Phase Molecular Absorption Spectrometry Research Articles

Study on the Optimization of Determination of Total Nitrogen in Water by Gas Phase Molecular Absorption Spectrometry

Study on the Optimization of Determination of Total Nitrogen in Water by Gas Phase Molecular Absorption Spectrometry

Application of an ammonium ion-selective electrode for the real-time measurement of ammonia nitrogen based on pH and temperature compensation

Traditional methods for determining the ammonia nitrogen (NH3-N) concentration are the colorimetric method using Nessler’s reagent or salicylate. To prevent secondary pollution, minimise the time required for measurement, and reduce cation interference, new NH3-N measurement methods have been developed including fluorescence, gas phase molecular absorption spectrometry, and ammonia gas sensing electrode methods. However, in these techniques, the addition of a chemical reagent is unavoidable, so the real-time and accurate measurements of NH3-N are achieved hardly. In this study, we used an ammonium ion-selective electrode (ISE) for the real-time measurement of NH3-N with compensation for the ammonium ion (NH4+) component of the total NH3-N concentration. The basic mechanism is that an ammonium ISE can measure NH4+ concentration, and NH4+ ratio in NH3-N can be calculated based on pH and temperature. Experimental results indicate that the ammonium ISE exhibited near-Nernstian behaviour, having a fitted line with a slope of 56.4 mV/pNH4. The compensation effects and reproducibility are good. Furthermore, the difference in the temperature responses at different NH4+ concentrations agrees with the Nernst equation basically. Therefore, the proposed method can provide a real-time and environmentally friendly solution to determine NH3-N concentration.

Sequential flow injection analysis of ammonium and nitrate using gas phase molecular absorption spectrometry

A flow injection method on the basis of gas phase molecular absorption is described for the sequential determination of ammonium and nitrate. Two hundred microliters of sample solution is injected into the flow line. For ammonium determination, the sample zone is directed to a line in which reacts with NaOH (13M) and produces ammonia. But for nitrate determination, the sample zone is passed through the on-line copperized zinc (Zn/Cu) reduction column and produces ammonium ion and in the follows ammonia. The produced ammonia in both cases is purged into the stream of N2 carrier gas. The gaseous phase is separated from the liquid phase using a gas–liquid separator and then is swept into a flow through cell, which has been positioned in the cell compartment of an UV-Vis spectrophotometer. The absorbance of the gaseous phase is measured at 194nm. Under selected conditions for sequential analysis of ammonium and nitrate, linear relations were found between the peak heights of absorption signals and concentrations of ammonium (10–650μgml−1) and nitrate (20–800μgml−1). The limit of detections for ammonium and nitrate analysis were 8 and 10μgml−1, respectively. The relative standard deviations of repeated measurements of 50μgml−1 of ammonium and nitrate were 2.0, 2.9%, respectively. Maximum sampling rate was about 40 samples/h. The method was applied to the determination of ammonium in pharmaceutical products and the sequential determination of ammonium and nitrate in spiked water samples.

Simultaneous determination of organotin compounds by hydride generation–gas phase molecular absorption spectrometry

This study describes the determination of ternary mixtures of dimethyltin chloride (DMT), trimethyltin chloride (TMT) and monobutyltin chloride (BT) by hydride generation–gas phase molecular absorption spectrometry and the application of different chemometric methods: principal components regression (PCR) and partial least squares (PLS). The two methods are applied to the absorption spectra of mixtures of DMT, TMT and BT. Two different experimental designs are tested for the mixtures, a triangular design and a central composite design. The models obtained from the triangular design offer the best prediction results. The effects of the number of working wavelengths and the number of factors included in the calibration model is studied and a different behaviour is seen for each compound and calibration model. The methods are applied to the analysis of artificial aqueous samples containing different concentrations of DMT, TMT and BT species. No significant differences are observed between the calibration models investigated.

Determination of Acetic Acid in Vinegar by Gas Phase Molecular Absorption Spectrometry After Methyl Acetate Generation

This paper describes a method for the quantitative determination of acetic acid by gas-phase molecular absorption spectrometry. The proposed method is based on the generation of methyl acetate with subsequent measureme nt of the volatile absorbance at 216 nm. The generation, transport and measurement conditions are optimized. Under the recommended conditions, the analytical characteristics are obtained, with a detection limit of 0.005 M. The method is tested with vinegar samples. The analytical results obtained by the proposed method agree with those of a reference method.

