LEAD BY FIELD PORTABLE XRF: METHOD 7702, Issue 1, dated 15 January 1998 - Page 3 of 4
11. Set instrument parameters and analyze filter samples as specified by the manufacturer. The following measurement technique is based upon the NITON® 700 XRF. a. Analyze the middle of the sample filter first (see Figure 1, M). b. Allow the instrument to take a one source-minute reading (This may take longer than one real-time minute, depending upon the source strength). A one source-minute reading will assure the accurate L-shell reading necessary for the analysis of lead air filter samples. c. Analyze the filter sample at the top of the filter for one source minute (see Figure 1, T). d. Analyze the filter sample at the bottom of the filter for one source minute (see Figure 1, B). 2 e. The instrument software uses an algorithm that converts the three readings in µg/cm to an analytical result in µg of lead per sample. This result will be displayed following the third filter reading [1]. f. Analyze one standard every 2 hours (step 8). g. Repeat three-reading calibration check following completion of analyses (step 8). CALCULATIONS: 3 12. Using the measured lead concentration, W (µg), calculate the concentration, C (mg/m ), of lead in the air volume sampled, V (L):
C
NOTE: µg/L
W , mg/m 3 V
mg/m3
EVALUATION OF METHOD: This method was validated on field samples [1] by collecting lead particulate samples from bridge lead abatement projects. Airborne concentrations of lead within the containment of a sand blasting bridge 3 lead abatement project ranged from 1 to 10 mg/m . Area samples were collected for periods of time ranging from 15 seconds to 2 hours. This sampling protocol yielded 61 filter samples with lead loadings ranging between 0.1 to 1514.6 µg of lead per sample. Four personal samples were collected from a hand-scraping bridge lead abatement project for a total sample size of 65. The samples were first analyzed using a non-destructive, field portable XRF method. Samples subsequently were subjected to confirmatory analysis by the laboratory based NIOSH method 7105, Lead by GFAAS [3]. The method was statistically evaluated according to the NIOSH Guidelines for Air Sampling and Analytical Method Development and Evaluation [9]. The overall precision (rT) of the XRF method was calculated at 0.054 with a 95% confidence interval (CI) of 0.035 to 0.073, and the bias was 0.069 with a 95% CI of 0.006 to 1.515. The XRF method accuracy was determined to be ± 16%; however, at the upper 90% CI, the accuracy is ± 27%. Since the confidence interval includes the ± 25%, meeting the NIOSH accuracy criteria of ± 25% is inconclusive. However, the samples used to evaluate this method were field samples. Laboratory prepared aerosol samples would be expected to give better precision. Additionally, the XRF method is non-destructive; samples analyzed in the field can subsequently be analyzed in a laboratory using a method with greater accuracy, as needed. The filter sleeve used with the NITON® 700 Series XRF used a Mylar film to cover and seal the 37-mm filter. The lead particulate on the surface of the filter came into contact with the Mylar™ film. Both the Mylar™ film and the filter were digested with nitric acid and hydrogen peroxide as is specified in NIOSH Method 7105 [3].
REFERENCES: [1]
[2]
Morley JC [1997]. Evaluation of a portable x-ray fluorescence instrument for the determination of lead in workplace air samples [Thesis]. Cincinnati, OH: University of Cincinnati, Department of Environmental Health, College of Medicine. NIOSH [1994]. Lead by FAAS: Method 7082. In: Eller PM, Cassinelli ME, eds. NIOSH Manual of Analytical Methods (NMAM), 4th ed. Cincinnati, OH: National Institute for Occupational Safety and NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
