BS 5666-3-1991 Methods of analysis of wood preservatives and treated timber - Quantitative analysis of preservatives and treated timber containing copper chromium arsenic formulati.pdf

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”.BS5666-3:1991 This British Standard, having been prepared under the directionof the Wood PreservationStandards Policy Committee, was published underthe authority of the Board ofBSI and comes into effect on 28 February1991 BSI 07-199

3、9 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 comment89/50550 DC ISBN 0 580 18580 X Committees responsible for this British Standard The preparation of this British Standard was entr

4、usted 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 the Envi

5、ronment (Building Research Establishment) Ministry of Defence Amendments issued since publication Amd. No. Date CommentsBS5666-3:1991 BSI 07-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Method 1. Atomic absorption spectrometric method 1 3 Method 2. Colorimet

6、ric method 3 4 Test report 7 Figure 1 Apparatus for arsenic determination 8 Publication(s) referred to Inside back coverBS5666-3:1991 ii BSI 07-1999 Foreword This Part of BS5666 has been prepared under the direction of the Wood Preservation Standards Policy Committee. This Part of BS5666 was first p

7、ublished in1979. 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 This edition supersedes BS5666-3:1979 which is withdrawn. CAUTION. Attention is drawn to the Health and Safety at Work et

8、c. Act1974, 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 pre

9、cautions should be observed throughout the use of the methods. Attention is drawn to the general safety precautions mentioned in clause3 of BS5666-1:1987. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their c

10、orrect 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, pagesi andii, pages1 to8, an inside back cover and a back cover. This standard has been updated (see copyri

11、ght date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS5666-3:1991 BSI 07-1999 1 1 Scope This Part of BS5666 details procedures for the determination of copper, chromium and arsenic in preservatives and in treated timber containi

12、ng 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 specific for arse

13、nic 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 BS4072; for samples of other compositions it may be necessary to make adjustments. It is difficult to make recommendations as

14、 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 to8g in mass, but it may be necessary to a

15、djust 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 the inside back

16、 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 resulting solut

17、ions, after addition of sodium sulphate solution, are analysed using atomic absorption spectrometry 1) . 2.2 Reagents Reagents shall be of recognized analytical reagent grade, and water complying with the requirements of grade3 of BS3978 shall be used throughout. WARNING NOTE. Sulphuric acid ( 20= 1

18、.84g/mL) and hydrogen peroxide solution (100volumes) are corrosive and cause burns. Care should be taken to avoid their contact with eyes and skin. 2.2.1 Sulphuric acid solution, c(H 2 SO 4 ) = 2.5mol/L. Cautiously add, with stirring and cooling,280mL of sulphuric acid ( 20= 1.84g/mL) to1600 mL of w

19、ater. Cool and dilute to2 litres with water. 2.2.2 Hydrogen peroxide solution, c(H 2 O 2 ),300g/L (100volumes). 2.2.3 Sodium sulphate solution, c(Na 2SO 4 ) = 30g/L. Dissolve30g of anhydrous sodium sulphate in water and dilute to1 litre with water. 2.2.4 Sulphuric acid solution, c(H 2 SO 4 ) = 0.5mo

20、l/L/sodium sulphate 3 g/L solution. Dilute200mL of sulphuric acid solution(2.2.1) plus100mL of30g/L sodium sulphate solution (2.2.3) to 1 litre with water and mix. 2.2.5 Standard solution (1 mL 500g of copper,1000g of chromium and1000g of arsenic). Dissolve0.9825g of copper sulphate pentahydrate (Cu

21、SO 4 .5H 2 O) in a little water and transfer the solution to a500mL one-mark volumetric flask. Dissolve1.4135g of potassium dichromate (K 2 Cr 2 O 7 ) in a little water, add50mL of sulphuric acid solution (2.2.1) and10mL of hydrogen peroxide solution (2.2.2), boil until evolution of oxygen ceases an

22、d all the hydrogen peroxide is decomposed, cool and transfer the mixture to the one-mark volumetric flask containing the copper sulphate solution. Dissolve0.6600g of arsenic trioxide (As 2 O 3 ) by boiling it in a solution containing50mL of sulphuric acid solution (2.2.2) and75mL of water. Continue

23、boiling until evolution of oxygen ceases and all the hydrogen peroxide is decomposed, cool and transfer it to the one-mark volumetric flask. Add50mL of sodium sulphate solution (2.2.3) to the volumetric flask, dilute to the mark with water and mix. 2.3 Apparatus 2.3.1 Volumetric glassware, complying

24、 with the requirements for class A quality in accordance with BS700-2 (type 2), BS846, BS1583 or BS1792, as appropriate. 2.3.2 Atomic absorption spectrometer, together with suitable sources of resonance radiation for copper, chromium and arsenic, e.g. hollow-cathode lamps. 1) For reference, see Will

25、iams, A.I., Analyst,1970,95,670.BS5666-3:1991 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 instrument users manual. Copper is determined in a

26、fuel-lean air/acetylene flame at324.8nm, chromium in a fuel-rich air/acetylene flame or a fuel-lean nitrous oxide/acetylene flame at357.9nm or429.0nm, and arsenic in an argon/hydrogen or nitrous oxide/acetylene flame at193.7nm or197.2nm. 2.4.2 Safety precautions It is essential that particular care