Determination of Acetic Acid in Vinegar by Gas Phase Molecular Absorption Spectrometry After Methyl Acetate Generation

Determination of Acetic Acid in Vinegar by Gas Phase Molecular Absorption Spectrometry After Methyl Acetate Generation

Optimization of dimethyltin chloride determination by hydride generation gas phase molecular absorption spectrometry using a central composite design

A factorial design is applied to the optimization of the determination of dimethyltin chloride by hydride generation gas phase molecular absorption spectrometry (HG-GPMAS). A method is described for the determination of dimethyltin chloride after conversion into gaseous dimethyltin hydride by adding a sodium tetrahydroborate (III) solution. The hydride generated is collected in a liquid nitrogen cryogenic trap. This is revolatilized, driven to the quartz flow cell and measured with gas phase molecular absorption spectrometry (GPMAS) with diode array detection. A Plackett-Burmann design is used for the study of the factors that influence the absorption signal. The optimization of these factors is performed using a central composite design. The spectra obtained over a wide range of wavelengths, 190–220 nm, allow the multivariate calibration to be studied. The parameters affecting the production and collection of the dimethyltin hydride are studied. The detection limit obtained is 3.2 ng ml −1. The precision (RSD=4.1%) is calculated from a solution containing ten times the corresponding detection limit. The recoveries (99–108%) are satisfactory. A study is made of the influence of several interferent ions (hydride generators, transition metals and anions) in the presence of dimethyltin chloride.

Trimethyltin chloride determination by hydride generation — gas phase molecular absorption spectrometry: A sequential application of experimental designs

In this paper, a sequential experimental design is applied to optimize the determination of trimethyltin chloride (TMT) by hydride generation-gas phase molecular absorption spectrometry. The TMT is converted into gaseous trimethyltin hydride by adding a sodium tetrahydroborate (III) solution. The hydride generated is collected in a liquid nitrogen cryogenic trap. This is revolatilized, driven to the quartz flow cell and measured with gas phase molecular absorption spectrometry with diode array detection. A Plackett-Burman design is used to study the parameters affecting the production, collection and measurement of the hydrides. The optimization of these parameters is achieved using a central composite design. PLS, MLR and univariate calibration are applied to the spectra obtained. The detection and quantification limits are 1.5 and 4.6 ng ml −1, respectively, and the relative standard deviation ( n = 10) at 15 ng ml −1 was 5.5%. An interference study is presented.

Experimental design methodologies to optimize monobutyltin chloride determination by hydride generation gas phase molecular absorption spectrometry

A hydride generation gas phase molecular absorption spectrometry (HG-GPMAS) method for the determination of butyltin compound is optimized by experimental design. This method is based on the conversion of the butyltin chloride into gaseous monobutyltin hydride by adding a sodium tetrahydroborate (III) solution. The hydride generated is collected in a liquid nitrogen cryogenic trap. This is revolatilized, driven to the quartz flow cell and measured with GPMAS with diode array detection. A Plackett–Burmann design is used for the study of the factors that influence the absorption signal. The optimization of the parameters affecting the production and collection of the monobutyltin hydride is achieved using a central composite design. Partial least square (PLS), multiple linear regression (MLR) and univariate calibration are applied to the spectra obtained. The quality parameters (detection limits and precision) for the butyltin chloride are reported. An interference study is made.

Determination of monomethylarsenous acid by hydride generation – gas phase molecular absorption spectrometry

This paper presents a method for the determination of methylarsenous acid which is converted into gaseous methylarsine by adding a sodium tetrahydroborate(III) solution. The generated arsine is collected in a liquid nitrogen cryogenic trap. This is revolatilized and driven to the quartz flow cell and measured by gas phase molecular absorption spectrometry with diode array detection. The spectra obtained over a wide range of wavelengths allows multivariate calibration. The parameters affecting the production and collection of the arsines are studied. The detection limit, (6 × SD of blank) = 2.8 ng ml −1 and the relative standard deviation ( n = 10) at 28 ng ml −1 was 5.3%. An interference study is made.

Gas chromatography with UV-vis molecular absorption spectrometry detection: Increasing sensitivity of the determination of alcohols and phenols by derivatization

A method is proposed for the determination of alcohols and phenols based on their derivatization to benzoates and gas chromatography-gas phase molecular absorption spectrometry. All parameters affecting the derivatization reaction, such as the solvent, basic medium, benzoyl chloride and stirring time, were optimized. Chromatographic and instrumental conditions were also studied. Finally, a calibration study was performed and the results were compared to that obtained by the direct determination of the compounds.

