Apinya Obma^a, Keerada Nookaew^b, Ruamsiri Songsaeng^a,1, Apichai Phonchai^a,2, Peter C. Hauser^c, Prapin Wilairat^d, Rattikan Chantiwas^a,b,*,

^aDepartment of Chemistry and Center of Excellence for Innovation in Chemistry and Flow Innovation-Research for Science and Technology Laboratories (FIRST Labs), Faculty of Science, Mahidol University, Rama VI Rd., Bangkok 10400, Thailand
^bForensic Science Unit, Faculty of Science, Mahidol University, Bangkok, Thailand
^cThe University of Basel, Department of Chemistry, Klingelbergstrasse 80, CH-4056 Basel, Switzerland ^dAnalytical Sciences and National Doping Test Institute, Mahidol University, Rama VI Rd., Bangkok 10400, Thailand

* Corresponding author.E-mail addresses: rattikan.cha@mahidol.ac.th, rattikan.cha@mahidol.edu (R. Chantiwas). ¹ Current address: Analytical Sciences and National Doping Test Institute, Mahidol University, Rama VI Rd., Bangkok 10400, Thailand. ² Current address: Division of Health and Applied Sciences, Faculty of Science, and Forensic Science Innovation and Service Center, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand. Peer review under responsibility of King Saud University.

Abstract:

This study presents the analysis of lactate in sweat using capillary electrophoresis with contactless conductivity detection. Two cyclodextrin (CD) compounds, carboxymethyl-b-cyclodextrin sodium salt (CMb-CD) and heptakis (2,3,6-tri-O-benzoyl)-b-cyclodextrin (TRIME-b-CD), were evaluated as buffer modif iers for the separation of chloride, nitrate, sulfate, oxalate, maleate, acetate, lactate, and phosphate anions. The concentrations of these modifiers were tested at 0.05, 0.1, and 0.5 mM for eight anions separation. The buffer was 40.0 mM MES/L-His (pH 6.0) with 0.05 mM CTAB, resulting in anodic separation. Due to separation efficiency in resolving lactate and phosphate peaks, TRIME-b-CD at a concentration of 0.1 mM was selected as the suitable buffer additive for sweat lactate analysis. The calibration of the developed method, using maleate as an internal standard, resulted in the linear ranges of 0.1–5.0 mM, r2 of 0.9999, and an instrumental LOD of 0.042 mM. The intra-day and inter-day precisions of the relative migration time (RMT) were 0.3–0.4% and 3–4% RSD, respectively. Lactate levels in sweat samples from the same group of volunteers were measured after two distinct activities: exercise (after running) and non-exercise (after sauna). For non-exercise activities, lactate concentrations ranged from 15 ± 1 mM to 36 ± 2 mM. While, after exercise, the concentrations were between 26 ± 1 mM and 136 ± 1 mM. Further evaluation of the stability of sweat storage for monitoring lactate contents, it was found that the changes in lactate levels were insignificant when stored for up to 24 weeks at 4 ℃. This was conf irmed by paired t-tests (t-stat ragnes from-0.59 to 2.49; t-critical = 2.57, P = 0.05). The measured lactate concentrations from volunteers were significantly higher, approximately 2–6 times, in exercise activities compared to non-exercise activities. This substantial difference in lactate secretion indicates a clear distinction in the factors that stimulate sweat lactate production. To evaluate the intensity of exercise based on lactate levels in sweat, a proposed cut-off level of 36.0 mM, with a decision limit of 40.0 mM, can be proposed.

KEYWORDS

Lactate, Sweat, Exercise, Cyclodextrin, Capillary electrophoresis and C⁴D

Reference:

Obma, A.; Nookaew, K.; Songsaeng, R.; Phonchai, A.; Hauser, P. C.; Wilairat, P.; Chantiwas, R. Measurement of sweat lactate levels in exercise and non-exercise activities using capillary electrophoresis system with contactless conductivity detection and cyclodextrin-modified buffer. Arabian Journal of Chemistry 2023, 16 (11), 105255. doi: 10.1016/j.arabjc.2023.105255