Gas Phase Molecular Absorption Spectrometry Research Articles

A violet light-emitting diode-based gas-phase molecular absorption device for measurement of nitrate and nitrite in environmental water

A simple and sensitive device for the detection of nitrite and nitrate in environmental waters was developed based on visible light gas-phase molecular absorption spectrometry. By integrating a detection cell (DC), semiconductor refrigeration temperature-controlling system (SRTCY), and nitrite reactor into a sequential injection analysis system, trace levels of nitrite and nitrate in complex matrices were successfully measured. A low energy-consuming light-emitting diode (violet, 400–405 nm) was coupled with a visible light-to-voltage converter (TSL257) to measure the gas-phase molecular absorption. To reduce the interference of water vapor, an SRTCY was used to condense the water vapor on-line before the gas-phase analyte entered the DC. The DC was radiatively heated by the SRTCY to avoid water vapor condensation in the light path. As a result, the obtained baseline noise reduced 3.75 times than that of without SRTCY. Under the optimized conditions, the device achieved limits of detection (3σ/k) of 0.055 and 0.36 mmol/L (0.77 and 5.04 mg N/L) for nitrite and nitrate, respectively, and the linear calibration ranges were 0.1–15 mmol/L (R2 = 0.9946) and 1–10 mmol/L (R2 = 0.9995), respectively. Precisions of 5.2 % and 9.0 % were achieved for ten successive determinations of 0.3 mmol/L nitrite and 1.0 mmol/L nitrate, and the analytical times for nitrite and nitrate determination were 5 and 13 min, respectively. This method was validated against standard methods and recovery tests, and it was applied to the measurement of nitrite and nitrate in environmental waters. Moreover, a device was designed to enable the field measurement of nitrite and nitrate in complex matrices.

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

Determination of Chemical Oxygen Demand in Water Samples Using Gas-phase Molecular Absorption Spectrometry.

Chemical oxygen demand (COD) is important for water quality assessment as it represents the level of reductive organic pollution from eutrophication in aquatic systems. For surface water quality monitoring, permanganate is usually applied as an oxidizing reagent, and the routine CODMn determination is mostly achieved by titration method. However, this titration method is tedious and time consuming, and the results suffer from environmental temperature fluctuations and complicated operation techniques. In this study, a novel CODMn determination method was developed using gas-phase molecular absorption spectrometry equipped with an online automated digestion device for the first time. The effects of digestion temperature, digestion time and sulfuric acid content were thoroughly studied. This method exhibited good linearity (0.35 to 12 mg/L), a low detection limit (0.12 mg/L), and good RSD from various water samples (0.71 - 2.37%). When used for CODMn determination in routine water quality monitoring, this automated GPMAS can considerably improve analysis speed, efficiency, accuracy and stability compared to the traditional titration method.

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.

气相分子吸收光谱法测定硫化物校准曲线的研究

本文主要阐述了气相分子吸收光谱法测定硫化物时对其校准曲线斜率、截距参考值的分析。通过收集实验室近三年采用气相分子吸收光谱法测定硫化物时制作校准曲线的一系列原始数据，并用数理统计方法对校准曲线及其有关指标进行了详细讨论，得出气相分子吸收光谱法测定硫化物校准曲线的斜率参考值范围为：0.0961 ± 0.0013，截距参考值范围：−0.0018 ± 0.0030。此结果对实验室分析人员判定硫化物项目校准曲线制作是否合格具有一定的参考价值。 This paper mainly analyzed the reference value of the slope rate and intercept from the sulfide’s calibration curve by using gas-phase molecular absorption spectrometry. The calibration curve and its related indexes were discussed in detail by using mathematical statistics method through nearly three-year original data in laboratories. Results showed that the reference range of slope of the gas-phase molecular absorption spectrometry calibration curve is 0.0961 ± 0.0013, and that of intercept is −0.0018 ± 0.0030. These results provide reference for determining eligibility criteria of sulfide calibration curve.

Rapid determination of sulfide sulfur in anaerobic system by gas-phase molecular absorption spectrometry

A detection system was designed for rapid and accurate determination of sulfide sulfur in an anaerobic system by gas-phase molecular absorption spectrometry (GPMAS).

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.

Flow-injection analysis of nitrate by reduction to nitrite and gas-phase molecular absorption spectrometry.

Two flow-injection manifolds have been investigated for the determination of nitrate. These manifolds are based on the reduction of nitrate to nitrite and determination of nitrite by gas-phase molecular absorption spectrophotometry. Nitrate sample solution (300 microL) which is injected to the flow line, is reduced to nitrite by reaction with hydrazine or passage through the on-line copperized cadmium (Cd-Cu) reduction column. The nitrite produced reacts with a stream of hydrochloric acid and the evolved gases are purged into the stream of O2 carrier gas. The gaseous phase is separated from the liquid phase using a gas-liquid separator and then swept into a flow-through cell which has been positioned in the cell compartment of an UV-visible spectrophotometer. The absorbance of the gaseous phase is measured at 204.7 nm. A linear relationship was obtained between the intensity of absorption signals and concentration of nitrate when Cd-Cu reduction method was used, but a logarithmic relationship was obtained when the hydrazine reduction method was used. By use of the Cd-Cu reduction method, up to 330 microg of nitrate was determined. The limit of detection was 2.97 microg nitrate and the relative standard deviations for the determination of 12.0, 30.0 and 150 microg nitrate were 3.32, 3.87 and 3.6%, respectively. Maximum sampling rate was approximately 30 samples per hour. The Cd-Cu reduction method was applied to the determination of nitrate and the simultaneous determination of nitrate and nitrite in meat products, vegetables, urine, and a water sample.

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.

Gas-Phase Molecular Absorption Spectrometry as a Gas Chromatography Detector: Determination of Alcohols

A mixture containing methanol, ethanol, 2-propanol, 1-butanol, 1-pentanol, 1-hexanol, benzyl alcohol, phenol, 2,4-dimethylphenol, 2,3-dimethylphenol, and 2-nitrophenol is analyzed using a simple detection system for gas chromatography based on molecular absorption spectrometry in the gas phase. All of the parameters affecting the determination are optimized, including solvent, temperature, carrier gas flow, type of flow cell, injection volume, and measurement wavelength. The analytical characteristics of each compound are calculated, obtaining detection limits ranging from 2.5 to 15 mg/L for aromatic alcohols and from 47 to 120 mg/L for lineal alcohols. The method is applied to several synthetic mixtures with good results.

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.

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.

Gas-phase molecular absorption spectrometry: Determination of sulphite with diode-array detection

A method is described for determining sulphite by SO2 generation and UV-visible molecular absorption spectrometry with diode-array detection. The molecular absorption maximum of SO2 appears at 198 nm. The parameters affecting generation (particularly those relating to the kinetics of the process) and determination are optimized; under the optimum conditions found, only a 30 s preconcentration time is necessary. The linear response range is between 10 and 1000 μg ml−1 of SO 3 2− , the RSD is 3.5% and the detection limit is 3.2 μg ml−1. The effect of different species on the SO2 signal is also studied. The method is applied to the determination of SO2 in air 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.

Automated Determination of Sulfide as Hydrogen Sulfide in Waste Streams By Gas-phase Molecular Absorption Spectrometry

L. Ebdon, S. J. Hill, M. Jameel, W. T. Corns and P. B. Stockwell, Analyst, 1997, 122, 689 DOI: 10.1039/A700407I