WEF Discussion Forums
Laboratory Management and Technical Issues
HACH BOD Nutrient Buffer Pillows
Has anyone had any problems with the solubility of the HACH BOD Nutrient buffer pillows? I have noticed that when I add the pillows to the source water, the contents settle out at the bottom of the carboy and no amount of swirling helps them to dissolve. I have tried using source water from 3 different suppliers (one steam distilled) but am still having the same problem. I have also tried using pillows from 2 different lot numbers (HACH have confirmed both these lots are ok). I have only just started doing BOD recently and seem to be plagued with problems.Does anyone know what affect this would have on the BOD results (I am getting high blanks also and whilst changing the source water has helped, they are still around 0.6mg/L). Thanks.
Well, Paul, it seems to me that you are alone in the middle of a cow pasture without your boots on with regard to this one. I have never heard of the nutrient/buffer reagents not totally dissolving, and I would imagine that's what Hach told you, also. If your source water had a high ionic strength with anions/cations that precipitate with the nutrient/buffer reagents, it could explain it, but I can't imagine "steam distilled" water (which goes through DI columns among other things) having those ions in it. Even your own lab distilled water shouldn't have the ionic strength to precipitate anything. You could check the conductivity of the source water...low conductivity would mean few ions.
You could try making your own nutrient/buffer solutions using reagent grade or ACS grade chemicals, but I doubt that would help because I am confident your Hach pillows are not defective.
I hope somebody else will take a stab at this one...it has me intrigued!
Are you using the correct size nutrient pillow for the amount of dilution water you are making? I think they come in 3, 6, and 19 liter amounts. If you got the 19 liter volumes and are only using 3 liters of water, that might contribute. Otherwise, I can't come up with anything that would cause the nutrients to not completely dissolve.
It takes time for the Hach nutrient buffers to completely dissolve. I swirl the dilution water several times and let it sit for 15 - 20 minutes and still have solids in the bottom. They will eventually dissolve. I believe the problem is the combination of all the nutrient buffers into one ampule. If you make nutrients from scratch and mix them together you get a precipitate just like in the Hach ampules. This precipitate must take some time to redissolve.
It does take a little time for the reagents to dissolve. I only use them for the 300 ml BOD bottle when we need to add nutrients for a very low BOD. The individual solutions work well with no waiting for dissolution.
we use bottled arrowhead steam distilled water and confirm that the Hach pillows do NOT dissolve fully into the 3L. Swirl the bottles for 1minute after addition of pillows and after resting 15minutes, you can the nutrients at the bottom of container. We now use purchased liquid nutrient buffers.
The nutrient pillows I use from don't totally dissolve either. So I'm in the cow pature as well. So what is the answer, Ive do all that has been mentioned
I would continously stir the dilution water as I dispensed it into the BOD bottle. Then you are assured that a uniform dilution water is in each bottle for consistency. This is why I would use the individual solutions in the first place. I then know I have a homogonous solution.
When you are not sure about your source water the last thing you need is another variable such as nutrient solution variation. Dispensing 4 reagents is not that difficult. The time will be less than the time to ensure the solubility is complete.