估算一元弱酸溶液pH的近似式及约束条件

利用一元二次方程估算一元弱酸溶液的[H+]是化学分析工作者经常采用的方法。酸的离解常数Ka和浓度c的数值相对大小和其乘积cKa是获得各种近似式的关键因素。本文通过实例计算归纳出了如下结论:(1)当c Ka≥10Kw时,可忽略水的离解,则[H~+]=1/2(-K_a+(K_a~2+4_cK_a)(1/2)),并首次指出了c Ka≥10Kw判据的边界条件为c≥6×10~(-6)mol·L~(-1);(2)当Ka≥19c时,弱酸可做强酸处理,通常情况下有[H+]=c,对较强弱酸的稀溶液,该近似式有重要应用价值;(3)当满足c≥105Ka时,可忽略弱酸的离解,即认为[HA]≈c,则[H~+]=(K_w+cK_a)(1/2)。实际上,c≥6×10~(-6)mol·L~(-1)的弱酸溶液,都可用近似式获得令人满意的pH计算结果。     

基于滴定突跃的计算探讨多元弱酸分步滴定的准确条件

多元弱酸分步滴定的准确条件一直是酸碱滴定中的一个教学难点。基于分布分数的分析指出了当前分析化学教材中有关探讨磷酸分步滴定的某些错误结论,并在此基础上,通过滴定突跃大小的计算,对多元弱酸分步滴定的准确条件进行了探讨分析。结果表明：若人眼判断滴定终点时有±0.2pH的不确定性时,滴定误差控制在0.5%,强碱滴定多元弱酸时,分步滴定的准确条件是：Kai/Ka(i+1)≥105.0;cKai≥10-8.7。     

多元酸碱分步滴定的可行性研究

分析化学教科书中,对多元酸能否分步滴定都给出了判据。以二元酸的分步滴定为例,当△pK_a≥5,c_aK_(a_1)≥10~8,△pH=±0.3时,滴定误差|TE|≤0.5%。基于A.Ringbom误差公式导出的这一判据被广泛的采用。在我们的教学中,曾有人对此提出了疑向:(1)在c_aK_a≥10~(-8)的前提下,分步滴定的准确度是否仅决定于△pK_a,而与被滴酸的浓度大小无关?(2)c_aK_(a_1)≥10~(-8),是一元酸被准确滴定的条件,对一元酸准确滴定的误差要求是0.1%,而多元酸分步滴定的误差要求是0.5%。所以分步滴定中仍要求c_aK_(a_1)≥10~(-8)是否合理?本文拟从滴定过程的质子条件出发,导出计算分步滴定误差的精确算式,借助计算机进行计算,得到分步滴定的确切条件,同时引用浓度对数图对此条件作出直观形象的说明。     

数学方法推导一元弱酸溶液氢离子浓度的近似公式及适用条件

近似计算一元弱酸HA溶液的氢离子浓度[H+]（相对误差在±5%以内）是分析化学工作者需要掌握的方法。利用严谨的数学方法,获得了各类近似公式的使用条件和浓度适用范围。例如,从近似式[H+]AV1=1/2（-Ka+√Ka2+4cKa+4c）出发,推导出了计算氢离子浓度的其他2个近似公式：（1）c越小,[H+]AV1越趋向c。计算表明,当满足c≤1/19Ka和c≥5.0×10-7 mol/L时,弱酸HA就可作强酸处理,此时得到近似式[H+]AV4=c,这极大简化了弱酸溶液氢离子浓度的计算。（2）c越大,[H+]AV1越接近√cKa。当满足c≥105Ka和cKa≥10Kw时,弱酸溶液氢离子浓度可按最简式[H+]AV2=√cKa计算。还解释了c≥105Ka和c≤1/19Ka时所包含的物理意义。需要强调的是,本文首次给出了各近似式的浓度适用范围,比如忽略水的解离时,除了满足cKa≥10Kw,还必须要求c≥6.0×10-6 mol/L。     

