WO1998033065A1 - Process for determination of nitrogen - Google Patents
Process for determination of nitrogen Download PDFInfo
- Publication number
- WO1998033065A1 WO1998033065A1 PCT/SE1998/000090 SE9800090W WO9833065A1 WO 1998033065 A1 WO1998033065 A1 WO 1998033065A1 SE 9800090 W SE9800090 W SE 9800090W WO 9833065 A1 WO9833065 A1 WO 9833065A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- process according
- aracterised
- nitrogen
- distillation
- added
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/002—Determining nitrogen by transformation into ammonia, e.g. KJELDAHL method
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T436/00—Chemistry: analytical and immunological testing
- Y10T436/17—Nitrogen containing
- Y10T436/176152—Total nitrogen determined
Definitions
- the present invention relates to a process for determination of nitrogen, primarily Kjeldahl nitrogen, using an equipment which substantially comprises a multiple step working order.
- the working order comprises, besides sample preparation, an pre-treatment, such as digestion, of a sample of a nitrogen containing material, followed by distillation and determination/analysis of the nitrogen content, determination of to said nitrogen content directly related amounts of one or more compounds and/or determination of to said nitrogen content directly related analytical parameters.
- Said determination/analysis is suitably performed gravimetrically, volumetrically and/or chromatographically.
- the process of the present invention refers to a new sequence of the substeps of said distillation, whereby a number of surprising advantages, such as increased operational security and increased analytical accuracy, are obtained.
- the Kjeldahl method for determination of nitrogen was introduced in 1883 and has since been subject to substantial development efforts with the aim of improving said method. Determination of nitrogen according to Kjeldahl is today one of the most frequently used analytical methods for analysis of raw materials and final products within for instance the food and forage industry.
- the chemical principle behind the Kjeldahl method can in short be said to comprise a digestion step carried out at a high temperature, whereby a nitrogen containing sample, such as a protein, in the presence of an acidic reagent, usually comprising sulphuric acid, and a catalyst is transformed into ammonium ions.
- the sample is subsequently cooled and alkali is added to the digested sample, whereby said ammonium ions are transformed into gaseous ammonia and recovered as such during a distillation.
- the amount of distilled ammonia is finally determined, for instance titrimetrically.
- instruments designed to automatically perform said digestion, distillation and analysis normally used are nowadays instruments designed to automatically perform said digestion, distillation and analysis normally used. These instruments provide increased capacity and operational security as well as release operators time due to extended unattended operations.
- a typical working sequence when determining nitrogen according to Kjeldahl and using a commercially available equipment is digestion, distillation and titration and can be exemplified as follows.
- a prepared sample of a nitrogen containing material is weighed into a 100-1000 ml digestion tube in an amount of 0.1 -0.5 g followed by addition of 5-20 ml of an acidic reagent, normally concentrated sulphuric acid, and 3-9 g of a catalyst/salt mixture.
- the catalyst/salt mixture can for instance comprise potassium salts, such as potassium sulphate, in combination with copper and/or selenium and optionally a peroxide, such as hydrogenperoxide.
- the digestion tube is normally a cylindrical tube (a so called Kjeldahl tube) made of heat resistant glass.
- Digestion is normally performed at a temperature of 300-600°C, such as 400-500°C or preferably « 420°C, during for example 45-120 minutes.
- the digestion involves a chemical reaction wherein bonded nitrogen or nitrogen otherwise included in the material sample is transformed into ammonium ions.
- the material sample with added reagent and salt/catalyst is sometimes put on hold before distillation.
- a certain degree of digestion occurs, despite the lack of heating, during this hold.
- a certain amount, such as 2-15 ml, of acid is normally present in the digestion mixture after completed digestion.
- the digested sample is normally a liquid (acidic solution), but acidic salt crusts are sometimes formed during cooling of the sample.
- the digestion conditions can within certain limits be adjusted to avoid formation of said salt crusts.
- the use of high amounts of acid normally result in a liquid solution also after cooling.
