Standard Iron Solution

Calcium Lactate Dissolve 0.5 g in DW add 2 ml of a 20% w/v soln. of iron-free-citric acid and 0.1 ml of thioglycollic acid, mix, make alkaline with iron-free-ammo-nia soln., dilute to 50 ml with DW and allow to stand for 5 minutes. Any colour produced is not more intense than that obtained by treating in the same manner 2.0 ml of iron standard solution (20 ppm Fe) in place of the soln. being examined. 

Iron Dilute 4.3 mL (5 g) of sample to 40 mL with water, and add about 40 mg of ammonium persulfate and 10 mL of ammonium thiocyanate TS. Any red color produced does not exceed that produced by 2.5 mL of Iron Standard Solution (25 pig Fe) (see Solutions and Indicators) in an equal volume of solution containing the same quantities of ACS Reagent-Grade Hydrochloric Acid and the reagents used in the test. Lead Determine as directed for Method I in the Atomic Absorption Spectrophotometric Graphite Furnace Method under Lead Limit Test, Appendix IIIB. 

Iron Add 2 mL of hydrochloric acid to 1 g of sample, and evaporate to dryness on a steam bath. Dissolve the residue in 2 mL of hydrochloric acid and 20 mL of water, add a few drops of bromine TS, and boil the solution to remove the bromine. Cool, dilute with water to 25 mL, then add 50 mg of ammonium persulfate and 5 mL of ammonium thiocyanate TS. Any red or pink color does not exceed that produced in a control containing 1.0 mL of Iron Standard Solution (10 P-g Fe). 

Iron Standard Solution (10 pig Fe in 1 mL) Dissolve 702.2 mg of ferrous ammonium sulfate [Fe(NH4)2(S04)2-6H20] in 10 mL of 2 N sulfuric acid in a 100-mL volumetric flask, dilute to volume with water, and mix. Transfer 10.0 mL of this solution into a 1000-mL volumetric flask, add 10 mL of 2 N sulfuric acid, dilute to volume with water, and mix. 

Tris (l-phenyl-l,3-butanediono) iron(III) NBS No. 1079, ca. 10.3% iron, for preparation of organo-iron standard solution. 

The prescribed quantity of the substance to be examined is dissolved in water R and diluted to 10 ml with the same solvent. Alternatively, 10 ml of the prescribed solution is used. Two ml of a 200 g/1 solution of citric acid R and 0.1 ml of thioglycollic acid R are added. The solution is mixed, made alkaline with ammonia R, and diluted to 20 ml with water R. A standard is prepared in the same manner, using 10 ml of iron standard solution (1 ppm Fe) R. After 5 min, any pink color in the test solution is not more intense than that in the standard. 

Another reducing titrant is ferrous ammonium sulfate, Fe(NH4)2(S04)2 6H2O, in which iron is present in the +2 oxidation state. Solutions of Fe + are normally very susceptible to air oxidation, but when prepared in 0.5 M 1T2S04 the solution may remain stable for as long as a month. Periodic restandardization with K2Cr20y is advisable. The titrant can be used in either a direct titration in which the Fe + is oxidized to Fe +, or an excess of the solution can be added and the quantity of Fe + produced determined by a back titration using a standard solution of Ce + or... 

Pipette 25 mL iron(III) solution (0.05M) into a conical flask and dilute to 100 mL with de-ionised water. Adjust the pH to 2-3 Congo red paper may be used — to the first perceptible colour change. Add 5 drops of the indicator solution, warm the contents of the flask to 40 °C, and titrate with standard (0.05M) EDTA solution until the initial blue colour of the solution turns grey just before the end point, and with the final drop of reagent changes to yellow. 

Weigh out accurately about 0.3 g potassium persulphate into a conical flask and dissolve it in 50 mL of water. Add 5mL syrupy phosphoric)V) acid or 2.5 mL 35-40 per cent hydrofluoric acid (CARE ), 10 mL 2.5M sulphuric acid, and 50.0 mL of the ca 0.1 M iron(II) solution. After 5 minutes, titrate the excess of Fe2+ ion with standard 0.02 M potassium permanganate. 

Discussion. Chromium (III) salts are oxidised to dichromate by boiling with excess of a persulphate solution in the presence of a little silver nitrate (catalyst). The excess of persulphate remaining after the oxidation is complete is destroyed by boiling the solution for a short time. The dichromate content of the resultant solution is determined by the addition of excess of a standard iron(II) solution and titration of the excess of the latter with standard 0.02 M potassium dichromate. 

Procedure (copper in copper(I) chloride). Prepare an ammonium iron(III) sulphate solution by dissolving 10.0 g of the salt in about 80 mL of 3 M sulphuric acid and dilute to 100 mL with acid of the same strength. Weigh out accurately about 0.3 g of the sample of copper(I) chloride into a dry 250 mL conical flask and add 25.0 mL of the iron(III) solution. Swirl the contents of the flask until the copper(I) chloride dissolves, add a drop or two of ferroin indicator, and titrate with standard 0.1 M cerium(IV) sulphate. 

Discussion. Satisfactory results are obtained by adding the nitrite solution to excess of standard 0.1 M cerium(IV) sulphate, and determining the excess of cerium(IV) sulphate with a standard iron(II) solution (compare Section 10.96). 

