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Related Information: Chemical Sampling - Vanadium Pentoxide


This backup report was revised April, 1991


Introduction

The general procedure for the collection and X-ray confirmation of vanadium pentoxide (V2O5) exposures is given in OSHA Method ID-185 (9.1). The general procedure for the collection and analysis of air samples for V2O5 is given in OSHA Method ID-125G (9.2). The sampling technique and analytical instrumentation of these two methods differ in both detail and purpose. The inductively coupled plasma atomic emission spectroscopy (ICP-AES) approach in ID-125G is an elemental analysis and cannot identify the vanadium-containing compound. OSHA Method ID-185 is used when there is doubt as to the specific V compound that is the source of the V exposure.

This method was evaluated when the OSHA Permissible Exposure Limit (PEL) was a ceiling value and was for exposures to total dust or fume. Currently, the V2O5 PEL is a time weighted average (TWA) for either a respirable dust or fume.

This back-up report consists of the following sections:

(1) Experimental procedure
(2) Analysis
(3) Determination of the accuracy and precision
(4) Determination of detection limits
(5) Effect of particle-size distribution on X-ray recoveries
(6) Method comparison
(7) Summary of results
(8) Conclusions


Notes:

1) This method is for confirmation use, where heavier sample loadings are expected, and therefore larger amounts were used in the validation than might be expected in a 8-h TWA sample.

2) The evaluation was additionally designed to assess the effect of particle size on the analytical accuracy of X-ray analyses V2O5.



1. Experimental Procedure

1.1 Two analytical X-ray techniques were investigated and compared against an atomic absorption spectrometry (AAS) procedure for analyzing V.

1.1.1 X-ray diffraction (XRD) was performed using custom OSHA Laboratory software and two Model 3500 Automated Powder Diffractometers (APDs) (Phillips Electronics Instruments Co., Mahwah, NJ) sharing the same generator. Results for these APDs are labeled APD-A or APD-B in this report.

1.1.2 X-ray fluorescence (XRF) was performed using a Model 77-800 (upgraded to Model 77-900A) Energy Dispersive X-ray Fluorescence (EDXRF) Spectrometer (Finnigan Corporation, Sunnyvale, CA) consisting of: a an X-ray generator with a direct-beam Rh end-window X-ray tube and an X-ray spectrometer console using a Computer Automation Alpha 16 computer.

More recently, field samples submitted to the Laboratory for V2O5 analyses have been analyzed using a Kevex 770/8000 Delta EDXRF system (Kevex Instruments Inc., San Carlos, CA) consisting of: Kevex 770 X-ray generator, its associated satellite box, vacuum system, helium flush system, firmware-based 8000 keyboard console, computer monitor, Digital Equipment Corporation (DEC) 11/73 computer, graphics memory, Kevex spectrum analyzer, and Toolbox II software. This latter system uses an Fe secondary target for this analysis and offers improved sensitivity, lower background and greater resolution of interferences (9.1). The system parameters for both XRF systems are given in the experimental section of the method (9.1).

1.1.3 For the purpose of comparison, the V2O5 samples on Ag membranes were re-analyzed for V by AAS procedure (9.3) using a Model 603 Atomic Absorption Spectrometer (Perkin-Elmer Corp., Norwald, CT).

1.2 Three particle-size distributions were investigated:

  1. "M" samples simulating respirable particle size range (0 to 10 m with median of approximately 3 m). The "M" samples are referred to by the label "Respirable".
  2. "W" samples simulating fine-respirable particle size range (0 to 3 m). The "W" samples are referred to by the label "Fine respirable".
  3. "Fine W" samples simulating fume-like particles.

1.2.1 Quantitation of V2O5 dust (approximating respirable dust) was assessed using spikes at nominal levels of 233, 467 and 700 g V2O5 ("M" samples).

1.2.2 Quantitation of V2O5 dust (approximating fine-respirable particle size) was assessed using spikes at levels of 237, 474, and 710 g V2O5 ("W" samples). The spiked levels indicated in the NIOSH study were duplicated and are not the usual validation levels of 0.5, 1, and 2 times the OSHA PEL. The respirable characterization and spiking levels are further described in Reference (9.4).

1.2.3 To assess analyte sensitivities to very small fume-like particles, aliquots of an unstirred acetonitrile suspension of the finest particles in the "W" material were analyzed (See Section 2.4.2).

1.2.4 All samples were analyzed by XRD, XRF, and AAS techniques.

2. Analysis

2.1 Filter Membranes

2.1.1 FWS-D (0.5 m pore size) membranes were spiked with sonicated acetonitrile suspensions of V2O5. Small pore size membranes were used during the evaluation to prevent the loss of small particles during the spiking with liquid suspensions. During sample collection of particles suspended in air, the 5.0-m pore size PVC membrane should sufficiently retain the smaller particles due to static charge and collection characteristics. Collection efficiencies exceeding 99% have been reported of 0.3-m Dioctyl phthalate aerosol collection on PVC filters (9.5).

2.1.2 Silver metal membranes (25-mm diameter, 0.45-m pore size) were used to support the prepared thin films for presentation in X-ray analyses.

2.2 Preparation of Standard Materials

Procedure:

2.2.1 Reagent grade V2O5 (99.8%, J.T. Baker, Phillipsburg, NJ) was used as the starting material for the X-ray methods. For the AAS comparison method, a 1,000 g/mL V standard in a dilute HCl matrix (Lot #J141, RICCA Chemical Company, Arlington, TX) was used for preparing AAS standards.

2.2.2 Respirable stock material ("M") was prepared by hand grinding reagent grade V2O5 in an alumina mortar and pestle at room temperature. The ground material was added to 50 to 75 mL of tetrahydrofuran (THF) in a glass beaker. The sonicated suspension was west-sieved through 10-m nylon mesh using a sieving bottle as shown and described in Section 6.4. of the method (9.1). The dust was isolated from the suspension by filtering it onto a Ag membrane. This material was used in preparing only spikes.