Simultaneous determination of arsenic, antimony, selenium and tin by gas phase molecular absorption spectrometry after two step hydride generation and preconcentration in a cold trap system

A cold trap system for the simultaneous determination of arsenic, antimony, selenium and tin by continuous hydride generation and gas phase molecular absorption spectrometry is described. The hydride generation is carried out in two steps; first, tin hydride is generated at low acidity and second, arsenic, antimony and selenium hydrides are formed at higher acidity. All the hydrides are collected in a liquid nitrogen cryogenic trap and transported to the flow cell of a diode array spectrophotometer, where molecular absorption spectra are obtained in the 190–250 nm range. Five calibration solutions containing arsenic, antimony, selenium and tin are solved using multiple linear regression analysis. Tests are performed in order to extend the same manifold to other hydrides but no signals are obtained for bismuth, cadmium, lead, tellurium and germanium. Under the optimum conditions found and using the wavelengths of maximum sensitivity (190, 198, 220 and 194 nm), the analytical characteristics of each element are calculated. The detection limits are 0.050, 0.020, 0.12 and 1.1 μg ml −1 and the RSD values are 3.7, 3.1, 3.5 and 3.0% for As, Sb, Se and Sn, respectively. The method is applied to As, Sb, Se and Sn determination in natural spiked water samples.

Determination of dimethylarsinic acid by hydride generation gas phase molecular absorption spectrometry

A method is described for the determination of dimethylarsinic and monomethylarsonous acids. The procedure involves NaBH 4 reduction of the arsenic compounds to the corresponding gaseous arsines. After generation, the hydrides are collected in a liquid nitrogen trap. They are revolatilized and carried to the flow cell where they are measured by gas phase molecular absorption spectrometry (GPMAS). Various parameters affecting the production and collection of the arsines, such as the sample volume, generation conditions, and analyte retention and volatilization are discussed. The spectra obtained over a wide range of wavelengths, allows the reactions which take place during arsine generation, retention and revolatilization and their effects on the analytical signal to be studied. The quality parameters (detection limits, precision and accuracy) for two arsenic species are reported.

New approaches on gas phase molecular absorption spectrometry detection in gas chromatography.

A hyphenated technique for coupling a spectrophotometric detector to a gas chromatograph with a packed column is described. The packed column was connected directly to the flow cell (path length 1 cm) which was placed in a UV-visible molecular absorption spectrophotometer with diode array detector. This detection system was employed for separating and determining benzene, toluene, 1,4-xylene, 1,2-xylene and mesitylene. Molecular absorption spectra of all the separated compounds have also been obtained. A new possibility for coupling capillary gas chromatography and gas phase molecular absorption spectrometry is currently being tested. In this new case, two fibre optics are used and the measurement is performed in the capillary column.

Gas generation and preconcentration coupled to gas phase molecular absorption spectrometry: a powerful tool for the simultaneous determination of analytes forming volatile compounds.

Different methods for a simultaneous determination of several analytes forming volatile compounds at room temperature are described. The main steps of these methods are: continuous generation, collection in a cryogenic trap, revolatilization, measurement of the volatile compounds by Gas Phase Molecular Absorption Spectrometry and resolution by multi-wavelength methods. Several mixtures containing 2, 3 or 4 components have been studied: 1) elements forming covalent hydrides; 2) arsenic organometallic compounds forming volatile gases with a similar structure to arsine; and 3) sulphur species that can evolve volatile compounds. Under the optimum conditions obtained for each mixture, detection limits range from 0.8 ng/mL (dimethylarsinic acid) to 2 microg/mL (SCN(-)).

A Simple, Innovative Method for the Determination of Iodide by Using Gas-Phase Molecular Absorption Spectrometry After Volatile Species Evolution

Abstract A simple, innovative method for the determination of iodide has been developed and described based on evolution of halogen gas and followed by gas- phase molecular absorption spectrometry (GPMAS) with a conventional hollow cathode lamp as primary radiation source. A convenient reaction vessel is designed for vapor generation and a flow-through absorption tube is used to replace the atomizer of a commercial atomic absorption spectrometer. Concentrated sulfuric acid is used as reaction agent to oxidize the iodide, and the produced iodine gas is carried into light path of the absorption cell. Measurement of the molecular absorption has been performed at wavelength 518 nm with a conventional Mg lamp. The detection limit for iodide attained is about 0.89 μg/ml and the relative standard deviation is usually less than 3% at the analyte concentration of 50 μg/ml. An interference study shows that the proposed method is selective and effective. The method has also been tested for real sample analysis.

