GB/T 7363-2021 Test method for polynuclear aromatic hydrocarbons in petroleum wax

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GB/T 7363-2021, Test method for polynuclear aromatic hydrocarbons in petroleum wax, specifies the apparatus, reagents and materials, test preparation, sampling, test procedure and reporting for the determination of polynuclear aromatic hydrocarbons in petroleum wax.

Evidence note: The content of this page was compiled from the original text of this standard held in the Origin Standard library (where marked [to be verified], the source is [source unclear]); for individual values and the current status, please refer to the original standard page and the product certificate.

Scope: This document specifies the apparatus and equipment, reagents and materials, test preparation, sampling, test procedure and reporting for the determination of polynuclear aromatic hydrocarbons in petroleum wax. Applicable to food-grade paraffin wax, food-grade microcrystalline wax, fully refined paraffin wax and special packaging wax and similar products. Not applicable: the available material does not provide it.

Principle: Dimethyl sulfoxide is used as the solvent to extract the aromatic hydrocarbons from the petroleum wax, and the aromatic hydrocarbons dissolved in the dimethyl sulfoxide are then back-extracted with isooctane. The extract is concentrated to a concentration equivalent to 1 g of sample per millilitre of isooctane, and its ultraviolet absorbance is measured. If the absorbance value exceeds the specified limit, the extract is treated with sodium borohydride, adsorbed on magnesium oxide-diatomaceous earth to separate the polynuclear aromatic hydrocarbons, and the ultraviolet absorbance is measured again. If the absorbance value is still greater than the specified limit, the result is reported as not passing. If the absorbance measured at the first or the second determination is not greater than the specified limit, the result is reported as passing.

Apparatus: Ultraviolet spectrophotometer: wavelength range 250 nm to 400 nm, with a slit of 2 nm or smaller. Under the operating conditions for absorbance measurement, the performance of the spectrophotometer shall meet the following requirements: a) absorbance repeatability: ±0.01 at 0.4 absorbance; b) absorbance accuracy: ±0.05 at 0.4 absorbance; c) wavelength repeatability: ±0.2 nm; d) wavelength accuracy: ±1.0 nm. 6.2 Fused silica absorption cell for spectroscopy: path length within 5.000 cm ± 0.005 cm. A quartz cell of 1.000 cm ± 0.005 cm path length may be used to check the performance of the ultraviolet spectrophotometer (6.1). With water as reference, determine the difference in absorbance values. 6.3 Separatory funnel: pear-shaped, capacities 250 mL, 500 mL, 1000 mL and 2000 mL; with polytetrafluoroethylene stopcock. 6.4 Container: glass, 500 mL, with an 18/30 or 24/40 conical ground joint at the bottom and a suitable nitrogen inlet adapter at the top. There shall be a glass hook above the ground joint (see Figure 1). 6.5 Adsorption column: column length 180 mm, inside diameter 15.7 mm ± 0.1 mm, with a coarse-porosity fritted glass plate (or other suitable support) at the lower end, and an 18/30 or 24/40 conical ground joint at the upper end (total length of column and adapter 235 mm); a glass hook shall be provided below the ground joint (see Figure 1). 6.6 Gasket disc: polytetrafluoroethylene disc 50 mm in diameter and about 5 mm thick, with a central hole whose diameter exactly matches the outside diameter of the column body. 6.7 Heating jacket: conical or cylindrical, suitable for heating 500 mL separatory funnels, with adjustable voltage for temperature control. 6.8 Suction flask: 250 mL or 500 mL. 6.9 Condenser: with an 18/30 or 24/40 joint (see Figure 2), connected to a drying tube of optional length. 6.10 Evaporation flask: 250 mL or 500 mL glass flask, fitted with a standard conical stopper having inlet and outlet tubes so that nitrogen can be passed to the surface of the liquid to be evaporated in the flask (see Figure 2). 6.11 Vacuum distillation apparatus: mainly used for purification of dimethyl sulfoxide. Made entirely of glass (see Figure 3), comprising a 2 L distillation flask with heating mantle, a vacuum-jacketed condenser about 45 cm long (or an equivalent condenser) and a distillation head with a detachable cold-finger condenser. The use of polytetrafluoroethylene sleeves at glass joints prevents freezing; no grease shall be used on stopcocks or joints. 6.12 Ground-joint conical flask: 1000 mL. 6.13 Pipette: 25 mL, 50 mL, graduated, graduation accuracy 0.2 mL. 6.14 Acid-resistant funnel: glass, 40 mL, G1. 6.15 Constant-temperature oven: capable of heating to 175 °C and maintaining constant temperature, accuracy 1 °C. 6.16 Standard sieve: 250 μm (60 mesh), 80 μm (180 mesh). 6.17 Water bath (or steam bath): capable of heating to 100 °C and maintaining constant temperature, temperature accuracy 0.2 °C. 6.18 Small glass scoop: for measuring sodium borohydride, one scoop equivalent to 0.3 g of sodium borohydride. 6.19 Glass rod: 250 mm to 300 mm long, about 5 mm outside diameter, one end flattened and rounded, for tamping the adsorbent. 6.20 Metal rod: 250 mm to 300 mm long, about 5 mm outside diameter, one end pointed, for loosening the adsorbent. 6.21 Volumetric flask: 250 mL, 500 mL.

