SH/T 0659-1998 Determination of hydrocarbon types in saturated hydrocarbon fractions of gas oil (mass spectrometry)

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Card type: Test method

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

• Standard number: SH/T 0659-1998 (confirmed in 2004)
• Chinese title: Determination of hydrocarbon types in saturated hydrocarbon fractions of gas oil (mass spectrometry)
• English title: Standard test method for hydrocarbon types analysis of gas-oil saturates fractions by high ionizing voltage mass spectrometry
• Replacement relationship: not provided in the available source (no standard replaced is mentioned)
• Adoption relationship: equivalent adoption of ASTM D2786-91(1996)
• Main differences from ASTM D2786-91(1996) (as listed in the source): In 1. ASTM D2786-91(1996) Chapter 4, the saturated hydrocarbon fraction is obtained by separation using ASTM D2549-91(1995) "Separation of non-aromatic and aromatic portions of high-boiling fractions (chromatographic separation method)"; this standard uses the method in Annex A to separate the sample, and its separation yield can meet the requirements of ASTM D2549-91(1995). In 2. ASTM D2786-91(1996), Note 2 of 8.2 mentions that this standard method was established on a CEC21-103 type mass spectrometer; the instrument used when this standard was established was Varian MAT311, Finnigan MAT90 type, which is not the same model as the CEC21-103 type, but its n-hexadecane ratio can meet its requirements.
  3. ASTM D2786-91(1996) does not contain the content of 9.2 in this standard; considering actual operation, this standard adds this content.
• Annex A is an annex of the standard.
• Responsible body: Petrochemical Research Institute of China Petrochemical Corporation; drafting unit: Petrochemical Research Institute of China Petrochemical Corporation; main drafter: Gao Hong.
• Approval/implementation: approved by China Petrochemical Corporation in 1998-06-23, implemented in 1998-12-01.

2. Scope of application and non-applicability

• 1.1 This standard specifies a method for determining hydrocarbons in samples by high-voltage mass spectrometry.
• 1.2 It is applicable to saturated hydrocarbon fractions in gas oil with a distillation range of 205 to 540℃ (average carbon number C16 to C32), and determines the content of paraffins, one-ring naphthenes, two-ring naphthenes, three-ring naphthenes, four-ring naphthenes, five-ring naphthenes, six-ring naphthenes, monocyclic aromatics and other hydrocarbon types therein.
• 1.3 It is not applicable to samples containing olefins and with a monocyclic aromatic content exceeding 5%(V/V).
• 1.4 The hydrocarbon type composition data measured by this standard are expressed in volume percent.
• 1.5 This standard involves certain hazardous materials, operations and equipment, but it is not intended to address all safety issues related thereto. Therefore, users should establish appropriate safety and protective measures and determine applicable management systems before using this standard.

3. Method principle

The saturated hydrocarbon fraction separated from the sample according to Annex A is subjected to mass spectrometric determination. The sum of the largest characteristic mass fragment peaks for each molecular type is used to determine the relative abundance of paraffins, one-ring naphthenes, two-ring naphthenes, three-ring naphthenes, four-ring naphthenes, five-ring naphthenes, six-ring naphthenes and monocyclic aromatics in the saturated hydrocarbon portion. The calculation method is carried out by selecting inverse matrix coefficients for different average carbon numbers (derived from the sensitivity after ion intensity correction). The saturated hydrocarbon fraction is obtained by chromatographic separation.

