In a pH 2.3 - 3.0 acid medium, the resonance Rayleigh scattering (RRS) intensity is greatly enhanced when vitamin B1 reacts with Methyl Orange to form an ion-association complex. The maximum RRS peak appears at 588 nm, another higher peak is at 403 nm and there are two smaller RRS peaks at 800 nm and 288 nm. The RRS intensity is directly proportional to the concentration of vitamin B1 in the range of 0 - 400 ng ml-1. The method has high sensitivity and the detection limit (3σ) for vitamin B1 is 7.2 ng ml-1. The effects of coexisting substances on the determination of vitamin B1 were investigated, and the results show that this method has good selectivity and can be applied to the direct determination of vitamin B1 in composite vitamin B tablets and multivitamin tablet samples.
A spectrofluorometric method for the determination of ascorbic acid (AA) based on its activation on the hemoglobin-catalyzed reaction was proposed. The fluorescence intensity of the product was measured under the optimal experimental conditions, i.e. 4.0 × 10-6 M H2O2, 6.0 × 10-5 M p-cresol, 1.2 M NH3-NH4Cl (pH 10.4) and 2.0 × 10-7 M hemoglobin. The order of additions of the reagents was also studied. The activation of AA was found to be associated with a high ammonia concentration. The linear range of the method was 9.0 × 10-10 - 3.6 × 10-8 M of AA. The detection limit was calculated to be 3.0 × 10-10 M. The relative standard deviation of this method is 1.6% at 7.0 × 10-9 M for 11 determinations.
A simple and highly sensitive spectrophotometric method for the determination of biologically active thiols based on the fading of eosin-silver(I)-adenine ternary complex was established. In the determination of 6-mercaptopurine (MP), Beer’s law was obeyed in the range 0.02 - 0.30 µg ml-1, with an effective molar absorptivity at 562 nm and the relative standard deviation being 3.5 × 105 dm3 mol-1 cm-1 and 0.72% (n = 5). Analytical data for various biologically active thiols were determined with the proposed method. This method is about 5 - 10 times more sensitive than the conventional spectrophotometric methods. A compound having a disulfide bond (-S-S-), such as cystine, could also be determined by the conversion of disulfides to free thiols with the sulfite ion. The procedure was successfully applied to assays of various biologically active thiols in actual medicines.
A PVC membrane electrode for lead ions based on phenyl disulfide as the membrane carrier was developed. The electrode exhibits a good Nernstian slope of 29.3 ± 0.7 mV/decade and a linear range of 2.0 × 10-6 - 1.0 × 10-2 M for Pb(NO3)2. The limit of detection is 1.2 × 10-6 M. It has a response time of 45 s and can be used for at least fifty days without any divergence in potential. The proposed membrane sensor revealed high selectivity for Pb2+ over a wide variety of other metal ions and could be used in the pH range of 3.5 - 6.3. The electrode was used as an indicator electrode in potentiometric titration of lead ions.
Trace amounts of thallium(I) can be determined using adsorptive cathodic stripping voltammetry in the presence of Xylenol Orange (XO). The reduction current of the thallium(I)-XO complex ion was measured by square-wave cathodic stripping voltammetry. The peak potential was at -0.44 V vs. Ag/AgCl. The effect of various parameters (pH, ligand concentration, accumulation potential and collection time) on the response are discussed. The response was linearly related to the thallium concentration in the range 0.5 - 110 ng ml-1 and 110 - 2000 ng ml-1. The limit of detection was 0.2 ng ml-1. The relative standard deviation for the determination of 80 ng ml-1 thallium was 2.8%. Many common anions and cations did not interfere with the determination of thallium. The interference of lead was reduced by the addition of 0.003 M sodium carbonate. The voltammetric procedure was then successfully applied to the determination of thallium in various complex samples.
The electrochemical behavior of 2′-halogeno-N,N-dimethyl-4-aminoazobenzene derivatives was investigated using various polarographic and voltammetric methods. The peak potentials of these derivatives were observed to shift towards negative values along with an increase in the pH. A reduction of the azo linkage took place via two electrons at pH > 4, but four electrons at pH < 4 in aqueous-ethanol mixtures. The standard rate constants were determined with (Laviron technique) or without (Nicholson technique) taking the adsorption phenomena into account. The diffusion coefficients were calculated from the cyclic voltammetric data using a method developed by Garrido. The amount of adsorbed substances and transfer coefficients for the electron transfer were also determined. A mechanism for the electrode reaction is proposed. These compounds can be quantitatively determined between 1 × 10-5 M and 1 × 10-7 with DPP and CV.
