SH/T 0662-1998 Determination of ultraviolet absorbance of mineral oils

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Card type: Test method

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

• Standard number: SH/T 0662-1998
• Chinese name: Determination of ultraviolet absorbance of mineral oils
• English name: Method for Determination of Ultraviolet Absorbance of Mineral Oils (the source text source-text extraction reads “M l - al oi l- Det erm i-Anon of ultraviol et ahcnrbance”, requires confirmation against the source standard (source-text extraction))
• Method number: This standard includes the A method and the B method
• Replacement relationship: not provided in the available source
• Year confirmation: confirmed in 2004
• Adoption relationship: equivalent adoption of the test methods in the United States Food and Drug Administration FDA 21CFR178.3620(196)(b), (c) (the source text source-text extraction reads “FDA 2]CFR178-3620(196)(b),(.)”, requires confirmation against the source standard (source-text extraction))
• Main differences from the adopted method: This standard supplements “Appendix A Reagent purification and treatment methods”; Appendix A is an appendix of the standard

2. Scope of application and non-applicability

• This standard specifies a method for determining the ultraviolet absorbance of mineral oils, including the A method and the B method.
• This standard applies to mineral oils used on component parts of non-food products that come into contact with food.
• The A method applies to mineral oils whose color, determined according to GB/T 3555 “Petroleum products—Determination of Saybolt color (Saybolt colorimeter method)”, is not less than 20.
• The B method applies to mineral oils whose initial boiling point is not less than 232℃ and whose color, determined according to GB/T 6540 “Petroleum products—Determination of color”, is not greater than 5.5.
• Not applicable: not provided in the available source.

3. Method principle

• A method (Chapter 2 Method summary): Extract the sample with dimethyl sulfoxide, and measure the ultraviolet absorbance of the extract in the wavelength range 280 to 350nm.
• B method (Chapter 5 Method summary): Extract the sample with dimethyl sulfoxide, then back-extract with isooctane, and measure the ultraviolet absorbance in the wavelength range 280 to 400nm. If the measured value exceeds the specified value, treat with sodium borohydride, carry out adsorptive separation with magnesium oxide-diatomaceous earth, and finally measure the ultraviolet absorbance.

4. Reagents and materials (purity / preparation)

A method (Article 3.2)

• 3.2.1 n-Hexane: analytical reagent; when measured with a 1cm absorption cell, using water as reference, in the wavelength range 260 to 350nm, the ultraviolet absorbance shall not exceed 0.02; if it does not meet the requirement, it must be purified; see Appendix A for the purification method.
• 3.2.2 Dimethyl sulfoxide: spectroscopically pure; measured with a 1cm absorption cell, using water as reference, its absorbance shall not exceed the requirement of Table 1.
• 3.2.3 Petroleum ether: analytical reagent, boiling range 60 to 90℃; it shall meet the specified indicators of 8.3.2, otherwise purification treatment is required; see Appendix A for the purification method.
• 3.2.4 Distilled water: it shall meet the specified indicators of 8.3.3, otherwise purification treatment is required; see Appendix A for the purification method.

Table 1 (maximum ultraviolet absorbance of dimethyl sulfoxide, per 1cm optical path):

(Note: in the source text, the wavelength column of Table 1, source-text extraction, reads “261.5 / 270.0 / 275.0 / 280.0 / 3[unreadable characters]0”, the last item requires confirmation against the source standard (source-text extraction))

B method (Chapter 7)

