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1、BRITISH STANDARD CONFIRMED NOVEMBER 1992 BS 684-2.26: 1986 Methods of analysis of Fats and fatty oils Part 2: Other methods Section 2.26 Determination of polyethylene-type plastics IMPORTANT NOTE. It is essential that BS 684-0, which is published separately, be read in conjunction with this Section.
2、 UDC 665.1.014:543.8.062:678.742.2 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.26:1986 This British Standard, having been prepared under the direction of the Food and Agriculture Standards Committee, was published under the auth
3、ority of the Board of BSI and comes into effect on 28 November 1986 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference FAC/18 Draft for comment 85/53924 DC ISBN 0 580 15492 0 A British Standard does not purport to include all the necessary provisions of
4、 a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 6, an inside
5、back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun
6、, na, Wed Dec 06 13:27:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.26:1986 BSI 09-1999i Contents Page 1Scope1 2Principles1 3Reagents1 4Apparatus1 5Sampling2 6Preparation of test sample2 7Method 1. Indirect gravimetric method2 8Method 2. Direct gravimetric method3 9Method 3. Infrared spect
7、roscopic method3 10Test report5 Table 1 Values to be used to plot the net absorbance4 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 1
8、3:27:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.26:1986 BSI 09-19991 1 Scope This Section describes three methods for the determination of polyethylene-type plastics in fats. For arbitration purposes, method 1 is appropriate. Method 1 is an indirect gravimetric method based on ISO 6656:1
9、984. Method 2 is a direct gravimetric method that is of use particularly when the examination of the plastics material is necessary. Method 3 is an infrared spectroscopic method used as a rapid routine method All three methods are increasingly imprecise at plastics levels below 50 mg/kg of sample. N
10、OTE 1The precision can be increased at any plastics level by carrying out several determinations. NOTE 2The titles of the publications referred to in this Section are given on the inside back cover. 2 Principles 2.1 Method 1 After acid treatment to decompose any soaps present, dissolution of a test
11、portion in chloroform (which leaves polyethylene-type plastics in suspension) and filtration through a sintered filter crucible containing a mat of filter aid. Washing the crucible and its contents, drying and weighing. Extraction of polyethylene-type plastics from the insoluble matter by boiling te
12、trachloroethylene. Drying the crucible with its contents and weighing again. 2.2 Method 2 After acid treatment to decompose any soaps present, dissolution of a test portion in chloroform (which leaves polyethylene-type plastics in suspension) and filtration through a sintered filter crucible contain
13、ing a mat of filter aid. Extraction of polyethylene-type plastics with hot tetrachloroethylene and precipitation of the plastics with methanol followed by filtering, washing, drying and weighing the precipitated plastics. 2.3 Method 3 After acid treatment to decompose any soaps present, dissolution
14、of a test portion in chloroform (which leaves polyethylene-type plastics in suspension) and filtration through a sintered filtered crucible containing a mat of filter aid. Extraction of polyethylene-type plastics with hot tetrachloroethylene. Calculation of the plastics content from the infrared abs
15、orption at 2 860 cm1, making allowance for the absorption due to extraneous material. 3 Reagents 3.1 Reagents for the direct and indirect gravimetric methods and the infrared spectroscopic method 3.1.1 All reagents shall be recognized analytical grade. The water used shall be distilled water or wate
16、r of at least equivalent purity. 3.1.2 Methanol, containing not more than 0.5 % (m/m) of water. 3.1.3 Acetone 3.1.4 Chloroform 3.1.5 Tetrachloroethylene. For method 3, the tetrachloroethylene shall be suitable for infrared spectroscopy and the absorbance at 2 650 cm1 shall not exceed 0.05. WARNING.
