The maturity of the gas chromatography technique belies the continuing search for improved operating methods. Cryogenic methods, applied in many forms, have been used for many years to trap volatile compounds in chromatography. Recent work has demonstrated an alternative approach to band accumulation. A small tube incorporating an inter-nal sleeve cooled cryogenically, placed over a gas chromatography capillary column, can be moved back-and-forward over the column to permit collection and remobilization of focused bands. The movement frequency or timing can be altered to give different operational modes and outcomes. Results demonstrate that peaks can be fully accumulated just prior to a detector then rapidly flushed into the detector, allowing considerable increase in peak height as the peak width diminishes. Applications illustrate that all or selected peaks in a chromatogram can be thus modified by the trap. Column bleed can likewise be collected and then re-eluted, leading to a novel presentation of the molecular constituents of the bleed. With multidimensional gas chromatography, heart-cuts from the first column can be trapped and focused at the head of the second column, then rapidly re-injected into the second column leading to certain advantages. Furthermore, by rapid modulation of the cold trap, a single peak can be cut into a series of separate pulses, either into a detector or into a second column. This allows unusual expression of a chromatographic peak profile, and can be incorpo-rated into a comprehensive GC experiment.
Ionization methods working under atmospheric pressure, such as ESI and APCI, are now indispensable for measuring non-volatile organic compounds, and provide LC/MS. These methods, however, have several disadvantages, e.g., they are less sensitive for less polar compounds and have limitations in the use of solvents. Liquid ionization mass spectrometry utilizes excited argon for ionizing organic compounds (liquids or in solution) at atmospheric pressure. Also, it is possible to use a variety of additives to obtain ions related to the molecular weight. Therefore, the method is useful to analyze a mixture containing non-volatile, either polar or non-polar, organic compounds, and also gives information about hydrogen-bonded clusters present in the gas phase and at the liquid surface. The method provides different applications in the field of mass spectrometry. This review describes the development and several applications of this method.
A simple and reproducible method is described for the determination of traces of tellurium(IV) based on differential pulse cathodic stripping voltammetry without the addition of any other metal ions to an acidic medium. Tellurium(IV) ions in a 0.18 mol dm-3 hydrochloric acid-0.20 mol dm-3 nitric acid solution (4 cm3) were electrodeposited on a rotating silver disk electrode (2000 rpm) as silver telluride at -0.45 V vs. Ag/AgCl for 30 min. A cathodic stripping voltammogram was then recorded in an another solution (2 mol dm-3 sodium hydroxide) at a scan rate of 50 mV s-1 to -1.5 V vs. Ag/AgCl. Only a single well-defined peak could be seen at -1.16 V vs. Ag/AgCl. The calibration curve was linear up to at least 300 ng cm-3 of tellurium(IV) (2.4×10-6 mol dm-3) and passed through the origin with an RSD of 6.8% for 50 ng cm-3 (n=5). The detection limit (3σ) was 0.62 ng cm-3. The possible interferences were evaluated.
A simple voltammetric method has been developed for the determination of V(V) and V(IV). When a mixture of V(V) and V(IV) is added last of all to a 50 mM Mo(VI)-0.3 M HCl-70%(v/v) CH3CN system, only V(V) reacts with Mo(VI) to form a 12-molybdovanadate(V) complex which undergoes a two-step reduction at the glassy carbon (GC) electrode; the reduction current is directly proportional to the V(V) concentration in the mixture. On the other hand, when HCl is added last after heating the Mo(VI)-CH3CN system containing a mixture of V(V) and V(IV) at 60°C for 10 min, V(IV) is com-pletely oxidized to V(V), and the total concentration of vanadium is determined. The V(IV) concentration is determined by subtracting the V(V) concentration before oxidation from the total concentration of vanadium. Interferences from foreign ions are also discussed.
Crosslinked N-(2-pyridylmethyl)chitosan (PMC), N-(2-thienylmethyl)chitosan (TMC), and N-[3-(methylthio)propyl]-chitosan(MTPC) were newly synthesized as adsorbents of mercury(II). The amino group of the active adsorption site of chitosan was protected by Schiff’s base formation prior to being crosslinked by 2-(chloromethyl)oxirane. The final chitosan derivatives were obtained by reducing the imine moiety of the Schiff’s bases with sodium borohydride. The adsorption behavior of metal ions on the chitosan derivatives was examined from hydrochloric acid using a batchwise method. These chitosan derivatives exhibited high selectivities for mercury(II) over base metals in hydrochloric acid. Among the chitosan derivatives, MTPC especially exhibited high selectivity and a high loading capacity for mercury(II). The stoichiometric relations in the adsorption of mercury(II) on PMC and MTPC were clarified from hydrochloric acid.