• 7.1.1 Isooctane (2,2,4- trimethylpentane): analytical reagent; it shall meet the inspection indicators of 8.3.2, otherwise purification treatment is required; see Appendix A for the purification method.
• 7.1.2 Benzene: analytical reagent; it shall meet the inspection indicators of the 8.3.2 method, otherwise it may be purified by distillation; see Appendix A for the purification method.
• 7.1.3 Acetone: analytical reagent; it shall meet the inspection indicators of the 8.3.2 method, otherwise purify by distillation; see Appendix A for the purification method.
• 7.1.4 n-Hexadecane: purity 99%, no olefins; it shall meet the inspection indicators of the 8.3.1 method, otherwise it must be purified by the activated silica gel column method; see Appendix A for the purification method.
• 7.1.5 Methanol: analytical reagent; it shall meet the inspection indicators of the 8.3.2 method, otherwise purify by distillation; see Appendix A for the purification method.
• 7.1.6 Dimethyl sulfoxide: same as 3.2.2.
• 7.1.7 Phosphoric acid: concentration 85%, analytical reagent.
• 7.1.8 Distilled water: same as 3.2.4.
• 7.1.9 Petroleum ether: same as 3.2.3.
• 7.1.10 Sodium borohydride: purity 98%.
• 7.1.11 Magnesium oxide: analytical reagent.
• 7.1.12 Anhydrous sodium sulfate: analytical reagent, granular; each bottle must be pre-washed according to 8.6.
• 7.1.13 Sodium chloride: analytical reagent.
• 7.2.1 Diatomaceous earth: chemically pure.
• 7.2.2 Nitrogen: purity 99.5%, in a steel cylinder, with the flow rate controlled at a pressure of 34.3kPa.

Reagent preparation (8.4)

• 8.4.1 Pre-equilibrated dimethyl sulfoxide-phosphoric acid solution and pre-equilibrated isooctane: place 300mL dimethyl sulfoxide in a 1000mL separatory funnel, add 75mL phosphoric acid, shake vigorously to mix evenly (exothermic reaction, take care to vent), let stand for 10min, then add 150mL isooctane and shake to mix so that the solvent equilibrates; draw off each layer separately and store in ground-glass stoppered bottles.
• 8.4.2.1 10%(V/V) benzene-isooctane solution: pipette 25mL benzene into a 250mL volumetric flask, add isooctane to the mark, and mix evenly.
• 8.4.2.2 20%(V/V) benzene-isooctane solution: pipette 50mL benzene into a 250mL volumetric flask, add isooctane to the mark, and mix evenly.
• 8.4.2.3 Acetone-benzene-water mixed liquid: take 380mL acetone and add it to 200mL benzene, then add 20mL distilled water, and mix evenly (the source text source-text extraction reads “380x & acetone”, requires confirmation against the source standard (source-text extraction)).

Preparation of adsorbent and anhydrous sodium sulfate

• 8.5 Magnesium oxide-diatomaceous earth adsorbent: add 700mL distilled water to 100g magnesium oxide to form a paste, heat in a water bath (70℃±2℃) for 30min while stirring continuously; vacuum-filter with a Buchner funnel until no water drips; spread a layer 1 to 2cm thick in an enamel tray, dry in an oven at a constant temperature of 160℃±1℃ for 24h; grind, sieve with standard sieves of 0.246mm and 0.088mm aperture, and collect 0.246 to 0.088mm magnesium oxide; mix with diatomaceous earth at 2:1 (mass ratio) in a 1000mL wide-mouth bottle, shake vigorously for 10min to mix evenly; before use, spread a layer 1 to 2cm thick in an enamel tray, dry at 160℃±1℃ for 2h, place in a wide-mouth bottle and store in a desiccator.
• 8.6 Anhydrous sodium sulfate: weigh 35g and place it in a 60mL or 100mL acid-resistant filter funnel, wash several times with the solvent used (for filtering isooctane solution, wash with isooctane; for filtering benzene solution, wash with benzene), each time for 15mL; collect the last 15mL washing liquid and inspect according to 8.3.2, until the ultraviolet absorbance per 1cm optical path is not greater than 0.00; generally, washing three times meets the requirement.

5. Instruments and equipment

A method (3.1)

• 3.1.1 Pipettes: 1mL, 2mL, 5mL, 25mL, 50mL.
• 3.1.2 Separatory funnels: 60mL, 125mL ground-glass stoppered; grease must not be applied to the ground-glass joints or stopcocks.
• 3.1.3 Quartz absorption cells: optical path lengths 1.000cm±0.005cm, 5.000cm±0.005cm.
• 3.1.4 Spectrophotometer: wavelength range 250 to 400nm (the source text source-text extraction reads “250[unreadable separator and characters])Onm”, requires confirmation against the source standard (source-text extraction)), with a slit smaller than 2nm; performance requirements: absorbance repeatability at an absorbance of 0.4 is ±0.01; absorbance accuracy at an absorbance of 0.4 is ±0.05 (the source text source-text extraction reads “*0.05”, requires confirmation against the source standard (source-text extraction)); wavelength accuracy ±1.0nm.

