Optimising ADC for ultra low power application

[hazin]

We are  using STM32L053R8.

What is the best method (Clock and Low power modes) to achieve lowest power consumption while taking ADC reading every one second? 

Also whether to use RTC or LPTIM or combination of both to wakeup the device from the Low Power mode and take the ADC readings?

What should be the ADC configuration and Power saving methods we can implement if we just want to take a single ADC reading and compare it with a threshold value if the ADC reading is lesser then the threshold value, it should go back to sleep as fast as possible?