Electrode ammonia

The above discussion does not mean that the use of urease and subsequently the use of an ammonia electrode is not practicable for a urea determination. Unfortunately, the commercial company that produced the urea analyzer, chose a conductivity procedure, which happens to be unsuitable for the laboratory of Neonatology. Had they chosen the ammonia electrode, which happens to be a relatively good electrode, and is especially specific, since only ammonia and not potassium can pass an air space, then the instrument could have been made highly specific for urea. In this case an ammonia determination would be done initially and then subtracted by the computer, from the amount which has been generated subsequently. In any case, with present technology, sensitivity is not adequate to use less than approximately 15fil of serum. 

A representative example of a biocatalytic membrane electrode is an electrode for L-arginine The bacterium streptococcus faecium is immobilized on the gas permeable membrane of an ammonia electrode. Arginine deiminase in the bacterium catalyzes the following reaction... 

L-arginine and the excellent selectivity of the ammonia electrode for NH3. The working range of biosensors of this type is typically only two to three orders of magnitude with a detection limit of 10 to 10 M. 

The extraliposomal ammonium ion concentration [(NH4)jJ yj ] was measured as ammonia with the ammonia electrode at pH 13.5. Under these conditions, all ammonium ions are converted to ammonia and no leakage of intraliposomal ammonium ion occurred during the measurement. For measurements of total ammonium ion plus ammonia present in both intraliposome aqueous phase and external medium ammonia [(NH4)jJ g4i y +(NH4)Jpg j ] the liposomes were sonicated under acidic conditions (pH 1.5-2.0) using the Transonic 460/H bath sonicator in sealed vials for 45 minutes. Then, in order to convert ammonium ion to ammonia, NaOH was added to bring the pH to... 

Therefore, the ISE potential depends on the CO2 partial pressure with Nernstian slope. Contemporary microporous hydrophobic membranes permitted the construction of a number of gas probes, developed mainly by the Orion Research Company (for a survey see [143]. The most important among these sensors is the ammonia electrode, in which ammonia diffusing through the membrane affects the pH at a glass electrode. Other electrodes based on similar principles respond to SO2, HCN, H2S (with an internal S ISE), etc. The ammonia probe has a better detection limit than the ammonium ion ISE based on the non-actin ionophore. The response time of gas probes depends mostly on the rate of diffusion of the test gas through the microporous medium [77,143]. 

Hikuma M, KuboT, Yasuda T, Karube I, Suzuki S (1980) Ammonia electrode with immobilized nitrifying bacteria. Anal Chem 52 1020 -1024... 

The sensitivity of the microbial sensor was almost at the same level as that of a ammonia electrode. The sensor did not respond to volatile compounds such as acetic acid, ethyl alcohol and amines... 

Busenberg, E. and Clemency, C.V., 1973. Determination of the Cation Exchange Capacity of clays and soils using an ammonia electrode. Clays, Clay Miner, 21, 213. 

Sulfuric acid (0.05 TV) — colorimetric phenate method or ammonia electrode method... 

Use an ammonia electrode (Orion Model 95-10, Beckman Model 39565 or equivalent) along with a readout device, such as a pH meter with expanded millivolt scale between -700 mV and +700 mV or a specific ion meter. The electrode assembly consists of a sensor glass electrode and a reference electrode mounted behind a hydrophobic gas-permeable membrane. The membrane separates the aqueous sample from an ammonium chloride internal solution. Before analysis, the sample is treated with caustic soda to convert any NH4+ ion present in the sample into NH3. The dissolved NH3 in the sample diffuses through the membrane until the partial pressure of NH3 in the sample becomes equal to that in the internal solution. The partial pressure of ammonia is proportional to its concentration in the sample. The diffusion of NH3 into the internal solution increases its pH, which is measured by a pH electrode. The chloride level in the internal standard solution remains constant. It is sensed by a chloride ion-selective electrode which serves as the reference electrode. 

Enzyme-selective electrodes (Fig. 17.11) have been made as a membrane containing immobilized enzymes placed over a pH electrode or over a gas electrode such as an ammonia electrode for potentiometric detection, or over an oxygen electrode for amperometric detection. The products of the reaction of enzyme with substrate are detected by the electrode. 

Figure 6 shows a typical calibration curve obtained for the inhibition of binding of a urease-cAMP conjugate to anti-cAMP antibody as determined by the ammonia electrode. One hundred percent of activity refers to blank tubes, which had rates of 11-12 mV/min in the absence of cAMP. Selectivity of the assay over structurally similar cGMP is also shown in Fig. 6. It takes approximately 1000 times more cGMP than...

