Gas-diffusion Flow Injection Analysis Research Articles

Determination of Total Ammonia Nitrogen by Gas-Diffusion Flow Injection Analysis (GD-FIA)-Spectrophotometry using Minnieroot Flower (Ruellia tuberosa) as Natural Reagent

Total ammonia nitrogen (TAN) is a pollutant agent found in water and generated from the metabolisms of living organisms and the decomposition of organic matter. This research aims to develop an efficient, low-cost, and environmentally friendly TAN analysis method. The principle of this method is based on the reaction of TAN injected in the donor stream with NaOH to form alkaline gaseous ammonia. The gaseous ammonia diffuses through a hydrophobic membrane into an acceptor stream containing Ruellia tuberosa extract. The presence of NH3 gas in the acceptor stream changes the extract color from pinkish to green, which is monitored by spectrophotometer at 620 nm. This method was also validated based on linearity, selectivity, and accuracy. Under the obtained optimum conditions of 1 M NaOH, 5% extract, a 120 cm mixing coil, and a 200 µL sample volume, the proposed method showed excellent linearity at 10–1000 ppm (R2 = 0.993). The selectivity test result shows that this method was selective against sulfite and nitrite compounds up to 600 ppm with a % error value <10%. This method was applied to measure the total ammonia concentration in agricultural water, and satisfying results were shown by high recoveries of 95.03%–98.84%.

A microfabricated electroosmotic pump coupled to a gas-diffusion microchip for flow injection analysis of ammonia

We have microfabricated two functional components toward developing a microchip flow injection analysis (FIA) system, i.e., an open-channel electroosmotic pump and a gas-diffusion chip, consisting of two microfabricated glass wafers and a porous polytetrafluoroethylene membrane. This is the first application of gas-diffusion separation in a microchip FIA system. To demonstrate the feasibility of using these two components for performing gas-diffusion FIA, we have incorporated them together with a regular FIA injection valve and a capillary electrophoresis absorbance detector in a flow injection system for determination of ammonia in environmental water samples. This system has a limit of detection of 0.10 mg L−1 NH3, with a good repeatability (relative standard deviation of less than 5 % for 4.0 mg L−1 NH3). Parameters affecting its performance are also discussed.

Determination of acetaldehyde in saliva by gas-diffusion flow injection analysis

The consumption of ethanol is known to increase the likelihood of oral cancer. In addition, there has been a growing concern about possible association between long term use of ethanol-containing mouthwashes and oral cancer. Acetaldehyde, known to be a carcinogen, is the first metabolite of ethanol and it can be produced in the oral cavity after consumption or exposure to ethanol. This paper reports on the development of a gas-diffusion flow injection method for the online determination of salivary acetaldehyde by its colour reaction with 3-methyl-2-benzothiazolinone hydrazone (MBTH) and ferric chloride. Acetaldehyde samples and standards (80μL) were injected into the donor stream containing NaCl from which acetaldehyde diffused through the hydrophobic Teflon membrane of the gas-diffusion cell into the acceptor stream containing the two reagents mentioned above. The resultant intense green coloured dye was monitored spectrophotometrically at 600nm. Under the optimum working conditions the method is characterized by a sampling rate of 9h−1, a linear calibration range of 0.5–15mgL−1 (absorbance=5.40×10−2 [acetaldehyde, mgL−1], R2=0.998), a relative standard deviation (RSD) of 1.90% (n=10, acetaldehyde concentration of 2.5mgL−1), and a limit of detection (LOD) of 12.3μgL−1. The LOD and sampling rate of the proposed method are superior to those of the conventional gas chromatographic (GC) method (LOD=93.0μgL−1 and sampling rate=4h−1). The reliability of the proposed method was illustrated by the fact that spiked with acetaldehyde saliva samples yielded excellent recoveries (96.6–101.9%), comparable to those obtained by GC (96.4–102.3%) and there was no statistically significant difference at the 95% confidence level between the two methods when non-spiked saliva samples were analysed.

Online ligand exchange in the determination of weak acid dissociable cyanide by gas diffusion-flow injection analysis

A novel ligand exchange method for on-line gas-diffusion flow injection (GD-FI) determination of weak acid dissociable (WAD) cyanide has been successfully developed using a binary ligand combination of 0.10% thiourea and 0.10% pentaethylenehexamine. Complete WAD cyanide recovery with insignificant contribution from the dissociation of stable metal cyanide complexes (non-WAD complexes) has been achieved in the concentration range from 3μg L−1 to 10mgL−1 cyanide. The proposed GD-FI method offers considerable advantages over the existing standard methods for determining WAD cyanide, as it provides an analysis rate of 60 samples h−1 with a satisfactory reproducibility (average RSD=1.0% at n=3) and can be fully automated. A very good agreement between the proposed method and the standard distillation method has been observed when both methods have been applied to the determination of WAD cyanide in samples from the gold mining industry.