On December 1997, 94 corpses of green turtles, Chelonia mydas, were found at the Ojo de Liebre lagoon (OLL) adjacent to the industrial operation of Exportadora de Sal S. A (ESSA), the largest saltworks in the world, owned by the Mexican Government and Mitsubishi Corporation, located in Baja California Sur, Mexico. Every year about 551 × 106 m3 of seawater is solar evaporated, producing 7 × 106 tons of salt and 24.6 × 106 m3 of bitterns, the latter being discharged into the OLL, which is a costal lagoon of the Pacific Ocean. ESSA claimed that bitterns contain the same salts present in seawater, but 20-fold more concentrated than the former. Ion chromatography with a conductivity detector and ion suppression was used to determine the F-, Cl-, SO42- and CO32- contents of seawater, brines and bitterns collected at ESSA. Furthermore, the osmolality of brines and bitterns from ESSA was measured. F- content in bitterns was 60.5-fold more than that in seawater. The bitterns osmolality was 11000 mosm/kg of water, whereas the turtle’s plasma osmolality was about 400 mosm/kg of water. We concluded that the dumping of bitterns into the ocean should be avoided.
The changes in the oxidation state of vanadium in artificial and natural seawater samples were studied by electrothermal atomic absorption spectrometry (ETAAS) with a direct injection of a resin suspension. V(IV) and V(V) were extracted as the complex with Chromazurol B and with N-cinnamoyl-N-2,3-xylylhydroxylamine, respectively, using a suspension of an anion-exchange resin and determined by ETAAS independently. The detection limits of both methods were 0.02 ng ml-1 for 40 ml of a sample solution. The recovery tests for an artificial seawater sample spiked with V(IV) and/or V(V) were carried out carefully. The results showed that the recoveries of V(IV) or V(V) were 99.2 - 109% and the standard deviations were 1 - 6%. The total V was also determined after V(V) was reduced by ascorbic acid. In artificial seawater at pH 7.8, V(V) was stable but V(IV) was oxidized rapidly. In acidified artificial seawater (pH 2.0), V(IV) was oxidized slowly but only a small tendency of such reduction of V(V) was observed. In a natural seawater sample, V(IV) was not detected. The acidification of the natural seawater sample resulted in the reduction of V(V).
To predict the 1-octanol/H2O partition coefficient, log P, based on molecular structures, we calculated the solvent accessible surface area and the solvation energy difference of 166 organic molecules between 1-octanol and water environments with the ab initio molecular orbital self-consistent reaction field method, and then analyzed the relationships among the measured log P values with these two structural quantities by multiple linear-regression analyses. Physicochemically meaningful correlations were obtained, suggesting that non-hydrogen bonding and hydrogen-acceptor molecules behave similarly to each other in partitioning, but that hydrogen-donor molecules behave differently from the former molecules. The results provide a new computational approach for predicting log P.
The resolutions of metal-4-(2-pyridylazo)resorcinol chelates by capillary zone electrophoresis (CZE) were investigated in the presence of some interacting reagents; also, equilibrium reactions between the chelates and the interacting reagents were analyzed in an aqueous solution. Among nine metal chelates formed in aqueous solution, the chelates of VV, FeII, CoIII, NiII, and CuII were resolved and detected by CZE, while other chelates were decomposed during electrophoretic migration. The electrophoretic mobility of the chelates of FeII, NiII, and CuII increased with increasing pH of the migrating solution; also, the acid-dissociation constants of these three chelates were determined by analyzing the mobility change. The ion-association constants of the five anionic chelates and pyridylazoresorcinolate ion with quaternary ammonium ions were also determined by analyzing the mobility change. The binding behavior of the ligand and its chelates with nonionic surfactant micelle, as well as with polyethylene glycol, were investigated, and their binding constants were determined through the mobility change. When Brij 35 was used as a nonionic surfactant interacting with the anionic chelates, the FeII chelate decomposed at Brij 35 concentrations over 6.67 mM. The equilibrium constants and the reactivity were compared with each other.
The high toxicity of the cyanide ion at low concentration necessitates its analysis in a variety of environmental samples with a very low cyanide content. A new sensitive spectrophotometric method has been developed for the trace determination of cyanide with ninhydrin (NH) in an alkaline medium. Beer’s law is obeyed in the range of cyanide concentration 0.04 - 0.24 μg cm-3, and the molar absorptivity at 590 nm is 2.20 × 105 dm3 mol-1 cm-1. The Sandell’s sensitivity of the product is 0.000118 μg cm-2. The optimum reaction conditions and other important analytical parameters have been investigated. The results obtained by using the proposed method for environmental samples agree well with those obtained by the Aldridge standard method.