Hallo Every Body.
I use MQ-4 for measurement CH4 in gas emission. The range of detection from a sensor 400 - 10000 ppm. We are measurement CH4 using gas choreograph in the lab. the result between 1 - 20 ppm. if the datasheet of sensor MQ-4 can detect range of methane 400 - 10000 ppm. My question is possible uisng MQ-4 detect CH4 in the range 1-20 ppm.
Probably not. The 1-20ppm is very little and the CH4 is very sensitive but also very inaccurate and sensitive for other gasses. It costs 1 dollar on Ebay, so don't expect to much from it.
do you have references for methane sensor. can detect 1-100 ppm.
Then you need something like this : http://www.gasleaksensors.com/products/sensit_pmd.html
I don't know what it costs, probably more than 1000 dollars.
The MQ gas sensor of 1 dollars are more or less for hobby electronics. For accurate results or to measure such low values as 1-100ppm, industrial/lab equipment is needed and those are very expensive.
thanks koepel.
what do you thing about tgs6810. that is methane sensor. if our buy industry very expensive
The Figaro TGS6810 is better than the MQ sensors. I have seen the Figaro website, but I missed that one. Luckily you found it 
The datasheet shows how to use it as a wheatstone bridge. I think you need an instrumentation amplifier for that. The INA125 is often used with an Arduino, or a digital amplifier.
To measure 1...100ppm, it will probably not be reliable because it varies some and there is some noise.
Methane : 13 to 23mV in 5000ppm.
That is 2.6 to 4.6 uV for 1ppm.
Suppose a 5V Arduino Uno board is used with 10-bit ADC and with analog INA125 amplifier. The resolution of the Uno is 5mV per bit, so the INA125 must amplify 2000 times. Hmmm, that is a lot. It will make it unreliable.
However, if you want to try something, then try the TGS6810.
According to the datasheet it needs 3.0V and 175mA. I suggest to use also 3.0V and not for example 3.3V.
Thank Koepel for your recommend. I will more search in internet. Thank you very much.