Combination pH Electrodes with Silver/Silver Chloride References 

Glass Body Units/Liquid-Filled 

Temperature 

Temperature Range 

Catalog pH Range Intermittent 

No. Range (OC) (OC) 

13-620-90 0 to 14 -5 to 110 

13-620-91 o to 14 -5 to 110 

13-620-92 0 to 14 -5 to 110 

13-620-93 0 to 14 -5 to 110 

13-620-94 0 to 14 -5 to 110 

13-620-285 0 to 14 -5 to 110 

13-620-291 0 to 14 -5 to 110 

13-620-292 0 to 14 -5 to 110 

Polymer Body Units/Liquid-Filled 

13-620-97 0 to 14 -5 to 80 -5 to 100 

13-620-98 0 to 14 -5 to 80 -5 to 100 

13-620-99 0 to 14 -5 to 80 -5 to 100 

13-620-83 0 to 14 -5 to 80 -5 to 100 

13-620-287 0 to 14 -5 to 80 -5 to 100 

13-620-289 0 to 14 -5 to 80 -5 to 1 oo 

Polymer Body Units/Gel-Filled 

13-620-104 0 to 14 -5 to 80 

13-620-106 0 to 14 -5 to 80 

t3"62u-1-08 o to 14 -- -:> (J8(t 

13-620-109 0 to 14 -5 to 80 

13-620-110 0 to 14 -5 to 80 

13-620-252 0 to 14 -5 to 80 

13-620-290 0 to 14 -5 to 80 

Fisher combination electrodes offer the convenience of having 

the reference and measu ring electrodes combined in a single 

housing. They are offered in a wide variety of configurations: 

meet most application needs. 

Basically, the design consists of a glass pH indicating e e:::: "' 

coaxially joined to a silver/silver ch loride reference elec ooe. - r.e 

glass pH indicating electrode is located at the center oft e e_ 

The reference electrode is located in the outer annular space o 

the probe. The outer annular space contains the silver/silver 

chloride reference element, electrolyte (4M KCI saturated with 

AgCI or gelled 4M KCI saturated with AgCI) and the junction 

(ceramic or porous plug). When immersed in a solution, the 

reference electrode makes contact with the sample through the 

junction thus completing electrical contact between the reference 

electrode, sample and pH indicating electrode. 

Fisher combination electrodes are responsive over the full 0 to 

14 pH range. Glass body liquid-filled units are available in standard and micro sizes, and are recommended for most routine 

applications. Polymer body liquid-filled units are available in standard and micro sizes and are recommended for applications 

where breakage is a problem. Polymer gel-filled units are 

available in both standard and micro sizes and are best suited for 

those applications where there is a need for both low maintenance 

and breakage resistance. 

Instrument 

Manufacturing 

Division 

INSTALLATION 

To place the combination electrode into service perform the 

following : 

CAUTION: Polymer-bodied electrodes should not be used in 

non-aqueous solvents, concentrated aceti c acid or concentrated 

oxidizing agents. 

I. Liquid Filled Units 

1. Carefully remove the plastic cot from electrode. Save the 

cot for future storage. Always exercise care when hand li ng 

the electrode, since a slig - a chon the glass bulb can 

re der the electrode useless. 

2. Rinse the electrode with dis· 1 e~ '"-:='- ::: emove crystal 

resi ue hat may have formed r -- 2::: _ ·::.::e curing 

sto age. he residue is caused 1 --= · 3:.:... ::_ eak.age and 

grao a e aporation of electrolyte a -:; :::·:-=.;:= 

3. If the .11 ole is located on the cap ring, ·--=-= -- =-·: e 

from t e losed to the open position. If e 

located -the electrode body, lower the ru -:e- :::c ==· e and 

remo e e • hite vinyl tape to expose the·· - : = 

4. Check e e ectrolyte level in the reference-::.. _ - _ :er 

annular spa e). If the fill hole is located 

electro! e le el should be approxima e · ~ i 

cap. If the fill hole is located on the body, the electro e 

level should be approximately V4 inch below the fill hole. If 

the electrolyte level is too low add electrolyte from the provided bottle of FJ.sh e.~o. SP135 (.4M-K81 saturatedcwitM 

AgCI). 

5. Prooer electrode function requires electro! e flow at the 

, .'1 · :- =e-- •ea:::e(:~a,e' .' .. e omthefollo• i g 

~ --e. 

