Looking for instructions on how to use the Measurement program (any other aquarium people here?)



  • I got the colorimeter kit because I am interested in the aquarium tests. I think I am almost there but am unsure how to operate the Measurement program.

    I have loaded the sample API nitrate calibration data, made a plot with curve fit, saved the test solution, selected that test solution in Measurement, but am now unclear on exactly how to measure my sample. Oh, I am using the .exe v04, as v05 is crashing on Windows 10.

    In the Measurement program I am unable to measure unless I first click Calibrate. But what am I calibrating with? Plain water? (And why is that necessary if we have a calibration curve?)

    After calibrating with water, I mashed Measure and my API nitrate test sample gave me values of about 25 uM.

    I was expecting to see approximately 20 PPM based on the color chart, but in the Measurement program I am unable to change from uM to PPM in the menu. Both are dimmed out.

    alt text

    But, since I got a value that looks about right for PPM, I wonder if there is a labeling bug and these are PPM values, even if they are labeled uM?

    OK, so let's assume we are looking at uM NO3. You can convert micromoles per liter NO3 to PPM if you divide by 16. 25 uM would be about 1.6 PPM, and based on the color of the kit, that cannot be right. It really does need to be approximately 20 PPM.

    So right now it looks like you have to calibrate with water, and you will get results in PPM even if the menu is stuck on uM.

    Assuming I was correct to calibrate with water, and I actually measuring 25 PPM NO3, this is super duper cool and I love this thing.

    Can anyone straighten me out?



  • Replying to myself here. I took another look at the instructions:

    http://public.iorodeo.com/docs/nitrate/api.html

    Here is the part I missed the first time: Before measuring blank the colorimeter against water or a distilled water sample developed with API reagent as described below

    This must be the sample that the "Calibrate" button requires.

    What I don't understand is why this sample is not handled by the calibration curve. It includes a 0 PPM sample. I guess the intent of the blanking step is to see what the current state of the LED and sensor is, so it can apply that correction to the curve?

    This does mean that each test would have to use 2x the reagent, which is unfortunate... but worth it if I can get a number I can trust.



  • Hi horseflesh,
    So, yes, you do need to do a calibration each time you start a new measurement.

    The calibration measures the light intensity that reaches the sensor after passing through the cuvette and your blank sample -- which should not be absorbing any light due to the substance you are measuring e.g. nitrate.

    The calibration is used as a reference when calculating the transmittance of light through your actual sample.

    For the API nitrate test, a 'blank' sample would be 5 mL of distilled water (zero nitrate) developed with the test kit i.e. 10 drops of bottle 1, 10 drops of bottle 2. The color should be yellow like the image shown below. You would pour some of this into a cuvette and calibrate the colorimeter.

    alt text

    I hope that helps !
    Jo


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