Raman spectroscopic analysis has been used to identify the chemical species that exist in aqueous chlorine solution. The pH dependence of the Raman spectra obtained indicates that there is an equilibrium among hypochlorite ion, hypochlorous acid and chlorine. Bactericidal activities of the acidic electrolyzed water, which is generated by electrolysis of an aqueous NaCl solution, were evaluated in the pH range 2 - 9 against Escherichia coli K12 and Bacillus subtilis PCI219 by a semi-quantitative bioassay. The maximum activity was observed between pH 4 and 5 in both bacteria. The Raman and the ultraviolet spectroscopic data, along with chemical analysis data, were used to conclude that the bactericidal activity is quantitatively correlated to the concentration of hypochlorous acid in solution.
The preparation of atrazine-receptor polymers by molecular imprinting was explored, focusing upon the role of functional monomer and solvent used for the preparation. Three functional monomers and six different solvents were examined from the viewpoint of the efficiency for molecular imprinting. Polymers were prepared using methacrylic acid, a stronger acid 2-(trifluoromethyl)acrylic acid and a three-point hydrogen bond donor/acceptor, glutethimide derivative. Methacrylic acid displayed the best effectiveness as functional monomer, which leads to an understanding that a functional monomer is required to have both strong binding and multiple binding capacity. By choosing less polar solvents for polymerization, polymers having better retention ability and higher selectivity were obtained. Those polymers exhibited capacity factors 2 - 2.5 times as large as that for chloroform. It was also suggested that the molecular shape and size of the solvent used have influence on the resultant polymer’s binding ability.
The solvent extraction of lanthanum(III), cerium(III), neodymium(III), samarium(III), gadolinium(III), dysprosium(III), erbium(III) and ytterbium(III) with decanoic acid in 1-octanol and benzene was carried out at 25°C and at an aqueous ionic strength of 0.1 mol dm-3 (NaNO3). In extraction systems using 1-octanol as a solvent, all of the lanthanides were found to be extracted as two kinds of monomeric decanoates; in those using benzene, the monomeric, dimeric and tetrameric lanthanide(III) decanoates were proven to be responsible for the extraction, except for gadolinium(III), whose extracted species were the monomeric and dimeric species. The dimerization, tetramerization and adduct formation constants of lanthanide(III) decanoates in the organic phase were estimated. A so-called “gadolinium break” was observed for the polymerization constants of lanthanide(III) decanoates.
Microwave-induced plasma mass spectrometry (MIP-MS) was used to determine the selenium concentrations in human blood plasma. Blood plasma from volunteers, the standard reference materials of human blood serum and bovine serum, were used to investigate the suitability of the digestion method and the matrix effects due to coexisting elements, and to confirm the accuracy of the obtained values. Two sample-preparation procedures, microwave digestion and simple dilution with 0.1% Triton X-100 solution, were examined. In the latter method, oxygen gas was mixed into plasma nitrogen gas at a gas flow of 30 ml/min to prevent any instability of the measurement caused by carbide formed from organic components. The selenium concentrations were calculated from the ion counts at m/z=80 using a calibration curve with an internal standard correction. Both sample-preparation procedures were suitable for human blood plasma. The concentrations of several other elements, such as magnesium, iron, copper, zinc, and rubidium in blood plasma and in serum sam-ples, could be measured simultaneously with selenium, indicating that MIP-MS was useful for a simple and rapid determination of elements in blood plasma.