2.2.3 For a finer particle-size distribution, additional stock material ("W") was prepared by a different grinding technique. Reagent grade V2O5 was ground in a freezer mill operated with liquid nitrogen for 10 minutes. This stock material was also wet-sieved through 10-m nylon mesh as described in Section 2.2.2. In addition to spiked sample preparation, this material was used to prepare calibration standards because the freezer mill produces more reproducible particle-size distributions than those produced from hand grinding with a mortar and pestle.

2.2.4 Results: The reagent grade material, "W", and "M" materials were analyzed by AAS and gave an assay of 101.3% V2O5 as shown below:

Reagent
"W" Material
"M" Material
mg Taken
Assay by AAS
mg Taken
Assay by AAS
mg Taken
Assay by AAS
1.307  104.59% 2.263  101.59% 2.069   102.66%
1.633 101.84   1.581 101.39 1.535 103.45
2.348 99.96 2.295   99.48 5.663   97.30
2.457
98.82

1.297
100.93

2.138
100.09

Mean 101.3% 100.8% 100.9%
 

The manufacturer's assay of 99.8% was used in calculations for all materials derived form the reagent grade V2O5.

2.3 Preparation and XRD Analysis of Calibration Standards

Procedure:

2.3.1 X-ray calibration standards preparation

Twenty-four calibration standards were prepared from THF suspensions of fine-respirable stock material ("W"). To avoid reduction of V2O5 by warm organic agents, fixatives were not used to secure the dust on the membranes. This also facilitated sample and standard re-analysis by AAS. Three standards were prepared on Ag membranes at each of the following levels:

"W" Material - Standards

Standard
Delivered
g V2O5
Volume (mL)
Reagent
Concentration
g/mL
50
100
200
250
499
998
1996
2495
  5
10
2
25
5
10
20
25
  10.040
10.040
100.02
10.040
100.02
100.02
100.02
100.02

2.3.2. Calibration and analysis (XRD)

These calibration standards were analyzed on two different APDs. The sample analysis order was scrambled to reduce instrumental drift effects. Two-theta calibrations were performed using the primary 38.15 two-theta (2q) Ag calibration line to avoid potential interferences from other V2O5 lines. (In practice, the strong secondary 44.33 2q Ag line is within 0.03 2q of a low intensity V2O5 peak; therefore, no significant error is introduced when using the secondary Ag line in 2q calibrations.) The X-ray generator settings were 40 kV and 40 mA. Integration times of 1 s and 0.02 2q steps were used throughout the study. The detection limit was determined at both 1- and 10-s integration periods. A custom OSHA computer program (9.6) was used to establish a two-piece calibration curve and calibration coefficients. Standard data is shown in Table 1. A two piece curve fit or a polynomial curve fit is generally performed to optimize recovery over the entire analytical range. A second-order polynomial fit for the low end allows for the correction of losses due to penetration of dust into the Ag membrane and to correct for the conservative heuristic used when establishing integration limits. The second-order fit of the upper end is smoothly spliced onto the upper end of the low range fit. The second-order fit of the upper end allows for partial correction for sample self-absorption effects. This is important because a Leroux correction (9.7) is not performed. In the past, Leroux corrections have been found to over-correct (9.8).

2.4 Preparation and X-ray Analyses of Spiked Samples

Procedure:

2.4.1 Sample preparation

Analyses were performed on a total of 36 samples (six samples at each of three test levels for the two different materials, "W" and "M"). Acetonitrile was used as the vehicle for spiking FWS-D membrane filters. Neither V2O5 nor the PVC filter medium dissolves appreciably in acetonitrile. The "W" spiked samples were prepared by filtration of acetonitrile suspensions of the freezer mill material upon FWS-D (0.5-m pore size) filters supported on a fritted-glass filtering support. The "M" spiked samples were prepared by similar filtration of acetonitrile suspensions of the mortar-and-pestle ground material. Upon drying, the filter membranes were transferred to centrifuge tubes and the 10 mL of THF was added to each to dissolve the membranes. The tubes were placed in an ultrasonic bath and the tube contents were sonicated for approximately 10 minutes. The sonicated suspension was filtered onto 25-mm Ag membranes (0.45-m pore size) for subsequent analysis. As in the preparation of the calibration standards (See Section 2.3.1), fixatives were not used. The three test levels were produced as follows:

Sample Delivered
g V2O5
Aliquot
(mL)
Reagent Concentration
g/mL
"W" 237
474
710
2
4
6
118.62
118.62
118.62
"W" 233
467
700
2
4
6
116.92
116.92
116.92

2.4.2 Fume-like sample preparation:

In order to assess the effect of very fine particles on recovery, three samples were prepared (10-mL aliquots) from the center of the same 118.62 g V2O5/mL acetonitrile suspension of fine-respirable stock material "W" after allowing the coarser material to settle out of the unstirred suspension. After 2.5 h, a significant fraction of the larger particles had settled out leaving a hazy suspension. Aliquots of the supernatant suspension were spiked directly onto 0.45-m pore size Ag membranes. These samples were referred to as "Fine-W" samples.

2.4.3 The "W", "M", and "Fine-W" Samples and blanks were analyzed by XRD, XRF, and AAS using the procedures which follow:

XRD analytical procedure

The Ag membrane samples and blanks were analyzed in the same manner as the calibration standards described in Section 2.3.2.

