eutech-instruments bromide epoxy Manuale Utente

Instruction Manual 

 

Bromide Electrode 

 

13

 
The upper limit of detection in pure sodium bromide solutions is 1M. In the presence of other ions, 
the upper limit of detection is above 1.0x10

-1

M bromide, but the possibility of a liquid junction 

potential developing at the reference electrode and the "salt extraction effect" are two limiting 
factors. Some salts may infuse into the electrode membrane at high salt concentrations, causing 
deviation from the theoretical response. Either dilute samples between 1M and 1.0x10

-1

M or 

calibrate the electrode at 4 or 5 intermediate points. 
The lower limit of detection is influenced by the slight water solubility of the electrode pellet.  
Refer to Figure 1 for a comparison of the theoretical response to the actual response at low levels of 
bromide. Bromide measurements below 10

-4

M Br

-1

 should employ low level procedures. 

 

 
Hydroxide ion interferes with measurements of low levels of bromide although the electrode can be 
used over a reasonable pH range. Table 3 should be used to determine the minimum pH at which 
low level bromide measurements can be made without more than a 10% error due to hydroxide ion 
interference. 
 

 
A bromide ion electrode will last six months in normal laboratory use. On-line measurements might 
shorten operational lifetime to several months. In time, the response time will increase and the 
calibration slope decreases to the point calibration is difficult and electrode replacement is required. 
 

 
The bromide electrode may be stored for short periods of time in 1.0x10

-2

M bromide solution. For 

longer storage (longer than two weeks), rinse and dry the sensing pellet and cover the membrane tip 
with any protective cap shipped with the electrode. The reference portion of the combination 
electrode (or the outer chamber of the reference electrode) should be drained of filling solution, if 
refillable, and the rubber insert placed over the filling hole. 
 
 
ELECTRODE THEORY 
 

 
A bromide ion electrode consists of a sensing membrane bonded into a glass or an epoxy body. The 
membrane is composed of silver bromide/silver sulfide. When an electrode potential develops 
across the membrane, the electrode is in contact with solution containing bromide ions and is 
capable of measuring free bromide ions. This electrode potential is measured against a constant 
reference potential, using a standard pH/mV meter or an ion meter. The level of the bromide ions, 
corresponding to the measured potential, is described by the Nernst equation: 
 
 

 

E = Eo - S log X 

 where: 
 

 

E = measured electrode potential 

 

 

Eo= measured potential (a constant) 

 

 

S = electrode slope (

∼57 mV/decade)