The separation of eleven priority (EPA) phenols and eighteen chlorophenols via micellar electrokinetic chromatography (MEKC) is described. Disodium 5,12-bis(dodecyloxymethyl)-4,7,10,13-tetraoxa-1,16-hexadecanedisulfonate (DBTHX), disodium 5,13-bis(dodecyloxymethyl)-4,7,11,14-tetraoxa-1,17-heptadecanedisulfonate (DBTHP) and disodium 5,13-bis(dodecyloxymethyl)-4,7,11,14-tetraoxa-9,9-dimethyl-1,17-heptadecanedisulfonate (DBTDMHP) were used as the double-chain surfactants. The EPA phenols were baseline separated by MEKC with 7.5 mM DBTHP. The detection limits of the phenols for a signal-to-noise ratio of 3 were in the range 0.5×10-2 - 3.0×10-2 mM. The relative standard deviation (RSD) of the capacity factors and peak areas for the phenols over the range of 0.31 - 1.8 mM were 0.21 - 1.4% and 1.9 - 4.3%, respectively. The separations of eighteen chlorophenols together with phenol were also carried out by MEKC with these surfactants. These phenols except for 2,3,5- and 2,4,5-trichlorophenol could each be separated with 10 mM DBTHX.
Hydrogen peroxide (H2O2) formed during the course of the Cu(II)-catalyzed oxidation of amino thiols with oxygen was detected by the Arthromyces ramosus peroxidase-catalyzed luminol chemiluminescence (CL) method. Two peaks appeared in the CL response curve in the catalytic oxidation of both cysteine (CySH) and gluthathione (GSH) and in that of both cysteamine and GSH. The resolution of two peaks corresponding to CySH and GSH was better than that corresponding to cysteamine and GSH. Only a strong CL flash appeared in the catalytic oxidation of both CySH and cysteamine. The differences in the resolution of two peaks of amino thiols could be explained on the basis of the differences in the stabiliy constants between Cu(II) and amino thiols.
A method for the determination of thiols by high-performance liquid chromatography (HPLC) with chemiluminescence detection has been developed. The method is based on the precolumn derivatization of thiols with o-phthalaldehyde and N-(4-aminobutyl)-N-ethylisoluminol to form isoindole derivatives and the reversed-phase HPLC separation of the derivatives, followed by successive postcolumn chemiluminescence reactions with hydrogen peroxide and hematin. The limits of the detection of glutathione (GSH) and cysteine were 1.5 nM (15 fmol/injection) and 3.5 nM (35 fmol/injection), respectively. The calibration curve for GSH was linear in the range 5 - 1000 nM (1 - 200 pmol/200 μl). The method was applied to the determination of GSH in human blood. The recovery of GSH added to the blood at the concentration level of 500 μM was about 70%. The GSH concentrations in the blood of three healthy male persons were 502 - 770 μM.
A chemiluminescence (CL) detection method for the determination of sulfite is described. The light produced in the reac-tion of Ru(bipy)32+(bipy=2,2′-bipyridyl)-SO32--K2S2O8 is detected. The concentration of sulfite is proportional to the CL intensity in the range 1.5×10-7 - 1.0×10-4 mol/l. The limit of detection is 4.1×10-8 mol/l and the relative standard devia-tion is 4.3% for 2×10-5 mol/l sulfite solution in 9 repeated measurements. This method has been successfully applied to the determination of sulfite in sugar and sulfur dioxide in air by using triethanolamine (TEA) as the absorbent material.
The extraction and determination of water and dilute-acid-soluble components in atmospheric dust has been investigated as a part of its systematic chemical state analysis. A sample was dispersed in acetone by ultrasonication, followed by centrifugation. After the supernatant was removed for the analysis of acetone-soluble components, succeeding extractions with water and dilute hydrochloric acid were carried out for the residue. The water-soluble components were extracted within 20 min under ultrasonication. Dilute hydrochloric acid was added to the residue after water extraction, and the soluble components were extracted by filtration and ultrasonication. Extraction with 0.1 M hydrochloric acid was recommended, because it dissolved the main soluble components, such as sulfate and carbonate (e.g., gypsum and calcite) within 20 min without any significant loss of iron oxides (e.g., magnetite and hematite), which could be determined by X-ray diffraction analysis. Sixteen cations, ammonium ion and five anions in the extracts were determined by inductively coupled plasma atomic emission spectrometry using a yttrium internal standard, an ion-selective electrode and ion chromatography, respectively. The determination of water and dilute-acid soluble components in atmospheric dust collected in bagfilters was achieved with reasonable precisions.
The evaluation of the hydrogen ion concentration using the glass electrode method sometimes gives very serious errors when the method is applied to natural water samples of low ionic strength such as rainwater. The activity coefficient of the hydrogen ion and the liquid junction potential of the reference electrode are the sources of the error. In this report, the relations between the pH reading and the ionic strength of the sample solutions of 10-4.5 N H2SO4 (N=equiv dm-3) were examined for eleven commercially available electrodes. Results were grouped into three typical patterns. Quantitative estimates of the inaccuracies of the determination of hydrogen ion concentration were given, based on the calculation of Donnan potentials over the liquid junction and Debye-Hückel estimates of the activity coefficient. Recommendations for the choices of the reference electrode as well as the choices of the measurement protocols are also reported.
