GB/T 17623-2026 Gas chromatographic determination of dissolved gas component content in insulating oil

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Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: GB/T 17623—2026
• Chinese title: Gas chromatographic determination of dissolved gas component content in insulating oil
• English title: Determination of component al contents of gases dissolved in insulating oil by gas chromatography method (the English title in the source text is written as Determinationofcomponentalcontentsofgasesdissolvedininsulatingoilbygaschromatographymethod, requires confirmation against the source standard (source-text extraction))
• Replacement relationship: replaces GB/T 17623—2017
• Previous versions: first issued in 1998 as GB/T 17623—1998, first revision in 2017; this is the second revision
• Publication/implementation: published on 2026-04-30, implemented on 2026-08-01
• Custodian: National Technical Committee for Standardization of Electrical Chemistry (SAC/TC322)
• Proposed by: China Electricity Council

2. Scope of application and non-applicability

• This document describes a method for determining the content of dissolved gas components (including hydrogen, methane, ethane, ethylene, acetylene, carbon monoxide, carbon dioxide, oxygen and nitrogen, etc.) in insulating oil by gas chromatography.
• It is applicable to the determination of dissolved gas component content in insulating oil (mineral oil, natural ester and synthetic ester, etc.) used in oil-filled electrical equipment.
• For the determination of component content of free gas in oil-filled electrical equipment (gas in the gas relay, gas on the oil surface in the equipment, etc.), refer to the relevant contents in 9.2 and 9.3.3.
• Not applicable: no explicit "not applicable" clause is provided in the available source (Appendix G, the secondary dissolution equilibrium determination method, states that "this method is not applicable to oil samples with very low gas concentration", which is a limitation of the appendix method).

3. Method principle

For a certain volume of oil sample, the dissolved gas in the sample is obtained by headspace gas extraction or vacuum degassing, and the gas components are separated, detected and calculated by a gas chromatograph to obtain the dissolved gas component content in the oil. The determination result of dissolved gas component content in oil is expressed as the number of microliters of each gas component contained per liter of oil (μL/L) under the conditions of temperature 20 ℃ and pressure 101.3 kPa. (See Chapter 4)

4. Reagents and materials (purity / preparation)

• 6.1 Nitrogen (or argon): purity not lower than 99.99%.
• 6.2 Hydrogen: purity not lower than 99.99%.
• 6.3 Helium: purity not lower than 99.999%.
• 6.4 Air: dry and oil-free.
• 7.9 Standard mixed gas: national standard samples/reference materials should be used, and their components should be consistent with the components to be detected; the typical concentration range is shown in Table 1.

Table 1 Typical concentration range of standard mixed gas (unit: micromole per mole)

• Preparation of other reagents: not provided in the available source.

5. Instruments and equipment

• 7.1 Oil-gas separation device
  • 7.1.1 Constant-temperature timed oscillator: reciprocating oscillation frequency 275 times/min±5 times/min, amplitude 35 mm±3 mm, temperature control accuracy ±0.3 ℃, timing accuracy ±2 min, internally equipped with a fixing clamp that can secure a 100 mL glass syringe.
  • 7.1.2 Vacuum degassing device: the degassing efficiency should be not less than 90%, and the change in average annual degassing efficiency should be not greater than 5%.
  • 7.1.3 Automatic headspace sampler: it should have the functions of mechanical oscillation, temperature control, pressure regulation and automatic quantitative injection, and should bring each dissolved gas component to equilibrium between the two phases within a certain time.
  • Note: One of the above oil-gas separation devices may be used during the test.
• 7.2 Gas chromatograph: it should include a gas path system, injection system, temperature control system, chromatographic column, detector, recording and data processing device. The detector should be equipped with a thermal conductivity detector (for determining hydrogen, oxygen and nitrogen), a hydrogen flame ionization detector (for determining hydrocarbon, carbon monoxide and carbon dioxide gases), a nickel catalyst converter (to convert carbon monoxide and carbon dioxide into methane), or a helium ionization detector. In the gas path system, the reaction temperature of the nickel catalyst converter should preferably be 350 ℃~360 ℃, the resolution of the chromatographic column for adjacent components to be detected should meet the requirements of quantitative analysis, and the detection sensitivity of the gas chromatograph should meet the requirements for the minimum detectable concentration of each component in the oil in this document. For commonly used gas path flows and chromatographic columns, see Appendix A.
• 7.3 Stainless steel injection needle: dental 5 gauge needle, length 40 mm; 18G1 gauge needle.
• 7.4 Double-ended needle (dedicated for the mechanical oscillation method): the schematic diagram is shown in Figure 1, and it may be made from a dental 5 gauge needle.
• 7.5 Glass syringe: capacities of 100 mL, 5 mL, 1 mL, should have good airtightness, and the plunger should move flexibly without jamming.
• 7.6 Rubber sealing cap for syringe: it should match the conical tip of the 7.5 glass syringe, have good elasticity, and not leak gas.
• 7.7 Headspace sampling vial: the schematic diagram is shown in Figure 2, capacity 20 mL, equipped with a perforated aluminum cap and a polytetrafluoroethylene gasket.
• 7.8 Crimper: it should be matched with the headspace sampling vial.

