Rosetta lander waits for more time in the sun

Surface of Comet 67P/Churyumov-Gerasimenko taken by Rosetta's navigation camera. [Credit: European Space Agency.]

Surface of Comet 67P/Churyumov-Gerasimenko taken by Rosetta's navigation camera. [Credit: European Space Agency.]

Philae, the lander released by the European Space Agency's Rosetta spacecraft on to the surface of a comet, is waiting for some sunlight to bring it back to life. 

Rosetta scientists speaking at a recent American Geophysical Union meeting said they did not know exactly where Philae had landed on Comet 67P/Churyumov-Gerasimenko after it was released. Philae bounced twice on the surface of the comet before settling in the shadow of a cliff.  The lander is powered by solar panels and requires sunlight to function.  

Rosetta is still circling the comet and has taken photographs of its surface, which the scientists hope will reveal Philae's precise location. The data must travel 483 million kilometres to Earth before being examined. 

The lead lander scientist, Jean-Pierre Bibring, said he believed Philae would come out of its hibernation as the comet moves closer to the sun, possibly by February or March. But he cautioned success will depend on Philae's solar panels receiving sufficient light, and also on whether it is able to survive the cold conditions on the comet's surface.

Bibring also confirmed large organic molecules had been found on the comet, which scientists were still working on identifying.

A Christmas comet moves closer to Earth

Comet Lovejoy on December 13 from the Astronomical Society of Victoria’s Astrophotography Observatory, Heathcote, Victoria. [Credit: Phil Hart, CC BY-SA]

Comet Lovejoy on December 13 from the Astronomical Society of Victoria’s Astrophotography Observatory, Heathcote, Victoria. [Credit: Phil Hart, CC BY-SA]

After a year where we have come closer than ever before to a comet, with the historic landing of a spacecraft on Comet 67P/Churyumov-Gerasimenko, the heavens have another treat for us in Comet Lovejoy C/2014 Q2.

By Tanya Hill, Museum Victoria

If you are away from the bustle of the city these holidays, then try your luck at spotting a faint comet in the northern sky.

Comet Lovejoy C/2014 Q2 is the fifth comet to be discovered by Brisbane amateur astronomer Terry Lovejoy. Comets are the only astronomical objects that are automatically named for the person who found them.

Lovejoy found the comet last August using an 8-inch telescope. It was about the same distance from the sun as the asteroid belt and was located around 420 million km from Earth. At that distance, the comet’s brightness was measured at 15th magnitude, which is about 4,000 times fainter than the eye can see.

However, in the last few months Comet Lovejoy has been moving closer and it is now about 100 million km away. Amateur astronomers have been watching its approach using telescopes and binoculars. And in the last few days it has become just bright enough to be seen with the naked eye.

Faint comet, dark skies

The comet seems to be brightening a little faster than expected and its brightness should continue to increase slightly as it travels by Earth. Even so, it’s always going to be a tough one to spot and you’ll need lovely dark skies away from any suburban lights to have a chance to see it without the help of binoculars.

The constellation of Orion – distinguished by the three ‘belt stars’ – as seen from the suburbs (on the left) and from a dark country sky (on the right). Globe at night

Comets are inherently unpredictable and it’s always hard to know exactly how bright they might become as they head towards the sun. The closest this comet will get to the sun is around 93 million km on January 30 (that’s about 15 million km closer than Venus).

It’s also not the first time that the comet has passed through the inner solar system. It has a period of the order of 10,000 years and spends most of that time heading out to the Oort Cloud. This a sphere of icy comets that extends from a few 100 billion to trillions of kilometres from the sun.

While we may have to watch the comet closely to see how it’s brightness changes, it is possible to map out its orbit very precisely.

Across the northern sky

What’s great about Comet Lovejoy’s path is that it passes above some of the best constellations in the summer sky. It will appear above Canis Major throughout December, then move past Orion during early January and by late January it appears above the constellation of Taurus.

These constellations can be found in the northern sky throughout the entire night across Australia. Although with the comet being so faint it’s best to start observing around two hours after sunset, when the sky is nice and dark.

