Final Exam Study Guide Flashcards

Question

Uses of Discharge Sources

Answer 1

- Elemental isotopic analysis - Trace metal analysis - Semiconductor, insulator, thin film analysis

Answer 2

- Sample is in vacuum - Does not atomize sample - Sample is placed on a probe tip, inserted into the MS source and bombarded with particles or photons - Soft technique (sample is not atomized)

Answer 3

- Useful for low (or no)-volatility and/or thermally unstable compounds - Typical samples: biomolecules, drugs, polymers, metal complexes, catalysts, inorganics - Different DI techniques yield different spectra - "Soft" ionization producing quasi-molecular ions with little fragmentation - Produces positive ad negative ions - Ions production is often matrix dependent, making quantitation difficult - MS/MS may be used to obtain structural info

Answer 4

- Common surface analysis technique - Bombarding Ion Species (Ar+, Xe+, or Cs+) - Bigger samples (proteins, peptides) can't be done as well - Large kinetic energy spread - Dynamic SIMS: used in surface analysis. Tool for identification and depth profiling of surface components. The ion beam may be scanned across the surface to map the spatial distribution of components. Involves ultra-low pressures to avoid O2 desorption on sample surfaces. - Organic SIMS: organic samples are deposited on a surface (sometimes monolayers) and subjected to SIMS. Ion formation is generally low. Bombardment may "eat up" sample quickly. To increase ion formation, samples may be deposited on Ag foil (which readily desorb Ag+ adduct ions) or mixed with "preionizing agents such as HCl or NH4Cl

Answer 5

- All DI features - Practical sample size down to nanomoles - Mass range usually below 5000 Da, but >20,000 Da is possible - WORKS WITH ALL MASS ANALYZERS - Ion guns can be pulsed or continuous but pulsed is usually better because it increases the sample lifetime. entire SPECTRUM OBTAINED FROM MILLISECOND BURST OF THE ION GUN. - Requires little sample prep, but SPECTRUM IS MATRIX DEPENDENT - Experiencing a resurgence in its use because of imaging (TOF-SIMS)

Answer 6

- Dramatically changed MS, leading to a routine analysis of low volatility species - Sample is dissolved in a low volatility matrix and bombarded with an atom or ion beam (1 - 10 KeV) Sample and matrix (want a matrix that won't be pumped away) ions are desorbed and ionized. Solution contains 10-20% of sample - Common bombarding species: Ar, Xe, Ar+ , Xe+ or Cs+ - Common liquid matrices (low volatility): glycerol, thioglycerol, m-nitrobenzyl alcohol - Bombarding a drop of sample on the probe - Different than SIMS because it uses atoms instead of ions and a liquid matrix instead of a solid matrix - Gives a higher yield of organic ions than SIMS - Been replaced by electrospray and MALDI

Answer 7

- All DI features - Not commercially sold anymore - Instrumentally simple and cheap - Was used in the analysis of biomolecules, drugs, environmental samples, peptide sequencing - Gives more fragmentation than other DI techniques - Works best for MW < 5,000 Da, however species up to 24,000 Da have been detected. - Works best on pre-ionized species and on polar molecules which will readily protonate ; poor for non-polar, but works good on molecules that want to polarize - High sensitivity for some species. - Spectra are very dependent on sample prep - Does the best job of analyzing organometallics

Answer 8

- Bombarding species: Laser light - Except for MALDI, ion formation is generally independent of wavelength but dependent on laser power (which is typically 10^7 to 10^10 Watts/cm^2 , a high power laser) - Laser is located outside of the MS and is allowed into the system through windows (sapphire or glass) or a fiber optic - Common LD lasers are pulsed ( Nd:YAG, nitrogen, CO2 or excimers) - With a pulsed laser, ionization is only for 5-50 ns/spectrum, but a pulsed mass analyzer MUST BE USED. (ToF, ICR, QIT, Orbitrap)

Answer 9

- Uses: biomolecules, polymers, inorganic species, and surface studies. Samples can have little to no volatility - More universal than FAB - Gives more ions than SIMS - However, lasers are more expensive than ion/atom guns. - Frequently used with inorganic samples. - Abundant positive and negative ions are common