6. Recommended operating conditions

• Typical conditions for automatic headspace sampler (Table 2):

  Parameter	Condition	Typical value
  Temperature	Sample	50 ℃
  Temperature	Injection line	150 ℃
  Temperature	Quantitative tube	150 ℃
  Pressure	Headspace vial	70 kPa
  Carrier gas	Nitrogen, argon or helium	12 mL/min
  Time	50 ℃ oscillation equilibration (high frequency)	40 min
  Time	Pressurization	0.25 min
  Time	Pressure equilibration	0.25 min
  Time	Filling quantitative tube	0.25 min
  Time	Injection	0.9 min

• The reaction temperature of the nickel catalyst converter should preferably be 350 ℃~360 ℃ (see 7.2).
• Oscillation time for the mechanical oscillation method: mineral insulating oil is oscillated for 20 min, synthetic ester insulating oil and natural ester insulating oil are oscillated for 40 min, then allowed to stand for 10 min (see 9.1.1.4).
• The constant-temperature timed oscillator is heated to 50 ℃ and kept at constant temperature for standby (see 8.4.1).
• For chromatographic columns and gas path flows, see Appendix A (Table A.1, Table A.2).

7. Sampling and specimen preparation

• 5.1 Oil samples taken from oil-filled electrical equipment shall be taken in accordance with the provisions of GB/T 7597.
• 5.2 Free gas sampling from oil-filled electrical equipment shall be carried out in accordance with the provisions of DL/T 722.
• 5.3 Samples should be protected from dust, shock, light and moisture during transportation and storage.
• 5.4 Oil samples should preferably be tested within 4 days after sampling, and gas samples should be tested as soon as possible after sampling.
• For specimen preparation (gas extraction), see Chapter 9 9.1 (mechanical oscillation method, automatic headspace gas extraction method, vacuum degassing method).

8. Analysis procedure

8.1 Preparatory work (Chapter 8)

• 8.1 Airtightness check of glass syringe: use a glass syringe to take an oil sample in which hydrogen content can be detected, store it for at least two weeks, analyze the hydrogen content in the sample at the beginning and end of storage; when the hydrogen loss per week is less than 2.5%, it indicates that the glass syringe has good airtightness.
• 8.2 Scale calibration of glass syringe: at room temperature, calibrate the 40.0 mL scale of the 100 mL glass syringe by the gravimetric method, and mark the position.
• 8.3 Scale calibration of headspace sampling vial: at room temperature, calibrate the 15.0 mL scale of the headspace sampling vial by the gravimetric method and mark the position, and calibrate the full scale.
• 8.4 Degassing device
  • 8.4.1 Constant-temperature timed oscillator: set the temperature control temperature and time, heat to 50 ℃ and keep at constant temperature for standby.
  • 8.4.2 Vacuum degassing device: measure the degassing rate once a month; for the test method, see Appendix B.
  • 8.4.3 Automatic headspace sampler: set according to Table 2 and start it for standby.
• 8.5 Gas chromatograph: connect the gas source, turn on the chromatograph, and operate according to the instrument manual so that it enters a stable standby state.

