Chromatography Forum

Do you find it degrading quickly and if so, what is your official shelf life? We use it (10%, v/v) for EPA 548.1 (endothall) and are finding our recovery tanking after using it when it's less than 1-2 weeks old. We have never had this problem before and could use the same solution over the course of weeks/months if need be. I double checked to make sure that we are using concentrated acid and there have been no changes to our HPLC grade methanol. The methanol is poured in using a dedicated beaker and our sulfuric acid uses a bottle top dispenser. The solution is prepared and stored in a dedicated volumetric flask located in a hood, so no water or extra glassware is used.

I did notice that it quickly loses it's viscosity "legs" when gently swirled (kind of like a glass of wine) but instead just sort of has a few bubbles around the same time recoveries start decreasing. It does still seem to work for standards that are not extracted, so I suspect something is going on with the elution process. To make it every time just prior to extraction would be terribly inconvenient to have to wait for it to cool down, and disposal of excess amounts would also be of concern. We plan on doing some investigating next week to see where the cutoff point occurs and also to see if we could change a few things about the actual elution, but optimally, I would love to hear if anyone knows or has ideas that involve some minor tweaking of the reagent, as opposed to more of an overhaul of our methodology. Thanks in advance!!

We use 10% sulfuric acid in methanol, but only for making fatty acid methyl esters. We have not noticed degradation.

We use 10% sulfuric acid in methanol, but only for making fatty acid methyl esters. We have not noticed degradation.

Could you tell me either by post or PM which brands and part numbers you use? After a year of low recovery for another method that I assumed was attributed to technique, it was discovered that the extraction cartridges were the actual culprit. Since then I have always kept it in the back of my mind that changes in manufacturing are always a possible root cause when a change in quality is sudden and/or drastic.

Could you tell me either by post or PM which brands and part numbers you use?

We made the stuff we use currently.

However, our safety folks would rather we not have concentrated sulfuric acid here, so when our stuff is depleted we'll order Sigma Aldrich #506516.

Could you tell me either by post or PM which brands and part numbers you use?

We made the stuff we use currently.

However, our safety folks would rather we not have concentrated sulfuric acid here, so when our stuff is depleted we'll order Sigma Aldrich #506516.

Really? No sulfuric acid? They would rather you pay over $2/mL on 10% pre-prepped solutions, than spend $80-100 on one 500mL bottle to make methanolic sulfuric acid yourselves?

Really? No sulfuric acid? They would rather you pay over $2/mL on 10% pre-prepped solutions, than spend $80-100 on one 500mL bottle to make methanolic sulfuric acid yourselves?

Our safety people are much happier if we don't use concentrated sulfuric on the premises.

We purchase 5N aqueous H2SO4, some 10% H2SO4, and some 0.500 N H2SO4 also. Our safety people would like if we did chemical analysis without chemicals.

Really? No sulfuric acid? They would rather you pay over $2/mL on 10% pre-prepped solutions, than spend $80-100 on one 500mL bottle to make methanolic sulfuric acid yourselves?

Our safety people are much happier if we don't use concentrated sulfuric on the premises.

We purchase 5N aqueous H2SO4, some 10% H2SO4, and some 0.500 N H2SO4 also. Our safety people would like if we did chemical analysis without chemicals.

Well, good luck with that. Remind them to look at the janitor's cleaning closet while they're at it.

Really? No sulfuric acid? They would rather you pay over $2/mL on 10% pre-prepped solutions, than spend $80-100 on one 500mL bottle to make methanolic sulfuric acid yourselves?

Our safety people are much happier if we don't use concentrated sulfuric on the premises.

We purchase 5N aqueous H2SO4, some 10% H2SO4, and some 0.500 N H2SO4 also. Our safety people would like if we did chemical analysis without chemicals.

Well, good luck with that. Remind them to look at the janitor's cleaning closet while they're at it.

I laughed like a loon reading both of your comments for obvious reasons and also for the parts about having safety, people, janitors and closets.

In any case, we make 10% sulfuric in methanol for our 552 analysis. I would need to ask the extraction guys if they have any issues with stability, but I think they may be going through it fast enough to not notice any problems. If you think you have stability issues, make enough to get through one week, and if you see a drop in recovery, make a new solution and re-extract using the same standards. If the recovery improves, you may have your culprit. We also run 548, so I'll ask that extraction person if he has to prep that solution frequently. I might not see him for a while though, he works nights and I don't. I'll post back when I have more info.

Remind them to look at the janitor's cleaning closet while they're at it.

Hey - we make and sell the products that janitors use....

Talked to one of the 552 guys. They make and use about a liter a month of 10% sulfuric acid in methanol, and haven't seen any stability issues (at least with the 552 analysis). I might see the 548 guy tomorrow night, I'll ask him how often he goes through his solution of 10% sulfuric in methanol.

EDIT - talked to the 548 analyst and one of the extraction techs - no issues with the 10% sulfuric in methanol. Sorry I couldn't be of more help.

Talked to one of the 552 guys. They make and use about a liter a month of 10% sulfuric acid in methanol, and haven't seen any stability issues (at least with the 552 analysis). I might see the 548 guy tomorrow night, I'll ask him how often he goes through his solution of 10% sulfuric in methanol.

EDIT - talked to the 548 analyst and one of the extraction techs - no issues with the 10% sulfuric in methanol. Sorry I couldn't be of more help.

Well I’m like 10 years late and became a quality manager but thank you lol. Just in case some poor prep person is pulling their hair out and runs across this, it turned out to be that the sodium hydroxide during the conditioning process was stripping the cartridges. I decreased the normality and didn’t leave it on any of them any longer than necessary. Also we have always pushed the phase down after the final 20 mL water is added because the sodium hydroxide makes it puff up and creates voids.