ChemInform Abstract: Photocatalytic Oxidation of Aqueous Ammonia (Ammonium Ion) to Nitrite or Nitrate at TiO2 Particles.

The photocatalytic oxidation of ammonia (ammonium ion) in the presence of air or pure oxygen at titanium(IV) oxide powder surfaces and induced by UV light was investigated. Experimental conditions were varied and the effect ofpH, sparging gas, as well as the concentration of both ammonia (ammonium ion) and photocatalyst were investigated. It has been established that the principal product of photocatalytic oxidation depends onpH, and is either nitrite or nitrate. A gas-diffusion flow injection analysis system with conductivity detection was used for on-line monitoring of ammonia concentration. In addition, ion-chromatography with UV detection was utilized for offline monitoring of nitrite and nitrate concentrations. The use of a photocatalyst such as TiO2 may prove to be a viable method for conversion of ammonia (ammonium ion) to either nitrite or nitrate.

Highly sensitive gas-diffusion sequential injection analysis based on flow manipulation

The present paper describes approaches utilizing the powerful flow manipulation capabilities of sequential injection analysis (SIA) to substantially improve the efficiency of gas-diffusion separation compared to its traditional implementation in flow injection analysis (FIA). Ammonia, ethylamine, diethylamine and triethylamine were used as model analytes in this study. Eleven flow manipulation approaches involving continuous flow, stop-flow, oscillating flow, and the introduction of air bubbles to separate the sample zone from the donor solution were tested. Improvement in sensitivity compared to traditional gas-diffusion FIA exceeding one order of magnitude was achieved. It was observed that this improvement increased with the molecular size of the analyte.

Optimization of a Flow Injection System with Amperometric Detection for Arsenic Determination

A selective and sensitive analytical procedure for rapid arsenic determination by gas-diffusion flow injection analysis with amperometric detection was developed. The method is based on the arsenite reduction by NaBH(4). Derived arsine diffuses through a PTF membrane into the acceptor flow stream and is amperometrically determined on a platinum working electrode. The limit of detection (3 sigma) at room temperature was 5 microg/dm(3) of As(III). The relative standard deviation for a 1 mg/dm(3) As(III) standard was 1.96% for six repetitive injections. Arsenic(V) was determined after its prereduction with potassium iodide. Arsenic determination was not interferred with by 1 mg/dm(3) Sb(III), 5 mg/dm(3) Sn(II), 10 mg/dm(3) Se(IV), 1 mg/dm(3) As(V), 1 mg/dm(3) hydrasine, 1 mg/dm(3) Fe(II) or 0.5 mg/dm(3) Fe(III) solution. The throughput of this method was 60 analyses per hour. This method was successfully applied to arsenic determination in some power plant waste water samples.

Sensitive and ultra-fast determination of arsenic(III) by gas-diffusion flow injection analysis with chemiluminescence detection

A novel chemiluminescence gas-diffusion flow injection system for the determination of arsenic(III) in aqueous samples is described. The analytical procedure involves injection of arsenic(III) samples and standards into a 0.3 mol L −1 hydrochloric acid carrier stream which is merged with a reagent stream containing 0.2% (w/v) sodium borohydride and 0.015 mol L −1 sodium hydroxide. Arsine, generated in the combined carrier/reagent donor stream, diffuses across the hydrophobic Teflon membrane of the gas-diffusion cell into an argon acceptor stream and then reacts with ozone in the flow-through chemiluminescence measuring cell of the flow system. Under optimal conditions, the method is characterized by a wide linear calibration range from 0.6 μg L −1 to 25 mg L −1, a detection limit of 0.6 μg L −1 and a sample throughput of 300 samples per hour at 25 mg L −1 and 450 samples per hour at 25 μg L −1.

Determination of mercury(II) at trace levels by gas-diffusion flow injection analysis with amperometric detection

A gas-diffusion flow injection (GD-FI) system for the determination of Hg(II) in aqueous samples at trace levels is described. The analytical procedure involved injection of Hg(II) samples and standards into a 1.5 M H 2SO 4 stream which was subsequently merged with a reagent stream of 0.6% SnCl 2 in 1.5 M H 2SO 4 to reduce Hg(II) to metallic mercury. The gas-diffusion cell was thermostated at 85 °C to enhance the vaporization of mercury. The mercury vapour diffused across a Teflon membrane into an acceptor stream containing 0.050 M KNO 3 where it was detected amperometrically at a gold electrode set at +600 mV versus Ag/AgCl reference electrode. Under optimal conditions, the flow injection method is characterized by a linear calibration range between 0 and 80 μg l −1, a detection limit of 900 ng l −1 and a sampling rate of 12 samples per hour. The flow injection system was successfully applied to the determination of mercury in freshwater samples containing colored compounds and suspended particulates and to digested sediment and soil samples. Satisfactory agreement with results obtained by cold vapour atomic absorption spectrometry was observed.

