Development of a Chemical
Stain for Identifying
Arsenic-Treated Wood
Amy Omae
August 18, 2005
Medley, FL
Background
Identification methods for arsenic-treated wood
Visual
method INACCURATE
Augmentation methods
XRF, LIBS, AA analysis EXPENSIVE
Arsenic test kits
Arsine gas HAZARDOUS
Wipe DAYS OR WEEKS
Copper specific stains (PAN indicator)
Alternative treated wood (ACQ, CBA, CC, CDDC)
IDENTIFIES COPPER NOT ARSENIC
Background
Similarity of phosphate and arsenate
Phosphate Arsenate
Colorimetric identification methods
Ascorbic acid
Unable to prevent phosphate interference
Vanadomolybdophosphoric acid
Unable to achieve a noticeable color
Stannous chloride…
Stannous Chloride Stain
Standard Methods, 1995
Intended for the detection of phosphate, PO43-
Colorimetric reaction BLUE
PO43- +12(NH4)2MoO4 +24H+ (NH4)3PO4•12MoO3 +21NH4+ +12H2O
(NH4)3PO4•12MoO3 + Sn2+ (molybdenum blue) + Sn4+
Interference: Arsenate, AsO43-
Phosphate Arsenate
Stannous Chloride Stain
Modifications
Reducing sensitivity to phosphate
1) Ammonium Molybdate
2) Stannous Chloride
Stannous Chloride Stain
Modifications
Reducing sensitivity to phosphate
1) Ammonium Molybdate
Combined Reagent
2) Stannous Chloride
Stannous Chloride Stain
Reagents Separated Reagents Combined
Phosphate
Arsenate
Dissolution Method
20-mL sample vial
10 mL distilled water
9 drops combined reagent
8 parts ammonium molybdate
1 part stannous chloride
0.5 g sample (shredded wood or sawdust)
Reaction time: 30-45 minutes
Maximum intensity: ~5 hours
Dissolution Method
(4.0 kg/m3)
Untreated CC CDDC CBA ACQ Borate CCA
ACZA-treated wood
Ammoniacal Copper Zinc Arsenate
Western U.S.
Maximum intensity: ~2 hours
Dissolution Method
4.0 kg/m3 CCA
1h 8m 0s 53m 30s 39m 15s
2h 30m 0s 31m 40s 22m 30s
5h 30m 0s
15m 0s
0m 0s
Medium Blue
(0.221–0.399)
Untreated
λ = 690 nm
Dissolution Method
Field test
Recycled wood
Result
Determined
Reaction Time of
Sample PAN Indicator Elements Detected by XRF Unit (Average, ppm) Chemical Treatment
Stannous Chloride Stain
(+/–) Preservative
Cr Cu As
A – <216.3 174.7 <10 Borate none
B – <205.3 <35.7 <9.3 Borate none
C + <284 <34 <10.3 Untreated none
D + <241.7 <51.3 <11.7 Untreated none
E + <261.3 10248 <9.7 Copper none
F + <253.3 1481 <18 Copper none
G + <236 6013 <10 ACQ none
H + 9194.3 5412.3 6431.7 CCA 17 min 24 sec
I + 2526.3 1418.7 1476.3 CCA 37 min 42 sec
Dissolution Method
Shelf life (6 months; ends August 26, 2005)
Reagents must be stored separately
60
55
50
45
Reaction Time (min)
40
35
30
25
20
15
10
5
0
0 2 4 6 8 10 12 14 16 18 20 22 24 26
Shelf Life (weeks)
Other Application Methods
Whole wood application
Interference with
Untreated Wood
Other Application Methods
Ash
Masking color of ash
Wipes
Simulate human hand
Analyze wipe with dissolution method stannous chloride
stain
New wood Effective; similar reaction time
Weathered wood Effective; reaction time ~4 hours
UNTREATED 4.0 kg/m3 CCA 40 kg/m3 CCA
Future Objectives
Additional field testing on playgrounds
MDL for phosphate and arsenate
Adjust pH to reduce reaction time
Prepare consumer instructions
Submit technical report to:
Thank you!
Questions?