Refraction and Mass Spectrometry

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Questions and Answers

What is an advantage of a specific type of detector in chromatography?

Easy removal and cleaning of the cell when filming or clogging occurs

High sensitivity to dirt and air bubbles in the cells

Universal response and low sensitivity to dirt and air bubbles in the cells (correct)

Ability to cover only a limited refractive index range

What is the primary function of a Mass Spectrometry Detector (MSD)?

Deflection of ions by an electric field

Ionization of atoms or molecules

Acceleration of ions to the same kinetic energy

Separation of ions according to their mass-to-charge ratio (correct)

What happens to ions of the same mass-to-charge ratio in a Mass Spectrometry Detector?

They are accelerated to different kinetic energies

They impact at the same place on the photographic plate (correct)

They are deflected to different places on the photographic plate

They are ionized again to increase their charge

What is the sequence of Mass Spectrometric detection?

Ionisation, acceleration, deflection Signup and view all the answers

What determines the amount of deflection of ions in a mass spectrometer?

The number of positive charges on the ion Signup and view all the answers

What type of detector was used in early mass spectrometers?

Photographic plate detector Signup and view all the answers

What is the purpose of acceleration in a mass spectrometer?

To give all ions the same kinetic energy Signup and view all the answers

What is the function of the mass analyzer in a mass spectrometer?

To separate ions according to their mass-to-charge ratio Signup and view all the answers

What is the relationship between the charge of an ion and its deflection in a mass spectrometer?

The more charged the ion, the more it gets deflected Signup and view all the answers

What is the purpose of varying the magnetic field in a mass spectrometer?

To bring each ion stream in turn to the detector Signup and view all the answers

What is the unit of measurement for the mass of an ion in a mass spectrometer?

12C scale Signup and view all the answers

What is the purpose of a 'stick diagram' in a mass spectrometer?

To simplify the output from the chart recorder Signup and view all the answers

What is the effect of increasing the internal diameter of a column in HPLC?

The sensitivity of the column decreases Signup and view all the answers

What is the effect of increasing the pump pressure in HPLC?

The separation power of the column increases Signup and view all the answers

What is a requirement for peaks in chromatography to be used for quantification?

They must be sharp, narrow, and well-separated Signup and view all the answers

What is the purpose of identifying peaks in chromatography?

To make standards for quantification Signup and view all the answers

What is a desirable characteristic of a peak in chromatography?

Symmetry Signup and view all the answers

What is the requirement for the detector response in the quantitation range?

Linear Signup and view all the answers

Which of the following solvents is used in increasing polarity order?

Uracil, Benzene, Toluene, Ethylbenzene Signup and view all the answers

What is the purpose of the acknowledgment section in the text?

To acknowledge the input of Dr Mzamo Shozi Signup and view all the answers

Which of the following authors is associated with the book 'Undergraduate Instrumental Methods of Analysis'?

James W. Robinson Signup and view all the answers

What is the typical application of mass spectrometry in toxicology?

Toxicology analysis Signup and view all the answers

Which of the following is a type of mass analyzer?

Mass spectrograph Signup and view all the answers

What is the purpose of chromatographic separation in analytical chemistry?

To separate and purify analytes Signup and view all the answers

Study Notes

Refractive Index Detector (RID)

Universal response and low sensitivity to dirt and air bubbles in the cells
Can cover the entire refractive index range from 1.000 to 1.750 RI with a single, easily balanced cell
Relatively low sensitivity and difficult to remove and clean or replace the cell when filming or clogging occurs

Mass Spectrometry Detector (MSD)

Separates bunches or streams of ions according to their individual mass-to-charge (m/z) ratio and transfers by deflection through a magnetic field for counting and quantitation
Detector generates a signal from incident ions by either generating secondary electrons, which are further amplified or by inducing a current generated by a moving charge
All ions of a given m/z would impact at the same place on the photographic plate making a spot

Components of Mass Spectrometer

Ionisation: Atom or molecule is ionised by knocking one or more electrons off to give a positive ion
Acceleration: Ions are accelerated so that they all have the same kinetic energy
Deflection: Ions are then deflected by a magnetic field according to their masses
Detection: The beam of ions passing through the machine is detected electrically

Detecting Ions

Ion stream most deflected will have the smallest value of m/z (the mass–to-charge ratio)
Larger m/z value (the heavier ions if the charge is +1) are brought to the detector by deflecting using a larger magnetic field
Magnetic field is varied, each ion stream can be brought in turn to the detector to produce a current which is proportional to the number of ions arriving
Mass of each ion being detected is related to the size of the magnetic field used to bring it to the detector

Mass Spectrometer Output

Output from the chart recorder is usually simplified into a "stick diagram" showing the relative current produced by ions of varying mass/charge ratio
Vertical scale is related to the current received by the chart recorder - and so to the number of ions arriving at the detector
Mass is measured on the 12C scale

Factors Influencing HPLC Performance

Internal diameter of column: smaller in diameter, the higher in sensitivity
Pump pressure: higher in pressure, the higher in separation
Sample size
Polarity of sample, solvent, and column
Temperature: higher in temperature, the higher in separation

Quantitation

Each peak for quantification must be identified so standards can be made
Peaks must be sharp, narrow, well-separated from each other (resolved)
Baseline should be relatively stable
Peaks should be symmetrical (see peak tailing and broadening)
Detector response must be linear in the quantitation range

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Description

This quiz covers the advantages and disadvantages of refractometry, including its universal response and low sensitivity, as well as the basics of mass spectrometry detectors.