27、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 of0.5,1,2,3,4,5,6 and7mL of the standard solution (2.2.5) to a series of100mL one-mark volumetric fla

28、sks, dilute to the mark with the sulphuric acid/sodium sulphate solution (2.2.4) and mix. 1mL portions of the solutions so constituted contain2.5,5,10,15,20,25,30 and35 g, respectively, of copper and5,10,20,30,40,50,60 and70g, respectively, of chromium and of arsenic. NOTEThe range of the set of cal

29、ibration 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 test solution for presentation to the instrument in order to obtain optimum conditions, after

30、 checking that the possible interferences remain corrected and that others do not appear. 2.4.4 Analysis of preservatives Transfer by pipette a suitable quantity 2)of preservative to a250mL conical flask, add40mL of sulphuric acid solution (2.2.1) and, with caution,8mL of hydrogen peroxide solution

31、(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 a200mL one-mark volumetric flask. Add20mL of sodium sulphate solution (2.2.3), dilute to the mark with water and mix t

32、o 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 suitable range of calibration solutions and then the test solution(s). Check the calibration solutions afte

33、r 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. Plot calibration graphs of g/mL of copper, chromium, and arsenic against absorbance. Determine the

34、 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 for analysis Prepare the sample for analysis by converting the treated timber into a form suitable fo

35、r extraction (i.e. shavings or sawdust) as described in clause 5 of BS5666-1:1987. Divide the prepared sample into two unequal portions, (0.5g and5g respectively). Determine the moisture content on the0.5g portion according to the procedure described in clause 6 of BS5666-1:1987. Reserve the5g sampl

36、e for the analysis (2.4.5.2). 2.4.5.2 Extraction and preparation of test solution Weigh about5g of the prepared test sample(2.4.5.1) to the nearest0.1g into a250mL conical flask, add50mL of the sulphuric acid solution (2.2.1) and, with caution,10mL of the hydrogen peroxide solution (2.2.2). Heat at7

37、5 C in a water bath for30min with occasional swirling to mix the contents of the flask. Filter the solution through a filter paper 3)into a second conical flask and thoroughly wash the solids on the filter paper with a maximum of100mL of water. Boil the filtrate and washings until evolution of oxyge

38、n ceases and all the hydrogen peroxide is decomposed. Cool to room temperature and transfer the solution to a250mL one-mark volumetric flask, add25mL of the sodium sulphate 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 conditio

39、ns 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 solutions and then the test solution(s). Check the calibration solutions after the last test solution has been run (see note in2.4.

40、4). Plot calibration graphs of g/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) For30g/L solutions of preservatives complying with BS4072-1, trans

41、fer2mL of the solution. 3) A Whatman No.44 filter paper has been found to be suitable.BS5666-3:1991 BSI 07-1999 3 NOTEThis procedure is suitable for samples in the mass range from3g to8g. For smaller samples use100,50 or25mL one-mark volumetric flasks, as appropriate, and correspondingly smaller vol

42、umes of reagents. 2.4.6 Calculations 2.4.6.1 The concentration of metals in a preservative The concentration, ing/100 mL, of copper or chromium or arsenic is given by: where: To express the results in terms of copper sulphate (as CuSO 4 .5H 2 O), of potassium dichromate (asK 2 Cr 2 O 7 ), of sodium

43、dichromate dihydrate (asNa 2 Cr 2 O 7 .2H 2 O) and of arsenic pentoxide (asAs 2 O 5 .2H 2 O), multiply the concentrations of the respective metals by the following factors: 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 gi

44、ven by: where To express the results in terms of copper sulphate (as CuSO 4 .5H 2 O), of potassium dichromate (asK 2 Cr 2 O 7 ), of sodium dichromate dihydrate (asNa 2 Cr 2 O 7 .2H 2 O) and of arsenic pentoxide (asAs 2 O 5 .2H 2 O), multiply the concentration of the appropriate metal by the correspo

45、nding factor given in2.4.6.1. 2.4.6.3 The dry salt retentions in treated wood The analysis result may also be expressed as kg/m 3if the density of the actual sample of timber is known; it is not satisfactory to take an average density figure for the species of timber concerned. Adjustments for the m

46、oisture content (see Part1 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 wood (expressed inkg/m 3 ) is given by: where 3 Method 2. Colorimetric method 3.1 Principle Copper, chromium a

47、nd 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. Copper and chromium, in portions of the resulting solution, are allowed to react with zinc dibenzyldithiocarba

48、mate and diphenylcarbazide respectively 4) . The arsenic is converted to arsine, and reacted with silver diethyldithiocarbamate. The concentrations of the resulting coloured complexes are measured spectrometrically. 3.2 Reagents Reagents shall be of recognized analytical reagent grade, and water com

49、plying with the requirements of grade3 of BS3978 shall be used throughout. WARNING NOTE. Sulphuric acid ( 20= 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(H 2 SO 4 ) = 2.5mol/L. Cautiously add, with stirring and cooling,140mL of sulphuric acid ( 20= 1.84g/mL) to800mL of water. Cool and dilute to one litre with water. 3.2.2 Hydrogen peroxide solution, c(H 2 O 2 ),300g/L (100 volumes). 3.2.3 Sulphuric acid solution, c(H 2 SO 4