BibTeX, biblatex and biber ⇒ In text References

[Dochollywood1]

I am a fairly new user to LaTeX. I am currently writing my thesis and I am using the achemso style for my bibliography and a thesis class from my university.
I have encountered a strange problem. My intext references are not separated by commas. A friend of mine who is using the same bibliography style and class does get intext references separated by commas.
I will upload three pics to better display the problem visually.
You can clearly see that in the picture at the bottom the intext references are not separated by commas where in my friends thesis her intext references are either separated by commas or hyphens (for more than two consecutive references). What is odd is that we are both using the same class file and bibliography style. The only difference is I am using a mac with TexShop and she is using a windows computer.
I would like Latex to add commas or hyphens accordingly.
Thanks in advance.
AD

[Dochollywood1]

I solved this myself. I was using the wrong syntax. For example, to cite two references I would write:
\cite{ref1} \cite{ref2}
while I found the syntax that works to be:
\cite{ref1, ref2}