Lithium-EDTA chelate

Ethylenediamine tetraacetic acid (EDTA) [60-00-4] (Sequestrene), an anticoagulent at 1 mg of the disodium salt per mL blood, complexes with and removes calcium, Ca ", from the blood. Oxalate, citrate, and fluoride ions form insoluble salts with Ca " and chelate calcium from the blood. Salts containing these anticoagulants include lithium oxalate [553-91-3] 1 mg/mL blood sodium oxalate [62-76-0]2 mg/mL blood ... 

Calcium in lithium salts has been determined by EDTA titration after a preliminary separation of the calcium from lithium using a chelating resin. 

In t ie case of animal plasma preparation, an anticoagulant is necessary to maintain solubility of blood components, and sodium citrate or lithium heparin would be preferable over any alternatives that contain EDTA. EDTA will chelate magnesium and zinc ions and require much higher concentrations of the two ions in the assay buffer for acceptable hnal ion concentrations, possibly to the point of precipitation. 

Other substances are often retained on the sex support that cannot be eluted with 1.2 N sodium (or lithium) chloride at pHs of 7.5 or 8. Divalent cations such as calcium can be especially hard to remove and will poison the support, making it unusable. Therefore, it is common practice to regenerate the column either after every sample or on a routine basis. The most common regeneration mobile phase is 0.2 N sodium or lithium hydroxide. Many regeneration mobile phases will also contain a divalent chelater, usually EDTA [(ethylenedinitrilo)-tetraacetic acid]. 

---