Substituted or condensed pyridines in a process for the detection of substances having a peroxidatic effect and a diagnostic agent containing such pyridines
The invention relates to the use of substituted or condensed pyridines in a process for the detection of substances having a peroxidative effect and to a pertinent process, and especially to an agent for increasing the sensitivity of the detection of substances having a peroxidative effect, which agent is used above all in a diagnostic agent comprising a carrier, a chromogen, a hydroperoxide, a stabilizer, a detergent and an activator. 
     The detection of substances having a peroxidative effect, which include hemoglobin and myoglobin in the animal organism, is of high importance for the discovery of small amounts of blood invisible to the eye in body fluids such as urine, or in other excrements, for example feces or vomited matter. In the case of a microscopic hematuria, a high sensitivity, besides the ready availability of the result, is a decisive factor for supporting the blood detection. In tests to increase the sensitivity by adding activating substances to the detection system, it has been found already in 1928 (Zschr. f. gerichtl. Med. 12, 216 (1928)) that quinoline, isoquinoline and derivatives thereof accelerate the detection. 
     Based on these findings, further quinoline and isoquinoline derivatives have been tested in later years and have been considered suitable (German Auslegeschrift No. 1,242,905, German Offenlegungsschrift No. 2,640,211, German Offenlegungsschrift No. 2,548,279, German Pat. No. 2,235,152). Certain pyridine derivatives have likewise been found to be effective accelerators (German Pat. No. 2,363,344). Thiazole and benzothiazole derivatives represent a further class of substances with accelerating effect (German Offenlegungsschrift No. 2,652,545). Substances of this kind are employed especially in the preparation of rapid diagnostic agents (for example test strips). 
     Surprisingly, it has now been found that besides the known vinyl pyridines, benzothiazoles or benzopyridines, all heteroaromatic hydrocarbons with at least one nitrogen atoms in the nucleus are in principle suitable accelerators. In this connection, phenyl-, benzyl- and benzoyl pyridines have proved to be novel accelerators having a high efficiency. The efficiency and stability values correspond to those of the vinyl pyridines of German Auslegeschrift No. 2,363,344. A surprising increase in the stability and efficiency is found, if a second bond between the phenyl and the pyridine nucleus is present in the above-mentioned compounds. 
     The subject of the invention are agents for increasing the sensitivity of the detection of substances having a peroxadative effect, which agents consist partially or totally of a compound of the formula I ##STR1## or a salt thereof in which X is CH 2 , CHR 1 , CR 1  R 2 , C═O or  X  represents a bond between the two nuclei, m and n represent an integer from 0 to 3, m+n being 3, and if X stands for C═O or  X  is a bond between the two nuclei, each A is a hydrogen atom, and--if X is CH 2 , CHR 1  or CR 1  R 2  --each A is hydrogen or both --A together represent a bond between the two nuclei, and in which R 1  and R 2  are hydrogen, halogen or alkyl of from 1 to 4 carbon atoms. 
     The symbols preferably have the following meanings: 
     X is CH 2 . 
     R 1  and R 2  are hydrogen. 
     --A  A-- represent a bond. 
     Preference is given in particular to &#34;azafluorenes&#34; or &#34;indenopyridines&#34;. 
     The agent of the invention is preferably employed in a diagnostic agent which consists of a solid carrier material in the form of a strip, preferably of plastic material, onto which a water-absorbing test field has been applied which contains an accelerator of the formula I in addition to buffer salts, hydroperoxide, chromogen, stabilizers and surface-active substances. 
     Test strips prepared with the accelerators of the invention react very sensitively to the smallest amounts of hemoglobin: in this manner it is possible to detect microscopic hematurias up to 0.03 mg of hemoglobin/1 of urine (=1-2 erythrocytes/μl of urine). 
     By adding one of the known stabilizers (for example hydroquinone, ascorbic acid), the stability of the chemical system may be further increased, while the sensitivity is reduced. The resulting increase of the indication threshold to about 5 erythrocytes/μl or urine is desirable for screening tests, since generally microscopic hematurias are considered to be pathological only with more than 2 to 3 erythrocytes per μl being present. 
     Suitable buffers are, for example citrates, phosphates or phthalates which produce a pH value of from 4 to 7, preferably from 5 to 6, when the test field is moistened. 
     Suitable hydroperoxides are, for example, cumene-, tetralin-, decalin- or pinane hydroperoxide. As chromogens, benzidine derivatives, preferably the non-carcinogenic tetramethyl benzidine, may be used for example. 
     Stabilizers of the type of ethylene diamino-tetraacetic acid protect the hydroperoxide by catching heavy metal traces, and thickeners of the gelatin or polyvinyl pyrrolidone type stabilize the chromogen and prevent an excess bleeding of the moistened test field. 
     Examples for further stabilizers have been indicated in German Pat. No. 2,235,127, U.S. Pat. Nos. 4,071,317 or 4,071,318. Detergents are surface-active substances, such as sodium dodecyl sulfonate or dioctyl sodium-sulfosuccinate. 
     The water-absorbing test field may in principle consist of any material. There are generally used fiber fleeces of cellulose or plastic material, preferably filter paper. However, there have also been known systems in which non-fibrous materials are used, the chemicals being contained in a water-absorbing film. 
    
