Round-robin coal sample

The overall mercury recovery in the process is 67 15%. The precision of the method is about 20%, and the detection limit is about 0.01 ppm mercury for a 1-g sample of coal. Reliability of the method was determined by the accurate analysis of two coal samples used in the Bureau of Mines study of the problems involved in determining mercury in coal (9) and then by the agreement within experimental error of the results from the 11 Bureau of Mines round-robin coal samples and their probable mercury contents (4). 

Table X. Precision on NBS—EPA Round-Robin Coal Sample...

Radiochemical yields are quantitative. The relative standard deviation of a measurement is usually better than 10%. Analysis of SRM 1630 gave 2.0 =b 0.13 ppm selenium, and results for the NBS-EPA round-robin coal and fly ash samples agreed within experimental error with the probable certified values of selenium in those samples. The selenium concentrations of 101 coals analyzed by the above method range from 0.45 to 7.7 ppm and have a median value of 1.9 ppm (16). 

The flameless atomic absorption method has a reproducibility of about 2% or better for homogeneous specimens. Checks (3) between AA and NAA (with radiochemical separation after irradiation) and isotope dilution spark source mass spectroscopy on thoroughly homogenized tuna fish and Bureau of Mines round-robin coal specimens indicate good agreement between the methods. (0.425 0.9%, 0.45 3.5%, and 0.45 4.4% for tuna by AA, NAA, and SSMS, respectively, and 1.004 is the average ratio of NAA to AA results for five coal samples.) The similar results indicate that the technique used in sample preparation... 

In the round-robin analysis, a minimum of five samples each of coal, fly ash, gasoline, and fuel oil were analyzed. The NBS Probable Certified Value for certain elements are shown in Table IX along with PBR values. Since no data were reported on gasoline, there are no comparisons. The most inconsistent comparison was for mercury. Only four laboratories reported mercury by INAA in coal, three by INAA in fly ash, and two by INAA for fuel oil. Most other laboratory results reported were based on atomic absorption spectrometry. With one exception, all mercury values reported by INAA (a nondestructive method) were higher than... 

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