This is analytical chemistry assignment questions: this is the whole complete qu

Question

This is analytical chemistry assignment questions: this is the whole complete questions, no other information given.

1. For each of the following, suggest one or more experimental conditions that might be changed to improve the gas chromatographic separation a) Retention times of 9.2, 10.3 and 12.5 min are obtained for the sample constituents on a 1 meter column, operated at 120°C. The peaks are rather broad. (4m) b) On a column containing Carbowax-600 as stationary phase, sample constituents A and B are nicely separated but resolution of constituents C and D is very poor. Doubling the length of the column improves the resolution of C and D only slightly. (2m) c) On a column packed with OV-1 on Chromosorb-W at 80°C, the following retention times are noted for sample constituents: 2.1, 2.3, 3.4, 7.8, 10.7 and 13.5 min. The later peaks are so broad that quantitative determination is difficult. (4m) 2. Consult recent scientific journals and find one paper dealing with the column-chromatographic separation of each of the following: a) drugs or drug metabolites b) steroids c) metal-ion complexes d) pesticides e) vitamins or sugars Give complete journal reference and outline the conditions for the separation. (30m)

Explanation / Answer

1. a) As we can see that retention times for the constituents of the sample are quite close and peaks are broad therefore these following changes should be made for better resolution-

(i) Both decrease in tube diameter and increase in tube length improves reolution

(ii) Increase in temperature produces better resolution of peaks

(iii) Increase in stationary phase thickness also increases resolution

  

     b) As resolution of C and D are poor so these two constituents are definitely non-polar (carbowax-600 is a strongly polar stationary phase). Hence for effective resolution of C and D, non-polar stationary phase (like polysiloxane ) should be used.

     c) Here two improvements can be done-

      (i)As the latter peaks are broad as well as possessing higher retention time therefore the resolution of these peaks can be improved by using small and uniform particle size in stationary phase.

      (ii) Increase in temperature also increases resolution

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