use R&D spectrometer for all test

[LadyTang2]

I dont have direct experience with the Hanna checkers. I have no reason to suspect any problems with the hardware.

I chose a spectrophotometer because (a) it's one instrument for all tests, and (b) as I understand it, the Hanna checkers don't allow setting a blank or reading raw absorbance values.

Assuming the Hanna hardware is fine (which I assume), it should be possible to do the same thing with some workarounds using Hanna checkers, assuming you buy one for each wavelength you need.

Thanks for the response, does each test require a reagent? Or do some compounds that produce color not need reagent and ones that do, do need reagent? What do you test for and do all need reagent?

 

[EMeyer]

Thanks for the response, does each test require a reagent? Or do some compounds that produce color not need reagent and ones that do, do need reagent? What do you test for and do all need reagent?

Sorry for the delay, missed that. All the tests I've run on this instrument are reagent-based. I have been simply using hobbyist kits but with several steps that help to make the test both more accurate and higher resolution.

For NO3 and NO2 I have used Red Sea and SeaChem.
For NH3 I have used Red Sea and API.
The list is only limited by what I've needed to test at a resolution that I trusted to use for calculations.

In principle, any colorimetric test can be measured on a visible wavelength spectrophotometer. It is definitely more work than the Hanna Checkers. If a person is not already familiar with lab procedures around spectrophotometry, this may be more work than the benefits justify. For anyone already familiar with these procedures, who has access to an instrument, I think it can make testing much more satisfying by removing a lot of uncertainty.

For example, I read people worrying about false positives with ammonia tests read by eye, which this approach completely resolves. Uncertainty in test results hurts my OCD, so I went with this approach

 

[LadyTang2]

Theres another thread similar to this one people were discussing today.

The result you get, what units is it? Or is it like a wavelength of light and how do you convert that to say units of calcium?

 

[EMeyer]

Theres another thread similar to this one people were discussing today.

The result you get, what units is it? Or is it like a wavelength of light and how do you convert that to say units of calcium?

The short answer is you get a reading in absorbance that is easily converted to ppm.

The longer answer is best shown by example. Here is an example of the procedure I've used for NH3 with the Red Sea test. I didn't do anything special here, just applied standard procedures from spectrophotometry to analyze the results of this test, instead of reading them by eye. I am sure the Hanna checkers use similar math, with built-in constants instead of calculating them from a series of dilutions. (I'm showing this only to discuss how it can be done in principle for any colorimetric test, not recommending that anyone needs to do so for ammonia)

First make a standard curve using a stock solution of ammonium sulfate, by preparing a series of dilutions at known concentrations. They look like this

Next measure their absorbance on the spec, in this case at 680 nm. Here is an example figure

You can calculate the slope and intercept* of this equation, expressed as

Abs = Slope * [NH3] + Intercept

To test your sample, you can measure Absorbance on the spec then calculate the concentration in ppm as

[NH3] = (Abs - Intercept) / Slope

It all takes much longer to explain than to do; the math is straightforward so it's handled by a spreadsheet or app.

(*the intercept should be and is very close to zero, but to account for any errors in the blank I always include this in the calculation)

One of these days I'm gonna get around to doing Phosphate, since this is one of the only tests where I'm actually interested in the precise numbers at low levels. In principle even my cheap spec is surely at least as sensitive as the Hanna checker and possibly more sensitive (I seem to remember that sensitivity is a function of path length with spectrophotometry, and isnt the Hanna less than 1 cm path length?)

 

[Dan_P]

The short answer is you get a reading in absorbance that is easily converted to ppm.

The longer answer is best shown by example. Here is an example of the procedure I've used for NH3 with the Red Sea test. I didn't do anything special here, just applied standard procedures from spectrophotometry to analyze the results of this test, instead of reading them by eye. I am sure the Hanna checkers use similar math, with built-in constants instead of calculating them from a series of dilutions. (I'm showing this only to discuss how it can be done in principle for any colorimetric test, not recommending that anyone needs to do so for ammonia)

First make a standard curve using a stock solution of ammonium sulfate, by preparing a series of dilutions at known concentrations. They look like this

Next measure their absorbance on the spec, in this case at 680 nm. Here is an example figure

You can calculate the slope and intercept* of this equation, expressed as

Abs = Slope * [NH3] + Intercept

To test your sample, you can measure Absorbance on the spec then calculate the concentration in ppm as

[NH3] = (Abs - Intercept) / Slope

It all takes much longer to explain than to do; the math is straightforward so it's handled by a spreadsheet or app.

(*the intercept should be and is very close to zero, but to account for any errors in the blank I always include this in the calculation)

One of these days I'm gonna get around to doing Phosphate, since this is one of the only tests where I'm actually interested in the precise numbers at low levels. In principle even my cheap spec is surely at least as sensitive as the Hanna checker and possibly more sensitive (I seem to remember that sensitivity is a function of path length with spectrophotometry, and isnt the Hanna less than 1 cm path length?)

Hey, nice demonstration of the standard curve. Just wanted to emphasize one of your points.

It is important not to force the regression equation through zero because the spectrometer can detect no difference between zero ppm and the limit of detection concentration of around 0.05 ppm. It is a good idea to be reminded by the non-zero constant in the equation about the method’s limitations at the low end.

