The horrors of scientific analysis, episode 1: The DGT Menace

Scientists make Dr. Evil look tame when it comes to creative ways of destroying things. Sharks with lasers on their heads? Meh. Look at the methods section of research papers and you’ll find an enormous variety of elaborate tortures, dressed up in innocent-sounding jargon.

I’ve mentioned it before, but we’ll start with an example I’m most familiar with: the sinister DGT (Diffusive Gradients in Thin films). This has been deceptively termed a ‘passive’ sampling technique, but what you’re about to hear will blow that misconception right out of the water. Let’s take a look at what DGT’s all about.

Don't be fooled. The glass is probably bulletproof to stop what's inside getting out.

DGT is a method used to catch chemicals, usually metals, from water. The aim is to find out how many, and what kinds, of metals are present. Making the device starts with taking a hacksaw to some innocent plastic pipe, leaving a mess of torn scraps on the floor. The severed pipes have a piston smashed onto them with a hammer, then the trap is laid – the resin gel.

This gel is made of the neurotoxic carcinogen acrylamide. Inside the gel are tiny beads of Chelex-100; imagine a miniscule football covered in mousetraps, just waiting for unsuspecting metal ions to brush into them so they can snap shut.

No, don't go near it! (Flickr: Memkaos)

You might think it sounds harsh so far, but we’ve only just gotten started. The devices are dropped into a waterway in a cage: that’s right, they’re so dangerous they need to be put in a cage. Of course, the official line is that the cage is to stop the devices from being interfered with, but we all know the truth. It’s to stop them escaping. After a time, ranging from hours to days, they’re gingerly retrieved, having trapped a payload of metals from the water. The evil geniuses scientists take them back to the lab. That’s when the real terror begins.

The DGT devices are pried apart with a screwdriver and the gels, full of the trapped metals, are dropped into tubes of nitric acid. This searing solution tears the metals off the Chelex traps, leaving them suspended in a pool of acid. Small samples are drawn off the acid pool, and prepared for the final, fatal phase. (Put on your Dr Evil voice here) Activate the ICP-MS.

If you’ve eaten recently, you might want to stop reading now. The poor little metal atoms, having been trapped from their natural environment and doused in acid, are sucked up into a tube and sprayed in vapour form to the hellish ‘quartz torches’. A flow of argon, combined with a spark, creates a fireball between the torches. It’s not just any fireball: it’s around 10 000 degrees Celsius, hotter than the surface of the sun.

Imagine, after all the torment, being put to a fiery death here... (Flickr: Lights In The Dark)

The metals don’t know what hits them. They are burned thoroughly, usually having some of their precious electrons torn from their grasp. The ICP (Inductively Coupled Plasma) machine counts them after they’ve been torched, after which the charred remains are unceremoniously dumped into a waste container and forgotten.

And then the scientist gets a number in a spreadsheet.


Why do they do it? Well, in this particular study, the team were testing to see if DGT metal trap devices can be used to study environmental processes, like tidal cycles, in estuaries. These important environments, where rivers meet the sea, are notoriously complicated because of how many factors affect their chemistry over the course of hours, days and months. The DGT method, which operates over a longer time period, proved to be a useful alternative to normal sampling methods, which only take a snapshot of the conditions at one time point.

I still don’t think it’s an excuse.
Dunn, R., Teasdale, P., Warnken, J., & Schleich, R. (2003). Evaluation of the Diffusive Gradient in a Thin Film Technique for Monitoring Trace Metal Concentrations in Estuarine Waters Environmental Science & Technology, 37 (12), 2794-2800 DOI: 10.1021/es026425y

Categories: Science | Tags: , , , , , , , , | 7 Comments

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7 thoughts on “The horrors of scientific analysis, episode 1: The DGT Menace

  1. Pingback: The horrors of scientific analysis, episode 1: The DGT Menace (via David Robertson) « Engaging Talk

  2. Oh. The holocaust of science… :)

  3. Hmm – you kept me on the edge of my seat the whole way through – quite a feat! :)

  4. Yes, it’s rather violent when you personalise it!

  5. Chris

    You bas….ds. It is almost enough to make me religious and anti-science, Then I remember the old testament.

  6. Pingback: The horrors of scientific analysis, part 2: Ferocious FM-TOX « David Robertson

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