Page:NIOSH Manual of Analytical Methods - 7302.pdf/3

 ELEMENTS by ICP (Microwave Digestion): METHOD 7302, Issue 1, dated 21 July 2014 - Page 3 of 9

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 the preprogrammed digestion procedure for 12vessel digestion: 1200 W power, ramp to 150 °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 25-ml volumetric flasks with ASTM Type ll water. 8.	Dilute to the mark with ASTM Type ll water and mix. 9.	Submit extracted and diluted samples for analysis. CALIBRATION AND QUALITY CONTROL 10.	Calibrate the spectrometer according to the manufacturer recommendations. NOTE:	Typically an acid blank and multi-element working standards 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, Sn, Te, Tl; c.	 Ag, Cd, Sb; 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 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 are preferred. MEASUREMENT 13.	Set 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 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 ) V

, mg/m3

NOTE: µg/Liter air is equivalent to mg/m3. EVALUATION OF METHOD Method 7302 was evaluated using multi-element filter spikes at six spiking levels, based on the estimated LOQ for each element [8]. Using microwave digestion is less time consuming and more NIOSH Manual of Analytical Methods (NMAM), Fifth Edition