The path of Comet Lovejoy across the Australian northern sky. Museum Victoria/Stellarium

The comet will make its closest approach to Earth on January 7, at a distance of about 75 million km. It’ll be interesting to see how much the comet brightens from now until December 25.

After that, the moon will start appearing in the northern sky, making it harder to see the comet. Two weeks later, from January 9, there will be an hour or so of dark sky to catch the comet before the moon rises.

That week, from January 9-16, should be a good time to view the comet because even though it will be moving away from Earth it will still be heading towards the sun. This means its intrinsic brightness should continue to rise. It’s currently estimated that the comet will peak in apparent brightness at a magnitude of 4.4 on January 10.

By the last week of January, the comet will have moved too far north to be seen from Australia. During February, it’ll travel between Andromeda and Perseus, two prominent constellations for the northern hemisphere.

You can find out where to see the comet from your specific location and get up-to-date information regarding its expected brightness at the website maintained by British astronomer Domenic Ford.

A comet’s green glow

Comet Lovejoy is faint to see with the naked eye, but astrophotographers are already getting some great shots of the comet. One thing that’s easily noticed is the comet’s bright green colour.

Very few astronomical objects are coloured green. Damien Peach/SEN

The colour is likely due to the presence of two gases – cyanogen (CN)2 and diatomic carbon (C2) – which glow green when their molecules are ionised or excited. Ionisation causes electrons within the molecules to gain energy and when the electrons drop back down to their normal state, they give off light of a certain wavelength. For these molecules they emit green light and since they are very strong emitters, their green colour dominates the comet.

Christmas comets

This is the third comet of Lovejoy’s to be visible around Christmas time. Last year, Comet Lovejoy C/2013 R1 could be seen faintly from the northern hemisphere throughout November and December.

While back in 2011, Comet Lovejoy C/2011 W3 was a lovely comet for Australian skies with an impressive tail. This comet was a sun grazer, and it passed just 140,000km above the surface of the sun on December 16, 2011.

The current Comet Lovejoy may only be seen as a faint fuzzy blob in the night, but it’s in such a rich and interesting part of the sky and it won’t be around again for another 8,000 years, so why not take some time out to enjoy the evening sky this Christmas.

Comet Lovejoy C/2011 W3 as seen on December 23, 2011 from Cape Schanck, VIctoria. Alex Cherney

The Conversation

This article was originally published on The Conversation. Read the original article.

Planet-hunting spacecraft Kepler makes a comeback

An artist's impression of NASA's planet-hunting Kepler spacecraft operating in a new mission profile called K2. Using publicly available data, astronomers have confirmed K2's first exoplanet discovery proving Kepler can still find planets. [Image Credit: NASA Ames/JPL-Caltech/T Pyle]

An artist's impression of NASA's planet-hunting Kepler spacecraft operating in a new mission profile called K2. Using publicly available data, astronomers have confirmed K2's first exoplanet discovery proving Kepler can still find planets. [Image Credit: NASA Ames/JPL-Caltech/T Pyle]

Last year it seemed that NASA’s Kepler spacecraft – and its mission to search for Earth-like planets in deep space – was crippled for good. But now comes the exciting news that engineers have devised an ingenious way to repurpose Kepler to continue its search of the cosmos for other worlds.

And, what is more, the craft has marked the occasion with the discovery of a new exoplanet.

Astronomers have confirmed the find of  HIP 116454b, a planet 2.5 times the diameter of Earth that follows a close, nine-day orbit around a star that is smaller and cooler than our sun, making the planet too hot for life as we know it.

HIP 116454b and its star are 180 light-years from Earth, toward the constellation Pisces.

It's a triumph for engineering and its ability to solve problems as much as for astronomy.

Kepler was designed to "stare" intently at the same patch of space for long periods in an attempt to identify new planets – and hopefully ones with the right conditions for life. It does that by looking for "transits" – where a distant star dims slightly as a planet crosses in front of it. 

But all this needs a very accurate orientation system.

