Due to the impact of organotin compounds in the environment, a necessity exists for a rapid, sensitive and accurate analytical method to determine the levels of the compounds in the different environmental components. A variety of analytical techniques has been developed for the speciation of organotin compounds. Most of them are based on gas chromatography (GC) connected with atomic absorption spectrometry (AAS), flame photometry (FPD), mass spectrometry (MS), inductively coupled plasma (ICP) or microwave-induced plasma atomic emision spectrometry (MIP-AES). Since GC requires volatility of analytes, their derivatization into volatile species is usually indispensable. Direct GC of organotin halides without derivatization, however, could offer a highly selective and sensitive analytical technique for the trace determination at the level of less than ng l-1 in aquatic samples. As an alternative approach, high performance liquid chromatography, has become a popular technique. It mainly uses AAS, ICP-MS and fluorometry for the eluate detection. ICP-MS has been applied practically because of its inherent selectivity and sensitivity.
This work proposes a sequential injection procedure to determine the total, volatile and acid detergent insoluble nitrogen content in silage. An ammonium tubular selective electrode coupled to a sequential injection manifold was used as detector to accomplish the potentiometric determinations made after on-line ammonia diffusion in alkaline medium through a Teflon membrane and NH3/NH4+ conversion. Different sample treatments, taking into account the species to be analyzed, were adopted to apply the proposed procedure to silage samples. An analytical frequency of 30 samples h-1 and a detection limit of 3.0 mg N l-1 were observed when 300 µl of 3.0 mol l-1 NaOH solution and a sample volume of 150 µl were employed. The use of the proposed procedure allowed the automation of the determinations, low sample and reagent consumption and small waste production, emphasizing the versatility and potentiality of the flow methods when applied to animal nutrition laboratories.
Acidic electrolyzed water (acidic EW), which is prepared by the electrolysis of an aqueous NaCl solution, has recently become of great importance for disinfection in a variety of fields, including medicine, the food industry and agriculture. In a previous paper we showed that: 1) acidic EW is a mixture of hypocholorite ion, hypochlorous acid and chlorine, depending upon the pH; 2) hypochlorous acid is primarily responsible for disinfection in the case of Escherichia coli K12 and Bacillus subtilis PCI219, both in clean culture media. In practice, however, the use of acidic EW is in many cases severely hampered due to the presence of a variety of non-selective reducing agents. In view of the salient nature of acidic EW, it is therefore strongly urged to establish an optimum way to use acidic EW in a variety of systems. The present paper is the first report on our attempt along this line in order to characterize the nature of the chemical changes that the bactericidal activity of the acidic EW deteriorates in the presence of organic materials, which include amino acids and proteins.
UV/vis spectrophotometry/channel flow electrode was developed in order to determine the dissolution rate of metallic ions from the corroded metal electrode. In the present method, the relation between absorbance As and the flux of dissolved ions ψ is expressed by the following equation: As = εκψVm-2/3, where ε is molar absorptivity, κ a constant, and Vm the mean electrolyte flow rate. The present method was applied to the simultaneous determination of Fe(II) and Fe(III) dissolved from Fe during the active dissolution and the pitting initiation.
A sensitive stripping voltammetric determination of Co(II) is described, based on the selective accumulation of its complex with ammonium 2-aminocyclohexene-1-dithiocarbamate on HMDE and subsequent reduction of the complex in the presence of nitrite as a catalyst. The peak potential is about -1.35 V vs. Ag/AgCl reference electrode at pH = 10.0. The calibration graph was linear for the range of 0.01 - 40 ng/ml, with a limit of detection of 8.0 pg/ml. The relative standard deviation for ten replicate analyses of 1.0 ng/ml of Co(II) is 2.6%. The method is very selective and has been applied for the determination of cobalt in natural water and serum samples.
The potential response of an electrode based on an o-nitrophenyl octyl ether (o-NPOE)-plasticized poly(vinyl chloride) (PVC) membrane with no added ion-exchanger to several cations of different hydrophobicity was examined. Furthermore, the hydrophobicity of the cations was evaluated by measuring the selectivity coefficient, KPotNa,cation, of a sodium ion-selective electrode based on an o-NPOE-plasticized PVC membrane containing a cation exchanger, since the selectivity coefficient is closely related to hydrophobicity of the ions. From these results, the o-NPOE-plasticized PVC membrane electrode with no added ion-exchanger showed a Nernstian response to the cations for which the sodium ion-selective electrode has a selectivity coefficient, KPotNa,cation, of more than 106.0. In addition, an electrode based on only the plasticizer (o-NPOE) was fabricated by using an ion-sensitive field-effect transistor (ISFET); the response of the electrode to the cations was examined in order to evaluate the contribution of the plasticizer, itself, to the electrode response of the PVC membrane electrode with no added ion-exchanger. From the response of the o-NPOE-plasticized PVC membrane electrode and that of the ISFET electrode based on only the plasticizer to the cations, the response mechanism of the o-NPOE-plasticized PVC membrane electrode with no added ion-exchanger to the hydrophobic cations is discussed.
