Chromatography Forum

Hi, Everyone


I am new to ion chromatography, and to the company wherein I work. How often should a calibration be performed on a Metrohm 940 IC that analyzes chloride and sulfate on boiler and condensed steam water samples (power plant industry here) twice a shift on a daily basis? The quantity of samples run through the IC is usually ~10 samples per shift.

We have a young, experienced chemist who calibrates the instrument every 3 days or so because his check standards fail their theoretical concentration. I have worked with HPLC and GC before, but I have never found the need to calibrate the instruments in at least month. This is my first time seeing an instrument being calibrated in at least 2 times a week.

Any thoughts on this? Does anybody, especially from the power industry handling the same type of analysis on the same type of samples, have an opinion on this? I would love to hear and learn from all of you.

Many thanks in advance.

Hi, Everyone


I am new to ion chromatography, and to the company wherein I work. How often should a calibration be performed on a Metrohm 940 IC that analyzes chloride and sulfate on boiler and condensed steam water samples (power plant industry here) twice a shift on a daily basis? The quantity of samples run through the IC is usually ~10 samples per shift.

We have a young, experienced chemist who calibrates the instrument every 3 days or so because his check standards fail their theoretical concentration. I have worked with HPLC and GC before, but I have never found the need to calibrate the instruments in at least month. This is my first time seeing an instrument being calibrated in at least 2 times a week.

Any thoughts on this? Does anybody, especially from the power industry handling the same type of analysis on the same type of samples, have an opinion on this? I would love to hear and learn from all of you.

Many thanks in advance.

I ran an older Metrohm for chloride and sulfate on drinking water and waste water and unless there was some very high matrix sample calibrations would hold about a month with no problem. We were running about 50-75 samples per day.

Boiler water I can imagine would have much higher levels of salts so unless you have a way to treat the sample to remove the metal ions, you would probably need to calibrate more often. Iron was what seemed to wreck our calibrations the fastest, and we used the inline guard column to capture that. About once a week we had to change it out and it would be a reddish orange like rust from the iron it was capturing. Once the iron gets on the column we would experience earlier retention times and broad peaks.

Dear king-kemiker

I fully agree with James.

We now cases where a calibration was stable for half a year or even more.
I do not recommend to wait that long anyway.

The procedure of recalibration after a check standard injection out of range is typically recommended.

But in your case of typically very low concentrations the situation is may be a little more difficult.

You need to make sure that your check standard solution is securely prevented from contamination from the ambient.
On the other hand your eluent needs to be prepared ultrapure water and with highest quality chemicals. Her I recommend to apply Inline Eluent Production. While using the eluent it needs to be prevented from contamination.

Best regards