    
     The following Examples serve to illustrate the invention. 
     EXAMPLE 1 
     
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Solution 1 300    mg of polyvinyl pyrrolidone,                            
           10     mg of EDTA-di-sodium salt,                              
           7.5    mg of tartrazine,                                       
           20     mg of dioctyl sulfosuccinate-Na salt,                   
           20     mg of 4-azafluorene,                                    
           2.2    mmols of citric acid and                                
           30     mg of 3,3&#39;,5,5&#39;-tetramethyl benzidine                   
                  are dissolved in                                        
           6      ml of methanol and                                      
           4      ml of water.                                            
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     The pH value is adjusted to 5.5. 
     
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Solution 2                                                                
         60     mg of decalin hydroperoxide are                           
                dissolved in 10 ml of toluene.                            
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     100 cm 2  of filter paper are impregnated with solution 1 and after drying with solution 2. 
     After having been dried again, the paper clearly indicates a hemoglobin concentration of about 0.14 mg of Hb/liter of urine by a green discoloration (corresponding to about 5 erythrocytes/μl). 
     EXAMPLE 2 
     
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300       mg of polyvinyl pyrrolidone,                                    
10        mg of EDTA-di-sodium salt,                                      
7.5       mg of tartrazine,                                               
20        mg of dioctyl sulfosuccinate-sodium salt,                       
2.2       mmols of citric acid,                                           
250       mg of cumene hydroperoxide,                                     
30        mg 3,3&#39;,5,5&#39;-tetramethyl benzidine and                          
20        mg of 4-azafluorene are dissolved in                            
6         ml of methanol and                                              
4         ml of water.                                                    
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     The pH value is adjusted to 5.5. 
     100 cm 2  of filter paper are impregnated with this solution and dried. 
     The finished paper makes it possible to detect 0.03 mg of Hb/liter of urine (corresponding to about 1-2 erythrocytes/μl of urine) by a green discoloration of the paper, i.e. 1 to 2 intact erythrocytes/μl of urine are marked as clear green dots on the otherwise yellow background. 
     If the 4-azafluorene is replaced by 20 mg of 2-benzyl pyridine, 2-phenyl pyridine or 9-bromo-4-azafluorene, the sensitivity of the test papers corresponds to that of Example 1. If said 4-azafluorene is replaced by 20 mg of 2-, 3-, or 4-benzoyl pyridine or 3- or 4-benzyl pyridine, the sensitivity of the test papers corresponds to an indication of 5 to 10 erythrocytes per/μl of urine. 
     EXAMPLE 3 
     
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300       mg of polyvinyl pyrrolidone,                                    
10        mg of EDTA-di-sodium salt,                                      
7.5       mg of tartrazine,                                               
20        mg of dioctyl sulfosuccinate-sodium salt,                       
2.2       mmols of citric acid,                                           
250       mg of cumene hydroperoxide,                                     
30        mg of 3,3&#39;,5,5&#39;-tetramethyl benzidine and                       
20        mg of 4-azafluorene are dissolved in                            
6         ml of methanol and a solution of                                
200       μg of ascorbic acid in                                       
4         ml of H.sub.2 O.                                                
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     The pH value is adjusted to 5.5. 
     100 cm 2  of filter paper are impregnated with this solution and dried. The detection sensitivity of the finished paper is comparable with that of the paper of Example 1.