Determination of iohexol clearance by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS).

We have developed a simple, rapid, and accurate HPLC-MS/MS method for the determination of iohexol in serum. The column used was a Zorbax Eclipse XDB-C8 (100 mm x 2.1 mm i.d., 3.5 microm). Mobile phases consisted of water containing 2mM ammonium acetate and 0.1% formic acid (A) and methanol containing 2 mM ammonium acetate and 0.1% formic acid (B). After simple protein precipitation with ZnSO4, serum samples were mixed with I.S. (bromperidol) and centrifuged for 3 min. The obtained extraction recovery at three levels was 94.6-107.4%. Quantitative analysis was performed in the multiple reaction-monitoring mode (m/z 822.0-->804.0 for iohexol, 420.1-->122.7 for I.S.) with the total running time of 3 min for each sample. The assay was linear between 0.5 and 1500 microg/mL (r2 > 0.997). The intra- and inter-assay coefficient of variations were 2.4-6.2% and 5.5-6.5%, respectively. Our method provided sufficient analytical range and specificity for the 210 clinical samples analyzed.