Effect of acoustic frequency and power density on the aqueous ultrasonic-assisted extraction of grape pomace (Vitis vinifera L.) – A response surface approach

Aqueous ultrasound-assisted extraction (UAE) of grape pomace was investigated by Response Surface Methodology (RSM) to evaluate the effect of acoustic frequency (40, 80, 120 kHz), ultrasonic power density (50, 100, 150 W/L) and extraction time (5, 15, 25 min) on total phenolics, total flavonols and antioxidant capacity. All the process variables showed a significant effect on the aqueous UAE of grape pomace (p < 0.05). The Box–Behnken Design (BBD) generated satisfactory mathematical models which accurately explain the behavior of the system; allowing to predict both the extraction yield of phenolic and flavonol compounds, and also the antioxidant capacity of the grape pomace extracts. The optimal UAE conditions for all response factors were a frequency of 40 kHz, a power density of 150 W/L and 25 min of extraction time. Under these conditions, the aqueous UAE would achieve a maximum of 32.31 mg GA/100 g fw for total phenolics and 2.04 mg quercetin/100 g fw for total flavonols. Regarding the antioxidant capacity, the maximum predicted values were 53.47 and 43.66 mg Trolox/100 g fw for CUPRAC and FRAP assays, respectively. When comparing with organic UAE, in the present research, from 12% to 38% of total phenolic bibliographic values were obtained, but using only water as the extraction solvent, and applying lower temperatures and shorter extraction times. To the best of the authors’ knowledge, no studies specifically addressing the optimization of both acoustic frequency and power density during aqueous-UAE of plant materials have been previously published.     

Effect of quenching time and quenching agent dose on total organic halogen measurement

Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts (DBPs) in a water sample. TOX measurement involves concentration of halogenated organic DBPs by adsorption onto activated carbon. Prior to activated carbon adsorption, quenching the chlorine residual in a water sample is an indispensable step to eliminate the positive interference resulting from continued chlorination with organic compounds adsorbed on the activated carbon surface or with the activated carbon surface itself. Arsenite is generally applied as the quenching agent. In this study, the arsenite quenching agent dose that was 100% of the stoichiometric amount of the chlorine residual in a water sample was demonstrated to be most appropriate. In practice, to ensure complete reduction of chlorine residual, slight overdose of arsenite is often recommended, but this was found to cause negative interferences in the TOX measurement due to two reasons. First, the competitive adsorption existed between halogenated organic DBPs and the excessive arsenite on the activated carbon. This competitive adsorption effect was pronounced within a quenching time of 15?min. After 15?min of quenching, a large fraction of arsenite might have reacted with some easily-reduced halogenated DBPs to become arsenate, which is partially ionized at pH 2 and less likely adsorbed on the activated carbon. In this case, more halogenated organic DBPs could be adsorbed on the activated carbon, resulting in the measured TOX concentrations to be much closer to the actual one contained in the sample. Second, excessive arsenite might lead to reduction or decomposition of halogenated organic DBPs with a prolonged quenching time (>60?min). Thus, to avoid the negative interferences, the appropriate quenching time should be 15–60?min.     

离子色谱法测定水中常见阴离子和消毒副产物

建立了离子色谱法同时测定水中7种常见阴离子、3种无机消毒副产物和5种卤代乙酸的分析方法。采用IonPac AS19阴离子分离柱,以KOH为淋洗液,大体积进样,采用浓度梯度洗脱,可在33min内同时测定15种成分。7种常见阴离子的测定下限为2.3~10.0μg/L,3种无机消毒副产物的测定下限为3.3~10.0μg/L,5种卤代乙酸的测定下限为5.3~34.3μg/L。对杭州市4个自来水厂的源水及出水进行测定,发现其中4个水厂出水均有二溴乙酸检出,3个水厂有三溴乙酸检出,两个水厂有氯酸盐检出,一个水厂有三氯乙酸检出。     

离子色谱法测定水中7种阴离子

建立了离子色谱法同时测定水中7种阴离子的方法。样品过滤后,采用IonPac AS-19阴离子色谱柱分离,KOH溶液梯度淋洗,电导检测器检测水中氟离子、亚氯酸盐、溴酸盐、氯离子、硝酸盐、氯酸盐、硫酸盐的含量。7种阴离子线性关系良好r0.998 8,加标回收率为91.6%~108%,相对标准偏差(RSD)为0.13%~8.8%。样品前处理简便,分离度和加标回收率均较高,适用于水中7种阴离子的测定。