 2 μl of 100 ng/μl n-hexadecane-isooctane solution into the sample with a micro syringe. Next, calculate the arithmetic mean of the area of ??the n-hexadecane peak. Calculate the detection limit according to the following formula: DFID=2NW/A
DFID: FID detection limit ( g / s); N: baseline noise (A); W: injection volume of n-hexadecane (g)
Peak area of ??n-hexadecane (A.S) Acceptable standard: detection limit ≤ 5 × 10-10g / s
6.3 Quantitative repeatability determination
6.3.1 Quantitative repeatability According to the detector conditions used, the measured peak area of ??the component is expressed as relative standard deviation RSD.
6.3.2 Calculate the relative standard deviation by pressing the formula:
n 1
RSD = [∑(Ai- A )2]/(n-1) × ×100%
I=1 A
RSD: relative standard deviation (%); n: number of measurements; Ai: peak area measured at the ith
A: arithmetic mean of peak area of ??n injections; I: injection number; acceptable standard: RSD ≤ 3%
7. Performance confirmation
7.1 Use standard products or test articles to confirm that the performance of the instrument meets the requirements for use;
7.2 First confirm the performance of the column, including: resolution, symmetry factor, theoretical plate number and peak area standard deviation.
7.3 Confirmation of GC column
7.3.1 Test standard: 250 ppm CH2Cl2 solution of hexanediol, p-chlorophenol, methyl decanoate, 4-propylaniline, n-tridecane, undecyl alcohol, pentadecane.
7.3.2 Instrument conditions: The gasification chamber temperature is 260 ° C, the detector temperature is 320 ° C, the constant flow rate is 1.0 ml / min, the column constant temperature is 130 ° C, the injection volume is: 1 ul, running 15 min., diversion 1:50 .
7.3.3 Column: HP-1 30m×0.25mm×0.25um; HP-5 30m×0.32mm×0.25um; TDX-01 stainless steel column with inner diameter 2-3mm and length 1-2m.
7.3.4 Evaluation criteria: 5 consecutive analyses, resolution R>1.5; pentadecane symmetry factor S in the range of 0.80~1.50; pentadecane column efficiency>3000m-1; standard deviation of pentadecane peak area ≤ 3.0%.
7.4 Step by step according to the performance verification method, and record the spectrum; according to the results of the performance test, evaluate whether the instrument meets the performance requirements.
8. Correction result processing and correction cycle
8.1 Calibration Results All items that meet the technical requirements can be used. If some items fail to meet the specification requirements, the instrument owner will report to the QC manager in the form of a maintenance report, and the QC manager will approve the maintenance plan.
8.2 The calibration period is 1 year.
9. Formed records

This is the end of the introduction of  How to calibrate a gas chromatograph. I hope it can help you.


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