GB/T 11081-2005 Determination of Ultraviolet Absorbance of White Oil

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Card type: Test method

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

• Standard number: GB/T 11081-2005
• Chinese name: Determination of Ultraviolet Absorbance of White Oil
• English name: Standard test method for ultraviolet adsorption of white oils
• Replacement relationship: replaces GB/T 11081-1989 "Determination of Ultraviolet Absorbance of White Oil"
• Adoption relationship: modified adoption of ASTM D 2269:1999 "Standard Test Method for Evaluation of White Mineral Oils by Ultraviolet Absorption" (English version), redrafted according to ASTM D 2269:1999
• Publication/implementation: published on 2005-05-25, implemented on 2005-11-01
• Issuing bodies: General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China, Standardization Administration of China
• Technical committee: Fushun Research Institute of Petroleum and Petrochemicals, China Petroleum & Chemical Corporation
• Drafting organization: Fushun Research Institute of Petroleum and Petrochemicals, China Petroleum & Chemical Corporation
• Main drafters: Zhao Bin, Qi Bangfeng
• First publication: 1989 year

2. Scope of application and non-applicability

• 1.1 This standard specifies the method for determination of ultraviolet absorbance of white oil.
• 1.2 Applicable to cosmetic, medicinal and food-grade white oils.
• 1.2 Not applicable to white oils containing additives that are soluble in dimethyl sulfoxide and can exhibit fluorescence or fluorescence quenching.
• 1.3 This standard uses the International System of Units (SI); values expressed in mesh are for reference only.
• 1.4 This standard does not purport to address all safety problems associated with its use. It is the responsibility of the user of this standard to investigate and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use; specific precautionary statements are given in 7.1 to 7.2.

3. Method principle

• Chapter 4 Method summary: extract the sample with dimethyl sulfoxide, and measure the ultraviolet absorbance of the extract in the wavelength range 260 nm to 420 nm.
• Chapter 5 Significance and use:
  • 5.1 This method is used to determine the possibility of application of white oil in food, medicine and cosmetics.
  • 5.2 Product specifications such as food-grade white oil, cosmetic white oil, white oil for food machinery, and liquid paraffin in the Chinese Pharmacopoeia (Part II) all require determination of ultraviolet absorbance.

4. Reagents and materials (purity / preparation)

• 7.1 n-Hexane: analytical reagent grade. When measured with a 1 cm absorption cell, using distilled water as reference, at wavelengths above 260 nm, the ultraviolet absorbance shall not exceed 0.02. Warning: n-Hexane is extremely flammable, harmful if inhaled, and may cause nerve cell damage. Solvent purity shall meet the following requirements: at any wavelength in the range 260 nm to 420 nm, the absorbance curve of the "reference solution" specified in clause 8.3, using distilled water as reference, shall not show extraneous impurity peaks, and the absorbance shall not exceed that of dimethyl sulfoxide using distilled water as reference.
  • Note: If the requirements are not met, purify by the following method: use an adsorption column of length 1 m and diameter 5 cm, packed with 0.149 mm to 0.074 mm (100 mesh to 200 mesh) activated (150 ℃, 3 h) fine-pore chromatographic silica gel to three-quarters of the column height; usually 3 L to 4 L of n-hexane can be purified.
• 7.2 Dimethyl sulfoxide: used as spectroscopic solvent (see note). Warning: dimethyl sulfoxide is combustible and rapidly absorbed through the skin. Clear, water-white, content 99.9%, melting point 18.5 ℃. When using a 1 cm absorption cell with distilled water as reference, the absorbance curve shall not exceed 1.0 at 264 nm, and there shall be no extraneous impurity peaks in the wavelength range below 420 nm.
  • Note: When dimethyl sulfoxide does not meet the above requirements, it can be purified by percolation, passing it through an adsorption column packed with activated carbon of particle size 1.68 mm×0.420 mm (12 mesh×40 mesh). The adsorption column is 1.2 m long and 25 mm in diameter, with the bottom drawn into a narrow tip of diameter 6.4 mm, and a liquid reservoir at the top of the column. Place glass wool at the bottom of the adsorption column, spread a layer of 25 mm thick silica gel of particle size 0.707 mm to 0.074 mm (25 mesh to 200 mesh) or particle size 0.149 mm to 0.074 mm (100 mesh to 200 mesh) on the glass wool, then pack the adsorption column with activated carbon, pour dimethyl sulfoxide into the container at the top of the adsorption column, and percolate through the activated carbon under atmospheric pressure; the purified dimethyl sulfoxide is collected at the bottom of the adsorption column. Because dimethyl sulfoxide readily absorbs moisture from the air and can react chemically with certain metal containers, it should be stored in glass-stoppered bottles.
• 7.3 Distilled water: single-distilled water or purified distilled water.

