A65-15
AMERICAN WOOD PROTECTION ASSOCIATION STANDARD
© 2015 All Rights Reserved
STANDARD METHOD TO DETERMINE THE AMOUNT OF BORON IN
TREATED WOOD USING AZOMETHINE-H OR CARMINIC ACID
Jurisdiction: AWPA Technical Committee P-5
Adopted in 2011, this standard was developed from AWPA Standard A2, Method 16. It was revised in 2015.
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 boron trioxide in borate-treated wood.
1.2. The method employing Azomethine-H is adapted from
M. John, H. Chuaha and J. Newfield, Analytical Letters
8(8):559-568, 1975. The method employing Carminic Acid
is adapted from J. Harcher and L. Wilcox, Analytical
Chemistry 22(4):567-569, 1950.
2.0 Summary:
2.1. The amount of boron trioxide in treated wood is
determined by reacting the boron with one of two reagents
then measuring the UV absorbance.
2.2. This standard replaces AWPA Standard A2.16.
3.0 Safety Precautions:
3.1 The collection, storage, handling, and disposal of
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. Suitable analytical balance.
4.2. Titration glassware, for Azomethine-H method.
4.3. Hot plate.
4.4. Magnetic stirring plate.
4.5 Spectrophotometer, for Carminic acid procedure,
suitable for absorbance measurements at 585 nm.
4.6. Drying oven.
4.7. Grinding mill, suitable to grind small amounts of wood
to 30 mesh.
5.0 Reagents:
5.1. Standard Boron Solutions. A stock solution, containing
100 ppm boron, is prepared by dissolving 0.5715 g of
reagent grade boric acid in one liter of water. Standards
containing 1 to 10 ppm boron are prepared by diluting stock
solution with water. (Note: boric acid contains 17.48%
boron).
5.2. Azomethine-H Analysis
5.2.1. Buffer Solution. Dissolve 250 g ammonium acetate in
400 ml of distilled water. Add 15 g of disodium EDTA,and
125 ml (131 g) of glacial acetic acid.
5.2.2. Azomethine-H Reagent: The reagent is 0.45%
azomethine-H, monosodium salt hydrate dissolved in 1%
ascorbic acid. It can be prepared by adding 1.0 g of ascorbic
acid and 0.45 g of azomethine-H to 100 ml volumetric flask
and bringing to volume with deionized water. Fresh reagent
should be prepared weekly and stored in the refrigerator.
Because azomethine-H reagent degrades over time,
calibration standards should be analyzed every day.
5.3. Carminic Acid Analysis
5.3.l. Concentrated sulfuric acid, analytical reagent grade,
96% or greater concentration.
5.3.2. Carminic Acid Solution: Add 0.250g of carminic
acid, about 950 ml of concentrated sulfuric acid (caution:
corrosive) and a magnetic stirring bar to a one liter
volumetric flask. Stopper flasks and stir magnetically for 3
to 4 hours. Remove the magnet with the magnet thief, add
concentrated sulfuric acid to the mark and mix well. The
solution should be stored preferably in a boron free glass
stoppered bottle. However, if none is available, a clean
commercial 9 lb. concentrated sulfuric acid bottle is
adequate. Fresh carminic acid solutions should be stored in
the same bottle. The bottle should be tightly closed when not
in use.
6.0 General Method Procedures:
6.1. Sample.
6.1.1. The sample should be obtained in such a manner as to
ensure it uniformly represents a sub-part of the entire
material to be tested.
6.1.2. Dry wood, at 105°C to constant weight.
6.1.3. Grind wood sample to a fine powder, 30 mesh (U.S.
Standard).
6.1.4. Weigh 1 to 2 g of sample, to nearest 0.01 g, into 250
ml Erlenmeyer flask.
6.1.5. Add 75 to 100 ml of distilled water to the flask
containing the wood sample.
6.1.6. Bring the contents of the flask to a gentle boil and
continue heating for 30 minutes.
6.1.7. Allow the contents to cool and filter through Whatman
#4 filter paper. Rinse the flask 3 times with 10 ml of distilled
water, pouring the washings through the filter paper. Dilute
to 250 ml in volumetric flask.
6.2. Azomethine-H Analysis Procedure
6.2.1. 1.0 ml of each of the standard and unknown solutions
is pipetted into 1 cm cuvettes. A cuvette with 1.0 ml of
distilled water is also prepared as a reagent blank.
6.2.2. 1.0 ml of the buffer solution is added to each cuvette
and the solutions mixed.
6.2.3. 1.0 ml of azomethine-H reagent is added and the
solutions mixed again. The absorbance at 420 nm is
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A65-15
STANDARD METHOD TO DETERMINE THE AMOUNT OF BORON IN
TREATED WOOD USING AZOMETHINE-H OR CARMINIC ACID
Page 2 of 2
© 2015
measured 30 to 40 minutes after the addition of the
azomethine-H. The reagent blank is used to zero the
instrument.