Symbols in Chapter 3 (sum of characteristic ion peak group intensities for each hydrocarbon type):

• Σ71 = 71+85+99+113 (paraffins)
• Σ69 = 69+83+97+111+125+139 (one-ring naphthenes)
• Σ109 = 109+123+137+151+165+179+193 (two-ring naphthenes)
• Σ149 = 149+163+177+191+205+219+233+247 (three-ring naphthenes)
• Σ189 = 189+203+217+231+245+259+273+287+301 (four-ring naphthenes)
• Σ229 = 229+243+257+271+285+299+313+327+341+355 (five-ring naphthenes)
• Σ269 = 269+283+297+311+325+339+353+367+381+395+409 (six-ring naphthenes)
• Σ91 = 91+105+117+119+129+131+133+143+145+147+157+159+171 (monocyclic aromatics)

4. Reagents and materials (purity / preparation)

• 7 Reagent: n-hexadecane, analytical reagent. Note: flammable, vapor harmful.
• Annex A (A3 Reagents and materials):
  • A3.1 n-Pentane: chemical grade.
  • A3.2 Dichloromethane: chemical grade.
  • A3.3 Benzene: chemical grade.
  • A3.4 Anhydrous ethanol: chemical grade.
  • A3.5 Fine-pore silica gel: 100 to 200 mesh.
• Annex A (A4.4): Prepare benzene and anhydrous ethanol in a ratio of 1:1 (volume ratio) to make 100 mL mixed liquid.

5. Instruments and equipment

• 6.1 Mass spectrometer: meets the requirements of GB/T 6041.
• 6.2 Sample introduction system: this sample introduction system must ensure that the sample is not lost, not contaminated, and its composition is not changed. This system is a dedicated sample introduction device that can raise temperature within the range of 125 to 350℃ and maintain a constant temperature.
• 6.3 Microsyringe: 10 μL.
• Annex A (A2 Equipment):
  • A2.1 Chromatographic column: as shown in Figure A1 (original figure, unit: mm).
  • A2.2 Conical flask: 25 mL, 250 mL.
  • A2.3 Graduated cylinder: 100 mL.
  • A2.4 Water bath.
  • A2.5 Analytical balance: sensitivity 1 mg.

6. Recommended operating conditions

• 8.2 Instrument conditions: adjust the repeller of the ion source so that the molecular ion peak m/e 226 of n-hexadecane is maximized. Magnetic field scanning can be performed from m/e 65 to 410. The ionization voltage is 70 eV, and the ionization current is 10 to 70 μA.
• 8.3 Calibration standard: the inverse matrix calibration coefficients are obtained under conditions where the ion source parameters are adjusted so that the ratio of Σ69/Σ71 of n-hexadecane is 0.20/1.0. Studies show that the acceptable range of the ratio of Σ69/Σ71 for this standard is 0.18 to 0.22.
• 9.3 The instrument performs magnetic field scanning from m/e 65 to 410 to obtain the mass spectrum of the sample.
• 10.3.2 Note: Under mass spectrometric operating conditions, if the ratio m/e 127/226 of n-hexadecane is adjusted approximately to 1.4, the above sensitivity factors are also valid. If this ratio cannot be achieved, the sensitivity factors consistent with actual conditions need to be obtained separately in the laboratory.

7. Sampling and sample preparation

• The sample is the saturated hydrocarbon fraction in gas oil, obtained by separation according to Annex A.
• Annex A (A4 Test procedure):
  • A4.1 Place silica gel in an oven, activate at constant temperature 150℃ for 5 h, then place in a stoppered glass bottle for later use.
  • A4.2 Weigh 2 to 3 g sample, accurate to 1 mg.
  • A4.3 Place the weighed sample in an oven, melt it, then add 15 mL n-pentane to dilute.
  • A4.4 Prepare benzene and anhydrous ethanol in a ratio of 1:1 (volume ratio) to make 100 mL mixed liquid.
  • A4.5 Fix the adsorption column vertically, and plug the end of the column tightly with absorbent cotton. Then add the activated silica gel, and tap the chromatographic column lightly with a rubber rod so that the silica gel automatically compacts to the marked line. Add 50 mL n-pentane to wet the chromatographic column. After the wetting liquid completely enters the adsorption layer, quantitatively transfer the weighed and diluted sample solution into the chromatographic column. Use 20 mL n-pentane to continuously rinse the 25 mL conical flask containing the sample solution, and add the rinse liquid to the chromatographic column. After the sample solution completely enters the adsorption layer, sequentially add 130 mL n-pentane; after the n-pentane completely enters the adsorption layer, add 150 mL dichloromethane; after the dichloromethane completely enters the adsorption layer, add 100 mL benzene and anhydrous ethanol mixed liquid to respectively elute the saturated hydrocarbon, aromatic and resin fractions. Use 250 mL conical flasks under the chromatographic column to collect the eluate. The elution rate is 1 to 3 mL/min. Then evaporate the solvent from the n-pentane, dichloromethane, and benzene and anhydrous ethanol eluates collected in the 250 mL conical flasks on a water bath respectively, quantitatively transfer the saturated hydrocarbon, aromatic and resin from which the solvent has been removed to weighed 25 mL conical flasks, heat, cool and keep constant weight. 15 to 20 min is one cycle, until the loss between two consecutive weighings is less than 20 mg, but its yield must reach above 95%(m/m).