B method (Chapter 6)

• 6.1 Separatory funnels: 250mL, 500mL, 1000mL and 2000mL ground-glass stoppered; grease must not be applied to the ground-glass joints or stopcocks.
• 6.2 Container: capacity 500mL, with a 24/40 conical ground-glass joint at the bottom, a suitable connector at the top for introducing nitrogen, and a glass hook on the upper side of the ground-glass joint.
• 6.3 Chromatographic column: length 180mm, inner diameter 15.7mm±0.1mm, with a coarse-porosity sintered glass plate at the lower part, a 24/40 conical ground-glass joint at the upper part, and a glass hook on the lower side of the ground-glass joint.
• 6.4 Gasket: polytetrafluoroethylene sheet with diameter 50mm and thickness about 5mm, with a central hole diameter matching the outer diameter of the chromatographic column body.
• 6.5 Suction filter flask: 250mL or 500mL filter flask.
• 6.6 Condenser: with a 24/40 connector, connected to a drying tube of any length.
• 6.7 Evaporation flask: 250mL or 500mL glass flask, with a conical stopper, the stopper having inlet and outlet tubes so that nitrogen can be passed to the surface of the liquid to be evaporated in the flask.
• 6.8 Acid-resistant filter funnel: 60mL or 100mL.
• 6.9 Pipettes: same as 3.1.1.
• 6.10 Volumetric flasks: 25mL, 50mL, 200mL, 250mL.
• 6.11 Measuring cups: 10mL, 25mL, 50mL, 100mL, 500mL.
• 6.12 Beaker: 50mL, 100mL, 2000mL.
• 6.13 Oven: capable of controlling the temperature at 160℃±1℃ (the source text source-text extraction reads “1[unreadable character]℃[unreadable sign]19c”, requires confirmation against the source standard (source-text extraction)).
• 6.14 Small glass measuring spoon: self-made, used for measuring sodium borohydride, one spoonful is equivalent to 0.3g sodium borohydride.
• 6.15 Glass rod: self-made, length 250～300mm, outer diameter about 5mm, one end is flat and round, used for compacting the adsorbent.
• 6.16 Metal rod: self-made, length 250～300mm, outer diameter about 5mm, one end is sharpened, used for loosening the adsorbent.
• 6.17 Quartz absorption cell: same as 3.1.3.
• 6.18 Spectrophotometer: same as 3.1.4.
• 6.19 Wide-mouth bottle: 1000mL ground-glass stopper.

6. Recommended operating conditions

• Wavelength range for determination by the A method: 280～350nm (4.4).
• Wavelength range for determination by the B method: 280～400nm (9.1.5, 9.2.6).
• Spectrophotometer slit: less than 2nm (3.1.4).
• Evaporation rate: amount of liquid evaporated per minute is about 4mL (8.3.2).
• Vacuum degree for chromatographic column packing: about 18.0kPa (9.2.2).
• Chromatographic column elution/permeation downflow rate: 2～3mL/min (9.2.2, 9.2.3).
• Nitrogen control pressure: flow rate under 34.3kPa (7.2.2).
• Magnesium oxide water bath heating temperature: 70℃±2℃ (8.5).
• Magnesium oxide drying: 160℃±1℃, 24h (8.5); before use 160℃±1℃, 2h (8.5).
• Silica gel activation: activate at 180℃±1℃ for 5～6h (Appendix A note, the source text source-text extraction reads “lso' C t l℃”, requires confirmation against the source standard (source-text extraction)).
• The entire test process must be carried out under soft light (8.2).

