Surface-modified microchip electrophoretic separation and analysis of functional components in health care products

doi:10.3724/SP.J.1123.2023.08019

Abstract

Abstract:

Microchip electrophoresis (MCE) is widely applied in food, environment, medicine, and other fields, owing to its high separation efficiency, low consumption of reagents and samples, and ease of integrating multiple operating units. Polymer microchip materials like cycloolefin copolymer (COC) are low-cost and easy to fabricate. However, their practical applications are limited by the non-specific adsorption on channel surface during electrophoresis and the instability of electroosmotic flow. These shortcomings can be solved by COC surface modification. In this study, a static coating and dynamic/static coating combined strategy was used to develop a channel-surface-modified COC microchip. Combined with laser-induced fluorescence (LIF) detection, a MCE-LIF separation and analysis method was developed for detecting functional components in health care products. The separation performance of MCE was improved by the static coating microchannel surface modification method. The static coating was constructed by hydrophobic amino acid adsorption, glutaraldehyde immobilization, and hydrophilic amino acid functionalization on the COC microchannel surface. The separation performance of MCE was improved by microchannel surface modification combined with dynamic/static coating. The static coating was constructed by valine adsorption, carboxyl activation, and ethylenediamine functionalization on the COC microchannel surface. The dynamic coating is automatically formed by introducing a buffer solution containing hydroxypropyl methylcellulose and sodium dodecyl sulfate into the microchannel. The physical and chemical properties of surface-modified microchannels and the factors governing electrophoretic separation were studied. Combined with LIF detection, the MCE-LIF separation and analysis of lysine and γ-aminobutyric acid present in children’s health care products, as well as aspartic acid and taurine in sport drinks, were developed. The recoveries of lysine and γ-aminobutyric acid in children’s health care products were 84.8%-118%, and the relative standard deviations (RSDs) were less than 7.2% (n=3). The recoveries of aspartic acid and taurine in sport drinks were 97.5%-118%, and the RSDs were less than 6.4% (n=3). The analysis results are consistent with the HPLC results, and the method has potential for application in the separation and analysis of anionic amino acids in health care products.

Key words: surface modification, microchips, electrophoresis, cycloolefin copolymer (COC), health care products

CLC Number:

O658

LAU Waichun, CHEN Yali, XIA Ling, XIAO Xiaohua, LI Gongke. Surface-modified microchip electrophoretic separation and analysis of functional components in health care products[J]. Chinese Journal of Chromatography, 2023, 41(10): 937-948.

Figures/Tables 12

Fig. 1 Schematics of (a) the microchip electrophoresis, surface modification processes of (b) negative charge coating and (c) positive charge coating on the surface of COC COC: cycloolefin copolymer; GA: glutaraldehyde; EDC: 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride; NHS: N-hydroxy succinimide; EDA: ethylenediamine.

Fig. 2 (a) Survey XPS spectrum and the deconvolution analysis of (b) C 1s, (c) N 1s, and (d) O 1s XPS spectra of static coating COC surface, (e) contact angle on COC plate and (f) profiles of air-water interface in COC microchannel with negative charge coating unmodified and modified, adsorption to amino acids on COC channel surfaces with static coating (g) unmodified and (h) modified XPS: X-ray photoelectron spectroscopy.

Fig. 3 Effects of hydrophobic amino acid types on (a) the peak shape and (b) theoretical plate height (H) of arginine,effects of hydrophilic amino acid on (c) the peak shape and (d) H of arginine For b and d: n=3.

Fig. 4 Effects of operating voltage (φ) on (a) the fluidic transport rate (u) and (b) the H of Lys and GABA, measured Rs on (c) different separation distances (L) and (d) different φ of Lys and GABA (n=3)

Table 1 Analysis of Lys and GABA in children’s health products (n=3)

Analyte	This method					Original with HPLC method/(mg/kg)	Relative error/%
Analyte	Original/(mg/kg)	Spiked/(mg/kg)	Found/(mg/kg)	Recovery/%	RSD/%	Original with HPLC method/(mg/kg)	Relative error/%
Lys	3.08±0.03	3.00	6.51	107	3.6	3.05±0.02	0.98
		6.00	10.8	118	2.1
		12.0	15.7	104	1.0
GABA	2.53±0.15	3.00	4.69	84.8	7.2	2.32±0.04	9.1
		6.00	8.25	96.7	7.2
		12.0	16.6	114	2.6

Fig. 5 Electropherograms of original and 3.00 mg/kg spiked children’s health products BGE: 0.1 mmol/L sodium tetraborate; φ: 800 V; separation distance: 2.0 cm.Peaks: 1. Lys; 2. GABA.

Fig. 6 (a) Survey XPS spectrum and the deconvolution analysis of (b) C 1s, (c) N 1s and (d) O 1s XPS spectra of static coating COC surface, (e) contact angle on COC plate and (f) profiles of air-water interface in COC microchannel with positive charge coating unmodified and modified, adsorption to aspartate and taurine on COC channel surfaces with static coating (g) unmodified and (h) modified

Fig. 7 Effect of mass fractions of HPMC and SDS on the u of (a) aspartate acid and (b) taurine, and effect of mass fractions of HPMC and SDS on the total peak width σ2 of (c) aspartate acid and (d) taurine (n=3)

Fig. 8 Effect of φ on the u of (a) aspartic acid and (b) taurine, and effect of φ on H of (c) aspartic acid and (d) taurine (n=3) For a and b, 1. dynamic only; 2. dynamic & static; 3. static only. For c and d, 1. dynamic & static; 2. static only; 3. dynamic only.

Fig. 9 (a) Effect of the coating type on the separation resolution of aspartic acid and taurine, measured Rs of aspartic acid and taurine under (b) different separation distances and (c) different φ For b and c: n=3. Peaks: 1. aspartic acid; 2. taurine.

Fig. 10 Electropherograms of original and 8.00 mg/kg spiked sport drink samples BGE: 0.1 mmol/L sodium tetraborate containing 0.005%(mass fraction) HPMC and 0.015% (mass fraction) SDS; φ: 800 V; L: 1.5 cm.Peaks: 1. aspartic acid; 2. taurine.

Table 2 Analysis of aspartic acid and taurine in sport drink (n=3)

Analyte	This method					Original with HPLC method/(mg/kg)	Relative error/%
Analyte	Original/(mg/kg)	Spiked/(mg/kg)	Found/(mg/kg)	Recovery/%	RSD/%	Original with HPLC method/(mg/kg)	Relative error/%
Asp	9.89±0.55	8.00	18.2	102	1.0	9.75±0.15	1.4
		16.0	25.3	97.5	6.4
		32.0	43.9	105	3.6
Tau	15.9±0.8	8.00	24.2	101	4.1	14.6±0. 1	9.4
		16.0	37.4	117	2.6
		32.0	56.6	118	3.0

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