- the disadvantages using high amounts of acid are obvious and comprise increased energy consumption, increased raw material costs, increased costs for waste disposal, hygienic problems related to handling of concentrated acid and reduced analytical accuracy and operational security.
- the tube containing the digested sample is subsequent the digestion transferred to a distillation equipment and most often diluted with for instance water.
- the dilution is primarily made to reduce the acid strength in the digested sample.
- the dilution is in simpler equipment made manually and in more sophisticated equipment by means of an automatic control system.
- Alkali such as sodium or potassium hydroxide
- Alkali is now added to increase the pH value from « 0 to more than 10, preferably « 12.
- Heat is developed when alkali is added to the sample, which despite the dilution is strongly acidic, and the solutions are normally allowed to mix, at least partly, before distillation. Distillation, most often an steam distillation, is then commenced and obtained ammonia containing distillate is recovered, suitably in an acidic and/or complexing medium such as boric acid. Determination of ammonia, protein and nitrogen, that is Kjeldahl nitrogen, is performed titrimetrically, so called acid-base titration.
- Standard methods such as ISO, CEN, SIS, AOAC, etc., for determination of Kjeldahl nitrogen are normally adapted to manual handling of samples. These methods basically follow above disclosed procedure, including the substeps of the distillation step. The same is valid for control systems used in commercially available automatic equipment.
- the process steps and substeps is always performed in below sequence: a) Sample pre-treatment, normally digestion, b) Distillation comprising the substeps: a) Dilution, b) Alkali addition, c) Distillation, such as steam distillation, c) Determination/analysis.
- Added alkali is normally slowly descending towards the bottom of the tube, forming interfacial layers, and if a salt crust is formed during the digestion towards the liquid layer beneath the salt crust.
- Addition of alkali is uncertain and a heavy heat generating reaction may occur between acid and alkali.
- the alkali solution has a tendency to form a layer beneath the water diluted sample solution, why a large excess of alkali will be added before reaction between alkali and acid occurs.
- the heat generated by reaction between alkali and acid is proportional to the amount of acid remaining in the digested sample.
- the subsequent step, the distillation step is normally commenced 5-30 seconds after the alkali addition.
- the acid containing digested sample solution and the alkali solution are during said 5-30 seconds mixed to a certain degree through, mainly diffusion processes in the interface between these solutions.
- Inlet of steam for steam distillation implies a rapid mixing of the acidic sample and the alkali with pendant increased temperature.
- a large acid excess or the presence of salt crusts may give rise to a heavy and even hazardously heavy reaction.
- Alkali and/or sample may escape the tube due to tube cracking or activation of safety lock gates and the like.
- the present invention makes it quite unexpectedly possible to avoid disclosed drawbacks and problems related to nitrogen determination according to for instance Kjeldahl.
- the present invention comprises a completely new working sequence in regard of the substeps in the distillation step.
- the step and substeps of the present invention comprises (a) pre-treatment, such as said digestion of a sample of a nitrogen containing material, (b)(i) dilution of the pre-treated sample with for instance water or a weak aqueous alkali solution giving a sample pH of 7-9, (b)(ii) inlet of steam and commencement steam distillation, (b)(iii) addition of alkali, preferably as an aqueous solution and (c) determination/analysis by for instance titration.
- the alkali in the weak alkali solution added in step (b) substep (i) and the alkali added in step (b) substep (iii) are suitably an alkali metal hydroxide, such as potassium and/or sodium hydroxide.
- Step (b) substep (ii) gives a thorough mixing of the digested and acidic sample and the diluting liquid added in step (b) substep (i) and disintegration and solution of possible salt crusts formed during the pre-treatment/digestion. Inlet of steam is always commenced before addition of alkali according to step (b) substep (iii), which implies a thorough mixing and minimised formation of layers having different acid or alkali concentrations.
- a suitable time difference between substeps (ii) and (iii) of step (b) is within the interval 1 -60 seconds. There will, should the time period between initiating said substeps (ii) and (iii). be too long, be a certain risk of over heating said pre-treated/digested and diluted sample during the addition of alkali. The risk is related to the heat generated by reaction between acid and alkali during said step (b) substep (iii).
