J. Ning, J. Zhao, L. Meng, and L. Bi, “Vortex-Assisted Surfactant-Enhanced Emulsification Microextraction Combined with High Performance Liquid Chromatography-Fluorescence Detector for Determination of Nitrite in Urine”, ajc, vol. 26, no. 21, pp. 7129–7132, Sep. 2014.