Kepler was fitted with three electric-powered reaction wheels – spinning, gyroscope-like devices. It had a spare in case one failed but when two did, it appeared the spacecraft would not be able to re-orient itself.

Rather than give up, though, scientists and engineers crafted a resourceful strategy to use pressure from sunlight as a “virtual reaction wheel” to help control the spacecraft. The illustration below explains how the system works - click on the image to expand.

Using the sun and the two remaining reaction wheels, engineers have devised an innovative technique to stabilise and control the spacecraft in all three directions of motion. This technique of using the sun as the 'third wheel' to control pointing is currently being tested on the spacecraft. To achieve the necessary stability, the orientation of the spacecraft must be nearly parallel to its orbital path around the Sun, which is slightly offset from the ecliptic, the orbital plane of Earth. The ecliptic plane defines the band of sky in which lie the constellations of the zodiac. [Image credit: NASA Ames/W Stenzel]

The amazing history of the Pulsar watch

When we reached out to Abe Megahed at the watch retail site Time Trafficker to source an image of a Pulsar P2 watch to illustrate Alan Finkel's column on LED lights we also received a fascinating history into the timepiece we thought we'd share:

The Pulsar P2 was the first digital wristwatch to enter mass production. It became available in 1973 and made its public debut in the opening scene of the Roger Moore James Bond film Live and Let Die. After this, it became a sensation and was worn by movie stars and other celebrities and high rollers. The P2 cost $395 in 1973, which was more than a Rolex Submariner at the time. 

Although the P2 was a huge success, as with most revolutionary advances, the digital watch was almost a disaster.  

As you can infer by the name, the P2 was actually the second model produced by Pulsar. The very first digital watch was the Pulsar P1, introduced in April of 1972. The P1 was a limited edition model, a step beyond a prototype, but not really a production model.

Only 400 were produced. The P1 featured a solid 18 kt case and the crystal was made out of a solid slab of synthetic ruby. It cost an astounding $2,200. However. the real innovation of the P1 was the 25-chip module inside of the case.

It had 25 individual tiny integrated circuit chips and over 400 gold connections, each of which had to be painstakingly hand soldered. It was rumored that the module was by far the most expensive part of the watch and that Hamilton Pulsar was building them at a loss, even at the astronomical price.  

It was thought that they would last 100 years without maintenance so the cases were soldered permanantly shut using gold solder. Unfortunately, the modules started failing within a few months and Pulsar recalled them all, replacing the overly complex 25 chip modules with a variant of the single chip modules that were made for the P2.

The original 25 chip modules were destroyed and currently only about 6 are now known to exist. 

Since the P1 was such a technological revolution, I thought I'd also put together a link to a set of images of the Pulsar P1 25 chip module.

It's a pretty interesting story. Since the digital watch preceded calculators and computers and was the first consumer electronic gadget to employ microelectronics, you could rightly say that is where the entire digital age began.


Abe Megahed

Methane detected on Mars

The Gale Crater on Mars, showing the position of NASA's Curiosity Rover.

The Gale Crater on Mars, showing the position of NASA's Curiosity Rover.

The NASA robot rover Curiosity has detected methane on Mars while exploring the Gale crater, fuelling speculation that life might be its source. Animals and other organisms on Earth produce methane as a waste gas.

But astrobiologist Michael New is being more cautious. Speaking at NASA's Washington headquarters he said: "You need to know what is going on right at the source. You need to know the context. It's very hard to look at the methane alone and say it came from life."

NASA first detected methane on Mars in 2009, when telescopes revealed methane plumes on the planet's northern hemisphere. The finding suggested Mars had a replenishing supply of the gas because methane molecules would last for an average of 340 years in the Martian atmosphere before being broken down by sunlight.

Methane can also be made in a number of non-organic ways, including as a reaction between cosmic dust and ultraviolet rays from the sun.

The latest results from Curiosity confirm the 2009 finding. They show methane is present in the Martian atmosphere at one part per billion, or at concentrations 4,000 times less than on Earth.

The Curiosity Rover was sent to Mars in order to ascertain whether life once existed, or could exist there. During its mission it will analyse the planet's soil and rocks. 

