Separation and characterization of millet starch based on asymmetrical flow field-flow fractionation

doi:10.3724/SP.J.1123.2019.05014

Abstract

Abstract:

A method based on asymmetrical flow field-flow fractionation (AF4) coupled with a multi-angle light scattering detector and a differential refractive detector was developed for the separation and characterization of millet starch. In this study, the effects of sample loading, cross-flow rate, half-life, and ionic strength and pH value of the carrier liquid on the AF4 analysis of millet starch were investigated. In addition, the molecular structure of millet starch was determined under the optimum conditions. The optimized operation conditions for the AF4 analysis of millet starch were as follows:injection mass concentration, 0.50 g/L; injection volume, 50 μL; cross-flow rate, 1.2 mL/min; half-life, 3 min; and the carrier liquid, demonized water containing 10 mmol/L pH 7.00 NaNO₃ (add 3 mmol/L NaN₃). The method developed in this study showed good reproducibility. The relative standard deviations for the radius of gyration (R_g) and molar mass (M_w) were 3.4% and 7.0%, respectively.

Key words: asymmetrical flow field-flow fractionation (AF4), millet starch, separation

ZHANG Jing, GUO Panpan, LI Huili, SHEN Shigang, DOU Haiyang. Separation and characterization of millet starch based on asymmetrical flow field-flow fractionation[J]. Chinese Journal of Chromatography, 2020, 38(2): 169-176.

Figures/Tables 11

Table 1 Elution procedure

Entry	Mode	Duration/min	V_{c, initial}/(mL/min)	V_{c, final}/(mL/min)
V_{c, initial}: initial cross flow rate; V_{c, final}: final cross flow rate.
1	elution	2	0	1.20
2	focus	2	1.20	1.20
3	focus+injection	1.4	1.20	1.20
4	focus	2.7	1.20	1.20
5	elution	1.4	1.20	0.87
6	elution	1.4	0.87	0.63
7	elution	1.4	0.63	0.46
8	elution	1.4	0.46	0.34
9	elution	1.4	0.34	0.24
10	elution	1.4	0.24	0.18
11	elution	1.4	0.18	0.13
12	elution	1.4	0.13	0.09
13	elution	1.4	0.09	0.07
14	elution	1.4	0.07	0.05
15	elution	10	0.05	0.01
16	elution	5.0	0.01	0

Fig. 1 Principle of AF4 (asymmetrical flow field-flow fractionation)

Fig. 2 AF4-UV-MALS-dRI (AF4 coupled with ultraviolet-visible, multi-angle light scattering, and differential refractive index detectors) fractograms and Mw (molar mass) distributions of bovine serum albumin

Fig. 3 AF4-MALS-dRI fractograms, Rg (radius of gyration) and Mw (relative molecular mass) distributions of millet starch obtained at different dissolution temperatures a. AF4-dRI and Rg of millet starch; b. AF4-MALS and Mw of millet starch; c. AF4-dRI and Rg of millet starch filtered through a 0.45 μm filter; d. AF4-MALS and Mw of millet starch filtered with 0.45 μm. MALS 90°: MALS signal was observed at the scattering angle of 90°.

Fig. 4 AF4-MALS-dRI fractograms, Rg, and Mw distributions of millet starch obtained at different sample concentrations

Fig. 5 AF4-MALS-dRI fractograms, Rg, and Mw distributions of millet starch obtained with different cross-flow rates

Fig. 6 AF4-MALS-dRI fractograms, Rg, and Mw distributions of millet starch obtained with different half-lives (t1/2)

Fig. 7 AF4-MALS-dRI fractograms, Rg, and Mw distributions of millet starch obtained with different ionic strengths

Fig. 8 AF4-MALS-dRI fractograms, Rg, and Mw distributions of millet starch obtained with different pH values

Fig. 9 Repeatabilities of AF4-MALS-dRI fractograms, Rg, and Mw distributions for analysis of millet starch

Fig. 10 Apparent density and Rg/Rh of millet starch

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