Ion selective electrodes

Twenty-four-hour urine samples were collected at baseline and on day seven of each intervention period. Twenty-four hour urine collection was obtained with the first voided urine upon waking on the day of collection being discarded and participants then collecting all voided urine up to, and including, the first void the following morning. Participants were instructed to keep collected samples inside cooler bags provided and stored in a cool, dark place until completion when a research assistant was contacted to collect the sample. The times at the beginning and the end of urine collection were recorded. The samples were kept frozen at −40 °C until analysis. Urinary concentrations of sodium were determined using ion-selective electrodes (Hitachi, Ltd., Tokyo, Japan). The 24-h urinary excretion of sodium and potassium was calculated by multiplying the concentration of sodium and potassium, respectively, by the 24-h total urine volume.

24-h urine samples were collected at baseline and on day 7 of each intervention period. Any urine collections less than 500 mL or with a creatinine excretion lower than the population mean minus two SDs were discarded to ensure the completeness of the collection [24 (link)]. The samples were kept frozen at −40 °C until analysis. Urinary concentrations of sodium, potassium and creatinine were determined with ion-selective electrodes (Hitachi, Ltd., Tokyo, Japan). The 24-h urinary excretions of sodium, potassium and creatinine were quantified by multiplying the sodium, potassium and creatinine concentrations by the 24-h total urine volume.