High salt in HPLC system

[MGagne]

I'm using an anion exchange column to separate carbohydrates with a mobile phase composed of A:100mM NaOH and B: 100mM NaOH and 500mM Sodium acetate on a Dionex system.

I've always been afraid of using high salt concentration on a HPLC system. Is it justified? Is there high risk of damaging the equipment, even if used properly (no long term storage in salt, etc).

If it's ok, is it correct to go up to 1M NaCl or Sodium acetate?

The purpose for the use of high salt concentration in my method is to make sure to wash out all the impurities that may build up in my column, that is a major issue with the sample used.

Thanks

[machi_ya]

We use 0.3M-1M NaCL and 0.5N NaOH for the assay.
And we got following recommendations from Agilent.
It's working well for us.

Basic recommendation is to flush, flush, and then flushed some more with water and replace stainless with peek where possible.

- Permanent degassing (corrosion needs the presence of air!)

- Pump must have the seal wash option

- Mobile phase flow should never cease while the system contains the modifiers

- The system must be flushed with HPLC grade water after use

It should be noted that they increase the stress for the instrument and may require more frequent maintenance - for example for seats and valves. "

So depending on your use and your observation of the condition of the your 1100 LC system an annual or bi-annual PM might be required. We have found that it is important NOT to switch between organics and aqueous buffers frequently. These buffers are somewhat incompatible and have a tendency to precipitate out and can clog your capillaries. Having the Seal Wash option is a must - it is extremely convenient to have a peristaltic pump recirculation on your seal wash. That way you can have a closed looped system where the seal wash goes back into the original container. You then need to make sure that you change out the seal wash buffer (We use 20% EtOH in water) about once a week.

[Bill Tindall]

I have used sodium hydroxide in Perkin Elmer and Waters 510 pumps for years without any particular precautions. A metallurgist told me that sodium hydroxide was not corrosive to the kind of stainless steel used in LC equipment and as far as I have ever seen this advice was correct.

More recently sodium acetate has been used, again without any noticable bad effect.

Sodium chloride is a different story. Chloride can break down the protective oxide layer on stainless steel under some conditions. I would be cautious trying chloride eluants.

[Chris Pohl]

MGagne,

I'm not sure from your post whether you wanted to know if high salt was an issue with the DX600 or if you are investigating the advisability of doing the same work on a stainless steel instrument. If you were referring to the DX600, it can certainly tolerate 1 molar salt solutions but the seal life will certainly be diminished unless you set up the piston seal wash. Chloride containing eluents are possible but detection limits are a better on a gold electrode when the eluent is free of chloride.

If you are referring to the use of stainless steel instrumentation for this application, another consideration not mentioned is the chemical compatibility of the injection rotor seal. The most commonly used rotor seal material is Vespel and this material is not compatible with a pH greater than 10. Hydrolysis products from the seal will contaminate an ion exchange columns, greatly shortening column life.

[MGagne]

Thanks for the advices,

I'll feel safer...

[syx]

What about this method?
Column:
—size: l = 0.15 m, Ø = 4.6 mm,
—stationary phase: spherical end-capped octadecylsilyl silica gel for chromatography R (5 µm) with a 10 nm pore size and a carbon loading of about 19 per cent,
—temperature: 15 °C.
Mobile phase:
—mobile phase A: mix 26 volumes of acetonitrile R and 74 volumes of a 59.7 g/l solution of ammonium dihydrogen phosphate R, adjusted to pH 4.3 with dilute sodium hydroxide solution R,
—mobile phase B: water R, acetonitrile R (30:70 V/V),
run in gradient elution.
Flow rate 1.1 ml/min.
Injection 20 µl, using an injector maintained at 8 °C

Is it safe enough to run?

[Uwe Neue]

Syx

I don't know what your question is, but it is a junk method, as you can see from the pH. It is possible to run junk methods, but I would not want to use one in my QC department....

[syx]

Dear Mr. Neue,
I just worried about my column lifetime when I want to run this compendial method (Roxithromycin - BP2004). High salt concentration is used in this method. Is it safe? I want to hear any input from everyone who has experience with this method without trouble

[Uwe Neue]

There is no problem with the column. I would make an experiment in a flask first to see if the two mobile phases do not create a precipitation problem, but a C18 column does not have a problem with high salt at this pH.

[Supercritical]

SYX, I don't know what Mr. Neue is all worked up about. I see no problems with this method. When you are done, wash your system with 50:50 ACN:water.

[syx]

When you are done, wash your system with 50:50 ACN:water.

... I better use ACN : water (26:74).