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1、BRITISH STANDARD BS 5666-3: 1991 Methods of analysis of Wood preservatives and treated timber Part 3: Quantitative analysis of preservatives and treated timber containing copper/chromium/arsenic formulations NOTEIt is essential that this Part is read in conjunction with Part 1 “Guide to sampling and
2、 preparation of wood preservatives and treated timber for analysis”. BS 5666-3:1991 This British Standard, having been prepared under the direction of the Wood Preservation Standards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 28 February 1991 BSI
3、 07-1999 First published February 1979 Second edition February 1991 The following BSI references relate to the work on this standard: Committee reference WPC/11 Draft for comment 89/50550 DC ISBN 0 580 18580 X Committees responsible for this British Standard The preparation of this British Standard
4、was entrusted by the Wood Preservation Standards Policy Committee (WPC/-) to Technical Committee WPC/11, upon which the following bodies were represented: Association of Consulting Scientists British Drier Manufacturers Association British Wood Preserving and Damp-proofing Association Department of
5、the Environment (Building Research Establishment) Ministry of Defence Amendments issued since publication Amd. No.DateComments BS 5666-3:1991 BSI 07-1999i Contents Page Committees responsibleInside front cover Forewordii 1Scope1 2Method 1. Atomic absorption spectrometric method1 3Method 2. Colorimet
6、ric method3 4Test report7 Figure 1 Apparatus for arsenic determination8 Publication(s) referred toInside back cover BS 5666-3:1991 ii BSI 07-1999 Foreword This Part of BS 5666 has been prepared under the direction of the Wood Preservation Standards Policy Committee. This Part of BS 5666 was first pu
7、blished in 1979. This edition introduces technical changes but it does not reflect a full review or revision of this Part of the standard, which will be undertaken in due course. This edition supersedes BS 5666-3:1979 which is withdrawn. CAUTION. Attention is drawn to the Health and Safety at Work e
8、tc. Act 1974, and the need for ensuring that the methods of test specified in this standard are carried out with suitable precautions. The procedures described in this standard are intended to be carried out by qualified chemists or other suitably trained and/or supervised personnel. Normal safety p
9、recautions should be observed throughout the use of the methods. Attention is drawn to the general safety precautions mentioned in clause 3 of BS 5666-1:1987. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for the
10、ir 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 8, an inside back cover and a back cover. This standard has been updated (se
11、e copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. BS 5666-3:1991 BSI 07-19991 1 Scope This Part of BS 5666 details procedures for the determination of copper, chromium and arsenic in preservatives and in treated timbe
12、r containing those water-borne preservative compositions which consist essentially of copper, chromium and arsenic compounds. The wood sample may be in the form of sawdust, wood flour, or thin sections. There is no inter-elemental interference during the determinations and the procedures are specifi
13、c for arsenic even in the presence of phosphorus compounds. The procedure for the analysis of preservatives has been primarily designed for solutions complying with the requirements of BS 4072; for samples of other compositions it may be necessary to make adjustments. It is difficult to make recomme
14、ndations as to the quantity of sample to be taken in the case of treated wood because the predominant factor is the quantity of preservative within the wood rather than the mass of the wood itself. The digestion procedure has been designed to deal with wood samples up to 8 g in mass, but it may be n
15、ecessary to adjust the concentration of the resulting solution before a satisfactory analysis can be carried out. Two methods are described, the first involving atomic absorption spectrometry and the second colorimetry. NOTEThe titles of the publications referred to in this standard are listed on th
16、e inside back cover. 2 Method 1. Atomic absorption spectrometric method 2.1 Principle Copper, chromium and arsenic compounds are leached quantitatively from the wood sample with a mixture of dilute sulphuric acid and hydrogen peroxide solution. Preservatives are treated with the same mixture. The re
17、sulting solutions, after addition of sodium sulphate solution, are analysed using atomic absorption spectrometry1). 2.2 Reagents Reagents shall be of recognized analytical reagent grade, and water complying with the requirements of grade 3 of BS 3978 shall be used throughout. WARNING NOTE. Sulphuric
