Atomic spectroscopy Flashcards
what is sample extraction technology
- seperation of the metals for analysis from other components of urine
- eg. solid phase extraction
- analyte is retained or eluted selectively
what are the main contents of urine
water, urea, chloride, electrolytes, creatinine, uric acid, salts/ions, ammonia
what materials are used in solid phase extraction
- silica/alumina
- porous plastics and polymers
- ionic resins
what is Beers law and calibration used for
used ubiquitously in quality control
what is standard addition used for
- used as a counter to matrix effects (often seen in complex samples)
- sample +1 or multiple aliquots (set added volume) of a standard included
what is internal standard spiking used for
- used as a counter to sampling inconsistency (eg using Lvov platform)
- add known quantity of similar analyte (eg methanol/ethanol)
describe the applications of calibration
used in cases of:
- response variation
- difficulty in conditions reproduction (eg. urine compositional differences)
- quality control and quality assurance
what is the theory of atomic absorption and emission spectroscopy
- non bonded electronic excitation
- principal of measurement
- characteristic spectral lines
- emission and absorption
what are the methods of atomic absorption and emission spectroscopy
- atomic absorption spectroscopy
- atomic emission spectroscopy
- flame photometry
what are the properties of an atom defined by
Defined by associated electrons
- these are promoted or demoted depending on absorption or emission of energy
what is atomic emission
- state of an atom defined by 4 quantum numbers
- principal (n), state (l), magnetic (m), spin (s) - characteristic emission spectra (radiation)- composed of lines
- line is 0.005nm - line spectrum of atom- series related to occupancy of specific energy states by electrons
- this can be demonstrated in an electron energy level diagram
what are spectral lines due to
due to difference between electron energy states
what is emitted radiation
specific l^ light generated by outer electrons on fall from various elevated excited states, called resonance lines
what is a photon
a particle (quantum) of energy - wavelength defines that energy
what can electrons do in relation to photons
electrons can absorb or give out photons
- principle of flame photometry
- principle of atomic absorption
describe atomic emission spectroscopy
- flame atomic emission spectrometry
- Kirchhoff and bunsen initiators
MX (s) –> MX(g) –> M(g) + X (g)
nebulise –> vaporise –> dissociate
- resonance of light emitted - emission line= emission resonance line
what are the requirements of an atomic emission spectrometer
- small uniform sized droplets <20um
- constant feed rate
- clean samples
what other emission techniques could be used
plasma (Ar) excitation up to 8000K
- inductively high frequency coupled
- direct current
what chemical processes take place in a flame
- evaporation of solid particles in flame
2. gaseous phase equilibrium
what are the 2 types of plasma emission spectroscopy
- inductively coupled plasma unit
2. direct current plasma unit
describe what atomic absorption spectroscopy and flame atomic emission spectroscopy are used for
- very specific technique
- electronic excitation of volatilised dissociated atoms
- excitation achieved: electric glow discharge of hollow cathode lamp
- sample specific cathode element
give 2 examples of radiation sources
- hollow cathode lamp
2. electrode less lamp
what 2 factors does the Beer-lambert law look at
absorbance and increasing concentration
how does absorption occur in FAAS
- polychromatic light is little use
- specificity achieved via monochromatic light
- the flame is the absorption cell
how does an FAA spectrometer work
- monochromator/filter/grating selection varies by 1nm
2. detector only sees wavelength of interest
what is the difference between atomic emission spectroscopy and atomic absorption spectroscopy
- atomic emission spectroscopy- a quantity of light is given out by the atom
- atomic absorption spectroscopy- a quantity of light is taken in by the atom
give examples of atomic emission spectroscopy
flame photometry or plasma emission spectroscopy
give examples of atomic absorption spectroscopy
FAAS, AAS
which metals is flame photometry used for
used for Li, Na, K, Ca
describe an alternative to flame (FAAS) method
graphite furnace
- Lvov platform: a shelf inside the graphite tube
give examples of specialised atomisation
- glow discharge- solids
- sputtering M(s) by Ar+(g) - hydride atomisation- metalloids (As, Bi, Se)
- gas + sample/NaBH4 –> burner tube - cold vapour
- eg. Hg –> Hg(g)
what are rich and lean gas mixtures
fuel to oxidant ratios used to alter the ideal burn zone in the flame
how is light used as energy
if a body gives off light of flux, Q, then its mass diminishes as Q/c^2
E= mc^2
describe how the light signal from the D2 lamp works
- spinning chopper blocks and permits additional D2 lamp signal
- intermittent signal compensate for HCL fluctuations
what does the flame produce
the flame contains and produces colour absorbing species
- eg. lithium is pink
what is the continuum source correction
absorbance of materials in the flame which are energised by the deuterium lamp generate a signal
- this background can then be removed electronically
what are spectral interferences
- overlap of emission and absorption lines (broad and narrow)
- combustion products
- simple matrix
- Ti, Zr, W, V, Mo, and b- form refractory oxides
- reversible reactions in the flame (poly atoms)
what is the background of AES and AAS interference
- flame: emission/absorption
- other elements, molecules, polyatoms
what is the ionisation of AES and AAS interference
-ions don’t work well, need single atoms
M+ + e–> M
- suppression by using an electron liberator
what is the matrix of AES and AAS interference
- viscometric
- salt effect
- sequestration (eg. EDTA)
what is optimal flame performance
- use pure nitric acid for digestion because they are quite soluble and are a good oxidising agent so will degenerate any organic material into water and various salts and co2
- all organic tissue that might act as contaminants/interferences will get degenerated into inorganic material
- produces a nitrate salt of the metal which is water soluble and oxidises organic material present to reduce matrix effects normally seen
give examples of common chemical interference agents
oxides, silicates, aluminates, complex salts
what is the role of AES and AAS interferences
- block light from passing through onto a detector
- but the detector measures whether light is scattered away from the linear line that would normally hit the detector
- means that it measures the scattering of light
- more scattered it is, the more absorption there is, and the more absorption there is, the more interfering agents there are between the light and detector
what would be useful to combat AES and AAS interferences
deuterium lamp- shines directly onto the detector in a straight line, and when it gets blocked, the detector sees the difference between the 2 lights
how can interference be reduced
- elevation of burner temperature
- use preferential flame reaction binding
- stable chelated ions
- reducing environmental flame
what is a preferential binding reaction
to avoid aluminium or silicon binding with strontium, can add a preferential binding agent such as lanthanum
what are the advantages of microwave plasma atomic emission spectroscopy
- can be left unattended- no flames/expensive gas supply and handling of dangerous gas cylinders
- dramatically reduces operating cost
- superior detection limits and larger linear dynamic range compared to flame AA
- can set the detector to look for a specific wavelength of light and therefore the amount of light is related to the amount of ions and atoms of that species within the sample
what is atomic spectroscopy quality control
- metal salts of drugs (Ca, Mg, Fe)
- highly toxic metals in consumed matter
- metal catalysts of oxidative changes
- metals used for pigments in pharmaceutical products
- electrolytes, kidney function tests
give examples of radioisotope metals
Cr^51, Co^60
- many radoopharmaceuticals used in pharmacy
what is ICH atomic spectroscopy for pharmaceutical analysis
- impurities profile studied for potential impurities
- degraded product according to ICH guidelines using analytical methods
- estimation of trace level heavy metals by AAS
- common metallic drugs
- Au, Ag, Cu phosphines for cancer
- barium sulphate, lithium carbonate
- ferroquine- anti malarials
give examples of other forms of atomic spectroscopy
- mass spectrometry
- x ray fluorescent spectrometry
- use with almost all elements but very costly
- often uses copper as a source of x rays