7. Sampling and sample preparation

• 8.2 Sample handling: great care must be taken when handling samples to avoid contamination, and it must be ensured that no foreign impurities are introduced due to improper packaging; some of the tested polycyclic aromatic hydrocarbons are susceptible to photo-oxidation, so the entire test process must be carried out under soft light.
• 8.1 Operational requirements: this test has high sensitivity, so operations must be carried out with great care to avoid errors caused by contamination; all glass apparatus, including stopcocks and stoppers, must be carefully cleaned to remove all organic substances such as lubricating oils, greases, and residual detergents, and must be inspected under ultraviolet light for any fluorescence contamination; before use, the apparatus must be rinsed with purified isooctane; no grease may be applied to glass stopcocks.
• Sampling amount for the A method: 25mL sample (4.1).
• Sampling amount for the B method: weigh 20g sample (9.1.1).
• Other sampling details: not provided in the available source.

8. Analytical procedure

A method (Chapter 4)

• 4.1 Place 25mL sample, 25mL n-hexane, and 5mL dimethyl sulfoxide in a 125mL separatory funnel, shake vigorously for 1min to fully extract, and let stand until the lower layer solution is transparent.
• 4.2 Put the lower layer solution into another separatory funnel, add 2mL n-hexane, shake vigorously for 1min, let stand until the lower layer solution is transparent, put the lower layer solution into a 1cm absorption cell, and label it as “sample extract”.
• 4.3 Place 25mL n-hexane and 5mL dimethyl sulfoxide in a 60mL separatory funnel, shake vigorously for 1min, let stand until the lower layer solution is transparent, put the lower layer solution into another 1cm absorption cell, and label it as “reference solvent”.
• 4.4 Using the reference solvent as reference, measure the ultraviolet absorbance of the “sample extract” in the wavelength range 280～350nm; if the absorbance is greater than 2.0, dilute with dimethyl sulfoxide and re-measure, and multiply the measured absorbance by the dilution factor.
• 4.5 If the measured ultraviolet absorbance complies with the values specified in Table 2, the sample is considered to pass the A method; otherwise the sample does not pass the A method.

Table 2 (pass criteria for the A method, maximum ultraviolet absorbance per 1cm optical path length):

(Note: the value column source-text extraction of Table 2 in the source text is missing/garbled, with only noise such as “2[garbled characters]- 299” visible, requires confirmation against the source standard (source-text extraction))

B method (Chapter 9)

9.1 Extraction and determination stage

• 9.1.1 Extraction: weigh 20g sample into a beaker, transfer it into a 500mL separatory funnel already containing 100mL pre-equilibrated dimethyl sulfoxide-phosphoric acid solution; rinse the beaker with 50mL pre-equilibrated isooctane and transfer to the same separatory funnel, shake vigorously for 2min. Separately prepare three 250mL separatory funnels, each containing 30mL pre-equilibrated isooctane. After the liquid phases in the 500mL separatory funnel separate, put the lower layer extract into the first 250mL isooctane separatory funnel, then successively wash each lower layer extract with the second and third 250mL separatory funnels containing 30mL isooctane, shaking for 1min for each wash. After the extract in the third 250mL separatory funnel separates, put the lower layer extract into a 2L separatory funnel containing 480mL distilled water; then extract the sample in the above 500mL separatory funnel twice with two portions (each 100mL) of pre-equilibrated dimethyl sulfoxide-phosphoric acid solution, and each time the extract is successively washed through the above three separatory funnels containing 30mL isooctane, and the washed extracts are all put into the above 2L separatory funnel.
• 9.1.2 Back-extraction: mix the collected extract (total volume 300mL) uniformly, cool for a few minutes, add 80mL isooctane and shake for 2min; after the liquid phases separate, put the lower layer solution into a 2L separatory funnel, then add 80mL isooctane and repeat the extraction once; after the liquid phases separate, discard the lower layer solution, and wash each 80mL isooctane extract three times with distilled water, 100mL each time, shaking for 1min.
• 9.1.3 Filtration: filter the 80mL isooctane extract in the first separatory funnel through an acid-resistant filter funnel, into which 35g isooctane-prewashed anhydrous sodium sulfate has been added; collect the filtrate into a 250mL evaporation flask. Then use the 80mL isooctane extract in the second separatory funnel to wash the first separatory funnel, and pass the wash liquid through the same anhydrous sodium sulfate acid-resistant filter funnel, combining the filtrate into the same evaporation flask. Then use 20mL isooctane to first wash the second separatory funnel and then the first separatory funnel, and pass all wash liquids through the aforementioned same anhydrous sodium sulfate acid-resistant filter funnel, combining the filtrate into the same evaporation flask.
• 9.1.4 Concentration: add 1mL n-hexadecane to the evaporation flask, place the evaporation flask on a water bath, and blow-evaporate the isooctane with nitrogen until the residual liquid volume is not greater than 1mL, with the same evaporation rate as before; then add 10mL isooctane, operate as before, and evaporate until the residual liquid volume is not greater than 1mL.
• 9.1.5 Transfer the residual liquid to a 200mL volumetric flask, add isooctane to the mark, and mix uniformly; put the solution into a 1cm absorption cell (there must be no loss when pouring the solution into the absorption cell), and measure the ultraviolet absorbance in the wavelength range 280～400nm using isooctane as reference.
• 9.1.6 Blank test: follow steps 9.1.1～9.1.5.
• 9.1.7 Judgment: correct the ultraviolet absorbance of the sample with the ultraviolet absorbance of the blank test; if the ultraviolet absorbance of the blank test and the corrected ultraviolet absorbance of the sample comply with the values specified in Table 4, the sample is considered to pass the B method. If the corrected ultraviolet absorbance per 1cm optical path length is greater than the value specified in Table 4, the test must be continued according to 9.2.

