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# Spike Cover

Have you ever thought of the virtues of checking your test kits for accuracy? well maybe you should, not only will this show you if they are past their sell by date and useless , but in the past i have found some test kits leave a lot to be desired for accuracy.
If you know the error in the kit, this will give you the luxury of allowing for that error when testing your water parameters, this can only be a good thing.

#### Testing the test kits

By Spike Cover, April 7, 2003

##### Word definitions

Precision – reproducibility

Sensitivity – smallest increment that can be measured - resolution

Accuracy – variance from actual

Stock solution – ammonia test

Prepared by mixing 3.14 grams of ammonium chloride (NH4Cl) into1 liter of distilled water – the 3.14 grams was arrived at by taking the atomic weights of the chemical and then determining how much of the ammonium chloride is required to yield the desired amount of ammonia (NH3).

The relevant numbers are (ref: periodic chart):

N = nitrogen, atomic weight of 14.0067

H = hydrogen, atomic weight of 1.0079

Cl = chlorine, atomic weight of 35.453

So NH4Cl has an atomic weight of 14.0067 + 4x1.0079 + 35.453 = 53.49

And NH3 has an atomic weight of 14.0067 + 3x 1.0079 = 17.03

If we desire 1000 ppm of NH3, we need 1000 mg of NH3 per 1 liter of water

But since we have NH4Cl and not NH3, we will need 53.49/17.03 x 1000 mg = 3141 mg of NH4Cl to yield 1000 mg of NH3, or 3.141 g of NH4Cl

If we desire to make up 1 liter of ‘stock solution,’ we will need to add 3.141 g NH4Cl or 3.14 g when rounded to two decimal places, i.e., this is the amount of NH4Cl that would be added to 1 liters of distilled water to make a 1000 ppm solution of NH3.

Exercise - Test ammonia kit

Using the pre-made stock solution of 1000 ppm ammonia, make diluted solutions to test your ammonia test kit.

Example: take 1 ml of the stock solution and add to 1 liter of distilled water to make 1 ppm or 1 mg/l, stock solution of NH4Cl,

2 ml of stock added would make 2 ppm or 2 mg/l

0.5 ml to 1 liter would make 0 .5 ppm or 0.5 mg/l, etc:

Then fill the test tube of your kit to the kits required level and test

Use at least 4 data points (5 would be better), including zero ammonia, to generate a curve of actual vs. readings to show the spectrum of error, (use graph paper) for your (individual) ammonia test kit.  Make sure you span the manufacturer’s stated range of your kit.

On your graph, label the x and y axes, actual and reading, respectively and show values in ppm or mg/l which ever you prefer.

Additional tests for NO2 and NO3 - using sodium nitrite (NaNO2) and potassium nitrate (KNO3), respectively

Stock solution – nitrite test, the relevant numbers are (ref: periodic chart):

Na = sodium, atomic weight of 22.9898

N = nitrogen, atomic weight of 14. 0067

O = oxygen, atomic weight of 15.9994

K = potassium, atomic weight of 39.0983

Sodium nitrite, (NaNO2) has an atomic weight of 22.98978 + 14.0067 + 2x 15.9994 = 31.9988. = NaNO2 atomic weight of = 68.9953

Nitrite alone (NO2), has an atomic weight of 14.0067 + (2X 15.9994) = 46.0055

If we desire 1000 ppm of NO2, we need 1000 mg of NO2 per 1 per liter of water.

But since we have NaNO2 and not NO2, we will need, 68.9953 / 46.0055 x 1000 mg = 1482.1755 mg of NaNO2 to yield 1000 mg of NO2.

If we desire to make up 1 liters of ‘stock nitrite solution,’ we will need to add 1.48 g of sodium nitrite, when rounded to two decimal places, i.e., this is the amount of NaNO2 that would be added to 1 liters of distilled water to make a 1000 ppm solution of NO2.

Stock solution – nitrate test, the relevant numbers are (ref: periodic chart):

K= potassium, atomic weight of 39.0983

N= nitrogen, atomic weight of 14.0067

O = oxygen, atomic weight of 15.9994

Potassium nitrate (KNO3) has an atomic weight 39.0983 +14.0067 + (3X 15.9994) = 101.1032.

Nitrate alone (NO3) has an atomic weight of 14.0067 + (3X 15.9994) = 62.0049

If we desire 1000 PPM of NO3, we need 1000 mg of NO3 per 1 liter of water.

But since we have KNO3 and not NO3, we will need 101.1032 / 62.0049 x 1000 mg =  1630 mg of KNO3 to yield 1000 mg of NO3.

If we desire to make up 1 liters of ‘stock nitrate solution,’ we will need to add 1.63 g of sodium nitrite, when rounded to two decimal places, i.e., this is the amount of KNO3 that would be added to 1 liters of distilled water to make a 1000 ppm solution of NO3.

pH

Sodium hydrogen carbonate; sodium acid carbonate; baking soda; bicarbonate of soda
Molecular Weight: 84.01
NaHCO3

Solubility: 7.8g/100g water @ 18C (64F).
pH: 8.3 (0.1 molar @ 25C (77F))

Add 7.8 gm of Sodium Bicarbonate to 100ml of tap water this should settle to give a pH of 8.3-8.4 check your test kit using this buffered solution.