AsV does not form complex with APDC; so, prior reduction to AsIII is necessary to detect AsV. As proven previously, 0.01 M Na2S2O3 in 0.1 M HCl solution completely reduced AsV to AsIII in urine in 1–5 min at room temperature (Minakata, Suzuki, & Suzuki, 2009). As a reductant, thiourea was found less effective. However, fruit juices, with presence of MMA and DMA, pose addi-tional challenges vs. water samples. Because Na2S2O3 also reduce MMAV to MMAIII, and MMAIII also forms complex with APDC and