Patent GB-888039-A (GB)
Title: Indicator strip
IPC: C12Q1/58
Filed: 1960-03-11
Abstract: <PICT:0888039/III/1> A test strip for body fluids comprises a bibulous material impregnated with a plurality of materials in separate bands extending the width of the strip, said bands respectively comprising the following materials from one end toward the other: (1) a reagent system which with a biochemical substance in the body fluid reacts to form a gas, (2) a material which releases said gas from solution, (3) an inert impregnant which prevents capillary flow though the strip and (4) a colour indicator for the released gas.  In Fig. 2, a preferred test strip is shown in which blank areas 1a, 2a and 4a are provided adjacent to some of the bands, and a pressure sensitive tape 5 covers both sides of the bands 1 and 2.  In specific embodiments band 1 comprises (a) (for determining urea nitrogen) urease/phosphate buffer of pH 7-8, which liberates ammonia (b) (for serum trypsin) a -benzoyl-L-arginine amide hydrochloride which liberates ammonia; (c) for histidine) histidine a -decarboxylase buffered to pH 4-5 which liberates carbon dioxide or histidine diaminase buffered to pH 7,5-8,5 which liberates ammonia. Band 2 may comprise, where ammonia is liberated, a basic material producing a pH of at least 10, e.g. sodium and potassium phosphates, carbonate and acetates, and lithium carbonate; or where carbon dioxide is liberated, an acidic material producing a pH of less than 4, e.g. benzoic, lactic, fumaric, salicyclic, sulphosalicyclic, tartaric and oxalic acids.  Band 3 may comprise paint, varnish, enamels and plastic compositions, e.g. polymerized methyl methacrylate, and polymers and copolymers of vinyl chloride, vinyl acetate, acrylic acid and methacrylic acid and their esters.  Band 4 comprises a substance which neutralizes the evolved gas together with an indicator for the neutralization.  Suitable acidic substances for the neutralization of ammonia are citric, oxalic, maleic, benzoic, sulpho-salicylic and tartaric acids and indicators for use therewith, which should be in the basic form at a pH of 6,5 or less, are brom thymol blue, alizarin red S, brom phenol blue, brom cresol purple, brom cresol green and methyl red.  Suitable basic substances for the neutralization of carbon dioxide are the bases mentioned in connection with Band 2 and indicators for use therewith are phenolphthalein, thymolphthalein, thymol blue and metacresol purple. In preparing the strips it is preferred to use mixtures of water with a volatile solvent such as ethanol as the media for the reactants for bands 1, 2 and 4, whereby drying is facilitated; in preparing the third band, volatile solvents are employed and in the case of paints and varnishes, heat may be applied during drying to cure the impregnant.  In use, the lower end of the strip is contacted with a small known amount of the liquid to be tested which is insufficient to react with all the impregnated reagent (e.g. 0,1-0,2 mls.), and the strip supported vertically in a test tube which may be stoppered: the area of the band 4 which has changed colour in a given time, e.g. 30 mins. is said to be proportional to the quantity of gas evolved and thus to the substance to be tested and may be compared with a standard colour chart to obtain the result.ALSO:A buffered urease extract, suitable for converting urea nitrogen to ammonia, is prepared in Example 1 by adding jack bean meal to a dilute aqueous/alcoholic solution containing K2HPO4, KH2PO4, sodium acetate and acetic acid, shaking for 15 mins. and centrifuging at 1000g and 0 DEG C.