17、Avoid contact of chloroform and tetrachloroethylene with the skin. Do not inhale the vapours. Perform all operations under a suitable fume-hood. 3.1.6 Hydrochloric acid, ethanolic solution. Mix 1 volume of hydrochloric acid (20 = 1.19 g mL) with 9 volumes of 95 % (V/V) ethanol. 3.1.7 Diatomaceous ea
18、rth type filter aid, acid washed. 3.2 Additional reagents for the infrared spectroscopic method (see clause 9) 3.2.1 Sodium sulphate, anhydrous. 3.2.2 Polyethylene, pure, unfilled. 3.2.3 Tallow, or other fat being tested, free from polyethylene. 3.2.4 Stearic acid, minimum purity 99 %. 4 Apparatus W
19、ARNING. Plastics apparatus is likely to be affected by solvents (particularly chloroform or tetrachloroethylene). Check that care is taken to ensure that the solvents used do not come into contact with plastics. 4.1 Apparatus for the direct and indirect methods and the infrared spectroscopic method
20、4.1.1 Ordinary laboratory apparatus 4.1.2 Clamp-type filter 4.1.3 Crucibles with sintered filters, of porosity grade P 40 (16 4m to 40 4m). NOTESintered filters complying with BS 1752 are suitable. 4.1.4 Desiccator 4.1.5 Hotplate, with magnetic stirrer. 4.1.6 Oven, capable of being maintained at 103
21、 2 C. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.26:1986 2 BSI 09-1999 4.2 Additional apparatus for the infrared spectroscopic method (see clause 9) 4.2.1 50 mL and 100 mL bottles, with screw tops lined with aluminium foil. 4.2
22、.2 10 mL hypodermic syringe, glass, with a connector for secure attachment (e.g. Luer lock fitting). 4.2.3 Infrared spectrophotometer, suitable for quantitative measurements. 4.2.4 Cells, made of sodium chloride and of path length 1.0 min. 4.2.5 Cell heater, capable of maintaining the cells at 85 3
23、C. In the absence of a cell heater, hot air may be used, for example, from a hair dryer. 4.2.6 Oven, capable of being maintained at 85 3 C. NOTEPolyethylene commences to separate from solution at about 70 C, and at temperatures above 90 C the sodium chloride cells are liable to fracture. 5 Sampling
24、The laboratory sample shall be taken in accordance with BS 627. Because the plastics are often heterogeneously distributed in a lot, particular care is necessary to obtain representative samples. If required for greater precision, more than one laboratory sample shall be submitted. NOTEA separate la
25、boratory sample should be submitted if characteristics that can be affected by heat are to be measured. 6 Preparation of test sample Heat the laboratory sample (clause 5) to between 110 C and 120 C. Stir the sample for 3 min to 4 min to ensure complete homogenization. 7 Method 1. Indirect gravimetri
26、c method 7.1 Procedure 7.1.1 Test portion. Weigh, to the nearest 0.1 g, about 100 g of the test sample (clause 6) into a 1 000 mL beaker. NOTEFor samples expected to contain more than 500 mg of polyethylene-type plastics per kilogram, the test portion may be reduced to 50 g. 7.1.2 Acid treatment. Ad
27、d 75 mL of the ethanolic hydrochloric acid (3.1.6) to the test portion, cover the beaker and stir on the hotplate (4.1.5) for 5 min at 60 C to 70 C. Cool to below 35 C, then add 270 mL of the chloroform (3.1.4) and stir until the fat or oil is dissolved (the solution may not be clear). Add 1.0 g of
28、the filter aid (3.1.7) suspended in 30 mL of the chloroform (to avoid the formation of lumps). 7.1.3 Determination 7.1.3.1 Prepare a filter mat by suspending about 0.5 g of the filter aid in 30 mL of the chloroform and filtering through the sintered filter crucible (4.1.3). Using suction if necessar
29、y, filter the contents of the beaker (stirred immediately before filtration) into a 1 000 mL filter flask. 7.1.3.2 Rinse the beaker with about 50 mL of chloroform and pour the rinsings slowly through the sintered filter crucible under suction, keeping the chloroform level in the crucible about 5 mm
30、above the filter mat. Repeat the rinsing with 50 mL of the methanol (3.1.2), taking the same precautions. 7.1.3.3 Repeat the washing procedure, rinsing the crucible alternately with chloroform and methanol (50 mL portions) until a total of 150 mL of chloroform and 100 mL of methanol has been used. C
31、ontinue suction until the crucible is dry. 7.1.3.4 Wash the underside of the crucible with chloroform. Wash the contents of the crucible twice under suction with 25 mL of the acetone (3.1.3) in order to remove absorbed water. Suck air through the crucible for 1 min. 7.1.3.5 When the crucible appears
32、 to be dry, place it in the oven (4.1.6) at 103 2 C, and leave for 15 min to 30 min. 7.1.3.6 Allow the crucible to cool in the desiccator (4.1.4) for 30 min and weigh to the nearest 0.1 mg. Repeat the drying, cooling and weighing procedures until the difference between two successive weighings does
33、not exceed 1 mg. Record the mass (m1). 7.1.3.7 Warm the crucible and its contents to 103 2 C and wash the contents of the crucible with 25 mL of boiling tetrachloroethylene (3.1.5) without suction if possible, using a clean dry 250 mL filter flask to collect the filtrate. Repeat the washing procedur
