CHEM 209 Quiz 3 Latest Update with Verified Solutions

CHEM 209 Quiz 3 Latest Update with Verified Solutions Provide a diagram illustrating the key components of a GC instrument. Answer: Reservoir for Mobile Phase (pressurized helium cylinder) - Oven - Sample Injector (micro-syringe) - Stationary Phase (column) - Detector (thermal conductor or flame ionization detector) - Readout (computer) What variables are typically plotted on the x- and y- axes of (a) a chromatogram and (b) a calibration curve? a. x: time, y: detector signal b. x: concentration, y: peak area Define the following terms in chromatography: a. stationary phase b. mobile phase c. partition coefficient (formula) d. retention time a. Material coating the column, can be solid or liquid 2 b. Substance moving analyte through the column c. [A]stationary / [A]mobile d. Time for a compound to appear as a peak In general, how would you identify which peak in a chromatogram of mouthwash corresponds to ethanol? Is this method infallible? How do you quantify ethanol content? Compare peaks by running ethanol alone. Not completely reliable. Quantify ethanol by measuring the peak area. Typically, does increasing the operating temperature lengthen or shorten a peak's retention time? Why? Shortens; molecules move faster through the mobile phase. Usually, does increasing the mobile phase flow rate extend or shorten a peak's retention time? Why? Shortens; higher flow rate accelerates column passage. If you need to expedite a chromatogram, suggest three specific GC adjustments you could make. 1. Reduce column length 3 2. Elevate column temperature 3. Boost flow velocity/rate