2.4.4 XRF analytical procedure

The "W" calibration standards were analyzed by XRF using the program described in Appendix 1. Count data were collected on all channels in air at 20 kV, 0.5 mA, for 100 s with a narrow collimator and without an X-ray filter. After analyzing the standards, a concentration-response curve was prepared to calibrate on the integrated counts in the 17-channel (~0.64 kV) region spanning the V Ka peak at 4.949 kV. Background counts were estimated using a linear background model between 3.4 to 5.9 kV. The equations obtained (Table 1) were used to calculate the amount of V2O5 present in spiked ("M" and "W") samples.

For the "Fine-W" spiked samples, a separate regression was performed using single representative "W" standards at each of the loadings.

2.5 Calibration and Analysis (AAS) - Stock Materials and Spiked Samples

Procedure:

2.5.1 Preparation of atomic absorption standards:

Eight standards were prepared in a 4% HCl matrix by serial dilutions of the 1,000 g/mL V standard. Concentration of the final standards ranged from 100 to 0.1 g/mL.

2.5.2 Analytical procedure (AAS) - stock materials:

To check the purity of the stock materials used in the evaluation of the X-ray methods, four samples of each of the reagent, "W", and "M" materials were weighed out and transferred to 100 mL volumetric flasks using a total of 4-mL HCl and approximately 5 mL deionized water (DI H2O). These were brought just to a boil on a hot plate. After cooling, the samples were diluted to volume with DI H2O to give a 4% HCl matrix. Analysis was performed according to reference 9.3 The results are shown in Section 2.2.4.

2.5.3 Analytical procedure (AAS) - silver membrane samples:

The blanks and the spiked "W", "M", and "Fine-W" samples were re-analyzed by AAS after the XRD and XRF analyses. The edges of the membranes were bent before acid extraction to encourage the free flow of acid above and below the membrane. The membranes were agitated and sonicated for 10 to 15 s in 250-mL Phillips beakers containing 10-mL DI H2O and 1 mL concentrated HCl. After the dust was visually released from the membranes, the beakers were placed on a hot plate and brought just to a boil. They were then removed to cool to ambient temperature (20 to 25 C) while being agitated. The solutions were then quantitatively transferred to 25-mL volumetric flasks using 4 to 5 small rinses of DI H2O. The volumetric flasks were then diluted to volume with DI H2O to give a 4% HCl matrix. Analysis was performed according to Reference 9.3.

2.6 Results: The results for the three different analytical techniques and sample materials are presented as follows:

Table
Results
2
3
4
5
6
7
8
9
XRD results for "W" material
XRD results for "M" material
EDXRF results for "W" material
EDXRF results for "M" material
AAS results for "W" material
AAS results for "M" material
Summary - analyses of "Fine-W" material
Summary - analyses of "W" and "M" material

Tables 8 and 9 contain summary results of the three analytical techniques performed on each sample.

3. Determination of the Precision and Accuracy

3.1 Outlier and Bartlett's Tests (XRD and EDXRF)

The calibration data (Table 1) and all of the "W" and "M" spiked-sample data passed the ASTM test for outliers at the 99% confidence level (9.9). All the spiked-sample data passed Bartlett's test (9.10), so the results were pooled as appropriate. Statistical test results are shown below:

Bartlett's Test Results

"W" Reference Material (also used for calibration standards)


Bartlett's variance homogeneity tests:
Critical Chi-squared value  =  9.21 (99% Confidence Level and N  =  3)
XRD (APD-A)
XRD (APD-B)
EDXRF
Chi-squared  =  1.11
Chi-squared  =  2.11
Chi-squared  =  9.21
N  =  3
N  =  3
N  =  3


 
"M" Reference material (coarser than calibration standards)
 
Bartlett's variance homogeneity tests:
Critical Chi-squared value  =  9.21 (99% Confidence Level and N  =  3)
XRD (APD-A)
XRD (APD-B)
EDXRF
Chi-squared  =  0.26
Chi-squared  =  0.49
Chi-squared  =  2.04
N  =  3
N  =  3
N  =  3

3.2 The precision and accuracy (9.11.) for the XRD method:

Recoveries, precision, and overall errors are shown below. X-ray diffraction results for "W" stock material (AAS results are shown in parentheses) are:

Recovery: APD-A Ave. Recovery
APD-B Ave. Recovery
Combined XRD Recovery
 
 =  0.894
 =  0.880
 =  0.887 (0.900)
 
Precision: APD-A CV1(Pooled)
APD-B CV1(Pooled)
Combined XRD CV1(Pooled)
 
 =  0.117  
 =  0.125  
 =  0.121 (0.031)  
 
Overall Error:  =  36%

X-ray diffraction results for "M" stock material
(AAS results are shown in parentheses) are:

Recovery: APD-A Ave. Recovery
APD-B Ave. Recovery
Combined XRD Recovery
 
 =  1.680
 =  1.867
 =  1.774 (0.933)
 
Precision: APD-A CV1(Pooled)
APD-B CV1(Pooled)
Combined XRD CV1(Pooled)
 
 =  0.062  
 =  0.073  
 =  0.068 (0.015)  
 
Overall Error:  =  91%

3.3 Precision and Accuracy - XRF method

Recoveries, precision, and overall error are shown below. 
X-ray
fluorescence results for "W" material
(AAS results shown in parentheses) are:

Ave. Recovery:
Precision: CV1(Pooled)
Overall Error:
 =  0.871 (0.900)
 =  0.097 (0.031)  
 =  32%

X-ray fluorescence results for "M" material
(AAS results shown in parentheses) are:

Ave. Recovery:
Precision: CV1(Pooled)
Overall Error:
 =  0.965 (0.933)
 =  0.064 (0.015)  
 =  16%

4. Determination of Detection Limits

4.1 Procedure: Blanks were analyzed in order to estimate the microgram detection limits. Blanks were analyzed by XRF using the total analytical times indicated in Appendix 1. The blanks were also analyzed by XRD as described in Section 2.3.2 using total analytical times of 65 and 650 s (corresponding to integration times of 1 and 10 s respectively). The X-ray detection limit estimates were based on the International Union of Pure and Applied Chemistry (IUPAC) definition as three times the standard deviation of the measurements performed on blanks divided by the slope (9.12), (9.13). The AAS detection limit was estimated using three times the minimum AAS reading.

