Development of Rapid System for Ion-pair Reversed-phase Partition Mode HPLC by Using Hydrophilic Counter ion

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A new method for HPLC with ion-pair reversed-phase partition mode has been developed by using hydrophilic counter ion such as buffer components and alkaline metal ion. The advantages of the proposed method are rapid elution and efficient separation. A marked improvement was attained compared with the conventional method by using hydrophobic counter ion such as quarternary ammonium ion and long chain alkylsulfonic ion.For example, anionic metal chelates with 2,2'-dihydroxyazobenzene resulted in base-line resolution within 6 min, In the conventional method with tetrabutylammonium on, it look 30 mm to separate these chelates. Furthermore, the proposed method has been successfully extended to the anionic metal chelates with 4-(2-pyridylazo) resorcinol and its analogues, polyaminocarboxylic acid such as Quin-2, and hydorazone derivatives. Compared to the conventional method, a significant improvement was achieved in retention time. The separation efficiency was comparable to that with tetrabutylammonium ion.It has been found that alkaline metal ions such as sodium, lithium and cesium ion, ammonium ion such as tetramethylammonium ion, and guanidium ion effectively work as the hydrophilic counter ion. The mechanism of the rapid retention is attributed to the size and hydration of the hydrophilic ion which leads to specific characteristics of the ion-pairs.The underlying retention mechanism of the charged anlyte in the proposed method with hydrophilic counter ion is also based on the partition of ion-pairs similar to that of hydrophobic counter ion. The proposed method serves as a innovative system for HPLC with ion-pair reversed-phase partition mode.