A rapid and sensitive method for the determination of impurity elements in high purity tantalum metals is proposed. Tantalum metals were digested with nitric acid (HNO3) and hydrofluoric acid (HF). The digested sample solutions were injected into a flow injection system with a cation exchange column. Impurity elements adsorbed were eluted with the mixture of HNO3 and HF, and then the effluent was introduced into an ICP plasma with conventional pneumatic nebulization. In the present flow injection/ICP-MS system, the detection limits, based on 3 times the standard deviation of the blank, were in the range 0.03 - 6 ng/g for the 16 impurity elements (Li, Na, Mg, Mn, Co, Cu, Zn, Ga, Rb, Sr, Cd, In, Ba, Tl, Pb, and Bi).
This work presents a two-step HNO3+HClO4/HF(1:2:1, v/v) acid mixture microwave digestion method for determining the elemental concentrations in suspended particulates collected on glass fiber filters by a beta-gauge monitoring system. Eighteen elements (Al, As, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, S, Sb, V and Zn) were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) and mass spectrometry (ICP-MS). The interference from the glass fiber filters and the variations of the detection limits of the major elements with total suspended particulates (TSP) were thoroughly examined. According to these results, the concentrations of most of the elements in suspended particulates can be determined via the proposed method. On the other hand, determining Na is relatively difficult owing to significant interference from glass fiber filters of the beta-gauge monitoring system. In addition, real samples collected from an air-pollution episode in Taiwan during the spring of 1995 were analyzed, in which the proposed method’s effectiveness was confirmed. The analysis results also indicate that “Kosa” aerosols, having originated in China, might have been the culprit of that episode.
In the present work we investigated the atomization mechanisms of indium in electrothermal atomic absorption spectrometry with pyrolytically coated graphite (PG) and non-pyrolytically coated graphite (NPG) furnaces treated with a refractory element, such as Hf, Ti, W or Zr, by a one-drop coating method. A single-peak signal was observed in Hf-, Ti- and Zr-treated PG and NPG furnaces, and an unresolved double peak signal was observed in W-treated PG and NPG furnaces. The effects of the surface treatment on the charring curve (charring temperature-absorbance curve), kinetic data and Raman spectroscopic data were investigated. The charring curve was shifted to a high-temperature side with a great sensitivity enhancement after the surface was treated, corresponding to suppression of the sensitivity loss reaction of In (In2O3(s)+2C(s)→In2O(g)+2CO(g)). The Arrhenius activation energy (Ea) was estimated to be 158±10, 146±10 and 145±10 kJ mol-1 and 170±15, 194±15 and 165±10 kJ mol-1 with Hf-, Ti-and Zr-treated PG and NPG furnaces, 180±15 kJ mol-1 for the first peak with W-treated NPG one, 115±10 and 111±10 kJ mol-1 for the second peak with W-treated PG and NPG ones, respectively. The Raman spectra of the treated graphite surface were measured at various sites in the sample compartment. The ratio of the intensity of the D band (disordered mode) to that of the G band (E2g mode), ID/IG, was increased by a surface treatment. This suggests an increase in the number of disordered sites, such as edge carbon atoms and the boundaries of graphite crystallites, which exist in uncoated regions of graphite within the treated area. Arrhenius activation energy, except for the second peak with the W-treatment, decreased along with an increase in ID/IG when using a treated furnace. From this relationship, it was proposed that the atomization of indium in treated furnaces takes place due to collisions between In2O(g) and the uncoated region of graphite. When using a W-treated furnace, dissociation of the indium dimer was attributed to a rate-determining step for the second peak.