- the time difference between said substeps (ii) and (iii) of step (b) is suitably less than 60 seconds, preferably less than 30 seconds such as 2-20 or 2-5 seconds.
- the alkali addition suitably in the form of an aqueous solution of potassium and/or sodium hydroxide, is continued until the pH value of obtained mixture of digested and diluted sample and added alkali reaches a value of 10-14, preferably 1 1 -13 and most preferably 12 ⁇ 0.2. Said pH value should, in order to obtain as accurate an analytical result as possible, not be less than 10.
- Addition of alkali is substantially performed synchronised with inlet of steam whereby said inlet of steam provides a continuous mixing and whereby layers having different acid and alkali concentrations is avoided.
- step (b) The distillate formed during step (b) is suitably recovered by means of conventionally used methods, for instance in an acidic and/or ammonia complexing medium such as an aqueous solution of boric or sulphuric acid.
- Step (c) comprises a determination/analysis, which suitably is performed according to known gravimetric, volumetric, chromatographic etc. procedures, such as titration.
- the process according to the present invention is very suitable for determination of nitrogen according to Kjeldahl including determination of to said nitrogen directly related compounds and/or analytical parameters.
- Compounds which can be directly related to said nitrogen can be exemplified by proteins, amines and amino acids as well as by nitrogen containing compounds such as ammonium, urea, nitro, azo, hydrazo compounds, nitrates and nitrites.
- sequence of substeps in the distillation step of the present invention is furthermore suitable to be included in processes for determination of compounds such as cyanides and phenols.
- the process of the present invention comprises a pre-treatment step.
- a pre-treatment may comprise mixing a nitrogen containing material with an acidic reagent followed by digestion at a temperature of 300-600°C, preferably 400-500°C and most preferably 400-450°C, or mixing a nitrogen containing material with an acidic reagent at a temperature of 0-50°C, preferably 20-25°C, followed by a hold at said temperature until distillation can be performed with requested effect.
- the process of the present invention furthermore comprises at least one determination or analysis as previously disclosed, such as a titration.
- the utility and application of the process according to the present invention are highly improved compared to conventionally used processes wherein large amounts of acidic reagents, such as sulphuric acid, are present.
- a wider acidic interval can be used with high analytical accuracy (correct nitrogen yield), which is an advantage in many standard methods, such as ISO, IDF, AOAC etc., which methods require or demand analytical conditions wherein large amounts of acidic reagents are used.
- Example 1 teaches an embodiment of the present invention used for determination of Kjeldahl nitrogen
- Example 2 comparative example
- Example 3 refers to nitrogen yields obtained according to the process of the present invention and according to a conventionally used process. Said nitrogen yields are presented as a graph (Graph 1 ). While particular embodiments of the invention are shown, it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended Claims any such modifications as fall within the true spirit and scope of the invention.
- Digestion 1.000 g of a homogeneous nitrogen containing sample of a grain product was weighed into a digestion tube, a so called Kjeldahl tube. 12 ml of concentrated sulphuric acid and a catalyst/salt mixture consisting of 7.0 g of
- the digestion tube containing the digested sample was connected to a distillator. 70 ml of water was initially added to dilute the remaining acid. Steam was now let in and steam distillation commenced. Salts crusts were disintegrated and gradually dissolved. 50 ml of a 40%-w/w aqueous sodium hydroxide solution was 2 seconds later added to increase the pH value to more than 10. The ammonium ions were at this high pH value transformed into ammonia and formed ammonia was steam distilled to a collector containing 25 ml of a 4%-w/w aqueous boric acid solution. The boric acid solution contained a pH indicator (bromocresol green/methyl red). A total volume of 150 ml was distilled to the collector. The boric acid formed complexes with the ammonia.
