Omenetto Cume Flashcards

Question

Author proposes 2 ways to increases effiency of atomization what are they

Answer 1

1) understand every process and optimzie 2) Brute force - high enough temp so each sample 100% atomized 3) find a new high efficiency atomization which gentle action that can thoroughly atomize

Answer 2

_ HE IS ONLY FOCUSING ON THE INVESTIGATIONS IN HIS LABORATORY WHICH IS ATOM FORMATION IN ANALYTICAL FLAMES AND PLASMA

Answer 3

In understanding atomization with plasma and flame - an issue is that aerosols are uneven so they created a set up in which one droplet is sent at a time and took a single flash photograph showing the single stream being sent to an acetylene torch - (rate of 1k/second) - due to stability can treat this as a time lapse even though different droplets Can see it moves to flame, evaporate as they move upward and solute particle vaporizes leaving luminescent plume -Ultimate conclusion though is even though can visualize each step - don't know enough about it to assess/manipulate - this is for the future - long term goal

Answer 4

inductively coupled plasma is created by a coil around a quartz tube containing plasma gas (usually argon). t 1)through inductive coupling - the coil generates a field that 2)accelerates ions in the gas which collide with argon atoms and ionzie them which causes electrons to be released. 3)The electrons are accelerated to produce further ionization 4) final result is plasma with max temp of 10k C into which we can spray our sample

Answer 5

The calculated energy to atomize a molecule is not very high but the effective temperature needed for it is very high - considerable - they point to probably the most successful as using thermally hot sources for atom formation and excitation - particularly ICP

Answer 6

Strength - atomization relatively complete due to high temp Leads to high sensitivity and low interferences (small) High temp at which emission generatedalso helps sensitivity DOwnsides: 1 Spectral background very high due to hot plasma gases 2 Due to high heat a variety of elements are ionized including alkali and alkaline earth metals which have strong emission spectra which are scattered within in the monochromator or spectrometer used to separate elemental emission lines - and this scattering causes erroneous signal (this requires a high resolution detection system to distinguish this emission) 3 The source has flickering noise which causes variations in the atomic elemental signal and background (difficult to detect single atoms) 4 Large dilution with argon gas necessary (15-20 mL/min) - 1 ug/mL of sample reduced to 10^10 atoms/cm^3 in plasma - of course an issue for SAD and detection limits 5 Also appears to be near or at its theoretical limit for detection

Answer 7

Can be designed for the most specific methods such as fluorescence in mind which is good They mostly involved thermal generation of relatively volatile elements held in quiescent environment for longer observation times However this is specific and most elements are not volatile and require more energy (such as the furnace) to vaporize Likes sputtering

Answer 8

1st) Sample is conductive (if not make conductive by mixing (admixing) with graphite) 2) put in chamber with inert gas (several torr pressure- high pressure) 3) Hold sample at high negative voltage (500 V( - current of 5-300 mA allowed to pass (at the cathode?) 4) this results positive ions of inert gas are generated and attracted to cathode - causing bombardment of this cathode with inert gas ions which fragments the surface (these fragments are hopefully our atoms 5) atoms now in a dense cloud above sample surface ready for SAD hopefully

Answer 9

Pros: "outside in process" cloud of atoms in a gradient (less as move farther away) so can sample the various depths 2) no explosive sample fragmentation in thermal volatilization 3) Generated in a quiescent environment allows for long observation times(better sensitivity9) 4) High efficiency CONS: 1) Slow- requires minutes to form a stable population 2) samples must be conductive 3) must be held in a closed, evacuated chamber which is the biggest issue (real samples I guess)-experimentally inconvenient

Answer 10

Atmospheric sputtering can make it quicker (micro arc technology) - also requires no vacuum and can use non conductive samples (just requires conductive substrate) Author sees potential for this and MIP (microwave ICP microwave induced plasma - like ICP but worse less efficient, less dilution though ) in conjunction as promising

Answer 11

chamber at reduced pressure Currently can do in a closed d like sputtering OR let atoms slowly escape from a heated tube (semi enclosed) - this is what is done in furnaces -however short of SAD capabilities (not as good as enclosed as well - shorter time) His ideal is trapping for VERY long times hours , day minutes etc - undersuch times could identify every element in a sample

