Chlorine Detection and Neutralization Questions

[Resilient]

I have a couple chlorine related questions. I use bleach to sterilize my glass jars for phyto cultures. I made a dilution of sodium thiosulfate that should neutralize my bleach. This has worked fine for a couple months but recently I has a culture crash and tonight I smelled bleach when I was getting ready to multiply my culture, tested for chlorine using the test kit I have for my hot tub and found there was still significant bleach.

So I have two questions... 1st is that my test kit is super old and low on reagent. What is the best test kit out there that can give essentially a binary "Yes, there is chlorine" or a "No, there is zero chlorine"? I don't actually know how sensitive my reagent is. I don't think it is really designed for trace levels of chlorine and I need a new test kit for it. I suspect the last culture crashed because there was still chlorine but not at a high enough level for this reagent to detect.

Second question is, can sodium thiosulfate offgas or otherwise somehow become less effective over time after being mixed in a solution with water? I am wondering if I messed up my measurements or if for some reason my neutralizer has become less effective over the past couple months.

 

[Dan_P]

I have a couple chlorine related questions. I use bleach to sterilize my glass jars for phyto cultures. I made a dilution of sodium thiosulfate that should neutralize my bleach. This has worked fine for a couple months but recently I has a culture crash and tonight I smelled bleach when I was getting ready to multiply my culture, tested for chlorine using the test kit I have for my hot tub and found there was still significant bleach.

So I have two questions... 1st is that my test kit is super old and low on reagent. What is the best test kit out there that can give essentially a binary "Yes, there is chlorine" or a "No, there is zero chlorine"? I don't actually know how sensitive my reagent is. I don't think it is really designed for trace levels of chlorine and I need a new test kit for it. I suspect the last culture crashed because there was still chlorine but not at a high enough level for this reagent to detect.

Second question is, can sodium thiosulfate offgas or otherwise somehow become less effective over time after being mixed in a solution with water? I am wondering if I messed up my measurements or if for some reason my neutralizer has become less effective over the past couple months.

What solution are you testing for the presence of chlorine/bleach? Can you briefly describe your sterilization process so we understand where in the process testing occurs?

 

[Resilient]

What solution are you testing for the presence of chlorine/bleach? Can you briefly describe your sterilization process so we understand where in the process testing occurs?

I use 3 liter containers I clean with soap and fill around 2/3 full with salt water, with SG between 1.015 and 1.026 depending on the variety of plankton. I add bleach to get to 100ppm for a minimum of 2 hours, this is just by measurement, I don't test at this stage.

After it has sat for at least 2 hours with heavy aeration, I add sodium thiosulfate to neutralize the bleach. This is where I would like to test every batch to ensure that I have, in fact, eliminated all the bleach and that there wasn't a measurement error or something along the way. It should be at 0ppm at this point as the next step is inoculating it with the prior culture. So a cheap, quick test that will accurately and precisely read 0ppm is important. If it is anything above that, I don't really care about the specific value as something has gone wrong.

 

[Dan_P]

I use 3 liter containers I clean with soap and fill around 2/3 full with salt water, with SG between 1.015 and 1.026 depending on the variety of plankton. I add bleach to get to 100ppm for a minimum of 2 hours, this is just by measurement, I don't test at this stage.

After it has sat for at least 2 hours with heavy aeration, I add sodium thiosulfate to neutralize the bleach. This is where I would like to test every batch to ensure that I have, in fact, eliminated all the bleach and that there wasn't a measurement error or something along the way. It should be at 0ppm at this point as the next step is inoculating it with the prior culture. So a cheap, quick test that will accurately and precisely read 0ppm is important. If it is anything above that, I don't really care about the specific value as something has gone wrong.

Isn’t the most straightforward method a titration? The amount of thiosulfate titrant to reach the end point tells you exactly the amount of thiosulfate to add 3 liter container. A second titratiion could be conducted to confirm no chlorine is left.

 

[Resilient]

Isn’t the most straightforward method a titration? The amount of thiosulfate titrant to reach the end point tells you exactly the amount of thiosulfate to add 3 liter container. A second titratiion could be conducted to confirm no chlorine is left.

Certainly not opposed to that. Suggestions on a good test kit to use for that titration? Most of the ones I find are for 0-200ppm for spas or kitchen cleaning. But I worry that would be to insensitive for the low levels of chlorine I am worried about.

 

[EnterName]

I think it is reasonable to expect at least some loss of thiosulfate over time:

• Air exposure (headspace in the container)
• Contamination by repeatedly dipping used syringes into the solution
• Contamination through insufficiently filtered water
• Photolysis during exposure to light
• Bacteria growth when not working perfectly sterile (e.g. laminar flow hood, sterilized pipette/syringe tips, etc.)

I had a similar experience as @Resilient with a sodium thiosulfate solution and decided to switch to autoclaving, which also avoids byproducts created when the chlorine reacts with organic matter.
A quick websearch reveals that there are ways to stabilize the solution (even though they might not be fit for the purpose of treating culture media), this implies that the solution does degrade over time.

 

[Dan_P]

Certainly not opposed to that. Suggestions on a good test kit to use for that titration? Most of the ones I find are for 0-200ppm for spas or kitchen cleaning. But I worry that would be to insensitive for the low levels of chlorine I am worried about.

I have no good ideas for kits but continue to look for options