Answer 10

- "Soft" laser desorption - Laser is used for ionization - Sample is mixed with a solid matrix and placed on a target (probe) - Matrix must have low volatility and form solid crystals

Answer 11

- Desorption of very large analyte ions (Greater than 1,000,000 m/z has been observed) - MALDI is very dependent on sample prep (layering, mixing, etc.) - Additives to the matrix can increase ion formation - Preferred method for ORGANIC POLYMERS. - Low fragmentation - Bigger molecules can give too many isotopic distribution. Causes broader peaks. - All DI features - Widely commercially available - Mass range : >1,000,000 - Common for both organic and inorganic samples - Amount of sample used = very small - May not work as well as FAB for some organics less than 5000 Da, but it will ionize heavier and less volatile species that don't give FAB spectra - Can be used for surface analysis and imaging - Easily automated - No background gas pressure and few matrix ion problems - RESULTS VERY DEPENDENT ON SAMPLE PREP - A large number of experimental variables can be controlled, which gives more control over ionization parameters - MORE TOLERANT OF IMPURITIES THAN ESI OR FAB - CAN'T WORK WITH A LOT OF MASS ANALYZERS - MOSTLY WORKS WITH TOF AND FT-ICR

Answer 12

- A variation of MALDI - Modified surfaces on the target plate retain specific classes of proteins - Surfaces may be modified chemically or biologically - Used in proteomics discovery studies and biomarker research - NOT GOOD FOR QUANTITATIVE RESEARCH DUE TO LIMITED REPRODUCIBILITY - Some proteins bind to the plate and others are washed away by a solvent. matrix is then added on top of the bound proteins

Answer 13

- Atmospheric pressure ion source that ionizes the sample at ground potential in open air - LOW MW WEIGHT MOLECULES (LESS THAN 1000 Da) - Low voltage at sample inlet (1-5 V); no risk of energy if sample orifice is accidentally touched - DI where sample is placed under ambient conditions into the path of bombarding particles produced by Penning Ionization - Has been used to analyze solids, liquids, and gases. Sample requires some volatility - Requires no sample prep - Ionization can take place directly on the sample surface - A form of Penning Ionization - Sampling Inlet is held at about 80 degrees Celsius to prevent condensation - NOT AS WIDELY AVAILABLE BUT HAS BEEN SOLD WITH MS

Answer 14

- Atmospheric pressure ion source that ionizes the sample under ambient conditions in open air. - Similar to DART but bombarding species is the spray from ES - VOLATILE SPECIES WORK ONLY - Has been used to analyze solids, liquids, and gases - Ionization can take place directly on the sample surface - Combination of ESI and DI - High molecular weight samples give ESI-like spectra that contains multiply charged ions - VERY LITTLE FRAGMENTATION - NEGATIVE MODE IS POSSIBLE - ADJUSTABLE BASED ON ANGLE, MORE ADJUSTABLE THAN DART. - NO SAMPLE PREP

Answer 15

Mass spectrometer

Answer 16

- mature, routine. - Gaseous output of GC column (silicon oxide based) is passed through the interface and into the ion source. - Requires volatile compounds that are thermally stable. If the sample decomposes upon heating, use LC. - Ionization by EI or CI&EI - No ESI or MALDI because the samples are not volatile enough - All mass analyzers may be used, but Q and QIT are the most common. TOF can also be used - Mass spectra is taken continuously but the rates are dependent on the mass analyzer. (1-10 spectra/second for Q and sectors) - GC-TOF is an excellent choice for fast chromatography (40,000 spectra/sec) - 1 GC run may yield hundreds of spectra

Answer 17

- Equivalent to FID's output. - Gives relative abundance of each ion - Can look for fragment ion and precursor ion - MS equivalent of a GC detector output - The ion current from only one ion is displayed

Answer 18

1) Capillary Column | 2) Packed Column

Answer 19

10^-4 Torr but prefer lower

Answer 20

- Typical carrier gas flow rate of 1 cm^3/min at 1 atm. - At 10^-4 Torr, this becomes 10^7 cm^3/ min or 166 L/s - Typical capacities of turbopumps and diffusion pumps used in mass spectrometry are 50 to 1000 L/s - Capillary columns have acceptable volumes of gas flow that can be handled by the MS pumps without additional hardware - NO INTERFACE - Capillary effluent is sent directly in the source

Answer 21

- Typical carrier gas flow rate of 20 cm^3/min at 1 atm - At 10^-4 Torr, this becomes 3300 L/s (not possible with standard pumps) - Eluent from a packed column CANNOT be sent directly to the source because of the high pressure that would result. - Packed column eluent is first split or the analytes concentrated prior to its input into the mass spec source. - Need interface for packed columns.

