00:00:01 This was a test camera, and it needed to go farther in in order to identify elements

00:00:09 in compounds when the mass spectrometer was called on.

00:00:15 We need to use more equipment in order to determine which components are produced through which

00:00:20 massive visible spectrometer Studies were conducted.

00:00:25 All matter is composed of atoms.

00:00:41 Every atom has a nucleus made of protons, shown in orange, and neutrons, shown in blue.

00:00:50 These are about equal in mass, and together they make up the mass of the atom, the orbiting

00:00:56 electrons being of negligible mass.

00:01:04 Identical atoms grouped together form an element, like beryllium.

00:01:13 The atom of beryllium has four protons, the number above.

00:01:18 But no other element has this number.

00:01:22 Each element is distinguished by the number of protons in its atom.

00:01:34 The number of protons is fixed for any one element, but the number of neutrons may vary,

00:01:40 depending on the number below.

00:01:51 Lithium, for instance, can have three neutrons or four.

00:01:56 So there are two atoms of lithium, of mass six and mass seven, because the numbers of

00:02:02 protons and neutrons added together come to different totals.

00:02:07 These two different atoms form the two isotopes of this element, lithium-6 and lithium-7.

00:02:18 Every element and every isotope is distinguished by the unique composition of its atom.

00:02:30 But in nature, pure elements are rare.

00:02:34 Such things are compounds formed from particular atoms linked together in specific structures.

00:02:42 These structures are molecules.

00:02:49 By finding the mass of an atom and the structure and total mass of the atoms in a molecule,

00:02:57 we could identify almost any substance.

00:03:00 But to do so, we would need a tool which could handle things as small as atoms and molecules.

00:03:11 It's easy to find the mass of an object as large as a ball.

00:03:16 We weigh it with a pair of scales.

00:03:26 If the ball were made of one isotope of a pure element, with every atom identical,

00:03:32 their total number and mass would give the mass of one atom.

00:03:39 But most things are mixtures of all sorts of atoms and molecules.

00:03:45 The individual masses can't be measured simply by weighing.

00:03:48 Two stages are needed.

00:03:51 First, to separate the masses, then to measure them.

00:04:00 These wooden balls vary in mass.

00:04:03 If they are released down this slope, they all run straight on.

00:04:16 Each ball has an identical core of iron.

00:04:21 So a magnet at the bottom of the chute ought to change the process.

00:04:39 The large mass is hardly affected, but the smaller the mass, the more the path is changed.

00:04:45 This device separates a mixture according to mass.

00:05:11 The amount of deflection is a measure of the mass.

00:05:14 The traps record the numbers in each mass group.

00:05:20 By combining gravity and magnetism, the masses are separated, measured, and recorded, all with the one device.

00:05:33 But what device could handle minute atoms and molecules?

00:05:39 An atom or molecule can be electrically charged by removing an electron.

00:05:45 A charged atom or molecule is called an ion.

00:05:50 In vacuum, ions are affected both by electric and by magnetic fields.

00:05:58 By combining these two effects, ions of different mass can be separated.

00:06:05 The electric field sets the ions moving.

00:06:09 The magnetic field deflects them according to mass.

00:06:14 Here is the basis of a tool to separate, to measure, and to record the masses of atoms and molecules, all with the one device.

00:06:26 At the beginning of the century, J.J.

00:06:28 Thompson built a machine to work in this way.

00:06:31 With it, he separated groups of ions.

00:06:36 But the records were diffuse and out of focus.

00:06:42 In the 20s, machines were improved.

00:06:46 Aston, Dempster, and others succeeded in focusing the ions into spectra of lines.

00:06:51 Each line a recording of the mass of a different group of ions.

00:06:58 Since then, machines have become more and more intricate.

00:07:07 The modern mass spectrometer can be used to analyze any kind of substance, producing in one form or another its mass spectrum.

00:07:22 Here is a typical mass spectrometer.

00:07:28 The substance to be analyzed is held in the reservoir.

00:07:33 It will be a gas or the vapor from a heated liquid or solid.

00:07:41 The reservoir is connected to the tube of the spectrometer.

00:07:47 It is seen now in diagram form.

00:07:49 The bend of the tube is set in a strong magnetic field.

00:08:01 The vapor leaks through to the ionization chamber.

00:08:05 Atoms and molecules are ionized.

00:08:13 The ions are accelerated through the slit by the electric field and travel down the tube into the magnetic field where they are all deflected.