Table 4 (criteria for the B method, ultraviolet absorbance per 1cm optical path length):

(Note: the wavelength column source-text extraction of Table 4 in the source text reads “300- 359”, which requires confirmation against the source standard with respect to the range 280～400nm of the B method and common segmentation (source-text extraction))

9.2 Adsorption separation and determination stage

• 9.2.1 Transfer all the isooctane solution in the volumetric flask and absorption cell to the original 250mL evaporation flask, rinse the volumetric flask and absorption cell clean with a small amount of isooctane, combine the wash liquid into the evaporation flask, and blow-evaporate on a water bath with nitrogen until the residual liquid is not greater than 1mL, with the same evaporation rate as before. Remove the evaporation flask, cool, add 10mL methanol and about 0.3g sodium borohydride (to keep sodium borohydride from being exposed to air as much as possible, use a small glass measuring spoon), immediately attach a water condenser, and shake the flask until the sodium borohydride dissolves; leave at room temperature for 30min, shaking occasionally; then remove the water condenser, place the evaporation flask on a water bath and evaporate the methanol with nitrogen until sodium borohydride begins to precipitate from the solution; then add 10mL isooctane, concentrate the mixture to 2～3mL, then add 10mL isooctane, and evaporate again to about 5mL, shaking the flask continuously to ensure that the sodium borohydride is fully washed.
• 9.2.2 First, connect the chromatographic column to the suction filter flask with a polytetrafluoroethylene gasket; weigh 14g magnesium oxide-diatomaceous earth adsorbent, under vacuum (about 18.0kPa), load it into the chromatographic column in portions, each time loading about 3cm of the highly adsorbent layer; after each layer is loaded, use a glass rod to uniformly compact the adsorbent surface, use the tip of a metal rod to loosen the upper few millimeters of the surface layer of each layer, and then add the second layer of adsorbent; by this method, load all of the 14g adsorbent into the chromatographic column, use a glass rod to compact the adsorbent layer so that the total height of the adsorbent layer is about 12.5cm, stop the vacuum, remove the suction filter flask, and attach the 500mL container to the upper end of the chromatographic column; first wet the chromatographic column with 100mL isooctane, adjust the nitrogen pressure so that the downward flow rate of isooctane is 2～3mL/min; when the last portion of isooctane is about to reach the upper plane of the adsorbent, stop applying pressure (note: at no time may the liquid level be lower than the top surface of the adsorbent).
• 9.2.3 Add the above isooctane concentrate to the chromatographic column already filled with adsorbent (hereinafter referred to as the adsorption column), apply a slight nitrogen pressure so that the liquid level drops to just slightly above the adsorbent surface; use two portions of 5mL isooctane to thoroughly wash the evaporation flask, and quickly pour it into the adsorption column; before the last 5mL of washing liquid just reaches the top surface of the adsorbent, add 100mL isooctane, with a permeation downward flow rate of 2～3mL/min; when the last portion of isooctane just reaches the top surface of the adsorbent, add 100mL 10% benzene-isooctane eluent to the container, and continue permeation at the above rate; when the last portion of the mixture just reaches the top surface of the adsorbent, add 25mL 20% benzene-isooctane eluent to the container, and continue permeation at the above rate until all solvent has passed through the adsorption column, and discard all elution solutions; add 300mL acetone-benzene-water displacing agent to the container, and collect the displaced solution in a clean 1000mL separatory funnel until the solution has finished dripping.
