EDTA滴定法测定萤石中氟化钙含量的方法改进

建立了EDTA滴定法测定矿石中氟化钙的方法。引入了钙乙酸为溶解试样的溶剂,溶解样品中的碳酸钙,同时,通过同离子效应减少氟化钙的溶解度。实验中探究了钙离子的浓度与氟化钙溶解度的关系,通过对比实验确定选择了含钙乙酸的最佳浓度(10g/L)。同时,对实验中的其他条件也进行了相应的探究与优化,确定最佳实验条件为:最小称样量为0.5g,洗涤沉淀用水量为50mL左右,第二次过滤时的洗涤次数为8～10次,滴定时加入氢氧化钾的量为20mL。方法的精密度(0.10%)和准确度(0.08%)皆能满足实验要求。     

高含量碳酸钙基体中氟化钙的准确测定

采用GB/T 5195.1–2017方法检测高含量碳酸钙基体中氟化钙时,采用乙酸为浸取液,不能完全溶解碳酸钙,且使氟化钙部分溶解,导致测定结果不准确。对方法进行优化,用稀盐酸溶液直接溶解样品,加入氯化钙溶液辅助氟化钙沉淀,用EDTA法进行滴定。试验确定,pH值为5(用4.0 g/L NaOH溶液调节),加入5 mL 0.10 mol/L氯化钙溶液。用优化后的方法对6个自制模拟样品进行分析,测定结果与计算值相符,相对误差为0.059%～2.008%,测定结果的相对标准偏差不大于1%(n=6)。该方法解决了乙酸分离碳酸钙和氟化钙带来的误差问题,适用于基体碳酸钙含量较高时氟化钙的检测。     

电感耦合等离子体原子发射光谱法同时测定多金属矿石中氧化钙、氧化镁、砷

建立电感耦合等离子体原子发射光谱仪同时测定多金属矿石中氧化钙、氧化镁、砷含量的方法。以盐酸、硝酸、高氯酸、氢氟酸四元混合酸溶解样品,以硝酸作为介质溶解盐类,对实验条件进行优化,确定了最佳仪器工作条件和各组分的最佳谱线。氧化钙、氧化镁的质量浓度在1.00～20.00 μg/mL、砷的质量浓度在0.50～10.00μg/mL范围内与光谱强度具有良好的线性关系,相关系数均大于0.999,各组分的检出限为0.008～0.100μg/mL。测定结果的相对标准偏差为1.91%～6.69%(n=11),样品加标回收率为97.79%～107.79%。该方法分析速度快,准确度和精密度高,适用于大批量多金属矿石样品中氧化钙、氧化镁、砷的同时测定。     

EDTA络合滴定法测定选铁尾矿中CaF2含量

采用EDTA络合滴定法测定选铁尾矿中的氟化钙含量。选用稀乙酸浸取试样中的碳酸钙,分离过滤氟化钙,用锆-二甲酚橙褪色分光光度法测定浸取液中的氟含量,折算为在稀乙酸中微溶的氟化钙的量;同时沉淀部分用氯化铝溶液在沸水浴中溶解浸取氟化钙,以三乙醇胺掩蔽干扰离子,在KOH介质中,以钙指示剂为指示剂,用EDTA标准滴定溶液测定沉淀中氟化钙的量,两者之和为试样中氟化钙的含量。用此法对试样进行11次平行测定,相对标准偏差（RSD）小于1.0%。在选铁尾矿试样中加入萤石标准物质进行加标回收实验,加标回收率在99%-102%。方法流程短,操作简单。精密度和加标回收率均能满足要求。     

对苯二胺荧光探针测定水质样品中的溶解态汞

为获得水质样品中的溶解态汞简便、灵敏的测定方法,以含有荧光基团和氨基活性基团的对苯二胺作为荧光探针,基于其荧光猝灭程度与Hg(Ⅱ)浓度呈线性关系,建立荧光光度法测定水质样品中溶解态汞的检测方法。对缓冲体系的类型、pH值、浓度以及荧光探针的浓度等条件进行实验,确定采用pH 5.0的0.010 mol/L AABS体系和0.40 μg/mL对苯二胺荧光探针的荧光探针实验条件,并应用于实际水质样品中。结果表明,当Hg(Ⅱ)浓度在0.64 μg/mL ~1.36μg/mL内,荧光探针对苯二胺浓度的荧光淬灭程度与Hg(Ⅱ)浓度成良好的线性关系(R=0.9991),重复性实验的相对标准偏差为0.72 %,方法检出限为0.032 μg/mL,加标回收率均在90%~110%之间。该方法简便、灵敏度高、选择性好、可用于实际水质样品中溶解态汞的测定,具有较好的应用前景。     

