Studies And Applications On The Detection Method Of Molecular Weight Of Sodium Alginate

In this study, the algin-the middle production of sodium alginate, was used as material and degradated under high temperature, high pressure and oxidation. The grading production was translated into sodium alginate in absolute ethanol with NaOH, and M_ηand M_w were detected by Ubbelohde viscometer and High Performance Liquid Chromatography (HPLC) separately. The two methods were contrasted, and molecular weight was determined using sodium alginate which made in this study as substance. The main results were as follows:1. Although Ubbelohde viscometer method was simple, result of detection was influenced by a good many factors. Meanwhile, M_ηdetected by Ubbelohde viscometer was not definite molecular weight but calculated by empirical formula which led to big mistake.2. In HPLC, dextran were used as substance. Each chromatogram showed one narrow peak and symmetrical shape. The linear regression equation between the log number of molecular weight (logM_w) and the retention time (t) was esTab.lished, which was logM_w=-2.0338t+25.834, R²=0.9926, ranging from 4320 to 521000.3. Six group of sodium alginate S₁～S₆ was graded by ultrafiltration and dialysis, whose molecular were 50～100 k,14～30 k,7～10 k,3.5～5 k,1～3 k and 0.5～1 k. After analysis by HPLC, the result showed that there was only one peak in every chromatogram, with narrow peak width and symmetry peak shape, which indicated a nice separation result, pure sample and narrow molecular weight distribution. A linear regression equation between the log number of molecular weight (logM_w) of S₁～S₆ and the retention time (t) was established, which was logM_w=-0.6772t +15.238, R²=0.9934, ranging from 1000 to 100000. The inter-assay CV﹤5%, which indicated that the grading method had a good reproducibility and high precision. The total sugar of grading productions were determined by phenol-sulfuric acid method, whose results showed that the total sugar in grading process was conserved basically . Purity of sodium alginate was determined by welts thiazole colorimetric method, whose result showed that the purity of grading production was up to 96%, and the highest purity had already achived at 97.59%. From the above, the sodium alginate S₁～S₆ were fit to be substance of molecular weight of sodium alginate.4. HPLC was with high precise, speed, effect, destinguish and delicacy, which was more suitable for the determination and being applied abord.5. Sodium alginate was degradated under high temperature, high pressure and oxidation. After determined by HPLC, the result showed that, under 60℃and 100℃, molecular weight of sodium alginate droped from 330 k to 150 k and 18 k separatly after 180 min. However under 121℃, molecular weight of sodium alginate droped from 330 k to 22 k after 5 min, to about 10 k after 2 h. 121℃was better than 60℃and 100℃, no matter from the angle of degree or speed of degradation. So degree of degradation was in direct radio of degradation tempreture and time. In oxidation degradation, the degradation function of algin pricked up with H₂O₂ increasing, when the protion fall to 0.8%, the degree of degradation was no longer effected by H₂O₂. So the degree of degradation was in inverse radio of propotion of mass of algin and volume of H₂O₂. L9-3-4 orthogonal test was done with the factors of tempreture, time and propotion of mass of algin and volume of H₂O₂, the result showed that M_w would degrade to 100～300 k, under 60℃, after 5 min; to 50～100 k, under 100℃, after 5 min, with protion of 2.4%; to 10～50 k, under 100℃, after 30 min, with protion of 0.8%; to 5～10 k, under 121℃, after 30 min; below 5 k, under 121℃, after 90 min, with protion of 2.4%.