Answer 22

- bring GC effluent to an acceptable MS pressure - transfer as much of the sample as possible into the MS ( if it doesn't do this the LOD and sensitivity decr.) - Avoid broadening the peak

Answer 23

1) Direct Transfer | 2) Jet Separation

Answer 24

- Capillary Column Only - End of the column is placed in the MS source (EI or CI) - No interface needed due to the low gas load of the column

Answer 25

- Most common interface for packed columns - GC effluent flows through a small nozzle and is directed to a skimmer - After leaving the nozzle, light carrier gas molecules fan out. A higher % of heavy sample molecules stay on axis and reach the skimmer. - Achieves about 50-60% efficiency in transporting sample - Usually made of glass and located in a heated chamber - ION SOURCE ALSO HAS TO BE HOT TO PREVENT CONDENSATION - MOST COMMON CARRIER GAS IS HELIUM - SITS IN OVEN TO PREVENT CONDENSATION OF SAMPLE - HEAVIER SPECIES GO TO MASS SPECTROMETER

Answer 26

Greater than 760 Torr

Answer 27

10^-5 to 10^-8 Torr ; can take 10^-4 Torr

Answer 28

constant ; minimize

Answer 29

Pressure of sample in source

Answer 30

Pulsed ; rapid acquisition

Answer 31

1) requires very little sample 2) provides structural confirmation 3) Has extremely low LOD

Answer 32

Decrease ; scanning

Answer 33

for selected reaction monitoring

Answer 34

semi-volatile organic compounds (semi-VOC)

Answer 35

- What type of chromatography column is used - What temp is the column - What the flow through rate is - What the retention time range is

Answer 36

internal standards

Answer 37

1) Increase sample volatility or thermal stability 2) Enhance the molecular ion (or quasi-molecular ion) 3) Incr. , decr., or direct fragmentation 4) Enhance the selectivity or sensitivity of the ionization process (Make more ions) 5) Improve the GC separation

Answer 38

1) Quantitative, producing a single product in good yield 2) Fast and simple (No synthetic organic products) 3) Work well with small amounts of materials

Answer 39

Triakylsilyl Derivatives ; React readily with OH, SH, and NH to replace the active H with a silyl group. No hydrogen bonding = more volatile compound. Enhances volatility, improves GC properties, and gives a more easily interpretable mass spectra.

Answer 40

- Trimethylchlorosilane (TMCS) and N,O- bis(trimethylsilyl)-trifluoroacetamide (BSTFA)

Answer 41

Trimethylchlorosilane

Answer 42

N,O-bis(trimethylsilyl)-trifluoroacetamide

Answer 43

In solution, not in mass spectrometer. You then inject the sample into the instrument.

Answer 44

N,O-bis(trimethylsilyl)-trifluoroacetamide

Answer 45

Locating double bonds, which is especially difficult in long chains

Answer 46

dimethyldisulfide derivative; alpha cleavage is directed to the C-C bond between the two sulfurs. Tells you where the double bond was

Answer 47

- For samples that aren't volatile enough or thermally stable enough for GC-MS. - Possible to obtain their spectra by DI (MALDI) and spray (ESI) techniques, with separation by MS/MS. - Chromatographic introduction requires LC-MS - Usually has a UV-Vis Detector (this is std. for LC-MS)

Answer 48

Interface must take flowing liquid stream to acceptable MS pressure (10^-4 to 10^-6 Torr) while transferring as much sample as possible with little peak broadening

Answer 49

- Decr. LOD - Decr. Sensitivity - Would broaden peaks that are already broad with this technique

Answer 50

1) Mechanical Transport Device 2) Direct Liquid Introduction 3) Continuous Flow FAB 4) Thermospray 5) Monodisperse Aerosol Generation Interface (MAGIC) or Particle Beam (PB) 6) API

