农药pH值测定方法的研究

通过对原国家标准 GB1601-79(83)农药氢离子浓度的测定方法,以及 CIPACMT75 pH 值的测定方法的研究比较,建立了一种适用于农药原药、粉剂、可湿性粉剂、乳油等的水分散液(或水溶液)pH 值测定的新方法,即新的国家标准方法。新法等效采用了 CIPAC MT75 pH 值的测定方法,使农药 pH 值的测定更加准确合理,并可在国际范围内通用。     

不同炮制方法对山楂pH值及有机酸含量变化的研究

目的:本研究以蔷薇科山楂的干燥成熟果实为材料,探讨不同炮制方法下山楂有机酸含量及pH值的变化,以期为山楂药理作用的研究提供一定的理论依据。方法:采用2015年《药典》中山楂总有机酸含量测定方法,通过对不同烘制方法的山楂有机酸含量及pH值的测定,来探讨不同烘制方法对山楂有机酸含量及pH值值的影响.结论:生山楂,炒山楂,焦山楂,山楂炭中有机酸含量逐渐降低,pH值值逐渐升高。     

聚丁二酸丁二醇酯(PBS)在不同pH条件下的降解

对聚丁二酸丁二醇酯(PBS)薄膜在不同pH值水溶液中的降解进行对比研究.用失重率及薄膜表面形貌观察等时降解结果进行表征,结果表明:PBS薄膜在不同pH值水溶液中的降解速度为:碱性溶液>酸性溶液>中性溶液.降解过程中不同降解溶液的pH值均有一定程度的下降.     

酚醛增粘树脂酸值测定方法的研究

对比常见的13种酸值测定方法,研究溶解溶剂、滴定液溶剂、指示剂、常规化学指示剂滴定和电位滴定对酚醛增粘树脂酸值测定结果的影响。结果表明：因树脂酸值测试不同于常规的酸碱中和反应,无明显反应终点,无论是指示剂滴定或电位滴定,本质上都是设置了某个pH值作为滴定终点,因测定方法不同,滴定终点的pH值不同,树脂酸值测定结果并不可比,但不同方法下树脂酸值的变化趋势具有一致性。     

乙醇对溶液酸碱性的影响研究

使用电位法,分别用KOH溶液和HCl溶液对水、30%乙醇溶液以及60%乙醇溶液进行滴定,测定溶液的pH值。通过研究发现,乙醇会对溶液的pH值产生一定的影响,乙醇浓度越大,影响越大,当溶液中的酸度达到一定值时,乙醇产生的影响会稳定在一定的数值,产生的影响基本上是稳定的,在绝对酸度相同情况下,随着溶液中酸或碱的量的增加,不同浓度的乙醇溶液与其偏离对应的水溶液pH值的ΔpH有减小的趋势。     

水煤浆pH值的测定方法研究

对水煤浆pH计的测定装置及pH测试中的有关规定要求、测试所需的标准溶液和确定pH值测定重复性限等方面进行了一些初步研究，为制定科学合理的水煤浆pH值测定方法提供依据。     

溶剂对顺丁烯二酸酐含量测定的影响

顺丁烯二酸酐是一种重要的有机原料,对其含量的测定有很大意义.目前,文献上提到的顺丁烯二酸酐含量测定方法的误差较大.因此,研究了各种条件下测定顺丁烯二酸酐的含量.实验结果表明:用纯水、40 % DMF水溶液或40 %丙酮水溶液做溶剂时,都能够较准确测定顺丁烯二酸酐的含量,在有机体系中用40 %丙酮水溶液较纯水或40 %DMF水溶液好.     

