Ammonia Copper Zinc Arsenate Wood Treatment Analysis

Wood treatment is used to give protection to lumbers against insects, fungi, general wear and ultraviolet damage. Typical wood treatment formulations contain ammonia copper zinc arsenate (ACZA), Penta, CCA and copper. ACZA is typically used for treating wood species, which do not retain other treatments. For a successful wood treatment, it is essential to monitor the proper balance of treatment solution in order to obtain the highest quality possible, while reducing waste and cost associated with product rejection or treatment usage. For ensuring proper retention, the levels of As, Zn, and Cu in the solution are monitored before treatment, and then in the wood. A rapid, user-friendly, and reliable instrument is needed to perform the analysis throughout the quality control process. X-ray fluorescence (XRF) can serve this purpose. This article demonstrates the measurement of ACZA treated wood and wood treatment solutions using the NEX QC energy dispersive XRF (EDXRF) system from Rigaku.

Rigaku NEX QC EDXRF System with number

Figure 1. Rigaku NEX QC EDXRF System with number

Experimental Setup

Model: Rigaku NEX QC
X-ray tube: 4 W Ag-anode
Detector: Semiconductor
Sample Type: Wood (ground) and Solutions
Film: Mylar
Environment: Air
Analysis Time: 100 seconds
Options: 6-position Autosampler

Sample Preparation

Sample preparation involves grinding of wood samples into homogeneous powder and subsequent drying. Samples are quantified as loose powders by packing a 32 mm XRF sample cup 3/4 full (5g). Solution samples are prepared by mildly shaking them in order to ensure homogeneity, followed by filling a 32mm XRF sample 3/4 full (5g).

Calibration – ACZA in Wood

Using a set of assayed wood standards and a measurement period of 100 seconds per sample, an empirical calibration was developed.

CuO Std Error of Est: 0.0225
Units: % Correlation: 0.99961
Sample I.D. Assay Value Calculated Value
W-A 0.518 0.531
W-B 0.789 0.788
W-C 1.150 1.145
W-D 0.989 0.963
W-F 1.660 1.685
W-G 2.990 2.984

ZnO Std Error of Est: 0.0087
Units: % Correlation: 0.99975
Sample I.D. Assay Value Calculated Value
W-A 0.264 0.266
W-B 0.382 0.381
W-C 0.518 0.506
W-D 0.457 0.464
W-F 0.771 0.775
W-G 1.440 1.439

As2O5 Std Error of Est: 0.0269
Units: % Correlation: 0.99722
Sample I.D. Assay Value Calculated Value
W-A 0.518 0.531
W-B 0.789 0.788
W-C 1.150 1.145
W-D 0.989 0.963
W-F 1.660 1.685
W-G 2.990 2.984

Repeatability – ACZA in Wood

From the suite of calibration standards, the low and high samples were selected in order to demonstrate repeatability (precision). Using a measurement time of 100 seconds per sample, the measurement of each sample was performed in static position for 10 repeat analyses.

CuO       Units: %
Sample I.D. Standard Value Average Value Std Dev % Relative
W-A 0.518 0.5209 0.0014 0.3
W-G 2.990 3.047 0.015 0.5
ZnO        Units: %
Sample I.D. Standard Value Average Value Std Dev % Relative
W-A 0.264 0.2601 0.0010 0.4
W-G 1.440 1.455 0.005 0.4
As2O5       Units: %
Sample I.D. Standard Value Average Value Std Dev % Relative
W-A 0.189 0.1874 0.0011 0.5
W-G 1.280 1.289 0.002 0.2

Typical Detection Limits – ACZA in Wood

Utilizing the empirical method, the lower limit of detection (LLD) values of the 10 repeat analyses of a blank wood sample were measured in order to calculate the standard deviation. The LLD was defined as threefold the standard deviation. The following are the detection limits determined using a measurement time of 100 seconds per sample:

Compound LLD
CuO 4 ppm
ZnO 4 ppm
As2O5 3 ppm

Calibration – ACZA in Solution

Using a set of assayed wood standards and a measurement period of 100 seconds per sample, an empirical calibration was developed.

