SH/T 0653-1998 Determination of Carbon Number Distribution of Normal Paraffins and Non-Normal Paraffins in Petroleum Waxes (Gas Chromatography)

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

• Standard number: SH/T 0653-1998
• Chinese title: Determination of Carbon Number Distribution of Normal Paraffins and Non-Normal Paraffins in Petroleum Waxes (Gas Chromatography)
• English title: Petroleum waxes-Determination of carbon number distribution of normal paraffin and non-normal paraffin hydrocarbons-Gas chromatography
• Supersession relationship: not provided in the available source (no supersession of any standard is mentioned)
• Adoption relationship: identically adopts ASTM D5442-93 "Petroleum Wax Analysis Method (Gas Chromatography)"
• Differences from ASTM D5442-93:
  1. The title of this standard is changed to "Determination of Carbon Number Distribution of Normal Paraffins and Non-Normal Paraffins in Petroleum Waxes (Gas Chromatography)"
  2. In this standard, all the content of the clause notes at 5 in the original text is compiled into Annex A
• Annex A is an informative annex
• Approval/implementation: approved by China Petrochemical Corporation 1998-03-13, implemented on 1998-10-01
• Proposing units: proposed by the Refinery Research Institute of Beijing Yanshan Petrochemical Company and Fushun Research Institute of Petroleum and Petrochemicals
• Custodial unit: under the custodianship of Fushun Research Institute of Petroleum and Petrochemicals
• Drafting units: responsible for drafting by the Refinery Research Institute of Beijing Yanshan Petrochemical Company and Fushun Research Institute of Petroleum and Petrochemicals
• Main drafters: Zheng Bo, Hu Yanqiu

2. Scope of application and non-applicability

• 1.1 This standard specifies the determination, by gas chromatographic internal standard method, of the carbon number distribution in petroleum waxes in the range from n-C17 to n-C44 and the content of normal paraffins and non-normal paraffins for each carbon number. Hydrocarbons above C44 are determined by the difference of 100%(m/m) minus the sum of the mass percentages of hydrocarbons at n-C44 and below, and are reported as C45+.
• 1.2 This standard applies to petroleum waxes, including blended waxes. This standard does not apply to oxidized waxes and natural waxes, such as synthetic polyethylene glycol and beeswax, carnauba wax.
• 1.3 This standard cannot be used directly for waxes with an oil content greater than 10% as determined by the GB/T 3554 method.

3. Method principle

• 4.1 Accurately weigh a certain amount of wax sample and internal standard substance, completely dissolve them in a suitable solvent, and inject into a gas chromatographic column to separate them into hydrocarbon components in order of increasing carbon number. The column temperature is increased linearly at a reproducible rate until the sample has completely flowed out of the chromatographic column.
• 4.2 The eluted components are detected by a hydrogen flame ionization detector and recorded by a recorder, integrator, or computer system. The hydrocarbons of each carbon number are qualitatively identified by comparing the retention time of a qualitative standard substance with the retention time of the wax sample components, until the mass percentage of each carbon number of C44 is calculated by the internal standard method.
• 4.3 Samples with boiling points higher than 538℃ cannot completely flow out of the chromatographic column under the specified conditions. Therefore, the content of hydrocarbons above C44 is determined by the difference of 100%(m/m) minus the sum of the mass percentages of hydrocarbons at C44 and below.

