Question

5. A water sample is analyzed for chloroform by using a purge and trap system. A 5-ml water sample is purged for 10 min. with nitrogen. The trap is dried for a minute, then the trap is heated and the chloroform is desorbed into the GC column. The chloroform peak area from the sample is 23,823. A 10 ul injection of a 20 ug/ml chloroform standard in methanol gives a peak area of 44,523. What is the concentration of the chloroform in the water in ug/l?

Answer 1

First, we have to calculate the response of CHCl3 on chromatogram = area/mass

given that 10 ul 20 ug/mL solution gave an area of 44523

10 ul solution contains = 20 microgram * 10* 10^-3 = 0.2 microgram chloroform'

(Note: 1 uL= 0.001 mL )

Response factor for chloroform = 44523/0.2 = 222615 unit/microgram

The area obtaines for chloroform from water = 23823

the amount of CHCl3 in 5 mL water = 23823/222615 =0.107 microgram

or if we want to convert to ug/L = (0.107/5) *1000 = 21.4 ug/L

answered by: anonymous