Penniston KL, Nakada SY, Holmes RP, Assimos DG Quantitative Assessment of Citric Acid in Lemon Juice, Lime Juice, and Commercially-Available Fruit Juice Products Journal of Endourology 22/3 2008 http://www.liebertonline.com/doi/pdfplus/10.1089/end.2007.0304PDF pmid=18290732 pages 567 doi 10.1089/end.2007.0304+