Mg-Al水滑石的溶解动力学及热力学

研究了Mg-Al水滑石在水溶液中的溶解性能及其机理,考察了温度和pH对其溶解性能的影响, 探讨了溶解过程中动力学和热力学规律。动力学研究表明,Mg-Al水滑石在水溶液中的溶解符合外扩散及表面化学反应控制模型,且不同pH区间其控制步骤不同。pH 1.0～3.8,水滑石完全溶解,其溶解速率随pH的提高而减小,受解吸控制。而pH 4.2～9.4,水滑石部分溶解,溶解速率与pH值无关,受表面交换反应控制。另一方面,对水滑石溶解反应的Gibbs自由能变进行定量估算,其值为29.516 kJ·mol^-1。经实验验证,理论估算可很好地与实验结果吻合。     

Mg-Al水滑石的溶解动力学及热力学

研究了Mg-Al水滑石在水溶液中的溶解性能及其机理,考察了温度和pH对其溶解性能的影响,探讨了溶解过程中动力学和热力学规律。动力学研究表明,Mg-Al水滑石在水溶液中的溶解符合外扩散及表面化学反应控制模型,且不同pH区间其控制步骤不同。pH=1.0~3.8,水滑石完全溶解,其溶解速率随pH的提高而减小,受解吸控制。而pH=4.2~9.4,水滑石部分溶解,溶解速率与pH值无关,受表面交换反应控制。另一方面,对水滑石溶解反应的Gibbs自由能变进行定量估算,其值为29.516 kJ·mol-1。经实验验证,理论估算可很好地与实验结果吻合。     

过硫酸铵容量法分析电解锰渣中锰含量的条件研究

对电解锰渣中准确测定锰的实验条件进行研究,测定方法是将电解锰渣用硫磷混酸分解,硝酸银为催化剂,用过硫酸铵将锰(Ⅱ)氧化为锰(Ⅶ),然后用硫酸亚铁铵进行滴定。研究了待测溶液的pH值、过硫酸铵的用量及煮沸时间对测定结果的影响。结果表明,电解锰渣的用量在0.2g,加过硫酸铵前的pH值为3,过硫酸铵的用量1.5～3.5g,煮沸时间为4min,测定准确度最高,加标回收率在99.6%～100.4%之间,在该条件下不同来源电解锰渣中锰含量测定结果与原子吸收分光光度计测定结果一致。     

紫外分光光度法测定核酸含量的影响因素分析

选择寡聚核苷酸、鲑鱼精单链DNA、小牛胸腺双链DNA标准物质为样本,系统研究了溶液pH、苯酚、丙酮、蛋白质、多糖等对紫外分光光度法测量结果的影响情况,另外考察了核糖核酸(RNA)和脱氧核糖核酸(DNA)的相互影响情况。研究发现基于分光光度法的核酸定量分析,易受溶液pH、苯酚、丙酮、蛋白质、多糖等的影响,另外,DNA和RNA之间也会相互干扰。因此,紫外分光光度法测定核酸含量时,特别是该方法用于核酸标准物质特性量值确定时,需要样品高度纯化,pH确定的条件下才能保证测量结果的准确可靠。     

聚醚大单体溶液pH对减水剂性能的影响

以甲基烯丙醇聚氧乙烯醚和丙烯酸为主要原料,对聚醚单体溶液(底料)pH进行调控合成聚羧酸减水剂。通过测定聚醚转化率及减水剂相对分子质量及其分布以及评价减水剂的应用性能,确定了聚醚大单体溶液pH变化范围以及不同酸种类对减水剂性能的影响。结果显示,通过控制底料pH提高了聚醚大单体转化率,并且当底料pH控制为3时其转化率最高,由未调控pH的87.41%提升至pH为3时的95.43%,此时合成减水剂的分子量分布指数较小,由未调控pH时的3.183降至2.884;采用硫酸控制底料pH时,溶液中存在的硫酸盐为硫酸钠,其快速溶解减少了聚羧酸减水剂被水泥水化产物的包裹和消耗,更有利于提高聚羧酸减水剂分散性能。结果表明,通过控制聚醚大单体溶液pH的方式,在不改变减水剂合成工艺操作的前提下也可提升聚羧酸系减水剂的整体性能。     

凹凸棒基高分子固沙材料的表征及性能研究

以酸化凹凸棒石和丙烯酰胺为原料,N-N亚甲基丙烯酰胺为交联剂,过硫酸钾为引发剂,采用水溶液聚合法合成了凹凸棒石基高分子固沙材料.通过研究不同浓度硫酸活化的凹凸棒石基高分子固沙材料的吸水性能、保水性能、pH值以及X衍射以及扫描电镜,结果表明4 mol/L硫酸改性的凹凸棒石基高分子固沙材料具有更好的吸水性能和保水性能;pH值的变化对4 mol/L硫酸改性的凹凸棒石基高分子固沙材料具有较大的影响;X衍射以及扫描电镜表明3 mol/L和4 mol/L硫酸改性的凹凸棒石基高分子固沙材料具有更好的吸附性能.研究结果对于加强深入硫酸改性的凹凸棒石基高分子固沙材料的研究重具有要意义,以期制备出一种新型环保型复合高吸水性凹凸棒石基高分子固沙材料.     