吸附管采样-气相色谱法测定空气和废气中9种卤乙酸

采用硅胶填料吸附管吸收采集空气或废气中9种卤乙酸,经解吸后采用气相色谱法同时测定其含量。在吸附管的前段和末段分别填入硅胶200,100mg,将吸附管与大气采样器连接,在采气流量为0.5L·min~(-1)的条件下,采集样品40min。将吸附管两端的硅胶分别移入具塞试管中,分别先后两次用水超声解吸,每次用水5mL,解吸5min。将解吸液移入于已盛有水30mL的分液漏斗中,加入硫酸2mL使溶液的酸度小于pH 0.5,确保卤乙酸均以分子形式存在,随即加入NaCl 8g并使其迅速溶解。加入4.00mg·L~(-1)的1,2,3-三氯丙烷内标物溶液4mL,萃取3min。分层后取上层醚液3mL,置于分液漏斗中,加入新配制的硫酸-甲醇(2+8)溶液3 mL,密封,于50℃磁力搅拌条件下酯化2h,冷却,先后用250g·L~(-1) NaCl溶液7mL和饱和NaHCO3溶液1mL各洗涤1次。分层后取上层醚液,按仪器工作条件进行测定。结果表明:9种卤乙酸(包括一氯乙酸、二氯乙酸、三氯乙酸、一溴乙酸、二溴乙酸、三溴乙酸、一溴一氯乙酸、一溴二氯乙酸和一氯二溴乙酸)的质量浓度在0.001～2.0mg·m~(-3)内与相应卤代酸甲酯与内标物的峰面积之比值呈线性关系。在方法的测定条件下测得9种卤乙酸的检出限(3S/N)在0.20～1.0μg·m~(-3)之间。分别进行精密度和回收试验,测得回收率在91.6%～116%之间,测定值的相对标准偏差(n=6)在4.3%～7.9%之间。     

响应面法优化石榴叶多酚闪式提取的工艺研究

为建立快捷、高效、绿色的石榴叶多酚的提取工艺,通过单因素实验确定其主要影响因素,在单因素实验的基础上利用响应面法进行分析,确定提取石榴叶多酚的最佳提取条件为:乙醇浓度58%、料液比1∶9 (g/mL),提取时间4 min,在此条件下石榴叶多酚的理论提取量为:29.37 g GAE/100 g,实际提取量为:29.12 g GAE/100 g.     

加速溶剂萃取快速洗脱印迹聚合物中的模板分子

通过优化实验条件,选择洗脱温度80℃、加热时间5min、萃取压力10.4MPa、洗脱溶剂为300mL的甲醇/乙酸(90∶10,V/V),静态萃取时间8min、吹扫时间100s,对1.000g尼古丁印迹聚合物中的模板分子进行连续6次的萃取洗脱,洗脱效率达94.2%,模板渗漏量仅为9.8μg/L,萃取时间<70min。将2000mg洗脱后的印迹聚合物颗粒装填于3mL的聚丙烯固相萃取小柱中,用10mL甲醇/乙酸(90∶1,V/V)淋洗小柱,用高效液相色谱检测淋洗液中的尼古丁,获得模板的渗漏量为9.8μg/L。     

食品中罂栗碱金标快速检测试剂条的研究

首先以1-乙基-3-(3-二甲氨基丙基)碳二亚胺盐酸盐(EDC·HCI)方法合成罂粟碱完全抗原;通过改变还原剂加入量,确定纳米金合成条件为每50.0 ml,氯金酸加入1.5 mL柠檬酸三钠;合成金标保护剂量为20.0 mL胶体金溶胶加入1100稀释抗体(12 mg/L)2.0 mL,标记pH值为8.65.以罂粟碱多克隆抗体-纳米金复合物作为分析探针,罂粟碱完全抗原作为竞争抗原,构建分析体系.点样条件抗原质量浓度为1.0 g/L(以蛋白浓度计算);抗原点样量1 μL/条;金标点样量5 μL/条;二抗浓度(羊抗兔)3.3 g/L稀释至13 500;二抗点样量1μL/条.同时在实验中确定了样品提取方法.检测的灵敏度达到10 μg/L,检测时间不超过20 min.与ELISA方法对照结果,对比检测123份样品,准确率100%.     

