Mass Spec Instrumentation (6)

Question 1

List the components of a mass spectrometer

Answer 1

Inlet systems, ion sources, mass analyzers, detectors, signal processors and vacuum systems

Question 2

inlet system

Answer 2

Introduces small amounts of sample

Question 3

ion sources

Answer 3

Convert sample to ions

Question 4

mass analyzers

Answer 4

disperses ions by m/x ratio; analogous to monochromatic in photon spectroscopies

Question 5

detectors

Answer 5

Converts ion beam into electrical signal

Question 6

vacuum systems

Answer 6

Must maintain high vacuum 10e-4 to 10e-8 torr

Question 7

What are the 3 ways to introduce samples into the ion source?

Answer 7

Batch inlet, direct probe, chromatographic inlet

Question 8

What are the methods used to introduce gases in MS?

Answer 8

batch inlet; introduce through reservoir then leak the gas through a small aperture
chromatographic inlet

Question 9

What are the methods used to introduce solids in MS?

Answer 9

direct probe inlet; insertion probe with sample held on end

Question 10

What are the methods used to introduce liquids in MS?

Answer 10

batch inlet; syringe injection then heated
chromatographic inlet

Question 11

GC chromatographic inlet

Answer 11

jet separator, packed capillary columns

Question 12

What are the different types of LC-MS interfaces

Answer 12

direct liquid injection or thermospray or electrospray or CF-FAB

Question 13

Direct injection used in?

Answer 13

microbore or capillary LC

Question 14

Electrospray?

Answer 14

nebulize effluent by charging and extracting ions; liquid sample; high electric field; ions drawn into vacuum; analysis of high MW and nonvolatile analytes

Question 15

Faraday cups advantages

Answer 15

Well shielded; can detect more than 10e-15 A currents

Question 16

electron multipliers

Answer 16

most common; like a PMT without photocathode; each successive dynode held at higher voltage; can detect less than 10e-15 A currents

Question 17

electro-optical detection (Array transducers)

Answer 17

like multichannel array detectors; arrays of metallic electrodes are used, each acting as an individual electron multiplier detector causing an electron cascade; optical coupling by phosphorescent screen converting electrons to light

Question 18

LC chromatographic inlet

Answer 18

used for samples that are not volatile, not suited for gas phase; elution solvent must be eliminated

Question 19

Faraday cups disadvantages

Answer 19

high impedence amplifier limits speed at which it can be scanned

Question 20

Faraday cups principle

Answer 20

current passes through sensor to ground, but potential held at ground; charge of ions striking plate is neutralized by flow of electrons from ground through resistor; resulting potential drop is amplified

Question 21

electron multipliers disadvantages

Answer 21

problems if exposed to atmospheric pressure because of reactive coatings

Question 22

Which is more difficult: LC or GC?

Answer 22

LC because elution solvent must be eliminated