Fluoride ion selective electrode

Abstract

A fluoride monitoring electrode comprises a single crystal of a lanthanum series fluoride doped with alkaline earth ions. The sample pre-treatment solution used in conjunction with the electrode includes a buffer that maintains a pH of 5 to 8 and a complexing agent that complexes iron and aluminum.

1 . A fluoride ion-selective electrode for monitoring the fluoride ion concentration in a sample solution, said electrode comprising a single-crystal membrane of a rare earth fluoride doped with alkaline earth ions.  
   
   
       2 . The electrode of  claim 1  in which the rare earth fluoride is lanthanum fluoride and the alkaline earth ions are from the group of strontium, barium, and calcium ions.  
   
   
       3 . The electrode of  claim 1  in which the dopant concentration is in the range of 0.1 to 20 percent m/m.  
   
   
       4 . A sample pre-treatment solution for use with the electrode of  claim 1  containing: 
 A. a buffering agent capable of maintaining a pH in the range of 5-8; and    B. a complexing agent capable of complexing aluminum and iron    
   
   
       5 . The sample pre-treatment solution of  claim 4  in which the complexing agent and the buffering agent are the same compound.  
   
   
       6 . The sample pre-treatment solution of  claim 4  in which the buffering agent and complexing agent are different compounds.  
   
   
       7 . A sample pre-treatment solution as in  claim 4  in which the buffering agent is an acid compound selected from the group of MOPS, MOPSO, HEPES, MES, PIPES, BIS-TRIS and DIPSO.  
   
   
       8 . The sample pre-treatment solution of  claim 4  in which the complexing agent is from the group of 5-sulfosalicylic acid, citric acid, tartaric acid, CDTA, EDTA, and Tiron.  
   
   
       9 . A fluoride ion-selective electrode for monitoring the fluoride ion concentration in a sample solution, said electrode comprising a single crystal membrane of a rare earth fluoride doped with alkaline earth ions, said electrode used with a sample pre-treatment solution containing a buffering agent capable of maintaining a pH in the range of 5-8 and a complexing agent capable of complexing aluminum and iron.  
   
   
       10 . An electrode as in  claim 9  in which the rare earth fluoride is lanthanum fluoride and the alkaline earth dopant is from the group of strontium, barium, and calcium ions.  
   
   
       11 . The electrode as in  claim 9  in which the dopant ion concentration is in the range of 0.1 to 20 percent m/m.  
   
   
       12 . The sample pre-treatment solution as in  claim 9  wherein the complexing agent and the buffering agent are the same compound.  
   
   
       13 . The sample pre-treatment solution of  claim 9  in which the complexing agent and buffering agent are different compounds.  
   
   
       14 . A sample pre-treatment solution as in  claim 9  in which the buffer solution is an compound selected from the group of MOPS, MOPSO, HEPES, MES, PIPES, BIS-TRIS and DIPSO.  
   
   
       15 . A sample pre-treatment solution as in  claim 9  wherein the complexing agent is selected from the group of 5-sulfosalicylic acid, citric acid, tartaric acid, CDTA, EDTA and Tiron.