Residual Blank Titration

A residual blank titration may be stipulated in assays and tests involving a back titration in which a volume of a volumetric solution larger than is required to react with the sample is added, and the excess of this solution is then titrated with a second volumetric solution. Where a residual blank titration is specified or where the procedure involves such a titration, a blank is run as directed in the preceding paragraph. The volume of the titrant consumed in the back titration is then subtracted from the volume required for the blank. The difference between the two, equivalent to the actual volume consumed by the sample, is the corrected volume of the volumetric solution to be used in calculating the quantity of the substance being determined. 

Assay Transfer about 250 mg of the sample, accurately weighed, into a glass-stoppered flask, and add 100 mL of water, 5 g of dibasic potassium phosphate, 2 g of monobasic potassium phosphate, and 2 g of potassium iodide. Mix well to dissolve, add 50.0 mL of 0.1 A iodine, stopper the flask, and mix. Allow to stand for 30 min, add starch TS indicator, and then titrate the excess iodine with 0.1A sodium thiosulfate. Perform a residual blank titration. Each milliliter of 0.1 A iodine is equivalent to 9.563 mg of C7H13N03S. 

Ester Value Add 25.0 mL of 0.5 N alcoholic potassium hydroxide and 50 mL of alcohol to the solution resulting from the determination of Acid Value, heat the mixture under a reflux condenser for 4 h, and titrate the excess alkali with 0.5 N hydrochloric acid. Perform a residual blank titration, and calculate the Ester Value as the number of milligrams of... 

Assay Dissolve about 100 mg of sample, accurately weighed, in 20 mL of water add 40.0 mL of 0.1 N ceric sulfate prepared as directed for Volumetric Solutions under Solutions and Indicators (or use a commercially available solution) mix well and add 2 mL of silver sulfate solution (5 g of Ag2S04 dissolved in 95 mL of concentrated sulfuric acid). Cover, heat nearly to boiling, and continue heating for 30 min. Cool to room temperature, and titrate with 0.1 A ferrous ammonium sulfate to a pale yellow color. Add 2 drops of orthophenanthroline TS, and continue the titration to a salmon-colored endpoint, recording the volume required, in milliliters, as S. Perform a residual blank titration (see General Provisions), and record the volume required as B. Each milliliter of the volume B - S is equivalent to 2.650 mg of NaH2P02H20. 

Procedure Transfer an accurately weighed quantity of sample, as specified below, into a 250-mL glass-stoppered flask. Add 75.0 mL of Hydroxylamine Solution to this flask and to a similar flask for a residual blank titration (see General Provisions). Attach the flask to a suitable condenser, reflux the mixture for the time specified, and then cool to room temperature. Titrate both flasks with 0.5 N hydrochloric acid to the same green-yellow endpoint using bromophenol blue TS as the indicator or, preferably, using a pH meter, to a pH of 3.4. (If the indicator is used, the endpoint color must be the same as that produced when the blank is titrated to a pH of 3.4.) Calculate the percent ketone by the equation... 

Transfer about 5 g, accurately weighed, of the sample into a 150-mL flask having a standard-taper neck. Pipet exactly 10 mL of a 1 10 solution of acetic anhydride in anhydrous pyridine into the flask, and pipet exactly 10 mL of this solution, preferably measured with the same pipet, into a second 150-mL flask for the residual blank titration (see General Provisions). Connect the flasks to condensers, reflux for 1 h, and cool to a temperature below 100°. Add 25 mL of water to each flask through the condensers, and reflux again for 10 min. Cool the flasks, add phenolphthalein TS, and titrate with 0.5 N potassium hydroxide. Calculate the percentage of free phenols by the equation... 

Black Pepper Oil, 47, 572, (S 1)5 Black Peppier Oleoresin, 391, 392 Blank Tests, 4 Blank Titration, Residual, 4 Bleached Starch, 159 Bleidner Apparatus, (S3)17 Blue Litmus Paper, 861 Bois de Rose Oil, 47, 576 Boric Acid-Potassium Chloride, 0.2 M, 848... 

Peel the fruit, weigh to the nearest 0.1 g, and cut a sample of 25 to 50 g from the edible portion. Weigh the sample to the nearest 0.1 g. Slice the sample into many small pieces, transfer to a mortar, and grind with 25 mL of the metaphosphoric acid solution. Pour the liquid from the extract into a 100-mL volumetric flask. Grind the solid residue in the mortar twice using 25 mL of the metaphosphoric acid solution. Add the liquid extract each time to the 100-mL volumetric flask. Add metaphosphoric acid solution to the volumetric flask to a total volume of 100 mL. Filter the solution through a rapid flow, fluted filter paper. Transfer 10.0 mL of the filtrate into a 50-mL Erlenmeyer flask. Titrate rapidly with the DCIP solution. Repeat the titration on two more 10.0-mL samples of the filtrate. Titrate 10.0 mL of metaphosphoric acid solution as a blank. 