毛细管离子分析法测定人发中钙和锌

适量人发试样经洗涤、冲洗,并于60℃干燥至恒重后称取1.000 g于600℃灰化后用盐酸(1+1)溶解残渣,溶液定容为100 mL供CIA分析。在10 mmol.L-1咪唑、10 mmol.L-1α-羟基乙酸、pH 4.0的电泳介质中,两离子在10 min内实现了分离。以间接紫外法检测(214 nm),外标法定量。钙(Ⅱ)及锌(Ⅱ)的峰面积与其质量浓度之间在0.5~40 mg.L-1范围内呈线性关系,相关系数分别为0.999 1和0.998 9,检出限(S/N=3)为0.1和0.2 mg.L-1,回收率在97.9%~102.5%之间,相对标准偏差小于2.5%。     

Interaction of Citric or Hydrochloric Acid with Calcium Fluorapatite: Precipitation of Calcium Fluoride

The interaction of citric acid (H₃Ci) with calcium fluorapatite(Ca₁₀ F₂(PO₄)₆) was explored for two reasons: (i) to determine the role of the acid in the dissolution process and hence in the mechanism of tooth fluoridation and (ii) to determine whether there is any formation of calcium citrate. It was found that the concentration of calcium or fluoride ions is not stoichiometric with respect to that of phosphate ions in the solution and the stoichiometric deficiency of the amount of fluoride ions in the solution is twice that of the calcium ions and this demonstrates that some calcium fluoride is precipitated. The interaction may be represented by the following chemical equation (pH ≈ 2.5):where x (presently < 1) is related to the amount of CaF₂ that has precipitated and may be calculated from the experimental ratio of Ca to P in the solution. In order to establish that the interaction occurs generally with all acids, the reaction of hydrochloric acid with fluoroapatite was studied, and exactly analogous behavior was observed. These facts are also in accord with the solubility of fluorapatite and calcium fluoride. When the amounts of Ca and P in solution are corrected for the precipitated CaF₂, the ratio of Ca to P becomes stoichiometric (= 1.67). Preliminary X-ray analysis of the reacted fluorapatite showed that it contained calcium fluoride. The precipitated CaF₂ may act as a reservoir for the subsequent fluoridation of the mineral and may inhibit bacterial action in the mouth. The concentration of citrate ions does not change in solution, and no formation of calcium citrate is observed.     

X射线荧光光谱法测定萤石中氟化钙

采用X射线荧光光谱仪可以快速准确测定萤石中总钙的含量.但测定其中氟化钙含量时,一方面,由于样品中碳酸钙计入钙量,从而造成氟化钙测定结果准确性较差.另一方面,铜、锌等金属元素在熔融制样时对铂金坩埚腐蚀较大,因此需要进行酸处理除去碳酸钙及铜、锌等金属元素.然而,样品经过酸处理后,质量会发生变化,造成熔剂与样品的比例不一致,从而影响测定结果.对样品前处理条件、XRF分析中熔片和仪器工作条件等进行了优化,建立了熔融制样、X射线荧光光谱法（XRF）准确测定萤石中氟化钙含量的方法.方法干扰少,具有良好的准确度和精密度,操作简单,提高了分析效率.     

Optimization of Fluoride Adsorption on Acid Modified Bentonite Clay Using Fixed-Bed Column by Response Surface Method

Using small-scale batch tests, various researchers investigated the adsorptive removal of fluoride using low-cost clay minerals, such as Bentonite. In this study, Column adsorption studies were used to investigate the removal of fluoride from aqueous solution using acid-treated Bentonite (ATB). The effects of initial fluoride concentration, flow rates, and bed depth on fluoride removal efficiency (R) and adsorption capability (qe) in continuous settings were investigated, and the optimal operating condition was determined using central composite design (CCD). The model’s suitability was determined by examining the relationship between experimental and expected response values. The analysis of variance was used to determine the importance of independent variables and their interactions. The optimal values were determined as the initial concentration of 5.51 mg/L, volumetric flow rate of 17.2 mL/min and adsorbent packed-bed depth of 8.88 cm, with % removal of 100, adsorptive capacity of 2.46 mg/g and desirability of 1.0. This output reveals that an acid activation of Bentonite has made the adsorbent successful for field application.     

