Starch solutions, preparation

Place 10 ml. of 1% starch solution (prepared as described above) in a boiling-tube, add 2 ml. of 1% sodium chloride solution and place the tube in a water-bath maintained at 38-40 . Place about 5 ml. of water in a series of test-tubes and to each add a few drops of 1% iodine solution. Now add 4 ml. of the diluted saliva solution to the starch solution, mix well and note the time. At intervals of about 30 seconds transfer 2 drops of the reacting mixture, by means of a dropping tube, to one of the test-tubes, mix and note the colour. As in the previous experiment, the colour, which is blue at first, changes to blue-violet, red-violet, red-brown, pale brown, and finally disappears at this stage the solution will reduce Fehling s solution. If the reaction proceeds too quickly for the colour changes to be observed, the saliva solution should be diluted. 

Add an equal volume of one of the above buffer solutions to 2.0 ml of the 20 g 1 1 starch solution prepared in step 1. The resulting solution should contain 10 g 1—1 of starch in a buffered environment. 

Prepare the starch substrate by diluting the 20 g l-1 starch solution prepared in step 1 with an equal volume of pH 7.0 phosphate buffer solution. This results in a working starch concentration of 10 g 1 1. Add 2 ml of the starch solution to each of the test tubes. 

Add 0.5 ml of the bacterial amylase solution to 50 ml of the 20 g 1 1 nonbuffered starch solution prepared in Step 1. Periodically place a few drops of the reaction mixture on a glass plate and add one drop of the iodine reagent. The color should finally turn red, indicating the total conversion of starch to dextrin. This liquefaction step should last for approximately 10 min. 

When the starch solution prepared in step 1 has cooled, add the solution (250 ml) to 250 ml of 0.8 M phosphate buffer in a 1-liter Erlen-meyer flask... 

Reagent Starch solution Prepared from commercially available water-soluble products designated lodocolor , Thiodene Vitey . ... 

Fanta GF, Felker FC, Shogren RL. 2002c. Formation of crystalline aggregates in slowly-cooled starch solutions prepared by steam jet cooking. Carbohydr Polym 48 161-170. 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

Dissolve 46-5 g. (45-5 ml.) of aniUne in a mixture of 126 ml. of concentrated hydrochloric acid and 126 ml. of water contained in a 1-htre beaker. Cool to 0-5° in a bath of ice and salt, and add a solution of 36-5 g. of sodium nitrite in 75 ml. of water in small portions stir vigorously with a thermometer (1) and maintain the temperature below 10°, but preferably at about 5° by the addition of a httle crushed ice if necessary. The diazotisation is complete when a drop of the solution diluted with 3-4 drops of water gives an immediate blue colouration with potassium iodide - starch paper the test should be performed 3-4 minutes after the last addition of the nitrite solution. Prepare a solution of 76 g. of sodium fluoborate (2) in 150 ml. of water, cool, and add the chilled solution slowly to the diazonium salt solution the latter must be kept well stirred (1) and the temperature controlled so that it is below 10°. Allow to stand for 10 minutes with frequent stirring. Filter... 

Standard 1/10 N nitrite is used to titrate a solution prepared by dissolving 10—100 mg of sulfamic acid and about 6 mL of (1 + 1) H2SO4 in 300 mL of distilled water at 40—50°C. At the end point, the colorless external potassium iodide starch-paste indicator changes to blue. A 1-mL solution of 1/ION NaN02 is equivalent to 9.709 mg of sulfamic acid. The 1/10 N nitrite titrant solution is standardized using primary standard-grade sulfamic acid. For sulfamate assay determination, the same procedure is used as for sulfamic acid. 

Preparation and use of starch solution. Make a paste of 0.1 g of soluble starch with a little water, and pour the paste, with constant stirring, into 100 mL of boiling water, and boil for 1 minute. Allow the solution to cool and add 2-3 g of potassium iodide. Keep the solution in a stoppered bottle. 

Only freshly prepared starch solution should be used. Two millilitres of a 1 per cent solution per 100 mL of the solution to be titrated is a satisfactory amount the same volume of starch solution should always be added in a titration. In the titration of iodine, starch must not be added until just before the end point is reached. Apart from the fact that the fading of the iodine colour is a good indication of the approach at the end point, if the starch solution is added when the iodine concentration is high, some iodine may remain adsorbed even at the end point. The indicator blank is negligibly small in iodimetric and iodometric titrations of 0.05M solutions with more dilute solutions, it must be determined in a liquid having the same composition as the solution titrated has at the end point. 

How the oxidation of iodide ions to form molecular iodine by the sonochemi-cally generated radicals can be monitored by the blue colour generated in the presence of freshly prepared starch solution. 

Procedure 10% aqueous solution of potassium iodide, KI, when exposed to sunlight, liberated I2 due to the photolytic decomposition and gave blue colour with freshly prepared starch solution. The intensity of blue coloured complex with the starch increased many fold when the same solution was kept in the ultrasonic cleaning bath. As an extension of the experiment, the photochemical decomposition of KI could be seen to be increasing in the presence of a photocatalyst, Ti02, showing an additive effect of sonication and photocatalysis (sono-photocatalysis) However, the addition of different rare earth ions affect the process differently due to the different number of electrons in their valence shells. 

