I typed your question into Google and got the following hit near the top of the list: Zhang et al. 2011. Analysis of deoxyribonucleotide pools in human cancer cell lines using a liquid chromatography coupled with tandem mass spectrometry technique. Biochem Pharmacol. 2011 August 15; 82(4): 411–417. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3138996/