• 9.2.4 Wash the displacement solution three times with distilled water, using 300mL each time, and shake for 1min; after the liquid phases separate (if emulsification occurs, sodium chloride may be used to break the emulsion), discard the lower layer solution; filter the upper benzene residue through anhydrous sodium sulfate pre-washed with benzene into a 250mL evaporation flask, wash the upper benzene residue in the separatory funnel twice with benzene, using 20mL each time, and put the washings into the same anhydrous sodium sulfate acid-resistant filter funnel for filtration, combining them into the evaporation flask.
• 9.2.5 Add 1mL n-hexadecane to the evaporation flask, blow-evaporate on a water bath with nitrogen gas, at the same evaporation rate as before, until the residual liquid is no more than 1mL, then add two portions of 10mL isooctane, each time evaporating until the residual liquid is no more than 1mL.
• 9.2.6 Transfer the residual liquid to a 200mL volumetric flask, add isooctane to the mark, and mix uniformly; place the solution in a 1cm path length absorption cell, and measure the ultraviolet absorbance of the solution in the wavelength range 280～400nm.
• 9.2.7 For the blank test, follow steps 9.2.1～9.2.6; if in the wavelength range 250～260nm the characteristics of the benzene spectrum appear, then blow-evaporation must be repeated to remove all benzene, and then its ultraviolet absorbance is measured again.
• 9.2.8 Judgment: the measured value is corrected using the ultraviolet absorbance measured in the blank test; if the ultraviolet absorbance of the blank test and the corrected ultraviolet absorbance of the test sample conform to the specified values in Table 4 of the standard, the test sample is considered to have passed the B method; otherwise the test sample has not passed the B method.

Solvent inspection (8.3)

• 8.3.1 Inspection of n-hexadecane: take 1mL n-hexadecane, directly dilute with isooctane to 25mL, use isooctane as reference, and measure ultraviolet absorbance with a 5cm path length absorption cell; in the wavelength range 280～400nm, the ultraviolet absorbance per 1cm path length should not be greater than 0.00 (the source text source-text extraction reads “0.00a”, requires confirmation against the source standard (source-text extraction)).
• 8.3.2 Inspection of isooctane, petroleum ether, acetone, benzene and methanol: place the specified amount (see Table 3) of solvent into a 250mL evaporation flask, add 1mL n-hexadecane, evaporate on a water bath with nitrogen gas until the residual liquid amount is no more than 1mL; control the evaporation rate so that the amount of liquid evaporated per minute is about 4mL; for the residual liquid of benzene and acetone, two more portions of 10mL isooctane should be added, with the same operation as before, to ensure removal of all benzene or acetone; dissolve the residual liquid in isooctane so that the total volume is 25mL, use isooctane as reference, and measure the ultraviolet absorbance of the solution with a 5cm path length absorption cell; in the wavelength range 280～400nm, the ultraviolet absorbance per 1cm path length should not be greater than the value specified in Table 3.
• 8.3.3 Inspection of distilled water: take 500mL distilled water and place it in a 1000mL separatory funnel, add 25mL isooctane, shake vigorously for 5min, let stand for 30min, after layering discard the aqueous layer, use isooctane as reference, and in the wavelength range 280～400nm, measure ultraviolet absorbance with a 5cm path length absorption cell; the ultraviolet absorbance per 1cm path length is not greater than 0.00 (the source text source-text extraction reads “O.OOo”, requires confirmation against the source standard (source-text extraction)).

