BS 5666-7-1991 Methods of analysis of wood preservatives and treated timber - Quantitative analysis of preservatives containing bis(tri-n-butyltin)oxide determination of total tin.pdf

1、BRITISH STANDARD BS 5666-7: 1991 Methods of analysis of Wood preservatives and treated timber Part 7: Quantitative analysis of preservatives containing bis(tri-n-butyltin)oxide: determination of total tin NOTEIt is essential that this Part is read in conjunction with Part 1 “Guide to sampling and pr

2、eparation of wood preservatives and treated timber”.BS5666-7:1991 This British Standard, having been prepared under the directionof the Wood PreservationStandards Policy Committee, was published under the authority of the BoardofBSI and comes into effecton 31January1991 BSI 11-1999 First published J

3、anuary 1980 Second edition January 1991 The following BSI references relate to the work on this standard: Committee reference WPC/11 Draft for comment 89/50549 DC ISBN 0 580 18591 5 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Wood Pr

4、eservation 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 Environment (Building Re

5、search Establishment) Ministry of Defence Amendments issued since publication Amd. No. Date CommentsBS5666-7:1991 BSI 11-1999 i Contents Page Committees responsible Inside front cover Foreword ii 0 Introduction 1 1 Scope 1 2 Method 1. Atomic absorption spectrometric method 1 3 Method 2. Colorimetric

6、 method 4 4 Test report 6 Publication(s) referred to Inside back coverBS5666-7:1991 ii BSI 11-1999 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 published in1980. This edition introduces technic

7、al changes but it does not reflect a full review or revision of this Part of the standard, which will be undertaken in due course. BS5666-7:1980 is withdrawn. CAUTION. Attention is drawn to the Health and Safety at Work etc. Act 1974, and the need for ensuring that the methods of test specified in t

8、his standard are carried out with suitable precautions. The procedures described in this standard method are intended to be carried out by qualified chemists or other suitably trained and/or supervised personnel. Normal safety precautions should be observed throughout the use of the methods. Attenti

9、on 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 correct application. Compliance with a British Standard does not of its

10、elf confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indic

11、ated in the amendment table on the inside front cover.BS5666-7:1991 BSI 11-1999 1 0 Introduction Wood preservative solutions containing bis(tri-n-butyltin)oxide are usually formulated with technical grade material containing at least95% bis(tri-n-butyltin)oxide, e.g. material complying with the requ

12、irements of BS4630. It is known that this compound can be degraded to give dibutyltin and monobutyltin compounds that will result in a decrease in fungistatic activity. It may, therefore, be necessary to determine the organotins present, but in many cases the determination of the total tin content g

13、ives adequate information. A further Part of this standard will be published dealing with the determination of the different organotins. 1 Scope This Part of this British Standard details procedures for the determination of the total tin content present in solutions and in treated wood containing bi

14、s(tri-n-butyltin)oxide. The methods have been found suitable for the determination of tin in the presence of the following: copper naphthenate; dieldrin (HEOD); -hexachlorocyclohexane ( -HCH, lindane); pentachlorophenyl laurate; pentachlorophenol and other chlorophenols; 2-phenylphenol; zinc naphthe

15、nate; water-repellent waxes and resins. It is assumed that all the tin determined by thesemethods has been derived from bis(tri-n-butyltin)oxide and hence the tin contents are expressed in terms of bis(tri-n-butyltin)oxide. With aged samples of treated wood, it is occasionally difficult to acid extr

16、act all the tin, particularly if iron or some other cations are present. The method described in2.4.4 has been shown to ensure that, in all cases, the proportion of tin not extracted is unlikely to affect the validity of the determination. The wet ashing technique used in the colorimetric method (se

17、e clause3) ensures that tin in all types of samples is brought into solution. The recommendations made as to the size of sample to be taken for the analysis of preservative solutions assume that the bis(tri-n-butyltin)oxide content is about1% by mass. For samples of other compositions, adjustments m

18、ay have to be made in the quantity taken for analysis. It is difficult to make recommendations as to the mass of the wood sample to be analysed since the predominant factor is the quantity of preservative within the wood rather than the mass of the wood itself. It may be necessary to make some adjus

19、tment to the values quoted in the standard, either to the mass of the treated wood sample taken for analysis or to the level of dilution of the tin solution resulting from extraction. Furthermore, it should be noted that the range of concentrations suggested for the calibration solutions used in the

20、se methods may have to be adjusted to suit the sensitivity of the instruments being used. 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 cover. 2 M

21、ethod 1. Atomic absorption spectrometric method 2.1 Principle The tin contents of suitably diluted preservative solutions or wood samples quantitatively extracted with hydrochloric acid in ethanol are analysed using atomic absorption spectrometry. In this method, any variation in response due to the

22、 presence of other butyltin compounds is considered to be within the limits of experimental error of the procedure 1)2) . It has been found with some atomic absorption spectrometers that the presence of easily ionized metals in the solution, e.g. the alkali metals, enhance the tin absorbance signal.

