An oligonucleotide tends to release hydrogen atoms from a phosphoric acid group and to form negative ions that can be detected by mass spectrometry. Usually, with a solution-spray based ionization technique, the negative ions are present in different charge states. Ion formation for the nucleotide is quite complicated and is easily influenced by matrix and other constituents in a sample solution, as well as by the operating parameters for a mass spectrometer. In this work, we studied oligonucleotide ion formation by using an ion trap mass spectrometer combined with a sonic spray ionization (SSI) source. An oligonucleotide with 20 bases was measured. Effects from contaminants and parameters affecting the ion production, such as a high voltage applied to the ionization source and sample solution-flow rate, were investigated. Our results showed that an ion with about one charge for every three bases was most abundant. However, the signal intensity and the mass spectrum pattern were sensitive to the matrix and operating parameters. One of the reasons for such sensitivity is that there are various ion states for an oligonucleotide. Any change in the matrix or an operating parameter may shift the balances between the ion states. Adding Tris, or (hydroxymethyl)aminomethane, enhanced the signal intensity of the oligonucleotide and promoted formation of the oligonucleotide ion with higher charges, while adding acetic acid favored the ions with lower charges, compared with that obtained in the medium without adding Tris and acetic acid. The effects on charged droplets and chemical enhancement were investigated. The mechanism for oligonucleotide ion formation is discussed.
The fluorescence spectral characteristics and interaction of bis(ethylene)tin(bis(salicylidene)ethylenediamine)[Et2Sn(salen)] with DNA are described. The polarity of the solvent has a strong effect on the fluorescence characteristics of Et2Sn(salen). Et2Sn(salen) bound to DNA showed a marked decrease in the fluorescence intensity with a bathochromic shift of the excitation and emission peaks. A hypochromism in the UV absorption spectra was also observed. KI quenching and competitive binding to DNA between Et2Sn(salen) and ethidium bromide (EB) were studied in connection with other experimental observations to show that the interactive model between Et2Sn(salen) and DNA is an intercalative one. The pH and salt effect on the fluorescence properties was also investigated. The intrinsic binding constant was estimated to be 1.071 × 105 mol L-1 in base pairs and the binding site number is 1.98, respectively. A linear relationship between F/F0 and the concentration of calf thymus DNA covers 5.1 × 10-6 - 2.41 × 10-4 mol L-1, which can be utilized for determining traces of calf thymus DNA with a detection limit of 1.1 × 10-7 mol L-1 in base pairs.
A piezoelectric immunosensor was developed for detecting Mycobacteria Tuberculosis (M. TB). Protein A was modified onto a silver-coated piezoelectric quartz-crystal sensor. Antibodies could be bond onto the crystal surface in an ordered orientation through protein A. An impendence analyzer was employed to record the admittance-frequency curve. The experimental results showed a successful and less-rigid bonding of protein A and antibodies. Compared with other traditional detection methods of TB, the method suggested in this paper was sensitive, selective and effective. The nonspecific response was limited by using control antibody-rabbit anti-honey bee venom (anti-HBV). A glycine-HCl buffer solution (pH = 2.4) was used to release antibodies from a crystal coated with protein A, and 0.5 mg/mL anti-TB was used to remove TB from a crystal that was bonded by an antibody. Good reusability was exhibited. Spike samples of sputum and saliva from normal people with and without adding M. tuberculosis were diagnosed using the proposed method. Good results were obtained.
A novel piezoelectric immunosensor has been developed for the determination of β-indole acetic acid (IAA) in dilute solutions. The detection is based on competitive immunoreaction between a hapten (IAA) and an antigen (IAA-BSA, hapten-protein conjugation) bound to an anti-IAA antibody, immobilized on a quartz crystal microbalance (QCM). The frequency change (y) of the sensor caused by antigen is linearly related to the logarithm of the concentration of IAA (x) in the range of 0.5 ng/ml - 5 μg/ml with a regression equation of the form y = -23x + 151 (r = 0.9937).
A CE method for investigating the chemico-physical characteristics of the active components of low molecular weight in Gastrodia elata Bl. is described. First, the dissociation constants of five active components were determined based on the relation between the effective mobility of the solutes and the buffer pH value. Second, an equation that describes the relation of the migration time and the molecular weight was developed and used to predict the migration order and to calculate the electroosmotic velocity. The results predicted by theory agreed well with that from experiments.
