Which testing kit do I trust?

[justingraham]

Mr or mrs Hannah person

Some times when I test the alk it takes about ten times the normal limit for the c2 to show up when it does this I start over as I think of it as a bad test. Usually when I run thru it the second time it only takes the five seconds for the c2 to show up.


My question is why does it do that? I have figured out that it's not the vial as I have 8 bottles in a rotation and it has happened to everyone of them at least once.

Thanks

Justin

 

[Hanna Instruments]

Mr or mrs Hannah person

Some times when I test the alk it takes about ten times the normal limit for the c2 to show up when it does this I start over as I think of it as a bad test. Usually when I run thru it the second time it only takes the five seconds for the c2 to show up.


My question is why does it do that? I have figured out that it's not the vial as I have 8 bottles in a rotation and it has happened to everyone of them at least once.

Thanks

Justin

Hello Justin,

As long as your Checker goes from C1 to C2 there is nothing to worry about. The difference of 5 seconds or 30 seconds is not going to effect the accuracy of the alkalinity test. Do not consider a delayed response to be a bad test, we are aware this occurs and there are no negative consequences to the accuracy of the alkalinity test associated with that timing delay.

 

[Hanna Instruments]

I used the new syringe and tip with the new bottle. I rinse the tip (inside and out) with rodi after each use and make sure it is dry before using again. There is no dried reagent in the tip or syringe. In fact no reagent even makes it into the syringe itself as the tip is large enough to hold 1ml.

You seem to be doing everything correctly, if your results are always within the measure of uncertainty then there is no cause for concern. We use a conservative accuracy statement on the alkalinity Checkers.

 

[Catfish2]

You seem to be doing everything correctly, if your results are always within the measure of uncertainty then there is no cause for concern. We use a accuracy statement on the alkalinity Checkers.

Ok, if I'm unstanding this correctly, the measure of uncertainty for the hanna dkh checker is +/- 5% of the reading +/-0.3 dkh.

That means for the 8.8 reading on 7/29, it could be 9.54-8.06 and the 7.6 reading on 7/30 it could be 8.28-6.92.
So, the 2 readings, even though they are 1.2 dkh different, are within the measure of uncertainty.

Furthermore, now the hanna checker reads 8.1, which can be between 7.4-8.8 and the red sea reads 9.1. I can't find red seas measure of uncertainty listed, but I'm sure with its range, the two testing methods would be within the measure of uncertainty of each other.

 

[justingraham]

Hello Justin,

As long as your Checker goes from C1 to C2 there is nothing to worry about. The difference of 5 seconds or 30 seconds is not going to effect the accuracy of the alkalinity test. Do not consider a delayed response to be a bad test, we are aware this occurs and there are no negative consequences to the accuracy of the alkalinity test associated with that timing delay.

Thank you

Is there anything I'm doing to cause this to happen? Or is it just a natural process?

 

[Hanna Instruments]

Thank you

Is there anything I'm doing to cause this to happen? Or is it just a natural process?

Its just a natural process, nothing to worry about.

 

[Hanna Instruments]

Ok, if I'm unstanding this correctly, the measure of uncertainty for the hanna dkh checker is +/- 5% of the reading +/-0.3 dkh.

That means for the 8.8 reading on 7/29, it could be 9.54-8.06 and the 7.6 reading on 7/30 it could be 8.28-6.92.
So, the 2 readings, even though they are 1.2 dkh different, are within the measure of uncertainty.

Furthermore, now the hanna checker reads 8.1, which can be between 7.4-8.8 and the red sea reads 9.1. I can't find red seas measure of uncertainty listed, but I'm sure with its range, the two testing methods would be within the measure of uncertainty of each other.

On the HI772 dKH Alkalinity Checker the accuracy statement = Accuracy @ 25°C/77°F ±0.3 dKH ±5% of reading

So if your Checker reads 10.0 dKH the measure of uncertainty would be ±0.5 dKH or a range from 9.5-10.5 dKH.

If 5% of the total reading is great than 0.3 dkH then the use the 5% as your accuracy. If 5% of your total reading is equal to or less than 0.3 dKH then use 0.3 dKH as your accuracy statement.

8.1 dKH, (accuracy statement= 5% of 8.1 dKH =0.4 dKH) measure of uncertainty range of 7.7 dKH -8.5 dKH
7.6 dKH (accuracy statement= 5% of 7.6 dKH= 0.38 dKH (round up to 0.4 dKH)= measure of uncertainty range of 7.2 dKH -8.0 dKH

We do not use accuracy statements for any chemical test kits, nor do most analytical chemistry brands. This is because an accuracy statement is usually reserved for instrumentation with digital displays of some sort. Human interpretation of color is subjective and thus you cannot measurably quantify what that measure of uncertainty will be due to differences in how people observe colors.

Companies who manufacture testing equipment only, like Hanna, use this same principle. Most titration based alkalinity tests, like LaMotte, will use a range/resolution/sensitivity but that is not the same thing as accuracy/measure of uncertainty.

Our HI84531-01 Mini Titrator for Measuring Titratable Alkalinity in Water and Wastewater has an Accuracy (@25ºC/77ºF) Low Range: ±1 mg/L or 3% of reading, whichever is greater; High Range: ±10 mg/L or 3% of reading, whichever is greater. Even though this is a titration, it has an accuracy statement because it doesn't rely on the human eye to determine an end point, but rather a pH electrode and automatic dosing system. Same is true for things like the kH guardian, pH electrodes, ORP electrodes, conductivity/TDS meters, refractometers but not chemical test kits which use color changes. It would be disingenuous to put an accuracy statement on something you cannot quantify.

If you are using a chemical test kit which uses a color change there are somethings you must do in order to adequately determine your end point.
1. Color must be observed under a full spectrum light (different light wavelengths can cause colors to appear differently)
2. Color must be observed under the same intensity light each time
3. Color should be observed against a white background
4. Make sure syringe is properly filled and you are not over/under tirtrating the sample
5. Some Chemical Test Kits for alkalinity require to observe any color change or a change to a specific color, make sure you know whether the kits wants you to observe a color shift in general or a shift to a specific color (i.e yellow to blue).

Our HI3811 Alkalinity Chemical Test Kit requires a color change from green or blue to yellow, following an acid titration using phenolphthalein and bromophenol blue.