When emphasizing a parenthetical statement, an m-dash should be used. In LaTeX, an m-dash is typeset using three hyphens: ---. There should not be spaces around the m-dash.

Incorrect: This is a sentence --- but I stop to make a parenthetical statement.
\(\text{This is a sentence — but I stop to make a parenthetical statement.}\)

Correct: This is a sentence---but I stop to make a parenthetical statement.
\(\text{This is a sentence—but I stop to make a parenthetical statement.}\)

Be careful when writing an m-dash at the end of a line of LaTeX code because LaTeX will inject a space at each line break. You can suppress the added space by ending the line with “%” immediately after “---”:

% Incorrect
This is a sentence---
but I stop to make a parenthetical statement.

% Correct
This is a sentence---%
but I stop to make a parenthetical statement.