离子色谱法测定食品添加剂磷酸二氢铵中氟离子含量

建立了离子色谱测定食品添加剂磷酸二氢铵中的氟离子含量的方法。结果表明,在最佳实验条件下,食品添加剂磷酸二氢铵中的NH4+,PO43-及SO42-等杂质均不干扰F-的测定。采用标准曲线法定量,F-浓度在4~50μg/mL的范围内,线性方程为y=0.099 48x-0.108 0,线性相关系数为0.999 9,方法的检出限为0.15μg/mL,加标回收率为96.9%~101.6%,该方法具有简单、快速、重现性好等优点。     

EDTA滴定法测定矿石中铅含量的方法改进

对以往测定铅的方法进行了改进。消解样品的体系为盐酸-硝酸-硫酸和氟化铵,氟化铵(200 g/L)的加入量为3 mL;硫酸加入量为10 mL,浓度为1+1;硫酸铅沉淀静止时间为45 min;除去铋干扰的方法为调节溶液的pH值用EDTA溶液进行分步滴定;将过滤后的滤液进行回收测定,与滴定的结果相加以得到最终结果,滤液中铅含量的大概范围为0.13 %~0.27 %。本方法的精密度为0.12%~0.15% ,准确度为0.24%~0.43%。     

Microdetermination of fluorine in organic compounds by oxygen flask combustion and conductometric titration

For the conductometric titration of fluoride with calcium acetate, solvent system in sample solution and titrant, concentration, and acidity of sample solution were examined to establish the titration conditions. Results of these examinations were transferred to the microdetermination of fluorine in organic compounds using oxygen flask combustion method.Comparative examination between quartz and Pyrex flasks for the combustion of fluorine samples indicated that good results were obtained by the use of the former flask, whereas the use of the latter one gave negative values of 1.0–1.6% due to the formation of boron fluoride during the combustion.     

Thermal and Chemical Properties of a Glass in the SiO2-CaO-F System for Dental Applications

The crystallization behaviour of a glass in the SiO₂-CaO-F system was analyzed using differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Three crystalline phases were detected according to ICDD patterns. The first phase formed at 583°C was identified as CaF₂. The morphology was spherulitic with a diameter of approximately 100 nm. The second phase was formed at 664°C. It was identified as calcium fluoride silicate ‘Ca₂SiO₂F₂’ (ICDD 35-0002). SEM investigation showed that the crystals were spherulitic with a diameter smaller than 100 nm. The crystals were precipitated in the volume of the glass and homogeneously distributed. As a third phase, cristobalite crystallized at 895°C. The simultaneous release of calcium and fluorine ions from the vitreous glass in lactate buffer solution at pH 4.0, simulating an acidic oral environment, was investigated using X-ray photoelectron spectroscopy (XPS). The release of calcium and fluorine ions is of special interest for dental applications. The atomic ratios of the components Si, Ca and F at the glass surface after different leaching periods were determined. In order to investigate the leaching process, concentration profiles were measured using ion beam sputtering with Ar⁺ -ions. The dependence of the atomic ratios of Si, Ca and F on the sputter time was determined in order to measure the depth of the leaching layers. Most probably, the release of calcium and fluoride was controlled by a surface layer rich in calcium and flourine ions which dissolved with increasing leaching time. After 2 min leaching, a fluoride-rich surface layer measuring approximately 10 nm was detected. The atomic ratios of Si, Ca and F were different from the bulk composition ratios in a surface reaction layer of 800 nm thickness. After 30 min leaching time, a calcium- and fluoride-rich surface layer approximately 50 nm thick was formed. The bulk composition was reached at a depth of approximately 500 nm. The main component in the surface layer, after 12 days leaching in acidic environment, was silicon. This revised version was published online in August 2006 with corrections to the Cover Date.     

乙醇-水介质中氟-铝沉淀电位滴定体系研究

由于氟-铝的多级络合反应,在水溶液中用氟化物直接滴定铝没有明显的电位突跃,若用乙醇-水介质,则电位突跃明显^[1～3].本文对乙醇-水介质中氟-铝沉淀电位滴定体系的化学平衡进行了研究.测定了在不同浓度的乙醇介质中氟-铝的络合比及各级络合物的稳定常数等参数.实验表明用F^-电位滴定测定铝可取得较好结果.