A61-11
AMERICAN WOOD PROTECTION ASSOCIATION STANDARD
© 2015 All Rights Reserved
STANDARD METHOD FOR THE DETERMINATION OF
COPPER IN COPPER CONTAINING PRESERVATIVES
Jurisdiction: AWPA Technical Committee P-5
Adopted in 2011, this standard was developed from AWPA Standard A2, Method 6.
This AWPA Standard is promulgated according to an open, consensus procedure. Using this standard in no way signifies standardization of a
chemical or wood protection system in AWPA Standard U1.
1.0 Scope:
1.1 This test method is employed to determine the amount of
copper, as cupric oxide (CuO), in copper-treated wood or
waterborne preservative solutions.
2.0 Summary:
2.1. Determination of the copper oxide content is done by
iodometric titration.
2.2 The sample in solid form, solution, or a solution aliquot
from wet ashed wood borings should contain about 0.02 g of
CuO.
2.3 This standard was formerly listed as AWPA Standard A2
Method 6.
3.0 Safety Precautions:
3.1 This method involves strong reducing and oxidizing
agents, and can become exothermic. The collection,
handling, and disposal of all materials should be done in
accordance with standard laboratory safety procedures. Not
all general safety concerns associated with this standard are
addressed here. It is therefore the responsibility of the user
to establish and follow appropriate good laboratory practices
and general safety precautions where applicable.
4.0 Apparatus:
4.1. Standard steam bath or flame heating apparatus such as
a Bunsen burner.
4.2 Suitable analytical balance.
5.0 Reagents:
5.1 Ammonium hydroxide, concentrated.
5.2 Hydrochloric acid, concentrated.
5.3 Sulfuric acid, concentrated.
5.4 Alcohol, methanol or ethanol.
5.5 Potassium iodide solution, 20 percent. Dissolve 20 g KI
in 80 ml of water.
5.6 Sodium thiocyanate solution, 20 percent. Dissolve 20 g
NaCNS in 80 ml. of water.
5.7 Starch indicator solution. Make a paste of 1 g soluble
starch in about 5 ml of water, add 100 ml water and boil for
1 minute with stirring. Cool and add 1 drop of chloroform.
This solution is subject to decomposition and fresh solution
should be prepared if a dark-blue color is not produced with
a drop of tincture of iodine in 100 ml water on addition of a
drop of indicator.
5.8 Acetic acid, glacial.
5.9 Copper foil or shot.
5.10 Nitric acid, concentrated.
5.11 Urea solution, 5 percent. Dissolve 5 g urea in 95 ml
water.
5.12 Sodium thiosulfate solution, 0.1 N. Dissolve 24.85 g
Na 2S 2O 3.5H 2O in water, add 1.0 g of Na 2CO3
preservative and dilute to 1 liter.
as a
5.13 Sodium thiosulfate solution, 0.05 N. Dilute exactly 25
ml of the standardized 0.1N sodium sulfate solution to
exactly 50 ml with freshly boiled distilled water, which has
been cooled to room temperature. The normality of this
solution, which should be made up immediately before use,
is exactly 0.5 times that of the 0.1 N solution as determined
by standardization procedure in paragraph 4.
5.14 Potassium chlorate-nitric acid mixture - dissolve 5
grams potassium chlorate in 100 ml concentrated nitric acid.
Make up this solution just before use and do not save any
surplus solution for reuse.
6.0 General Method Procedures:
6.1 Treated wood samples should be prepared according to
Standard A7, "Standard for Wet Ashing Procedures for
Preparing Wood for Chemical Analysis".
6.2 Carefully weigh the sample to obtain an estimated 0.03 g
of CuO.
6.3 Place the sample in a 300 ml Erlenmeyer flask and add
10 ml water. Add 10 ml concentrated hydrochloric acid and
a few glass beads. Add 15 ml alcohol carefully, warm to
boiling and heat until all chromium is reduced, as evidenced
by the absence of any yellowish-green color. The solution
should be clear bluish-green. (With ammoniacal copper zinc
arsenate a hood should be used for the boiling.) Important
Warning: If the sample being analyzed is a wood sample
digested with a perchloric acid mixture as in Standard A7, it
now contains perchloric acid and a strong reducing agent,
alcohol. If it is evaporated too much, it may explode with
dangerous violence. Keep the Erlenmeyer flask covered and
boil gently in the above step to minimize evaporation.
6.4 Wash down side of flask with water. Boil for 1 minute,
cool and neutralize cautiously with concentrated ammonium
hydroxide until a permanent precipitate just forms. With
samples containing small amounts of copper, a precipitate
may not form. In this case, adjust the pH to slightly basic
with concentrated ammonium hydroxide as measured with
pH indicating paper. Add concentrated sulfuric acid drop by
drop until the precipitate just dissolves or until the solution
becomes acidic. Boil down to a volume of 30 ml. Cool to
below 20°C. Dilute to 125 ml.
