Measurement of serum iohexol by determination of iodine with inductively coupled plasma-atomic emission spectroscopy

We used inductively coupled plasma-atomic emission spectroscopy to measure serum iodine to determine plasma clearance of iohexol, an iodinated radiographic contrast agent. We determined I at 178.276 nm on the phosphorus 178.287 nm channel of the polychromator by utilization of spectrum shifter offset software, while correcting for P with the sequential P 214.914 nm emission line. Determination of I on the polychromator provided excellent precision in the measurement of serum I, even though the interelement correction of P was done with a sequential P line. Total imprecision (CV) (n = 13) was 16% (at 13.7 mg/L I), 8.6% (28.7 mg/L), 3.6% (59.0 mg/L), 2.6% (120.5 mg/L), 1.7% (237.8 mg/L), 1.2% (478.7 mg/L), and 1.8% (597 mg/L). The linear range was 15 to 600 mg/L. Iohexol added to serum (mg/L I) and recoveries (%) were 15 (91.3%), 30 (95.7%), 60 (98.3%), 120 (100.4%), 240 (99.1%), 480 (99.7%), and 600 (99.5%). Studies on dogs and cats administered a single intravenous injection of iohexol indicated that a dose of 300 mg I/kg body weight was sufficient for measurement of glomerular filtration rate by using a single compartment model for plasma clearance with three samples drawn 3 to 7 h after treatment. With this protocol, correlation coefficients were >0.99 on the beta phase of the plasma disappearance curve.