Answer following 5 questions, will rate
Check the required figure of merits, and state, in each case, if GC-MS with auto- sampler is suitable (can be used) or not suitable (limitations of the instrument). 1 v It is desired to do unattended instrumental analysis. Size of the analyte is around 3000 Da Analysis of trace constituents in a sample (in ppm or even ppb) is desired Volatile compound that does not degrade at high temperatures 1. GC-MS is suitable 2. GC is not suitable Interested to use it as a 2. GC is not suitable Interested to use it as a hand-held instrument To purify monoclonial antibodies (mAb) Looking for high throughput analysis (100 samples per hour) To characterize (identify) small molecules (less than 500 Da) GC-FID system having 10% Trifluoropropyl methyl di-methyl-polysiloxane as a stationary phase is used to separate components of a sample having 100 ppm decane and 100 ppm hexanol in acetone. At initial settings, decane is coming out at 4 mins (completely separated from acetone) and hexanol at 20 mins. The disadvantage of this run is that it is too long. Select all applicable suggestions that can reduce the retention time of hexanol. (Note: Trifluoropropyl forms hydrogen bonding with hexanol acting as hydrogen bond acceptor) Derivatize hexanol, using esterification reaction with acetic acid, to form hexyl acetate Reduce the length of the column Reduce the flow rate of the mobile phase Increase the split ratio Use oven program to increase the temperature after 4 mins into the run Use oven program to reduce the temperature after 4 mins into the run Replace stationary phase with another having a lower percentage of Trifluoropropyl groups Replace stationary phase with another having a higher percentage of Trifluoropropyl groups Change the solvent from acetone to hexane Increase the flow rate of the mobile phase Select the statements that are true about sample introduction in GC: Split inlets are useful to allow a percentage of the injection to go to the column. Specifically useful for concentrated sample (in which the analyte constitutes more than 0.1% of the sample). Cold needle, having cone shape, technique is the main method used by GC autosamplers Septum is a rubber composite disk used to isolate the inlet from atmospheric pressure. Liquid samples are injected into a glass liner in a heated inlet. Split line in GC inlets is used to clean any septum debris generated. Hot needle technique is the most precise and accurate method in GC manual injection. Liquid samples are injected into a metallic heated inlet that is connected directly to the column. Sandwich technique is the most precise and accurate method in GC manual injection. Select all statements that are true about GC delivery system: The common concern among all gas cylinders is that they contain gas under pressure and poses physical hazard Always chain or strap cylinders to stationary objects or wall whether in-use or in-storage. When moving gas cylinders, gas regulator should be kept installed at all times. Helium, usually used as carrier gas in GC analysis, is a flammable and toxic gas. Gas tanks should be completely emptied and only replaced when they hit 0 psi mark. Regulators reduce the gas cylinder pressure to line pressure (60 - 100 psi), and then EPC system is used to reduce the pressure according to set parameters. Select all the statements that are correct about GC and LC detectors: GC instrument is connected to an MS system through a heated transfer line to direct the eluates into the ion source. Mass spectrometer is the detector that can generate both a chromatogram (relationship between counts and time), and mass spectrum (relationship between % abundance and mass to charge ration) Mass spectrometer (MS) can be coupled to both LC or GC system. FID detector works at room temperature, but it requires high purity filtered Helium gas, hydrogen gas and compressed air, FID and MS are considered to be destructive and mass flow type of detectors. Mass spectrometer works under atmospheric pressure and is not effected by air leaks or water leaks. Refractive index detector is considered to be selective and has very low detection limits (LOD). Mostly used for ultra-trace analysis. Detectors do not play role in the figure or merits of an instrument
