Urea and ammonia removal from dialysate in an oxygenator: Effects of dialysate and air flow rates

This paper reports the effects of dialysate and air flow rates on the transport characteristics of an oxygenator for the removal of urea as ammonia from dialysate. Urea was first hydrolyzed to ammonia and bicarbonate by urease. This was followed by alkalinization to increase free ammonia concentration. Ammonia is removed by stripping with air in an oxygenator. It was shown that the ammonia removal rate increases with increasing dialysate flow rate or air flow rate, but reaches a plateau value when the flow rates are above 1000 ml/min for dialysate and 1000 ml/sec for air.     

Flow/sequential injection determination of gaseous ammonia with a glass diffusion denuder

A new combination of a flow/sequential injection method for the analysis of ammonia has been developed. Gaseous ammonia is selectively absorbed in a phosphoric acid coated glass tube and determined with Berthelot reagents by flow injection. The combination of the gas diffusion denuder sampler with flow injection makes this method very sensitive and selective. The limit of detection of 0.15 mug NH(3).     

Sampling small volumes of ambient ammonia using a miniaturized gas sampler

The development of a gas sampler for a miniaturized ambient ammonia detector is described. A micromachined channel system is realized in glass and silicon using powder blasting and anodic bonding. The analyte gas is directly mixed with purified water, dissolving the ammonia that will dissociate into ammonium ions. Carrier gas bubbles are subsequently removed from the liquid stream through a venting hole sealed with a microporous water repellent PTFE membrane. A flow restrictor is placed at the outlet of the sampler to create a small overpressure underneath the membrane, enabling the gas to leave through the membrane. Experiments with a gas flow of 1 ml min(-1), containing ammonia concentrations ranging from 9.4 ppm to 0.6 ppm in a nitrogen carrier flow have been carried out, at a water flow of 20 microl min(-1). The ammonium concentration in the sample solution is measured with an electrolyte conductivity detector. The measured values correspond with the concentration calculated from the initial ammonia concentration in the analyte gas, the fifty times concentration enhancement due to the gas-liquid volume difference and the theoretical dissociation equilibrium as a function of the resulting pH.     

A polypyrrole-based amperometric ammonia sensor

An ammonia sensor is described in this work. The sensing membrane is a thin layer of oxidized polypyrrole (PPy) on a platinum substrate. This sensor is used as the working electrode in a conventional three-electrode system for amperometric measurement of ammonia in aqueous solutions in the potential range of + 0.2 to + 0.4 V (vs. Ag/AgCl). Contact with ammonia causes a current to flow through the electrode. This current is proportional to the concentration of free ammonia in the solution and ammonium ions do not contribute to the measured signal. The signal is due to reduction of PPy by ammonia with subsequent oxidation of PPy by the external voltage source. The sensor is able to detect ammonia reproducibly at the muM level. The main interference is the doping effect of small anions such as Cl(-) and NO(3)(-), also giving a response on PPy at the mM level. This anionic response can, to a certain degree, be reduced by covering the polymer surface with dodecyl sulfate. The sensor gradually loses its activity when exposed to ammonia concentrations greater than 1 mM. The sensor has been tested by the flow injection analysis technique.     

Photoassisted NO reduction with NH3 over TiO2 photocatalyst

Photoassisted selective catalytic reduction of NO with ammonia (photo-SCR) at low temperature over irradiated TiO2 in a flow reactor was confirmed to proceed efficiently and the adsorbed ammonia reacted with NO under irradiation of TiO2.     

Simultaneous flow-injection flourimetric determination of ammonia and hydrazine with a novel mode of forming pH gradients

A flow injection configuration is suggested for the simultaneous determination of ammonia and hydrazine at the μg ml^?1 level by formation of zones of different pH. The analytes react with o-phthalaldehyde and mercaptoethanol to form fluorescent derivatives at different pH values. In addition to the normal flow method, a stopped flow method is proposed to increase the ranges that can be quantified. The analysis of samples containing hydrazine and ammonia in ratios between 0.3 and 70.0 is described.     

Miniaturized measurement system for ammonia in air

The development of a miniaturized ammonia sensor made using microsystem technology is described. Gas is sampled in a sampler comprising two opposite channels separated by a gas permeable, water repellent polypropylene membrane. Subsequently, the acid sample solution is pumped into a selector where an alkaline solution is added to ionize all sampled ambient acid gasses, resulting in an enhanced selectivity. In the selector, the ammonia can diffuse through a second membrane into a purified water stream where an electrolyte conductivity sensor quantifies the resulting ammonium concentration. The realized system is shown to be selective enough not to be influenced by normal ambient carbon dioxide concentrations. Experiments with a gas flow of 3 ml/min, containing ammonia concentrations ranging from 9.8 to 0.3 ppm in a nitrogen carrier flow, into a 15 μl/min sample solution flow and finally into a 5 μl/min purified water stream have been carried out and show that the system is sensitive to ammonia concentration below 1 ppm.     

