Problem Set 4: Standard Addition and Internal Standards

1. The US Department of Defense is in the process of disposing of all VX nerve agent chemical warfare stocks to meet Chemical Disarmament Treaty requirements. Chemical neutralization and incineration are the technologies being used for disposal. Prior to operations, one of the on-site laboratories had developed and validated standard addition methodology to verify the effectiveness of the neutralization process in destroying VX. Samples from a recent VX neutralization process batch were sent to the chemical plant’s on-site lab for standard addition analysis. The following data were obtained:

VX Spike (pg/ml)	VX Peak Area
0	7,989
5	8,952
10	20,885
15	22,318
20	28,068
30	46,734

Determine the amount of remaining VX in the chemically neutralized batch, in units of ppb (pg/ml). Make a plot of the data and the standard addition curve. Clearly show your work.

2. The laboratory also has developed an internal standard method to determine the amount of VX in plant samples. Listed below are the calibration data for this method using the same amount of internal standard in each of the calibration samples analyzed:

VX Spike (pg/ml)	IS Peak Area	VX Peak Area
0	28,028	1,170
5	29,149	3,888
10	28,449	10,732
15	29,412	16,589
20	28,972	21,049
30	29,186	33,457

The lab then used this internal standard calibration data to analyze a plant sample prepared with the same amount of added internal standard. The analysis of this plant sample yielded a VX peak area of 25,345 and an internal standard peak area of 28,523.

Set up an internal standard calibration curve, plot it, show all regression calculations, and determine the amount of VX in the plant sample.