I am performing a phenol-chloroform extraction in which precipitation is enhanced by linear polyacrylamide. The SDS for linear polyacrylamide mentions that it should be used such that its final concentration is ~20 ug/mL.

The protocol I am following mentions 20 ul/mL. Page 21, 3rd line of the second paragraph under precipitation.

Am I misunderstanding one or both of these instructions? 20 ul/mL seems like a lot, especially given that it is sold in 5 mg/mL solution (i.e. ~5 ul/mL).

Are they referring to different concentrations, i.e. one is 20 ug LPA/mL extraction volume, and the other is 20 ul 5 mg/mL LPA solution/mL extraction?

Is there a typo in this paper?

Thank you.

  • 1
    $\begingroup$ Questions here should be standalone, so, ideally you shouldn't have to follow a link to understand what is going on. You should add the quote to your question - that is one massive paper and the link takes you to the webpage, which doesn't have page numbers etc, so you then have to download. $\endgroup$
    – bob1
    Jun 29, 2023 at 21:34

1 Answer 1


The simplest answer here is that they have made a typographical mistake in the paper and it should be 20 ug/ml.

The other possibility is that they have a stock concentration of this reagent, which they add at 20 ul per ml of precipitation volume - in which case this stock will be 1 ug/ul (1 mg/ml), assuming they use your standard concentration. When writing the paper, they forgot to convert this into standard concentration, probably (in my experience) through familiarity with it noted this way and forgetting to change it.

I note that polyacrylamide is mentioned exactly twice in the paper you linked - once in the text and once in the references, but curiously enough, not in the methods section, only in results. For completeness; the referenced paper1 adds 4 ul (20 ug) to a reaction.


  1. Andrea K. Bartram, Calvin Poon, and Josh D. Neufeld. Nucleic acid contamination of glycogen used in nucleic acid precipitation and assessment of linear polyacrylamide as an alternative co-precipitant. BioTechniques 2009 47:6, 1019-1022
  • $\begingroup$ Confirmed by the author it was a typo. ug was meant not mL. $\endgroup$
    – donkey
    Jul 6, 2023 at 19:11

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