Mass Spectrometry

What is mass spectrometry?

Microanalytical technique that provides information on the structure/mw of an analyte and its fragmentation pattern

How does Electron Impact Ionization work?

Sample molecules colliding with an electron beam inside system will result in its ionization

What is a quadruple?

Mass analyzer with 4 parallel rods and allows fragment ions to pass through

What is an electron multiplier detector?

Helps amplify an ion signal by causing a release of many electrons when the ion hits the detector surface

What is a mass to charge ration (m/z)?

The ratio of mass number of a given particle to the number of electrostatic charges it carries

Why is the m/z referred to as the mass of the particle?

Most ions have one electrostatic charge so m/z is usually equal to MW

Does m/z refer to the whole analyte or the fragmented ions?

Fragmented ion

What is the m/z if the ion is doubly charged?

It will be MW/2

What is a molecular ion?

Intact molecule minus one electron resulting from ionization of analyte and m/z is ~MW of analyte

What is the base ion?

Most intense peak in mass spectrum

Why is Data Handling important in mass spectrometry?

Having a database can help compare the unknown graph to stored ones and find a match

It can also help reduce interference by subtracting background noise

What is Deconvulation?

Extracting a signal from a complex mixture by treating background noise, correcting baseline drift, and determining if one area has several peaks

What are the three things to look at when a library match is done to unknown analyte?

Must make sure fragment ions look similar in correct proportions, retention time should be ± 0.15 minutes, and visually inspect both

Why is mass spectrometry a disadvantage for some compounds?

Methadone and oxazepam are heat labile, acetaminophen gives poor peaks, opiates do not extract well

What is Full Scan monitoring?

All ions are selected for and monitored

What is Selected Ion Monitoring (SIM)?

Selected ions are measured and quantitated

What is an advantage of SIM?

Increased sensitivity

What is a disadvantage of SIM?

Can only detect limited number of ions

What are the advantages of LC + Mass spect?

Good for volatile and nonvoltaile solutes, good for ionic/polar analytes, has good sensitivty

What are the disadvantages of LC + Mass Spect?

Low HPLC flow rate required, must be able to form ions in solution, ion suppression with high salt and certain matrix conditions can occur

What is electron spray ionization?

Analyte is dissolved in solvent and an electrical field is applied. At high voltage, electron force overcomes surface tension leading to small charged droplets (spray) being produced

What is the theory behind Tandem Mass Spectrometer?

There are three quadruple analyzers

Q1: single m/z selected

Q2: collision cell

Q3: m/z of fragmented ions selected

What is Time-of-Flight Mass Spectrometry?

Separation of ions is based on how long it takes for it to “fly” through the analyzer

Do smaller m/z accelerate faster or slower in TOF?

Faster because it is lighter

How can you create higher resolution in TOF?

Have longer tubes, reflectors, increase acceleration

What is TOF-MS/MS (QTOF)?

TOF replaces Q3 in tandem

Q1: filters, Q2: fragmentation, TOF: separates ions