17.7 Flashcards
what is qualitative analysis
purpose is to find out which elements are present in a compound
what is quantitative analysis
purpose is to find the percentage composition by mass of a compound
what is combustion analysis
a known mass of the compound are burned and the mass of CO2 and O2 formed are measured by measuring the increase in the mass of the U-tubes containing absorbers
what is high resolution mass spectrometry
a value for a relative molecular mass accurate for 4 or more decimal places
what are the limitations of using high resolution mass spec to determined a compound
the compounds may have the same high resolution mass spec such as propanone and propanal
what does Rf stand for
retention factor
what are the key feature of high performance liquid chromatography (HPLC)
- sample is injected into column
- solvent is forced through a metal tube under high pressure
- particle size of stationary phase is very small which leads to better separation of the components
- components are detected by their absorbance of uv radiation
- it is automated and computerized
- obtains retention time for the component
what is retention time
the time taken for the injection of the sample to be detected
what factors effect retention time
nature of the solvent
pressure used
temperature inside the column
what are the key features of gas chromatography (GC)
- sample is injected in
- the metal tube is several meters long and is coiled up
- the stationary phase is a solid or liquid coat on the inside of the tube
- the mobile phase is an inert gas
- it is automated and computerized
summarize how gas chromatography (GC) works
a sample is injected and the components vaporize and move through the coiled tube with the carrier gas at different speeds depending on how strongly they are attracted to the stationary phase
weaker attractions = move quickly = shorter retention times
what are the limitations of GC and HPLC
only good for small quantities of components
not very good at identifying components as it is difficult to control variables
data must be compared to a data base which may be limited
what areas is GC and HPLC useful
forensic science
drug and explosive detection
analysis of pollutants
space probes
define NMR
nuclear magnetic resonance spectrum - a technique used to find the structures of organic compounds dependent on the ability of nuclei to resonate in a magnetic field
what is chemical shift of a proton
a number that indicates its behaviour in a magnetic field relative to tertamethylsilane