4.2 Results: Detection limit results are summarized below and shown in Table 10. Detection limits determined for the analytical methods used (g V2O5):

X-ray Diffraction X-ray Fluorescence Atomic Absorption
DL
Total time
DL
Total time
DL
Total time
25 g
25 g
65 s
650 s  
14 g
  2 g
100 s
1,000 s  
9 g
-
4 s
-

Some XRD blank results were abnormally high. This gave a large detection limit for the XRD method. No V was identified using XRF or AAS analyses on the same blanks; therefore, V2O5 contamination was ruled out as a possible cause. A sample of ten Ag membranes from the same lot also did not have the XRD interference. This indicates that the PVC membranes and/or the THF solvent may be responsible. Salt (NaCl) has its primary peak near the V2O5 analytical peak. The non-stoichiometric compound, K0.2Na0.8Cl, has its primary diffraction line at the V2O5 analytical peak. Finger prints which potentially contain salt did not produce significant peaks in the range scanned.

5. Effect of Particle-Size Distribution on X-ray Recoveries

Comparisons were performed on the results for the three different particle-size distributions. Due to the sample preparation method used for the fume-like samples, the amount of V2O5 taken was not known beforehand. Using result ratios (Mean Relative Recoveries) allows making a comparison.

5.1 The data used for this comparison study were taken from Tables 8 and 9.

5.2 The mean relative recoveries for the materials studied:

   Mean Relative Recoveries
   XRD/AAS
XRF/AAS
Fume-like particles "Fine-W"
Fine-respirable particles "W"
Respirable dust particles "M"
0.651
0.986
1.901
0.998
0.968
1.034

6. Method Comparison

Related to the evaluation of accuracy and precision is method (system) comparison which normally employs duplicate sampling (or spiking) to holistically compare the quality of a known analytical system with one or more untested analytical systems. Duplicate spiking (a separate set for each method) was not performed in these comparisons because the non-destructive nature of the XRD and XRF analyses made that unnecessary and counter-productive. Westgard and associates (9.14) have proposed a detailed scheme for method comparison. This evaluation scheme calls for the application of a least-squares linear regression of the results from the candidate method and comparative analytical method (assumed to be dependent and independent variables respectively). The regression is then analyzed by statistical techniques such as the F-test, t-test, least-squares analysis and correlation coefficients. This scheme is based on the assumption that the comparative method gives the true value (9.15). The approach is possibly biased against discovering a better analytical system. In these analyses, however, the AAS technique should give the most accurate value for the amount of V2O5 captured on and in the Ag membrane and is considered the reference method. The statistical evaluation is meaningful in that limited context. Comparisons of the XRD and XRF candidate methods with the AAS comparison method are presented below.

6.1 A summary of the AAS versus X-ray comparison data from the computer calculations follows:

a
Slope
Sslope
Bias
r
r2
APD-A "W" dust
APD-A "M" dust
  2.11
-28.02
0.9848
1.8826
0.057
0.074
  -4.33
340.92
0.9739
0.9886
0.9484
0.9773
APD-B "W" dust
APD-B "M" dust
-23.69
-35.38
1.0440
2.0999
0.063
0.088
  -4.99
424.44
0.9717
0.9870
0.9441
0.9743
EDXRF "W" dust
EDXRF "M" dust
  -3.69
-23.34
0.9779
1.0988
0.046
0.041
-13.06
 17.95
0.9838
0.9900
0.9679
0.9800
Where:
a (in g)   =   intercept of regression line
Slope   =   slope of regression line
Sslope   =   standard deviation for the slope
Bias (in g)   =   mean g V2O5 found by candidate method less
mean g V2O5 found by reference method
r   =   correlation coefficient
r2   =   Coefficient of determination (fraction of variation in candidate measurements due to variation in reference measurements)

The coefficients of determination are between 0.94 and 1.00. This indicates that, at most, only 6% of the variance in the candidate measurement is not accounted for by variance in the "independent" reference measurement.

The slopes approaching a value of 1 indicate small relative bias between the candidate and comparison methods. This is the case in all but the XRD results for the "M" dust. The slope of approximately 2 indicates an unacceptable relative bias.

6.2 Results (t-tests and F-tests)

t
t-crit
F
F-crit
df
APD-A "W" dust
APD-A "M" dust
-.4557
9.0564
2.110
2.120
1.02257
3.62634
2.30
2.33
17
16
APD-B "W" dust
APD-B "M" dust
-.4683
9.0849
2.110
2.120
1.15448
4.52635
2.30
2.33
17
16
EDXRF "W" dust
EDXRF "M" dust
-1.659
2.3854
2.120
2.120
1.01211
1.23193
2.33
2.33
16
16
Where:
t   =   calculated Student t-test value
(bias indicated by sign)
t-crit   =   two-sided critical t value for 0.05 probability (from Reference 9.16)
F   =   calculated F-test value
F-crit   =   critical F value for 0.05 probability (from Reference 9.16)
df   =   degrees of freedom
(no. paired observations - 1)

For the fine respirable dust ("W") samples, no significant difference was detected between the performance of the test and comparative methods.

The t-test data above indicate that for the respirable dust ("M") samples there is a significant difference in means between the X-ray test methods and the AAS comparison method.

In the case of the "M" dust samples, the F-test data indicate that there was a significant difference in precision between the XRD and AAS methods, but there was not a significant difference in precision between the XRF and AAS methods.