8.2 Gas extraction (9.1)

• 9.1.1 Mechanical oscillation method (manual headspace gas extraction method)
  • 9.1.1.1 Prepare the gas storage glass syringe: take a 5 mL glass syringe A, after checking that the plunger is flexible and not jammed, draw a small amount of test oil to rinse the inner wall of the syringe barrel 2 times, then draw about 0.5 mL of test oil, put on the rubber sealing cap, insert the double-ended needle with the needle pointing vertically upward. Slowly discharge the air and test oil in the syringe so that the test oil fills the gaps on the inner wall of the syringe.
  • 9.1.1.2 Adjust the test oil volume: push out part of the oil sample from the 100 mL glass syringe B, accurately adjust the syringe plunger end to the 40.0 mL scale (V1), immediately put on the rubber sealing cap, and seal the conical tip of the syringe. When putting on the rubber sealing cap, the recess should be filled with test oil or the cap should first be flattened with fingers to squeeze out the air in the recess, so as to avoid air bubbles entering the oil sample syringe B.
  • 9.1.1.3 Add balance gas: take a 5 mL glass syringe C, connect a dental 5 gauge needle, after purging with balance gas 2 times, draw about 5.0 mL of balance gas, slowly inject the gas inside the syringe C into the syringe B after adjusting the test oil volume, the injection speed should be such that the bubbles from the needle tip in the oil are just continuous. For test oil with low gas content, the volume of balance gas injected may be appropriately increased, but after equilibration the gas phase volume should not exceed 5 mL. For general analysis, nitrogen is used as the balance gas; if nitrogen components are to be determined, argon must be used as the balance gas instead.
  • 9.1.1.4 Oscillation equilibration: place the syringe B on the oscillation tray inside the constant-temperature timed oscillator. After placing the syringe, the head of the syringe should be about 5° higher than the tail, and the syringe cone should be at the lower part. Start the oscillator oscillation operation button, oscillate continuously to the specified time (mineral insulating oil oscillate 20 min, synthetic ester insulating oil and natural ester insulating oil oscillate 40 min), then let stand 10 min. When the room temperature is below 10 ℃, before oscillation, the syringe B should be appropriately preheated, then oscillated. If after oscillation equilibration the amount of gas in the syringe is visually judged to be too little to meet the amount required for chromatographic analysis, balance gas may be directly added to the syringe B, and oscillation equilibration repeated; the amount of added gas should be such that the total gas phase volume after equilibration does not exceed 5 mL.
  • 9.1.1.5 Transfer the balance gas: take the syringe B out of the oscillation tray, immediately transfer the balance gas therein through a double-ended needle into the syringe A; the transfer process should use the slight positive pressure method, that is, slightly press the plunger of the syringe B so that the gas passes through the double-ended needle into the syringe A. Let the syringe A stand at room temperature for 2 min, accurately read its volume Vg (accurate to 0.1 mL).
• 9.1.2 Automatic headspace gas sampling method
  • 9.1.2.1 Headspace vial preparation: use a crimper to seal the headspace vial with a perforated aluminum cap and a polytetrafluoroethylene septum, insert two 18G1 needles into different positions on the edge of the headspace vial septum, one for inlet and one for venting; the inlet needle should be near the bottom of the vial, purge the headspace vial with nitrogen (or argon) at a flow rate of 2 L/min for at least 1 min, then first withdraw the vent needle, then quickly withdraw the inlet needle, obtaining a well-sealed headspace vial E filled with carrier gas.
  • 9.1.2.2 Inject test oil: after connecting a 18G1 needle to a 100 mL glass syringe B, push out part of the oil sample, adjust the syringe plunger to an integer scale greater than 20 mL. Quickly insert the syringe B from the edge of the headspace vial septum into the headspace vial E and bring the needle tip near the bottom of the vial, insert a vent needle into the upper part of the headspace vial, push the syringe B to accurately inject the test oil 15.0 mL into the headspace vial, immediately withdraw the vent needle and the syringe B, place the headspace vial E in the headspace sampler, and perform automatic processing according to the conditions in Table 2.
• 9.1.3 Vacuum degassing method
  • 9.1.3.1 Prepare the syringe A according to 9.1.1.1, connect it to the gas collection port of the vacuum gas sampling device; vacuum gas sampling devices with automatic sampling function do not have this step.
  • 9.1.3.2 100 mL The test oil glass syringe B is connected to the oil filling port of the vacuum gas sampling device, and should be sealed without air ingress.
  • 9.1.3.3 The gas sampling process is carried out according to the instruction manual of the device used.
  • 9.1.3.4 After gas sampling is completed, record the volume of gas in the syringe A, accurate to 0.1 mL. Vacuum gas sampling devices with automatic sampling function do not have this step.
  • 9.1.3.5 Drain all residual oil.
  • Note: The gas sampling step uses one of the above methods; the gas sampling principle is given in Appendix C.

