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Vanadium Pentoxide Backup Data Report (ID-185)

OSHA Method ID-185 Backup | Revised April 1991

For problems with accessibility in using figures and illustrations, please contact the Salt Lake Technical Center at 801-233-4900.
These procedures were designed and tested for internal use by OSHA personnel. Mention of any company name or commercial product does not constitute endorsement by OSHA.

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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 μm with median of approximately 3 μm). The "M" samples are referred to by the label "Respirable".
         2. "W" samples simulating fine-respirable particle size range (0 to 3 μm). 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 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 (SeeSection 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 5 10.040
        100 10 10.040
        200 2 100.02
        250 25 10.040
        499 5 100.02
        998 10 100.02
        1996 20 100.02
        2495 25 100.02
      • 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 (2θ) Ag calibration line to avoid potential interferences from other V2O5 lines. (In practice, the strong secondary 44.33° 2θ Ag line is within 0.03° 2θ of a low intensity V2O5 peak; therefore, no significant error is introduced when using the secondary Ag line in 2θ calibrations.) The X-ray generator settings were 40 kV and 40 mA. Integration times of 1 s and 0.02° 2θ 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 atwo-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
        237 2 118.62
        "W" 474 4 118.62
        710 6 118.62
        233 2 116.92
        "W" 467 4 116.92
        700 6 116.92
      • 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 Kα 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 XRD results for "W" material
        3 XRD results for "M" material
        4 EDXRF results for "W" material
        5 EDXRF results for "M" material
        6 AAS results for "W" material
        7 AAS results for "M" material
        8 Summary - analyses of "Fine-W" material
        9 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) Chi-squared  =  1.11 N = 3
      XRD (APD-B) Chi-squared  =  2.11 N = 3
      EDXRF Chi-squared  =  9.21 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) Chi-squared  =  0.26 N  =  3
      XRD (APD-B) Chi-squared  =  0.49 N  =  3
      EDXRF Chi-squared  =  2.04 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  =  0.894
      APD-B Ave. Recovery  =  0.880
      Combined XRD Recovery  =  0.887 (0.900)
      Precision: APD-A CV1(Pooled)  =  0.117
      APD-B CV1(Pooled)  =  0.125
      Combined XRD CV1(Pooled)  =  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  =  1.680
      APD-B Ave. Recovery  =  1.867
      Combined XRD Recovery  =  1.774 (0.933)
      Precision: APD-A CV1(Pooled)  =  0.062
      APD-B CV1(Pooled)  =  0.073
      Combined XRD CV1(Pooled)  =  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:  =  0.871 (0.900)
      Precision: CV1(Pooled)  =  0.097 (0.031)
      Overall Error:  =  ± 32%
    • X-ray fluorescence results for "M" material
      (AAS results shown in parentheses) are:

    • Ave. Recovery:  =  0.965 (0.933)
      Precision: CV1(Pooled)  =  0.064 (0.015)
      Overall Error:  =  ± 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
      DL     Total time
      25 μg 65 s
      25 μg 650 s  
      X-ray Fluorescence
      DL    Total time
      14 μg    100 s
      2 μg 1,000 s  
      Atomic Absorption
      DL    Total time
      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"    0.651          0.998   
      Fine-respirable particles "W"    0.986          0.968   
      Respirable dust particles "M"    1.901          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 2.11 0.9848 0.057 -4.33 0.9739 0.9484
      APD-A "M" dust -28.02 1.8826 0.074 340.92 0.9886 0.9773
      APD-B "W" dust -23.69 1.0440 0.063 -4.99 0.9717 0.9441
      APD-B "M" dust -35.38 2.0999 0.088 424.44 0.9870 0.9743
      EDXRF "W" dust -3.69 0.9779 0.046 -13.06 0.9838 0.9679
      EDXRF "M" dust -23.34 1.0988 0.041 17.95 0.9900 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 -.4557 2.110 1.02257 2.30 17
      APD-A "M" dust 9.0564 2.120 3.62634 2.33 16
      APD-B "W" dust -.4683 2.110 1.15448 2.30 17
      APD-B "M" dust 9.0849 2.120 4.52635 2.33 16
      EDXRF "W" dust -1.659 2.120 1.01211 2.33 16
      EDXRF "M" dust 2.3854 2.120 1.23193 2.33 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. TheX-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 inSection 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 Kβ 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.