8. Analysis procedure

• 9.1 If the mass spectrometer has just been started, it needs to be calibrated according to the instrument manual to ensure the stability of the instrument during use. If the mass spectrometer is running continuously, no further calibration is needed before analyzing samples.
• 9.2 Use a microsyringe to draw 0.4 to 1.0 μL of sample, close the evacuation valve of the sample introduction system, inject the sample into the sample reservoir of the sample introduction system, and start scanning after the total ion current stabilizes.
• 9.3 The instrument performs magnetic field scanning from m/e 65 to 410 to obtain the mass spectrum of the sample. Record two mass spectra continuously, calculate them separately, and take their average as one determination result.

9. Qualitative and quantitative determination and calculation formulas

• 10.1 From the recorded mass spectral data, read the relevant mass spectral peak intensities listed in Chapter 3, and perform heavy isotope correction on the two adjacent peaks before each peak.
• 10.2 Sum the ion peak group intensities listed in Chapter 3.
• 10.3 Select appropriate inverse matrix coefficients from Table 1. Note: understanding the sample source and its physical properties helps in selecting appropriate inverse matrix coefficients for reference.
• 10.3.1 Use the carbon number of the largest spectral peak after deducting the heavy isotope contribution from the CnH2n+2 series of spectral peaks as the average carbon number.
• 10.3.2 The ratio Ya in the sample is calculated according to formula (1):
  • Ya = (a·b)/[(a·b)+(c·d)] ………………(1)
  • Where: a— relative sensitivity factor of normal paraffins, found from Table 2; b— average CnH2n+2 spectrum peak after deducting the heavy isotope contribution (equivalent to the molecular weight of normal paraffins); c— relative sensitivity factor of isoparaffins, found from Table 2; d— peak intensity of the CnH2n+1 spectrum peak that is two carbon numbers less than the selected maximum CnH2n+2 peak (that is, the intensity of the spectrum peak obtained by subtracting 29 from the maximum normal paraffin peak).
  • If the value of Ya is 0.50 or greater than 0.50, then use the corresponding inverse matrix coefficients for normal paraffins. Otherwise, use the inverse matrix coefficients for isoparaffins. When necessary, interpolation may be used to calculate the data in Table 2.
• 10.4 After suitable inverse matrix coefficients are selected, the paraffin ion peak intensity a1 is calculated according to formula (2):
  • a1 = (b1C1)+(b2C2)+(b3C3)+……+(b8C8) ………………(2)
  • Where: b1—Σ71 peak intensity; b2—Σ69 peak intensity; b3—Σ109 peak intensity; b4—Σ149 peak intensity; b5—Σ189 peak intensity; b6—Σ229 peak intensity; b7—Σ269 peak intensity; b8—Σ91 peak intensity; C1—Σ71 inverse matrix coefficient; C2—Σ69 inverse matrix coefficient; C3—Σ109 inverse matrix coefficient; C4—Σ149 inverse matrix coefficient; C5—Σ189 inverse matrix coefficient; C6—Σ229 inverse matrix coefficient; C7—Σ269 inverse matrix coefficient; C8—Σ91 inverse matrix coefficient.
  • By repeating the above corresponding calculations, the data for paraffins, one-ring naphthenes, two-ring naphthenes, three-ring naphthenes, four-ring naphthenes, five-ring naphthenes, six-ring naphthenes, and monocyclic aromatics can be obtained.
• 10.5 After normalizing the ion peak intensities of each hydrocarbon type to 100.0, the volume percentage content of each hydrocarbon type can be obtained.
• Table 1 Inverse matrix coefficients: according to average carbon number C16, C17, C18, C19, C20, C21, C22, C23, C24, C25, C26, C27, C28, C29, C30, C31, C32, respectively list the coefficients for normal paraffins and isoparaffins corresponding to paraffins, one-ring naphthenes, two-ring naphthenes, three-ring naphthenes, four-ring naphthenes, five-ring naphthenes, six-ring naphthenes, and monocyclic aromatics for Σ71, Σ69, Σ109, Σ149, Σ189, Σ229, Σ269, Σ91 (specific values are in Table 1 of the original text and are not transcribed one by one here).
• Table 2 Sensitivity factors:

  Average carbon number	Normal paraffins	Isoparaffins
  16	0.347	0.0364
  20	0.606	0.0505
  24	1.250	0.0735
  28	2.439	0.1061
  32	4.01 (requires confirmation against the source standard, source-text extraction)	0.1380

• Appendix A (Calculation of A5):
  • A5.1 The content of saturated hydrocarbon fraction in the sample X1[%(m/m)] is calculated according to formula (A1): X1 = [m1/(m1+m2+m3)] × 100 ………………(A1)
  • A5.2 The content of aromatic hydrocarbon fraction in the sample X2[%(m/m)] is calculated according to formula (A2): X2 = [m2/(m1+m2+m3)] × 100 ………………(A2)
  • A5.3 The content of resin fraction in the sample X3[%(m/m)] is calculated according to formula (A3): X3 = [m3/(m1+m2+m3)] × 100 ………………(A3)
  • Where: m1— mass of the received saturated hydrocarbon fraction, g; m2— mass of the received aromatic hydrocarbon fraction, g; m3— mass of the received resin fraction, g.

10. Precision

• 11 Precision and bias: judge the reliability of test results according to the following provisions (95% confidence level).
• 11.1 Repeatability: the difference between two results obtained by the same operator in repeated determinations shall not exceed the value specified in Table 3.
• 11.2 Reproducibility: the difference between two results obtained by different laboratories in their respective determinations shall not exceed the value specified in Table 3.
• Note: If the composition of the analyzed sample is significantly different from the samples used in Table 3, this precision shall not be used.
• 11.3 Bias: the measured data are determined by empirical methods, and therefore it is impossible to propose bias.
• Table 3 Precision (volume percentage):

  Item	Average value	σr	σR	r	R
  Paraffins (0 rings)	10.5	0.5	1.6	1.5	5.4
  One-ring naphthenes	17.3	0.5	1.5	1.8	5.0
  Two-ring naphthenes	15.8	0.2	1.5	0.5	4.9
  Three-ring naphthenes	16.7	0.2	1.0	0.8	3.2
  Four-ring naphthenes	30.1	0.6	3.4	2.0	11.0
  Five-ring naphthenes	6.8	0.3	1.3	0.9	4.3
  Six-ring naphthenes	2.8	0.2	1.1	0.7	3.5

  • σr: repeatability standard deviation; σR: reproducibility standard deviation; r: repeatability; R: reproducibility.

11. Report

not provided in the available source (the original text does not have an independent "Report" section).

12. Normative references

• GB/T 6041 General rules for mass spectrometry analysis methods for chemical products
• Cited in the adoption notes: ASTM D2786-91(1996), ASTM D2549-91(1995)

13. Source and verification

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