- a pH indicator bromocresol green/methyl red
- N Normality of titrant
- the digestion tube containing the digested sample was connected to a distillator. 70 ml of water was initially added to dilute the remaining acid followed by addition of 50 ml of a 40%-w/w aqueous sodium hydroxide solution to increase the pH value to more than 10. Salt crusts were not or only to a very small extent affected by addition of water and/or sodium hydroxide solution. The ammonium ions were at this high pH value transformed into ammonia. Steam was 5 seconds after addition of sodium hydroxide let in and steam distillation commenced. Formed ammonia was steam distilled to a collector containing 25 ml of a 4%-w/w aqueous boric acid solution. The boric acid solution contained a pH indicator (bromocresol green/methyl red). A total volume of 150 ml was distilled to the collector. The boric acid formed complexes with the ammonia. Titration and calculation: As in Example 1.
- Nitrogen yield during distillation and titration according to the present invention (Example 1) and according to a conventionally used process (Example 2) was determined by means of a known amount of nitrogen, in the form of ammonium sulphate, added to 0-18 ml of sulphuric acid. The results were after distillation and titration calculated and plotted as a graph (Graph 1 below).
- Graph 1 shows unambiguously that the process according to the present invention has a substantially increased analytical accuracy and that said process can be utilised when very high amounts of acid is used.
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Abstract
Description
Claims
Priority Applications (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU58881/98A AU5888198A (en) | 1997-01-29 | 1998-01-22 | Process for determination of nitrogen |
DE69836203T DE69836203T2 (en) | 1997-01-29 | 1998-01-22 | PROCESS FOR DETERMINING THE NITROGEN CONTENT |
JP53039498A JP4248606B2 (en) | 1997-01-29 | 1998-01-22 | Nitrogen determination method |
EP98902325A EP0960331B1 (en) | 1997-01-29 | 1998-01-22 | Process for determination of nitrogen |
US09/362,722 US6287868B1 (en) | 1997-01-29 | 1999-07-29 | Process for determination of nitrogen |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE9700249A SE508220C2 (en) | 1997-01-29 | 1997-01-29 | Procedure for determining nitrogen according to Kjeldahl |
SE9700249-7 | 1997-01-29 |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/362,722 Continuation US6287868B1 (en) | 1997-01-29 | 1999-07-29 | Process for determination of nitrogen |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1998033065A1 true WO1998033065A1 (en) | 1998-07-30 |
Family
ID=20405550
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/SE1998/000090 WO1998033065A1 (en) | 1997-01-29 | 1998-01-22 | Process for determination of nitrogen |
Country Status (8)
Country | Link |
---|---|
US (1) | US6287868B1 (en) |
EP (1) | EP0960331B1 (en) |
JP (1) | JP4248606B2 (en) |
AU (1) | AU5888198A (en) |
DE (1) | DE69836203T2 (en) |
ES (1) | ES2275298T3 (en) |
SE (1) | SE508220C2 (en) |
WO (1) | WO1998033065A1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
NL1018545C2 (en) * | 2001-07-13 | 2003-01-14 | Energieonderzoek Ct Nederland | Measuring nitrogen content of solid or liquid samples e.g. animal feeds or foodstuffs, by measuring conductivity of aqueous liquid containing diffused ammonia |
KR100882770B1 (en) * | 2008-05-27 | 2009-02-10 | (주)한일랩테크 | Kjeldahl distillation apparatus and method for operating the same |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN102353574B (en) * | 2011-07-14 | 2014-03-26 | 安徽省电力科学研究院 | Analysis method of iron content in cationic exchange resin |
