How can the General Elution Problem by fixed? 1.Temperature programming in GC 2.Solvent programming in LC 3.Density programming in SFC

Determination of Appropriate Method N =

Resolution How many theoretical plates are necessary to resolve 2 PCBs with retention times of and minute? Void time is 2 minutes. Resolve at a resolution of 1.0.

Practical: How can you increase resolution? Increase N by reduction in H or increase in L Which is preferable? How is this done?

Practical: How can you increase resolution? What else? A. changes in mobile phase composition including changes in pH B. Column temperature changes C. Stationary phase changes D. Special chemical effects

Internal Standards Vital in GC Why? 1. When choosing an appropriate internal standard, choose one that behave similarly to the analytes you want to quantitate a. comes of the column near the same time as analyte b. similar chemical properties

Internal standards 2. Analysis involving multiple quantitations, multiple internal standards are advisable 3. Relative response ratio between known quantity of standard & known quantity of analyte should be determined daily

Example: The amount of diphenyl (DP) in a sample was to be measured. Phenyl ether (PE) was chosen as the internal standard. In a preliminary experiment, a solution containing mM DP And mM PE gave peaks of 423 for DP and 347 for PE. To analyze the unknown, 10.0mL of 0.146mM PE was added to 10.0mL of the unknown containing only DP. The mixture was diluted to 25mL in a vol. flask. This gave the chromatogram above. The area of the DP peak is 553 and the area of the PE peak is 582. Find the concentration of DP in the unknown.