HPLC Grade

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

9 posts Page 1 of 1
Hey all,

I have a question regarding the grades of acid used in HPLC. If most solvents like water and the organic solvent are already HPLC grade, do I still need HPLC grade acids for buffers or could I opt out for it?

You certainly do! First of all, HPLC-grade reagents generally have had particulate matter filtered out. Even if you routinely filter your solutions, though, you still need HPLC-grade. Example: ACS-grade phosphate and methylphosphonate reagents contain impurities that absorb light at low wavelengths. They accumulate on some types of HPLC columns during equilibration with the starting mobile phase and then elute during the gradient, resulting in a large, artifactual peak. HPLC-grade reagents generally have these impurities removed.

if you can't find an HPLC-grade salt but the corresponding acid is available in HPLC grade, then prepare the salt by adding the purest grade that you can find of the appropriate base to a solution of the acid.
PolyLC Inc.
(410) 992-5400
You need HPLC grade salts and buffers.
I've found that Analar grade formic acid works pretty well for most applications instead of LC-MS grade for mixed PDA/Mass spec methods. I may have been lucky: I have a sneaky suspicion that LC-MS grade isn't necessarily made differently, it might just be Analar that has been tested to pass appropriate specifications, so perhaps I've just hit a few good batches.
We rarely used HPLC grade acids and salts for HPLC buffers. On the other hand, we typically used wavelengths higher than 250 nm.

Yes, we filtered all buffers through 0.45µ membranes before use.
We too use 'regular' ('for analysis' for Merck and 'purris p.a' for Sigma's products) buffers and we filter all buffer solution through 0.45um.
We normally just use ACS Reagent grade salts for our buffers and the inorganic acids we just use Trace Metals grade we get from the ICP department.
The past is there to guide us into the future, not to dwell in.
In view of these recent comments, let me elaborate a bit on my earlier remarks. Sometimes the impurities of concern in salts, especially phosphates, are heavy metals or anions other than phosphate. Those wouldn't interfere with reversed-phase columns. With an ion-exchange column it's another story; the impurity ion could accumulate during equilibration and then elute in a concentrated peak during a gradient. The above comments should be qualified, then, with regard to the type of chromatography that is being used.
PolyLC Inc.

(410) 992-5400

Yes, I assumed typical reverse phase applications. If you're doing "clever" stuff it's worth being careful. When using pulsed amperometry detection with an old Dionex LC system, we found that bottled electrochemical-grade water gave consistent results for a month or more between cleanings, while the best grade of bottled HPLC water we could obtain caused the instrument to lose sensitivity drastically over just a day or two (our own 18.2MOhm RO water had the same problem). We have no idea what was special about the bottled electrochemical grade water, but it was magic.
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