Answer 12

Can use linear ion trap to hold atoms for longer periods of times Know the basic 4 rods RF and DC create potential well to trap our ions - - should be able to probe with a laser only issue - requires ionization - LOW efficiency not great for detection

Answer 13

In generating the ions and the detection process - (and in fluorescence you have the excitation and fluorescence processes which can be made more selective

Answer 14

1) Using very specific narrow band dye laser - often selective enough to excite specific elements or specific isotopes, (can still be interfered with by background radiation or secondary ionization)

Answer 15

ANy attempt here jst reduces detection efficiency (eg incorporating a mass spec) - often ions can only be analyzed once as well (fluorescence not the case) - but generally reduces the efficiency Believed would make it unusable for SAD

Answer 16

THe following are LEAF specific: 2)Using non resonance fluorescence (so the emission isn't at the same wavelength at absorption - somewhat separating it (still has general issue of noise though - also considering hot environment of furnace and multiple elements fluorescence - can still have overlap 3) Can use a two photon or double resonance process in which 2 lasers are used - one is done continuously - brings it to one energy level - the other is pulsed and brings it to another high energy level - can detect time wise for this second higher emission - distinguish from other elements that might have that first energy level 4) Can do resolution on a chemical means - - separate elements -modify atmosphere to scavenge selectively unwanted elements (can also use specific discharge gases like He Ar or Ne ) to do this 5) Can do it time based either by A) Elements volatilize at different times - can employ temperature ramps to either avoid or set it at specific times for detection B) AToms have intrinsic excited state lifetime so can time its fluorescence -, Atoms excited by laser under go first order kinetic decay characteristic of a specific atom (also importantly scattering is much shorter time scale - see figure - can wait to just analyze fluorescne)

Answer 17

1) determine the limiting noise source - determines the lowest concentration that can be measured 2) Determine the magnitude of signal expected from an atom based on its fundamental characteristics 3) Teh degree to which free atoms are generated

Answer 18

Often it is photon detectors - receiving unwanted photons - often noisy -

Answer 19

SO starts with talking about intrinsic LOD – ultimate limit for a method determined statistically – based on physical interaction of analyte atoms or ions with photons, electric or magnetic fields

Answer 20

2 equations one for the MEAN NUMBER OF EVENTS REGISTERED AT DETECTOR fd * Np Fd is detection efficiency – which relates to mean probability of generating one event per sample atom in the probe volume per second Np is mean number of analyte atoms in probe volume ANd Minimum # of atoms detectable in robe volume k^2 / (fd * R) k is the S?N ratio at the detection limit (also statistical confidence level) fd is still fd and R is the number of repeated probings

Answer 21

This equation is dependant on k being the S/N at detection limit AND THE PROBABILITY OF OBSERVING AN EVENT FOR ON EATOM PRESENT IN VOLUME IS SMALL - Also presupposition that the background and detector dark current counts are negligible (which is a simplificaition) -

Answer 22

ultimate limit for a method determined statistically – based on physical interaction of analyte atoms or ions with photons, electric or magnetic fields

Answer 23

So 3 equations - Absorbanced measured minimum number of atoms detectable which is what we care about and number density THe key is number of atoms detectable is Amin * pi * r^2 / Qa of which r ^2 is in meters and Qa is generally given (ranges between) 1E-19 and 5E-16 this produces 6E7 to 3E11 atoms BUT to get to a single atom it would need to be 0.01 - 0.8 uM diameter - and would need an optical beam that size which is not possible

Answer 24

Npmin = k^2 / (fd * ea * ei * Tm) fd no units ea no units atomizer efficiency e1 - Hz laser reptition frequency Tm secondsmeasuring time (residence time in the furnace) Fd - depends on a lotAtomizer volume Illumination of volume Collection efficiency for fluorescence radiation The solid angle and transmission of the optical system The quantum efficiency of the detector Other factors related to specific atomic transitions involved

Answer 25

Can achieve SAD - HOWEVER - requires continuous wave laser or pulsed laser with high repetition frequency and these have not yet been performed at the time

Answer 26

IN terms of momentum when an atom absorbs - takes the unimolecular momentum of the in coming light beam - -the momentum changed caused is h/lp with h being planks and lp being photon wavelength The emission resulting Goes everywhere - canceled out - no resulting momentum so all that remains is the momentum from the incoming This can be used to influence direction of atoms or trap in a sense

Answer 27

Planck constant h is equal to exactly 6.626 070 15 × 10-34 Joule seconds.

