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ELEMENTS by ICP (Microwave Digestion): METHOD 7304, Issue 1, dated 25 June 2014 - Page 3 of 11

NOTE: In order to avoid a violent exothermic reaction, do not add water to concentrated nitric acid. Acid should be added after the water has been placed in the vessel. 5. Place digestion vessels in microwave and run preprogrammed PVC digestion procedure. Example microwave conditions for 12-vessel digestion: 1200 W power, ramp to 215 °C over 20 min, hold for 10 min at 215 °C followed by at least a 5 min cool down (power will be adjusted lower for fewer vessels). 6. Allow the samples to cool to room temperature. 7. Remove vessel lids and rinse contents into 50-mL volumetric flasks with ASTM Type ll water. 8. Dilute to the mark with ASTM Type ll water and mix. 9. Submit samples for analysis. NOTE: A residual solid may be present after digestion. Filter/centrifuge the samples before analysis, as appropriate. CALIBRATION AND QUALITY CONTROL: 10. Calibrate the spectrometer according to the manufacturers’ recommendations. NOTE: Typically an acid blank and a single or multi-element working standard are used. The following multi-element combinations are chemically compatible in 20% HNO3. a. Al, As, Ba, Be, Ca, Co, Cr, Cu, Fe, Li, Mg, Mn, Mo, Na, Ni, Pb, Se, Sr, Ti, V, Y, Zn, Zr; b. B, K, P, Te, Tl; c. Cd; d. Pt. 11. Analyze all applicable standards at least once every twenty (20) analyses (minimum frequency 5%). 12. Check recoveries with at least one media blank and two spiked media blanks per twenty samples. Use a spike level that is within the range of 10 to 20 times the Limit of Quantitation (LOQ.) NOTE: Whenever possible, QA/QC samples should be prepared from certified reference materials in a matrix similar to the bulk material sampled.  Liquid spiked filters are only surrogates for real world samples and QC data based upon certified samples would be ideal. MEASUREMENT: 13. Set the ICP-AES spectrometer to conditions specified by manufacturer. 14. Analyze standards and samples at applicable wavelengths for each element (target analytes are in Table 3). NOTE: If the values for the samples are above the linear range of the instrument, dilute the solutions with dilution acid, reanalyze, and apply the appropriate dilution factor in the calculations. CALCULATIONS: 15. Obtain the solution concentrations for the sample, Cs (µg/mL), and the average media blank, Cb (µg/ mL), from the instrument. 16. Using the solution volume of sample, Vs (mL), and media blank, Vb (mL), calculate the concentration for the sample, C (mg/m3), of each element in the air volume sampled, V (L), as follows:

C=

(Cs Vs )-(Cb Vb ) , mg/m3 V

NOTE: µg/Liter air is equivalent to mg/m3.

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition

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