Answer 51

- LC-MS interface - Moving belt (no longer used) - LC Effluent was sprayed onto a moving polyimide belt; solvent removed by heating; belt rotates to source for EI, CI, or DI; belt cleaned; process restarts - Problems: Limited volativity range, volatile compounds lost before source; less volatile stay on belt and get it dirty; belt would break; things would pump out of belt before it reached MS source

Answer 52

- Also no longer common - LC-MS interface - Lifespan of 3 years - LC effluent sprayed directly into MS source, sometimes with a splitter between the column and the source. - Solvent evaporates and becomes a CI reagent gas (bath gas). CI only needs a source pressure of about 10^-3 Torr at best - Problems: Capillary clogs. Only works with volatile samples vaporized in the source. Only CI spectra was obtained and that was not very useful.

Answer 53

- LC-MS interface - No longer common - LC mobile phase either contains glycerol (1-5%) or effluent of the sample that is mixed with glycerol after the column. - Flowing effluent flows into hollowed probe tip, placed in DIP inlet of machine, and bombarded with FAB/SIMS beam - Problems: Tricky to set up. Source gets very dirty from glycerol. Salts from LC buffers can clog the probe capillary. Caused electrical arcing, messy, etc.

Answer 54

- No longer common - LC-MS interface - Makes singly charged ion - Was popular until ESI came along - LC effluent passes through a heated capillary into the MS source - Combo of spray ionization and CI (b/c buffer is doing CI making) - Soft ionization: [M+H]+ or [M+NH4]+ or [M-H]- with few fragments. Ammonium acetate buffers usually required (used b/c it won't clog interface by making salts) - Problem: The heated capillary clogs repeatedly.

Answer 55

- LC-MS interface - 2 jet separators in tandem - LC effluent (0.1-2 mL/min) passes through an orfice (5-10 um in diameter) into a desolvation chamber at atmospheric pressure - Orfice produces an aerosol jet spray of uniform drop size (about 2 times the nozzle diameter) - Spray is hit by a perpendicular He flow to break up drops and prevent recombination - Drops enter a two stage aerosol-beam separator where the pressure goes from atmosphere to 10^-6 Torr. - Solvent particles are volatilized, separated by diffusion and pumped away, leaving less volatile liquid droplet by analyte - Ionization by EI or CI - Major advantage: EI SPECTRA (SAME SPECTRA AS DIP) CAN BE GENERATED FOR COMPOUNDS WITH SUFFICIENT VOLATILITY TO GIVE AN ADEQUATE PRESSURE IN THE SOURCE - ONLY COMPOUNDS OF MW < 1000 ARE VOLATILE ENOUGH FOR PB - HEATED ASSEMBLY

Answer 56

Where lighter molecules will fan out, and heavier molecules will go through center

Answer 57

Big molecules such as polymers and peptides. Won't vaporize as easily/quickly as the instrument needs

Answer 58

DIP requires pure compounds | PB can do mixtures but give similar spectra

Answer 59

- Atmospheric Pressure Ionization - Very soft ionization - Very common interface for LC-MS - Form of high pressure CI, with interface and ionization in one stage - Very soft ionization technique - Gives singly charged ions for compounds up to MW 1500 (Fairly light compounds) - May work for samples not polar enough for good ESI - Almost 100% Ionization efficiency - Detection limit is not necessarily better than EI because the total ion current is not sampled by the MS - Instrumentation is relatively simple. Often sources combine API and ESI (or two very similar sources)

Answer 60

- Electrospray ionization - Interface and ionization technique - MOST GENTLE IONIZATION TECHNIQUE. OFTEN COUPLED WITH MS/MS - For LC-MS - Useful for very high mass samples - Works for polar compounds with MWs around 100. - Sample must have some polarity to accept or donate H+ - LC effluent flows through stainless steel needle, the ESI chamber, which has a cylindrical electrode at 3500 V. The electric field at the needle tip charges the liquid surface, dispersing a fine spray of charged droplets - Droplets are driven by the field toward a glass or metal capillary and pass through a flow of bath gas (N2) - Coloumb explosions tear the droplets apart and produce highly-charged quasi-molecular ions