Studies of selectivity in the amaranth method for chlorine dioxide

Studies were designed to evaluate the amaranth method for measuring chlorine dioxide in water. Specifically, the effects of pH and temperature are examined for the amaranth method. The results of interference studies are reported for free available chlorine species, chlorite ion, chlorate ion, iron (III) ion, oxidized manganese, and monochloramine. Additional research focused on selectivity enhancement for chlorine dioxide over free available chlorine using ammonia/ammonium chloride buffer and gas diffusion-flow injection analysis. The results of method detection limit and accuracy and precision studies are reported for measuring chlorine dioxide in the presence of free available chlorine.

Determination of sulfur dioxide in wines by gas-diffusion flow injection analysis utilizing modified electrodes with electrostatically assembled films of tetraruthenated porphyrin

Reported is a new method for the determination of both free and total SO 2 in wine, specially designed for FIA. The method involves separation of the analyte using a flow through gas diffusion unit, in line with an amperometric detector consisting of a glassy carbon electrode modified with electrostatically assembled films of a tetraruthenated porphyrin. The results demonstrate a good accuracy, comparable with those obtained using the conventional iodometric method. In addition, the method can be readily applied to red, white and rose wines; it is free from interference of the other compounds of wine, consumes small amounts of sample and is faster than the iodometric method.

An on-line determination of chlorine dioxide using chlorophenol red by gas diffusion flow-injection analysis

An on-line determination of chlorine dioxide (ClO2) in potable water using chlorophenol red (CPR) by gas diffusion flow-injection analysis (FIA) was investigated in the presence of various chlorinated species that can occur under normal water-treatment conditions. A gas diffusion membrane is used to separate the donor (sample) stream from the acceptor (detecting) stream (the donor stream transports the sample stream to the membrane separate device, and the acceptor stream collects all of the penetrated analytes and transports quantitatively to the detector) and makes it possible for this method to eliminate interference from metal ions, as well as other oxychlorinated compounds such as chlorite and chlorate. The system is more selective for chlorine dioxide than chlorine. The linear range of ClO2 concentration is 0–0.5 mg·mL−1 with a detection limit of 0.02 μg·mL−1 (S/N = 3) and a sampling frequency of 50 h−1. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 157–161, 1999

An on‐line determination of chlorine dioxide using chlorophenol red by gas diffusion flow‐injection analysis

An on-line determination of chlorine dioxide (ClO2) in potable water using chlorophenol red (CPR) by gas diffusion flow-injection analysis (FIA) was investigated in the presence of various chlorinated species that can occur under normal water-treatment conditions. A gas diffusion membrane is used to separate the donor (sample) stream from the acceptor (detecting) stream (the donor stream transports the sample stream to the membrane separate device, and the acceptor stream collects all of the penetrated analytes and transports quantitatively to the detector) and makes it possible for this method to eliminate interference from metal ions, as well as other oxychlorinated compounds such as chlorite and chlorate. The system is more selective for chlorine dioxide than chlorine. The linear range of ClO2 concentration is 0–0.5 mg·mL−1 with a detection limit of 0.02 μg·mL−1 (S/N = 3) and a sampling frequency of 50 h−1. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 157–161, 1999

Determination of ammonium in Kjeldahl digests by gas-diffusion flow-injection analysis with a bulk acoustic wave-impedance sensor

A novel flow-injection analysis (FIA) system has been developed for the rapid and direct determination of ammonium in Kjeldahl digests. The method is based on diffusion of ammonia across a PTFE gas-permeable membrane from an alkaline (NaOH/EDTA) stream into a stream of diluted boric acid. The trapped ammonium in the acceptor is determined on line by a bulk acoustic wave (BAW)-impedance sensor and the signal is proportional to the ammonium concentration present in the digests. The proposed system exhibits a favorable frequency response to 5.0 × 10 −6−4.0 × 10 −3 mol l −1 ammonium with a detection limit of 1.0 × 10 −6 mol l −1, and the precision was better than 1% (RSD) for 0.025–1.0 mM ammonium at a through-put of 45–50 samples h −1. Results obtained for nitrogen determination in amino acids and for proteins determination in blood products are in good agreement with those obtained by the conventional distillation/titration method, respectively. The effects of composition of acceptor stream, cell constant of conductivity electrode, sample volume, flow rates and potential interferents on the FIA signals were discussed in detail.