CuO Std Error of Est: 0.0394
Units: % Correlation: 0.99952
Sample I.D. Assay Value Calculated Value
S-A 0.53 0.552
S-B 1.03 1.032
S-C 1.56 1.541
S-D 2.11 2.061
S-E 2.52 2.574
S-F 5.09 5.086

ZnO Std Error of Est: 0.019
Units: % Correlation: 0.99956
Sample I.D. Assay Value Calculated Value
S-A 0.26 0.290
S-B 0.52 0.510
S-C 0.76 0.759
S-D 1.01 1.019
S-E 1.30 1.281
S-F 2.49 2.495

As2O5 Std Error of Est: 0.0302
Units: % Correlation: 0.99896
Sample I.D. Assay Value Calculated Value
S-A 0.26 0.285
S-B 0.53 0.528
S-C 0.80 0.788
S-D 1.08 1.039
S-E 1.30 1.334
S-F 2.63 2.633

Repeatability – ACZA in Solution

From the suite of calibration standards, the low and high samples were selected in order to demonstrate repeatability (precision). Using a measurement time of 100 seconds per sample, the measurement of each sample was performed in static position for 10 repeat analyses.

CuO       Units: %
Sample I.D. Standard Value Average Value Std Dev % Relative
S-A 0.53 0.525 0.003 0.6
S-F 5.09 5.088 0.027 0.5
ZnO       Units: %
Sample I.D. Standard Value Average Value Std Dev % Relative
S-A 0.26 0.263 0.002 0.8
S-F 2.49 2.479 0.008 0.3
As2O5       Units: %
Sample I.D. Standard Value Average Value Std Dev % Relative
S-A 0.26 0.269 0.002 0.7
S-F 2.63 2.618 0.021 0.8

Typical Detection Limits – ACZA in Solution

Utilizing the empirical method, the lower limit of detection (LLD) values of the 10 repeat analyses of a blank wood sample were measured in order to calculate the standard deviation. The LLD was defined as threefold the standard deviation. The following are the detection limits determined using a measurement time of 100 seconds per sample:

Compound LLD
CuO 4 ppm
ZnO 4 ppm
As2O5 3 ppm

Reliable Measurement of Copper and Zinc

Prop counters, which are used gas-filled proportional counter detectors, were used by past generations of analyzers. The prop counter detection system provides broad peaks, thus zinc and copper were measured as one peak, as illustrated in Figure 2. Separation of the single peak determined by a prop counter into copper and zinc measurements must be done utilizing large mathematical overlap correction factors or through the sequential utilization of Ross filters. This eventually increases the count time twofold.

Typical prop counter ACZA spectrum, which gives one single peak for Cu and Zn that must be heavily deconvoluted.

Figure 2. Typical prop counter ACZA spectrum, which gives one single peak for Cu and Zn that must be heavily deconvoluted.

This problem can be resolved by the NEX QC as it uses a rugged and reliable semiconductor detector, which yields much sharper resolution of peaks. The ACZA analysis utilizing the NEX QC is illustrated in Figure 3. Using the NEX QC, it is now possible to measure the individual copper and zinc without introducing additional errors caused by the use of Ross filters or large mathematical overlap corrections.

Typical NEX QC ACZA spectrum, which demonstrates clear, distinct peaks for Cu, Zn and As.

Figure 3. Typical NEX QC ACZA spectrum, which demonstrates clear, distinct peaks for Cu, Zn and As.

Retention Report

To measure a wood sample, the density of the wood needs to be entered. The measurement quantifies concentrations of As2O5, ZnO, and CuO, and yields balance and retention values.

Figure 4.

Conclusion

From the results, it is evident that the Rigaku NEX QC is an ideal instrument throughout the quality control process in treated lumber production. The tool is an economical solution of improving quality in the production process, while reducing costs, production rejection and waste.

This information has been sourced, reviewed and adapted from materials provided by Rigaku.

For more information on this source, please visit Rigaku.

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