Answer 28

v = (2kT/m) ^ (1/2) where k is boltzmann and T is temp and m is atomic mass velocity change per absorption is dV = h/(m*lp)

Answer 29

1.380649 × 10−23 joule per kelvin (K)

Answer 30

- when atoms are deccelerated - their resonance frequency shifts (Doppler effect) - it's detuned with respect to the frequency of the counter propagating laser beam - Need to do something to overcome this (TABLE 2)

Answer 31

using 3 perpindicular lasers to cool and trap neutral atoms requires lower energy so can be done with diode laser - simple tech - can trap atoms for 0.2 seconds at temp of 100 uK can have some issues eg need deceleration length of 1 M

Answer 32

See document - basically shoot it intersecting the atom beam so some of them take a different trajectory where they are then detected with a suitable laser beam using fluorescence signal for LEAFS detection (note this is OPTICAL COOLING not optical molasses)

Answer 33

simpler spectral background, higher sensitivity and completel elemental coverage and isotpic resolution

Answer 34

Using teh efficiencies of each part of the MS - one can get an overall detection probability for ICP-MS P det = 3E-11 - 1 E-9 counts per atom So using equation 2 (for NP(min)) the overall LOD becomes (Namin)^8 - 3E8 atoms - read article dependant on operating in SIM mode with measuring time of 10s

Answer 35

LOD increases proportionally to number of elements Also depending on parts used (eg ionization source - can adjust LOD at current point in time - WAY too inefficient for SAD capability - efficiency too low at sample interface and throughout the quadrupole (will not reach below 1E6 atoms

Answer 36

1 more efficient than triple quad 2 Can volatilize our sample under vacuum with TOFMS (no need for the multi step pressure change - again loss of ions) Can use electrothermal volatilization 3While the TOF needs to be pulsed can use an ATOMIC BEAM TOF - AB TOFMS which has an ion source trap to pulse ions into the TOF aLSO IS tof - HIGHER RES (at time > 1000) Mechanically moderate compared to QQQ requires fast data processing (fast instrument 27 kHz frequency of operation

Answer 37

t FLIGHT = L * (2 /Ua)^ (1/2) * (m/z) ^(1/2) With t flight being time of flight l being flight length Ua being acceleration voltage and m/z is m/z

Answer 38

not far from sad capability with isotpic reoslution

Answer 39

Used a tungsten toil for volatilizer - used a reflection and an MCP for detection

Answer 40

LEAFS should be capable of achieving SAD it optimum excitation lasers become available Atom trapping and laser interaction can theoretically do SAD Elemental MS should be able to do SAD but isn't there currently but lots of potential (increase efficiency, of sample inlet or mass filters, TOF is promising like it - ALSO MS really promising due to its full elemental range, multi element capacity, expect MS to be much broader

Answer 41

absolute is the minimum amount of analyte detectable relative is the minimum concentration

Answer 42

No as long as it is clear what it is referring to analytically - As long as the data is interpreted correctly - and what you are writing is linked to a specific analytical task

Answer 43

In developing a new methdology - the goal is to tune instrumental parameters for best S/N whereas a new detection procedure - care about sample amount available precision , absence of systematic error etc THe key here is USING THE RIGHT TERMS TO STRESS the goals of your method and emphasize its benefits

Answer 44

Method using RIMS for Pd and Rh in sea water - really good sensitivity however the LODs are for concentration and INCLUDE THE WHOLE METHOD - including sample concentration and separation (so good relative LOD) the actual absolute LOD is not very impressive compared to other methods Another example - they say they have a method for SAD with RIS - this refers to simply being able to see one atom - absolute - NOT relative - cannot see one atom in a sample

Answer 45

So again relative vs absolute - one can have much better absolute but not be great at relative Keeping parameters the same when comparing a major one being maybe sample volume (eg HR ICP MS can consume several mL and have a giant integration time allowing for low [] detection whereas another method can use a few micro liters have a better absolute but worse relative LOD Instrumental limitations in amount of sample that can be analyzed is key for thinking between the two absolute and relative

