Microchimica Acta

Wang, Cong; Zhang, Li; Guo, Zhihua; Xu, Jigui; Wang, Hongyan; Zhai, Kefeng; Zhuo, Xin

doi: 10.1007/s00604-010-0304-6pmid: N/A

An ultrasensitive platform is presented for the determination of hydrazine by combining the high specific surface area and higher electrical conductivity of poly(sodium styrenesulfonate) (PSS) graphene nanocomposite film with amperometric detection. The PSS-graphene were synthesized by the Hummers method and used to modify a glassy carbon electrode. The material was characterized by scanning electron microscopy and is found to be suitable for sensing hydrazine. The overpotential of hydrazine on the modified electrode is 0.31 V which is lower than in many electrochemical sensors. The calibration curve for hydrazine is linear in the range from 3.0 to 300 µmol L−1, and the detection limit is as low as 1 µmol L−1. This is the first report in which such a high sensitivity and low limit of detection has been achieved. It is concluded that PSS graphene represents an efficient electron mediator for sensing hydrazine.

Pyrzynska, Krystyna

doi: 10.1007/s00604-010-0305-5pmid: N/A

The sorption behaviour of Cd(II) on three carbon-based materials including activated carbon (AC), carbon nanotubes (CNTs) and carbon-encapsulated magnetic nanoparticles (CEMNPs) which were prepared under similar conditions by nitric acid treatment were investigated. Generally, sorption of cadmium on these materials increased with the increase of pH. For AC and CNTs very similar results were obtained, while CEMNPs exhibits much higher affinity for Cd(II) despite of almost the same surface acidity. Thus, cadmium retention on tested sorbents was more dependent on the concentration of specific active sites than the total surface area available. The equilibrium sorption data were better fitted to Langmuir isotherm. The theoretical saturation capacity of the monolayer derived from this model at pH 8.0 for AC, CNTs and CEMNPs are 9.91 mg g−1, 20.37 mg g−1 and 91.0 mg g−1, respectively. The kinetic of Cd(II) sorption is fitted for pseudo-second order equation and could be described as a combination of film diffusion and intra-particle diffusion, whereby the last one dominates. The experimental parameters for preconcentration of cadmium on a microcolumn packed with CEMNPs prior to its determination by flame atomic absorption spectrometry have been investigated. Cadmium can be quantitatively retained at pH 8 from sample volumes up to 150 mL and then eluted completely with 3 mL of 0.5 mol L−1 HNO3.

Han, Juan; Wang, Yun; Kang, Wenbin; Li, Chunxiang; Yan, Yongsheng; Pan, Jianming; Xie, Xueqiao

doi: 10.1007/s00604-010-0298-0pmid: N/A

An ionic liquid-salt aqueous two-phase system (ILATPS) based on the hydrophilic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) and inorganic salt was developed for direct separation and analysis of macrolide antibiotics coupled with molecular fluorescence spectrophotometry. Liquid–liquid equilibria of [Bmim]BF4-salt aqueous two-phase systems were studied for different salts and temperatures. It was found that the salting-out ability of different salts may be related to the Gibbs energy of hydration of the ions, and the two-phase area was expanded with a decrease in temperature. The partition coefficients as well as extraction efficiencies of azithromycin and mydecamycin in [Bmim]BF4-salt aqueous two-phase system were influenced by the types of salts, concentration of salt, and the extracting temperature. Under the optimum conditions, the average partition coefficient of azithromycin in [Bmim]BF4-Na2CO3 ILATPS was 162, and that of mydecamycin in [Bmim]BF4- NaH2PO4 ILATPS was 90.9. This method has been satisfactorily applied to the determination of azithromycin and mydecamycin in real water samples with detection limits of 0.059 µg mL−1 and 0.019 µg mL−1. This extraction method is a simple, non-toxic and effective sample pretreatment technique with promise also for the separation of other small biomolecules.

Deb, Manas; Verma, Devsharan

doi: 10.1007/s00604-010-0308-2pmid: N/A

Experimental parameters were optimized for rapid and precise determination of ammonium ion by FTIR spectroscopy in presence of nitrate ion in water and in samples collected from humans. Nitrates, whose FTIR spectra strongly overlap with those of ammonium ion, were removed from the sample matrix by treating it with zero-valent iron nanoparticles in acidic medium. The infrared peak at 1,400 cm−1 was selected for determination of ammonium ion. Diffuse reflectance FTIR gives both qualitative and quantitative information on ammonium in a KBr matrix. The limit of detection and the limit of quantification of the method are 0.15 ng per 20 µL−1, and 0.5 ng per 20 µL−1, respectively. The relative standard deviation is 6% (n = 8). The results were compared to those of ion chromatography and show a high degree of acceptability. The method can be applied over a wide concentration range using small sample volumes.

Tu, Xinman; Luo, Xubiao; Luo, Shenglian; Yan, Liushui; Zhang, Feng; Xie, Qingji

doi: 10.1007/s00604-010-0307-3pmid: N/A

A method is presented for the carboxylation of multiwalled carbon nanotubes (MWCNTs) via a two-step process. The hydroxy groups of MWCNTs were first reacted with epichlorohydrin, then with iminodiacetic acid. The resulting MWCNTs were characterized by means of Fourier transform infrared spectroscopy and transmission electron microscopy. The glassy carbon electrode modified with the MWCNTs thus prepared exhibited enhanced electrocatalytic activity and good stability for the determination of guanine and adenine in pH 7.0 phosphate buffer solution. The experimental parameters were optimized, and a direct electrochemical method was developed for the simultaneous determination of guanine and adenine. The detection limits (at S/N = 3) for guanine and adenine are 0.02 and 0.08 μM, respectively. A sensitive method was also developed for the determination of guanine and adenine in calf thymus DNA.