4. Reagents and materials (purity / preparation)

• 7.1 Carrier gas: suitable for hydrogen flame ionization detector; hydrogen and helium are recommended; the carrier gas purity should be greater than 99.95%(mol).
• 7.2 n-Hexadecane: a hydrocarbon used as an internal standard added to the sample; purity should be greater than 98%(m/m).
• 7.3 Standard substances used for calibration and qualitative identification: the standard samples of normal paraffins should cover the carbon number range of the wax sample (up to C44); purity should be greater than 95%(m/m).
• 7.4 Solvent: the solvent used to prepare the normal paraffin mixture and dissolve the wax sample; purity should be greater than 99%(m/m); cyclohexane is recommended. (Note: in the original text, source-text extraction here is "9%", suspected to be 99%, requires confirmation against the source standard (source-text extraction))
• 7.5 Linearity standard substances: weigh each normal paraffin in the range from n-C16 to n-C44, prepare a mixture, and dissolve it in cyclohexane. The amounts of normal paraffins added should be approximately equal and their difference should be within the range of 1%(m/m). This mixture requires at least one normal paraffin linearity standard substance among every four normal paraffins from n-C16 to n-C44. The prepared standard sample must be sealed to prevent solvent loss.
• 7.6 Internal standard solution: prepare a dilute solution of the internal standard substance dissolved in cyclohexane. It is divided into the following two steps.
  • 7.6.1 Accurately weigh about 0.4g n-C16 and place in a 100mL volumetric flask, add 100mL cyclohexane and weigh again to prepare a 0.5%(m/m) n-C16 stock solution. Record the mass of n-C16, accurate to 0.001g; at the same time record the mass of n-C16 and the cyclohexane solution, accurate to 0.1g.
  • 7.6.2 Dilute 1 parts of the stock solution with 99 parts of cyclohexane to prepare a diluted n-C16 internal standard solution, and use formula (1) to calculate the concentration of the internal standard substance in the diluted solution (CISTD):
    • CISTD = (W1 / W2) × 100% × (1/100) ……(1)
    • Where: CISTD— mass percentage of n-C16 in the diluted solution; W1— mass of n-C16 obtained from clause 7.6.1, g; W2— mass of n-C16 and the cyclohexane solution obtained from clause 7.6.1, g; 100%— coefficient for converting mass fraction to mass percentage; 100— dilution factor.

5. Instruments and equipment

• 6.1 Chromatograph
  • 6.1.1 A gas chromatographic apparatus capable of installing a capillary column, equipped with a hydrogen flame ionization detector and capable of operating under the conditions shown in Table 1, with retention time repeatability for a single peak within the range of 0.1min.
  • 6.1.2 The chromatograph can inject an appropriate amount of sample in splitless mode and is equipped with a cold on-column injector.
• 6.2 Sample injection system: for cold on-column injection, using automatic or manual injection, a syringe with a needle of 0.15 to 0.25mm outer diameter can be used for capillary columns with an inner diameter of 0.25mm or larger, while a standard syringe with a needle of 0.47mm outer diameter is used for capillary columns with an inner diameter of 0.53mm or larger. Select the injection volume range so that certain chromatographic peaks are not allowed to exceed the linear range of the detector or overload the column capacity.
• 6.3 Chromatographic column: meets the chromatographic resolution requirements in clause 9.5. A capillary column of length 25 to 30m is recommended, with a stationary phase of methyl silicone or 5% phenyl methyl silicone, preferably a cross-linked or bonded stationary phase.
• 6.4 Recorder: full scale less than or equal to 5mV, used to measure the detector signal changing with time. The full-scale response time should be less than or equal to 2s. The sensitivity and stability should be such that, under the operating conditions used, injection of 0.05%(m/m) hydrocarbons produces a recorder deflection greater than 2mm.
• 6.5 Integrator or computer: provides integration of the detector signal and summation of peak areas within a certain time range. Peak areas are measured by computer or integrator. The computer, integrator, or gas chromatograph must have the function of subtracting the corresponding baseline area (blank) from the sample peak area and the function of drawing the baseline used for peak area integration.

6. Recommended operating conditions

Table 1 Typical chromatographic conditions (original text Table 1, source-text extraction contains noise, some values require confirmation against the source standard):

7. Sampling and sample preparation

• 8.1 To ensure homogeneity, melt the entire wax sample at a temperature above its melting temperature 10℃, stir to mix uniformly, and use a clean dropper to place a few drops of the wax sample onto the surface of a clean aluminum foil sheet. After it solidifies, break it into pieces. This wax sample can be used directly as described in Chapter 11 or placed in a sealed sample bottle for later use. Usually, the aluminum foil sheet used has a thin oil film on its surface during processing, and it should be removed with n-hexane or ethanol-type solvents before use.
• 11.1 Preparation of petroleum wax sample solution
  • 11.1.1 Obtain the petroleum wax sample as described in clause 8.1.
  • 11.1.2 Accurately weigh about 0.0100g of wax sample into a glass bottle of about 15mL in volume, add about 12mL of dilute internal standard solution, cap the bottle, and accurately weigh the mass of the internal standard solution added. Record both masses.
  • 11.1.3 Shake the glass bottle to completely dissolve the wax sample, heating slightly if necessary.
  • 11.1.4 For manual injection, the syringe can directly draw the sample from the glass bottle; for automatic injection, transfer an appropriate amount of sample to an autosampler vial.

