The Mass Spectromètre Flashcards

1
Q

How to calculate relative atomic mass

A

relative atomic mass = average mass of 1 atom
Twelfth of mass of 1 atom of Carbon -12

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2
Q

How to calculate Relative molecular mass

A

relative molecular mass = average mass of molecule
Twelfth the mass of 1 atom of 12C

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3
Q

What are mass spectrometers used for with chemists

A

by forensic scientists to help identify substances such as illegal drugs.

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4
Q

What happens in a time of flight mass spectrometer brief

A

In outline, the substance in the sample are converted to positive ions, accelerated to high speeds , and arrive at a detector.

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5
Q

What order does the mass spectroscopy go in

A

Vacuum
Ionisation
Acceleration
Ion drift
Detection
data analysis

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6
Q

What happens in the vacuum

A

The whole apparatus is kept under a high vacuum to prevent the ions that are
produced colliding with molecules from the air.

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7
Q

What happens in electrospray ionisation

A

sample is dissolved in a volatile solvent

forced through a fine hyperdermic needle that is connected to a positive terminal of a high voltage supply

And particles gain a proton from the solvent as they leave the needle
Forming xH ions

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8
Q

What happens in electron impact ionisation

A

In electron impact, the sample is vaporised and high energy electrons are fired at it from an electron gun,
which is a hot wire with a current running through it that emits beam of high energy electrons
This usually knocks off one electron from each particle forming a l+ ion.

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9
Q

What happens in acceleration

A

The positive ions are attracted towards a negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed.

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10
Q

What happens In ion drift

A

The ions pass through a hole in the negatively charged plate, forming a beam and travel along a tube, called the flight tube, to a detector.

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11
Q

What happens in detection

A

When ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities. The flight times are recorded. The positive ions pick up an electron from the detector, which causes a current to flow.

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12
Q

What happens in data analysis

A

The signal from the detector is passed to a computer which generates a mass spectrum

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13
Q

What is high and low resolution mass spectrometry

A

High resolution measures the relative atomic mass to five decimal places
Low resolution measure the relative atomic mass to one decimal place

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14
Q

What is relative atomic mass

A

the mass of an atom compared to 1/12 of a carbon-12 atom

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15
Q

What is relative molecular mass

A

the mass of an molecule compared to 1/12 of a carbon-12 atom

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