Quanmin Li

Study on electrochemical behaviors and the reaction mechanisms of dopamine and epinephrine at the pre-anodized inlaying ultrathin carbon paste electrode with nichrome as a substrate

In this paper, nichrome was adopted as a substrate, to fabricate the pre-anodized inlaying ultrathin carbon paste electrode (PAIUCPE). The electrochemical behaviors of dopamine (DA) and epinephrine (EP) at the electrode were investigated by cyclic voltammetry (CV). The reaction mechanisms of DA and EP have also been put forward. It was found that the electrode showed an excellent electrochemical behavior for electrode reaction of DA and EP. The cathodic potential difference of DA and EP was about 370 mV and the simultaneous determination of DA and EP was achieved based on it. The reduction peak current was proportional to the DA and EP concentrations in the range of 8.0×10(-7)-3.0×10(-4) M and 2.0×10(-6)-1.5×10(-4) M with the detection limits of 1.70×10(-7) M and 3.27×10(-7) M, respectively. Because the oxidation of ascorbic acid (AA) is an irreversible reaction at the PAIUCPE, the interferences of AA for determining DA and EP were eliminated. The method has been successfully applied to the determination of DA and EP in hydrochloride injection with satisfactory results.

Spectrophotometric determination of methimazole in pharmaceutical, serum and urine samples by reaction with potassium ferricyanide-Fe(III)

This paper describes a novel method to determine methimazole by spectrophotometry using a potassium ferricyanide-Fe(III) reaction. The study indicates that at pH 4.0 Fe(III) is reduced to Fe(II) by methimazole and in situ formed Fe(II) reacts with potassium ferricyanide to give soluble Prussian Blue which is characterized by means of XRD analysis. The absorbance of Prussian Blue is measured at the absorption maximum of 735 nm, and the amount of methimazole can be determined based on this absorbance. Beer’s law is obeyed in the range of methimazole concentrations of 0.02–6.00 μg/mL. The equation of the linear regression is A = −0.0058 + 0.49988c (μg/mL), with a correlation coefficient of 0.9998 and RSD of 0.80%. The detection limit (3σ/k) is 0.015 μg/mL, and the apparent molar absorption coefficient of indirect determination of methimazole is 5.7 ± 104 L/mol cm. This method has been successfully applied to the determination of methimazole in pharmaceutical, serum and urine samples, and average recoveries are in the range of 98.6–102.4%. Analytical results obtained with this novel method are satisfactory.

Spectrophotometric determination of perphenazine with the detection system of potassium ferricyanide–Fe(III) in pharmaceutical and serum samples

In this paper, a novel spectrophotometric method has been established to determine perphenazine using the detection system of potassium ferricyanide-Fe(III). In the presence of potassium ferricyanide, it has been demonstrated that Fe(III) is reduced to Fe(II) by perphenazine at pH 4.0. In addition, soluble prussian blue (KFe(III)[Fe(II)(CN)(6)]) is produced by the reaction between the in situ formed Fe(II) and potassium ferricyanide. The absorbance of soluble prussian blue is measured at the absorption maximum of 735 nm, and the amount of perphenazine can be calculated based on this absorbance. The absorbance is linear to perphenazine concentration in the ranges of 0.05-25.00 microg/mL with correlation coefficients of 0.9997, and the linear regression equation is A = 0.0069 + 0.1285C (microg/mL). The detection limit (3sigma/k) is 0.049 microg/mL, and the relative standard deviation (R.S.D.) is 0.86% (n = 11). Moreover, the apparent molar absorption coefficient of indirect determination of perphenazine is 5.2 x 10(4) L/mol cm. The parameters with regard to determination are optimized, and the reaction mechanism is discussed. This method has been successfully applied to the determination of perphenazine in pharmaceutical and serum samples. Analytical results obtained with this novel assay are satisfactory.

A novel electrochemical sensor based on FeS anchored reduced graphene oxide nanosheets for simultaneous determination of dopamine and acetaminophen.

In this paper, FeS nanoparticles anchored on reduced graphene oxide (rGO) nanosheets are synthesized via a facile direct-precipitation method. For the first time, a novel electrochemical sensor is developed based on FeS/rGO nanosheets modified glassy carbon electrode (GCE). It has been proved that the resultant FeS/rGO/GCE sensor is very suitable for the individual and simultaneous measurement of dopamine (DA) and acetaminophen (AC) and delivers excellent anti-interference ability to ascorbic acid (AA) and uric acid (UA). Under optimum conditions with differential pulse voltammetry method, a broad linear response versus the concentrations of DA and AC has been observed in the ranges of 2.0 to 250.0μM and 5.0 to 300.0μM, respectively. The detection limits for DA and AC are 0.098μM and 0.18μM, respectively. Furthermore, the as-obtained sensor has been successfully utilized in real samples and satisfactory results have been achieved. Consequently, by virtue of its outstanding electrocatalytic activity, excellent sensitivity, and long time stability, the as-obtained FeS/rGO modified electrode can be considered as a new promising DA and AC sensor.

Selective spectrophotometric determination of paracetamol with sodium nitroprusside in pharmaceutical and biological samples

A novel simple method to determine paracetamol with good selectivity has been established by using sodium nitroprusside as the chromogenic reagent. The experiment indicates that sodium nitroprusside can react with paracetamol in a basic solution to form a product with colored O-nitrosamines. The maximal absorption wavelength (λmax) and the apparent molar absorption coefficient of the product are 700 nm and 3.4 × 103 L/mol cm, respectively. A Good linear relationship is obtained between the absorbance and the concentration of paracetamol in a wide range of 0.19–96 μg/mL. The linear regression equation is A = 0.01695 + 0.02240C (μg/mL), with a correlation coefficient of 0.9993. The detection limit (3σ/κ) is 0.10 μg/mL, and the relative standard deviation (RSD) is 0.90% (n = 11). The parameters with regard to determination are optimized, and the reaction mechanism is discussed. The method has been successfully applied to the selective determination of paracetamol in pharmaceutical and biological samples.

