Quite often when I see scientific papers I see the following:
“The samples concentrated to 2.3M and then stored in 0.5ml aliquots at -80C.”
While this is not a terrible writing sin it is one that no scientist should make because it’s so easy to avoid.
Quite simply units are simply stand ins for full words and should thus be treated in much the same manner. Between a number and a unit there should always be a space. The exception is the percent symbol which is used directly after a number without a space (15%).
Thus the initial sentence should be written ” The samples concentrated to 2.3 M and then store in 0.5 mL aliquots at -80 °C”
Capitalization is also a point of confusion and the rules about capitalization are more fluid. However, a unit’s capitalization is constant and not interchangeable with the other case—for example: volt (V), or meter (m)—an exception is liter which can be capitalized or not, the reason being that a lowercase ‘l’ can be confused with the number ‘1’ in many fonts. To note, in the United States the uppercase ‘L’ is preferred.
Finally, be careful of using non-standard abbreviations such as sec for second (it is properly just the letter ‘s’) or double quotation marks (“) for inch. These type of colloquial abbreviations may not be understood by all readers.