I working in research lab. dealing in method develoment and validations of HPLC methods. Please suggest if it is possible to use nitrogen as sparging gas instead of helium for degassing the mobile phase.

No, it is not possible.

Nitrogen has a much higher solubility in liquid than helium. Using nitrogen as a sparge gas would totally defeat the purpose of degassing in the first place.

We do not even use N2 streams to concentrate samples prior to injection, as we obtained immense gas peaks in many cases. We now usually use vacuum (rotary evaporator) to concentrate samples.

He sparging is used to remove dissolved air. Air is about 70% N2. Hence, one would not expect N2 sparging to be effective.

If you can't get or afford He, you can try the ancient vacuum and stir method (use safety precautions). If that doesn't work well enough you can invest in one of the continuous vacuum degassing systems Agilent and Waters supply with their new systems (expensive, but will pay for itself eventually). It only requires electricity to work.

Some systems, my HP 1050 for example, will simply not run correctly if the solvents are not degassed properly.

Vacuum and ultrasound bath (simultaneously) also
works.

I think it's funny that the recent HP machines 1050 and 1100 seem to have pump problems when operated without degassing! We use the older 1090 "workhorse" (beside 1100), seldom degass (He sparging) and never have pump problems due to that. The 1090 low pressure mixing system is in my opinion the pump with the least trouble. Even if run dry, the pump primes itself without support. On the other hand, our 1100 had to be primed with maximum flow und opened flush valve every time they are powered up.

I had terrible baseline problems using MeCN mobile phases in my 1050 while my sparge unit was broken. Vacuum filtration was useless.