23、 Of these metals, lithium was found to have the greatest effect, and hence lithium is added to all test and calibration solutions. The presence of lithium also minimizes differences in the responses of other organotins. 1) The responses of monobutyltin and dibutyltin compounds differ slightly from t

24、hat of tributyltin compounds. With equivalent tin contents, dibutyltin compounds give an absorbance signal of3% to5% more than tributylin compounds. As the dibutyltin contents of fresh solutions or recently treated wood are low, this difference is unlikely to be significant. 2) For reference, see “T

25、he determination of bis(tri-n-butyltin)oxide and di-n-butyltin oxide in preserved softwood by atomic absorption spectrometry and polarography” Williams, A.I., Analyst, 1973, 98, 233.BS5666-7:1991 2 BSI 11-1999 2.2 Reagents Reagents shall be of recognized analytical reagent grade. Ethanol (C 2 H 5 OH

26、), 99% (V/V) complying with BS507 or99% (V/V) industrial methylated spirits complying with BS3591 shall be used to make up the reagents where ethanol is specified. NOTEThe use of industrial methylated spirits is governed by the Methylated Spirits Regulations 1987 (SI 1987, No.2009). It is not permis

27、sible to use duty-free ethanol received under the provisions of the Alcoholic Liquor Duties Act1979, Section10, for purposes for which industrial methylated spirit is an acceptable alternative to ethanol. 2.2.1 Hydrochloric acid solution A, c (HCl) about21g/L. Quantitatively transfer25.0mL ofconcent

28、rated hydrochloric acid solution ( 20 =1.18g/mL) into a500mL one-mark volumetric flask and make up to the mark with ethanol. 2.2.2 Hydrochloric acid solution B, c (HCl) about2.1g/L. Quantitatively transfer100.0mL of the hydrochloric acid solution A (2.2.1) into a1000mL one-mark volumetric flask and

29、make up to the mark with ethanol. 2.2.3 Lithium chloride solution (1mL = 5000g oflithium). Dissolve15.30g of anhydrous lithium chloride (LiCl) in350mL of ethanol. Transfer quantitatively to a500mL one-mark volumetric flask, add50.0mL of the hydrochloric acid solutionA (2.2.1) and make up to the mark

30、 with ethanol. 2.2.4 Standard bis(tri-n-butyltin)oxide solution.(1mL =200g of bis(tri-n-butyltin)oxide) (C 4 H 9 ) 3 Sn 2 O. Dissolve 0.1000g of pure bis(tri-n-butyltin)oxide 3)in100mL of ethanol. Transfer quantitatively to a500mL one-mark volumetric flask, add50.0mL of the hydrochloric acid solutio

31、n A (2.2.1) and make up to the mark with ethanol. CAUTION. Bis(tri-n-butyltin)oxide is toxic; it is essential that care is taken in handling it. 2.3 Apparatus 2.3.1 Volumetric glassware, complying with the requirements for class A quality in accordance with BS700-2 (type2), BS846, BS1583 or BS1792,

32、as appropriate. 2.3.2 Atomic absorption spectrometer, together with a suitable source of the resonance radiation for tin, e.g. a hollow-cathode lamp. 2.4 Procedure 2.4.1 Instrument settings and operation The instrument settings and operating conditions for the determination of tin shall be as recomm

33、ended by the manufacturer of the spectrometer. NOTE 1The solvent, ethanol, will contribute to the fuel in the flame and hence the acetylene flow given for aqueous solutions should be reduced. In order to minimize interference effects from neighbouring resonance lines of copper and zinc, the band pas

34、s accepted by the monochromator should be as small as possible, bearing in mind that the additional amplification required for low light levels could result in an unacceptable noise level. NOTE 2The tin absorbance signal is enhanced by the presence of easily ionized metals (e.g. the alkali metals) i

35、n the solution. Of these metals, lithium has been found to have the greatest effect and hence lithium chloride is added to all test and calibration solutions. The addition of lithium chloride however will necessitate frequent cleaning of the burner head either by scraping or by flushing through with