6.5 Add 10 ml 20 percent potassium iodide solution and 5
ml 20 percent sodium thiocyanate solution and mix
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A61-11
STANDARD METHOD FOR THE DETERMINATION OF
COPPER IN COPPER CONTAINING PRESERVATIVES
Page 2 of 2
© 2015
thoroughly by rotating the flask. Titrate from a 10 ml Class
A buret with 0.05N sodium thiosulfate solution, adding 2 ml
starch solution just before the brownish color of the iodine
disappears. Stop the titration when the color changes from
dark blue to light green. With ammoniacal copper zinc
arsenate, the end-point change is from dark blue to cream
color. (If poor end-points or checks are obtained, see Note
below.)
6.6 For standardization of the 0.1 N sodium thiosulfate
solution, dissolve in a 250 ml Erlenmeyer flask an accurately
weighed portion of pure copper foil or shot (about 0.25 g) in
10 ml of concentrated nitric acid. Evaporate the solution
until about 3-4 ml remains. Cool. Wash down sides of flask
with distilled water. Add 10 ml 5 percent urea solution and
boil 3 minutes. Cool the solution to room temperature and
add concentrated ammonium hydroxide cautiously until the
solution just turns to a deep blue color. The use of a
dropping bottle facilitates this step. Add 5 ml glacial acetic
acid, swirl, and wash down the sides of the flask with
distilled water. Dilute to 50 ml with distilled water and cool
to room temperature. Add 10 ml 20 percent potassium iodide
solution, do not swirl, and 5 ml of 20 percent sodium
thiocyanate solution. Titrate with sodium thiosulfate
solution. When about 20 ml of sodium thiosulfate have been
added, swirl the flask and continue the titration until the
solution color changes from dark brown to light tan. Add 5
ml of fresh starch indicator solution and continue the
titration until the solution color just changes from blue to
cream-white.
6.7 If inconsistent copper titrations are obtained, this may be
due to weathered wood sample for used treating solution
where the accumulation of organic materials may interfere
with the copper analysis. These may be destroyed as
follows; before proceeding with the analysis:
6.7.1 Place the sample in a 300 ml Erlenmeyer flask, add 10
ml of the potassium chlorate-nitric acid mixture, and boil to
dryness, with constant agitation. When dry, bake the residue
over an open flame for about 1 minute.
6.7.2 Cool, then add 20 ml water and 10 ml concentrated
hydrochloric acid. Boil to destroy excess chlorate and
dissolve salts.
6.7.3 Cool, and proceed as in "Analytical Procedure" starting
with the addition of 15 ml alcohol in paragraph 6.3.
7.0 Calculations:
7.1. Standardization of sodium thiosulfate:
Normality of sodium thiosulfate solution
Calculations of results:
g copper x 15.74
ml titration
(ml Na 2S 2O 3)(Normality Na 2S 2O 3)(Aliquot Factor)(7.96)
G of Sample
%CuO
CuO retention
(% CuO)(wood density)
100
Note: AWPA Standard A12 should be used for wood
density selection.
8.0 Report:
8.1 Report the sample code and the copper content on an
oxide basis, CuO.
9.0 Precision Statement:
9.1 The following statements and tables should be used to
judge the acceptability of analysis or duplicate samples
under the conditions stated below:
Repeatability. Duplicate single determination on the same
sample by the same operator using the same equipment
should not be suspect at the 95% confidence level if they do
not differ from one another by equal to or less than that
limiting percentages shown in the following table.
Reproducibility. Duplicate single determinations on the
same sample made by different operators in different
laboratories should not be considered suspect at the 95%
confidence level if they do not differ from one another by
equal to or less than the limited percentages shown in the
following table.
PRECISION TABLE FOR CuO BY ANALYSIS OF CCA IN SOLUTION
Expressed as
Oxide
CuO
Solution Oxide
Concentration Level (%)
0 to 0.45
0.46 to 1.05
1.06 to 1.60
Limiting Percentages
Repeatability
.008
.021
.014
Limiting Percentages
Reproducibility
.380
.085
.236
Element
Copper
Copper
Copper
The above precision statements are based on round robin data by six laboratories, each running three replicate determinations
on each of three samples covering the concentration range 1.40% to 8.12% CCA in solution. The samples included both
CCA-B and CCA-C.
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A62-11
AMERICAN WOOD PROTECTION ASSOCIATION STANDARD
© 2015 All Rights Reserved
STANDARD METHOD TO DETERMINE THE PH OF WATERBORNE TREATING SOLUTIONS
Jurisdiction: AWPA Technical Committee P-5
Adopted in 2011, this standard was developed from AWPA Standard A2, Method 8.
This AWPA Standard is promulgated according to an