7. Summary of Results

In order to get the best estimate of the Overall Error, the recoveries and CV1 Pooled results for the two different APDs used in the validation were averaged. Averaging was not necessary for the XRF results, since only one instrument was used. The ranges shown are for all experiments performed and are therefore somewhat larger than if only a single APD instrument were used.

The results for the accuracy and precision calculations in Section 3 were based on the assumption that the theoretical amount of V2O5 delivered to each PVC membrane represented the true amount. The X-ray stock material was verified against the AAS standard giving approximately 100% V2O5. The XRD, XRF, and AAS analyses of the "W" dust samples and the XRF and AAS analyses of the "M" dust samples agreed well. A 10% negative bias was noted in recoveries of the "W" dust samples. It was concluded that the negative bias in these cases was probably due to losses incurred in spiking the PVC membrane with a V2O5 suspension in acetonitrile. Because the same samples were analyzed by XRD, XRF and AAS, any physical losses incurred in spiking and transfer to the Ag membrane were the same for each sample regardless of the analytical technique. The recoveries for "M" dust samples by XRD disagreed considerably with the other methods investigated and followed the trend expected for larger particles. The process of spiking by means of a suspension does not duplicate aerosol sampling and may not be ideally representative of samples taken with a cyclone.

The ability of each analytical technique to accurately determine each V2O5 material was assessed using overall error. The overall error should be within 25% and is calculated using the following equation:

Overall Error  =  ( |mean bias|  +  2[CVT pooled])100%

CV1 pooled was used instead of CVT pooled in this study. In Section 3 the low end of the range for the overall error for "M" dust analyzed by XRD was reported as 91%. Regardless, all the XRD work exceeds a 25% cutoff for overall error. Only the "M" dust XRF results satisfy an overall error limit of 25%.

8. Conclusions

8.1 X-ray diffraction (XRD) is the method of choice in identifying V2O5. Due to the significant dependence of XRD analytical sensitivity upon particle-size distribution, XRD is only used as a confirmation technique for this analyte. Analytical lines are available for qualitative verification in addition to the line available for quantitation. In order to quantitate using XRD, the standard material must approximate the analyte particle-size distribution of the samples. This may not be practical for the OSHA dust and fume standards for V2O5. If fume is present in an operation, the results in Section 5.2 indicate that recovery may be low due to the reduced XRD analytical sensitivity for finer particles. Therefore, XRD is used for confirmation only.

8.2 X-ray fluorescence (XRF) is the method of choice in quantitating V2O5 because particle-size effects are much less severe for XRF compared to XRD. In XRF, the V K peak is also available for qualitative verification of V.

8.3 Due to the common sample preparation technique and superior performance of the XRF methodology, this work suggests a hybrid method incorporating quantitation by XRF and chemical species verification (and semi-quantitative support) by XRD. There is a potential for multi-analyte analyses by such a hybrid approach. If the industrial hygienist desired, both respirable V2O5 and respirable quartz [which coexist in certain industrial operations (9.4)] could be determined on the same prepared sample if the quartz sampling procedure is employed (9.17)

8.4 The XRD method was patterned after the NIOSH study (9.4). A discussion of the effects of deviation in V2O5 methodology between OSHA and NIOSH can be found in reference 9.18.

8.5 Concluding remarks:

As noted above, there was good agreement between the AAS and XRF results in this study for all three particle-size distributions. The major biases observed for the XRD analyses are most readily explained as due to the change in sensitivity with respect to particle size.

The results in this report support the proposition that the quantitative analysis of V2O5 by XRD would require close matching of the particle-size distribution of the standard material to that of air samples collected during industrial operations on PVC filters. As seen in the samples subjected to removal of coarse particles by sedimentation ("Fine-W"), XRD evidenced decreased analytical sensitivity when compared to both XRF and AAS. As shown in Section 5.2, there was a large positive bias in the XRD analyses when the particle-size distribution was biased towards larger particles. This was most clearly shown when the analyses of V2O5 finely ground in a freezer mill ("W" samples) are compared to the analyses of V2O5 more coarsely ground in a mortar and pestle ("M" samples). The coarse material provided a doubling of recoveries when compared to the recoveries of the fine material. The quantitative analysis of V2O5 by XRF was more immune to the particle-size distribution, thus giving improved recoveries and better precision than analysis by the XRD method. Aerosol generation and particle sizing would be advantageous in more fully evaluating these particle-size effects.

9. References

9.1 Occupational Safety and Health Administration Technical Center:Confirmation of Vanadium Pentoxide in Workplace Atmospheres by M.C. Rose (USDOL/OSHA-SLTC Method No. ID-185). Salt Lake City, UT. Revised 1991.

9.2 Occupational Safety and Health Administration Technical Center:Metal and Metalloid Particulated in Workplace Atmospheres (ICP Analysis) by J.C. Septon (USDOL/OSHA-SLTC Method No. ID-125G). Salt Lake City, UT. Revised 1991.

9.3 Occupational Safety and Health Administration Analytical Laboratory:OSHA Manual of Analytical Methods edited by R.G. Adler (Method No. I-1). Salt Lake City, UT. 1977.

9.4 Carsey, T.P.:Quantitation of Vanadium Oxides in Airborne Dusts by X-ray Diffraction. Anal. Chem. 57:2125-2130 (1985)

9.5 Gelman Sciences:The Filter Book. Ann Arbor, MI: Gelman Sciences, 1991

9.6 Occupational Safety and Health Administration Analytical Laboratory:X-ray Diffraction Program Documentation. Salt Lake City, UT. 1981 (unpublished)

9.7 Leroux, J. and C. Powers:Direct X-ray Diffraction Quantitative Analysis of Quartz in Industrial Dust Film Deposited on Silver Membrane Filters. Occup. Health Rev. 21:26-34:26-34 (1970).

