Two liquid samples containing the iodide ion in an unknown concentration were an

Question

Two liquid samples containing the iodide ion in an unknown concentration were analyzed by mass spectrometry. The analytical signal, measured as the integrated iodide ion current of both samples, a method blank, and a standard known to be 500 ppm are provided below.

What is the sensitivity to the iodide ion for this instrument? I believe the answer is supposed to be 297 uA/ppb.

What is the limit of detection of Iodide for this method?

a) 10 ppm b) 500 ppm c) 25 ppm d) 7 ppm e) no limit

Are the standard deviations of the standard and Sample 1 significantly different at the 95% confidence level?

a) yes b) no c) unable to determine

Explanation / Answer

The sensitivity to the iodide ion can be found using the data for the standard, which is 500ppm. The mean analytical signal is 149.940uA for the standard. So, the sensitivity is : (149.940/500)uA/ppm = 299.88 uA/ppb.

There is no limit to the detection of Iodide for this method. It will all depend on the current sensor being used. If the current sensor can detect currents of the order of 100uA, then we can measure the iodide concentration in ppb also. (This can be seen in the answer of first part)

No, the standard deviations of the standard and Sample 1 don't differ much at 95% confidence level. This is so because the number of samples is the same, i.e. 5. So, the 95% confidence interval will be of the same width for both the cases.

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