The rover detected a 10-fold rise in methane in the atmosphere around it as well as organic molecules in powdered rocks collected by its drill. This was the first time organics have been detected on surface material on the planet. It is believed they could have formed on the planet itself or landed there on a meteorite. The methane levels dropped when Curiosity moved about a kilometre away, suggesting the methane was produced by a local source. 

The findings have been published in Science. The NASA authors cautiously suggest that microbial bugs known as methanogens might be a possible source of the methane.

"In the best of all possible worlds you would crack open a Martian rock and there would be eyes staring back at you," said New.  "Or at least endolithic communities [organisms such as moss or lichen that live in rock cracks], which you can find living inside rocks in the desert and in Antarctica. The rocks can provide protection, but sometimes they are using the chemistry of rocks for energy as well. So if you cracked open a rock and saw a band of green or orange, that could mean life. That would be great, but we can't expect it to happen," said New. 

Gale Crater was formed by a meteor impact 3.5 billion to 3.8 billion years ago. Mount Sharp lies at its centre, and it is believed flowing water once carved channels into the mountain and crater walls. Curiosity has discovered that water is bound to the soil within the crater.  

Crows show off their smarts

Crows have long been considered intelligent birds. [Credit: Lomonosov Moscow University]

Crows have long been considered intelligent birds. [Credit: Lomonosov Moscow University]

Crows have shown a capacity to reason in an experiment devised by biology researchers at Lomonosov Moscow State University in Russia.

"What the crows have done is a phenomenal feat," says Ed Wasserman, a University of Iowa psychology professor and corresponding author of the study. "That's the marvel of the results. It's been done before with apes and monkeys, but now we're dealing with a bird; but not just any bird, a bird with a brain as special to birds as the brain of an ape is special to mammals."

"Crows spontaneously exhibit analogical reasoning," was published in Current Biology. The Russian experiment involved two hooded crows that were at least two years old. In phase one of the experiment, they were presented with three small cups each covered with a card showing two coloured shapes. The middle cup was the sample cup. The crows were trained to recognise that when one of the cups on either side of it carried a card that matched the sample cup card they would find two worms inside.

In phase two of the experiment, the card concealing the worms did not precisely match the sample cup card, but bore a relationship to it. For example, the card concealing the worms might show two same-sized circles, when the sample card displayed two same-sized squares.

"That is the crux of the discovery," said Wasserman. "Honestly, if it was only by brute force that the crows showed this learning, then it would have been an impressive result. But this feat was spontaneous."

Anthony Wright, neurobiology and anatomy professor at the University of Texas-Houston Medical School agrees. "For decades such reasoning has been thought to be limited to humans and some great apes. The apparent spontaneity of this finding makes it all the more remarkable."

Global life expectancy rises by six years since 1990

Enjoying life to the fullest everyday

Life expectancy around the world is rising, according to the Global Burden of DIsease Study 2013, which looked at mortality rates between 1990 and 2013.

GBD 2013 examined the number of yearly deaths due to 240 different causes in 188 countries over 23 years. It found global life expectancy rose by 5.8 years in men and 6.6 years in women.

A significant exception is in southern sub-Saharan Africa where deaths from HIV/AIDS has erased more than five years from life expectancy. 

"The progress we are seeing against a variety of illnesses and injuries is good, even remarkable," said lead author Christopher Murray, Professor of Global Health at the University of Washington.

"The huge increase in collective action and funding given to the major infectious diseases such as diarrhoea, measles, tuberculosis, HIV/AIDS, and malaria has a real impact."

But he warned the study showed "some major chronic diseases have been largely neglected but are rising in importance, particularly drug disorders, liver cirrhosis, diabetes, and chronic kidney disease".

Rates of liver cancer caused by hepatitis C is up by 125%; atrial fibrillation (serious disorders of heart rhythm) have risen by 100%; and drug use disorders have increased by 63%.

At the same time in high income regions, death rates from cancers are down by 15%, while deaths from cardiovascular disease have fallen by 22%. 

HIV/AIDS remains the greatest cause of premature death in 20 of 48 countries in sub-Saharan Africa.