Sun, Qian; Yuan, Dongxing; Chen, ZuLiang; Megharaj, Mallavarapu; Naidu, Ravendra

doi: 10.1007/s00604-010-0311-7pmid: N/A

Metal ions, in the form of their EDTA complexes, can be separated and determined by ion chromatography coupled to inductively coupled plasma mass spectrometry (ICP-MS). However, polyatomic interferences can occur during ICP-MS process and this requires techniques for removing or reducing them. ICP-MS combined with an octopole reaction system was used to reduce polyatomic interferences during the detection of metal ions (55Mn, 56Fe, 59Co, 60Ni, 63Cu, 64Zn, 208Pb) as their EDTA complexes followed by the separation of IC. The results indicated that polyatomic interferences can be reduced for the detection of 56Fe, 60Ni, 63Cu and 64Zn if either helium or hydrogen gas was added to the collision/reaction cell. Hydrogen was preferred since it resulted in higher sensitivity and lower background intensity. The separation of seven metal ions was achieved on an anion-exchange column within 7 min using diammoniumhydrogen phosphate buffer of pH 7.5 as the mobile phase. The detection limits were in the range of 0.1–0.5 μg L−1 with the exception of Fe (5.0 μg L−1) if hydrogen was the reaction gas. The method was applied to the determination of metal ions in natural water samples.

Babu, T.; Ramachandran, T.; Nair, Bipin

doi: 10.1007/s00604-010-0306-4pmid: N/A

A non-enzymatic sensor was developed for the determination of glucose in alkaline medium by anodisation of copper in sodium potassium tartrate solution. The morphology of the modified copper electrode was studied by scanning electron microscopy, and its electrochemical behavior by cyclic voltammetry and electrochemical impedance spectroscopy. The electrode enables direct electrocatalytic oxidation of glucose on a CuO/Cu electrode at 0.7 V in 0.1 M sodium hydroxide. At this potential, the sensor is highly selective to glucose even in the presence of ascorbic acid, uric acid, or dopamine which are common interfering species. The sensor displays a sensitivity of 761.9 μA mM−1 cm−2, a linear detection range from 2 μM to 20 mM, a response time of <1 s, and a detection limit of 1 μM (S/N = 3). It was tested for determination of glucose level in blood serum.

Morante-Zarcero, Sonia; Sánchez, Alfredo; Fajardo, Mariano; Hierro, Isabel; Sierra, Isabel

doi: 10.1007/s00604-009-0287-3pmid: N/A

A hexagonal mesoporous silica (HMS) functionalized with a 5-mercapto-1-methyltetrazole derivative was employed to prepare a chemically modified carbon paste electrode for Pb(II) detection in aqueous solution by square wave adsorptive stripping voltammetry. The optimal operating conditions were 5 min preconcentration time at pH 6.5, and 120 s electrolysis time in 0.2 mol L−1 HCl. Under these conditions, the voltammetric signal increased linearly with the preconcentration time in the range 1 to 10 min and with the Pb(II) concentration in the range 1 to 100 µg L−1. The electrode was reproducible and sensitive. Simultaneous determination of Pb, Cd and Cu was also carried out with the electrode. The accuracy of the method was validated by analysing Pb(II) in tap water and groundwater samples.

Li, Yan; Wang, Peng; Wang, Xin; Cao, Ming; Xia, YunSheng; Cao, Chun; Liu, MeiGui; Zhu, ChangQing

doi: 10.1007/s00604-010-0310-8pmid: N/A

A method for determination of vitamin B1 has been developed that is based on the enhancement effect of vitamin B1 on the luminescence of water-soluble CdTe nanorods modified with thioglycolic acid and cysteine. The effect of variables including the size of the nanorods on the enhancement of luminescence have been investigated. A preliminary mechanistic study showed that the passivating action of vitamin B1 on the surface of the CdTe nanorods is likely to be responsible for the enhancement. Interferences by shortwave fluorescence are effectively eliminated because measurements are performed in the near-infrared. Due to the near-infrared measurement character, the fluorescence interference of vitamin B2 can be effectively eliminated. Under the optimum conditions, the extent of luminescence enhancement is proportional to the concentration of vitamin B1 in the range from 0.1 to 3.0 μmol L−1 and the detection limit is 0.03 μmol L−1. The relative standard deviation for 2.0 μmol L−1 vitamin B1 is 1.3% (n = 6). The method is highly sensitive and selective, avoids the sample treatment needed in other procedures, and can be applied to the determination of vitamin B1 in real samples with satisfactory results.

Li, Shifeng; Tao, Shanjun; Wang, Fenfen; Hong, Jianguo; Wei*, Xianwen

doi: 10.1007/s00604-010-0302-8pmid: N/A

The chemiluminescence (CL) of luminol–H2O2 system is strongly enhanced on addition of nanoparticles composed of a gold/silver alloy (ratio 5:4). The effect is attributed to a catalytically enhanced decomposition of H2O2 to produce reactive oxygen species. A reaction mechanism is proposed. Organic compounds containing hydroxy, amino, or thiol groups (such as amino acids, dopamine, pyrocatechol) can inhibit the CL signal of the system. It is concluded that the system has a large potential in terms of the determination of such compounds.