Based on the fact that mefenamic acid reacts quantitatively with tV-bromosuccinimide (NBS) in an acidic medium, Hassib et al. [8] reported the titrimetric determination of mefenamic acid. A solution of mefenamic acid in acetic acid (0.02% m/V) was prepared. A volume of this solution containing 1.5-3.5 mg of mefenamic acid was allowed to react with 40 mL of 0.05 M NBS solution for 10 min in the dark (temperature of 25 2°C). Potassium iodide solution (10 mL) was added, and the solution was titrated with 0.01 N sodium thiosulfate to the starch end-point. A blank determination was carried out. For the determination of mefenamic acid in the capsules, the contents of 20 Ponstan capsules were mixed thoroughly and an accurately weighed portion of the mixed powder (nominally containing 25 mg of mefenamic acid) was extracted with diethyl ether (3 x 10 mL). The residue remaining after evaporation of diethyl ether was dissolved in acetic acid, and the procedure was continued as described for the determination of mefenamic acid. 

Assay With the aid of 10 mL of water, quantitatively transfer about 500 mg of sample, accurately weighed, into a separator Add 2 mL of 2.7 A hydrochloric acid, and extract the precipitated saccharin, first with 30 mL, then with five 20-mL portions of a solvent comprising 9 1 (v/v) chloroform alcohol. Filter each extract through a small filter paper moistened with the solvent mixture, and evaporate the combined filtrates to dryness on a steam bath with the aid of a current of air. Dissolve the residue in 75 mL of hot water, cool, add phenol-phthalein TS, and titrate with 0.1 A sodium hydroxide. Perform a blank determination (see General Provisions), and make any necessary correction. Each milliliter of 0.1A sodium hydroxide is equivalent to 20.02 mg of C7H8N203S. Benzoate and Salicylate Add 3 drops of ferric chloride TS to 10 mL of a 1 20 aqueous solution previously acidified with 5 drops of glacial acetic acid. No precipitate or violet color appears. 

Free Fatty Acids (as stearic acid) Transfer 2 g of sample, accurately weighed, into a dry, 125-mL Erlenmeyer flask containing 50 mL of acetone, fit an air-cooled reflux condenser onto the neck of the flask, boil the mixture on a steam bath for 10 min, and cool. Filter through two layers of Whatman No. 42, or equivalent, filter paper, and wash the flask, residue, and filter with 50 mL of acetone. Add phenolphthalein TS and 5 mL of water to the filtrate, and titrate with 0.1 A sodium hydroxide. Perform a blank determination (see General Provisions) using 100 mL of acetone and 5 mL of water, and make any necessary correction. Each milliliter of 0.1 A sodium hydroxide is equivalent to 28.45 mg of stearic acid (CigH gOi). Lead Determine as directed in the Flame Atomic Absorption Spectrophotometric Method under Lead Limit Test, Appendix NIB, using a 10-g sample. 

Unsaturation (as vinylpyrrolidone) Suspend 4 g of sample in 30 mL of water, stir for 15 min, and filter through a sintered-glass filter having a porosity between 9 and 15 pun, collecting the filtrate in a 250-mL flask. Wash the residue with 100 mL of water, add 500 mg of sodium acetate to the combined filtrates, and titrate with 0.1 N iodine until the color of iodine no longer fades. Add an additional 3.0 mL of 0.1 N iodine, allow to stand for 10 min, and titrate the excess iodine with 0.1 N sodium thiosulfate, adding 3 mL of starch TS as the endpoint is approached. Perform a blank determination (see General Provisions), and make any necessary correction. Not more than 0.72 mL is consumed. 

Transfer the benzene layer into a 500-mL round-bottom flask, and rinse the separator with 10 mL of benzene. Add a few boiling chips to the flask, and evaporate the benzene, preferably on a thin-film evaporator, under partial vacuum at about 60°. Dissolve the residue in the flask in 10 mL of methanol, add 10 mL of water and 5 drops of phenolphthalein TS, and titrate with 0.02 N Sodium Hydroxide in Methanol. Perform a blank determination (see General Provisions), make any necessary correction, and record the net volume of alkali, in milliliters, as V2. 

Transfer the quantity of acetylated oil specified in the monograph, and accurately weighed, into a tared 125-mL Erlen-meyer flask, and add 10 mL of neutral alcohol, 10 drops of phenolphthalein TS, and 0.1 N alcoholic potassium hydroxide, dropwise, until a pink endpoint is obtained. If more than 0.20 mL is needed, reject the sample, and wash and test the remaining acetylated oil until its acid content is below this level. Prepare a blank for residual titration (see General Provisions), using the same volume of alcohol and indicator, and add 1 drop of 0.1 /V alkali to produce a pink endpoint. Transfer 25.0 mL of 0.5 N alcoholic potassium hydroxide into each of the flasks, reflux them simultaneously for 1 h, cool, and titrate the contents of each flask with 0.5 N hydrochloric acid to the disappearance of the pink color. Calculate the percentage of Total Alcohols (A) by the equation... 

After the passage of the gas the liquid is evaporated in a platinum (or porcelain) capsule on the water bath to a volume of 2-3 ml. and then 2 drops of acetic acid are added and the evaporation continued almost to dryness. The residue is redissolved in 2-3 ml. water and again evaporated to dryness to decompose the sodium biacetate which is formed. The residue is once more dissolved in 2 ml. water, a drop of potassium chromate solution added and then titrated with N/40 silver nitrate. It is advisable to carry out a blank determination. The amount of phosgene present in the sample is calculated from the number of ml. of N/40 silver nitrate solution employed in titration. 

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