Flow-injection determination of ammonia in kjeldahl digests by gas diffusion and conductometry

A flow injection/conductometric method is proposed for determing ammonia in solutions obtained from Kjeldahl digestion. The method is based on diffusion of ammonia through a PTFE membrane from an alkaline (NaOH/EDTA) medium to a deionized water stream. The change in conductance of the deionized water stream is proportional to the ammonia concentration present in the digest. The effects of flow parameters, temperature and potential interferences are reported. Approximately 100 samples can be injected per hour; the precision is about 1%. Results for total nitrogen in vegetable tissues, animal feeds and fertilizers are in good agreement with those obtained by the usual distillation/titration method.     

Ammonia decomposition catalysis using non-stoichiometric lithium imide

We demonstrate that non-stoichiometric lithium imide is a highly active catalyst for the production of high-purity hydrogen from ammonia, with superior ammonia decomposition activity to a number of other catalyst materials. Neutron powder diffraction measurements reveal that the catalyst deviates from pure imide stoichiometry under ammonia flow, with active catalytic behaviour observed across a range of stoichiometry values near the imide. These measurements also show that hydrogen from the ammonia is exchanged with, and incorporated into, the bulk catalyst material, in a significant departure from existing ammonia decomposition catalysts. The efficacy of the lithium imide–amide system not only represents a more promising catalyst system, but also broadens the range of candidates for amide-based ammonia decomposition to include those that form imides.     

Fluorescence Spectrophotometric Determination of Trace Ammonia

Measurement of trace ammonia (or ammonium ion) is important for environmental monitoring. Hiroshi Mikasa et al and Satoshi Sasaki et al had reported the determination of trace ammonia by flow injection analysis based on the reaction of ammonia and o-phthaiadehyde in the presence of 2-mercaptoethanol. The reaction equation is as follows.     

Separation of ammonia with a gas-permeable tubular membrane

Ammonia concentrations in reaction mixtures at pH ? 7.1 are measured by diffusion of the ammonia through a hydrophobic microporous poly (tetrafluoroethylene) tubular membrane placed in the solution. The ammonia is absorbed in an acidic (pH 5) carrier flowing the bore of the tubing, and measured in portions of the effluent with an ammonia electrode. The slopes of the linear responses are influenced by pH, flow rate and tubing dimensions.     

Ammonia abatement in an enzymatic flow system for the determination of creatinine in blood sera and urine

The abatement of ammonia in standard solutions, and in human blood and urine samples is achieved by adding suitable amounts of NADPH and α-ketoglutarate to the sample and passing it through a 2-m nylon tube with glutamate dehydrogenase immobilized on the inner wall. The procedure provides removal of 98% of the ammonia (1–5 × 10^?4 M) in the original sample in 50 s. The abatement of ammonia permits the use of an ammonia probe coupled with an immobilized degradative enzyme for the determination of creatinine. Creatinine was determined in clinical blood and urine samples by first removing the ammonia from the sample and then cleaving the creatinine to N-methylhydantoin and ammonia with immobilized creatininase. Only 200 μl of sample is needed and the entire process is conducted in a single flow stream.     

Determination of Ammonia/Air Diffusion Coefficient Using Nafion Lined Tube

Abstract

Trace gaseous ammonia in air was removed in a laminar flow Teflon tube lined with Nafion film. The ammonia deposition pattern was obtained by sectioning the Nafion lining, extracting with an aqueous solution, and measuring the concentration with an ammonia gas electrode. Mass transport analysis of the deposition pattern demonstrated that the ammonia was removed from the air stream at a rate controlled by gaseous diffusion. The ammonia/air diffusion coefficient equalled 0.228 ± 0.012 cm² s^?1 at 1 atm 25°C. No dependence on relative humidity was observed over the range 10–92%.     

Tissue- and bacteria-loaded tubular reactors for the automatic determination of glutamine

Porcine kidney tissue or Sarcina Flava bacterial cells are used as biocatalysts for the conversion of glutamine to ammonia, which is monitored with a gas-sensing membrane electrode in an automated flow system. Conversion to ammonia is 100% for ? 10^-4 M glutamine.     