9.8 National institute for Occupational Safety and Health:Collaborative Tests of Two Methods for Determining Free Silica in Airborne Dust (DHHS Publication No. 83-124). Cincinnati, OH: National Institute for Occupational Safety and Health, and the Bureau of Mines, 1983.

9.9 Mandel, J.: Accuracy and Precision, Evaluation and Interpretation of Analytical Results, The treatment of Outliers. In Treatise on Analytical Chemistry, 2nd ed., edited by I. M. Kolthoff and P. J. Elving. New York: John Wiley and Sons, 1978. pp. 282-285.

9.10 Youden, W.J.: Statistical Methods for Chemists. New York: John Wiley and Sons, 1964. p 20.

9.11 Occupational Safety and Health Administration Analytical Laboratory: Precision and Accuracy Data Protocol for Laboratory Validations. In OSHA Analytical Methods Manual. Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.

9.12 Long, G.L. and J.D. Winefordner: Limit of Detection -- A Closer Look at the IUPAC Definition. Anal. Chem. 55: 712A-724A (1983).

9.13 Analytical Methods Committee: Recommendations for the Definition, Estimation and Use of the Detection Limit. Analyst 112:199-204:199-204 (1987).

9.14 Westgard, J.O. and M.R. Hunt.: Use and Interpretation of Common Statistical Tests in Method Comparison Studies. Clinical Chemistry 19:49 (1973).

9.15 Ripley, B.D. and M. Thompson: Regression Techniques for the Detection of Analytical Bias. Analyst 112:337-383:337-383 (1987).

9.16 Gore, W.L.: Statistical Methods. New York: Interscience, 1952, pp. 189-191.

9.17 Occupational Safety and Health Administration Analytical Laboratory: OSHA Analytical Methods Manual (USDOL/OSHA-SLCAL Method No. ID-142). Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.

9.18 Occupational Safety and Health Administration Analytical Laboratory: The effects of Deviation in Methodology - OSHA vs. NIOSH Results by M.C. Rose. Salt Lake City, UT. 1987 (unpublished).

Table 1
 
Calibration Data
Freezermill ("W") Material
 
APD-A X-Ray Diffractometer
V2O5
g Taken
Counts
g Calculated
Mean
Std Dev
CV1
  50
  50
  50
  818
  827
  860
  46.9
  47.4
  49.3
(46.4 - 49.4)*   47.9   1.27 0.0264
100
100
100
1522
1634
1718
  87.8
  94.4
  99.3
(87.2 - 100.4)   93.8   5.77 0.0615
200
200
200
3444
3573
3306
202.2
210.0
193.9
(192.7 - 211.3) 202.0   8.05 0.0399
250
250
250
4040
4195
4509
238.5
248.1
267.4
(234.4 - 268.2) 251.3 14.72 0.0586
499
499
499
8054
9131
9270
495.3
568.2
577.7
(495.3 - 598.9) 547.1 45.08 0.0824
998
998
998
14909  
13309  
15791  
969.3
855.8
1032.7  
(849.5 - 1055.7) 952.6 89.62 0.0941
1996  
1996  
1996  
29359  
27312  
27943  
2096.7  
1923.8  
1976.5  
(1897.1 - 2100.9) 1999.0   88.62 0.0443
2495  
2495  
2495  
35312  
34389  
35014  
2632.4  
2545.7  
2604.3  
(2543.2 - 2645.0) 2594.1   44.24 0.0171
* Acceptable ranges from the ASTM test are shown in parentheses.

Calibration fit spliced at 500 g, 8125 counts:
Low fit : 
High fit: 
Counts  =  
Counts  =  
0  +  17.562281      g  -  0.002626      g2
399.9865  +  15.962334      g  -  0.001026      g2

Table 1 (Continued)
 
Calibration Data
Freezer mill ("W") Material
 
APD-B X-ray Diffractometer
V2O5
g Taken
Counts
g Calculated
Mean
Std Dev
CV1
  50
  50
  50
1327
  812
  974
*
  43.5
  52.3
(Test not applicable)   47.9   6.22 0.1299
100
100
100
1736
1593
1888
  94.0
  86.1
102.4
  (84.8 - 103.6)**   94.2   8.15 0.0865
200
200
200
3691
3720
3922
204.5
206.1
217.9
(201.1 - 217.9) 209.5   7.32 0.0349
250
250
250
4440
4358
4456
248.2
243.4
249.2
(243.3 - 250.5) 246.9   3.10 0.0126
499
499
499
8097
9462
9216
475.9
567.9
551.0
(475.3 - 587.9) 531.6 48.97 0.0921
998
998
998
15331  
13357  
15996  
968.6
831.7
1015.2
(828.8 - 1048.2) 938.5 95.38 0.1016
1996  
1996  
1996  
31381  
29308  
29709  
2163.3  
1999.8  
2031.2  
(1965.0 - 2164.6) 2064.8   86.76 0.0420
2495  
2495  
2495  
36411  
36811  
34880  
2573.9  
2607.4  
2446.8  
(2445.3 - 2640.1) 2542.7   84.72 0.0333
* One of the 50 g standards appeared as an outlier. Although the result was acceptable on APD-A, the standard was not used for calibrating APD-B.
** Acceptable ranges from the ASTM test are shown in parentheses.
Calibration fit spliced at 500 g, 8461 counts:
Low fit : 
High fit: 
Counts  =   Counts  =   0  +  18.836058      g  -  0.003830      g2
773.2365  +  15.743113      g  -  0.000737      g2

Table 1 (Continued)
 
Calibration Data
Freezer mill ("W") Material
 
EDXRF
V2O5
g Taken
Counts
g Calculated
Mean
Std Dev
CV1
  50
  50
  50
  246
  206
  220
  60.7
  50.6
  54.2
  (49.3 - 61.0)*   55.2   5.12 0.0928
100
100
100
  412
  359
  415
102.4
  89.1
103.2

