A coated-wire ion-selective electrode (ISE) based on cyclam (1,4,8,11-tetraazacyclotetradecane) as a neutral carrier in a polyvinyl chloride (PVC) matrix was fabricated for the determination of Ag(I) ions. The coated-wire ISE exhibited a linear Nernstian response over the range 1 × 10-1 to 1 × 10-7 M with a slope of 59 ± 2 mV per decade change and a detection limit of 5 × 10-8 M. The ISE shows a greater preference for Ag over other cations with good precision. The electrode was selective towards Ag(I) ions in the presence of 13 different metal ions tested. The selectivity coefficients (Kij) were determined for Na(I), K(I), Mg(II), Ca(II), Ba(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II). The selectivity coefficients of these cations are in the range of 10-4 to 10-2. This ISE was used for the determination of free silver and total silver in electroplating bath solutions, additives and brighteners.
A detailed study using the cyclic voltammogram was done on the live cells of Aspergillus terreus. The peak current values were obtained for different days of growth and plotted against time. The response of cyclic voltammogram showed the phases of the growth of the fungus. The growth curve obtained matched well with the conventional methodology, which assesses the increase of dry weight of the organisms against time. The electrochemical method is more advantageous because it is easy to assess and consumes less time. Further the electrochemical method clearly shows the decline phase which is generally not very defined in the conventional method of assessment of the growth curve. It was confirmed by further experiments that the metabolites were responsible for the anodic peak and not the biomass. Further work is in progress in order to analyze the metabolite(s) that is/are responsible for the anodic peak.
A silicone ladder-type polymer was successfully utilized for a matrix of an ion sensing membrane to fabricate an ion-sensitive field-effect transistor. An ion sensing membrane was readily fabricated by mixing a silicone ladder-type oligomer with a quaternary ammonium salt, casting onto the gate of the field-effect transistor, and polymerizing with heating. Since no acid catalysts were needed to prepare the ion sensing membrane, it was possible to keep the quaternary ammonium salt in the matrix without decomposition. The ion-sensitive field-effect transistor based on the silicone ladder-type polymer and the quaternary ammonium salt showed a linear response with a slope of -58.1 mV decade-1 very close to the theoretical Nernstian response over an NO3- range between 3.0 × 10-6 and 1.0 × 10-1 M. The time required to reach 90% total response was within 5 s, when the NO3- concentration was changed from 1.0 × 10-3 to 3.0 × 10-3 M. The newly fabricated ion-sensitive field-effect transistors have kept their original sensitivity for more than half a year.
A facile supported liquid membrane (SLM) system for the selective and efficient transport of silver ion is introduced. The SLM used is a thin porous polyvinyldifluoride membrane impregnated with hexathia-18-crown-6 (HT18C6) dissolved in nitrophenyloctyl ether. HT18C6 acts as a specific carrier for the uphill transport of Ag+ ion as its picrate ion paired complex through the SLM. In the presence of thiosulfate ion as a suitable stripping agent in the strip solution, transport of silver occurs almost quantitatively after 4 h. The selectivity and efficiency of silver transport from aqueous solutions containing other Mn+ cations such as Mg2+, Ca2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+, Hg2+, Fe3+ and Cr3+ ions were investigated.
In the present paper, nitrate and nitrite in foodstuffs and saliva were simultaneously determined using a non-suppressed ion chromatography (IC) method with a bulk acoustic wave sensor (BAW) as detector, and 1.5 mmol/L potassium hydrogenphthalate (KHP) as mobile phase. The IC-BAW method is simple, rapid and accurate. The determination limits for nitrite and nitrate are 0.20 and 0.30 mg/L, respectively. The IC-BAW is comparable and agrees with the conventional spectrophotometric method for nitrite and nitrate determination.
High-performance liquid chromatography using a Chrompack P-300-RP column containing a polystyrene-divinylbenzene copolymer-based packing was examined to analyze bovine milk protein components. The separation of major raw-milk proteins could be performed rapidly and reliably with this HPLC/UV method. The determinations were performed in the linear ranges of 0.01 - 2.0 mg/ml for α-lactalbumin, 0.04 - 2.5 mg/ml for caseins and 0.02 - 2.0 mg/ml for β-lactoglobulin. The validity of the method was verified. Since the chromatographic column enabled the quantification of only “native” milk proteins, the extent of denaturation and loss of milk proteins could be examined. Thus, evaluation of heat-induced proteins denaturation was carried out in raw milk heated for 5 min at pre-determined temperatures.