1 OTE: Tne fiq to 1u oca ed on the side of glass 

bodied units (whUe ceramic dot) and in the silicon ung<=~ 

the base of the electrode on polymer bodied units (w · e 

ceramic rod or dot). 

a. Hold the electrode upright at a 45° angle betwee- -- e 

thumb and the forefinger of the left hand , so tha< --, " -

ing hole faces out and is directly opposite the ::se ' 

the thumb. 

b. Insert the spout of the electrolyte dispensi" _ :; - e 110 

the fill hole. 

c. Making sure that the electrode is supoo-:e;: • ne base 

of the thumb, firmly press the spou· ,.. t e fill hole to 

make an airtight seal. 

NOTE: Normally, the spout tip ,• nl not touch the internal 

element. While applying pressure, care should be exercised to prevent contact with this element. If contact 

occurs, it will be necessary to cut off a small portion of 

the tip. 

d. While maintaining the seal, squeeze the filling bottle so 

that the electrode becomes pressurized. A bead of 

liquid should form at the liquid junction in about 30 

seconds; in some cases it may be necessary to maintain pressure for several minutes . 

6. Mount the elec rode on a suitable holder and connect the 

jack/jacks to the meter. 

NOTE: If the electrode was supplied with a removable 

plastic bulb protector, it can be placed on the electrode at 

this time. 

0 Fisher Scientific 
7. Allow the electrode to soak in buffer for 10 minutes prior to 

standardization. 

8. Check the electrode response. 

a. Using a one-point standardization , proper response is 

indicated if the error is less than ± 0.05 pH per pH unit 

from the standardization point when using fresh Fisher 

certified ± 0.02 pH buffers. 

b. Using a two-point standardization, an efficiency > 0.95 

or slope > 95% indicates proper response. _,....,.......__ __ ~-

II. Gel-Filled Units 

1. Carefully remove the plastic cot from the tip of the electrode . Save the cot for future storage. Always exercise 

care when handling the electrode, si ce a slight scratch on 

the glass bulb can render the elec rode useless. 

2. Rinse the electrode to remove an crystal residue that may 

have formed during storage. 

3. Remove the excess water o tne electrode by shaking he 

probe. 

4. Mount the electrode on as itable holder, and connec e 

jack/jacks o t e e e . 

NOTE: Since e b lb is protected, the electrode may be 

placed directly into the solution and used to stir the solu ·a 

to enhance response time. 

5. Allow the electrode to soak in buffer for 10 minutes prior :o 

standardization. 

6. Check the electrode response. 

a. Using a one-point calibration proper response is indicated if the error is less than ± 0.05 pH per pH u i ' m 

the standard ization point w en sin 'res >="is e 

certified ± 0.02 pH b ffers. 

b. Using two-poin standardization, an efficiency > 0.95 or 

slope > 95% indicates proper response. 

OPERATION 

For optimum operation observe the following precautions. 

I. Liqu id Filled Units 

1. The ·11 hole must be open when taking measurements. 

2. The elec·rode need only be immersed far enough to cover 

both the glass pH sensing bulb and refere ce junction to 

obtain accu a:e readings. 

3. The level of elec·ro' e in the outer cavi must always be 

kept above the le el o e solution bei g easu red. 

4. The level of electrolyte mus always co e he reference 

element; otherwise electrical contact cannot be established. Add electroyte as needed . (See INSTALLATION 

procedure.) 

5. Always rinse the electrode witn dislllletrwa1eriYetween 

samples. 

6. To optimize electrode life avoid prolonged measurements 

in strong alkaline solutions . 

7. Due to the high impedance (resistance) of the pH glass 

membrane, the electrode cable should not be moved or 

touched while measurements are being made; otherwise 

unstable readings may res lt. 

II. Gel Filled Units 

1. The electrode need only be immersed far enough to cover 

both the glass pH sens ing bu lb and the reference junction 

to obtain accurate readings. 

2. Always rinse the electrode with distilled water between 

samples. 

3. To optimize the electrode life avoid prolonged measure- -._......' 

ments in strong alkaline solutions. 

4. Avoid taking measurements in samples with widely varying 

temperatures. Failure to do so may shorten electrode life 

due to contamination of the gel with sample. 

5. Due to the high impedance (resistance) of the pH glass 

membrane, the electrode cable should not be moved or 

touched while measurements are being made; otherwise 

unstable readings may resu lt. 

STORAGE 

1. Never store the electrode in distilled or deionized water. This 

may lead to slow sluggish response caused by junction 

clogging. 

2. Between measurements immerse the electrode in a buffer 

solution (4 or 7 recommended). For liquid filled units keep the 

ill hole open to avoid co amin ation of the electrolyte from the 

b ffer solution. 

