Chromatography : HPLC method is used to separate and identify pesticide residues

Question

Chromatography: HPLC method is used to separate and identify pesticide residues from a soil sample. The stationary phase is a non-polar coating on inert support beads. The mobile phase is a polar mixture of water and alcohol. Answer the questions with reference to the chromatogram shown.

a) Which pesticide is most polar? ____________ Which pesticide is least polar?____________

(b) Calculate the capacity factor for each pesticide. (all three)

(c) Calculate N for methyl parathion, peak A.

(d) Calculate H for the methyl parathion peak, if the HPLC column is 15 cm long.

Explanation / Answer

For the given chromatogram,

a) The most polar pesitcide would be A : methyl parathion. The lest polar pesticide would be C : Diazinon.

b) Capacity factor for,

A : 9.75 - 3.55/3.55 = 1.75

B = 14.8 - 3.55/3.55 = 3.17

C = 16.4 - 3.55/3.55 = 3.62

c) N for methyl parathion, peak A = 16 x (9.75/2.75)^2 = 201

d) N for methyl parathion peak, = 16 x 15 = 240

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