00:08:23 But the ions of lesser mass are deflected rather more than those of greater mass.

00:08:28 Ions of lesser mass take the inside of the curve.

00:08:34 Each stream comes to focus near the detector.

00:08:39 The magnetic field changes and each stream is registered as a peak on a graph.

00:08:55 So a mass spectrum has been built up.

00:09:00 A record of the masses and amounts of ions.

00:09:10 This is the function of all mass spectrometers, to measure the mass of atoms and molecules.

00:09:17 But each machine is designed with a particular problem in view.

00:09:22 What are these problems?

00:09:24 Who works at them?

00:09:26 And how?

00:09:33 In the chemical industry, much of our time has to be spent identifying unknown compounds from oils and plastics, paints and dyestuffs.

00:09:43 By classical methods, each job may take days or even months.

00:09:48 A mass spectrometer can cut the time involved to a fraction, provided its results are accurate enough.

00:09:57 For some of these substances may be built from molecules which are almost identical in mass.

00:10:06 So we have to know the exact mass of the molecule and its structure before we can give a name to the unknown substance.

00:10:16 We use a specially designed machine.

00:10:26 This one, with two deflecting systems, can boost the accuracy of any measurement a hundredfold.

00:10:34 The molecules of the substance are ionized at the top right.

00:10:40 Some of them ionize whole and unbroken.

00:10:50 But other molecules break at their weakest points and produce a complete range of smaller fragment ions.

00:11:02 All the groups are recorded to form the mass spectrum.

00:11:09 Now let's examine the spectrum, starting with a whole molecule.

00:11:15 The position records the mass, the total mass of all the atoms in the molecule, mass 176.

00:11:23 But this is only to the nearest unit.

00:11:26 And these computed tables show, under mass 176, 38 different organic molecules, each varying only slightly in mass.

00:11:37 We need a much more accurate measurement.

00:11:40 To get it, we select the part of the spectrum which includes mass 176 and magnify it on the oscilloscope.

00:11:50 The left-hand peak records the whole molecule.

00:11:53 The central peak is an accurately known reference mass.

00:11:59 Adjust the oscilloscope controls, and as the settings become exact, the left-hand peak will gradually move to the center.

00:12:17 The two peaks come together.

00:12:29 With control readings, the exact mass of the molecule is now calculated.

00:12:50 From 176.0836 to four decimal places.

00:13:09 So we know the number and kinds of atoms in the molecule.

00:13:16 Seven carbon atoms, 12 hydrogen, and two oxygen.

00:13:20 So far, so good.

00:13:22 But these same 25 atoms can fit together in many different ways.

00:13:27 Here are four of the molecules they can make up.

00:13:31 Four different structures, four different substances.

00:13:38 Which is the right structure of the unknown substance?

00:13:42 One of these, or some quite different one?

00:13:46 The rest of the spectrum, which records the fragments into which the molecule broke, gives the answer.

00:13:52 For the way the molecule breaks up is the clue to the way it fits together.

00:13:58 We simplify the spectrum to see the pattern more clearly.

00:14:04 The lines record the masses of the molecule and of its fragments.

00:14:10 From the differences in mass, the parts of the molecule can be identified.

00:14:17 And the chemist can start to build up the whole structure of the molecule, bit by bit.

00:14:29 The hydrocarbon end group links the hydrogen, carbon, and oxygen atoms to a benzene ring.

00:14:44 The unknown molecule is built up from the pattern on the mass spectrum.

00:14:52 Using only a few specks of the sample, the chemist has needed just half an hour to find the molecule and name the substance.

00:15:03 Omega-butanil-benzoate, identified with economy and speed.

00:15:19 Materials of fantastic purity for nuclear reactors or spaceships.

00:15:28 Materials with measured amounts of impurities deliberately added to them, like the substances used in making transistors.

00:15:39 In many industries today, the efficiency of the final product depends on new standards of purity, hygiene, and control.

00:15:48 All the way down the line of manufacture.

00:16:00 Behind it all is material research, and an ever-growing demand to analyse all sorts of solids rapidly and sensitively.

00:16:11 This type of spectrometer can detect one part in a thousand million, like finding one person in Russia, China, and America put together.

00:16:23 It handles the toughest materials. These are tiny rods of alloy steel being brought together in the vacuum of the spectrometer.

00:16:40 A 50,000 volt electric spark is created across them.

00:16:45 The steel vaporises at its edges, and all the different component atoms become ions and pass through the deflecting fields of the spectrometer.