辣根过氧化酶在磁性纳米修饰的离子注入电极上的电化学和电催化行为

辣根过氧化酶(HRP)在Co/NH2/ITO离子注入电极上有一对良好的氧化还原峰,峰电位分别为Epc=-0.2 V,Epa=-0.01 V(vsAg/AgCl)。该修饰电极对H2O2具有催化作用,可以用作H2O2的生物传感器,峰电流与H2O2的浓度分别在1.0×10-10~2.0×10-8mol/L和2.0×10-8~1.0×10-7mol/L范围内呈线性关系,线性回归方程分别为Ip(mA)=2.2986+0.06632c(nmol/L)和Ip(mA)=3.5788+7.3053E-4c(nmol/L),相关系数分别为0.9972和0.9688。检出限为1.0×10-10mol/L。     

荧光猝灭法测定叶酸

以维生素B2作为荧光探针,基于荧光猝灭法对叶酸进行了定量检测,考察了维生素B2浓度、激发波长、反应时间等多种因素的影响。实验结果表明,在水溶液中,反应时间为8 min,叶酸浓度在1.5×10-6～1.0×10-5mol/L范围内,其线性回归方程为F0/F=0.6838+0.214 c(×10-6mol/L),相关系数和检测限分别为0.9988和6.7×10-7mol/L。     

强弱酸混合体系被分步直接准确滴定的判据

以一元强酸和一元弱酸组成的混合体系为对象,并以指示剂确定终点,推导能否实现混酸分步直接准确滴定的判据。研究发现:只有待滴定酸的浓度≥0.544 mol·L-1且弱酸的p Ka处于5.6–8.3之间时,才有可能在滴定误差不超过0.1%的要求下实现同浓度混合液中一元强酸和弱酸的分步直接准确滴定,这两个条件会随着滴定准确度要求的变化而变化。     

盐酸异丙嗪的微波增敏方波伏安法测定

以玻碳电极作工作电极,在微波作用下用循环伏安法和方波伏安法研究了盐酸异丙嗪的电化学特性,结果表明微波可以增大峰电流,并应用于盐酸异丙嗪的检测,建立了一种新的检测盐酸异丙嗪的电化学方法.在最佳实验条件下,无微波作用时用方波伏安法检测盐酸异丙嗪,其响应电流与盐酸异丙嗪的浓度在4.0×10-6 ～1.0×10-4 mol/L范围呈线性关系(r=0.998 2,n=7),线性回归方程为I(A)=0.040 3c(mol/L)+5.0×10-7,检出限为4.0×10-7 mol/L;在微波作用下用方波伏安法检测盐酸异丙嗪,其响应电流与盐酸异丙嗪的浓度在4.0×10-6 ～1.0×10-4 mol/L范围有很好的线性关系(r=0.999 1,n=7),线性回归方程为I(A)=0.045 7c(mol/L)+6.0×10-7,检出限为2.0×10-7 mol/L.在4.0×10-6 ～1.0×10-4 mol/L范围微波增敏的峰电流与无微波条件下峰电流的比值平均值为1.22.该方法用于盐酸异丙嗪片的测定,结果满意.     

功能性CdTe量子点荧光增敏法测定盐酸多巴胺

以CdTe量子点作为荧光探针,基于荧光增敏法对盐酸多巴胺进行了定量检测,考察了缓冲溶液体系、量子点浓度、反应时间等多种因素的影响。实验结果表明,在pH7.5的0.2 mol/L Na2HPO4-NaH2PO4缓冲液中,反应时间为20 min,盐酸多巴胺浓度为1.2×10-8~1.0×10-7mol/L时,其线性回归方程为△F=-27.47+25.54c(10-8mol/L),相关系数和检测限分别为0.9992和6×10-11mol/L。该方法为盐酸多巴胺的测定提供了新的方法。     

多壁碳纳米管修饰电极检测盐酸氯丙嗪的研究

制备了多壁碳纳米管修饰玻碳电极,采用循环伏安法(CV)研究了盐酸氯丙嗪在修饰电极上的电化学特性,发展了一种新的检测盐酸氯丙嗪的电化学分析方法。在最佳实验条件下,用循环伏安法检测盐酸氯丙嗪,其响应电流与盐酸氯丙嗪的浓度在8.0×10-5~1.0×10-3mol/L范围内有很好的线性关系,线性方程为Ip(A)=0.0106c(mol/L)-8×10-8(R2=0.999,n=6),检出限为6.2×10-6mol/L(S/N=3)。方法可用于盐酸氯丙嗪片的测定。     