Determination of Tellurium by Gas Phase Molecular Absorption Spectrometry After Hydrogen Telluride Generation

Abstract A method for determination of tellurium(IV) or tellurium(VI) is described that involves hydrogen telluride generation by reduction with sodium tetrahydro-borate(III), evolution of hydride with HCl solution, transport into a flow-cell placed in a UV-visible molecular absorption spectrophotometer and measurement of gas at 190 nm. Hydride generation and determination procedures are optimized, based on height and area of absorbance versus time profile of hydrogen telluride generated. Using the best experimental conditions found the calibration curve is linear from 5 to 100 μg/ml of tellurium, 1.1 μg/ml of tellurium(IV) or 3.1 μg/ml of tellurium(VI) can be detected, and relative standard deviation ranges from 4 to 7%. The method is applied to the analysis of additives for synthetic rubber making.

Simultaneous determination of arsenic, antimony and selenium by gas-phase diode array molecular absorption spectrometry, after preconcentration in a cryogenic trap

This paper describes a method for the simultaneous determination of As(III), Sb(III) and Se(IV) by combining hydride generation and gas phase molecular absorption spectrometry. A system for continuous hydride generation has been designed and developed, based on the use of a double process of gas-liquid separation, and optimal compromise operation conditions for the three compounds have been found. After generation, the hydrides are collected in a liquid nitrogen cryogenic trap, and then evaporated and driven to the flow cell of a diode array spectrophotometer, in which the transient signals over the 190–250 nm wavelength interval are measured. Under the recommended conditions (sample flow: 35 ml min −1, 0.5 M HCl; reductor flow: 4 ml min −1 of 4% NaBH 4, solution) linear response ranges above 50 μg 1 −1 for As(III), 30 μg 1 −1 for Sb(III) and 200 μg 1 −1 for Se(IV) are obtained with detection limits of 22 μg 1 −1, 15 μg 1 −1 and 65 μg 1 −1, respectively. Multiwavelength linear regression equations were used for the simultaneous determination of the three elements in different synthetic samples, with good precision and accuracy and to study simultaneously the interference from different chemical species for the three compounds. Results were similar to those obtained by other techniques using hydride generation.

Ammonium determination in wine by gas phase molecular absorption spectrometry

A procedure for the determination of ammonium is described, based on its transformation into ammonia gas and subsequent measurement by UV-visible molecular absorption spectrometry at 194 nm. Two different procedures for generating the ammonia are proposed, using NaOH solution and solid NaOH, respectively. After generation conditions for both procedures had been optimized, better sensitivity was observed with solid NaOH. In these conditions, the method showed two ranges of linear response: from 1 to 100 μg and from 100 to 400 μg of ammonium. Finally, we determined ammonium in wine samples. Preliminary studies indicated that the only observable interfering species was ethanol, which could be eliminated by subjecting the sample to vacuum evaporation until nearly dry. This process also increased the sensitivity of the method by as much as ten times. The values obtained from three different wine samples yielded results within the range of the concentration obtained by other authors. The recovery of ammonium added to the wine samples was around 95%.

Evaluation of a method for arsenic(III) and antimony(III) determination by vapour phase molecular absorption spectrometry using graphite furnace volati

This paper presents a procedure for determining As(III) and Sb(III) by vapour phase molecular absorption spectrometry (VPMAS). The chlorides of these elements are volatilized from aqueous solutions in a L'vov platform inside the graphite furnace of an atomic absorption spectrophotometer. Molecular absorption is measured at 205 nm for arsenic chloride and 220 nm for antimony chloride. Both species are formed in the sample drying stage. A study of the temperature program led to different results in each case. In the case of arsenic, a two-step program (one mixed drying and volatilization step, and another cleaning step) is found to be best, whereas in the case of antimony, three separate steps can be used (drying, volatilization and cleaning). In both cases, optimum volatilization was obtained with low HCl concentrations, and volatilization fell off sharply as HCl concentration increased. Under optimum generation and determination conditions, the linear response range is from 0.06 to 3.75 μg for As(III), and from 0.30 to 5.0 μg for Sb(III) with relative standard deviations of 2.1% for As(III) and 2.5% for Sb(III). The effect of other anions and cations on the arsenic analytical signal was studied, and other halides were found to interfere. The method was applied to arsenic determination in an arsenic ore.