Page:NIOSH Manual of Analytical Methods - 7304.pdf/4

 ELEMENTS by ICP (Microwave Digestion): METHOD 7304, Issue 1, dated 25 June 2014 - Page 4 of 11

EVALUATION OF METHOD: This method is less time consuming and more convenient than using the acid hotplate approach. The elimination of perchloric acid in the sample digestion procedure helps to improve the safety of the method. [9] Use of the PVC filters allows for the acquisition of total mass per filter in addition to total metals concentration. The evaluation of this method, 7304, for PVC filters was determined at six concentration levels based on the LOQ for each element listed on page 1 [13]. All of the precision data was evaluated for homogeneity for all concentration levels tested using the Bartlett’s test and the results are listed in the method backup data report [12] and summarized in Tables 3 and 4. In many cases the highest concentration level (300 times the LOQ) was not poolable due in every case to the precision being so small relative to the other values, usually less than CV = 0.001 (<0.1%). Therefore, the overall precision (ŜrT) and accuracy as given in Table 4 is an upper limit predictor of precision; precision at concentration levels greater than 300 times the LOQ (see Table 3) will probably be much smaller. For many of the metals, precision at the 3 times and/or 1 times the LOQ levels was reasonable (CV less than 10%) but were not poolable due to the precisions at the higher concentration levels being so much smaller. In one case (strontium) the lowest level was not poolable because its CV was an inlier (less than 1%), being much smaller than those at the higher concentration levels. In most cases the precision appeared to be a function of concentration. This is observable in Table 3 where the CVs for the 10 times the LOQ (lower level) and 300 times the LOQ (higher) levels are compared. Three elements, antimony, silver, and tin, had poor recoveries. It is believed that the chloride ions produced in the digestion of the PVC filters is causing the formation of precipitates. These metals are preferably sampled on MCE filters. The values in Tables 3 and 4 were determined using several different ICP-AES instruments and also several different microwave ovens. All were operated according to the manufacturer’s instructions. REFERENCES: [1]	 ACGIH [2013]. TLVs and BEIs based on the documentation of the Threshold Limit Values for chemical substances and physical agents and Biological Exposure Indices. Cincinnati, Ohio: American Conference of Governmental Industrial Hygienists. [www.acgih.org]. [Data accessed April 2014.] [2]	 Institut fur Arbeitsschutz der Deutschen Gesetzlichen Unfallversicherung [2013]. GESTIS database on hazardous substances (German Social Accident Insurance). Sankt Augustin, FRG: [http://www. dguv.de/ifa/Gefahrstoffdatenbanken/GESTIS-Stoffdatenbank/index-2.jsp]. [Data accessed April 2014.] [3]	 Hull, RD [1981]. Multi-element analysis of industrial hygiene samples, NIOSH internal report presented at the American Industrial Hygiene Conference, Portland, Oregon, May. [4]	 NIOSH [1994]. Elements: Method 7300 (Supplement Issued 3/15/2003). In: Schlecht PC, O’Connor PF, eds. NIOSH Manual of analytical methods, 4th ed. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS Publication No. 94-113 [www.cdc.gov/niosh/nmam/]. [5]	 Harrison, GR [1969]. Massachusetts Institute of Technology wavelength tables, 2nd ed. West Hanover, MA: Halliday Lithograph, Volume 1. [6]	 ASTM International [2010]. ASTM D7035, Standard test method for the determination of metals and metalloids in airborne particulate matter by inductively coupled plasma atomic emission spectrometry. West Conshohocken, PA: ASTM International [www.astm.org]. [7]	 NIOSH [1994]. NIOSH manual of analytical methods (NMAM). 4th ed. Schlecht PC, O’Connor PF, eds. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 94-113 [www.cdc.gov/niosh/nmam/]. NIOSH Manual of Analytical Methods (NMAM), Fifth Edition