Membrane fouling and chemical cleaning in water recycling applications

Fouling and subsequent chemical cleaning are two important issues for sustainable operation of nanofiltration (NF) membranes in water treatment and reuse applications. Fouling strongly depends on the feed water quality, especially the nature of the foulants and ionic composition of the feed water. Consequently, appropriate selection of the chemical cleaning solutions can be seen as a critical factor for effective fouling control. In this study, membrane fouling and chemical cleaning under condition typical to that in water recycling applications were investigated. Fouling conditions were achieved over approximately 18 h with foulant cocktails containing five model foulants namely humic acids, bovine serum albumin, sodium alginate, and two silica colloids in a background electrolyte solution. These model foulants were selected to represent four distinctive modes of fouling: humic acid, protein, polysaccharide, and colloidal fouling. Three chemical cleaning solutions (alkaline solution at pH 11, sodium dodecyl sulphate (SDS), and a combination of both) were evaluated for permeate flux recovery efficiency. The results indicated that with the same mass of foulant, organic fouling was considerably more severe as compared to colloidal fouling. While organic fouling caused a considerable increase in the membrane surface hydrophobicity as indicated by contact angle measurement, hydrophobicity of silica colloidal fouled membrane remained almost the same. Furthermore, a mechanistic correlation amongst cleaning efficiency, characteristics of the model foulants, and the cleaning reagents could be established. Chemical cleaning of all organically fouled membranes by a 10 mM SDS solution particularly at pH 11 resulted in good flux recovery. However, notable flux decline after SDS cleaning of organically fouled membranes was observed indicating that SDS was effective at breaking the organic foulant—Ca²⁺ complex but was not able to effectively dissolve and completely remove these organic foulants. Although a lower permeate flux recovery was obtained with a caustic solution (pH 11) in the absence of SDS, the permeate flux after cleaning was stable. In contrast, the chemical cleaning solutions used in this study showed low effectiveness against colloidal fouling. It is also interesting to note that membrane fouling and chemical cleaning could permanently alter the hydrophobicity of the membrane surface.     

Vapor-liquid equilibria of some pollutants in aqueous and saline solutions Part I: experimental results

Vapor-liquid equilibria were measured for dilute aqueous solutions of formic acid, acetic acid, pyridine, aniline, isobutyl alcohol, isoamyl alcohol, n-butyl acetate, dimethyl phthalate, diethyl phthalate and dioxane, respectively, at various pH, temperatures and concentrations of sodium chloride.The substances chosen are very important raw materials or intermediates in chemical industry and are widely used. Phthalates are used as plasticizers and leach, in small amounts, into water from plastics. Recently in Japan, we are recognizing phthalates as a new polluting material in sea water and river water.The vapor-liquid equilibria were severely affected by the pH of the solution, not only for the electrolytes (such as formic acid and pyridine), but also for esters. This is probably due to the effect of pH on the degree of the dissociation of electrolytes and on the hydrolysis of esters. The phase equilibria of some organic materials which are less soluble in water (such as phthalates and higher alcohols) were greatly affected by the salting-out effect of salinity.If the feed sea water to distillation plants is contaminated by volatile organic materials, some of them concentrate in the distilled water. Therefore, attention must be given to the properties of volatile, polluting materials in sea water when the product water from desalination processes is for human consumption.     

