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View Full Version : Could Hanna-style colorimeters be used to measure nitrates, etc?


niqiri
01/11/2011, 11:39 PM
Could one use a a Hanna-type colorimeter with the classic color-changing test kits and convert the measured absorbance (or lack thereof) into a reading? I imagine the factory would program the unit with known nitrate (or whatever test was being performed) readings, say 1, 5, and 10, along with their measured absorbances. Would something like this be possible?

Verti
01/12/2011, 03:38 AM
I don't know how Hanna checkers works , but for Milwaukee low-range digital checker it works as the following (at least for PO4):

- You first need to read 10ml of water (with no powder at all).
- Set the above reading as "zero".
- Add the powder.
- read your nitrate level (the device actually compare the coloring of the "zero" to the one with the powder which is your NO3\PO4\whatever level).

bertoni
01/12/2011, 11:27 AM
Most of the tests won't work on saltwater. I think phosphate should be okay. I don't think nitrate is one of the tests that work, but it might be. Generally, those colorimeters aren't cost-effective for saltwater.

niqiri
01/12/2011, 01:03 PM
bertoni- I'm not sure what you mean about most tests won't work on saltwater. Do you mean when a colorimeter is used? It seems like you could measure the maximum absorbed wavelength of each type of test, say nitrate, phosphate, and pH, and then create a sort of "all-in-one" colorimeter which would measure a the transmittence/absorbance at a given wavelength which would be selected for whichever test was being performed. Sure, it might be more costly than a Hanna colorimeter, but it might also be an all in one, one time buy thing. I was thinking about this when using my API test kits. They're relatively cheap and I imagine with the addition of a colorimeter, the accuracy would be pretty good.

bertoni
01/12/2011, 02:16 PM
It might be possible to make a bunch of saltwater standards and program A Hanna (or other brand) colorimeter to use them. It'd be a lot of work and effort, though, to get a reliable set of parameters. For some tests, the method might not work at all in saltwater, but I think that's not much of an issue in practice.

UVvis
01/13/2011, 04:15 AM
Nitrate without any form of reagent will have some absorption in the UV range. Spectrophotometers and other UV light detectors can do a direct measurement if you have calibrated solutions to standardize the response.

Your colorimeter can analyze for nitrate using nitrite methods, provided you have a way to convert the nitrate into nitrite, analyze for nitrite separately, and then subtract your nitrite from your nitrate value. (this is where the nitrogen as X comes into play for stoichiometery) The problem here is most of the reduction systems to convert nitrate to nitrite are toxic, or difficult to use reliably for a single cell application.

With flow injection and some discreet analyzers, you can analyze nitrate down to the ppb range. IC's can get low detection limits to but have a hard time with the matrix effects.

By the 'all in one' colorimeter, you are actually talking about a spectrophotometer. Anything doing a dye based reaction, like azo dyes, are pretty easy to analyze for with a spectrophotometer.

Also, take a look at the Hach 890 and related series colorimeters. They can do a wide variety of analysis with the onboard programming. Remember that the onboard programming isn't always that accurate.