Thus, the enzyme can be coupled to ammonia electrodes, field effect transistors or chemical methods of ammonia determination [115]. Alternatively, a bi-enz5mie system can be applied combining glutaminase with glutamate oxidase (Eq. (11.4)) ... 

A. Vita, The Determination of Bound Nitrogen in Uranium Hexafluoride with an Ammonia Electrode, Analytical Chimica Acta, 81 (1976) 45-52. 

Direct coupling of the enzymes with the ammonia electrode is not possible, since the sensitivity of the electrode is too low at the optimum pH of the reductases (7.4-7.8). 

A urease packed bed reactor combined with an ammonia electrode is being used in a blood urea nitrogen (BUN) analyzer marketed since 1976 by the Kimble Division of Owens-Illinois (USA). Urease is bound to aluminum oxide particles. The reaction is conducted at pH 7.5. In order to obtain a high sensitivity for the ammonia electrode, the product stream leaving the reactor is mixed with NaOH until a pH of 11 is attained (Watson and Keyes, 1976). 

Meyerhoff and Rechnitz (1976) developed a potentiometric creatinine sensor by inclusion of creatinine iminohydrolase between the gas-permeable membrane of an ammonia electrode and a dialysis membrane. Since the specific activity of the enzyme used was very low, 0.1 U/mg, only 43 mU could be entrapped at the electrode. Therefore the sensor was kinetically controlled and reacted to addition of the enzyme activator tripolyphosphate by an increase in sensitivity from 44 mV to 49 mV per concentration decade and a corresponding decrease of the detection limit. These effects agree with theoretical considerations of reaction-transport coupling. The samples were treated with a cation exchanger to remove endogenous serum ammonia. 

Sloan CH, Morie GP. 1974. Determination of ammonia in tobacco and tobacco smoke with an ammonia electrode. Anal Chim Acta 69 243-247. 

First potentiometric biosensor acrylamide-immobilized urease on an ammonia electrode to detect urea [9]... 

Entrapment of Bacterium cadaveris on an ammonia electrode using dialysis membranes L-aspartate [63]... 

Entrapment of porcine kidney tissue slices or Sarcina flava cells into nylon nets or hollow fiber dialysis units and placement in line with an ammonia electrode for flow-though analysis Glutamine [64]... 

Sloan, C.H. and G.P. Morie Determination of ammonia in tobacco and tobacco smoke with an ammonia electrode 27th Tobacco Chemists Research Conference, Program Booklet and Abstracts, Vol. 27, Paper No. 23, 1973, p. 19 Acta 69 (1974) 243-247. 

Specific ion and specific gas electrodes, as well as other electrode types, can be employed. Examples of the types of bacterial electrodes include the use of Streptococcus foecium immobilized on an ammonia electrode to sense arginine,the use of Sarcina flava and an ammonium electrode to sense L-glutamine, and the use of Lactobacillus fermenti and a platinum, silver peroxide electrode to sense vitamin... 

On interferences of the ammonia electrode, the effect of amines like methyl-amine [151] and trimethylamine [152] is quite noticeable and a simple correction in the latter case was made by adding a 1 1 formalin sample to eliminate ammonia and obtain the trimethylamine reading [152]. Amphetamines and antihistamines have no effect on the electrode [151]. 

Because of a build-up of product in the enzyme membrane, enzyme electrodes require washing prior to contact with the next sample. The washing time varies from just 20 s for urease in conjvmction with an ammonia electrode to as long as 10 min for urease with a pH electrode. The washing time increases with enzyme membrane thickness, as also observed for additional membranes discussed above. It will also depend on the enzyme used and on the characteristic of the base sensor itself, and will be affected by diffusion and kinetic effects. The use of flow injection analysis simplifies the procedures, since the carrier stream serves to wash out between samples. 

By using an ammonia electrode with a gas-permeable membrane that effectively excludes ions, it is possible to obtain the desired selectivity. Several assemblies have been studied to obtain rapid and reliable sensors. 

The colorimetric Nesslerization method uses alkaline phenol and hypochlorite to react with ammonia to form indophenol blue in an amount proportional to the ammonia concentration. The blue color is intensified with sodium nitroprusside, and the concentration is measured using a calibrated colorimeter. The titration of basic ammonia is accomplished with standard sulfuric acid using a mixed indicator. Determination of ammonia may also be based upon the indophenol reaction adapted to automated gas-segmented continuous flow analysis. Potentiometric determination of ammonia is performed by ion-selective ammonia electrodes. 

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