Question: 

Mice are widely used as a model for the investigation of renal diseases. The quantification of the ion composition in urine and serum is critical for the interpretation of renal function. Column based ion exchange chromatography (IC) is routinely used in industrial applications for the simultaneous quantification of different ions with high sensitivity and specificity. Our aim was the adaptation of the IC technique for the measurement of urine and serum samples from mice.

Methods: 

Cations and anions were measured in parallel with a dual ICS-1600 system connected to an autosampler (Dionex). Isocratic separation at 0.25 mL/min flow rate was done on 2 mm analytical columns (AS9-HC and CS12; Dionex) using 9 mmol/L sodium carbonate eluent for anions and 9 mmol/L sulfuric acid for cations. Inorganic ions were detected by conductivity after background suppression. Creatinine was measured at 210 nm with a UV detector. Urine was diluted with deionized water for injection. After dilution, serum was deproteinized by centrifugation through Amicon Ultra Filters (3K exclusion size, Millipore). At least 1mL of urine and 15 mL of serum were sufficient for the measurement. Standard dilution series from stock solutions were used to calculate sample ion concentration.

Results and discussion: 

The IC technique allowed simultaneous quantification of inorganic anions (F^-, Cl^-, NO3^-, PO4^-3, SO4^-2), cations (Na⁺, NH4⁺, K⁺, Mg⁺², Ca⁺²) as well as creatinine at a wide range of concentration. All peaks were well separated without any significant interferences of the analytes or matrix effects. Serum creatinine was measured separately in less diluted samples, because of the low concentration in mice. Overall, IC requires minimal sample preparation and is useful for rapid automated ion quantification in small urine and serum samples from mice.