Use of capillary electrophoresis with dual-opposite end injection for simultaneous analysis of small ions in saliva samples from wrestlers undergoing a weight training program

Capillary electrophoresis-capacitively coupled contactless conductivity detection (CE-C4D), conducted using an in-house-developed polyvinyl alcohol (PVA)-coated capillary system, was applied for the simultaneous analysis of small anions and cations in saliva samples from wrestlers undergoing a weight training program. Use of the PVA capillary for CE provided good reproducible ion separation with minimization of the electroosmotic flow and suppression of protein adsorption onto the capillary wall. Four cations and eight anions were separated in 12 min, using a background electrolyte of 20 mM MES/20 mM histidine and 18-crown-6 ether (pH 6) at 20 kV. The relative standard deviations (n = 5) of the migration times and peak areas were <1% and <8%, respectively. The detection limit at a signal-to-noise ratio of 3 ranged from 1.6 to 10 μM. Using the optimized CE-C4D system, we investigated the correlations between the concentrations of salivary ions and cortisol, which is commonly used as a stress marker. Analysis of saliva samples from ten wrestlers, who were attempting rapid weight loss before a competition, showed the following trends: (1) all ion concentrations, except for Ca2+, Na+, and Cl−, increased between the first and last days of weight loss; (2) Mg2+ increased to 166% (from 0.50 mM to 1.4 mM) between the first and last days of weight loss, being the highest increase of all the ions; and (3) K+, Mg2+, NO3−, and SCN− levels were strongly correlated (P < 0.05) with cortisol. The CE-C4D rapidly produced useful data on saliva ion contents, with good ion recovery as determined by the standard addition method (89-110%).