Saturday, September 16, 2006

Plumbing better than Mario and Luigi

Instead of dealing with large green pipes you have to jump into,

I have to deal with peristaltic pump tubing.

These little tubes are used to carry liquids into the mass spec. Other people use them too, such as chemists who use HPLC, IC, and SFA.

About twice a month, I have to run an analysis called FIAS or TTRA. Too make a long expanation short, the samples are mixed with buffer (pH 5.5) and internal standard (Y, In, Tb) all "online", then pushed through a column with an affinity resin that grabs the transition metals and lets the group I metals pass through. Then, the column is washed with acid, which rinses the transition metals into the mass spec which sorts them and counts them.

The way the literature describes to do this was unecessarily complicated. It explained using a sample loop and employing a water line to wash the column. It involved two valves, two pumps, four peristaltic pump lines, a double six-way valve, and finally the column.That's the way I did it and it worked for a while, but eventually it stopped working properly and I couldn't fix it. So instead of spending multiple days troubleshooting, I decided to just completely start over and re-think the whole thing.

I re-plumbed it much more simple and straight forward. Both valves, half of the double six-way valve, and the water line ended up being unnecessary. Now, loads of para-film were no longer needed to prevent leaks in the peristaltic pump tube connections. Also, less sample is used.

Wednesday, September 13, 2006

How to make a 1000 fold dilution

Making dilutions is an everyday thing when analyzing environmental samples. It's either diluting salt water samples by 10 because they have such a high ion content they suppress the plasma and cause internal standards to drop too low or diluting sediment samples because it takes more acid to digest them than is in the calibration standards.

Before entering into environmental analytical chemistry I would say to make a 1000 fold dilution, add 1000mL to 1 mL of what you're trying to dilute. But that's wrong, you add 999mL to 1mL of what you're trying to dilute. Reason is, it's already diluted once. If you start with pure copper for example, and stuck it in a beaker, then you would have to add 1000mL to dilute it 1000 fold. But if the copper is already dissolved in 1mL, then you would have to add 999mL to dilute to 1000 fold. I'm pretty sure you typically don't see pure metals, sitting around an environmental chemistry laboratory waiting to be dissolved into standards. It's much easier and cost effective to buy the metals already dissolved in water in nice, guaranteed concentrations, like 10,000ppm.

I can grow orchids --->