Lactulose 13c12

Calibrator solutions prepared via serial dilutions of 10 mg/mL mannitol and lactulose (Sigma-Aldrich) diluted in HPLC-grade water. Internal standards contained 0.01 mg/mL mannitol ¹³C6 and lactulose ¹³C12 (Sigma-Aldrich). Pooled blank urine (urine collected before the administration of lactulose and mannitol) was spiked with independently prepared solutions containing serial dilutions of 10 mg/mL for assay validation and for quality control on all runs. Linear responses in the calibration equation were observed with an r > 0.999 in the range of 10 to 4000 μg/mL for both lactulose and mannitol with 95% confidence intervals of 2%. A second transition was monitored for each analyte to confirm identity and required to be within 20% of the relative peak area of the first transition used for quantification.

Calibrator solutions were prepared from serial dilutions of 10 mg/mL mannitol and 40 mg/mL lactulose (Sigma-Aldrich, St Louis, MO) diluted in HPLC-grade water. Internal standards contained 750 μg/mL mannitol ¹³C6 and lactulose ¹³C12 (Sigma-Aldrich).
The previously collected pooled blank urine samples (collected in the absence of administration of lactulose and mannitol) was spiked with independently prepared solutions containing serial dilutions of 10 mg/mL for assay validation and for quality control on all runs. Linear responses in the calibration equation were observed with an r > 0.999 in the range of mannitol 0.5 to 2000 μg/mL, −0.125 to 500 μg/mL for lactulose with precisions of 5% to 10% CV.