The electrochemical behavior of thiamine on a self-assembled electrode of L-cysteine (Cys/SAM/Au) has been investigated and Cys/SAM/Au can be used to detect thiamine using square-wave voltammetry (SWV). At pH 11.40 Britton-Robinson buffer, thiamine exhibits a well-defined anodic peak on Cys/SAM/Au. Under the optimized conditions, the anodic peak current of SWV was linear with the content of thiamine in the range of 1.1 × 10-8 - 2.2 × 10-6 mol/L; the detection limit was 5.5 × 10-9 mol/L. The method was successfully applied to the determination of thiamine in pharmaceutical preparations.
We report on the selective determination of tryptophan, using a carbon paste electrode coated with an overoxidized polypyrrole film. Out of 21 protein amino acids, only tryptophan and tyrosine exhibited an oxidative voltammetric response with this electrode. Tryptophan, which was preferentially concentrated to the electrode under an open circuit condition, was determined by the stripping voltammetric technique with a linear response range of 10-100 μM. For the determination of 10 μM tryptophan, interference from a 15-fold excess of tyrosine gave an positive error of 6%, while the other amino acids did not exhibit any detectable interference.
In this paper, the synthesis of a novel ionophore, chloro[5,10,15,20-tetrakis[2-(2,3,4,6-tetraacetyl-β-D-glucopyranosyl)-1-O-phenyl]porphinato]manganese (MnT(o-glu)PPCl), and its application as a neutral carrier for a PVC membrane electrode are described. The MnT(o-glu)PPCl-based PVC membrane electrode shows a potentiometric responses to SCN- over a concentration range of 3.4 × 10-7 - 1.0 × 10-1 mol L-1 with a Nernstian slope and a response time of 20 s. The electrode exhibits an anti-Hofmeister selectivity toward SCN- with respect to common coexisting anions. As active materials, MnT(o-glu)PPCl shows better selectivity toward SCN- than chloro(tetraphenylporphinato)manganese (MnTPPCl). The effect of the electrode membrane compositions has been studied and the experimental conditions were optimized. The electrode was applied to the determination of SCN- in body fluids with satisfactory results.
Uranium(VI) is adsorbed as a uranium trifluoroethylxanthate (TFEX)-cetyltrimethylammonium (CTMA) ion-pair complex on microcrystalline naphthalene quantitatively in the pH range 4.2 - 7.0. Without cetyltrimethylammonium as the counter ion, the adsorption is hardly 70%. The metal has been desorbed with HCl and determined with a differential pulse polarograph. Uranium can alternatively be quantitatively adsorbed on TFEX-CTMA-naphthalene adsorbent packed in a column at a flow rate of 1 - 5 ml/min and determined similarly. A well-defined peak has been obtained in this medium at -0.20 V versus a saturated calomel electrode. Cyclic voltammetry, differential pulse polarography and D.C. polarography studies indicate that uranium has been reduced irreversibly under these conditions. The detection limit is 0.30 μg/ml at the minimum instrumental settings (signal-to-noise ratio of 2) (with a preconcentration factor of 10, the detection limit would be 30 ng/ml for uranium when the volume in the cell is 15 ml). However if the volume in the cell is 5 ml, it would have been 10 ng/ml with a preconcentration factor of 30. Linearity is maintained in a concentration range of 0.5 - 19.0 μg/ml (2.1 - 79.83 × 10-9 M) with a correlation factor of 0.9994 and a relative standard deviation of ±1.1% (in this case 7.5 μg may be concentrated from 150 ml of the aqueous sample where its concentration is as low as 50 ng/ml). Various parameters, such as the effect of the pH, volume of the aqueous phase, flow rate and the interference of a large number of metal ions and anions on the determination of uranium, have been studied in detail to optimize the conditions for its trace determination in various complex materials, like alloys, coal fly ash, biological, synthetic, and waste-water samples.
A very simple, ultra-sensitive and highly selective non-extractive spectrophotometric method for the determination of trace amount of molybdenum(VI) using 5,7-dibromo-8-hydroxyquinoline (DBHQ) has been developed. 5,7-Dibromo-8-hydroxyquinoline reacts in a slightly acidic solution (0.05 - 1.0 M H2SO4) with molybdenum(VI) to give a deep greenish-yellow chelate which has an absorption maximum at 401 nm. The reaction is instantaneous and the absorbance remains stable for over 24 h. The average molar absorption coefficient and Sandell’s sensitivity were found to be 4.13 × 103 L mol-1 cm-1 and 7 ng cm-2 of molybdenum(VI), respectively. Linear calibration graphs were obtained for 0.1 - 50 μg mL-1 of molybdenum(VI). The stoichiometric composition of the chelate is 1:3 (Mo:DBHQ). A large excess of over 50 cations, anions and some common complexing agents (e.g. EDTA, oxalate, citrate, phosphate, thiourea, SCN-) do not interfere with the determination. The method was successfully used in the determination of molybdenum in several Standard Reference Materials (alloys, steels and waters) as well as in some environmental waters (inland and surface), biological samples (human blood and urine), soil samples, solution containing both molybdenum(V) and molybdenum(VI) and complex synthetic mixtures. The method has high precision and accuracy (S = ± 0.01 for 0.5 μg mL-1).