(89.1 - 107.3)   98.2   7.92 0.0806
200
200
200
  869
  785
  848
217.2
196.1
212.0
(195.8 - 221.1) 208.4 10.99 0.0527
250
250
250
1005
  976
1015
251.4
244.1
253.9
(244.0 - 255.7) 249.8   5.09 0.0204
499
499
499
2076
2178
2093
520.5
546.2
524.8
(514.7 - 546.3) 530.5 13.77 0.0259
998
998
998
3924
3579
3811
984.9
898.2
956.5
(895.7 - 997.3) 946.5 44.20 0.0467
1996  
1996  
1996  
8361
7419
7750
2099.7
1863.0
1946.2
(1831.6 - 2107.8) 1969.7   120.07   0.0610
2495  
2495  
2495  
9941
9826
10449  
2496.8  
2467.8  
2624.4**
(2423.9 - 2615.5) 2529.7   83.31 0.0329
* Acceptable ranges from the ASTM test are shown in parentheses.
** Although this standard appeared outside of the ASTM test range, it was used in the calibration.
EDXRF curve fit:
Counts  =  4.427507051  +  3.979798615      g  +  0      g2

Table 1 (Continued)
 
Calibration Data
Freezer mill ("W") Material*
 
EDXRF
V2O5
g Taken
Counts
g Calculated
 
50
100
200
250
499
998
1996  
2495  
 
210
  404
  756
  945
2114
3873
7754
10146  
 
41.1
  93.7
188.6
239.3
548.9
1002.4  
1956.8  
2517.0  
* Standards prepared from this material were used to analyze fume-like "Fine-W" samples.
EDXRF curve fit:
Counts  =  59.00722287  +  3.670421406      g  +  1.33910E-04      g2

Table 2
 
Analysis - Spiked Sample Data
Freezer mill ("W") Material
 
APD-A X-ray Diffractometer
V2O5
g Taken
Recovery Range*
  N  
Mean
Std Dev
CV1
237 (0.738 - 1.085) 6 0.911 0.0895 0.0982
474 (0.639 - 1.149) 6 0.894 0.1314 0.1470
710 (0.706 - 1.046) 6 0.876 0.0877 0.1001
Average Recovery
CV1 (Pooled)
  =  0.894
  =  0.1173


APD-B X-ray Diffractometer
V2O5
g Taken
Recovery Range*
  N  
Mean
Std Dev
CV1
237 (0.690 - 1.028) 6 0.859 0.0871 0.1015
474 (0.601 - 1.174) 6 0.887 0.1476 0.1663
710 (0.731 - 1.059) 6 0.895 0.0846 0.0946
Average Recovery
CV1 (Pooled)
  =  0.880
  =  0.1250
*   Acceptable ranges from the ASTM test are shown in parentheses.

Table 3
 
Analysis - Spiked Sample Data
Alumina Mortar and Pestle ("M") Material
 
APD-A X-ray Diffractometer
V2O5
g Taken
Recovery Range*
N
Mean
Std Dev
CV1
233 (1.483 - 1.841) 6 1.662 0.0923 0.0555
467 (1.510 - 1.960) 6 1.735 0.1158 0.0668
700 (1.450 - 1.818)    5** 1.634 0.1052 0.0644
Average Recovery
CV1 (Pooled)
  =  1.680
  =  0.0624


APD-B X-ray Diffractometer
V2O5
g Taken
Recovery Range*
  N  
Mean
Std Dev
CV1
233 (1.560 - 2.158) 6 1.859 0.1543 0.0830
467 (1.629 - 2.176) 6 1.902 0.1414 0.0743
700 (1.622 - 2.060) 6 1.841 0.1129 0.0613
Average Recovery
CV1 (Pooled)
  =  1.867
  =  0.0734
* Acceptable ranges from the ASTM test are shown in parentheses.
** One of the 700 g spiked samples was damaged in transfer from APD-B to APD-A; it was not used in subsequent analyses.

Table 4
 
Analysis - Spiked Sample Data
Freezer-mill ("W") Material
EDXRF
V2O5
g Taken
Recovery Range*
N
Mean
Std Dev
CV1
237 (0.788 - 1.000) 6 0.8938 0.0547 0.0612
474 (0.632 - 1.064)    5** 0.8481 0.1235 0.1456
710 (0.744 - 0.992) 6 0.8681 0.0640 0.0737
Average Recovery
CV1 (Pooled)
  =  0.8713
  =  0.0966


Table 5
 
Analysis - Spiked Sample Data
Alumina Mortand and Pestle ("M") Material
EDXRF
V2O5
g Taken
Recovery Range*
N
Mean
Std Dev
CV1
233 (0.825 - 1.126) 6 0.9759 0.0776 0.0795
467 (0.839 - 1.076) 6 0.9574 0.0612 0.0639
700 (0.895 - 1.028)    5** 0.9615 0.0377 0.0392
Average Recovery
CV1 (Pooled)
  =  0.9651
  =  0.0642
* Acceptable ranges from the ASTM test are shown in parentheses.
** One sample was lost in analysis
*** One of the 700-g spiked samples was damaged in transfer from APD-B to APD-A; it was not used in subsequent analyses.

