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:
- "M" samples simulating respirable particle size range (0 to 10 µm with median of approximately 3
µm). The "M" samples are referred to by the label "Respirable".
- "W" samples simulating fine-respirable particle size range (0 to 3 µm). The "W" samples are referred
to by the label "Fine respirable".
- "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 µg 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 µg 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 µm 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-µm 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-µm Dioctyl phthalate aerosol collection
on PVC filters (9.5).
2.1.2 Silver metal membranes (25-mm diameter, 0.45-µm 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 µg/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-µm 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-µm
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
µg V2O5
|
Volume (mL)
|
Reagent
Concentration
µg/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).
2.3.2 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-µm 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-µm
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
µg V2O5
|
Aliquot
(mL)
|
Reagent Concentration
µg/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 µg 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-µm 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.
2.4.2 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 µg 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-µm 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 µg/mL V standard. Concentration of
the final standards ranged from 100 to 0.1 µg/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 (µg V2O5):
X-ray Diffraction |
|
X-ray Fluorescence |
|
Atomic Absorption |
DL
|
Total time
|
|
DL
|
Total time
|
|
DL
|
Total time
|
25 µg
25 µg |
65 s
650 s |
|
14 µg
2 µg |
100 s
1,000 s |
|
9 µg
- |
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 µg) |
= |
intercept of regression line |
Slope |
= |
slope of regression line |
Sslope |
= |
standard deviation for the slope |
Bias (in µg) |
= |
mean µg V2O5 found by candidate method less
mean µg 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 Kß
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
µg Taken
|
Counts
|
µg 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 µg, 8125 counts: |
Low fit :
High fit: |
Counts =
Counts = |
0 + 17.562281 × µg - 0.002626 ×
µg2
399.9865 + 15.962334 × µg - 0.001026 × µg2 |
Table 1 (Continued)
Calibration Data
Freezer mill ("W") Material
APD-B X-ray Diffractometer
V2O5
µg Taken
|
Counts
|
µg 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 µg 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 µg, 8461 counts: |
Low fit :
High fit: |
Counts =
Counts = |
0 + 18.836058 × µg - 0.003830 ×
µg2
773.2365 + 15.743113 × µg - 0.000737 × µg2 |
Table 1 (Continued)
Calibration Data
Freezer mill ("W") Material
EDXRF
V2O5
µg Taken
|
Counts
|
µg 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 × µg + 0 × µg2
Table 1 (Continued)
Calibration Data
Freezer mill ("W") Material*
EDXRF
V2O5
µg Taken
|
Counts
|
µg 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 × µg + 1.33910E-04 ×
µg2
Table 2
Analysis - Spiked Sample Data
Freezer mill ("W") Material
APD-A X-ray Diffractometer
V2O5
µg 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
µg 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
µg 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
µg 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 µg 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
µg 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
µg 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-µg 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
µg 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
µg 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-µg spiked samples was damaged in transfer from APD-B to APD-A; it was
not used in subsequent analyses. |
Table 8
µg 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
µg 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 |
µg 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/µg) |
17.562 |
18.836 |
3.9798 |
|
D.L. |
19.9 |
26.9 |
14.0 |
Estimated DL |
25 µg V2O5 (XRD) |
14 µg 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/µg) |
17.562 |
18.836 |
3.9798 |
|
D.L. |
15.4 |
23.7 |
2.10 |
Estimated DL |
20 µg V2O5 (XRD) |
2 µg 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 Kß
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.
|