The results of GBD 2013 have been published in The Lancet.

Oceans now hold 250,000 tons of plastic trash

[Credit: U.S. National Oceanic and Atmospheric Administration]

[Credit: U.S. National Oceanic and Atmospheric Administration]

There is more than quarter of a million tons of plastic floating in the oceans - 10 times more than previously thought – a survey by an international team of scientists has found.

And that does not include the plastic that has washed up on beaches or sunk to the sea bed.

The scientists from the 5 Gyres Institute came up with the figure after trawling nets during 24 expeditions between 2007 and 2013 across all five sub-tropical ocean gyres, coastal Australia, Bay of Bengal and the Mediterranean Sea.

Their research was published in PLOS One.

The discovery of the impact of discarded plastic is relatively recent. The Great Pacific Garbage Patch – about the size of Texas – was discovered when Charles Moore stumbled across it while returning from the Transpacific Yacht Race in 1997.

Moore returned earlier this year to discover that the plastic had coalesced into islands with their own ecosystems.

The latest estimates of the scale of the problem show that it has worsened rapidly in the past three decades. In the 1970s, studies suggested that about 45,000 tons of plastic littered the ocean.

There is now virtually no ocean that is free of the scourge but undoubtedly the North Pacific is the worst affected with more than a third of the total plastic found in the oceans, according to the latest study.

Moore, one of the paper's coauthors and founder of marine research and lobby group Algalita, said the estimate was conservative.

Genome study unlocks centuries-old mystery of birds

Something to sing about...scientists have worked out the evolutionary basis for birdsong like that of this marsh wren. [Credit: iStock]

Something to sing about...scientists have worked out the evolutionary basis for birdsong like that of this marsh wren. [Credit: iStock]

The family tree of modern birds with their spectacular biodiversity has baffled biologists for centuries, but they might finally be coming to grips with the problem thanks to a major genetic study.

The findings include a comprehensive family tree of the more than 10,000 species, more comprehensive than anything seen before, and answers to how birds lost their teeth, why they learnt to sing and how penguins adapted to Antarctica. 

The Avian Phylogenomics Consortium, which has sequenced, assembled and compared the full genomes of 48 bird species, are being released that will shed light on how birds emerged and evolved after the mass extinction that wiped out dinosaurs 66 million years ago.

The consortium of 200 scientists, 80 institutions in 20 countries looked at species including the crow, duck, falcon, parakeet, crane, ibis, woodpecker, eagle, representing all major branches of modern birds.

The results are being reported almost simultaneously in 23 papers – eight papers in a special issue this week of Science, and 15 more in Genome Biology and other journals.

"This is the largest whole genomic study across a single vertebrate class to date. The success of this project can only be achieved with the excellent collaboration of all the consortium members," said the leader of the consortium, Guojie Zhang of the National Genebank at BGI in China and the University of Copenhagen.

Thomas Gilbert of the Natural History Museum of Denmark said that no single study before this had deliberately targeted the full diversity of any major vertebrate group.

"This is what our consortium set out to do. Only with this scale of sampling can scientists truly begin to fully explore the genomic diversity within a full vertebrate class."

Bloomberg has a useful summary of the findings so far. We will be looking at the discoveries in more detail at Cosmos magazine:

Birds’ Big Bang: How and when birds diversified into a wide variety of species, including the 10,000 species alive today, has been a longstanding controversy. Using the new avian genomes, a team at Duke found compelling evidence that modern birds rapidly evolved 66 million years ago, in a “big bang” of evolution, right after the mass extinction event that wiped out the dinosaurs -- rather than before the event. While ancient birds existed before, the big bang marked a surge in diversification.
Predatory Family: The same Duke team compared the avian genomes to create the most solid family tree of modern birds to date. Past attempts had met with limited success, since scientists used just 10 to 20 genes per species to try to infer species relationships. From the new tree, they concluded that the common ancestor of all birds was an apex predator -- the term for a killer at the top of a food chain. As birds evolved, some of them, such as hawks and falcons, retained predatory traits from that ancestor. Many other species lost them.
Petite Genome: Bird genomes are known to be small -- only about one-third the size of the human genome. A team from BGI-Shenzhen in China found out why they are so petite by analyzing the 45 new genomes, plus three previously available genomes from the chicken, the turkey and the zebra finch. It turns out that birds have very little repetitive DNA (most other animal genomes are bloated with repeated sequences) and their genomes experienced massive gene loss over time, including the loss of genes essential for human reproduction, skeleton formation and lungs.
Sex and a Graveyard: Unlike the human Y chromosome, which contains many genes that no longer function, the avian W chromosome is full of active genes that are still evolving among bird species, according to a paper from the University of California at Berkeley. The finding challenges the classical assumption that the bird W chromosome is a gene graveyard like the human Y chromosome, which has lost lots of genes and has remnants of genes that aren’t used anymore.
Of Birds and Men: Humans and songbirds, unlike other animal species, share brain circuits that are important for speech and song, respectively, according to the Duke team. Singing or hearing a birdsong activates complex gene networks in birds, turning genes on and off in their brains. In fact, about 10 percent of the bird genome is activated and regulated by singing. The researchers found that vocal learning in birds evolved independently at least twice during their evolution -- in other words, different groups of our feathered friends learned to sing independently.
Going Viral: Mammal species have had 6 to 13 times more viral infections in the past than birds, as detected by remnants of viral DNA in a genome. Scientists at the Duke-NUS Graduate Medical School in Singapore and the University of Sydney said the results suggest that birds are either less susceptible to viral infection or better able to rid themselves of viral DNA after an infection.
Pulling Teeth: Numerous genetic mutations caused the elimination of enamel in birds, which is why birds today have no teeth, according to a report from Montclair State University in New Jersey, though all birds did descend from a toothy, enamel-capped ancestor. Those mutations and the subsequent loss of teeth began about 116 million years ago.
Mutant Speedsters: Bird genomes evolved much faster than their closest living relatives, the crocodilians, according to a team at the University of California in Santa Cruz that compared the genomes to those of an alligator, a crocodile and an Indian gharial. Mammals outpaced birds.
March of the Penguins: The 45 genomes in the project included 2 penguin genomes sequenced for the first time: Adelie and Emperor. Scientists at BGI-Shenzhen gained many insights into how penguins adapt to the hostile Antarctic environment: For instance, both species had expanded gene families of proteins that make up feathers and contained a gene known to be involved in the development of thick skin.

The science of airport bomb detection: chromatography

Science and technology is at work trying to improve our security at airports. Recent developments include the machine that can sniff out minute traces of explosives in the air. Here we look at some of the science behind the identification of dangerous compounds.

By Martin Boland, Charles Darwin University

As the holidays draw near, many of us will hop on a plane to visit friends and family – or just get away from it all. Some will be subjected to a swab at the airport to test clothes and baggage for explosives. So how does this process work?

The answer is chromatography – a branch of separation chemistry – along with mass spectrometry (which I will address in a later article).

The word “chromatography” is roughly translated from Greek as “the science of colours”. The reason for the name becomes obvious when you realise that most people have accidentally performed a simple chromatography experiment.

If you’ve ever spilled water onto a hand-written shopping list, then held it up to let the water run off, you’ve probably noticed the ink diffuses across the paper, and that the pen’s colour is made up from several pigments (if you’ve not, you can do the experiment – try it with a couple of pens of different brands, but the same colour). This separation is chromatography.

There are several different types of chromatographic separation. What they all have in common is that a mixture of materials that need to be separated (the analytes) is washed over a solid material (called the matrix), causing the analytes to separate.

That may sound like chromatography is just filtration, or separation by particle size. In some cases, that is almost exactly what happens (size exclusion chromatography is often referred to as gel filtration chromatography).

Lloyd Davis/Flickr

But most chromatography methods work by some other chemical effect than just the size of the materials being separated, including (but not limited to):

  • normal-phase chromatography, such as ink on paper
  • reverse-phase chromatography, often used in university lab experiments
  • gas chromatography, seen in airport bomb detectors
  • capture” chromatography, used to purify drugs.