An excess of a standard solution of iron(II) must therefore be added and the excess back-titrated with standard cerium(IV) sulphate solution. Erratic results are obtained, depending upon the exact experimental conditions, because of induced reactions leading to oxidation by air of iron(II) ion or to decomposition of the persulphate these induced reactions are inhibited by bromide ion in concentrations not exceeding 1M and, under these conditions, the determination may be carried out in the presence of organic matter. 

The method based upon the reduction of iron(III) solutions in the presence of sulphuric acid, boiling, and subsequent titration in the cold with standard 0.02M potassium permanganate frequently yields high results unless the experimental conditions are closely controlled ... 

With the exception of iron(II) and uranium(IV), the reduced solutions are extremely unstable and readily re-oxidise upon exposure to air. They are best stabilised in a five-fold excess of a solution of 150g of ammonium iron(III) sulphate and 150 mL of concentrated sulphuric acid per litre [approximately 0.3M with respect to iron] contained in the filter flask. The iron(II) formed is then titrated with a standard solution of a suitable oxidising agent. Titanium and chromium are completely oxidised and produce an equivalent amount of iron(II) sulphate molybdenum is re-oxidised to the Mo(V) (red) stage, which is fairly stable in air, and complete oxidation is effected by the permanganate, but the net result is the same, viz. Mo(III)- Mo(VI) vanadium is re-oxidised to the V(IV), condition, which is stable in air, and the final oxidation is completed by slow titration with potassium permanganate solution or with cerium(IV) sulphate solution. 

Synthetic standard solution (for analysis of steel). Dissolve an appropriate weight of pure iron (Johnson Matthey) in a mixture of equal volumes of concentrated hydrochloric acid and concentrated nitric acid with this solution as base, add a suitable amount of copper nitrate solution containing 0.01 g copper per L. 

Standard solution of iron(III). Use method (a), (b) or (c). (a) Dissolve 0.7022g ammonium iron(II) sulphate in 100mL water, add 5mL of 1 5 sulphuric acid, and run in cautiously a dilute solution of potassium permanganate (2 g L 1) until a slight pink coloration remains after stirring well. Dilute to 1 L and mix thoroughly. lmL = 0.1mg of Fe. (6) Dissolve 0.864 g ammonium iron(III) sulphate in water, add 10 mL concentrated hydrochloric acid and dilute... 

Iron (III) solution, 0.05M. Dissolve about 12.0 g, accurately weighed, of ammonium iron(III) sulphate in water to which a little dilute sulphuric acid is added, and dilute the resulting solution to 500 mL in a graduated flask. Standardise the solution with standard EDTA using variamine blue B as indicator (Section 10.56). 

Metal-free cotton material samples were impregnated with standard solutions of iron, copper, and manganese ions containing 10 to 100 )a,g of metal per gram of cotton material. It was completely dried and 1 g of cotton sample was combusted... 

The RQ flex test kit (Merck) which uses specific test strips is useful for the semi-quantitative determination of several analytes. D(+) ascorbic acid can be determined in fortified food products with an accuracy of 85-115% (unpublished data), however the procedure cannot be applied to coloured food products. Added iron salts may be extracted from food products with dilute sulphuric acid and adjusted to pH2 with NaOH solution. Fe3+ is reduced to Fe2+ with ascorbic acid. Fe2+ reacts with Ferrospectral to form a red-violet complex. An internal calibration is provided on a barcode which is read by the RQ-flex reflectometer prior to any measurements. This avoids the need to calibrate the instrument with standard solutions. 

Iron ammonium sulfate is an analytical reagent in titrations and colorimetric measurements to measure oxidizing substances, such as chlorine, or to measure the chemical oxygen demand in waste water. The compound is used to prepare Fe(II) standard solution for these analyses. It also is a cahbration... 

Elemental composition Fe34.43%, Cl 65.57%. The compound may he identified by x-ray methods. Iron may be analyzed by various instrumental techniques (See Iron). Chloride in the aqueous solution of the compound may be measured by titrating with a standard solution of sdver nitrate or mercuric nitrate or by ion chromatography. 

Elemental composition K 35.62%, Fe 16.96%, C 21.89%, N 25.53%. An aqueous solution of the salt may be analyzed for potassium and iron by various instrumental methods (see Iron, and Potassium Analysis). Its concentration in aqueous solution may be measured by adding excess potassium iodide to an acidified solution and titrating the iodine hberated with a standard solution of sodium thiosulfate using starch indicator. 

Elemental composition K 28.22%, Cl 25.59%, and 0 46.19%. An aqueous solution is analyzed for potassium by AA, ICP, and other methods (see Potassium). Perchlorate ion may be analyzed by ion chromatography or a liquid-membrane electrode. Iodide, bromide, chlorate, and cyanide ions interfere in the electrode measurement. Alternatively, perchlorate ion may be measured by redox titration. Its solution in 0.5M H2SO4 is treated with a measured excess standard ferrous ammonium sulfate. The excess iron(II) solution is immediately titrated with a standard solution of potassium dichromate. Diphenylamine sulfuric acid may be used as an indicator to detect the end point ... 

Adrenaline is present as a vasoconstrictor in some local anaesthetic injections in a much smaller amount than the local anaesthetic itself, which obscures the absorption of adrenaline in the UV region. The selectivity of UV/visible spectroscopy for the analysis of adrenaline can be increased by complex formation, which occurs between iron (II) and molecules containing a catechol group (Fig. 4.13). These complexes are purple in colour and absorb at ca 540 nm at much longer wavelengths than for instance local anaesthetics, which do not form such complexes. The adrenaline in the injection is quantified against a standard solution of adrenaline. 

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