    • 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
      50 818 46.9
      50 827 47.4
      50 860 49.3
      (46.4 - 49.4)* 47.9 1.27 0.0264
      100 1522 87.8
      100 1634 94.4
      100 1718 99.3
      (87.2 - 100.4) 93.8 5.77 0.0615
      200 3444 202.2
      200 3573 210.0
      200 3306 193.9
      (192.7 - 211.3) 202.0 8.05 0.0399
      250 4040 238.5
      250 4195 248.1
      250 4509 267.4
      (234.4 - 268.2) 251.3 14.72 0.0586
      499 8054 495.3
      499 9131 568.2
      499 9270 577.7
      (495.3 - 598.9) 547.1 45.08 0.0824
      998 14909 969.3
      998 13309 855.8
      998 15791 1032.7
      (849.5 - 1055.7) 952.6 89.62 0.0941
      1996 29359 2096.7
      1996 27312 1923.8
      1996 27943 1976.5
      (1897.1 - 2100.9) 1999.0 88.62 0.0443
      2495 35312 2632.4
      2495 34389 2545.7
      2495 35014 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: Counts = 0  + 17.562281  x  μg  ‐  0.002626  x  μg2
      High fit: Counts = 399.9865  + 15.962334  x  μg  ‐  0.001026  x  μg2
    • Table 1 (Continued)
      Calibration Data
      Freezermill ("W") Material
      APD-B X-ray Diffractometer
      V2O5
      μg Taken
       
      Counts
           
      μg Calculated
           
      Mean
       
      Std Dev
       
      CV1
      50 1327 *
      50 812 43.5
      50 974 52.3
      (Test not applicable) 47.9 6.22 0.1299
      100 1736 94.0
      100 1593 86.1
      100 1888 102.4
      (84.8 - 103.6)** 94.2 8.15 0.0865
      200 3691 204.5
      200 3720 206.1
      200 3922 217.9
      (201.1 - 217.9) 209.5 7.32 0.0349
      250 4440 248.2
      250 4358 243.4
      250 4456 249.2
      (243.3 - 250.5) 246.9 3.10 0.0126
      499 8097 475.9
      499 9462 567.9
      499 9216 551.0
      (475.3 - 587.9) 531.6 48.97 0.0921
      998 15331 968.6
      998 13357 831.7
      998 15996 1015.2
      (828.8 - 1048.2) 938.5 95.38 0.1016
      1996 31381 2163.3
      1996 29308 1999.8
      1996 29709 2031.2
      (1965.0 - 2164.6) 2064.8 86.76 0.0420
      2495 36411 2573.9
      2495 36811 2607.4
      2495 34880 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: Counts = 0  + 18.836058  x  μg  ‐  0.003830  x  μg2
      High fit: Counts = 773.2365 + 15.743113  x  μg  ‐  0.000737  x  μg2
    • Table 1 (Continued)
      Calibration Data
      Freezermill ("W") Material
      EDXRF
      V2O5
      μg Taken
       
      Counts
           
      μg Calculated
           
      Mean
       
      Std Dev
       
      CV1
      50 246 60.7
      50 206 50.6
      50 220 54.2
      (49.3 - 61.0)* 55.2 5.12 0.0928
      100 412 102.4
      100 359 89.1
      100 415 103.2
      (89.1 - 107.3) 98.2 7.92 0.0806
      200 869 217.2
      200 785 196.1
      200 848 212.0
      (195.8 - 221.1) 208.4 10.99 0.0527
      250 1005 251.4
      250 976 244.1
      250 1015 253.9
      (244.0 - 255.7) 249.8 5.09 0.0204
      499 2076 520.5
      499 2178 546.2
      499 2093 524.8
      (514.7 - 546.3) 530.5 13.77 0.0259
      998 3924 984.9
      998 3579 898.2
      998 3811 956.5
      (895.7 - 997.3) 946.5 44.20 0.0467
      1996 8361 2099.7
      1996 7419 1863.0
      1996 7750 1946.2
      (1831.6 - 2107.8) 1969.7 120.07 0.0610
      2495 9941 2496.8
      2495 9826 2467.8
      2495 10449 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  x   μg  + 0  x   μg2
    • Table 1 (Continued)
      Calibration Data
      Freezer mill ("W") Material*
      EDXRF
       V2O5
      μg Taken 
       