The effectiveness of cobalt as a chemical modifier was investigated for the determination of bismuth by electrothermal atomic absorption spectrometry using a tungsten furnace. A 10 μl aliquot of the 0.1% m/v cobalt modifier (CoCl2 in 1 M HCl) was dropped onto a tungsten metal board and pre-heating was carried out at 1200°C. Then a sample solution containing bismuth was added to the board, charred at a temperature of 1200°C, and the absorbance of bismuth was measured at an atomization temperature of 2400°C. The vaporization loss of bismuth during the charring stage could be suppressed up to 1450°C by the addition of the cobalt modifier. The relative standard deviation at 0.10 mg dm-3 (in 0.05 M HNO3) was less than 4% (n=6), and the detection limit (3σ) was 0.07 ng. The addition of the cobalt modifier can depress the deviation of the measurements, which usually depends on the concentrations of acid and other concomitant substances in the sample solutions.
The use of a combined mixed magnesium(Mg)-rhodium(Rh) chemical modifier allows a compromise higher pyrolysis temperature to be used for the simultaneous detection of chromium (Cr), copper (Cu), iron (Fe), manganese (Mn) and lead (Pb) in various human hairs by graphite furnace atomic absorption spectrometry (GFAAS). The recommended pyrolysis temperature for all of the analyte elements is 1000°C (ashing) and 2800°C (atomizing). Nitric acid (HNO3) and perchloric acid (HClO4) were used for the digestion of all human-hair samples. The detection limits (3σ, ng g-1) were 0.3 for chromium, 0.1 for copper, 0.4 for iron, 0.2 for manganese and 0.1 for lead, respectively. The accuracy and precision were examined by analyzing a certified reference material (NIES CRM No.13 Human Hair). All of the analytical results obtained by the proposed method were in good agreement with the certified values. The relative standard deviation (RSD) was less then 8 %.
A simple and specific solid-phase spectrophotometric (SPS) determination of zinc in μg dm-3 level has been developed based on the reaction of Zn(II) with 4-(2-pyridylazo)resorcinol (PAR) in the presence of potassium iodide; the product was then fixed on an anionic exchanger. The absorbance of the gel, packed in a 1 mm cell, is measured directly. PAR and KI concentrations were optimized simultaneously using response surface methodology (RSM) from sequential experimental Doehlert designs. The advantages of this methodology are discussed, as opposed to univariate optimization, which is also used. The method was validated by obtaining the performance characteristics: linearity, detection and quantification limits, precision, robustness and selectivity, using suitable chemometric techniques; the trueness was confirmed on environmental samples (water and milk).
The resonance Rayleigh scattering (RRS) spectra of selenium(IV)/iodide/basic triphenylmethane dye systems have been studied. Intense RRS appears when selenium(IV) reacts with iodide and a basic triphenylmethane dye, such as Crystal Violet (CV), Ethyl Violet (EV), Brilliant Green (BG), Malachite Green (MG) and Iodine Green (IG), to form an ion-association complex. The characteristics of the RRS spectra of the ion-association complexes and the suitable conditions for the reactions were investigated. The intensity of RRS is directly proportional to the concentration of selenium(IV) in the range 0 - 0.30 μg/25 ml for the CV and EV systems, and 0 - 0.40 μg/25 ml for other systems. The RRS methods have very high sensitivities for an indirect determination of selenium(IV); the detection limits are between 0.094 ng/ml and 0.86 ng/ml for different dye systems. A new way to determine trace amounts of selenium based on the RRS spectra of the ion-association complex has been developed.
In the table-salt manufacturing process, the mother liquid and the concentrated brine in a crystallizer are highly concentrated salt-mixture solutions comprising NaCl, MgCl2, KCl and CaCl2, and a determination of their concentrations plays an important role. A method is proposed to determine the concentration of each component in the mother liquid and the concentrated brine using the absorbance change relative to the water absorption at six wave numbers by attenuated total-reflectance IR (ATR-IR) spectrometry; an experimental confirmation can be used to accurately determine the composition. In particular, for MgCl2, whose spectral change is larger than that of the other components, its concentration can be quantitatively determined with an accuracy nearly equal to that of a chemical analysis.
A flow injection system based on multi-site detection for kinetic spetrophotometric determination of uric acid in urine is described. The system was studied regarding physical dispersion, elimination of sample matrix interferences and applicability to real samples. In the optimized system, the sample is inserted into a water stream which merged downstream with the reagent solution containing iron(II) chloride and TPTZ. This system enables the determination of about 30 samples/h, and yields precise results (RSD usually <2.9%). Sensitivity is 212 mAU l/mmol up to 0.60 mmol/l uric acid. Accuracy was assessed by running 32 samples already analyzed by a conventional enzymatic procedure. No statistical difference between methods was found at the 95% confidence level.