Midterm II CHEM 4251. Explain why the gas-solid chromatography is not used for the analysis of moderate-molecular weight polar molecules such as methanol, ethanol, and propanol. 5pt2. Polyethylene glycol (PEG) is one of the popular liquid stationary phases for GC column. 5pt (2pt for (a) and 3pt for (b))(a) Draw its chemical structure.(b) Generally PEG stationary phase is good for the separation of (polar, nonpolar) analyte. Pick one. 3. Assume that you use a very nonpolar stationary phase in GC. Please rank elution time from the shortest to the longest for the following three analyte species. (3pt)Isopropanol, Methanol, MethylbenzoateShortest:_______________, Middle:________________, Longest:________________4. Choose one of three detectors: flame ionization detector (FID), thermal conductivity detector (TCD), electron capture detector (ECD) 15pt (3pt each)(a) most insensitive detector in general(b) good for hydrocarbon analysis of petroleum (c) smallest dynamic range(d) not sensitive to H2O, CO2, SO2(e) most sensitive to polychlorinated biphenyls5. Use the retention data given below to calculate the retention index of 1-hexene. 10ptShow your work.Sample Retention time (min)Air 0.5n-pentain 2.5n-hexane 5.01-hexene 3.56. Ions in a bare silica capillary move as a result of electrophoretic migration and electroosmotic flow (EOF). True or False? 18pt(a) Electric field across the capillary affects the electrophoretic migration but does not affect electroosmotic flow. (b) Charge of analyte ions affects more the electroosmotic flow than electrophoretic migration.(c) Ionic strength of solution affects both the electrophoretic migration and electroosmotic flow.(d) Electrophoretic migration of analyte molecule is dependent on the molecular weight but not dependent on the shape of the analyte molecule.(e) The inner surface of the bare silica capillary has a negative surface charge at pH 7.(f) EOF can be shut down by removing the inner surface charge of the capillary with a certain surface chemical modification.7. In capillary zone electrophoresis with an unmodified silica capillary at pH 7, the correct elution order (fastest first, slowest last) for the Ca2+ (A), acetone (B), Cl- (C), SO42- (D), and Na+ (E) is: 5pta. A, E, B, D, C,b. A, E, B, C, Dc. D, C, A, E, Bd. D, C, B, E, Ae. None of the above8. In capillary zone electrophoresis (CZE) for the separation of anionic analytes, you would want to have (positive, negative) charges on the inner wall surface of capillary in order to have the same EOF (electroosmotic flow) direction with the electrophoretic movement direction of anionic analytes. Pick one. 5pt9. A certain cation has an electrophoretic mobility (μe) of 4.31 x 10-4 cm2 s-1 V-1. This same ion has a diffusion coefficient of 9.8 x 10-6 cm2 s-1. This cation was separated by CZE in a 50.0-cm capillary at 10.0 kV. Under the separation conditions, the electroosmotic flow rate was 0.85 mm s-1 toward the cathode. If the detector were placed 40.0 cm from the injection end of the capillary, how long would it take in minutes for the analyte cation to reach the detector after the field is applied?Hint: Electrophoretic migration rate, ν = μeE (E:electric field). 13pt10. In mass spec there are a variety of ionization techniques. Let’s compare three of them:Electron impact ionization (EI), Electrospray (ESI), Fast atom bombardment (FAB) and MALDI. Check (x) one for (a), (b), (c), (d), (e), (f), and (g). 21pt (3pt each)11. Which ofthe following is not a variable to acquire massspectra (intensity vs.m/z) in the magnetic sector analyzer? 5pta. Magnetic fieldb. Ion acceleration potentialc. Radius of magnetic sectord. Diameter of metal analyzer tube12. When a magnetic sector analyzer was operated with a constant magnetic field, an accelerating voltage of 3000V was required to focus the CH4+ on the detector. What accelerating voltage would be required to focus a doubly charged ion with mass 500? 10ptCharacteristic EI ESI MALDI(a) Most compatiblewith HPLC(b) Most compatiblewith GC(c) Causes mostextensivefragmentation(d)Yields most multiplecharged ions of thesame mass butdifferent m/z(e) Causes leastfragmentation(f) best for the analysis ofindustrial polymers (g) best for the analysis ofthermally unstable biomolecules13. Calculate the ratio of the (M + 4)+ to M+ peak height for C3H7ClBr. Please consider only the isotope effect of Cl and Br. 35Cl : 37Cl = 100 : 32.5, 79Br : 81Br = 100 : 98(10pt)14. With TOF (time of flight) mass analyzer, the flight time of molecular ion, t is given by t =L√m2 zeV . When L (distance from source to detector) is 1 m and V (electric field pulse for ion acceleration) is 10 kV, which of the following is the most closely estimated flight time of a singly charged molecular ion (MW = 120,000)? 5pt(a) 1 μs (b) 100 μs (c) 10 ms (d) 1 s (e) 100