18、 acid (L20 = 1.84 g/mL) and hydrogen peroxide solution (100 volumes) are corrosive and cause burns. Care should be taken to avoid their contact with eyes and skin. 2.2.1 Sulphuric acid solution, c(H2SO4) = 2.5 mol/L. Cautiously add, with stirring and cooling, 280 mL of sulphuric acid (L20 = 1.84 g/m
19、L) to 1 600 mL of water. Cool and dilute to 2 litres with water. 2.2.2 Hydrogen peroxide solution, c(H2O2), 300 g/L (100 volumes). 2.2.3 Sodium sulphate solution, c(Na2 SO4) = 30 g/L. Dissolve 30 g of anhydrous sodium sulphate in water and dilute to 1 litre with water. 2.2.4 Sulphuric acid solution,
20、 c(H2SO4) = 0.5 mol/L/sodium sulphate 3 g/L solution. Dilute 200 mL of sulphuric acid solution (2.2.1) plus 100 mL of 30 g/L sodium sulphate solution (2.2.3) to 1 litre with water and mix. 2.2.5 Standard solution (1 mL X 500 Xg of copper, 1 000 Xg of chromium and 1 000 Xg of arsenic). Dissolve 0.982
21、5 g of copper sulphate pentahydrate (CuSO4.5H2O) in a little water and transfer the solution to a 500 mL one-mark volumetric flask. Dissolve 1.4135 g of potassium dichromate (K2Cr2O7) in a little water, add 50 mL of sulphuric acid solution (2.2.1) and 10 mL of hydrogen peroxide solution (2.2.2), boi
22、l until evolution of oxygen ceases and all the hydrogen peroxide is decomposed, cool and transfer the mixture to the one-mark volumetric flask containing the copper sulphate solution. Dissolve 0.6600 g of arsenic trioxide (As2O3) by boiling it in a solution containing 50 mL of sulphuric acid solutio
23、n (2.2.2) and 75 mL of water. Continue boiling until evolution of oxygen ceases and all the hydrogen peroxide is decomposed, cool and transfer it to the one-mark volumetric flask. Add 50 mL of sodium sulphate solution (2.2.3) to the volumetric flask, dilute to the mark with water and mix. 2.3 Appara
24、tus 2.3.1 Volumetric glassware, complying with the requirements for class A quality in accordance with BS 700-2 (type 2), BS 846, BS 1583 or BS 1792, as appropriate. 2.3.2 Atomic absorption spectrometer, together with suitable sources of resonance radiation for copper, chromium and arsenic, e.g. hol
25、low-cathode lamps. 1) For reference, see Williams, A.I., Analyst, 1970, 95, 670. BS 5666-3:1991 2 BSI 07-1999 2.4 Procedure 2.4.1 Instruments settings and operation The instrument settings and operating conditions for the determination of copper, chromium and arsenic shall be as recommended in the i
26、nstrument users manual. Copper is determined in a fuel-lean air/acetylene flame at 324.8 nm, chromium in a fuel-rich air/acetylene flame or a fuel-lean nitrous oxide/acetylene flame at 357.9 nm or 429.0 nm, and arsenic in an argon/hydrogen or nitrous oxide/acetylene flame at 193.7 nm or 197.2 nm. 2.
27、4.2 Safety precautions It is essential that particular care be exercised when igniting the argon/hydrogen flame and that the instructions given in the instrument users manual be followed precisely. 2.4.3 Preparation of calibration solutions Transfer portions of 0.5, 1, 2, 3, 4, 5, 6 and 7 mL of the
28、standard solution (2.2.5) to a series of 100 mL one-mark volumetric flasks, dilute to the mark with the sulphuric acid/sodium sulphate solution (2.2.4) and mix. 1 mL portions of the solutions so constituted contain 2.5, 5, 10, 15, 20, 25, 30 and 35 Xg, respectively, of copper and 5, 10, 20, 30, 40,
29、50, 60 and 70Xg, respectively, of chromium and of arsenic. NOTEThe range of the set of calibration solutions is given as a guide; being a function of the instrumental sensitivity, it can be varied. If varied, it is for the analyst to adjust the concentration of the material to be analysed in the tes
30、t solution for presentation to the instrument in order to obtain optimum conditions, after checking that the possible interferences remain corrected and that others do not appear. 2.4.4 Analysis of preservatives Transfer by pipette a suitable quantity2) of preservative to a 250 mL conical flask, add
31、 40 mL of sulphuric acid solution (2.2.1) and, with caution, 8 mL of hydrogen peroxide solution (2.2.2). Boil the contents of the flask until evolution of oxygen ceases and all the hydrogen peroxide is decomposed, cool the flask to room temperature and transfer its contents to a 200 mL one-mark volu
32、metric flask. Add 20 mL of sodium sulphate solution (2.2.3), dilute to the mark with water and mix to give the test solution. Using the operating conditions suitable for the instrument, aspirate the sulphuric acid/sodium sulphate solution (2.2.4) to obtain the blank absorbance, followed by a suitabl
33、e range of calibration solutions and then the test solution(s). Check the calibration solutions after the last test solution has been run. NOTEIf a number of samples are to be analysed it may be advisable to check the instrument stability by bracketing each sample with appropriate standard solutions
34、. Plot calibration graphs of Xg/mL of copper, chromium, and arsenic against absorbance. Determine the contents of copper, chromium, and arsenic in the test solutions by comparing the absorbance readings with the calibration graphs. 2.4.5 Analysis of treated wood 2.4.5.1 Preparation of timber sample
