Chromatography Forum

I've read through the posts on alendronate sodium detection, but I'm hoping someone with more experience than me can help. I've been trying to use a methodology published by Merck several years ago:

Yieng-Hau R. Han, Xue-Zhi Qin. Determination of alendronate sodium by ion chromatography with refractive index detection. J Chromatography A. 719(1996)345-352.

It has a published sensitivity of .4x10^-4mg/mL. We have run the experiment with the same column (Waters IC-Pak anion HR column) and a newer model of the RI detector along with the 6mM nitric acid as the mobile phase however we can only achieve .04mg/mL sensitivity. We are trying to find a method that's very sensitive as we're looking at small quantities of alendronate (which is also why we're trying to use methodologies that do not require complexation). I have contacted Merck (where the article was published from but the authors are no longer there and am waiting on other response from the company). Any suggestions for how to get increased sensitivity? We're using the temp, mobile phase, and concentration of mobile phase that they found to yield the best results at current.

Any suggestions for very sensitive method for alendronate measurement? We only have an RI and a UV detector (no conductivity or other specialized detectors). Thanks so much!!

I checked the abstract Han et al and it is actually 4 x 10EE-4.
You should be able to get that ballpark with a modern RI detector.

I would suggest you try to reproduce the test that the manufacturer of the RI detector uses for it's spec and see if it is working properly.

I do remember seeing another method, which was by indirect HPLC/UV using a Cu salt in the mobile phase (I think). No idea about sensitivity.

One author was Drazen Ostovic, Pharm. Res. 10 (1993) 470-2

Mardexis: Sorry that was my mistake with the LOD amount (my notes have it as .0004 and I was debating which way to write it when I was typing the post).

I will check wrt the RI detector. Our system is brand new (we've only had it 3mo). I also tested ALN in .4 to .04 concentrations look good though, so I don't think its a problem with the RI detector, but its definitely worth looking into! (All concentrations from .01 and lower match the curve of water with no peak at 3.5min, which is where the alendronate should be (sodium appears earlier around 1.5 to 2min) Our peaks do match Han et al's published peaks, however, our peaks have a much larger magnitude.

I will look into the earlier Cu addition (the '93 paper). I also have a paper from Cornelio et al from J Liquid Chrom & Rel Tech using in line complexation of the ALN using a mobile phase of nitric acid & copper II nitrate that we will also try.

Thanks for your help! If anyone thinks of anything else we should try, please let us know!

I was successful in derivatisation of alendronate at the NH2 with the AccQ-Fluor-Reagent from Waters. The reagent is designed for amino acid analysis and works well with many other primary and secondary amines under aqueous derivatisation conditions. It is a fluorescent compound but may also be analysed with UV detection at 248-254 nm.

Good luck!

Hi CJW, could you please provide the RI conditions you have
tried? What are the critical variables for selectivity?