8. Analytical procedure

• 9 Preparatory work
  • 9.1 Aging of the chromatographic column: capillary columns with cross-linked or bonded stationary phases generally do not require aging. When a new column needs aging, use the following chromatographic operating procedure. Install the chromatographic column in the column oven of the chromatograph, connect one end to the injection system, and adjust the carrier gas flow rate to the flow rate used during analysis. Adjust the column oven temperature to the maximum temperature used during analysis and maintain for 30min. Then cool the column oven to room temperature and connect the other end of the chromatographic column to the detector. The end of the chromatographic column should be as close as possible to the hydrogen flame ionization detector nozzle. The temperature between the column oven and the detector nozzle must be higher than the maximum operating temperature of the chromatographic column.
  • 9.2 Operating conditions: Set the chromatograph operating conditions (recommended typical chromatographic operating conditions are shown in Table 1), so that the system reaches all temperature set points. Connect a recorder, integrator, or computer so that it can receive the detector signal. Before the process starts, the hydrogen flame ionization detector must be ignited.
  • 9.3 Blank baseline: After setting the required conditions, program the temperature up to the maximum operating temperature. Once the column oven temperature reaches the maximum operating temperature, immediately cool the column to the set initial temperature. Without injecting a sample, start the temperature program, recorder, and integrator. If the blank baseline is repeatable, perform two blank baseline determinations. If the detection signal is unstable or the blank baseline is not repeatable, further age the chromatographic column or replace the chromatographic column.
    • 9.3.1 Baseline drift: Observe the detector response during the blank run from the recorder. When the column temperature increases, some increase in detector response will be observed due to bleed of the stationary phase from the chromatographic column. As long as the two blank baselines are repeatable, column bleed is acceptable. The baseline should be a smooth curve with no chromatographic peaks.
  • 9.4 Solvent blank: Take 1μL cyclohexane solvent and inject it into the chromatographic injection system and start the temperature program. If no chromatographic peaks are detected within the retention time range in which the wax sample elutes, the purity of the solvent is considered acceptable.
  • 9.5 Chromatographic column resolution: Analyze the 1μL 0.05%(m/m) n-C20 and n-C44 cyclohexane solution under the conditions specified in clause 10.2 to check the column efficiency of the chromatographic column. It is required that the chromatographic column resolution (R)) calculated according to formula (2)) is not less than 3.00.
    • R = 1.699 × d / (W1 + W2) ……(2)
    • Where: R— chromatographic column resolution; d—n-C20 and n-C44 distance between peak apices, mm; W1—n-C20 half-peak width, mm; W2—n-C44 half-peak width, mm.
  • 9.6 Linearity of response: For accurate quantification, the detector response must be proportional to the injected mass, and it is assumed that the response values of non-normal alkanes are equal to the response values of normal alkanes with the same carbon number. In addition, the injection technique and the properties of the wax sample solution must make the wax sample injected into the gas chromatograph representative and authentic. Before use, the analytical system must be made to conform to the provisions of clause 9.6.1.
    • 9.6.1 Determine the response factor of the linear standard substance described in clause 7.5 relative to n-C16; its value must be within the range of 0.90～1.10.
    • 9.6.2 If the relative response factor is not within the above limited range, appropriate adjustments are required, and the linear standard substance must be reanalyzed to ensure linearity.
  • 9.7 Retention time repeatability: Repeatedly analyze the linear standard substance while checking the repeatability of retention time. The retention time repeatability of repeated analyses must be less than 0.10min.
• 10 Calibration and standardization
  • 10.1 Qualitative identification of normal alkanes: Inject a small amount of a cyclohexane solution of various alkanes or a known alkane mixture completely dissolved in cyclohexane, and determine the retention time of each normal alkane from n-C16～n-C44.
  • 10.2 Calibration: Inject the linear standard substance described in clause 7.5 into the chromatographic column, and determine the peak area of each normal alkane using an integrator or computer.
    • 10.2.1 Calculate the relative correction factor of the detector for each component in the linear standard substance relative to n-C16.
• 11 Test procedure
  • 11.2 Before analyzing the wax sample, program the column temperature up to the maximum temperature used. Once the column temperature reaches the maximum temperature, immediately cool the column oven temperature to the set initial temperature, and equilibrate at this temperature for at least 3min. Without injecting a sample, start the temperature program, recorder, integrator, or computer to perform a blank run, continuing for at least 2min after the retention time of n-C44. Store the blank run record in the computer or integrator for subtracting the baseline blank from the wax sample area.
  • 11.3 Following the same procedure as the blank run, inject the wax sample solution from 0.5～1.0μL obtained in clause 11.1 into the cold on-column injection port, immediately start the temperature program, recorder, and integrator or computer, and store the obtained detection signal. The typical chromatogram obtained is shown in Figure 1.
  • 11.4 Integrate the stored detector signal using the baseline structure types described below.
    • 11.4.1 Integrate the detector signal using the valley-to-valley baseline structure type to obtain the area of each normal alkane chromatographic peak in the chromatogram. Qualitatively identify each normal alkane peak according to the retention time determined in clause 10.1 and list their peak areas. The integration type is shown in Figure 2.
    • 11.4.2 Integrate the detector signal again using the vertical line to horizontal baseline structure type. Calculate the total area of all peaks for each carbon number and list the total area of all peaks for each carbon number. Define all chromatographic peaks between the valley bottom where the normal alkane peak of Cn-1 elutes and the valley bottom of the normal alkane peak of Cn as chromatographic peaks with carbon number n. The integration type is shown in Figure 3.
    • 11.4.3 To ensure correct and always consistent integration, when integrating under each baseline structure type, the chromatogram should be plotted and the baseline type matched with Figure 2 and Figure 3.
    • 11.4.4 Do not treat the solvent peak and internal standard peak as part of the wax sample.