Answer 61

Fragmentation ; precursor ion signal ; product

Answer 62

- Uses ESI and Ionization - Method for separating ionic species (including highly charged biomolecules) - Flow rates are hundreds of nL/min. (extremely low) - Major advantages: speed, high chromatographic resolution (of separations), and small sample volumes - These are all retained with nanospray

Answer 63

- Preferred method of analysis for metals - Method of atomizing and ionizing a sample - Gives charge, isotopic distribution, MW, identification - NOT THE TECHNIQUE FOR ANALYZING MOLECULES - Has temp of 10000 K, can vaporize anything - Allows the determination of the elemental chemical composition of virtually any material - Can quantitate all elements in the periodic table - Can perform multielement analysis - Can measure individual isotopes of the analyte elements - Has very low limits of detection (exceeds capability of any other instrument) - Can determine exactly what species are present - Highly accurate and precise - Large linear dynamic range (LARGEST OF ANY INSTRUMENTAL TECHNIQUE) - Minimal interferences - Have to use a rare gas to make the plasma for ICP (commonly argon) ; WHATEVER YOU USE AS YOUR PLASMA CAN NOT BE ANALYZED

Answer 64

-It has a high IP, high purity, and minimal chemical reactivity

Answer 65

- An electromagnetic field is generated by applying RF power (ca. 700-1500W) to an antenna (load coil) made of ca. 3 mm diameter copper wire - Copper wire is wrapped around a quartz torch assembly, which configures and confines the plasma - An inert gas (Ar, He , N2 or air) flows into the torch assembly at 10-20 L/min. - Plasma is a DISCHARGE FROM ARGON - Field oscillates at a frequency of the RF generator - "Seed electrons" are produced from a spark. These electrons are accelerated by the electromagnetic RF field, they collide with the neutral gas atoms and create the plasma. These collisions produce additional electrons, which propagates the process. - Results in high energy plasma, whose outer regions reach temperatures of 10000K, with core temp. of 5000-7000K

Answer 66

- Sample is converted into an aerosol if it is a liquid and introduced into the plasma . - Liquid samples are usually sprayed directly into the argon stream . - As you introduce Ar into plasma, you can flow sample into plasma also. - A variety of nebulization processes may be used to break up the liquid into small particles. The smaller the particle, the more ions it will produce - Gases and volatile compounds are directly introduced to Ar (meaning the samples go into the ICP torch where it is then vaporized, atomized, and ionized

Answer 67

elemental analysis

Answer 68

be inserted directly into the plasma. or solid sample is desorbed into a gas by a laser and then entrained in the argon flow

Answer 69

atmospheric

Answer 70

- ions produced in the plasma pass through a sampler or extraction cone. - A skimmer cone is located a few mm beyond the sampler cone. - The two cones are made of Ni or Pt and are water cooled - 2 stage pumping system lowers the pressure to about 1 Torr after the sampler cone and about 10^-5 Torr as ions enter the mass spectrometer. - After the interface, ions are guided into the analyzer with a series of metal lenses (electrostatic focusing) - Photon disk placed at the exit of the skimmer cone prevents photons and energetic neutrals produced in ICP from reaching the mass analyzer

Answer 71

- Skims off some of the ions

Answer 72

They produce a signal on the electron multiplier (EM)

Answer 73

FT-ICR's high magnetic field interferes with the plasma.

Answer 74

FT-ICR and orbitrap

Answer 75

electron multiplier

Answer 76

- Primarily for probing structures - Frequently used with CI and all DI and spray ionization techniques - ION SOURCE DOES NOT MATTER - MAJOR MS SCAN - Gives molecular formula not structural - NOT TYPICAL WITH EI, SINCE EI HAS ABUNDANT FRAGMENTS - Quad 1: fixed - Quad 2: scanning

Answer 77

- First mass analyzer passes all ions -Second mass analyzer is fixed to pass the m/z of the product ion of interest. ONLY WORKS WHEN MASS ANALYZERS ARE SCANNING ( LINEAR QUADS AN SECTORS (b OR e) -MIXTURE CHARACTERIZATION -Quad 1: scanning -Quad 2:fixed

Answer 78

- Quad 1 & 2 are both scanning quads with a fixed mass difference - PRIMARILY USED IN MIXTURE ANALYSIS