Question

4. A unknown soil sample was analyzed for arsenic. Determine the % As in the samples with the information listed below. Mass Beaker (8) Mass Beaker + Sample (8) Mass of Sample (6) Peak Intensity 49.0696 49.3149 16534 105.0982 105.3374 15546 107.0344 107.3002 19894 A sample of soil was masses and heated in the presence of 50 mL of 6 M HNO). The sample was then filtered and diluted to 100 ml. The calibration curve for the ICP analysis was prepared and the data is below. (As) (ppm) 0.112 0.0566 0.0257 0.0125 Peak Intensity 128902 53856 14670 189 Determine the % As in the soil sample with the Average and Standard deviation.

Answer 1

Based on the data given for standard,

Standard	As(ppm)	Peak intensity
1	0.112	128902
2	0.0566	53856
3	0.0257	14670
4	0.0125	189

The following calibration graph can be obtained.

140000 120000 Peak Intensity = 1,078,503.47* As R? = 0.95 100000 80000 Peak Intensity 60000 Series1 - Linear (Series1) 40000 20000 0.02 0.04 0.06 0.08 0.1 0.12 As, ppm

We can see that

Peak intensity = 1078503.47 * As

Therefore from the data of the soil sample we find,

Mass of Beaker + Sample (g)	Mass of Sample (g)	Peak intensity	As, ppm
49.3149	0.2453	16534	0.015331
105.3374	0.2392	15546	0.014414
107.3002	0.2658	19894	0.018446
		average	0.016064
		stdev	0.002113

Thus the average value of As in soil sample = 0.016064 ppm

The standard deviation for the soil sample = 0.002113 ppm