5. Apparatus and equipment

• 6.1 Spectrophotometer: equipped with a 1 cm path length liquid sample absorption cell holder; in the wavelength range near 290 nm, using a nominal spectral bandwidth of 1 nm or narrower, when the measured average absorbance is around 0.4, the repeatability of the instrument shall be ±1.0% (requires confirmation against the source standard (source-text extraction): the original text is "[unreadable sign]1.010", suspected to be ±1.0%).
• 6.2 Fused silica absorption cells: two, path length 1.00 cm±0.005 cm. This distance expressed in cm does not include the thickness of the absorption cell itself containing the sample.
• 6.3 Separatory funnel: 125 mL, pear-shaped, with glass stopper, equipped with polytetrafluoroethylene stopcock or other suitable stopcock that does not contaminate the solvents used, ensuring the separatory funnel does not leak.

6. Recommended operating conditions

• Wavelength range: 260 nm to 420 nm (8.4).
• Absorption cell path length: 1 cm (6.1, 6.2, 8.2, 8.3).
• Spectrophotometer spectral bandwidth: nominal spectral bandwidth of 1 nm or narrower near 290 nm (6.1).
• Room temperature requirement: during the experiment, room temperature shall not be lower than 20 ℃ (8.1 note).
• Temperature requirement: the "sample extract" and "reference solution" shall be at the same temperature (8.4 note).
• Wavelength range for obtaining precision data: 275 nm to 280 nm (10.1.3).

7. Sampling and sample preparation

• 8.1 Take 25 mL of sample and 25 mL of n-hexane, place in a separatory funnel and mix, add 5.0 mL of dimethyl sulfoxide, shake the mixture vigorously for at least 1 min to mix thoroughly, and let stand until the lower layer solution is transparent.
  • Note: If the room temperature is low, dimethyl sulfoxide easily crystallizes and makes the lower layer solution turbid. Therefore, during the experiment, room temperature shall not be lower than 20 ℃.
• 8.2 Put the transparent lower layer solution into another separatory funnel, add 2 mL of n-hexane, shake vigorously, and let stand until the lower layer solution is transparent. Put the lower layer solution into a 1 cm absorption cell, labeled as "sample extract".
• 8.3 Take 25 mL of n-hexane, place in a separatory funnel, add 5.0 mL of dimethyl sulfoxide, shake the mixture vigorously for at least 1 min, let stand until the lower layer solution is transparent, and put the lower layer solution into another 1 cm absorption cell, labeled as "reference solution".
• 8.5 For samples containing inhibitors, correct according to Appendix B.