Reversed-phase HPLC conditions for separation of chlorophyll (Chl) a, Chl a′ (the C132-epimer of Chl a), pheophytin (Pheo) a (the primary electron acceptor of photosystem (PS) II), and phylloquinone (PhQ) (the secondary electron acceptor of PS I), have been developed. Pigment extraction conditions were optimized in terms of pigment alteration and extraction efficiency. Pigment composition analysis of light-harvesting complex II, which would not contain Chl a′ nor Pheo a, showed the Chl a′/Chl a ratio of 3 - 4 × 10-4 and the Pheo a/Chl a ratio of 4 - 5 × 10-4, showing that the conditions developed here were sufficiently inert for Chl analysis. Preliminary analysis of thylakoid membranes with this analytical system gave the PhQ/Chl a′ ratio of 0.58 ± 0.03 (n = 4), in line with the stoichiometry of one molecule of Chl a′ per PS I.
Normal-phase HPLC conditions have been developed for separating the C173 isoprenoid isomers, which are expected to be formed as biosynthetic intermediates of chlorophyll (Chl) a, Chl a′ (C132-epimer of Chl a), pheophytin (Pheo) a and protochlorophyll (PChl). The application of these conditions to pigment composition analysis of greening etiolated barley leaves allowed us to detect, for the first time, the C173 isomers of Chl a′, a possible constituent of the primary electron donor of photosystem (PS) I, P700, and those of Pheo a, the primary electron acceptor of PS II, in the very early stage of greening. The C173 isomer distribution patterns were approximately the same between Chl a and Chl a′, but significantly different between Pheo a and Chl a′, probably reflecting the similarity and difference, respectively, in the biosynthetic pathways of these pigment pairs.
This study outlines some observations of the pressure effect for gas phase ion-molecule reactions of anthraquinone derivatives with dimethyl ether in an external source ion trap mass spectrometer. At the reagent pressure of 7.998 × 10-2 Pa, formation of the protonated ions, [M + 13]+, [M + 15]+, and [M + 45]+ ions, of anthraquinones can be observed. However, at the pressure of 1.066 × 10-2 Pa, formation of molecular ions and many fragment ions of the M+· or [M + H]+ ions have been observed. Since the pressure effect is notable within a small range of pressures for many compounds, it is important to draw attention to the use of the ion trap with an external source where other factors such as ion source residence time may play a role. This can also provide some information for better and more careful controls of the reagent pressure in order to obtain fair CI spectra in an external source ion trap mass spectrometer.
An analytical method, referred to as “derivatization-electron probe X-ray micro-analysis (XMA)”, has been developed to determine the distribution of a small amount of the functional groups in a polymer. The suitable conditions for the derivatization reaction with epoxy groups, which contribute to the hardening reactions of polymers, were investigated. It was found that epoxy groups in polymers were derivatized selectively using gas-phase esterification with hydrochloric acid (HCl). The most suitable amount of HCl in a 50 ml vial was 300 µl. After setting a sample in the vessel without directly contacting the reagent, by reacting the reagent and the sample at 25°C for 1 h, the highest reaction yield and selectivity were obtained. By derivatization-XMA using this reaction condition, the measurement of the distribution of epoxy groups in the polymer became feasible. Actual applications to a depth analysis of epoxy groups in the hardened acrylic coating and epoxy resin proved that this method is useful for the characterization of polymers and for the study of the hardening reaction of polymers.
A new approach to sample digestion, subsequent vaporization and introduction to an inductively coupled plasma (ICP) atomic emission spectrometer was developed for the direct determination of magnesium. To each small sample cuvette made of tungsten, a ground rock sample was precisely weighed. The cuvette was situated on a tungsten boat furnace. Ammonium fluoride solution was added to the cuvette as a chemical modifier. After the on-furnace digestion has been completed, the analyte, magnesium, in the cuvette was vaporized and introduced into the ICP atomic emission spectrometer. Since the powdered samples were wet-digested in the sample cuvettes prior to vaporization, they could be analyzed by using a calibration curve prepared from aqueous standard solutions. This method was applied to the determination of magnesium in several standard reference materials with satisfactory results.
