Pyridine-free Karl Fischer reagent

In today s lab, pyridine-free Karl Fischer reagents are used. The titration has been adapted to specialized automated titrators made by a variety of instrument manufacturers. The volumetric titration is monitored by two platinum electrodes held at a constant potential. The endpoint is reached when excess reagent results in a constant current. This test method has gained in popularity over LOD testing due to its accuracy, specificity, and smaller sample sizes. 

This test method is intended for use with standard Karl Fischer reagent or pyridine-free Karl Fischer reagents. 

Pyridine-free Karl Fischer reagent and two-component solvent used in the cooperative program and found to be satisfactory are available from Crescent Chemical Co., Inc., 1324 Motor Parkway, Hauppauge, NY 11788 under the name of Hydtanal a registered trademark of RMel Dehaen—Composite 5 and Hydranal—solvent. 

Pyridine-Free Karl Fischer (one-component) reagent diluted with xylene—Dilute three parts pyridine-free Karl Fischer (one-component) reagent (1 mL = 5 mg water) to 1 part xylene. Fresh Karl Fischer reagent must be used. (Warning—See Note 2) Must be used with solvent in 7.6.2. 

Commercially available Karl Fischer reagent is stabilized and can be obtained free of pyridine, which is toxic. It can also be prepared in the laboratory however, this requires the use ofS02, a poisonous, liquified gas. 

Pyridine-Free Chemistry In recent years, pyridine, and its objectionable odor, have been replaced in the Karl Fischer reagent by other amines, particularly imidazole, shown in the margin. These pyridine-free reagents are available commercially for both volumetric and coulometric Karl Fischer procedures. More detailed studies of the reaction have been reported. The reaction is now thought to occur as follows ... 

I. Nordin-Andersson and A. Cedergren, Spectrophotometric Determination of Water by Flow Injection Analysis Using Conventional and Pyridine-Free Two-Component Karl Fischer Reagents. Anal. Chem., 57 (1985) 2571. 

Karl Fischer Reagents, Standard reagent cqptaining pyridine (7.4.1) or pyridine-free reagent (7.4.2). 

Mass % Water Standard Karl Fischer Reagents Pyridine-Free Reagents ... 

---