A method that is both simple and rapid for the determination of mercury in Chinese-prepared medicine (CPM) was developed. The method uses closed-vessel microwave digestion with final analysis by CVAAS with a sodium borohydride and hydroxylammonium hydrochloride solution. The accuracy of the method was checked using botanical-certified reference materials (BCR62, olive leaves), and close agreement with certified values was achieved. The precision of the method, based on different types of CPM samples and different analysts on different days at different levels of mercury, was found to be between 5.0 and 13.3% (relative standard deviation, n = 6). A comparison between two different types of vessels for closed-vessel microwave digestion was performed. Potential matrix interference, such as undecomposed organics and others in CPM samples, was investigated. The effect of a hydroxylammonium hydrochloride solution was also investigated, and was found to have a strong impact on the accuracy of the method. Finally, the method was used to prepare in-house reference materials. A simpler approach of using a statistical quality control (SQC) chart was used to assess the stability of the reference materials and to monitor the stability of the analytical procedures.
The ability of Triton X-100 to affect thermooptical parameters of water is used for determining the surfactant by thermal lensing. The limit of detection of Triton X-100 in the presence of pre-synthesized cobalt(III) tris-(2-nitroso-1-naphtholate) as an inert colorant is 8×10-4 mol dm-3, which is close to the critical micelle concentration of the surfactant. A method for estimating the limits of detection of thermal lensing in a given solvent system based on the reproducibility of measurements for a single sample is developed. In this approach, Triton X-100 is applied for enhancing the sensitivity of thermal lensing in aqueous solutions. For the concentrations of Triton X-100 of 0.04 - 0.1 mol dm-3, a twofold enhancement in detection limits of iron(II) with 1,10-phenanthroline and cobalt(III) with 2-nitroso-1-naphthol as model systems without any change in the sample preparation is observed.
The femtosecond transient reflecting grating (TRG) method was developed and applied to monitor the ultrafast dynamics of photo-excited carriers on Si(111) surfaces. TRG responses were measured as a function of the pump beam intensity and fringe spacing, and two relaxation components were observed. An analysis of the results has suggested that the slow component corresponds to carrier diffusion and that the fast component corresponds to a combined process between ballistic transport and carrier-carrier scattering of non-equilibrium carriers.
Condensed-phosphate templated resins were prepared by a surface template polymerization method using oleylamine as a functional surfactant, oleyl alcohol as a co-surfactant, divinylbenzene as a matrix-forming monomer, and tripolyphosphate, pyrophosphate, and phosphate as templates. When tripolyphosphate-templated resins were prepared by using oleylamine alone as surfactant, a template effect was not observed. However, we successfully templated tripolyphosphate by using, along with oleylamine and oleyl alcohol or polyethylene glycol monooleyl ether (PGME) as a co-surfactant. The thus-prepared templated resin adsorbed the template molecule more effectively than did a non-templatedresin. A resin prepared using oleyl alcohol as a co-surfactant showed a higher adsorptivity than that prepared by using PGME (n = 2, 10). The amount of oleyl alcohol to be used in resin preparation was studied, and a double molar amount of oleylamine was found optimal. We also investigated the adsorption of other anions, such as phosphate, pyrophosphate, and ferrocyanide, on the tripolyphosphate-templated resin. Pyrophosphate and ferrocyanide ions were adsorbed more effectively on the templated resin than on the non-templated. Conversely, tripolyphosphate showed less adsorptivity on the phosphate- and pyrophosphate-templated resins than on the non-templated resin.
The linear relationship between electric resistance of the packed column for capillary electrochromatography and applied voltage was observed in several different effluents and packing materials (fluorinated-bonded silica and octadecylsilane). These linear relationships had different slope values which depended on the charges on the surface of the stationary phase. If there are the negative charges on the stationary phase during the application of the electric field, the slope was negative value as observed in the fluorinated-bonded silica packed column. On the other hand, the slope was positive value in the fluorinated-bonded silica packed column using 0.1% tetrabutylammonium chloride as an effluent. The inclination of the linear relationship between the electric resistance and applied voltage also depended on the kind of the effluent, the concentration of effluent and the ratio of the organic modifier used. In the case of octadecylsilane packed column, the electric resistance of the column did not depend on the applied voltage. The relationship between the electric resistance and the electroosmotic mobility was also studied.