Procedure. Ten tests are done in series 0.1ml of horse Hb solution is pipetted into each beaker 0.020 ml serum is added to nine of the beakers. The content of the remaining one is used as a blank. Three ml 0.1 M KI is added to each beaker. A mixture of 100 ml acetate buffer, 10 ml ethyl hydroperoxide solution and 10ml iodine solution (8) is then prepared. (This mixture is only fit for use for 20 minutes.) At 60-second intervals 10 ml of this mixture is added to the beakers. Nine minutes and 15 seconds after the addition, 2 drops of starch solution are added, and titration with 0.01 N Na2SaOa is started after 9 minutes and 30 seconds. The titration should last, as closely as possible, 30 seconds. The temperature is measured in the reaction mixture. 

This catalytic system was very flexible because by simple modification of the reaction conditions it was possible to prepare oxidized polymers with the desired level of carboxyl and carbonyl functions. No waste was formed because the process did not involve any acids, bases or buffer solutions. The incipient wetness process is very easy to scale up. Hydrophilic starch was prepared in batches of 150 L and incorporated successfully in paint formulations. Good results were also obtained with in vitro and in vivo tests for cosmetic formulation. Interestingly, this is a rather unique example of a heterogeneous catalytic process involving a soluble catalyst and a solid substrate. 

In this titration method an excess of iodine solution is added to the solution of the substance and thus, the latter gets oxidized quantitatively. The excess of iodine is subsequently back titrated with sodium thiosulphate using freshly prepared starch solution as indicator with an end-point from violet to colourless. 

Procedure Weigh accurately about 0.1 g of benzylpenicillin in DW and dilute to 100 ml in a volumetric flask. Transfer 10.0 ml to an iodine flask, add 5 ml of N sodium hydroxide and allow to stand for 20 minutes. Now, add 20 ml of freshly prepared buffer solution, 5 ml of N HC1 and 25.0 ml of 0.02 N iodine solution. Close the flask with a wet glass-stopper and allow to stand for 20 minutes in a dark place (i.e., protected from light). Titrate the excess of iodine with 0.02 N sodium thiosulphate, employing freshly prepared starch solution as an indicator added towards the end-point. 

Procedure Weigh accurately about 0.2 g of sodium metabisulphite and dissolve in 50.0 ml of 0.1 N iodine solution and add 1 ml hydrochloric acid. Titrate the excess of iodine with 0.1 N sodium thiosulphate employing freshly prepared starch solution, added towards the end of the titration, as indicator. Each ml of 0.1 N iodine is equivalent to 0.0047453 g of Na Oj. 

Procedure Transfer 25 ml of 0.1 N bromine solution with the help of a pipette into a 500 ml iodine flask and dilute it with 120 ml of DW. Add to it 5 ml of hydrochloric acid, moisten the glass-stopper with water and insert the stopper in the flask. Shake the contents gently. Now, add 5 ml of potassium iodide solution, again lace the stopper and allow the resulting mixture to stand for 5 minutes in the dark. Titrate the liberated iodine with previously standardized 0.1 N sodium thiosulphate solution, adding 3 ml of freshly prepared starch solution towards the end-point. Each ml of 0.1N sodium thiosulphate is equivalent to 0.01598 g... 

Procedure Weigh accurately about 0.2 g of ethacrynic acid, dissolve in 40 ml of glacial acetic acid in a 250 ml iodine flask. Add to it 20 ml of 0.1 N bromine and 30.0 ml of hydrochloric acid, immediately place in position the moistened stopper to the ffask, mix the contents vigorously and allow it to stand in a dark place for 60 minutes (to complete the reaction with bromine). Add to it 100 ml of water and 20 ml of KI Solution and titrate immediately with 0.1 sodium thiosulphate, employing freshly prepared starch solution as an indicator towards the end of the titration. Repeat an operation without the pharmaceutical substance (blank titration) thus the difference between the titrations represents the amount of bromine required by the ethacrynic acid. Each ml of 0.1 N bromine is equivalent to 0.01516 g of C13H12C1204. 

Starch is extensively used due to its adsorbing properties. In dissolved form, it is used as a skin emollient and as an antidote for iodine poisoning. Other applications include the use as a tablet filler and binder and disintegrant. Sterilized starch is used as a lubricant for surgeon gloves. Unlike talc, it is completely adsorbed by body tissues. Soluble starch is prepared by treating commercial potato starch with dilute hydrochloric acid until it forms an almost clear solution in hot water. 

Prepare a fresh solution from 1.6 g of KI, 20 mL of water, 5 mL of 1 wt% starch solution, and 5 mL of phenolphthalein indicator solution. (If the solution darkens after several days, decolorize it with a few drops of dilute Na2S203.) Soak the three layers of paper with the Kl-starch-phenolphthalein solution. Connect the stylus and foil to a 12-V DC power source, and write on the paper with the stylus. 

Iodic Acid. — The 1 20 solution freshly prepared with boiled water should not immediately give a blue color on adding starch solution followed by 2 or 3 drops of dilute sulphuric acid. 

Free Acid. — Dissolve about 0.5 gm. of potassium iodate in about 20 cc. of boiled water, and add a small crystal of neutral potassium iodide and a few drops of freshly prepared starch solution. The liquid should not immediately acquire a blue color. 

Iodates. — 20 cc. of the 1 20 solution, freshly prepared with recently boiled and cooled water, should not immediately acquire a blue color on the addition of starch solution and 2 to 3 drops of dilute sulphuric acid. 

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