8. Analytical procedure

• 8.4 In the wavelength range 260 nm to 420 nm, using the "reference solution" as reference, measure the absorbance of the "sample extract".
  • Note: When the temperatures of the "sample extract" and "reference solution" differ, the effect on absorbance measurement is significant. During measurement, ensure that the "sample extract" and "reference solution" are at the same temperature.
• 8.5 For samples containing inhibitors, correct according to Appendix B.
• Appendix B (Normative appendix) Correction of inhibitor content:
  • B.1 If a sample contains sufficient amount of the same inhibitor and such inhibitor-containing sample can be used to prepare a blend, the absorbance correction possibly caused by the inhibitor can be carried out as follows: the concentration of the added inhibitor in the inhibitor-containing sample shall be equal to the inhibitor concentration of the inhibitor-containing sample itself.
  • B.2 Weigh at least 50 mg of inhibitor, place in a volumetric flask, dilute to the mark with the inhibitor-containing sample, and mix well. If necessary, further dilute with inhibitor-containing white oil to obtain the required added inhibitor concentration.
  • B.3 Operate the original inhibitor-containing white oil sample according to this method, and label it as sample A.
  • B.4 Operate the blend containing a known added amount of inhibitor according to this method, and label it as sample B.
  • B.5 The absorbance difference ΔA between sample B and sample A at the corresponding wavelength is calculated as follows: ΔA = Ab − Ae (B.1); the absorbance correction at each wavelength is calculated as follows: A, = A. − ΔA (B.2). (requires confirmation against the source standard (source-text extraction): the formula symbol subscripts are suspected to be A_b, A_a, A_c, etc., the original text source-text extraction is unclear)
  • B.6 Mark inflection points on the sample spectrum at wavelengths below or above those with increments.
    • B.6.1 Draw a baseline tangent to the curve connecting these two points.
    • B.6.2 Read the absorbance A, at each wavelength position along the baseline.
  • B.7 At each wavelength position, compare Ad and A,; if A is less than Ad, it indicates that the inhibitor content in the original sample is less than the amount added.
  • B.8 Within the wavelength range of 260 nm to 420 nm (including 260 nm and 420 nm), use absorbance A. Or Ad (whichever is greater) compared with the reference solvent.

9. Qualitative and Quantitative and Calculation Formulas

• 3.2.1 Absorbance A: the logarithm to the base 10 of the reciprocal of transmittance T, A = log₁₀(1/T) = −log₁₀T (1). In the formula, T— transmittance (3.2.5).
• 3.2.2 Absorptivity a: absorbance divided by the product of the sample path length and concentration, a = A/bc (2). In the formula, A— absorbance (3.2.1); b— sample path length (3.2.4); c— concentration (3.2.3).
• 3.2.3 Concentration c: the amount of sample expressed in grams per liter.
• 3.2.4 Sample path length b: in the direction of propagation of the radiant energy beam, the measured distance from the sample surface where radiant energy enters to the surface where radiant energy exits, expressed in cm.
• 3.2.5 Transmittance T: the ratio of the radiant power transmitted through the sample extract contained in the absorption cell to the radiant power transmitted through the reference solvent contained in the absorption cell, T = P/P₀ (3). In the formula, P— radiant power transmitted through the sample extract; P₀—radiant power transmitted through the reference solvent. (requires confirmation against the source standard (source-text extraction): the original subscripts are two unreadable character groups, suspected to be P and P₀)
• Appendix B Correction formula: ΔA = Ab − Ae (B.1); A, = A. − ΔA (B.2). (requires confirmation against the source standard (source-text extraction): symbol subscripts unclear)
• 9 Report: report the ultraviolet absorbance of white oil at the specified wavelength, accurate to 3 decimal places.

10. Precision

• 10.1.1 Repeatability: the difference between consecutive test results obtained by the same operator, using the same instrument, under specified conditions, operating normally and correctly, on the same sample, in the long run, exceeds 0.014 absorbance units only once in 20 times.
• 10.1.2 Reproducibility: the difference between two separate test results obtained by different operators in different laboratories, under specified conditions, operating normally and correctly, on the same sample, in the long run, exceeds 0.044 absorbance units only once in 20 times.
• 10.1.3 These precision data for absorbance were obtained within the wavelength range of 275 nm to 280 nm.
• 10.2 Bias: this procedure has no bias, because the absorbance value can be defined only from the perspective of one test method.

11. Report

• Report the ultraviolet absorbance of white oil at the specified wavelength, accurate to 3 decimal places (Chapter 9).

12. Normative References

• ASTM E 131 Definitions of terms related to molecular spectroscopy (Chapter 2 normative references).
• For terms and definitions, see ASTM E 131 (3.1).

13. Source and verification

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14. Quick Q&A Reference