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To measure unbound VPA, blood samples are treated by ultrafiltration, followed by an immunoassay, also referred to as ELISA. By performing the ultrafiltration, the protein-bound form of VPA is separated from its unbound form. After that, the level of the unbound fraction can be measured by an immunoassay, e.g. an ELISA kit. Alternatively, LC-MS can be used to measure VPA.<ref name=”[40]”> ao, S., Miao, H., Tao, X., Jiang, B., Xiao, Y., Cai, F., … Chen, W. (2011, July 1). LC–MS/MS method for simultaneous determination of valproic acid and major metabolites in human plasma, Journal of Chromatography B
Volume 879, Retrieved November 28, 2019, at [https://www.sciencedirect.com/science/article/pii/S1570023211003278?via=ihub“https://www.sciencedirect.com/science/article/pii/S1570023211003278?via=ihub”].</ref>
In contrast to an HPLC assay, steps such as extraction, solvent or derivation must be executed prior to a HPLC assay, which takes significant more time<ref name=”[29]”> Free Valproic Acid Assay (2014, April). Retrieved from November 3, 2019, at [https://www.cadth.ca/sites/default/files/pdf/lab-tests/06_Free_Valproic_Acid_Assay_e.pdf/“https://www.cadth.ca/sites/default/files/pdf/lab-tests/06_Free_Valproic_Acid_Assay_e.pdf”].</ref>
Several innovations are being investigated for VPA testing. For example, 2D-LC system (two-dimensional chromatography) was studied, allowing large volume injection, reducing interfering components, and reducing the analysis time and preventing most interference components by selecting useful sections in the “heart-cut” column(1D) from entering the analysis column (2D).<ref name=”[11]”> Liu, W., Shang, X., Yao, S., & Wang, F. (2019, August 20). A novel and nonderivatization method for the determination of valproic acid in human serum by two‐dimensional liquid chromatography. Retrieved October 17, 2019, at [https://doi.org/10.1002/bmc.4695.“https://doi.org/10.1002/bmc.4695.”].</ref>
. Another example is dried blood spot (DBS) followed by gas chromatography mass spectrometry (GC–MS), which does not require solvent extraction or elution. The limit of quantitation was 200 ng/mL. <ref name=”[12]”> Guo, M., Shao, L., Chen, X., Li, H., Wang, L., Pan, Y., & Tang, D. (2019, September 13). Assay of dried blood spot from finger prick for sodium valproate via ink auxiliary headspace gas chromatography mass spectrometry, Journal of Chromatography A Vol. 1601 p. 335-339. Retrieved October 24, 2019, at [ https://doi.org/10.1016/j.chroma.2019.05.039“ https://doi.org/10.1016/j.chroma.2019.05.039”].</ref>
== References ==
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