Determination of creatinine in clinical samples with a creatininase reactor and an ammonia probe

A commercial nylon coil with immobilized creatininase in conjunction with a potentiometric ammonia probe is used in a continuous flow apparatus for the determination of creatinine in blood plasma and urine. The analytical characteristics of the coil are evaluated and its specific enzymatic activity is calculated. The determination of creatinine in plasma is viable provided that samples are processed quickly after they have been taken and that plasma ammonia is evaluated just before the creatinine determination. Analyses of urine require prior separation of ammonia. For plasma, 40 samples/hour can be processed with confidence. The precision of the procedure depends strongly on the plasma ammonia level and is about 5% for normal conditions.     

A selected ion flow tube mass spectrometry study of ammonia in mouth- and nose-exhaled breath and in the oral cavity

A study has been carried out, involving three healthy volunteers, of the ammonia levels in breath exhaled via the mouth and via the nose and in the static oral cavity using on-line, selected ion flow tube mass spectrometry (SIFT-MS), obviating the problems associated with sample collection of ammonia. The unequivocal conclusion drawn is that the ammonia appearing in the mouth-exhaled breath of the three volunteers is largely generated in the oral cavity and that the ammonia originating at the alveolar interface in the lungs is typically at levels less than about 100 parts-per-billion, which is a small fraction of the total breath ammonia. This leads to the recommendation that exhaled breath analyses should focus on nose-exhaled breath if the objective is to use breath analysis to investigate systemic, metabolic disease.     

Flow-injection determination of inorganic forms of nitrogen by gas diffusion and conductimetry

A flow-injection—conductimetric method was applied to the determination of ammonia, nitrate and nitrite at concentrations down to 5, 20 and 20 ng ml^?1, respectively. Ammonia was determined by merging the injected sample with an alkaline solution (NaOHEDTA) and passing the mixture through a diffusion cell. The ammonia released was collected by a flowing stream of deionized water that passed through a conductance flow cell. Nitrate and nitrite concentrations were determined after reduction to ammonia in alkaline medium using a column filled with metallic zinc. The ammonia produced was then measured as described above. About 60 samples per hour can be processed with a relative standard deviation of about 1%. Satisfactory agreement was observed between results for ammonia in samples of natural water and nitrate in tap and mineral water determined by the proposed method and by standard spectrophotometric procedures. Speciation can be achieved by adding sulphanilic acid to remove nitrite from the sample and determining the ammonia without the use of the column.     

Photocatalytic degradation of ammonia and butyric acid in plug-flow reactor: Degradation kinetic modeling with contribution of mass transfer

Photocatalytic treatment of polluted air by odorous contaminants – ammonia and butyric acid – is investigated in a plug-flow reactor covered by non-woven fiber textile coated with TiO₂. For the first time, the single-component degradation pathway of ammonia by photocatalysis at ambient condition is highlighted. It appears fundamentally different compared to the butyric acid degradation pathway. The ammonia degradation pathway highlights a possible auto-accelerated behavior of the reaction. The chemical degradation kinetics follows the Langmuir–Hinshelwood model, though observed oxidation rates depend upon flow conditions in the reactor. Thus, interpretation of degradation results through a model considering the Langmuir–Hinshelwood approach and mass transfer phenomenon is presented. This model succeeds with a pair of determined kinetic constants and mass transfer coefficients to describe experimental results for different flow rates and for both pollutants, though they present wide dissimilarities in their degradation pathways.     

Effect of pH and gaseous ammonia flow rate on the composition and structure of ammonium uranate

Ammonium uranate was precipitated from uranyl nitrate solution using gaseous ammonia, then filtered, washed with demineralized water and dried. The influence of pH and ammonia flow rate on their composition and structure were examined by X-ray diffraction analysis, making use of additional information obtained from infrared analysis.     

Influence of the preparation method on the textural properties of zirconia

Summary New composite sorbents &quot;chlorides of alkaline-earth metals confined to porous alumina&quot; were synthesized and tested for ammonia abatement in a fixed-bed flow adsorber at 25-300°C. It was found that the matrix modification with the salts leads to an increase in its dynamic sorption capacity in the row BaCl₂ < CaCl₂ < MgCl₂. This can be caused by a salt-ammonia interaction that results in the formation of ammonia complexes. The dynamic capacity was found to strongly decrease with temperature. The maximal sorption capacity was detected for a sorbent based on MgCl₂. It equals 58.6 and 11.6 mg/g at T = 25 and 300°C, respectively, or 3.2 and 0.6 mole of ammonia per 1 mole of the salt. The data obtained can be used for the analysis of the dynamic behavior of the new sorbents in flow systems for the ammonia removal from gas mixtures, which can be of high interest for gas separation, chemical engineering and catalysis.