36、 water and ethanol. The preferred fuel and oxidant are acetylene and nitrous oxide respectively, because interference effects are minimized and the sensitivity is improved. CAUTION. It is essential that the flow rates of the gases exceed the flame velocity, otherwise a flashback will occur with cons

37、equent explosion. It is essential that the operator follow the instructions given for the instrument. 2.4.2 Preparation of calibration solutions Into a series of100mL one-mark volumetric flasks transfer0, 1.0, 2.0, 3.0, 5.0, 10.0, 15.0, 20.0, 25.0 and50.0mL of the bis(tri-n-butyltin)oxide standardso

38、lution (2.2.4), add20.0mL of the lithium chloride solution (2.2.3) and dilute to the mark with the hydrochloric acid solution B (2.2.2). This will provide solutions containing 0, 2, 4, 6, 10, 20, 30, 40, 50 and 100g/mL respectively of bis(tri-n-butyltin)oxide. 2.4.3 Analysis of preservative solution

39、s Weigh out accurately 0.4000 g 4)of the preservative into a tared100mL one-mark volumetric flask. Add20.0mL of the lithium chloride solution (2.2.3) and dilute to the mark with the hydrochloric acid solution B (2.2.2). 3) Bis(tri-n-butyltin)oxide readily absorbs carbon dioxide from the atmosphere;

40、precautions should be taken to prevent this during storage. 4) See clause 1.BS5666-7:1991 BSI 11-1999 3 Using the operating conditions suitable for the instrument being used, aspirate successively the hydrochloric acid solution B (2.2.2) to obtain the blank absorbance and a suitable range of calibra

41、tion solutions, aspirating the hydrochloric acid solutionB (2.2.2) between each calibration solution. Then aspirate the test solution(s) and check the calibration solutions after the last solution has been run. NOTEIf a number of samples are to be analysed, it may be advisable to check the instrumen

42、t stability by bracketing each test solution with appropriate standard solutions. Plot a calibration graph of the concentration of bis(tri-n-butyltin)oxide in g/mL against absorbance. Determine the bis(tri-n-butyltin)oxide content of the sample solution by comparing the absorbance reading with the c

43、alibration graph andexpress the result in g/mL of bis(tri-n-butyltin)oxide in the test solution. 2.4.4 Analysis of treated wood 2.4.4.1 Preparation of timber sample for analysis Prepare the sample for analysis by converting the treated timber into a form suitable for extraction (i.e. shavings or saw

44、dust) as described in clause5 of BS5666-1:1987. Divide the prepared sample into two portions each of about0.5g. Determine the moisture content on one portion according to the procedure described in clause6 of BS5666-1:1987. Reserve the other portion for analysis (2.4.4.2). 2.4.4.2 Extraction and pre

45、paration of test solution Weigh about 0.5g of the prepared test sample(2.4.4.1) to the nearest0.01g into a suitableflask. Add25.0mL of the hydrochloric acid solution B (2.2.2) and fit a reflux condenser to the flask. Reflux for10min and allow to cool. Filter the flask contents through a filter paper

46、 5)into a50mL one-mark volumetric flask, wash the contents of the flask into the paper with the hydrochloric acid solution B (2.2.2), wash the paper and contents with this acid and dilute to the mark with these washings. Transfer2.00mL of the lithium chloride solution (2.2.3) into a10mL one-mark vol

47、umetric flask, make up to the mark with the extract solution and mix. 2.4.4.3 Measurement Using the operating conditions recommended for the instrument being used, aspirate successively the hydrochloric acid solution B (2.2.2) to obtain the blank absorbance and a suitable range of calibration soluti

48、ons, aspirating the hydrochloric acid solutionB (2.2.2) between each calibration solution. Then aspirate the test solution(s) and check the calibration solutions after the last solution has been run. NOTEIf a number of samples are to be analysed, it may be advisable to check the instrument stability

49、 by bracketing each test solution with appropriate standard solutions. 2.4.5 Calculations 2.4.5.1 The percentage of bis(tri-n-butyltin)oxide in solution The percentage by mass of bis(tri-n-butyltin)oxide in the solution under test is given by: where 2.4.5.2 The percentage of bis(tri-n-butyltin)oxide in treated wood The percentage by mass of bis(tri-n-butyltin)oxide in the dry wood is given by: where 5) A Whatman No. 42 filter paper has been found to be suitable. C is the concentration of bis(tri-n-butyltin)oxide, in the test solution (in g/mL); m 1 is the mass, of th