Dear [Manager Name],
It has been a pleasure working for this esteemed company for the last [duration since you joined]. I have always labelled myself as a professional and I am always keen to stay on top of my duties and tasks. I am perfectly comfortable facing new challenges and ready to step in to handle new responsibilities at any moment.
As you are aware, my list of responsibilities has been recently augmented to include: [list here new responsibilities]. I am now handling tasks that are not part of my job description but I am perfectly fine with it. I view this increase in responsibilities as an act of trust in my abilities and believe in my potential. This decision only increases my self confidence and is a driving force to my never ending quest for delivering best results.
Given the circumstances presented above, I think it would only be fair if my salary is adjusted to inline with the new level of responsibilities laid on my shoulders.
Thank you.
Sincerely,
[Your name]
[Date]