On-Line Determination of Water Activity at the Lean Surface of Meat Products During Drying and Its Relationship with the Crusting Development

One of the main problems in drying of meat products is the surface hardening or crusting. The crusted surface layer is harder and less permeable than the inner part of the product. A dramatic increase of hardness during drying in dry-cured meat products has been found when the water content reaches a critical value. The water content can be related with the water activity by sorption isotherms. Therefore, an on-line measurement of the water activity at the surface (a_ws) could be used by the control system in order to avoid the crusting problem. The aim of this study was to evaluate a methodology for the on-line water activity determination at the lean surface of raw or salted meat during drying and relate this determination with the crusting development. Water activity at the surface was estimated from the heat balance (a_ws^h) in salted meat slices and in unsalted and in salted loin samples. The proposed methodology was able to monitor the a_ws in both products. The estimated a_ws^h was related with the crusting development in loin samples, showing its potential application in control systems for avoiding the crusting development during the drying of meat products.     

Water desorption and shrinkage in mortars and cement pastes: Experimental study and poromechanical model

The aim of the present research was to study moisture changes and strains induced by smooth water desorption of several cement based materials. The main advantage of this small-steps drying is to dramatically limit the structural effect within tested samples, by lowering moisture gradients and therefore cracking due to differential shrinkage. Resulting data are of importance as they allow water retention curves, porosity distribution and desiccation shrinkage to be determined versus a large range of relative humidity. Experiments were conducted on ordinary mortars and cement pastes with water-to-cement ratio of 0.5 and 0.8. The role of the cementitious matrix and of aggregates over water-related behaviour of these materials can also be studied. Finally, a simple numerical model, based on experimental poromechanical results, was proposed to predict the shrinkage when the material is submitted to drying.     

Preparation of pH‐responsive crosslinked materials from natural rubber and poly(4‐vinylpyridine)

Stimuli‐responsive elastomers are smart materials for sensing applications. Natural rubber (NR) is a renewable elastomer with excellent elasticity and fatigue resistance. In this work, a straightforward method for the preparation of pH‐responsive crosslinked materials from NR and poly(4‐vinylpyridine) (P4VP) via free radical crosslinking reaction using benzoyl peroxide (BPO) as an initiator is described. The effects of P4VP and BPO concentrations, reaction time and reaction temperature on immobilization percentage were investigated. It was found that the immobilization percentage reached 90% when using a P4VP concentration of 150 phr and a BPO concentration of 10 phr for 24 h at 90 °C. The pH responsiveness of the crosslinked materials was studied via water swelling, water contact angle and dye release measurements. Unlike unmodified rubber, the P4VP‐crosslinked NR was found to be pH‐responsive in acidic solution. Indigo carmine adsorption studies showed the Langmuir isotherm suggesting monolayer coverage of dye on the rubber surface. The dye could also be released upon increasing the pH of solution above 4. Based on these results, the introduction of pH responsiveness to NR will lead to novel responsive rubber‐based materials that can be used in biomedical and sensing applications. © 2016 Society of Chemical Industry     

Periodic mesoporous silica and organosilica with controlled morphologies as carriers for drug release

In this paper, we report the effects of morphology, wall composition of mesoporous materials and different buffer solutions on drug delivery profiles. Hollow spheres of periodic mesoporous organosilica (PMO) were prepared and used as drug carriers which exhibited higher loading capacity and slower release rate compared to the conventional periodic mesoporous silica (PMS) spheres and solid spheres of PMO. This hollow PMO showed promising properties as a reservoir to encapsulate and store larger quantities of guest molecules within its “empty” core. Moreover, its organic reactive sites allowed stronger interactions to the hydrophobic guest molecules, in contrast to inorganic wall possessed by PMS materials. Antibiotic tetracycline was used as a model drug to study the effect of framework difference between PMO and PMS materials on the loading and release processes. Two kinds of release medium, simulated body fluid (SBF) solution (pH 7.4) and phosphate buffer (PB) solution (pH 1.5) were used in this study, which revealed very different release profiles. A slower delivery rate was observed in SBF solution, attributed to the different ionic interactions between the guest molecule and the host material in the two different pH solutions. Overall, hollow PMO shows the lowest release rate and the highest loading amount compared to the other two materials studied herein. The kinetic study reveals that drug release from host material follows the second order kinetic model better than the first order mass transfer model.