Answer 46

if random sampling defined by square root law of particle counting which represents the lower limit for sampling error. The counting error for quantitative determination will be 1% or less if 10,000 atoms counted which gives us a minimum mass to look at - I guess the idea is that below that your error goes up and analysis is less sure

Answer 47

femto is 10-15; 1 ag,10~18 g; 1 zg,10~21 g; 1 yg,10~24 g

Answer 48

ultra trace should use relative LOD, microanalysis for Absolute

Answer 49

1) absolute LOD is still great and can be relevant 2) should not stress absolute LOD when there are no limits to sample size available for analysis 3)For absolute LOD - consider EMP - electron microprobe, Auger Electron Spectormetry (AES) and SIMS (ag level sensitivity) 4) Detection limit should be reported in a way relative to the task at hand (or both) 5) The method of comparison again depends on the task at hand again as to what parameters are key to compare

Answer 50

On the X axis for concentration for Mole fraction not weight fraction - given equation 11 weight fraction doesn't equal mole fraction unless the molar masses of the nalayte an matrix are equal and really it comes down to the emission signal relates directly to the atoms and the moles and as such the mole fraction ins what matters not the weight fraction and more importantly they differ

Answer 51

X in A - so plotting weight fraction and mole fraction will show the difference between weight % and mole fraction but will ultimately show the same effect eventually = - self absorption so need to look at more interesting scenarios to show thecharm X in A vs X in B - At the same weight % If we see a differing signal when plotted one might be tempted to say matrix effects BUT (assuming weight % in solid translate to that in plasma) unless the molar masses of matrix A and B are the same - they're going to have different plots just given by our equation so can't chalk up and difference in plots to matrix effects. In this scenario when you plot mole fraction you get a unified plot showing no matrix effects The opposite case - so we have x in matrix a and b and AGAIN the same weight % But this time - the signal on the weight % plot is the same. The assumption would be NO matrix effect. However, again, if its the same signal - it should be the same mole fraction which we know cannot be true 9same weight % and mole% ) unless Molar mass A and molar mass B are equal

Answer 52

Xa = (wx * Rax)/(1+wx(Rax-1)) with wax being the weight fraction xa being mole fraction and Rax being the ratio of molar masses

Answer 53

HOMOGENEITY

Answer 54

If fluctuations in the chemical compositions determines across the sample volumeare not significantly larger than the error of the analytical procedure THIS MEANS HOMOGENITY IS NOT AN ABSOLUTE MATERIAL PROPERTY BUT RELATED TO THE ANALYTICAL METHOD

Answer 55

basically as the mass goes down sample heterogeneity becomes more and more important - above this critical mass Is only where we can see the difference between homogenous and htereogneous - see the image (figure 6 and explain) I think it's like at low masses - the variance due to sample heterogeneity is so big that can't tell the difference between heterogenous and homogenous but at higher masses - the variance from the heterogeneity plays less of a role and the homogenous eventually reaches the point where all the variance is just from the method whereas a heterogenous sample will reach a point below the variance from the method and m crit is where this divide is OK so at small masses - the heterogeneity plays a big role in variance as the mass gets bigger it plays a smaller role. At the critical mass is where their contribution to the total variance differs whereas the heterogeneity one approaches 0 the homogenous one approaches just the s from the method - so I guess if the variation stays at the level of the method so the contribution from heterogeneity can be seen better as its just whats beyond variance beyond the method variation (so while the variance due to heterogeneity goes down - it becomes easier to assess past the critical mass) and more importantly - BELOW this critical mass - you cant tell if hetero or homogenous because the variance is just so much higher than s method for both homo and heterogenous

Answer 56

OK so I think this graph is saying what % does each part of the sample contribute to the total variance Basically at low amounts it’s the same but as we increase mass – heterogenous goes down to being 0 homogenous just goes down to the s method amount

Answer 57

His example was having a sample with the same concentration but the sample amount kept decreasing - the ultratrace analysis (or relative LOD) remained the same while the absolute or microtrace had to be pushed farther

Answer 58

compared HR-ICP-MS to GF-LIF graphite furnace Laser induced Fluorescence - the idea being that ICP MS can use mL of sample while GF-LIF only uL despite having better absolute LOD Looking at thallim in water

Answer 59

Absorption is just a straight arrow up and emission is a wavy arrow up and a straight arrow down