lamotte colorimeter
lamotte colorimeter
I have a Lamotte SMART Colorimeter. The new model is the SMART2 Colorimeter, but that's why I got mine for a cheaper price.
One note on the colorimeters or even the spectrophotometers. They have been calibrated with 40+ test factors ranging from aluminum to zinc. We would probably be most interested in nitrate, phosphate, iron, iodine, and the like. The problem with these factory set programmed test factors is that they are intended to be used in freshwater.
If you want to test anything in saltwater, you're going to need to set up your own calibration curves and baselines. This is kind of a pain to do, but necessary if you want to get accurate results. I'm sure there are some test factors that aren't that far off between fresh and saltwater, but why even buy a one thousand dollar colorimeter if you only want something so inaccurate.
The problem with the user defined test factors is that it can only store 10 tests using your own reagents or Lamotte reagents. You could use Salifert or any reagent, granted that you have a known standard to compare the test kits with.
If you are calibrating in freshwater, there's no problem because you can easily obtain distilled or DI water, then add a known solution. CV1+CV2=CV3, right (where C= concentration and V= volume)? No problems there. If you know that your water has 0ppm or 0% anything except the hydrogen and oxygen molecules, CV1= CV3. Calibration is fairly straightforward.
But, when we use salt like Instant Ocean, Tropic Marin, or any other brand, we don't really know the concentration of solutes in there. For example, Instant Ocean claims to have 0 phosphates and nitrates, but is it really 0? Depending how much phosphate and nitrate we have in a known solution, we haven't accounted for this minute amount that might not be measurable with other test kits. I believe my colorimeter reads up to .1 ppm, but in the lab, we usually don't use that sig fig. Maybe that's not a big deal to some people.
Here's where it gets tricky, though. What if we're trying to test for calcium, or Iron, or something else that is absolutely in the synthetic salt. We need to rely on the manufacturers claims that they have some set range or test it against another test kit. The former might give us some really inaccurate readings to calibrate anything further with and the latter probably won't give us results too much better than that test kit itself.
I suppose you could go to the lab and ask the chemical supply house to get or make some pure sodium chloride or even try to get table salt. Mix it with DI or distilled water, then test it against a known solution. This might or might not work. There could be some interference doing it this way, but I definitely know there will be interference using synthetic salts. Personally, I haven't even started running calibrations because the time it takes is just not worth it. But, I suppose staring at an aquarium until I fall asleep, apparently, is worth my time. But honestly, I am just too lazy to do it, since I am not paranoid about test factors at the moment.
Now, if you're still reading this, and you can get a known standard somewhere or make up a batch, you need to input the data. No problem here. It's very straightforward. After you're done, or you've inputted enough data points to get a nice calibration curve, you test it with another known that's not one of the data points you used. This just tests if you correctly mapped the colorimeter. Spectrophotometers are a little more advanced because they aren't just finding color change, but %transmission and absorbancy. Basically, they calibrate the same way, though.
After all this is said and done, you've got yourself an expensive, and hopefully precise, piece of testing equipment. The accuracy is another monster altogether depending how well you set up your calibration curves and your known solutions. But even these devices can give inaccurate readings if the test tubes, cuvettes, or whatever are dirty, scratched, and have fingerprints on them.
I just figure that to make the known standard becomes costly. I waste reagents on plotting x amount of data points to not even be sure if the saltwater I mixed up truly has what I think it has in there. And I don't test on an hourly, or even daily basis, so it's not worth the hassle in the long run to test only 10 factors that I can plug and chug in the colorimeter less than 52 times a year. There's probably tons of other sources of error doing this BTW, but I figure if you buy something of this magnitude, you're going to have some idea of what you're doing. And, on the bright side, I don't need to change the test factor again unless I want to increase/decrease the range (.1-1ppm vs 1pm-10ppm). Yet, on the dark side, Murphy's Law tells me I'll accidentally delete the entire program and have to redo EVERYTHING.
I think I talked so much, my soapbox has petrified...
Mike