00:16:56 Each group of ions is recorded, in this case, as a line on a photographic plate.

00:17:02 Here is a series of exposures.

00:17:05 Every component element and isotope of the steel is recorded, from tantalum, the smallest component, to iron, the largest.

00:17:19 Here is part of a spectrum of the arsenic used in binary semiconductors.

00:17:24 The faint line on the left of this pair records a manganese impurity, one part in 50 million.

00:17:32 To record it is an achievement as tricky as finding this one grain of sugar lost in a lorry load of sand.

00:17:41 As we breathe, our lungs extract oxygen from the air and give out carbon dioxide from the bloodstream.

00:18:03 We see the carbon dioxide as the right-hand peak. In the centre is the oxygen, at the left, nitrogen.

00:18:18 With this spectrometer, we record the gases in a patient's breath as they continuously change.

00:18:31 For the first time, all the gases coming from a patient's lungs can be followed throughout the breathing cycle.

00:18:46 Now here is a way to test the responses of the lungs by introducing a foreign gas, argon.

00:18:54 The new gas makes another peak.

00:18:58 The way the lungs react to it is permanently recorded at the top of the paper.

00:19:04 The trace below is oxygen, then carbon dioxide.

00:19:08 We analyse these curves to find how efficiently the lungs react to special conditions.

00:19:15 But sometimes we need more localised information.

00:19:25 We use a bronchoscope to look right into the lungs of a patient under anaesthetic.

00:19:35 We explore the passages of the lungs and bronchial tubes.

00:20:06 But looking isn't always enough. We often want to analyse the gases in a specific segment of the lung.

00:20:14 We use a gas sampling tube connected to the spectrometer, its end guarded by a cage.

00:20:22 This we pass directly into the section we want to examine.

00:20:31 Partially withdrawing the bronchoscope, we leave the tube unobstructed.

00:20:48 The local gas concentrations are recorded.

00:20:52 They may be healthy traces or they may be typical of obstructions in the gas or blood flow of the lungs.

00:21:00 This detailed information is of immense importance.

00:21:04 It helps us both to diagnose ailments and to cure them.

00:21:22 To understand the structure of the earth, it helps to know the age of rocks.

00:21:30 As these rocks solidified long ago, minute traces of radioactive rubidium-87 were trapped in them.

00:21:38 Traces from which we can find the age of the rocks.

00:21:42 For radioactive rubidium-87 changes very, very gradually into strontium-87.

00:21:49 And as we know the rate of change, the age of the rock can be measured by the change.

00:21:55 Just as time is measured by the change in position of the sand in an hourglass.

00:22:03 The relative amounts of rubidium and strontium, which these rocks contain today, are different from the relative amounts present when they were formed.

00:22:12 By extracting and measuring the rubidium and strontium, we can work back to find the age of these rocks.

00:22:28 Here in the crushed sample are the minute traces of rubidium and strontium.

00:22:33 We must extract them carefully.

00:22:37 We use an automatic panning machine to separate out the fraction which is rich in these two elements.

00:22:49 Now we treat this fraction chemically to isolate the part containing the rubidium from the part containing the strontium.

00:22:58 This gives us two solutions, each containing one of the elements we want.

00:23:07 We coat the solutions in turn on the spectrometer filament.

00:23:11 This is the one containing strontium.

00:23:24 Now we're going to use the spectrometer to separate and measure the minute quantity of strontium-87.

00:23:37 We pass the coated filament through the vacuum lock into the ionization chamber.

00:23:48 Ions are formed as the substances evaporate from the heated filament.

00:24:00 This is the strontium run.

00:24:06 The peaks record all the strontium present.

00:24:21 The relative heights of the peaks give the exact amount of strontium present.

00:24:28 The relative heights of the peaks give the exact amount of strontium-87 obtained from the rock.

00:24:43 From these peaks, the rubidium-87 amount has been measured exactly.

00:24:50 From the amounts, the change is calculated.

00:24:58 From the change, the age of the rock.

00:25:06 As near as makes no difference, 740 million years.

00:25:12 A rock of the pre-Cambrian era, the dawn of the Earth's history.

00:25:27 Mass spectroscopy, analyzing the things around us, revealing more and more aspects of the world we live in.

00:25:49 With instruments of extreme delicacy, with techniques full of complexity.

00:25:57 Yet all evolving from man's understanding of how to control ions with electric and magnetic fields.

00:26:27 © BF-WATCH TV 2021