34、e four more times, using 25 mL portions of boiling tetrachloroethylene each time, and suck air through the crucible for 2 min. Retain the filtrate and washings if method 2 (see 8.1) or method 3 (see 9.3) is to be carried out, but they are not required for method 1. 7.1.3.8 Wash the crucible with 50
35、mL of the acetone (3.1.3) to remove traces of tetrachloroethylene and suck air through the crucible for 2 min. 7.1.3.9 Place the crucible in the oven (4.2.6) at 103 2 C and leave for 15 min to 30 min. Allow the crucible to cool it the desiccator (4.1.4) for 30 min and weigh to the nearest 0.1 mg. Li
36、censed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.26:1986 BSI 09-19993 7.1.3.10 Repeat the washings with boiling tetrachloroethylene (see 7.1.3.7) and with acetone (see 7.1.3.8) and the drying, cooling and weighing procedures (see 7.1.3
37、.9) until the difference between two successive weighings does not exceed 1 mg. Record the mass (m2). 7.1.4 Number of determinations. Carry out two determinations on the same test sample. 7.2 Calculation and expression of results The polyethylene-type plastics content P, in mg/kg, is calculated as f
38、ollows: Take as the result the arithmetic mean of the values obtained in the two determinations. 8 Method 2. Direct gravimetric method 8.1 Procedure Carry out the procedure described in 7.1.1 to 7.1.3.7. Quantitatively transfer the hot tetrachloroethylene solution obtained in 7.1.3.7 to a 600 mL bea
39、ker. Add 150 mL of the methanol (3.1.2) at 0 C to 5 C swirling gently to mix the liquids. Allow to stand for at least 1 h. Dry a glass fibre filter paper at 103 2 C for 30 min, cool in the desiccator (4.1.4) and weigh to the nearest 0.2 mg. Place the weighed filter paper in the clamp-type filter (4.
40、1.2) and filter the suspension. Wash the beaker and filter with four 20 mL portions of methanol, suck dry and draw air through the filter for 2 min. Carefully remove the paper from the funnel, place it in an evaporating dish and dry at 103 2 C. Cool in a desiccator. Weigh the paper and precipitate t
41、o the nearest 0.2 mg. Repeat the drying, cooling and weighings until the weighings are constant to within 1 mg. 8.2 Calculation and expression of results The polyethylene-type plastics content P, in mg/kg, is calculated as follows: where m0is the mass of the test portion (7.1.1) (in g); m1is the mas
42、s of the filter paper (in g); m2is the mass of the filter paper and plastics (in g). 9 Method 3. Infrared spectroscopic method 9.1 Checking the suitability of the tetrachloroethylene 9.1.1 Absorbance at the analytical frequencies. Fill one of the cells (4.2.4) with tetrachloroethylene and scan the s
43、pectrum from 4 000 cm1 to 1 250 cm1 compared with an empty cell. If the difference between the absorbance at wave numbers 2 860 cm1 and 2 650 cm1 exceeds 0.12, wash the tetrachloroethylene with water (one part of water to four parts of tetrachloroethylene) and dry with the anhydrous sodium sulphate
44、(3.2.1), filter and repeat the scanning procedure. If the difference between the absorbance at wave numbers 2 860 cm1 and 2 650 cm1 still exceeds 0.12, the batch of tetrachloroethylene is not suitable for use. 9.1.2 Effect of heat. Heat two approximately 25 mL portions of the tetrachloroethylene to
45、105 C, one portion for 2 h and the other for 15 min. Using cells (4.2.4) controlled at 85 3 C, with the portion heated for 15 min in the reference beam, scan the spectrum from 4 000 m1 to 1 250 cm1. If the difference between the absorbance at wave numbers 2 860 cm1 and 2 750 cm1 exceeds 0.01, the ba
46、tch of tetrachloroethylene is unsuitable for use. 9.2 Apparatus checks and calibration of the spectrometer 9.2.1 Instrument conditions. Set the infrared spectrophotometer (4.2.3) according to the manufacturers instructions as to obtain optimum performance at the required analytical wavelengths. The
47、analytical peaks are the CH2 band at 2 860 cm1, the fatty acid and glyceride carbonyl bands at about 1 750 cm1 and 1 715 cm1 respectively. The spectra are measured in the ranges respectively of 3 100 cm1 to 2 700 cm1 and of 1 825 cm1 to 1 500 cm1. 9.2.2 Cell checks. Check the path length of the samp
48、le cell (4.2.4) every 25 scans. The path length may increase due to erosion of the salt plates by hot solvent. Repolish the cell plates and rebuild the cell if the path length increases by more than 0.02 mm. Where m0is the mass of the test portion (7.1.1) (in g); m1is the mass of the crucible and in
49、soluble matter before extraction (7.1.3.6) (in g); m2is the mass of the crucible and insoluble matter after extraction (7.1.3.10) (in g). P m1m2 m0 -106= P m2m1 m0 -106= Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.26:1986 4 BSI 09-1999 The sample cell may be slowly contaminated by polyethylene plating out on to the surface; this is inhibited by maintaining the cell hot throughout the test. Check for con