Chromatography Forum

I've recently purchased some reagent grade chemicals to use as standards to make calibration curves for GC. The label on the bottle says that they are "98+%" pure, which is not much help since I need to know exactly how pure it is.

My question is this: Should I assume it's 98% pure or 100% pure?

Assume whatever you will.

The specifications according to the manufacturer says it is 98% plus purity.

After opening the bottle there is no guarantee to any purity.

I would assume it is 98% unless you know differently.

Very few things in the lab are 100%, even the water is less than that (although Ivory Soap is 99.94% pure).

You may be able to get an actual COA, certificate of analysis from the manufacturer if it is an important issue with your company.

best wishes,

Rod

Assume whatever you will.

The specifications according to the manufacturer says it is 98% plus purity.

After opening the bottle there is no guarantee to any purity.

I would assume it is 98% unless you know differently.

Very few things in the lab are 100%, even the water is less than that (although Ivory Soap is 99.94% pure).

You may be able to get an actual COA, certificate of analysis from the manufacturer if it is an important issue with your company.

best wishes,

Rod

Thanks for the helpful info, Rod. The main reason why I need to know the purity is because I'm using it to make a calibration curve and I feel like I need to know exactly how much I actually have. I will try and get a certificate of analysis.

although Ivory Soap is 99.94% pure

99.94% pure is the biggest hogwash I've ever heard, and I'm in the industry. P&G trademarked the slogan, maybe one of their raw materials once tested as that. Ivory soap has NaCl, trace glycerin, chelants, antioxidants, fragrance, and sodium soap (they formerly had potassium soap too, haven't assayed Ivory lately).

CPG,

Yes, I was aware, and was trying to be a bit humorous.

ROd

I've recently purchased some reagent grade chemicals to use as standards to make calibration curves for GC. The label on the bottle says that they are "98+%" pure, which is not much help since I need to know exactly how pure it is.

My question is this: Should I assume it's 98% pure or 100% pure?

If you really need to know the purity of the materials then you have to obtain certified reference materials - these come with a certificate stating purity and an uncertainty on the purity. They also, for obvious reasons, cost a lot more than reagent grade, and are not available (except as custom items) for a lot of chemicals that you can get as reagents.

The worse that can happen is that you have a 2% bias in your results - if that is unacceptable then certified meterials are the only off the shelf choice, or you have to do an exhaustive purity determination (Karl Fischer, loss on drying, ash, NMR et etc etc) on something of lower grade.

Peter

My industry (environmental) requires certified standards; neat materials are treated as 100 percent if it is 97 percent or greater. We also normally need two sources of the analyte, to run against each other.

I *think* reagent grades will come with a certificate, or it will be available at the manufacturer's website. So you likely have accurate purity information available.