 

[taricha]

One of these days I'm gonna get around to doing Phosphate, since this is one of the only tests where I'm actually interested in the precise numbers at low levels. In principle even my cheap spec is surely at least as sensitive as the Hanna checker and possibly more sensitive (I seem to remember that sensitivity is a function of path length with spectrophotometry, and isnt the Hanna less than 1 cm path length?)

The Hannah cuvette has a 10 mm inside diameter, so same path length as most commonly used. Interestingly the hanna phosphate checker uses a wavelength far from the maximum absorbance of the chemical test product. In fact, the checker wavelength is nearer a minimum absorbance, but it still works because the absorbance is so broad.

 

[EMeyer]

The Hannah cuvette has a 10 mm inside diameter, so same path length as most commonly used. Interestingly the hanna phosphate checker uses a wavelength far from the maximum absorbance of the chemical test product. In fact, the checker wavelength is nearer a minimum absorbance, but it still works because the absorbance is so broad.

Oh, interesting... so there may be some gains in sensitivity from doing the test on a spec at the optimum wavelength. Thanks, that makes me interested in moving this off the back burner. I've been curious about PO4 levels in some of my low nutrient tanks, maybe its time to finally do the PO4 test on the spec.

 

[LadyTang2]

So regardless of whether you are testing nitrate, calcium, or alk you get an absorbance value. Then there is some equation to get to ppm that is specific to each parameter? then you could go further to say dkh? Sorry I am noob!

 

[EMeyer]

So regardless of whether you are testing nitrate, calcium, or alk you get an absorbance value. Then there is some equation to get to ppm that is specific to each parameter? then you could go further to say dkh? Sorry I am noob!

The process I describe works for any colorimetric test. That means any test where you evaluate the level based on the color you see (e.g. if its darker green, its a higher level).

Other tests are titration based, like alkalinity (dkh). I don't see any advantage to doing that kind of test in a spec, since the resolution is based on how small you can make your drops, rather than on measuring tiny changes in color.

I don't know. Perhaps there is a colorimetric test out there for CO3 or HCO3? I havent needed to measure alkalinity at high resolution so I havent investigated.

 

[Dana Riddle]

Hach and Hanna both market a colorimetric test for alkalinity (as CaCO3). I ordered a Hanna alkalinity Checker along with the nitrite reagents. I'll compare alk results from the Checker to the Hach titration method I'm currently using.

Alkalinity (Total) TNTplus Vial Test (25-400 mg/L CaCO₃), 25 Tests

Alkalinity (Total) TNTplus Vial Test (25-400 mg/L CaCO₃), 25 Tests

www.hach.com

 

[Dan_P]

Hach and Hanna both market a colorimetric test for alkalinity (as CaCO3). I ordered a Hanna alkalinity Checker along with the nitrite reagents. I'll compare alk results from the Checker to the Hach titration method I'm currently using.

Alkalinity (Total) TNTplus Vial Test (25-400 mg/L CaCO₃), 25 Tests

Alkalinity (Total) TNTplus Vial Test (25-400 mg/L CaCO₃), 25 Tests

www.hach.com

Didn’t you write an article on the Hanna Alkalinity Checker? @Randy Holmes-Farley has also commented on the Hanna alkalinity method as well. I vaguely remember that titration to pH 4.3 (?) provides an alkalinity value closer to reality than the Checker methodology.

Ring a bell? Did I dream this discussion?

 

[Dana Riddle]

Didn’t you write an article on the Hanna Alkalinity Checker? @Randy Holmes-Farley has also commented on the Hanna alkalinity method as well. I vaguely remember that titration to pH 4.3 (?) provides an alkalinity value closer to reality than the Checker methodology.

Ring a bell? Did I dream this discussion?

I know I made some comparisons of results obtained through use of the Hanna alkalinity Checker and the Hach titration method (to pH of 4.2) and they were favorable. Don't recall if I published this info, and the Advanced Aquarist site is down (again.) FedEx said I'd get the new Hanna alk Checker today, but it's 7:15 pm and I doubt they're being honest with me. I'll do another comparison as soon as the Hanna stuff arrives.

 

[taricha]

Next measure their absorbance on the spec, in this case at 680 nm. Here is an example figure

just wanted to thank you for posting this raw Abs vs Conc curve. It's great info.
to clarify for others why I think it's so cool. Because absorbance is a standard measure, this means that since I have a spec also, I can use the red sea ammonia test, run it in my spec and use Emeyer's data curve to find the concentration for my absorbance reading.

 

[taricha]

Interestingly the hanna phosphate checker uses a wavelength far from the maximum absorbance of the chemical test product.

Oh, interesting... so there may be some gains in sensitivity from doing the test on a spec at the optimum wavelength. Thanks, that makes me interested in moving this off the back burner. I've been curious about PO4 levels in some of my low nutrient tanks, maybe its time to finally do the PO4 test on the spec.

For curiosity, a few times recently I've tested PO4 samples with some color to the end product so I checked the spectrum. Every time I get something like this.

You can see the blue end-product has plenty of detectable absorbance everywhere from 480nm and longer.
a couple of points:
1) hanna checker at 525nm is not looking for max absorbance, that wavelength must have been chosen for other reasons.
2) the 900nm absorbance - I don't really know if I trust my meter out there.
3) the 700-720nm absorbance peak does look like a good target.
4) this sample read as 0.19ppm PO4 on the hanna hi736 checker.