8.3 Sample analysis (9.2)

• 9.2.1 Calibration of the instrument: open the valve of the standard mixed gas cylinder, purge the residual gas in the pressure reducing valve, take a 1 mL glass syringe D, after flushing with the standard mixed gas no fewer than 3 times, accurately draw 0.5 mL (or 1 mL) of the standard mixed gas for injection calibration. If the automatic headspace injection method is used, follow the steps in 9.1.2.1, continue to purge with the standard mixed gas at a flow rate of 2 L/min for 1 min, then first withdraw the inlet needle, then quickly withdraw the vent needle, place the headspace vial in the headspace sampler, and calibrate according to the conditions in Table 1 (the oscillation equilibration time may be shortened to 5 min) (Note: the original text here says "conditions in Table 1", which is suspected to be an error for "Table 2", requires confirmation against the source standard (source-text extraction)). Calculate the peak area Ais (or peak height his) of each component from the obtained chromatogram. Calibration of the instrument should be carried out under stable and identical instrument operating conditions, and the repeatability of two adjacent calibrations should be within ±1.5% of their average value. The instrument should be calibrated before each test. Repeat the operation at least twice and take the average value Ais (or peak height his). Note: For automatic headspace method testing, standard oil of the same volume and known concentration can be used for verification.
• 9.2.2 Sample analysis: use a 1 mL glass syringe D to accurately draw from syringe A (mechanical oscillation method) or syringe A (vacuum gas sampling method) or gas relay gas sample the same volume of sample gas as the standard mixed gas used for calibration, and inject for analysis. The automatic headspace injection method directly and automatically takes the equilibrium gas in the headspace vial for analysis, and calculates the peak area Ai (or peak height hi) of each component from the obtained chromatogram. Repeat the degassing and injection operation once, and take the average value Ai (or hi). Sample analysis should use the same injection syringe and the same injection volume as instrument calibration. Note: For instrument calibration and sample analysis of vacuum gas sampling devices with automatic sampling function, see Appendix D.

9. Qualitative and quantitative determination and calculation formulas

9.1 Headspace gas sampling method (9.3.1)

• 9.3.1.1 Correction of sample gas and oil sample volumes for the mechanical oscillation method:
  • V'g = Vg × 323/(273+t) ……………… (1)
  • V'l = Vl[1+0.0008×(50-t)] ……………… (2)
  • Where: V'g—50 ℃, equilibrium gas volume under test pressure, mL; Vg— equilibrium gas volume at room temperature t and test pressure, mL; t— room temperature during the test, ℃; V'l—50 oil sample volume at ℃, mL; Vl— oil sample volume taken at room temperature t, mL; 0.0008— thermal expansion coefficient of the oil, ℃⁻¹.
• 9.3.1.2 Correction of sample gas and oil sample volumes for the automatic headspace injection method:
  • V'g = V - V'l ……………… (3)
  • Where: V'g—50 equilibrium gas volume in the headspace vial at ℃, mL; V— headspace vial volume, mL; V'l—50 oil sample volume in the headspace vial at ℃, mL.
• 9.3.1.3 Calculation of the concentration of each dissolved gas component in oil:
  • Xi = 0.929 × p/101.3 × Cis × (Ai/Ais) × (Ki + V'g/V'l) ……………… (4)
  • Where: Xi—101.3 kPa and 293 K (20 ℃), concentration of dissolved gas component i in oil, μL/L; 0.929— temperature correction coefficient for correcting the dissolved gas concentration in the oil sample from 50 ℃ to 20 ℃; p— atmospheric pressure during the test, kPa; Cis— concentration of component i in the standard gas, μL/L; Ai— average peak area of component i in the sample gas, mV·S; Ais— average peak area of component i in the standard gas, mV·S; Ki—50 Ostwald coefficient of each dissolved gas component in oil at ℃; V'g—50 ℃, equilibrium gas volume under test pressure, mL; V'l—50 oil sample volume at ℃, mL.
  • In the formula, Ai and Ais may also be replaced by average peak heights hi and his.
  • The Ostwald coefficients (Ki) of each dissolved gas component in oil for various insulating oils at 50 ℃ are shown in Table 3; the Ostwald coefficients (Ki) of natural esters in Table 3 cite data from DL/T 2217. Their determination method is given in Appendix E. The gas partition coefficients (Ki) of imported mineral insulating oils at 70 ℃ are given in Appendix F. For oil samples of unknown brand or oil type, when the gas partition coefficient (Ki) of dissolved gases cannot be determined, the secondary dissolution equilibrium determination method may be used, see Appendix G.

