A METHOD AND A DEVICE FOR THE QUANTITATIVE ASSAY OF NH3 IN A SAMPLE

Abstract: The NH3-concentration in a sample is determined by the aid of a device, comprising a layer of a polymer, based upon pyrrole or a derivative of pyrrole, or a derivative of such a polymer. The layer is acted upon by NH3, originating from the sample, and its resistance is measured before and after this action. Increasing concentrations of NH3 mean increasing resistance in said layer.

Description: A method and a device for the quantitative assay of NHg in a sample. This invention relates to a method and a device for the assay of H3 in a sample. Primarily agricultural samples like manure and barn air etc. are concerned. A number of more or less sophisticated methods for the quantita¬ tive assay of NH, in different types of samples have been sug- gested and applied. Thus there are electrodes for the determina¬ tion of NH 3 /NH 4 + . By adding alkali the equilibrium is dis¬ placed towards NH3. The method is primarily intended for labo¬ ratories and demands relatively advanced instrumental equipment and a sensitive electrode. Thus the method is relatively expen- sive. According to another laboratory method the sample is alkalized and NH, is driven off, and captured in a vessel with acid. The ammonia content is determined by titration. This method is in- tended for laboratories only and demands skilled staff. According to one further laboratory method a colour reaction with Nessler's reagent is utilized, the intensity of a yellow colour obtained being spectrophotometrically determined. Straight chemical methods are also employed, e.g. by oxidizing NHa j to N2 and measuring the change of volume or pressure obtained. None of these methods meets the demands of being simple, reli¬ able, inexpensive and giving sufficient accuracy of measurement. These demands are actual in many situations, for instance among farmers for samples of manure, barn air etc. The object of the present invention is to provide a method and a device for the quantitative assay of H β in a sample, espe¬ cially manure and the like, the demands just mentioned being met. According to the invention such a method is characterized in that the sample is brought into contact with a sensing body, comprising a polymer,- either based upon pyrrole or a derivative of such a polymer, in such a way, that the NH of the sample is caused to act upon the sensing body, the resistance of same being determined before and after said action. It has namely become obvious that the resistance of a polymer layer of the type just mentioned increases with rising NH,- concentration in a sample that is brought into contact with said layer. Either the sample can be brought into direct contact with the layer, or gas phase, originating from the sample can be brought into contact with the layer. As liquid water disturbs the measurement it may be suitable to provide a membrane that is permeable for a gas but not for a liquid, between the sample and said layer. This membrane may be somewhat spaced from the layer or be applied in direct contact with the polymer layer. Considering the fact that a liquid like water disturbs the measurement it can be suitable to maintain the layer at a some- what higher temperature than the sample, e.g. 10° higher, so that condensate is avoided. The invention shall now be described more in detail, reference being made to the accompanying figures, in which figure 1 schematically shows a device according to the inven¬ tion, and figure 2 shows the resistance of a sensing layer as a function of the time at different NH concentrations. In figure 1 a carrier plate of non conductive material is given number 1. On same there is applied a thin layer of polypyrrole 2, in contact with two leads 3,4, which are connected to a resistance meter 5, which is not further described. On the back side of the carrier plate there is glued a little circuit of resistor wire, which is not shown in the figure. This resistor wire is connected to a low voltage source. The carrier plate is fastened to a plug 6, which fits a cover to a test tube 7. In the figure this test tube is shown filled to about 1/3 with a sample 8. In figure 2 there is shown the result of measurements of three test solutions of water, containing 500-1000-1500 ppm NH,, and a manure sample. When measuring, at a temperature of 20° in the samples and 30°C in the polymer layer, a 4 ml sample was introduced into the test tube, and 0.1 ml 10 M NaOH was added, whereupon the measuring device was inserted quickly into the test tube 7, which was tr-en closed by the plug 6. By the addi¬ tion of NaOH H^ and Hg in the sample were transferred to the gas phase. The resistance was determined continuously during 10 minutes and the curves in figure 2 were drawn. With the aid of the calibration curves it can be established that the NHβ-concentration in the manure sample Is about 750 ppm.

Claims: Claims 1. A method for the quantitative assay of H3 in a sample c h a r a c t e r i z e d i n that the sample is brought into contact with a sensing body, comprising a polymer, either based upon pyrrole or a derivative of pyrrole, or a derivative of such a polymer, so that the NH, of the sample is caused to act upon the sensing body, the resistance of same being deter¬ mined before and after said action. 2. A method according to claim 1, c h a r a c t e r i z e d i n that the sample Is brought into direct contact with said sensing body. 3. A method according to claim 1, c h a r a c t e r i z e d i n that the sample is brought Into contact with the sensing body. 4. A method according to claim 3, c h a r a c t e r i z e d i n that said gas phase is brought Into contact with the sen- sing ^ body after having passed a membrane, which is permeable for a gas but not for a liquid. 5. A method according to any of claims 1-4, c h a r a c — t e r i z e d i n that the sensing body is heated to a tem¬ perature somewhat higher than the temperature of the sample in order to avoid condensate on same when measuring. 6. A device for carrying out the method according to any of claims 1-5, c h a r a c t e r i z e d by a sensing body, comprising a polymer, either based upon pyrrole or a derivative of pyrrole, or a derivative of such a polymer, connected by leads to a resistance meter. 7. A device according to claim 6, c h a r a c t e r i z e d i n that the sensing body comprises a carrier, onto which there is applied a relatively thin layer of said polymer. 8. A device according to claim 6, in which gas phase, origina¬ ting from the sample, is brought into contact with the sensing body, c h a r a c t e r i z e d i n that a membrane, per¬ meable for a gas, but not for a liquid, is provided between the sample and the sensing body. 9. A device according to claim 8, c h a r a c t e r i z e d i n that the membrane is made from polytetrafluorethylene. 10. A device according to any of claims 6-9, c h a r a c - t e r i z e d i n that the sensing body is provided with a circuit for electrical heating.

Inventors: ARMGARTH MAORTEN, LUNDSTROEM INGEMAR, NYLANDER CLAES, ARMGARTH, MAORTEN, LUNDSTROEM, INGEMAR, NYLANDER, CLAES
Applicants: ALFA LAVAL AGRI INT, ALFA-LAVAL AGRI INTERNATIONAL AB
Application year: 1984
Main classification: G01N27
IPC codes: G01N27, G01N31