How do you test liquid or solid samples with your DIY Spectrometer? Read about ways to prepare and scan samples here, and read about different tests you can do with your spectrometer.

Sample containers

What do you store liquid samples in? A good sample container has flat sides, so you can shine lights (and lasers) through it without lots of reflections. It's also good to have the light travel through a consistent amount of the sample -- many cuvettes (traditional spectrometry sample containers) are 1cm x 1cm, so the light always goes through 1cm of the sample.

A square-sided bottle, left, and a cuvette, right (photo from Wikipedia.

Water sampling

Water is usually very clear in small amounts -- even murky water in a small container will look pretty transparent. That makes it hard to measure with spectrometry unless you shine light through a lot of it. But some tests have been done -- see this example of a scan of water from the Charles River before and after 7 days of settling, by Jeff Hecht:

However, most research in Public Lab to date has focused on oil spectroscopy -- attempting to identify petroleum residue in sediments. Read on to learn more!

Oil sampling

To identify oil contamination, we have been attempting to illuminate oil samples with UV flashlights and green lasers, which can make some oils fluoresce, or glow.

The basics of sample preparation for oil identification are still being refined, but our best practices to date are:

1. Collect soil, sediment, tar, or other solids which you suspect contain petroleum contaminants.
2. Put a pea-sized amount of sample in a medium (1 cup or 300ml) jar and fill halfway with unscented mineral or baby oil (from a pharmacy). Stir up or mush until it breaks down.
3. Leave overnight or for up to 48 hours to settle in a dark place.
4. Use an eyedropper to move the clear, hopefully yellowish solution near the top into a new, small (1oz), glass, flat-sided container or cuvette.
5. Try shining a laser or UV light through; if it's too opaque, let it settle again and eyedrop it into another container with more mineral oil. It should look roughly like olive oil in darkness and color.

Read more about this process at this note by Scott Eustis: http://publiclab.org/notes/eustatic/08-01-2013/making-grand-isle-coffee

...more soon...