XRF and ICP-MS

What does XRF stand for?

X-ray fluorescence

General overview of how XRF work?

the substance is bombarded with x-rays which knock out the core electrons, causing valence electrons to fall down and refill the core shells, emitting xray fluoresence in the process, this fluorescence is expressed in a spectra which can be used to identify which elements are present in a sample

How is the XRF labeled?

By the vacancy in the core shell(s) that is being filled

list the shells in order from closest to the nucleus to furthest

K, L, M

general form labeling XRF photons

K/L/M with a greek letter (alpha, beta, gamma) as the subscript

How to know which letter is the one in the label?

It is the letter that corresponds to the energy shell that the valence electron is falling to/ending up

How to know which greek letter is the one in the label?

alpha means valence electron is falling from the level above, beta means falling from two levels above, gamma means falling from 3 levels above

which XRFs photons are unique to elements?

all of them

What is the x-axis of the spectra? for XRF

delta E (e- volts)

What do the height of peaks in the spectrum correspond to?

How much of that photon is emitted (higher peak means more of that photon is being emitted)

Why do K jumps have higher energy?

Since the K shell is closest to the nucleus it takes a large amount of E to eject its electrons

order of schematic for XRF

xray tube, sample, core electrons are knocked out, cascade of downward electrons (Letter/greek letter) to fluorescence

What does ICP-MS stand for?

Inductively-coupled plasma mass spectrometry (NOT SPECTROSCOPY)

What does ICP-MS do?

Determines concentration of trace elements and their isotopes

What is the LOD for ICP-MS?

low ppt to ppm

Order of schematic for ICPMS

sample, pump, nebulizer, spray chamber, plasma torch, collision cell to MS

What is an OES

a typical optical (light) detector

What does mass spec do?

separates ions by mass and charge ratio (m/z), gives a spectra of peaks where each one represents an element and its specifc isotope

What is needed in the mass spec to separate for mass and charge?

A pole system (we have a quadrupole system)

What is plasma

the fourth state of matter, a gas of charged particles (ions) which are generated by ionization

How does a plasma torch work?

Ar is put into the flame and when a radio frequency is passed thru the coil a current is induced by stripping e- away from Ar making it Ar+ (ionization), the Ar+ and e- collide with Ar to make more Ar+ (charged gas, making more plasma), the sample and more Ar+ are fed through the base of the flame ensuring it reaches the hottest part

What is the role of Ar in a Ar plasma torch?

a carrier (Ar+ is put in with the sample) and used to create the flame (put in as Ar which is then ionized by the radio frequency).

What happens in the collision cell in an ICP-MS system?

It is a pressurized quadrupole that removes spectral interferences from compounds that share the same m/z ratio as the analyte

Difference btw UV-Vis and XRF

UVvis deals with valence electrons, XRF deals with core electrons, XRF is better for elemental composition analysis

How does ICP-MS measure trace and ultratrace elements?

by ionizing samples in argon plasma and detecting the ions by m/z ratio

Is ICP-MS more frequently used to analyze liquid or solid samples?

liquid

What does the high temp of the plasma cause?

the atoms in the sample to be ionized (thermal energy is high enough to strip valence electrons)

What separates the ions by the m/z ratio?

the mass analyzer

What must you have to determine elemental concentration from ICP-MS data?

Standards

When does spectral interference arise in ICP-MS systems?

when non-analyte ions produce signals at the analyte mass

Which is better for higher concentration samples and routine elemental screening?

ICP-OES

Biggest energy gap is between which two energy levels?

Between k and L

Why is do you get the same XRF spectra from an isolated element vs that element in a compound with another element?

Because the electrons involved in giving off the XRF take no part in bonding