Validation of liquid chromatography mass spectrometry (LC-MS) methods

Self test 4.4B

You are validating a method of analysis of Glyphosate in surface water. Using data from analyzing your control sample, evaluate intermediate precision.

Date	C (μg/L)	Chemist
16.06.15	0.20	Ramon
17.06.15	0.21	Ramon
25.08.15	0.15	Ramon
25.08.15	0.18	Ramon
26.08.15	0.19	Ramon
31.08.15	0.20	Ramon
31.08.15	0.17	Ramon
3.09.15	0.18	Ramon
7.09.15	0.18	Ramon
14.09.15	0.19	Ramon
25.09.15	0.14	Susan
12.10.15	0.17	Ramon
27.10.15	0.13	Susan
17.12.15	0.15	Susan
22.02.16	0.13	Susan
29.02.16	0.15	Susan
11.04.16	0.13	Susan

1. Is it important to know the exact concentration of Glyphosate in the sample?

Yes

2. What is the relative intermediate precision of the method (in %)? Please give the answer with 2 significant digits.

3. What could be the reasons for observing decreasing Glyphosate concentration in the control chart (check all that apply)?

Loss of instrument sensitivity

Glyphosate is degrading in your control sample

Difference between the chemists doing the analysis