methylene blue

[RosalieL]

How do you have your methylene blue labelled? I tried to calculate the molarity based on the "simple stain" recipe in The Laboratory and it came out to about 0.0005M for the stain and 0.005M for the stock solution (which is dissolved in ethanol). Feel free to correct me if that doesn't sound right - It's Friday afternoon after all! Do I need a second label for the ethanol? I have some methylene blue here that was made up before my time so I'm not sure which recipe was used. Should I just make a fresh batch and use 0.0005M on the label? My brain is definitely not switched on for chemistry this week! I use RiskAssess for labelling.

[Labbie]

I would put that Ethanol was used on the label. to cover your back, if nothing else.

[Merilyn1]

I was in the same boat, Rosalie - inherited a batch of methylene blue with a Chemwatch label. God knows what was in it. I ended up making up a new batch and labelling it as a percentage concentration. Was easier than trying to work out molarity. Also included the percentage of ethanol.
I learnt the hard way last year - you keep a stock solution than you dilute down 1:10 just before you use it. Was I the only person that didn't know this! The old batch worked for a few years, then didn't.

[RosalieL]

I was in the same boat, Rosalie - inherited a batch of methylene blue with a Chemwatch label. God knows what was in it. I ended up making up a new batch and labelling it as a percentage concentration. Was easier than trying to work out molarity. Also included the percentage of ethanol.
I learnt the hard way last year - you keep a stock solution than you dilute down 1:10 just before you use it. Was I the only person that didn't know this! The old batch worked for a few years, then didn't.

I only know this because I just read it in the book! I honestly don't remember from my previous time as a labbie... maybe I knew it then? but I don't remember making it up fresh. I suspect I just used what I had inherited back then as well!! That was pre-GHS though... and as far as I know, it worked as required!