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ion-selective electrodes (ISE)

Discussion in 'General Plant Topics' started by yme, Oct 1, 2010.

  1. yme

    yme Lifetime Charter Member
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    browsing the www... I came across these ion selective electrodes for measuring nitrates.

    I didn't know they existed, so I wonder whether someone has some experience with this kind of electrodes.

    Would it be a nice gadget to buy?

    greets,

    yme
     
  2. Tom Barr

    Tom Barr Founder
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    Now can you think of interfering ions for some of these ISE probes?

    For exampole, for some species of ions, we must add chemicals to remove the interfering ions, such as other -1 charged ions. Say like Cl-.

    These probes are useful for large batches in some cases where we can add other chemicals or processes to remove the interference.
    We cannot do this effectively in aquariums. They do have autosamplers which take small samples and then process them post collection and then use these probes.

    But, it's far simpler to automate a water change and set up an automatic dosing pump to add ferts back.

    http://www.nico2000.net/book/guide1.html

    and NO3:
    http://www.nico2000.net/analytical/nitrate.htm

    Regards,
    Tom Barr
     
  3. yme

    yme Lifetime Charter Member
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    according to the manual:

    Interference: Organic solvents and cationic detergents must be absent.

    Ratio of interfering ion to NO3 must be less than the ratio indicated below:

    300 for F- fluoride
    100 for Cl- chloride
    4 for CO3 2- carbonate
    2 for NO2- nitrite
    0.01 for I- iodide
    0.0045 for ClO4- perchlorate

    I reconstitute RO water with sera mineral salt, with extra Mg and Ca. furthermore KNO3, H2KPO4 and traces are of course also given daily.

    This should more or less give rise to the following parameters:

    Sodium 16 mg/l
    Potassium 35 mg/l
    Magnesium 10mg/l
    Calcium 50 mg/l
    Chlorid 55 mg/l
    HCO3- 50 mg/l
    Sulfate 22 mg/l

    so again:

    not really?
    With organic solvents they only mean compounds like DMSO, right?
    To me it doesn't sound too bad...

    what do you think?

    yme
     
  4. Tom Barr

    Tom Barr Founder
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    You can try it, you also need to calibrate the probes and for NO3, this is more than you might think.
    A good colorimeter should be easier, cheaper and more user friendly.

    You do not require continuous monitoring of NO3 really, so a weekly check etc is fine.
    If you want to measure say 100 smaples and can quickly dip the probe into each, rinse then the next, then the ISE probes start to make more sense.

    A Hanna Colorimeter multi parameter(K+, NO3, Fe, Cu, PO4, KH, Ca, Mg etc.......) would cost about the same as the ISE set up for a single parameter and be as accurate.

    Regards,
    Tom Barr
     
  5. Biollante

    Biollante Lifetime Charter Member
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    Can't Help Myself, I Apologize In Advance…

    Hi,

    I have been using Nitrate-Nitrogen ion specific probes for a year or so.

    Tom Barr is right unless you are doing large batch samples there are easier more cost effective methods. However if like me you just like stuff, are patient and realize preparation is everything they are pretty good. :)

    I started out with some high-end probes, well high end for me like US$ 850-1050 for the probes. I sold those and bought a used one for US$ 100 I think it retails new for around US$280. It works well with pH/mV meter or ion meters. It is not as accurate within 2% in the ranges I use. Some drift, after a bit you learn to recognize the drift that is the result of interferences. :)

    My cheap probe needs very good temperature control small changes in temperature affect the results so much so that on my magnetic stirrer I have to put a Styrofoam sheet under the beaker. :p

    We deal with most of the interferences with Nitrate Ionic Strength Adjuster (ISA), if you have good scales, good volumetric flasks you can make your own with reagent-grade ammonium sulfate, (NH4)2SO4 and distilled water. Same goes for the Nitrate standards, just make sure you are using reagent grade sodium nitrate, NaNO3. :gw

    We occasionally have a problem with cyanide so we use silver sulfate, Ag2SO4. If Nitrites are a problem a little sulfamic acid, H3NSO3, yeah tile cleaning stuff. :eek:

    Then again http://www.hach.com/hc/search.product.details.invoker/VendorProductCode=LXV417.99.10002/View=PRODUCT_OVERVIEW/NewLinkLabel=NITRATAX%28TM%29+plus+sc+Sensor%2C+1+mm+path+length/SESSIONID|CWpreU16WXlNRGNtWjNWbGMzUlVTRVJLU1E9PUJURXlPRFl3Tg==| will solve all your measurement problems.