Table 3 (specified amounts and upper absorbance limits for solvent inspection):

Appendix A Reagent purification and treatment methods

• A1 Chromatographic column method: suitable for purification of isooctane, n-hexane, petroleum ether (boiling range 60～90℃), and n-hexadecane. Plug the lower end of a glass chromatographic column about 90cm long and with an inner diameter of 5～8cm with clean cotton, and while tapping, fill activated silica gel to three-quarters of the height of the chromatographic column; the amount of silica gel loaded is about 1kg; continue tapping the column until the silica gel no longer settles; place the column vertically and secure it with a clamp, then add the above reagents to be purified (the treatment amount for each reagent depends on the impurities therein); the first 200mL that drips down must be returned to the chromatographic column and treated once more; the liquid flow rate can be controlled at 4～5mL/min. Because the amount of n-hexadecane used is small, a small chromatographic column may also be used for purification; a chromatographic column with an inner diameter of 1.5cm and a column length of 60cm is suitable. Note: use 0.246～0.124mm pore size fine-pore silica gel activated at 180℃±1℃ for 5～6h (the source text source-text extraction reads “0.246[unreadable separator]0,124- pore size”, requires confirmation against the source standard (source-text extraction)).
• A2 Distillation method: suitable for purification of isooctane, petroleum ether (boiling range 60～90℃), benzene, acetone and methanol; ordinary distillation apparatus may be used, distilling at atmospheric pressure.
  • A2.1 Purification of isooctane: take 1500mL isooctane purified by the chromatographic column method, add it to a distillation flask, add a few boiling stones and distill, controlling the flow rate at 4～5mL/min; take 1300mL of the distillate for inspection.
  • A2.2 Purification of petroleum ether (boiling range 60～90℃): take 1500mL petroleum ether purified by the chromatographic column method, add it to a distillation flask, add a few boiling stones and distill; the flow rate and the amount of fraction collected are the same as for isooctane.
  • A2.3 Purification of benzene: take 1500mL benzene, add it to a distillation flask, add a few boiling stones and distill, controlling the flow rate at 4～5mL/min; take 1200mL of the distillate for inspection.
  • A2.4 Purification of acetone and methanol: the method is the same as for purifying benzene.
• A3 Extraction method: suitable for purification of distilled water. Take 1500mL of once-distilled distilled water and place it in a 2L separatory funnel, add 50mL pure petroleum ether (boiling range 60～90℃), shake for 10min, after standing and layering, take the lower layer solution for inspection.

9. Qualitative and quantitative determination and calculation formulas

• A method: using reference solvent as reference, measure the ultraviolet absorbance of the “sample extract” in the wavelength range 280～350nm; when the absorbance is greater than 2.0, dilute with dimethyl sulfoxide and measure again, and multiply the measured absorbance by the dilution factor (4.4). The criteria are shown in Table 2 (values require confirmation against the source standard (source-text extraction)).
• B method: using isooctane as reference, measure the ultraviolet absorbance in the wavelength range 280～400nm; the measured value is corrected using the ultraviolet absorbance measured in the blank test (9.1.7, 9.2.8). The criteria are shown in Table 4.
• Calculation formula: not provided in the available source (the standard judges directly by absorbance and does not give a calculation formula).

10. Precision

• Not provided in the available source.

11. Report

• 10.1 Report that the test sample passed the A method or passed the B method.
• 10.2 Report that the test sample did not pass the A method or did not pass the B method.

12. Referenced documents

• GB/T 3555 “Petroleum products—Determination of Saybolt color (Saybolt colorimeter method)” (cited for applicability of the A method)
• GB/T 6540 “Petroleum products—Determination of color” (cited for applicability of the B method)
• U.S. Food and Drug Administration FDA 21CFR178.3620(196)(b), (c) (equivalent adoption, the source text source-text extraction requires confirmation against the source standard)
• Appendix A (appendix to the standard) Reagent purification and treatment methods

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 for questions and answers