Chromatography Forum

Hi everyone, I am new in IC field and I am doing Sodium and Potassium analysis with Shimadzu HPLC system (Conductivity detector) with the following test conditions:

Mobile phase: 0.005M Nitric acid (HPLC grade) diluted with de-ionized water (conductivity less than 0.1 µS). It is filtered through 0.45µm membrane and sonicated for 30 minutes to eliminate all remained bubble.
Column oven: 40 C (there is another component that needs temperature to be kept at 43 C but I do not know what to call it, sorry for my bad English)
Flow rate: 1.0 mL/minute.
My sample are prepared by diluting high-purity Potassium Chloride and Sodium Chloride in the same de-ionized water used for mobile phase preparation.

Here is my problems.
1. Peak due to Sodium is fronting (Asymmetry factor: 0.755), whereas, peak due to Potassium is tailing (Tailing factor: 1.749) although I am using a totally newly-purchased column (Shimadu column IC - C1) which is certified to have great performance with alkaline analysis using test conditions same to mine.

2. Retention time fluctuates day after day although I used the same mobile phase.

Any advice would be highly appreciated. Thanks in advance.

Hi,

What is the detector temperature, this should be the same as the column temperature. A column temperature of 40°C may be too high, try 30 or 35°C.

Has the column been fully conditioned?

What do you mean by ‘alkaline analysis’. You are injecting salts into an acidic mobile phase.

Hi, Khanom. Thanks for your reply. We didn't make the pre-condition before analysis because pre-condition was not mentioned in column instructions. If possible, can you support me the guideline of column pre-conditioning.

Our sample, which consists of Potassium Sodium hydrogen citrate as active subtance and other excipients, are dissolved in DI-water with the concentration of Sodium+ and Potassium+ is 135ppm and 170 ppm respectively. Due to excessively high concentration which causes peak tailing of Potassium, reducing concentration by 4 times solves tailing problem but fronting still remains. Any suggestion from you are highly appreciated. Thanks in advance!

Dear Ultima,

Every new column should be conditioned, before it is used for analyses.

As a minimum, pump the mobile phase through the column for 60 minutes at a low flow rate, say 0.5 mL/minute. Many experienced users condition the analytical column at a lower flow rate, overnight for around 12 hours.

Some folk inject a standard onto the column, which often aids in column conditioning.

I am pleased that you have a more Gaussian potassium peak. After you have conditioned the column, if your sodium peak is still asymmetric, please display an image of the whole chromatogram.