Our group is trying to perform a chemical analysis of choline (as choline bitartrate) in clean water samples (containing only this chemical). We are using a Dionex ICS-5000 + DC Detector, with a CS16 column. We used 32 mM MSA as eluent and a flow rate of 0.36 ml/min. We are doing 35 min runs and we are getting a nice peak (likely choline) at about 8 min. However, the peak area is not concordant with the concentration. Can anyone give us more information on how to perform choline analysis using IC? Should we extend the run time, use other eluent,…? What, approximately, is the choline retention time under these conditions? Any help is kindly appreciated.
Kind regards
Fátima
Dear Sir. Concerning your issue about the Choline analysis by Ion Chromatography. Choline, a water-soluble micronutrient, is grouped with the B-complex vitamins, and is essential for the central nervous system and other physiological functions. Because of the importance of this micronutrient to infant health, the AOAC regulates choline with its Official Method 999.14, which describes the determination of choline in infant formula and milk using an enzymatic colorimetric method.The IC method is applicable for the determination of choline in a variety of complex matrices with excellent accuracy and precision e.g Infant Formula , Adult Nutritional , Whole Egg Powder and Soy Flour. Choline was determined in infant formula by ion chromatography with suppressed conductivity detection. Samples were digested with 1M hydrochloric acid, filtered, diluted, and injected into the chromatographic system. Choline and the alkali and alkaline earth metals were separated on a high-resolution cation-exchange column and detected by suppressed conductivity. The method was linear between 2 and 200 mg/L (r2 = 0.9999), the concentration range of the diluted samples. This method accurately determined choline in powdered, concentrated, and ready-to-feed infant formulas. Recoveries of choline spikes into powdered infant formula at approximately 1, 0.8, 0.5, and 0.2 times the labeled value ranged from 85 to 114%. This method had good agreement for 8 blind duplicates. The values determined for these samples, which were used in an AOAC collaborative study of an enzymatic method, were consistent with the values determined by the enzymatic method. For more details, I think the following below link may help you in your analysis:
http://analyteguru.com/ion-chromatography-analysis-of-choline-in-infant-formula/
http://lib3.dss.go.th/fulltext/Journal/J.AOAC%201999-2003/J.AOAC1999/v82n5(sep-oct)/v82n5p1156.pdf
Thanks
Thanks Farooq's sharing, which is a very good guidance. I have been this ACS meeting but missed this good topic. In order to identify its retention time, you can use both K+ and Mg2+ as indicators. Choline peak will be between them. Your eluent is no problem and its retention time is reasonable. What means of "the peak area is not concordant with the concentration"? Did the peak areas respond to the corresponding concentration un-linearly? Please provide us more information. Thank you!
Thank you Mr M. Farooq Wahab, Mr. Isam Eldin Hussein Elgailani and Mr Hongzhu Liao for your comments.
The question is that we do not have another column available, only the CS16. However, we managed to get a good chromatogram, using MSA 30mM as eluent. Choline had a retention time of about 30 min (the flux was low: 0.36 ml/min). Finally, we got peak areas responding to the corresponding concentration linearly, which did not happen previously. Interestingly, in this column, the choline peak was not between that of K+ and Mg2+, but after both of them.
Once again, thanks for your contribution and help.
Best regards
Fátima
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