For human urine beryllium (Be), each sample (500 µl) was diluted (1+1) with Nash reagent (containing 0.2% (v/v) acetylacetone and 2.0 M ammonium acetate buffer at pH 6.0) and then a 20-µl volume of Triton X-100 (0.4%, v/v) aqueous solution was added. An aliquot (10 µl) of the diluted urine mixture was introduced into a graphite cuvette and was atomized according to a temperature program. The method detection limit (MDL, 3σ) for Be was 0.37 µg/l in the undiluted urine sample and the calibration graph was linear up to 65.0 µg/l. Calibration graphs were prepared by the standard addition method. Accuracies of 98.6 - 102% were obtained when testing standard reference material (SRM 2670) freeze dried human urine samples. Precision (relative standard deviation, RSD) for urine Be was ≤2.3% (within-run, n = 5) and was ≤3.0% (between-run, n = 3). For human urine and serum selenium (Se), samples (100 µl) were diluted with HNO3 (0.2%, v/v) to make a (1+1) dilution for urine analysis or a (1+4) dilution for serum analysis. An additional aliquot (10 µl) of Triton X-100 (0.1%, v/v) was added to each 200 µl of (1+1) diluted urine (or 20 µl of the Triton X-100 was added to each 500 µl of (1+4) diluted serum) sample. After the diluted sample mixture (10 µl) was introduced into a graphite cuvette, the corresponding chemical modifier (10 µl, containing Ni2+ + Pd + NH4NO3 in HNO3 (0.2%, v/v)) was added to it and the mixture was atomized. The MDL (3σ) for Se in urine and in serum was 4.4 and 21.4 µg/l in undiluted sample, respectively, and the calibration graphs were linear up to 150 and 400 µg/l. Accuracies of urine Se were 98.9 - 99.4% by testing SRM 2670 (NIST) urine standards with RSD (between-run, n = 3) within 2.9%; and that of serum Se was 97.2% when testing a certified second-generation human serum (No. 29, #664) with RSD (between-run, n = 3) of 1.4%. The proposed method can be applied easily, directly, and accurately to the measurement of Be and Se in real samples (including six urine Se and four serum Se from patients of Blackfoot Disease in Taiwan).
A simple, rapid and sensitive spectrophotometric method for the assay of certain adrenergic drugs, [pyrocatechol (PC), levodopa (LD), methyldopa (MD) and dopamine (DP)] is described. The method involves the oxidation of o-dihydroxybenzene derivatives by K2CrO4 followed by oxidative coupling with sulfanilic acid (SPA), leading to the formation of a red or violet colored product having maximum absorbance at 490 - 495 nm for LD, MD and DP or at 560 nm for PC. This method has been successfully applied to the determination of LD, MD and DP in tablets and injections of pharmaceutical preparation. The common excipients do not interfere with the proposed method. A statistical comparison of these results with those of a reported method shows good agreement and indicates no significant difference in precision.
The on-chip derivatization of nitrite ions with 2,3-diaminonaphthalene (DAN) utilizing a pH gradient formed in a Y-shaped microchannel was investigated. Nitrite ions react with DAN at low pH, and strongly fluoresced at high pH. Therefore, a reaction at low pH followed by the addition of a strong alkaline solution is the usual procedure in a batch scheme. However, a strong alkaline solution, like an NaOH aqueous solution, erodes the wall of the microchannels in substrates made of glass or polymers, and has not been considered suitable for use in microchannels. We first investigated the derivatization reaction and fluorescent properties of nitrite ions with DAN. We found that the on-chip fluorescent derivatization reaction and detection without the addition of an alkaline solution is possible by controlling the pH values of the nitrite solution and the DAN solution to form a suitable pH gradient by utilizing a buffering effect of triethanolamine solution, which is used as an NO2 gas-absorption medium. These results have suggested the feasibility of novel reaction schemes which can provide the desired products due to a controlled pH gradient in the microchannels, as well as the possibility of an on-site monitoring microchip device for ambient NO2.
Coumarin-6-sulfonyl (6-CS) amino acid derivatives form inclusion complexes with α- and β-cyclodextrins (CD) in aqueous solution. The stoichiometry of the inclusion complex and the equilibrium constant were investigated. Using a fluorescence technique and alanine-β-CD as a model, a 1:2 guest-host complex was established, and K = 4.7 × 105 mol-2 l2 was obtained. Fluorescence enhancement was observed for all derivatives studied, with glycine exhibiting a greater enhancement, and tyrosine showing the least. The stability of the inclusion complex was found to depend on the respective sizes of the guest-host complex and their interaction.
Spectroelectrochemical properties of monosilane bridged diphenylamine (5,10-dihydro-2,8-diphenyl-5,10,10-trimethylphenazasiline, Phenaz) and disilane bridged diphenylamine (2,8-diphenyl-10,11-dihydro-10,11-disila-5,10,10,11,11-pentamethyldibenzo[b,f]azepine, DSiAzep) were investigated. The electrochemical oxidation of Phenaz was reversible and its cyclic voltammogram was almost the same shape as that of diphenylamine (DPA). The electrochemical oxidation of DSiAzep was followed by irreversible reactions leading to the cleavage of the Si-Si bond. On electrochemical oxidations of Phenaz and DPA, the formation of a stable radical cation was observed with UV-Vis spectroscopy. In comparison with the absorption characteristics of oxidized radical cations, it was seen that the oxidized radical cation of Phenaz was more delocalized than that of DPA. In the same way, absorption characteristics of oxidized DSiAzep were observed to be different from those observed in Phenaz and DPA.