35、for analysis Prepare the sample for analysis by converting the treated timber into a form suitable for extraction (i.e. shavings or sawdust) as described in clause 5 of BS 5666-1:1987. Divide the prepared sample into two unequal portions, (0.5 g and 5 g respectively). Determine the moisture content
36、on the 0.5 g portion according to the procedure described in clause 6 of BS 5666-1:1987. Reserve the 5 g sample for the analysis (2.4.5.2). 2.4.5.2 Extraction and preparation of test solution Weigh about 5 g of the prepared test sample (2.4.5.1) to the nearest 0.1 g into a 250 mL conical flask, add
37、50 mL of the sulphuric acid solution (2.2.1) and, with caution, 10 mL of the hydrogen peroxide solution (2.2.2). Heat at 75 pC in a water bath for 30 min with occasional swirling to mix the contents of the flask. Filter the solution through a filter paper3) into a second conical flask and thoroughly
38、 wash the solids on the filter paper with a maximum of 100 mL of water. Boil the filtrate and washings until evolution of oxygen ceases and all the hydrogen peroxide is decomposed. Cool to room temperature and transfer the solution to a 250 mL one-mark volumetric flask, add 25 mL of the sodium sulph
39、ate solution (2.2.3) and make up to the mark with water to give the test solution. 2.4.5.3 Measurement Using the operating conditions suitable for the instrument, aspirate the sulphuric acid/sodium sulphate solution (2.2.4) to obtain the blank absorbance, followed by a suitable range of calibration
40、solutions and then the test solution(s). Check the calibration solutions after the last test solution has been run (see note in 2.4.4). Plot calibration graphs of Xg/mL of copper, chromium and arsenic against absorbance. Determine the contents of copper, chromium and arsenic in the test solutions by
41、 comparing the absorbance readings with the calibration graphs. 2) For 30 g/L solutions of preservatives complying with BS 4072-1, transfer 2 mL of the solution. 3) A Whatman No. 44 filter paper has been found to be suitable. BS 5666-3:1991 BSI 07-19993 NOTEThis procedure is suitable for samples in
42、the mass range from 3 g to 8 g. For smaller samples use 100, 50 or 25 mL one-mark volumetric flasks, as appropriate, and correspondingly smaller volumes of reagents. 2.4.6 Calculations 2.4.6.1 The concentration of metals in a preservative The concentration, in g/100 mL, of copper or chromium or arse
43、nic is given by: where: To express the results in terms of copper sulphate (as CuSO4.5H2O), of potassium dichromate (as K2Cr2O7), of sodium dichromate dihydrate (as Na2Cr2O7.2H2O) and of arsenic pentoxide (as As2O5.2H2O), multiply the concentrations of the respective metals by the following factors:
44、 2.4.6.2 The percentages of metals in treated wood The percentage by mass of copper or chromium or arsenic in the dry wood is given by: where To express the results in terms of copper sulphate (as CuSO4.5H2O), of potassium dichromate (as K2Cr2O7), of sodium dichromate dihydrate (as Na2Cr2O7.2H2O) an
45、d of arsenic pentoxide (as As2O5.2H2O), multiply the concentration of the appropriate metal by the corresponding factor given in 2.4.6.1. 2.4.6.3 The dry salt retentions in treated wood The analysis result may also be expressed as kg/m3 if the density of the actual sample of timber is known; it is n
46、ot satisfactory to take an average density figure for the species of timber concerned. Adjustments for the moisture content (see Part 1 of this standard) of the timber are also necessary if the density figure does not apply to the dry material. The retention of the toxic ingredient of the oven-dry w
47、ood (expressed in kg/m3) is given by: where 3 Method 2. Colorimetric method 3.1 Principle Copper, chromium and arsenic compounds are leached quantitatively from the wood sample with a mixture of dilute sulphuric acid and hydrogen peroxide solution. Preservatives are treated with the same mixture. Co
48、pper and chromium, in portions of the resulting solution, are allowed to react with zinc dibenzyldithiocarbamate and diphenylcarbazide respectively4). The arsenic is converted to arsine, and reacted with silver diethyldithiocarbamate. The concentrations of the resulting coloured complexes are measur
49、ed spectrometrically. 3.2 Reagents Reagents shall be of recognized analytical reagent grade, and water complying with the requirements of grade 3 of BS 3978 shall be used throughout. WARNING NOTE. Sulphuric acid (L20 = 1.84 g/mL) and hydrogen peroxide solution (100 volumes) are corrosive and cause burns. Care should be taken to avoid their contact with eyes and skin. 3.2.1 Sulphuric acid solution, c(H2SO4) = 2.5 mol/L. Cautiously add, with stirring and cooling, 140 mL of sulphuric acid (L20 = 1.84 g/mL) to 800 mL of water. Cool and dilute to one litre with water. 3.2.2 Hydro