9. Qualitative and quantitative calculation formulas

• 12.1 Each carbon number: The mass percentage of each carbon number determined in clause 11.4.2 (Ci)) is calculated using formula (3):
  • Ci = (Ai / AISTD) × Ri × (Wm / Wsm) × CISTD ……(3)
  • Where: Ci— mass percentage of hydrocarbons with carbon number i; Ai— total area of hydrocarbons with carbon number i; AISTD—n-C16 internal standard peak area; Ri— relative correction factor of hydrocarbons with carbon number i relative to n-C16; Wm— mass of dilute internal standard solution, g; Wsm— mass of wax sample, g; CISTD— mass percentage of internal standard substance (n-C16)) in the dilute internal standard solution.
• 12.2 Normal alkanes: The individual peak area of each normal alkane determined in clause 11.4.1 is used to calculate its mass percentage (Ni)) using formula (4):
  • Ni = (Ai / AISTD) × Ri × (Wm / Wsm) × CISTD ……(4)
  • Where: Ni— mass percentage of normal alkane with carbon number i; Ai— peak area of normal alkane with carbon number i; AISTD— peak area of internal standard substance n-C16; Ri— relative correction factor of normal alkane with carbon number i relative to n-C16; Wm— mass of dilute internal standard solution, g; Wsm— mass of wax sample, g; CISTD— mass percentage of n-C16 in the dilute internal standard solution.
• 12.3 Non-normal alkanes: The mass percentage of non-normal alkanes (NONi)) is calculated from the difference of the mass percentage of hydrocarbons with carbon number i (Ci)) minus the mass percentage of normal alkanes with carbon number i (Ni)):
  • NONi = Ci - Ni ……(5)
  • Where: NONi— mass percentage of non-normal alkanes with carbon number i; Ci— mass percentage of hydrocarbons with carbon number i; Ni— mass percentage of normal alkanes with carbon number i.
  • 12.3.1 It is assumed that the response factor of components with the same carbon number is the same as the response factor of the normal alkane with the same carbon number determined in clause 10.2.
  • 12.3.2 For normal alkanes not determined in the calibration mixture, the relative correction factor can be calculated by interpolation.
• 12.4 Hydrocarbons above C44: The mass percentage of hydrocarbons above C44 (C45+)) is calculated according to formula (6):
  • C45+ = 100% - ΣCi ……(6)
  • Where: C45+—C44 sum of mass percentages of hydrocarbons above; ΣCi—C44 sum of mass percentages of hydrocarbons at and below.

10. Precision

• 14.1 Repeatability: The difference between two results obtained by the same operator, using the same instrument, under specified conditions, with the same wax sample in a long-term run exceeds the value in Table 2 only once in twenty times.
• 14.2 Reproducibility: The difference between independent results obtained by different operators, in different laboratories, with the same wax sample in a long-term run exceeds the value in Table 2 only once in twenty times.

Table 2 Repeatability and reproducibility (original table 2, source-text extraction has noise, some values require confirmation against the source standard):

Note: 1) Here X refers to the mass percentage of the component.

11. Report

• 13.1 Report the mass percentage of normal paraffins and non-normal paraffins for each carbon number in the wax sample, accurate to 0.01%(m/m), and simultaneously report the total mass percentage of hydrocarbons above C44 as C45+.

12. Normative References

• GB/T 3554 Determination of oil content in petroleum wax

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Reference Q&A