6.2.3. Prepare a standard curve by plotting the absorbance on
the y-axis and the ppm boron of the standard solutions on the
x-axis.
6.2.4. The ppm boron of the unknown(s) can be determined
from the graph by reading the concentration on the x-axis.
6.3. Carminic Acid Analysis Procedure
6.3.1. 1.0 ml of each standard and unknown solution, as well
as 1.0 ml of a water blank (0 ppm boron), is pipetted into
separate 30 ml glass bottles equipped with Found glass
stoppers. (A set of standards should be run each time the
unknown solutions are analyzed.)
6.3.2. From a burette or pipette, add 5.00 ml concentrated
sulfuric acid to each bottle at a fast drop rate. Because of the
viscosity of the sulfuric acid, it may be necessary to cut tips
to allow a fast drop delivery.
6.3.3. Stopper the bottles, cool and swirl gently to mix.
6.3.4. From a separate burette, add 5.00 ml of carminic acid
solution to each bottle at a fast drop rate.
6.3.5. Again, stopper the bottles, cool and swirl gently to
mix.
6.3.6. Allow solutions to stand for 1-1/2 hours to insure full
color development.
6.3.7. Transfer to cuvette and measure the absorbance at 585
nm.
6.3.8. Prepare a standard curve by plotting the absorbance on
the y-axis and the ppm boron of the standard solutions on the
x-axis.
6.3.9. The ppm boron of the unknown(s) can be determined
from the graph by reading the concentration on the x-axis.
6.4. Blank wood sample.
6.4.1. A blank wood sample should be analyzed with each
batch of boron treated wood. The % B 2O value determined
should be subtracted from the value of the unknown.
7.0 Calculations:
3
% B 2O 3
(ppm boron) (0.0805)
grams of sample
For the Carminic Acid procedure, if the absorbance of the
unknown is greater than the absorbance for the 10 ppm
standard, take 1 ml of the unknown solution and dilute to 5
ml using a volumetric flask and repeat the procedure. The %
B 2O 3 obtained must then be multiplied by 5 to obtain the
correct answer.
To convert % B 2O 3 to pounds B 2O 3/cubic foot of wood:
ܤ ܱ , ݂ܿ =
ଶ ଷ
ሺ% ܤ ܱ ሻሺݓ݀ ݀݁݊ݏ݅ݐݕ ݅݊ ݂ܿሻ
ଶ ଷ
100
Note: AWPA Standard A12 should be used for wood density
selection.
8.0 Report:
8.1 Report the pounds of B 2O 3 per cubic foot of treated
wood (pcf), and the method employed (Azomethine-H or
Carminic Acid).
9.0 Precision Statement:
9.1. The following statements and table should be used to
judge the acceptability of an analysis using this method. The
precision data were developed following the guidelines in
ASDTM Method E691.
Precision Table for Azomethine-H H 2O Extraction
Expressed as
Oxide
B 2O3
B 2O3
B 2O3
B 2O3
B 2O3
B 2O3
Concentration
Level (wt %)
0.00 - 0.61
0.62 - 0.81
0.82 - 1.00
1.01 - 1.26
1.27 - 1.64
1.65 - 2.19
Limiting Percentages
Repeatability
0.097
0.129
0.148
0.174
0.151
0.090
Element
Boron
Boron
Boron
Boron
Boron
Boron
Limiting Percentages
Reproducibility
0.106
0.129
0.190
0.290
0.258
0.281
The above precision statements are based on round robin data by six laboratories, each running three replicate determinations
on each of six samples covering the concentration range 0.00% to 2.19% B 2O 3 in wood.
Precision Table for Carminic Acid H 2O Extraction
Element
Boron
Boron
Boron
Boron
Boron
Boron
Expressed as
Oxide
B 2O3
B 2O3
B 2O 3
B 2O3
B 2O3
B 2O3
Concentration
Level (wt %)
0.00 - 0.61
0.62 - 0.84
0.85 - 1.06
1.07 - 1.32
1.33 - 1.71
1.72 - 2.19
Limiting Percentages
Repeatability
0.058
0.061
0.122
0.316
0.460
0.093
Limiting Percentages
Reproducibility
0.126
0.219
0.135
0.316
0.460
0.248
The above precision statements are based on round robin data by three laboratories, each running three replicate determinations
on each of six samples covering the concentration range 0.00% to 2.19% B 2O 3 in wood.
- 293 -
A66-11
AMERICAN WOOD PROTECTION ASSOCIATION STANDARD
© 2015 All Rights Reserved
STANDARD METHOD FOR DETERMINATION OF CHROMIUM
IN CHROMIUM CONTAINING PRESERVATIVES
Jurisdiction: AWPA Technical Committee P-5
Adopted in 2011, this standard was developed from AWPA Standard A2, Method 5.
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
chro