Table 3 Ostwald coefficients (Ki) of each dissolved gas component in various insulating oils at 50 ℃

9.2 Calculation of results of the vacuum gas extraction method (9.3.2)

• 9.3.2.1 Correction of the volumes of sample gas and oil sample:
  • V″g = Vg × p/101.3 × 293/(273+t) ……………… (5)
  • V″l = Vl[1+0.0008×(20-t)] ……………… (6)
  • Where: V″g—20 ℃, 101.3 kPa gas volume under the condition, mL; Vg— gas volume at room temperature t and pressure p, mL; p— atmospheric pressure during the test, kPa; t— room temperature during the test, ℃; V″l—20 oil sample volume under ℃, mL; Vl— oil sample volume at room temperature t, mL.
• 9.3.2.2 Calculation of the concentration of each component of dissolved gas in oil:
  • Xi = Cis/(Ri) × (Ai/Ais) × (V″g/V″l) ……………… (7)
  • Where: Xi— concentration of component i of dissolved gas in oil, μL/L; Cis— concentration of component i in standard gas, μL/L; Ai— average peak area of component i in sample gas, mV·S; Ri— degassing rate of component i of the vacuum gas extraction device, %; V″g—20 gas sample volume at ℃, 101.3 kPa, mL; A″is— average peak area of component i in standard gas, mV·S (the symbol in the original formula is written as A″is, which is inconsistent with Ais above, requires confirmation against the source standard (source-text extraction)); V″l—20 oil sample volume at ℃, mL.
  • In the formula, Ai and Ais may also be replaced by average peak heights hi and his.

9.3 Calculation of the concentration of each component of free gas (9.3.3)

• Xig = Cis × Aig/Ais ……………… (8)
• Where: Xig— concentration of component i in free gas, μL/L; Cis— concentration of component i in standard gas, μL/L; Aig— average peak area of component i in free gas, mV·S; Ais— average peak area of component i in standard gas, mV·S.
• Among them, Aig and Ais may also be replaced by average peak heights hig and his.

10. Precision

• 11.1 Repeatability
  • When the concentration of dissolved gas in oil is greater than 10 μL/L, the difference between two measured values shall be less than 10% of the average value.
  • When the concentration of dissolved gas in oil is less than or equal to 10 μL/L, the difference between two measured values shall be less than the sum of 15% of the average value plus twice the minimum detection concentration of that gas component.
• 11.2 Reproducibility
  • Relative deviation of the difference between measured values of two laboratories: when the concentration of dissolved gas in oil is greater than 10 μL/L, less than 15%; when less than or equal to 10 μL/L, less than 30%.
• Precision of Appendix E (partition coefficient determination method): within the same laboratory, the relative deviation of two measurement results shall not exceed 5%; the relative deviation of the difference between measured values of two different laboratories shall not exceed 10%.
• Appendix G Second dissolution equilibrium determination method: for precision, see Chapter 11.

11. Report

• Take the arithmetic mean of two parallel test results as the measured value; when the test result is less than the minimum detection concentration of the gas component in oil, it is preferable to report as not detected. (Chapter 13)
• Minimum detection concentration (Chapter 10, Table 4, unit is microliters per liter):

  Gas	Minimum detection concentration
  Hydrogen	2
  Hydrocarbon gases	0.1
  Carbon monoxide gas	5
  Carbon dioxide gas	10
  Nitrogen	50
  Oxygen	50

• Accuracy (Chapter 12): The accuracy of this method is verified by a recovery test on standard oil samples (method see Appendix B). The recovery shall not be less than 90%; otherwise, the cause shall be identified.

12. Normative references

• GB/T 7597 Sampling method for power oils (transformer oil, turbine oil)
• DL/T 722 Guidelines for the analysis and judgment of dissolved gases in transformer oil
• DL/T 2217 Guidelines for dissolved gas analysis of natural ester and synthetic ester oils for transformers
• References: [1] IEC 60567 Oil-filled electrical equipment—Sampling of free gases and analysis of free and dissolved gases in mineral oils and other insulating liquids—Guidance
• Appendix F Table F.1 Data source: IEC 60567 (noted in the original text)

13. Source and verification

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14. Quick reference for questions and answers