pH electrode types

 

上海雷磁：

E201-C or E201-F (water proof BNC connector)is most suitable. Both are refillable. Reply from TB sellers, 雷磁 brand E201-C response time is typically 1x to 2x seconds. So the main difference is just the good looking white casing.

三信 mini

From E+H:

For beer brewing:

Apera Labsense 213 electrode 

For wine brewing

Hanna HI10480, bench top

Hi981033 portable

HI98169 portable, using FC10483 electrode

Typical internal impedance is  200 to 250 M ohm. 

From MT:

Rule of thumb: sensor resistance to be 1000 times smaller than meter input resistance. 250M ohm x 1000= 250 G ohm, ie 2.5*10^11 ohm 

Dfrobot's pH electrode:

東莞胜輝 S-900 glass electrode， probably the same elctrode as DFRobot , without the casing:

From DfRobot wiki, claims that:

This pH combination electrode is made of sensitive glass membrane with low impedance.It can be used in a variety of PH measurements with fast response, good thermal stability.It has the good reproducibility, difficult to hydrolysis, and basically eliminate the alkali error .In 0 to 14pH range,the output voltage of the electrode is linear.The reference system which consist of the Ag/AgCl gel electrolyte salt bridge has a stable half-cell potential and excellent anti-pollution performance.The ring PTFE membrane is not easy to be clogged, so the electrode is suitable for long-term online detection.

Googling up from internet, it reveals:

Haoshi 東莞豪斯H-101 , used in DFRobot pH meter pro v2.¥140. detailed spec missing. Armor casing. PTFE ring junction. Some more info here

1. Low impedance coating or fast response is more like marketing. Such chemical reactions is slow anyways. Take 15 seconds or more is common.

2. PTFE ring is quite common material use. Nothing special.

3. Long term operation. is another marketing. As electrolytes ( KCL)is constantly ( slowly) leaking out, it will be used up eventually. If it is non refillable type. When you use up the electrolytes, You have no choice but to buy a new one. The leak rate is dependent on reference junction type 

4. It has 25mm O.D. NPT/ PG threads , long 5m cable and ABS casing,  make it easy to install and extend the length. Eg for  commercial  environment.

5. Need to be understand clearly your application need , to say if it's suitable for industrial use ( see above)

6. Most important in industrial applications, is to have electrical isolation. pH , EC probe can interfere pH measurement. Siemens forum , which is not designed/included in this DFRobot industrial grade kit. Radicaldiy

Apera pH electrodes. Good specification 

Reference junction type:( also known as liquid junction)

Some  say ceramic junction is easier to clog in vicious solutions.( Because of  big pore size)

Other material used:

Dacron 

Pellon

Application guide:

Response time:

'Low resistance' glass: So-called ‘low-resistance’(<=50 megaohm) glass electrodes offer quicker response times than standard glass for low temperatures (<10°C) and low conductivity (<100 μS/cm) applications. Eg Apera labsen 803 30 to 60 sec

6501/6502/6503 to stabilise in low ionic strength solutions, eg distilled water, deionised water.

From 越磁：

上海6501/6502/6503型玻璃PH复合电极（耐腐蚀、灵敏高、响应快）

Conductivity of sample:

low conductivity water (< 100 uS/cm) such as pure water

Screen printed electrode

Liquid junction contamination 

Troubleshooting to measure pH

From YSI:

- anatomy 

- troubleshooting calibration tips

- selection guide

Yet another one on diaphragm ( liquid junction)

Related articles on Sciencedirect 

Ionode sodium error on strong alkaline solutions,  

Reduce pH measurement error from Mettler Toledo 

Ion selective electrode wiki

Glass electride composition:

US patent 4297193A 

3372104A

Jp5335288B2 from horiba

Gainexpress e312, 313, 314 is non refillable type. No difference from e-201 series