聚苯胺/钴-氧化钴膜作传感元件的pH传感器的性能

本文研究了在玻碳电极上修饰不同物质所制得的pH传感器,通过电位滴定的方法比较得出先修饰聚苯胺,再修饰钴-氧化钴膜的电极对pH有较好的响应,能代替玻璃电极应用在实际样品测定中。探究了最佳修饰条件为：先在0.1mol/L苯胺的盐酸（1mol/L）溶液中, 电位范围为-0.2~1.0V,以100 mV/s 的扫描速度循环伏安扫描 10圈修饰聚苯胺膜;接着在含2.0×10-4 mol/LCo2+的PBS （pH=7.5）缓冲溶液中, 电位范围为-1.2~1.2V,以100 mV/s 的扫描速度循环伏安扫描 5圈修饰钴-氧化钴膜。得到的修饰电极响应斜率为-61.60 mV/pH,响应范围pH 0.5~13。     

修饰铂电极上Bi(Ш)的示波双电位滴定法

制备了Bi(Ⅲ)修饰铂电极,用循环伏安法表征了Bi(Ⅲ)在电极上的吸附特性,探讨了电极的响应机理。 通过优化实验条件,建立了一种测定Bi(Ⅲ)的示波双电位滴定法。 在0.1 mol/L的硝酸溶液中(pH=1.0),用制备的修饰铂电极作为双指示电极,以EDTA标准溶液滴定Bi(Ⅲ),利用示波器屏幕上荧光点的显著最大位移指示滴定终点。 Bi(Ⅲ)在1.19×10-4～1.44×10-2 mol/L时,回收率为99.8%～100.1%,检出限(S/N=3)为1.0×10-4 mol/L。 该修饰电极具有良好的稳定性和重现性,在含有1.0×10-2 mol/L Bi(Ⅲ)的溶液中,连续7次测定,所得终点电位值均在100 mV左右,其相对标准偏差(RSD)为0.04%。 应用该方法测定含铋样品,RSD值(n=7)小于0.25%,回收率为99.5%～100.5%,测定结果与指示剂法测定值相符。     

Determination of lomefloxacin, an antibacterial drug, in pharmaceutical preparations based on its polarographic catalytic wave in the presence of 2-iodoacetamide.

In a 0.125 mol/L phosphate (pH 6.6)/2.5 x 10(-4) mol/L 2-iodoacetamide solution, lomefloxacin yields a response of a polarographic catalytic current. The second-order derivative peak current of the catalytic wave of lomefloxacin is proportional to its concentration in the range of 1.0 x 10(-8)-1.0 x 10(-6) mol/L (r = 0.998). The sensitivity of the catalytic wave is 25-times higher than that of the corresponding reduction wave for 5.0 x 10(-7) mol/L lomefloxacin. The proposed method was applied to the determination of lomefloxacin in pharmaceutical preparations. The polarographic reduction wave is ascribed to a one-electron reduction of the C=C bond of lomefloxacin zwitterion accompanied by an acid-base equilibrium. The catalytic wave should be caused by regeneration of the lomefloxacin molecule at electrode surface due to the one-electron reduction product being further oxidized by electroreductive intermediate products of 2-iodoacetamide.     

Determination of ng rivanol in human plasma by SPE-HPLC method

A high-performance liquid chromatography assay is described for the determination of rivanol in human plasma. Solid-phase extraction cartridges are used to extract plasma samples. Separation is done by using a C18 column. The mobile phase is a mixture of methanol-0.05% sodium dodecylsulfonate (70:30, v/v, pH 3), with the flow rate at 1.0 mL/min. UV detection of rivanol is at 272 nm. The calibration curve is linear in the concentration range of 1x10(-8) mol/L to 1x10(-5) mol/L with linear correlation coefficient r equal to 0.9998. The limit of detection for the assay is 3x10(-9) mol/L, corresponding to 1.1 ng/mL. Precision, expressed as the within- and between-day coefficient of variation, is 3.3-8.1% and 4.1-9.5%, respectively, at plasma control samples of 5x10(-8), 5x10(-7), and 5x10(-6) mol/L. And the recovery ranges from 94.8% to 107.2%. The selectivity of the method is confirmed. Plasma samples are stable for at least 15 days if they are stored lightproof at -20 degrees C. This method is simple, sensitive, and accurate, and it allows for the determination ng rivanol in human plasma. It could be applied to assessing its plasma level in women receiving an intra-amniotic injection of rivanol.     