The effect of acidity, hydrogen bond catalysis and auxiliary electrode reaction on the oxidation peak current for dopamine, uric acid and tryptophan

A pre-anodized inlaying ultra-thin carbon paste electrode on a 316L stainless steel matrix (316L-PAIUCPE) was prepared and used for simultaneous determination of dopamine (DA), uric acid (UA) and tryptophan (Trp). The mechanism by which the acidity affects the size of the oxidation peak currents (ip) for DA, UA and Trp was discussed with respect to the strength of the hydrogen bonding or electrostatic interactions between DA, UA, Trp and the negatively charged functional groups at the surface of 316L-PAIUCPE, and the reduction reaction at the auxiliary electrode. Under optimized experimental conditions, the oxidation peak currents increased linearly with the concentrations of DA, UA and Trp in the range of 0.4–200, 0.5–150 and 0.1–200 μmol L−1, respectively. The detection limits for DA, UA and Trp were 6.8 × 10−8, 4.5 × 10−8, and 5.3 × 10−8 mol L−1 in PBS buffer solution (pH = 5.00), respectively. This method was successfully used to determine the concentrations of DA, UA, and Trp in different samples.

Determination of thiamazole in pharmaceutical samples by phosphorus molybdenum blue spectrophotometry.

A novel method is established to determine thiamazole by phosphorus molybdenum blue spectrophotometry. The experiment indicates that PO(4)(3-) reacts with Mo(7)O(24)(6-) in 0.30mol/L H(2)SO(4) solution to form a product with phosphorus-molybdenum heteropoly acid ([H(2)PMo(12)O(40)](-)). Then [H(2)PMo(12)O(40)](-) is deoxidized to form phosphorus molybdenum blue (H(3)PO(4)·10MoO(3)·Mo(2)O(5)) by thiamazole. The amount of thiamazole can be determined based on the absorbance of phosphorus molybdenum blue (λ(max)=710nm). A good linear relationship is obtained between the absorbance and the concentration of thiamazole in the range of 0.035-70μg/mL. The equation of the linear regression is A=0.03384+0.00834c (μg/mL), with a linear correlation coefficient of 0.9990. The apparent molar absorption coefficient is 1.0×10(3)L/(molcm). The method has been successfully applied to the determination of thiamazole in pharmaceutical samples with satisfactory results, and recoveries are in the range of 99.6-100.6%.

A novel visible spectrophotometric method for the determination of ethamsylate in pharmaceutical preparations and biological samples.

A highly sensitive visible spectrophotometric method has been developed to determine ethamsylate in this paper, which is based on using Cu(II) as spectroscopic probe reagent. The study indicates that in the presence of SCN(-) and KNO(3), Cu(II) is reduced to Cu(I) by ethamsylate at pH 5.0, and the in situ formed Cu(I) reacts with SCN(-) to form into the white emulsion CuSCN that could be stayed upon the surface of water. According to the amount of residual Cu(II), the amount of ethamsylate can be indirectly determined. Under the optimal conditions, Beers law is applicable in the range of 0.2-9.0 microg/mL (7.60x10(-7)-3.42x10(-5)mol/L) for aqueous standard solution of ethamsylate with linear correlation coefficient of 0.9998. The detection limit and relative standard deviation are 0.12 microg/mL and 1.5%, respectively. And the molar absorption coefficient of the indirect determination of ethamsylate is 1.0x10(5)L/mol cm. The method is successfully applied to determine ethamsylate in pharmaceutical preparations and biological samples.

Simultaneous determination of ascorbic acid and acetaminophen at the pre-anodized inlaying ultrathin carbon paste electrode

A pre-anodized inlaying ultrathin carbon paste electrode (PAIUCPE) was constructed using simple and fast electrochemical pretreatment for the simultaneous determination of ascorbic acid (AA) and acetaminophen (ACOP). The effect of pH on peak current and peak potential for the oxidation of AA and ACOP was discussed in detail. The results showed that the size of ip of AA and ACOP was closely related to the degree of oxygen reduction reaction at the auxiliary electrode. In pH 5.00 phosphate buffer solution, a linear relationship between oxidation peak current and concentration of AA and ACOP was obtained in the range of 1.0 × 10−5 to 1.5 × 10−3 mol L−1 and 3.0 × 10−7 to 2.0 × 10−4 mol L−1, and the detection limits were estimated to be 3.10 × 10−7 mol L−1 and 2.28 × 10−8 mol L−1, respectively. The constructed electrode exhibited excellent reproducibility and stability. Moreover, this method was employed to determine AA and ACOP in Vitamin C Yinqiao Tablets with satisfactory results.

Spectrophotometric determination of cefotaxime by using sodium 1,2-naphthoquinone-4-sulfonate

A novel method is established to determine cefotaxime by using sodium 1,2-naphthoquinone-4-sulfonate (NQS) as a chromogenic reagent. A russety product can be formed owing to the nucleophilic substitution reaction between cefotaxime and NQS in 0.1 M solution of NaOH. The maximal absorption wavelength of the product is 489 nm. Absorbance is linear with the concentration of cefotaxime in the range of 3.8–114.6 mg/L, and the regression equation is A = 0.04481 + 0.00567c (mg/L), with a correlation coefficient of 0.9992. The detection limit and the RSD are 3 mg/L and 1.2%, respectively. The average recovery is in the range of 98.9–101.2%. The results indicate that the method could be applied to the determination of cefotaxime in injection.