Hi all. I was wondering if anyone could help troubleshoot an experiment I'm working on.
I'm running an experiment to measure the microbial respiration of compost samples using a NaOH trap. Each sample is in a jar with 20 ml of 1M NaOH and is placed in an incubator for 24 hrs. After 24 hrs, 20ml of .5N BaCl2 and an indicator are added to the NaOH and it is then titrated with HCl. I run a few blanks each time, with an NaOH trap in a jar without a compost sample. This is repeated over 4 days In theory, I should need less HCl to neutralize the NaOH which has been sitting with the compost samples then the NaOH just by itself. Sadly, after hours and hours of work in the lab, this has not been the case!
I have 45 different samples of different types of compost. Each time I run the test, about a third of the samples require more HCl to neutralize than the blank.
The blanks are all consistent in the amount of HCl needed, I ran three last night and one the night before. The test also seems to be picking up samples which are respiring heavily- when there are moldy samples, they require only a small amount of HCl. I can't really decipher a trend with the ones that require more HCl to titrate than the blank other than that it's somewhat consistent. 41% of the samples which needed more HCl than the blank on day 2 also needed more on day 1, and of the day 2 "error samples", 88% were from a treatment which had an "error sample" on day 1.
I thought perhaps this had to do with ammonia volatilizing from some of the samples, but this doesn't necessarily make sense with the samples which are taking more HCl than the blank. I also noticed that on the samples which require more HCl to titrate than the blank, there seems to be more barium carbonate precipitate that settles out after the titration.
Do you have any idea what could be happening or what I am doing incorrectly? It's definitely a long process to do this measurement for 48 replicates over 4 days - I'm hoping the data isn't totally worthless.