modern analytical techniques Flashcards
what occurs in a mass spectrometer
sample introduced to spectrometer
low M weight samples vaporise in the vacuum of by heating
ionisation
ions are accelerated in an electric field so they have similar kinetic energy
by varying the magnetic field all ions are focused into detector
the ions are detected and the mass spectrum is plotted
what is the largest m/z value peak (furthest to the right) from
the parent ion
what is fragmentation
molecules may split into fragments when bombarded with fast moving electrons
only charges fragments are detected
what is the most abundant peak called
the base peak
what does high resolution mass spectroscopy do
measure the m/z values to enough accuracy to find the molecular formula
how does infrared spectroscopy work
all bonds vibrate at a characteristic frequency
frequency depends on mass of atoms in the bond,bond strength and type of vibration
frequencies are in the infra-red region of the electromagnetic spectrum
if infra-red light passed through compound, will absorb all or some of light at the frequency it’s bonds vibrate
what is IR light measured in
wave numbers (1/frequency) in cm
what is liquid or column chromatography used for
separating large quantities of soluble substances
what is the stationary phase of liquid chromatography
powder (silicon dioxide)
what is the mobile phase of liquid chromatography
liquid solvent
how does liquid chromatography work
mixture dissolved in solvent and placed at top of column
as solvent moves down through powder in column, substances in mixture move down the column at different rates
allows them to be collected separately
what does time taken to move down column (in liquid chromatography) depend on
balance between solubility of each substance in the mobile phase
and it’s retention in the stationary phase
HPLC high performance liquid chromatography advantages
use of fine particles increases surface area of stationary phase which results in greater separation
uses a pump to force mobile phase through column and provides higher resolution and faster analysis time
can be done at room temp- can be used to separate mixtures that would decompose on heating
how does HPLC work
eluent passes through a detector
(UV absorption is usually monitored)
detector indicates the presence of the substance of interest but cannot determine the concentration
what did early normal phase HPLC instruments use (and effect)
polar stationary phase
non polar solvent
more polar molecules absorbed more strongly to stationary phase
and take longer to appear in the eluent