      Counts
       
       μg Calculated 
      50 210 41.1
      100 404 93.7
      200 756 188.6
      250 945 239.3
      499 2114 548.9
      998 3873 1002.4
      1996 7554 1956.8
      2495 10146 2517.0
      * Standards prepared from this material were used to analyze fume-like "Fine-W" samples.
      EDXRF curve fit:
      Counts =  59.00722287 + 3.670421406  x  μg + 1.33910E-04  x  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  = 0.894
      CV1 (Pooled)  = 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  = 0.880
      CV1 (Pooled)  = 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  = 1.680
      CV1 (Pooled)  = 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  = 1.867
      CV1 (Pooled)  = 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  = 0.8713
      CV1 (Pooled)  = 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  = 0.9651
      CV1 (Pooled)  = 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  = 0.9000
      CV1 (Pooled)  = 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  = 0.9327
      CV1 (Pooled)  = 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 190.2 188.0 309.5 297.9
      B 199.3 227.2 329.0 344.9
      C 259.9 256.0 373.9 371.5
    • Table 9
      μg V2O5 "W" Recoveries
      Spiked on PVC Membranes
      Reported by Analysis
       "True"      APD-A      APD-B      EDXRF      AAS 
      237 234.5 236.7 233.6 225.3
      237 220.5 202.4 206.7 212.3
      237 245.9 218.8 221.3 218.8
      237 195.1 182.8 207.2 209.1
      237 204.4 188.5 202.7 218.8
      237 195.5 192.0 199.7 209.1

      474 498.0 500.9 489.6 430.1
      474 403.3 434.3 403.7 430.1
      474 482.0 496.5 * 443.6
      474 338.4 341.6 338.6 410.0
      474 375.5 346.4 360.2 410.0
      474 444.4 403.2 418.0 436.9

      710 548.7 614.5 555.0 598.1
      710 548.6 542.5 576.8 636.6
      710 658.3 682.3 677.1 640.0
      710 612.3 603.4 607.7 622.5
      710 669.9 662.5 640.9 650.6
      710 692.2 706.4 641.1 643.6
      μg V2O5 "M" Recoveries
       "True"      APD-A      APD-B      EDXRF      AAS 
      233 355.2 363.5 222.3 228.5
      233 412.2 443.3 255.7 222.0
      233 410.8 442.7 218.5 231.8
      233 378.6 433.5 202.2 225.3
      233 382.5 467.3 222.0 218.8
      233 384.5 448.5 236.8 225.3

      467 761.9 857.9 484.6 426.8
      467 886.6 990.2 482.3 433.5
      467 787.7 807.5 427.3 436.9
      467 867.2 941.8 425.5 443.6
      467 797.7 864.1 437.9 433.5
      467 760.2 868.9 425.0 430.1

      700 1079.0 1173.3 666.86 615.5
      700 * 1337.8 * *
      700 1111.3 1277.4 654.4 636.6
      700 1230.0 1382.2 709.7 626.0
      700 1215.6 1337.0 689.4 689.4
      700 1081.9 1223.3 644.9 629.5
      * 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 330 434 59
      B 135 113 11
      C 105 106 22
      D 187 165 41
      E 196 231 42
      F 108 191 8
      G 408 545 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 214 251 1.0
      B 27 21 4.3
      C 47 94 4.3
      D 42 24 8.4
      E 21 81 0
      F 15 84 4.4
      G 234 351 4.5
      H 195 435 1.2
      I 97 106 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 100 s 1,000 s
         1ST HALF
         CLEAR+CLEAR
         MARKER (Z=23)
         OUTPUT
      (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 Kα peaks).]
         START = 71
         SPAN = 5
         INTENS
       
      [Set background high energy region to ∼5.9 kV (just beyond the V Kβ peak).]
         START = 124 127 127
         SPAN = 5
         INTENS
      [Set region to span the V Ka analytical peak at 4.949 kV (∼0.64 kV span.)]
         START = 91 93 93
         SPAN = 17 14
         INTENS
      (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.

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