3. hen the electrode is n · - se. it is highly recommended 

hat the plastic cot be re 2 ::: s. er the probe tip. Wet the coton inside the cot wi · er. Then while squeezing 

the cot place it over · e :1p of the prooe and slide it on. This 

procedure keeps the obe in a ready state. (Close the fill hole 

on liquid filled uni s.) 

REJUVENATION 

pH electrodes wil l natu rally age and underg a reduction in their 

Nernstian response. Occasionally, this is accompanied by sluggish response. This aging is caused by either co amin ation of 

the glass membrane or by clogging of the liquid junction. (In rare 

ins a ces ooor ""S nse a be caused by a deterioration of the 

insula ~ d the internal element.) Separate 

proced ·es:: ·:; • e- "5- ·~ leaning the glass membrane surface an " ,- - ::.---

CLEANING T E GLASS pH MEMBRANE 

A dirty glass ~a =·~-e s _s ally indicated by beads of water 

forming on - e =-::: -:- -: is rinsed with distilled water. The bulb 

can be clean s.s '::: - • : 

1. For protei - e'S - soak in a freshly prepared solution of 

pepsin in 0. · • Cl (approximately V4 teaspoon/1 00 ml) for 30 

minutes. 

2. For inorganic deposits- wash with EDTA, ammonia, or acids. 

3. For grease and similar films- wash with acetone, methanol, 

etc. 

UNBLOCKING THE JUNCTION 

If the junction should become blocked or partially plugged, perform the following: 

I. Liquid Filled Electrodes 

1. Inspect the reference cavity for crystallization. If crystallization is present, go to step 2; if not, proceed to step 3. 

2. Remove crystals as follows: 

a. Remove the filling solution by shaking it out through the 

fill hole. 

b. Repeatedly rinse the reference cavity with distilled 

water until all crystals are dissolved. 

c. Empty the reference cavity and refill it with SP135. 

d. Pressurize the electrode (see step 5 under INSTALLA-

. TION) and determine if flow is re-established. If no flow 

is found , proceed to step 3. 
3. Perform the following procedures in sequence and as 

needed, depending upon the severity of the blockage. 

a. Soak the electrode tip in warm water and apply 

pressure to the filling hole (see step 5 under 

INSTALLATION). 

b. Soak the electrode tip in concentrated ammonium 

hydroxide for 5 to 10 minutes (use adequate ventilation 

and precautionary measures). Rinse with deionized 

water. Then, apply pressure to the filling hole (see step 

5 under INSTALLATION). 

c. If the junction remains clogged, you may carefully sand 

or file the porous plug on glass- body un;ts, making certain not to contact the glass bulb. 

II. Gel-Filled Electrodes 

Perform the following procedures in sequence and as needed, 

depending upon the severity of the blockage. 

1. Soak the electrode in warm water (approximately 60°C) for 

5 to 10 minutes. This should re-establ1 sh contact. 

2. Place the electrode in warm . satura eo Cl solution 

(approximately 60°C) and allo he e,ec1rode and solution 

to cool to room temperature. 

RECONDITIONING THE SENSING MEMBRANE 

Prolonged use, excessive alkaline immersion, or high e perature 

operation will cause surface leaching of the membrane glass , 

resulting in extremely noisy and/or sluggish response " ich cannot be remedied by the steps outlined above. If th is occ rs. the 

following procedures will often provide renewed stabili and pH 

sensitivity: - -

1. Immerse the electrode tip into 0.1 M HCI for about 15 seconds; 

rinse the water, and immerse into 0.1 M KOH for 15 seconds . 

Cycle the electrode through these solutions several times; 

then , recheck the electrode performance. If problem still 

persists, go to step 2. 

2. a. Immerse the electrode tip into a 20% ammonium bifluor e 

solution for 30 seconds or a 10% hydrofluoric acid solu 

for 15 seconds. 

WARNING: The above fluoride solutions are extre e 

corrosive and hazardous, and proper safety proced 'es 

must be observed when handling and using them. 

b. Thoroughly rinse the electrode with water, then i e se 

the electrode tip into concentrated hydrochloric ac1o or 30 

seconds to remove any residual fluorides and rinse again 

with water. 

c. Soak the electrode in buffer (pH 4 recommended) for at 

least 1 hour. Then recheck electrode performance. If performance has not been restored , the electrode should be 

replaced. 

NOTE: Frequent fluoride treatment can shorten the electrode life and may eventually cause membrane cracking.