Reagents and reference materials: Warning (original): phosphoric acid is corrosive; isooctane, n-hexadecane, acetone, benzene and methanol are flammable; acetone and benzene are toxic, and benzene is a class 1 carcinogen; sodium borohydride is strongly irritating; all the above reagents are harmful to health; beware of compressed nitrogen under high pressure. 5.1 Distilled water: shall meet the inspection requirements of 7.3.4. If necessary, purify through ion exchange resin or by other suitable methods, or purify as specified in A.1.2 of Annex A. 5.2 Phosphoric acid: analytical reagent. 5.3 Anhydrous sodium sulfate: analytical reagent, granular. Each bottle of anhydrous sodium sulfate used shall be pre-washed as specified in 7.4.2 to provide the filtering medium required by this method. 5.4 Nitrogen: purity not less than 99.5 %, with a control valve to control the flow at a pressure of 3.43 kPa. 5.5 Isooctane (2,2,4-trimethylpentane): analytical reagent, content not less than 99.0 %, tested as specified in 7.3.2 and shall meet the inspection requirements of Table 1. If necessary, purify as specified in A.2. 5.6 Dimethyl sulfoxide: analytical reagent, colourless transparent liquid, melting point 18 °C. Shall meet the inspection requirements of 7.3.3. If necessary, pretreat as specified in A.3 and purify as follows: take 1500 mL of dimethyl sulfoxide into a 2 L distillation flask with a glass stopper, then add 6.0 mL of phosphoric acid and 50 g of alkaline activated carbon (prepared as specified in A.4) or similar. Stopper the flask and stir with a magnetic stirrer for 15 min (the stirring bar shall be polytetrafluoroethylene-coated), and filter the dimethyl sulfoxide through four layers of fluted filter paper (about 18 cm diameter). If the initial filtrate contains carbon powder, return the filtrate to the same funnel and refilter until the filtrate is transparent. To prevent the dimethyl sulfoxide from contacting air and moisture, cover the surface of the reagent in the separatory funnel and receiving bottle with a layer of isooctane during the operation. Transfer the filtrate to a 2000 mL separatory funnel, run the dimethyl sulfoxide from the bottom into the 2 L distillation flask of the vacuum distillation apparatus, and distill at a pressure of about 400 Pa (3 mmHg) or less. Discard the first 200 mL of distillate, change to a clean distillate receiver, and continue distillation until 1000 mL of dimethyl sulfoxide has been obtained. Since this reagent is relatively hygroscopic and readily reacts with some metal containers in air, it shall be stored in a glass-stoppered bottle after distillation. 5.7 n-Hexadecane: analytical reagent, free of olefins, shall meet the inspection requirements of 7.3.1. If necessary, purify by distillation or by the adsorption column method specified in A.2. 5.8 Acetone: analytical reagent, tested as specified in 7.3.2 and shall meet the inspection requirements of Table 1. If necessary, purify by distillation as specified in A.1.3. 5.9 Benzene: analytical reagent, tested as specified in 7.3.2 and shall meet the inspection requirements of Table 1. If necessary, purify by distillation or other methods as specified in A.1.4. 5.10 Methanol: analytical reagent, tested as specified in 7.3.2 and shall meet the inspection requirements of Table 1. If necessary, purify by distillation as specified in A.1.4. 5.11 Sodium borohydride: analytical reagent. 5.12 Magnesium oxide: analytical reagent. 5.13 Diatomaceous earth: analytical reagent. 5.14 Sodium chloride: analytical reagent. 5.15 Activated carbon: for chromatography, granular. 5.16 Chromatographic silica gel: particle size 75 μm to 150 μm (100 mesh to 200 mesh), or silica gel of similar particle size. Table 1 Inspection requirements for some solvents | Solvent | Specified quantity/mL | Inspection requirement/(ultraviolet absorbance/cm) | |---|---|---| | Isooctane | 180 | Not greater than 0.01 | | Benzene | 150 | Not greater than 0.01 | | Acetone | 200 | Not greater than 0.01 | | Methanol | 10 | Not greater than 0.00 |

Key conditions: Ultraviolet measurement wavelength range: 280 nm to 400 nm for the extraction determination (9.1.7); 250 nm to 400 nm for the adsorption separation determination (9.2.6). Absorption cell path length: 5 cm (6.2). Evaporation rate of the nitrogen blow-down: about 4 mL/min (7.3.2). Downflow rate of isooctane through the adsorption column: 2 mL/min to 3 mL/min (9.2.3). Vacuum conditions for the adsorption column: about 18 kPa (9.2.2). Vacuum distillation pressure for dimethyl sulfoxide: about 400 Pa (3 mmHg) or less (5.6). Magnesium oxide drying: constant-temperature drying at 160 °C ± 1 °C for 24 h; the adsorbent is dried at 160 °C ± 1 °C for 2 h before use (7.4.4). Water bath heating of the magnesium oxide slurry: 70 °C ± 2 °C, 30 min (7.4.4). Water bath (or steam bath): capable of heating to 100 °C and maintaining constant temperature, temperature accuracy 0.2 °C (6.17).

Calculation and results: Quantitation: judgement is made by comparing the ultraviolet absorbance (per centimetre of path length) with the limit values specified in Table 2 and Table 3. Correction: the ultraviolet absorbance of the sample is corrected with the ultraviolet absorbance value of a blank test without sample (9.1.9, 9.2.8). Calculation formula: the available material does not provide one. Qualitative: in the NOTE to 9.2.6, the benzene spectral lines are detected in the 250 nm to 260 nm interval; if benzene spectral line characteristics appear, blow down again to remove benzene and then measure.

Verification note: [To be verified] and [source unclear] mark points that still need to be checked against the original standard text; they do not mean the values have been verified. Do not use these values or procedures directly as a basis for work.

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