Liquid chromatography/mass spectrometry (LC/MS) has been applied to analyze N,N′-ethylenebisdithiocarbamate fungicides (EBDCs: manzeb, maneb and zineb) in environmental water samples. The EBDCs that are zinc and/or manganese salts are transformed into readily water-soluble sodium salts by adding an alkaline EDTA solution. The N,N′-ethylenebisdithiocarbamate anion is extracted into chloroform-hexane (3:1) as an ion pair with tetrabutylammonium, and then S-alkylated with methyl iodide. The extraction and derivatization are carried out at room temperature. The derivatized ethylenebisdithiocarbamic acid dimethyl ester is introduced into an LC/MS equipped with a negative ion electrospray ionization interface. Identification of the compound is performed with the specific quasi-molecular ion, and the quantitative analyses are carried out using the peak areas. The average recoveries and coefficients of variation of EBDCs at sub-ppb level are 79.1% and 29.3% (n = 6), respectively. The limit of detection based on standard deviation of 0.043 μg/L for manzeb is achieved.
Liquid chromatography/mass spectrometry (LC/MS) has been applied to the analysis of triphenylboron, which has been produced as a substitute for organotin compounds, in water. Although commercial triphenylboron compounds are produced as pyridinyl complexes, the chemical form in water is supposed to be mainly triphenylboron after liberating pyridine. The triphenylborons were extracted from water with an Empore™ C18 extraction disk under acidic condition, and the extracts were introduced directly into a liquid chromatograph-mass spectrometer equipped with a negative ion electrospray ionization interface. Identification of the compounds was performed with specific ions produced from the triphenylboron, and a quantitative analysis was carried out using the peak areas. The average recoveries from distilled water, seawater and river water at 0.30 ng/ml were 92.3, 100 and 85.3%, respectively. A detection limit of 0.023 ng/ml for triphenylboron was achieved.
A new analytical approach for the detection of Ni2+ utilizing an attenuated total reflection (ATR) technique is discussed in this paper. Nickel detection was accomplished on a silicon ATR parallelogram crystal uniformly coated by a ca. 1.5-μm Nafion film embedded with dimethylglyoxime (DMG) probe molecules. The detection of Ni2+ is based on the appearance of a unique infrared absorption peak at 1572 cm-1 that corresponds to the C=N stretching mode in the nickel dimethylglyoximate, Ni(DMG)2, complex. The suitable operational pH range for the nickel infrared sensor is between 6 - 8. High alkalinity in the sample solution causes a leaching of Ni(DMG)2. The detection limit of the nickel infrared sensor is 1 ppm in a sample solution of pH = 8. Interference studies revealed that Cu2+ could compete with Ni2+ for the DMG sites in the Nafion matrix. The new nickel detection methodology can be potentially utilized, after further improvement, in field analysis to locate hot spots contaminated with a high ppm of Ni2+.
We studied the interaction of sodium dodecylbenzenesulfonate (SDBS) with Nile Blue (NB) and Safranine T (ST) by a spectral correction technique. The aggregations of NB and ST on an SDBS surface obeyed Langmuir isothermal adsorption. The adsorption ratios of NB and ST to SDBS were both 0.5, and the adsorption constants of the aggregates were 1.80 × 105 and 9.49 × 104. The aggregations were applied to the quantitative determination of anion detergent in samples; the recovery of SDBS was between 90.3 and 106% together with an RSD of 3.78%.
Ru(bpy)2(CE-bpy)2+ was prepared where bpy and CE-bpy were 2,2′-bipyridine and bpy having a crown-ether moiety at the 3,3′-positions, respectively. Although Ru(bpy)2(CE-bpy)2+ showed only very weak emission in acetonitrile, recognition of Na+, Li+, or K+ by the crown-ether moiety in CE-bpy resulted in increases in both the emission intensity and the lifetime of the complex, demonstrating that it acted as a photoreceptor. The results were discussed in terms of a steric hindrance between the 3,3′-substituents on CE-bpy and structural changes in both CE-bpy and the complex upon ion recognition, as studied by variable-temperature 1H-NMR and steady-state/dynamic emission spectroscopy of the complex.