Fluorimetric study of the interaction between human serum albumin and quinolones-terbium complex and its application

A highly sensitive spectrofluorimetric method is proposed for determination of human serum albumin (HSA) and some quinolone drugs. Using quinolones-terbium (Tb3+) complex as a fluorescent probe, in the buffer solution of pH 7.8, HSA can remarkably enhance the fluorescence intensity of the quinolones-Tb3+ complex at 545 nm and the enhanced fluorescence intensity of Tb3+ ion is in proportion to the concentration of HSA and quinolone drugs. Optimum conditions for the determination of HSA were also investigated. The linear ranges and limits of detection are 8.0 x 10(-9) to 8.0 x 10(-8) mol L(-1), 4.20 x 10(-9) mol L(-1) (for HSA); 1.0 x 10(-6) to 4.0 x 10(-6) mol L(-1), 1.87 x 10(-8) mol L(-1) (for norfloxacin) and 1.0 x 10(-7) to 1.0 x 10(-6) mol L(-1), 4.82 x 10(-8) mol L(-1) (for enoxacine), respectively. This method is simple, practical and relatively free interference from coexisting substances, as well as much more sensitive than most of the existing assays.     

Electrochemical behavior and electrocatalytic study of the methylene green coated on modified silica gel

The electrochemical behavior of methylene green (MG) adsorbed on a silica surface modified with niobium oxide (SN) was investigated, using modified carbon paste electrodes. It was also used in an electrocatalytic study of NADH oxidation. The electrode showed a high stability attributed to the presence of SN, which avoids the leaching of the mediator from the electrode surface. The formal potential (E(0')) of the adsorbed MG was -35 mV vs SCE, showing a shift of 30 mV toward more positive potential values, compared to the MG dissolved in aqueous solution. This shift was assigned to the interaction between the basic nitrogen of MG and the acid sites of SN. The variation of the solution pH between 4 and 8 did not affect the stability nor the formal potential. However, for solution pH lower than 4 the formal potential was affected by the acidity of the medium. The electrocatalytic oxidation of NADH at the electrode was investigated. In the solution pH between 5 and 8 the electrocatalytic activity remained almost constant, giving a response signal of 13.3 nA L micromol(-1) cm(-2) and a K(Mapp) of 1.4 x 10(-5) mol L(-1). The electrode gave a linear response range between 5.0 x 10(-4) and 4.0 x 10(-3) mol L(-1) NADH concentration at pH 7.0 at an applied potential of 50 mV vs SCE. Applying a flow injection analysis system, the electrode showed a better analytical performance for NADH detection, presenting a linear response range between 6.0 x 10(-5) and 1.0 x 10(-3) mol L(-1), with an analytical frequency of 30 determinations/h, a detection limit of 8.2 x 10(-6) mol L(-1), and a precision for 25 replicates of 1% expressed as a relative standard deviation.     

四种阴离子的毛细管电泳电导检测(英文)

 采用柠檬酸 柠檬酸钠作为缓冲体系 ,使用负高压 ,对Cl-,NO3 -,HCO3 -和H2 PO4 -等 4种常见阴离子进行了分离检测 ,研究了缓冲剂的种类、浓度、pH值及操作电压对分离的影响。在选定的条件下 ,4种离子的定量线性范围 :Cl-5 0× 10 -5mol/L～ 2 5× 10 -3 mol/L ,NO3 -6 0× 10 -5mol/L～ 2 0× 10 -3 mol/L ,HCO3 -5 0× 10 -6mol/L～ 2 0× 10 -4 mol/L ,H2 PO4 -6 0× 10 -5mol/L～ 1 0× 10 -3 mol/L ;检出限 :Cl-1 5× 10 -5mol/L ,NO3 -3 0×10 -5mol/L ,HCO3 -1 0× 10 -6mol/L ,H2 PO4 -2 0× 10 -5mol/L ;峰面积的RSD (n =6 ) :Cl-3 1% ,     