Table 6
 
Analysis - Spiked Sample Data
Freezer-mill ("W") Material
AAS
V2O5
g Taken
Recovery Range*
  N  
Mean
Std Dev
CV1
237 (0.857 - 0.963) 6 0.9096 0.0273 0.0300
474 (0.843 - 0.957) 6 0.9004 0.0294 0.0327
710 (0.838 - 0.942) 6 0.8900 0.0268 0.0301
Average Recovery
CV1 (Pooled)
  =  0.9000
  =  0.0309


Table 7
 
Analysis - Spiked Sample Data
Alumina Mortand and Pestle ("M") Material
AAS
V2O5
g Taken
Recovery Range*
N
Mean
Std Dev
CV1
233 (0.938 - 1.001) 6 0.9692 0.0163 0.0168
467 (0.905 - 0.954) 6 0.9295 0.0124 0.0134
700 (0.875 - 0.924)    5** 0.8994 0.0137 0.0153
Average Recovery
CV1 (Pooled)
  =  0.9327
  =  0.0152
* Acceptable ranges from the ASTM test are shown in parentheses.
** One of the 700-g spiked samples was damaged in transfer from APD-B to APD-A; it was not used in subsequent analyses.

Table 8
 
g V2O5 "Fine-W" Recoveries
Spiked on Silver Membranes
Reported by Analysis
 
Sample
APD-A
APD-B
EDXRF
AAS
A
B
C
190.2
199.3
259.9
188.0
227.2
256.0
309.5
329.0
373.9
297.9
344.9
371.5

Table 9
 
g V2O5 "W" Recoveries
Spiked on PVC Membranes
Reported by Analysis
"True"
APD-A
APD-B
EDXRF
AAS
237
237
237
237
237
237
 
474
474
474
474
474
474
 
710
710
710
710
710
710
234.5
220.5
245.9
195.1
204.4
195.5
 
498.0
403.3
482.0
338.4
375.5
444.4
 
548.7
548.6
658.3
612.3
669.9
692.2
236.7
202.4
218.8
182.8
188.5
192.0
 
500.9
434.3
496.5
341.6
346.4
403.2
 
614.5
542.5
682.3
603.4
662.5
706.4
233.6
206.7
221.3
207.2
202.7
199.7
 
489.6
403.7
*
338.6
360.2
418.0
 
555.0
576.8
677.1
607.7
640.9
641.1
225.3
212.3
218.8
209.1
218.8
209.1
 
430.1
430.1
443.6
410.0
410.0
436.9
 
598.1
636.6
640.0
622.5
650.6
643.6

g V2O5 "M" Recoveries
"True"
APD-A
APD-B
EDXRF
AAS
233
233
233
233
233
233
 
467
467
467
467
467
467
 
700
700
700
700
700
700
355.2
412.2
410.8
378.6
382.5
384.5
 
761.9
886.6
787.7
867.2
797.7
760.2
 
1079.0
*
1111.3
1230.0
1215.6
1081.9
363.5
443.3
442.7
433.5
467.3
448.5
 
857.9
990.2
807.5
941.8
864.1
868.9
 
1173.3
1337.8
1277.4
1382.2
1337.0
1223.3
222.3
255.7
218.5
202.2
228.8
236.8
 
484.6
482.3
427.3
425.5
437.9
425.0
 
666.8
*
654.4
709.7
689.4
644.9
228.5
222.0
231.8
225.3
222.0
225.3
 
426.8
433.5
436.9
443.6
433.5
430.1
 
615.5
*
636.6
626.0
640.1
629.5
* Sample lost in analysis.

Table 10
 
Detection Limit Determination
Blanks Prepared as Spiked Samples
 
100-s Analysis Time & Normalized Counts
 
Sample
APD-A
Counts
APD-B
Counts
EDXRF
Counts
A
B
C
D
E
F
G
330
135
105
187
196
108
408
434
113
106
165
231
191
545
59
11
22
41
42
8
39
Average 209.86 255.00 31.714
SD 116.46 168.96 18.599
Slope (Count/g) 17.562 18.836  3.9798
D.L. 19.9 26.9 14.0
Estimated DL
25 g V2O5 (XRD)

14 g V2O5 (XRF)


Detection Limit Determination
Blanks Prepared as Spiked Samples
 
1,000 s Analysis Time & Normalized to Compare with 100-s Results
 
Sample
APD-A
Counts
APD-B
Counts
EDXRF
Counts
A
B
C
D
E
F
G
H
I
214
27
47
42
21
15
234
195
97
251
21
94
24
81
84
351
435
106
1.0
4.3
4.3
8.4
0
4.4
4.5
1.2
0
Average 99.11 160.78 3.12
SD 90.10 148.95 2.78
Slope (Count/g) 17.562 18.836 3.9798
D.L. 15.4 23.7 2.10
Estimated DL
20 g V2O5 (XRD)

2 g V2O5 (XRF)
Where DL  =  3(SD) / sensitivity

Appendix 1

The multichannel analyzer was set to 512 channels and the instrument was calibrated using the TiO2-ZnO-Y2O3 calibration standard. The spectrum range was approximately 1.2 to 20.6 kV.

Finnigan EDXRF Program
 
Changes for analysis on different days
Steps to be entered
on instrument console
Analyses at 100 s
Analyses at 1,000 s
(Begin programming.)
    LEARN
"Fine-W" and DL DL
(Program system to set up analytical conditions.)
    100 SEC
    1ST HALF
    CLEAR+CLEAR
    MARKER (Z=23)
    OUTPUT
100 s 1,000 s
(Program system to acquire spectrum.)
    ACQUIRE
(Program the instrument to obtain net counts using background subtraction.)
    NET
    START/SPAN/SELECT

  [Set background low energy region to ~3.4 kV (between Ag La and V Ka peaks).]
        START  =  71
        SPAN   =  5
        INTENS

  [Set background high energy region to ~5.9 kV (just beyond the V K peak).]
        START  =  124
        SPAN   =  5
        INTENS
127 127
  [Set region to span the V Ka analytical peak at 4.949 kV (~0.64 kV span.)]
        START  =  91
        SPAN   =  17
        INTENS
93 93
14
(End of programming.)
    EXECUTE

Note: This program was written for a specific instrument (Finnigan 77-900A). Commands are capitalized. Background regions should be adjusted when interferences are present.