# Subscript destroys format

this is how things looks like without subscript:

in the other hand, when I try to put a subscript for MgCl_2, then the format is destroyed. I do that like this:

\item   Rabbit Erythrocytes (Rockland)
\item   HEPES–EGTA buffer (20 mM HEPES, 7 mM MgCl_{2},  10 mM  EGTA, 144 mM NaCl, pH 7.4)
\item   Normal serum (NHS)


The error I get is:

Command \item invalid in math mode. \item

I've seen documents that use subscript in an enumeration list. I don't know why this happens. Any help?

• You need MgCl$_{2}$, but even that is bad. Take a look at the mhchem package. You want \ce{MgCl2} and \SI{20}{\milli\mol}, most likely etc. – user31729 Jan 27 at 16:25
• Thanks a lot Christian! I'll take a look! :) – Andrés GD Jan 27 at 16:32
• Christian's answer is the way to go. The reason this happens is that _ can only occur in math mode. TeX sees the _ outside of math mode, raises an error, and then tries to keep going. As it tries to keep going, it assumes you want to be in math mode, which is why subsequent items are in the math font, and why it thinks you have \item in math mode. – Teepeemm Jan 27 at 19:14

I suggest the usage of the mhchem package that is designed for typesetting formulas of chemical substances, as well as siunitx for the units:

\documentclass{article}

\usepackage{mhchem}
\usepackage{siunitx}
\begin{document}
\begin{enumerate}
\item \SI{20}{\milli\mol} \ce{MgCl2} and \ce{CH4} as well as \ce{H2SO4}
\end{enumerate}
\end{document}


Just write:

$MgCl_{2}$


With this, everything will work.

• chemical formula are not normally written in math italic. – David Carlisle Jan 27 at 16:43
• Math mode for chemical elements is weird,that's why I suggested MgCl$_{2}$ above, but even that is not nice. – user31729 Jan 27 at 17:19