Each of these can be performed with one solvent, such as dropping water on your shopping list – known as isocratic (Greek for “equal power”) or with a changing mixture of solvents (known as a gradient).

So how does it work?

Technically speaking, it is the differential affinity of the analyte for the solvent and the solid matrix that drives chromatographic separation. So what does that mean, really?

You’ll need to bear with me here.

Have you ever been shopping with someone who stops to look at things while you’re trying to move though the store as quickly as possible?

That differential attraction to the stuff surrounding you – that’s what drives chromatography. You walk though the aisles only rarely interacting with the goods on sale, while your shopping partner has much greater affinity for the shelves and stops frequently. By the time you’re at the exit they are still only halfway through the shop – you’ve separated!

That is what happens to molecules. The solvent flows over the matrix (in the shopping list case, the paper) carrying the analytes. The relative affinity of the analyte for the matrix compared with the solvent determines the separation.

If a compound is totally insoluble in the solvent, it stays fixed to the matrix (you may have seen this when spilling water on a shopping list written in pencil). If the analyte is very soluble, it may move as fast as the solvent.

The shopping list example is called planar chromatography. The running ink seems to defy gravity, moving up the paper due to the capillary effect. More common in high-performance chromatography, the matrix is a column with the solvent forced over it, by gravity or pumping.

The grey box in the background is the most important part of this high-performance liquid chromatography system. Sanofi Pasteur/Flickr, CC BY-NC-ND

Using a column makes it easier to change the ratio of solvents by using a pump that can mix multiple materials (usually a mixture of water and a soluble organic solvent such as acetonitrile).

In the case of a gradient separation, the analyte has much higher affinity for the matrix than for the initial solvent mixture. As the solvent mix is changed, the analyte dissolves in the solvent and is carried out of the column separated from materials that are soluble in different solvent ratios.

Sometimes it’s a gas, gas, gas

For gas chromatography, the set up is a little different. The analytes are gases or volatile liquids (think petrochemicals, plant oils, chemical weapons). Such compounds are usually non-polar and hydrophobic – in other words, they don’t mix well with water.

The compounds are evaporated into an inert carrier gas (analogous to dissolving in a solvent). The carrier gas transports the compound over a hydrophobic matrix contained in a coiled column (often tens of metres long but only micrometres wide).

To improve separation, and allow analysis of materials with a higher boiling point (up to around 300C), the column is placed in an oven. Changing the temperature of the oven affects separation in a similar way to changing the mixture of solvents in liquid chromatography.

Quality control

When separating coloured compounds it’s pretty obvious when the process has worked. But how do you know if you’ve separated two colourless compounds, or separated microscopic amounts of analyte?

Linnie/Flickr, CC BY-NC-ND

There are several ways to detect the analytes depending on their chemical and/ or physical properties. Among the more common are:

  • ultraviolet or infrared (non-visible but optical wavelength) absorbance
  • non-visible fluorescence
  • conductivity or pH (how acidic the solution is)
  • collect samples and perform chemical tests
  • mass spectrometry.

Probably the most useful of these is mass spectrometry as it allows the analyst to work out exactly what compound they are seeing without needing prior knowledge of what was in the original analyte mixture.

An ever-developing world

Although instrumental chromatography is a mature technology (the first instruments were produced just after WWII), new applications frequently pop up.

Some are a matter of scale. Pharmaceutical companies that produce monoclonal antibodies (often used in cancer treatments) make use of capture chromatography to purify their products. On an industrial scale these can be tens of centimetres in diameter and metres in length (typical lab scale systems are a few millimetres diameter and 5-30cm long).

Other uses can either be in a specific new application, such as detecting cocaine on bank notes using the gas chromatography systems often seen at airports as bomb and drug detectors.

And even more exciting experiments are being done by chromatography instruments on board the Philae probe that detected organic chemicals on the comet 67P/Churyumov–Gerasimenko.

In the second part exploring the science of airport bomb detection, we delve into mass spectrometry.

The Conversation

This article was originally published on The Conversation. Read the original article.