Industrial isobutane (HC-600a) (2)

4 Test method

Unless otherwise specified, only reagents confirmed to be analytically pure and tertiary water conforming to GB/T6682 are used in the analysis

The standard solutions, preparations and products used in the analysis shall be prepared in accordance with the provisions of GB/T601 and GB/T603 when other requirements are not specified

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Take 10mL of the non-boiling cooled sample in a test tube with an inner diameter of 15mm.

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Using gas chromatography, under selected chromatographic conditions, the sample is vaporized and passed through the chromatographic column to separate the components.

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2 Chromatographic column:

a) Packed column: 3m×3mm (inner diameter) stainless steel or other suitable material column: the fixing solution is β, β'-oxydipropionitrile, and the carrier is a white silica gel support
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The preparation of the stationary phase is carried out in accordance with the provisions of 5.
1 in GB/T7375-1987, and the packing of the chromatographic column is carried out in accordance with the provisions in 5.
2 of GB/T7375-1987;

b) Capillary column: 100% dimethyl polysiloxane , 50m×0.
25mm (inner diameter)×0.
25um or PLOT-Al ₂ O ₃ , 50m×0.
53mm (inner diameter)×1.
5um;

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3 Recorder: chromatographic workstation or chromatographic data processor;

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4 Sampling cylinders: double-valve type small steel cylinders with working pressure greater than 3.
0MPa;

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5 Sampling catheter: dry copper pipe, about 50cm in length and 4mm in inner diameter;

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6 Injector: 1.
0mL gas-tight syringe, automatic injection valve or micro liquid injection valve
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4 Chromatographic analysis conditions

The recommended chromatographic operating conditions are shown in Table 2
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See Appendix A for typical chromatograms and relative retention values
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Other chromatographic columns and chromatographic operating conditions that can achieve the same degree of separation (the difficult-to-separate substances of the packed column have R≥1.
2 for isobutane and n-butane ) can be used
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Table 2 Recommended chromatographic operating conditions

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5 Analysis steps

Start the gas chromatograph, debug the instrument according to the chromatographic operating conditions listed in Table 2, and prepare for sample injection analysis after it is stable
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Invert the sampling cylinder, open the liquid phase port valve, adjust the appropriate flow rate, use the sampler to draw samples from the sample cylinder liquid phase port several times or continuously purge and empty the sampler, and take the liquid vaporized sample for analysis; Or use a micro-liquid injection valve for sample analysis.
Quantitative by area normalization
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6 Result calculation

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1 The mass fraction of isobutane content W ₁ · The value is expressed in %, calculated according to formula (1):

Where:

A—The peak area of ​​isobutane;

∑A _i — the sum of the peak areas of each component
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Take the arithmetic mean of the two parallel determination results as the determination result
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2 The mass fraction w _{2 of the} total unsaturated hydrocarbon content , expressed in %, calculated according to formula (2):

Where:

∑A _b —the sum of the peak areas of unsaturated hydrocarbons;

∑A _i — the sum of the peak areas of each component
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Take the arithmetic mean of the two parallel determination results as the determination result
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When the mass fraction of total unsaturated hydrocarbons is less than or equal to 0.
01%, the relative deviation of the two parallel determination results is not more than 15%
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When the mass fraction of total unsaturated hydrocarbons>0.
01%～≤0.
1%, the relative deviation of the two parallel determination results is not more than 10%
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When the mass fraction of total unsaturated hydrocarbons is greater than or equal to 0.
1%, the relative deviation of the two parallel determination results is not more than 5%
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7 Repeatability of isobutane content

In the same laboratory, the absolute difference between the two independent test results obtained by the same operator using the same equipment, using the same test method, and independently testing the same test sample within a short period of time is not more than 0.
10%.
If it is greater than 0.
10%, it is premised that it does not exceed 5%
.

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8 Use capillary column chromatography as the arbitration method