Oil-in-water emulsions as suitable working media for the direct polarographic determination of aziprotryne and desmetryne from its organic extracts in water samples

The electroanalytical behavior of the reduction of the herbicides aziprotryne (2-azido-4-isopropylamino-6-methylthio-1,3,5-triazine) and desmetryne (4-isopropylamino-6-methylamino-2-methylthio-1,3,5-triazine) in oil-in-water emulsions is reported. This medium allows the differential pulse polarographic determination of these s-triazines directly from their sample extracts in an appropriate organic solvent. Sodium pentanesulfonate was chosen as the most suitable surfactant to be used as emulsifying agent, whereas ethyl acetate was selected as the organic solvent to form the emulsions. The peak current was maximum in a 0.3 mol L(-1) HClO4 medium of the continuous aqueous phase for aziprotryne, and at pH 3.0 for desmetryne, and the potential became more negative as the pH increased for both herbicides. The limiting current is diffusion controlled and the electrode process is irreversible. Four electrons are involved in the overall electrochemical reduction process as determined by controlled potential coulometry, whereas the alpha n(a) values suggested that two electrons are involved in the rate-determining step. Using differential pulse polarography, aziprotryne and desmetryne can be determined in the emulsified medium over the concentration ranges 1.0 x 10(-7)-1.0 x 10(-4) mol L(-1), with limits of detection of 4.5 x 10(-8) mol L(-1) and 6.6 x 10(-8) mol L(-1), respectively. The method was applied to the determination of aziprotryne and desmetryne in spiked irrigation water. At concentration levels of 6.0 x 10(-7) mol L(-1) aziprotryne and 4.0 x 10(-7) mol L(-1) desmetryne, recoveries of 94 +/- 3% and 94 +/- 4%, respectively, were obtained after preconcentration on Sep-Pack C18 cartridges. Finally, partial least-squares regression (PLSR) has been used for treatment of the polarographic data obtained from mixtures of aziprotryne, desmetryne and simazine in oil-in-water emulsions. The size of the calibration set was of 29 samples by ninety two current measurements at different potentials. Prediction of the herbicides concentration within the range 1.0 x 10(-6)-1.0 x 10(-5) mol L(-1) was possible.     

Direct determination of amino acids by pressurized capillary electrochromatography with chemiluminescence detection

A pressurized CEC (pCEC) coupled with on-column chemiluminescence (CL) detection was developed for direct determination of amino acids, which was based on the principle of an enhanced effect of Cu(II)-amino acid complexes on the CL reaction between luminol and hydrogen peroxide in alkaline solution. The effects of some important factors on pCEC separation and CL intensity were systemically investigated. Baseline separation of amino acids including L-histidine (L-His), L-threonine (L-Thr), and L-tyrosine (L-Tyr) was achieved by using a monolithic column with a mobile phase of 5.0x10(-3) mol/L phosphate buffer at pH 8.0 that contained 25% v/v methanol and 5.0x10(-4) mol/L luminol and 1.0x10(-5) mol/L Cu(II) at an applied voltage of -5 kV. The calibration curves of the analytes by plotting the peak height against corresponding concentration were linear over the range of 3.2x10(-6)-3.2x10(-4) mol/L for L-His, 4.1x10(-6)-4.1x10(-4) mol/L for L-Thr, and 6.0x10(-7)-3.0x10(-4) mol/L for L-Tyr. The LODs for L-His, L-Thr, and L-Tyr were 6.4x10(-7), 8.4x10(-7), and 3.0x10(-7) mol/L (S/N = 2), respectively. The proposed method was applied to the analysis of amino acid injection sample with satisfactory results. Mean recoveries for three amino acids were from 84.3 to 89.6%.