    Biollante
     
  6. yme

    yme Lifetime Charter Member
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    interesting!

    I need to browse some more on the www....

    @tom:
    I have a Hanna Colorimeter multi parameter, but the NO3 measurements are WAY of. Once I measured after a 50% waterchange 40 mg/l. Since I add only 15 mg/l/week (or so) and virtually have no fish, it is really impossible to have these values. Inaddition, normal cheap test kits give me values of 10-30 mg/l. which is much more reasonable, altough also highly questionable.

    @boillante

    NITRATAX(TM) plus sc Sensor... sounds perfect. but probably unreasonable expensive??

    thanks!

    yme
     
  7. Biollante

    Biollante Lifetime Charter Member
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    Chump Change

    Only US$ 13,747.00 plus shipping, chump change! :cool:

    I am not getting the link, so I do not know the specific one you are talking about.

    Biollante
     
  8. Tom Barr

    Tom Barr Founder
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    If you calibrate the Hanna, it should be fairly accurate, if not..........
    I keep a set of volumetric flask for this purpose and a nice accurate scale.

    I honestly rarely test most common parameters these days, only when I a pretty specific question.
    You can also calibrate the cheaper test kit also.

    The issue with the Hanna is more related to the chemical reagent packets, not the colorimeter itself.
    If you can make the Asorbic acid regaents for the NO3 test, then you can save a lot of $$.

    Still, if you just like playing with techy stuff:)
    No harm there.

    It's your $$ to use how you like.

    I'll be reporting on some CO2 methods and dependentcys on filtration types, O2 and light if a few weeks.
    Since I now have a pair of CO2 meters and O2 meters, and a light meter etc.
    So I take these around to different tanks and measure things comparatively.



    Regards,
    Tom Barr
     
  9. yme

    yme Lifetime Charter Member
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    LOL!!! that cheap! I'll buy two...

    in RO water it is accurate... but I think it reacts to TMG and flourish iron.
    In any case, I cannot use the photometer with the nitrate reagents.

    I probably have access to the chemicals... but how do I make my own reagents?

    I do... :)

    greets,

    yme
     
  10. Tom Barr

    Tom Barr Founder
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    If it reacts with the TMG/flourish, it'll do this with the NO3 probe, or in theory, it should.....and cause some error. I'd make some reference solutions with your tank water, and a reference without ferts and a reference with the typical ferts you add, then see which method is consistent.

    Regards,
    Tom Barr
     
  11. Biollante

    Biollante Lifetime Charter Member
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    Normal, Who Me?

    Hi,

    {Disclosure: I do not use TMG and have messed up calculations involving TMG in the past :eek:}
    I cannot see anything in Flourish or TMG that should cause that big an error, even without compensating for the obvious interferences I have never seen anything that would account for more than 0.8-ppm high reading of NO3 in “normal” aquarium ranges. :)

    Testing tap water is the only time I found the interferences significant enough to cause me concern.

    The reagent grade I was referring to is generally the highest grade (purity) chemical generally available commercially. :gw

    Biollante
     
  12. yme

    yme Lifetime Charter Member
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    of course I have a spectrometer at work....

    so this is what I measured:

    standard curve of KNO3 in MQ water at 200 nm:

    0 ppm NO3 blanco
    5 ppm NO3 0,113
    10 ppm NO3 0,160
    20 ppm NO3 0,312
    30 ppm NO3 0,486


    standard curve of KNO3 in MQ water at 220 nm:

    0 ppm NO3 blanco
    5 ppm NO3 0,049
    10 ppm NO3 0,068
    20 ppm NO3 0,129
    30 ppm NO3 0,197


    standard curve of KNO3 in MQ water at 240 nm:
    30 ppm NO3: 0,004 (less NO3 gave 0,000)

    standard curve of KNO3 in MQ water at 260 nm:
    30 ppm: 0,000 (less NO3 gave also 0,000)

    and here my tankwater:

    200 nm: 2,847
    220 nm: 2,648
    240 nm: 1,64
    260 nm: 0,080

    absorbance measured on a beckman coulter du-530.

    would it be possible to calculate NO3 levels in tapwater from these values???

    greets,

    yme
     
  13. Tom Barr

    Tom Barr Founder
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    Yes, I just run the tapwater at 200nm

    I do not think there is much issue with the NO3 in the tap, might be an added source, but should not be detrimental to the tank.

    Regards,
    Tom Barr
     
  14. yme

    yme Lifetime Charter Member
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    oeps... I meant of course tankwater..... (the measured values...)
     
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