If samples decompose above their boiling points, which following is a good choic
ID: 524815 • Letter: I
Question
If samples decompose above their boiling points, which following is a good choice for sample injection of the in GC? (a) split injection: (b) splitless injection; (c) on-column injection; (d) flow injection Which of the following CE techniques is the simplest format for separating of charged molecules? (a) capillary zone electrophoresis (CZE) (b) micellar electrokinetic chromatography (MEKC); (c) capillary electrochromatography; (d) capillary gel electrophoresis A mixture of A*, A^2+, A^-, and A^2-was separated by using capillary zone electrophoresis at pH 9.0 in a bare silica capillary. Which one arrived at the UV absorption detector last? (a) A^+ (b) A^2+ (c) A^- (d) A^2- Capillary electrophoresis could produce greatly improved separation efficiency over HPLC because of the following factors except...: (a) Multiple path term is eliminated by the open tubular capillary; (b) Mass transfer term is eliminated because there is no phase; (c) Small capillary diameters can improve separation efficiency; (d) Electroosmotic flow produces clear-cut flow front instead of the bullet-like pressure driven flow in HPLC.Explanation / Answer
7)C)on-column injection
On-column injection technique is best suited for liquids and gases having both low as well as high boiling analytes,as the sample in this technique is delivered right over the heating space in the column ,so that no boiling point discrimination occurs and the sample is completely volatilized at one go.There is no room for sample evaporation or decomposition of low boiling analytes as the temperature is below the boiling point of the solvent.
in split injection ,only trace of the sample is introduced into the column as major part of it escapes through the split vent.This injection is useful if a concentrated sample is introduced ,so tht additional analytes are removed and a clear baseline separation appears for the analyte and the column is not overloaded when active chromatographic sites are completely filled by the analyte
Splitless injection is suitable for trace analysis when the sample has analyte is in low amounts(close to the detection limit of the GC)
flow injection is used for automated GC sample analysis using a system in which the different analytes(multiple) are introduced into liquid stream of solvent in regular time intervals to reach the detector and get analysed.
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