WO2014117868A1 (en) * | 2013-02-04 | 2014-08-07 | Opsis Ab | Method and apparatus for titration |
MX2017012703A (en) * | 2015-04-20 | 2017-11-23 | Halliburton Energy Services Inc | Methods for quantifying nitrogen-containing compounds in subterranean treatment fluids. |
CN106645560A (en) * | 2017-01-09 | 2017-05-10 | 沈阳伟嘉牧业技术有限公司 | Method for determining total nitrogen content of albendazole nitroclofene tablets |
CN108802264A (en) * | 2018-07-09 | 2018-11-13 | 天津华勘商品检验有限公司 | A kind of kjeldahl apparatus measures the detection method of nitrogen in carburant |
CN109939761A (en) * | 2019-04-10 | 2019-06-28 | 上海纤检仪器有限公司 | A kind of reflux bottle flowing backwards waste suction liquid for azotometer |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3905770A (en) * | 1972-09-15 | 1975-09-16 | Tecator Instr Ab | Apparatus for use in determination of nitrogen by the Kjeldahl method |
Family Cites Families (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2820699A (en) * | 1954-04-30 | 1958-01-21 | George M Morris | Anti-foaming material |
NL278868A (en) * | 1961-05-25 | |||
NL298225A (en) * | 1963-09-23 | |||
US3335097A (en) * | 1966-12-21 | 1967-08-08 | Pillsbury Co | Digestion catalyst |
DE2534773A1 (en) * | 1975-08-04 | 1977-02-17 | Max Planck Gesellschaft | METHOD AND DEVICE FOR DIRECT MICRO-DETERMINATION AND TRACE DETERMINATION OF NITROGEN IN THESE SUBSTANCES |
DK445277A (en) * | 1977-10-07 | 1979-04-08 | Foss Electric As | PROCEDURE AND CATALYST FOR DETERMINING NITROGEN IN A SUBSTANCE SUBSTANCE SAMPLE |
US4645745A (en) * | 1984-02-27 | 1987-02-24 | Hach Company | Digestion process |
US4645746A (en) * | 1986-01-06 | 1987-02-24 | Hach Company | Digestion process |
GB2290140B (en) * | 1994-06-06 | 1998-09-09 | Meidensha Electric Mfg Co Ltd | Device and method for estimating nitrogen-including ionic substances in water |
-
1997
- 1997-01-29 SE SE9700249A patent/SE508220C2/en not_active IP Right Cessation
-
1998
- 1998-01-22 WO PCT/SE1998/000090 patent/WO1998033065A1/en active IP Right Grant
- 1998-01-22 AU AU58881/98A patent/AU5888198A/en not_active Abandoned
- 1998-01-22 EP EP98902325A patent/EP0960331B1/en not_active Expired - Lifetime
- 1998-01-22 ES ES98902325T patent/ES2275298T3/en not_active Expired - Lifetime
- 1998-01-22 JP JP53039498A patent/JP4248606B2/en not_active Expired - Lifetime
- 1998-01-22 DE DE69836203T patent/DE69836203T2/en not_active Expired - Lifetime
-
1999
- 1999-07-29 US US09/362,722 patent/US6287868B1/en not_active Expired - Lifetime
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3905770A (en) * | 1972-09-15 | 1975-09-16 | Tecator Instr Ab | Apparatus for use in determination of nitrogen by the Kjeldahl method |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
NL1018545C2 (en) * | 2001-07-13 | 2003-01-14 | Energieonderzoek Ct Nederland | Measuring nitrogen content of solid or liquid samples e.g. animal feeds or foodstuffs, by measuring conductivity of aqueous liquid containing diffused ammonia |
KR100882770B1 (en) * | 2008-05-27 | 2009-02-10 | (주)한일랩테크 | Kjeldahl distillation apparatus and method for operating the same |
Also Published As
Publication number | Publication date |
---|---|
DE69836203D1 (en) | 2006-11-30 |
EP0960331B1 (en) | 2006-10-18 |
EP0960331A1 (en) | 1999-12-01 |
ES2275298T3 (en) | 2007-06-01 |
DE69836203T2 (en) | 2007-08-23 |
US6287868B1 (en) | 2001-09-11 |
JP4248606B2 (en) | 2009-04-02 |
AU5888198A (en) | 1998-08-18 |
SE9700249D0 (en) | 1997-01-29 |
SE9700249L (en) | 1998-07-30 |
JP2001508867A (en) | 2001-07-03 |
SE508220C2 (en) | 1998-09-14 |
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