Docs suggestion is a good one, you can also check if TLC2262 are available to you. I have actually used all three of these(including the TL0XX series) with good results. Basically you are looking for a rail to rail amp with low offset voltage and extremely low input bias current, after that most modern amps will have better performance then the old TL0XX series.
Yes I live in Malaysia. Thanks so much for the recommendation.
Thanks everyone for the suggestions.
But I was wondering how did you guys come to the conclusion of what op amp to use cause it all just looks the same to me?
Is there a difference between JFET and FET?
The type of sensor you are interfacing basically dictates what type of op-amp you are going to need.
pH probes are very high impedance sources that are slow to respond, when you are dealing with 500Mohm input impedance even a tiny current such as a pico amp can change your readings by a very significant amount. This is why we are looking at amps with ultra low input bias current, offset voltage can matter as well, but this can be calibrated out as long as its consistent through the measurement range and so this is also taken into account for which amp we picked out. Since the signals are relatively slow (and mainly DC) we don't care too much about slew rates and bandwidths, and is also why older op-amp designs are still quite effective today especially when cost is factored in.
When they talk about FET, JFET, LINMOS, CMOS they are referring to the physical topology and construction of the transistors which make up the op-amp. While they are all Field Effect Transistors, the methods for construction and materials used are very different and therefor yield the characteristics that we see in all the varying amps(or all ICs) out there. Each company has their own proprietary stuff too which shows up as the strange LINMOS type names, this stuff can get pretty exotic when you start getting down to this level.
If I were you, I would try to understand your circuit and why TL082 was used. Most of the times, those chips are used not for their jfet input stage but for their low prices. In those cases, pretty much any opamp will do.