Calibration methods for determination of ammonium and excess acid in Kjeldahl digests by flow injection analysis

Several modes of calibration for the determination of ammonium (protein) by gas diffusion flow injection analysis (FIA) in Kjeldahl sample solutions have been evaluated with the goal of reducing analytical variability caused by deviations in acid content. Univariate calibration based on peak area as a response function allows accurate and precise determination of the protein content only if small injection volumes, i.e., less than 80 μl, are used. No possibility to estimate the concentration of excess acid then exists. However, by using the entire FIA response curve (1098 data points) and partial least squares (PLS) calibration both protein and excess acid can be determined in one single run. The calibration set must be comprised of solutions covering both the expected protein and the excess acid concentration ranges. The method has been tested on feed samples. Typical values for the root mean square errors of prediction (RMSEP) were 0.8% for protein and 0.025 mol/l for sulphuric acid.

Determination of sulphite in wines by gas-diffusion flow injection analysis utilizing spectrophotometric pH-detection

A photometric flow injection analysis (FIA) method, using a gas-diffusion cell, has been developed for the determination of sulphite in wines. The method is based on the change of the absorbance of an indicator solution when sulphur dioxide, liberated from the matrix, diffuses via a permeable membrane into the indicator solution and locally shifts the pH. As indicator, bromocresol green was used. The method is applicable in the range of 1–20mg/l sulphite and the lower limits of detection is 0.1 mg/l. The reproducibility of the analysis for wines are in the range of 0.7–1.5%. Addition of 10% (v/v) ethanol to all solutions and extensively flushing off these solutions with nitrogen before use is crucial to obtain reliable results. The flushing with nitrogen may be considered as a disadvantage of the present method. The method is applicable to red, white and rosé wines. Carbon dioxide interferes the measurement and therefore the method cannot be used for sparkling wines and beers. The results obtained with the FIA method agrees well with the iodometric titration method using biamperometric detection.

Determination of arsenic by hydride generation gas diffusion flow injection analysis with electrochemical detection

Hydride generation gas diffusion flow injection analysis with two different electrochemical detectors — conductometric or amperometric — has been investigated for the determination of arsenic. With amperometric detection, where a detection limit (signal-to-noise ratio = 3) of 0.01 mg 1 −1 As was achieved, the method was successfully applied to the determination of arsenic in contaminated soil samples. The technique is highly sensitive, accurate and precise, with low susceptibility to interferences, significant reagent and instrument economy, and affords the possibility of the development of a portable field instrument which could be used at a contaminated site.

Flow injection analysis chemiluminescence detection of residual ozone

Chemiluminescent reagents for the determination of residual ozone were compared. Each method was automated using gas diffusion flow injection analysis. The luminol method gave a four order of magnitude working range with an LOD of 0.008 mg O 3/l. The luminol method has better analytical characteristics than the standard colorimetric Indigo Blue methods

Photochemistry of Aqueous Solutions of Dicyanomercury(II) and Potassium Tetracyanomercurate(II)

Photochemically induced reactions of dicyanomercury(II) and potassium tetracyanomercurate(II) in alkaline aqueous solutions were investigated in detail. The studies were conducted in the presence or absence of a titanium(IV) oxide semiconductor photocatalyst utilizing sunlight as the irradiation source. It was established that the cyanide ion liberated from the thermodynamically stable mercury-cyano species can be photocatalytically oxidized via cyanate and nitrite to nitrate. In addition, the process removes over 99 mol% of mercury from the solution. In the absence of the photocatalyst, no photoproducts were detected and mercury remained in solution. The results obtained may have ramifications for the use of solar power for the efficient treatment of large quantities of precious metals mill tailings wastes containing various cyanide species. In addition, in order to follow the fate of cyanide in these experiments, a novel gas-diffusion flow injection analysis system for the determination of cyanide from the thermodynamically stable mercury-cyano complexes was utilized.

Reverse dual phase gas diffusion flow injection analysis

A flow injection gas diffusion system for gas acceptor to liquid donor stream, reverse dual phase gas diffusion flow injection analysis, has been demonstrated. Feasibility was shown with a carbon dioxide chemistry. A series of methods was investigated for hydrazine determinations. Using bromthymol blue indicator and a Celgard 2500 membrane a detection limit of 0.01 ppm v/v hydrazine was observed.