Impregnated reagent paper

Pole Reagent Paper. Unsized paper impregnated with a win of 1-2 g phenolphthalein in 10 ml alcohol and 110 ml water and then passed, while still wet. through a soln of 20 g NajSO, (cryst) in 100 ml water the paper is then dried. 

The reagent does not keep well, hence it is preferable to impregnate filter paper with the reagent solution and allow the paper to dry in the air. The impregnated papers are stable for several months. In use, a drop of the test solution and a drop of m H2SO4 are placed upon the impregnated paper a purplish-pink colour results. 

Barium chloride-impregnated dry paper strips are dipped in mine samples for 30-120 s and then spotted with two drops of Fouchet s reagent (10% Feds, 25% trichloroacetic acid in water). A positive test is indicated by the appearance of a green color. 

The device shown in Fig. 26 is employed if a certain gas is to be identified in the presence of other gases. In this setup, the micro test tube is closed by a small glass funnel and the impregnated paper is laid on the latter in order to absorb the gas. This reagent paper allows indifferent gas to pass through and retains only the gas that is to be detected. 

Filter paper impregnated with the reagent solution may also be used. A drop of the neutral or extremely weak acid test solution is allowed to soak into the paper, and then is spotted with a drop of 1 N sodium hydroxide. A blue fleck or ring, depending on the copper content, appears on the red-violet reagent paper. The reagent paper is stable. 

Reagent 0.2 g dipicrylamine is dissolved in 2 ml of 2 N sodium carbonate and 15 ml water. The solution is filtered if necessary. Strips of filter paper (3x6 cm) are soaked in the solution, the excess liquid drained off, and the paper dried in a blast of heated air. If the paper moistened with the reagent solution is dried in the air, it is not so effective, though uniformly impregnated, as paper that has been spread on glass and then dried in a blast of heated air. This treatment results... 

Portable or fixed multipoint colorimetric detectors are available which rely on paper tape impregnated with reagent. A cassette of the treated paper is driven electrically at constant speed over a sampling orifice and the stain intensity measured by an internal reflectometer to provide direct readout of concentration. Such instruments are available for a range of chemicals including those in Table 9.7. 

ANALYZER (Reagent-Tape). The key to chemical analysis by this method is a tape (paper or fabric) that has been impregnated with a chemical substance that reacts with the unknown to form a reaction product on the tape which lias some special characteristic, e.g., color, increased or decreased opacity, change in electrical conductance, or increased or lessened fluorescence. Small pieces of paper treated with lead acetate, for example, have, been used manually by chemists for many years to determine the presence of hydrogen sulfide in a solution or in the atmosphere. This basic concept forms the foundation for a number of sophisticated instruments that may pietreat a sample gas, pass it over a cyclically advanced tape, and, for example, photo-metrically sense the color of the exposed tape, to establish a relationship between color and gas concentration. Depending upon tile type uf reactiun involved, the tape may he wet or dry and it may be advanced continuously or periodically. Obviously, there are many possible variations within the framework of this general concept. 

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