71.080.40 - Organic acids

The test may be carried out on products as received or on a dried sample. The method specified in ISO 2208 shall be applied for drying. The principle of the method consists in cooling the liquid or liquefied test portion and observation of the temperature during crystallization under defined conditions. A simplified crystallization point apparatus is given in the figure. It takes into account the properties of these products.

The method is applicable to products having high cresol contents. The principle consists in distillation of a test portion inder carefully defined conditions. Either determination of the temperatures corresponding to the condensate volumes defined or determination of the volume condensate when the thermometer indicates each of the distillaton temperatures (i.e. plotting temperature as a function of volume or plotting volume as a function of temperature).

Applicable to products having a high o-cresol content and a high m-cresol content. The principle consists in distillation of a tast portion under carefully defined conditions and determination of the mass of residue obtained. The distillation is carried out according to ISO 918. When all the water has distilled over, continue the distillation without intermediate measurements, until either the dry point or the final boiling point is reached.

Specifies the determination of total reducing matter and of reducing compounds other than formic acid. The principle consists in oxidation of formic acid and other reducing compounds in a test portion with an excess of sodium hypobromit solution. Determination of the excess sodium hypobromite by iodometry. Oxidation of reducing compounds other than formic acid with an excess of potassium bromide-bromate solution in an acid media. Determination of the excess potassium bromide-bromate by iodometry. Determination of the formic acid content from the difference between the two determinations. Is applicable to products having formic acid contents, between 0,02 % (m/m) and 0,35 % (m/m).

The principle consists in titration of a test portion with standard volumetric sodium hydroxide solution, using phenolphthalein as indicator. Calculation of the acid content, making allowance for any formic acid present, determined separately (see ISO 753/3). This International Standard has also been approved by the International Union of Pure and Applied Chemistry (IUPAC). International Standards ISO 753/1 to ISO 753/11 cancel and replace ISO Recommendation R 753-1968.

Gives general instructions and also specifies the methods to be used for the determination of dry residue after evaporation on a water bath, for the determination of the crystallizing point (temperature) of glacial acetic acid, for the determination of water content, for the measurement of colour and for the determination of arsenic content. The method is applicable to products having acedic acid contents in the range 98 to 100 % (m/m). This International Standard has also been approved by the International Union of Pure and Applied Chemitry (IUPAC). International Standards ISO 753/1 to 753/11 cancel and replace ISO Recommendation R 753-1968.

Specifies a method for a visual comparison of the tubitity obtained by adding a silver nitrate solution to a solution of a test portion acidified with nitric acid, with that similary obtained from a chloride solution of known concentration. Using a test portion of 50 g, the method is applicable directly to products having inorganic chloride contents in the range 0,0005 % (m/m) to 0,05 % (m/m). This range can be extended by adjusting the mass of the test portion. It has also been approved by the International Union of Pure and Applied Chemistry (IUPAC). ISO 753/1 to ISO 753/11 cancel and replace ISO Recommendation R 753-1968.

Specifies a method for a visual comparison of the turbitity obtained by adding a barium chloride solution to a solution of a test portion acidified with hydrochloric acid, with that similarly obtained from a sulphate solution of known concentration. Using a test portion of 100 g, the method is applicable directly to products having inorganic sulphate contents in the range 0,001 % (m/m) to 0,1 % (m/m). This range can be extended by adjusting the mass of the test portion. It has also been approved by the International Union of Pure and Applied Chemistry (IUPAC). ISO 753/1 to ISO 753/11 cancel and replace ISO Recommendation R 753-1968.

The method specified consists in heating a test portion in an acid medium to depolymerize any to paraldehyde present and to entrain, by distillation, both regenerated acetaldehyde and the monomeric acetaldehyde originally present. Reaction of the acetaldehyde in the distillate with an excess of sodium hydrogen sulphite solution. Iodometric titration of the residual sodium hydrogen sulphite solution. The method is applicable to products having total acetaldehyde contents equal to or greater than 0,004 % (m/m). It has also been approved by the International Union of Pure and Applied Chemistry (IUPAC). ISO 753/1 to iso 753/11 cancel and replace ISO Recommendation R 753-1968.

The principle consists in heating a test portion with an excess of potassium dichromate solution in the presence of sulphuric acid. Iodometric titration of the residual potassium dichromate. The method is applicable to products having dichromate inexes equal to or greater than 0,04 ml. It has also been approved by the International Union of Pure and Applied Chemistry (IUPAC). ISO 753/1 to ISO 753/11 cancel and replace ISO Recommendation R 753-1968.

The principle of the determination consists in reaction of the acetaldehyde present in a test portion with an excess of sodium hydrogen sulphite solution, and iodometric titration of the residual sodium hydrogen sulphite. The method is applicable to products having acetaldehyde monomer contents equal to or greater than 0,01 % (m/m). This International Standard as also been approved by the International Union of Pure and Applied Chemistry (IUPAC).International Standards ISO 753/1 to ISO 753/11 cancel and replace ISO Recommendation R 753-1968.

The principle consists in reaction of a test portion, under specified conditions, with an excess of potassium permanganate solution in the presence of dilute sulphuric acid. Iodometric titration of the residual potassium permanganate. The method is applicable to products having permanganate indexes equal to or greater than 10 mg/100 ml. It has also been approved by the International Union of Pure and Applied Chemistry (IUPAC). ISO 753/1 to ISO 753/11 cacel and replace ISO Recommendation R 753-1968.

The principle consists in conversion of heavy metals, such as lead, copper and iron, to their sulphides by treatment with sodium sulphide in ammoniacal solution, and visual comparison of the colour produced with that of a standard lead solution similarly treated. The method detects only the heavy metals present in non-complex form. Using a test portion of 25 g, the method is applicable directly to products having heavy metal contents in the range 0,00044 % (m/m) to 0,04 % (m/m). This range can be extended by adjusting the mass of the test portion. It has also been approved by the International Union of Pure and Applied Chemistry (IUPAC). ISO 753/1 to ISO 753/11 cancel and replace ISO Recommendation R 753-1968.

Gives also the procedure to be used for the determination of water content by the Karl Fischer method. This method is applicable only to liquefied phenol and m-cresol. The determination of density at 20 °C is applicable only to liquefied phenol, m-cresol, cresylic acid and xylenols.

Specifies a method for the comparison of the colour of a test portion against the colour of colorimetric standard colour matching solutions. The colour of cresols present in the test portion is liable to darken on keeping and on exposure to ligth. ISO 1897/7 replaces ISO Recommendation R 1909-1971.

The method is applicable to a product containing 35 % (m/m) to 60 % (m/m) of m-cresol, not more than 5 % (m/m) of phenol, and not more than 35 % (m/m) of o-cresol. The principle is based on dehydration of a quantity of the test sample. Formation of a complex between m-cresol and urea by addition of excess urea to a test portion of the dehydrated sample. Determination of the crystallizing point of the complex in a crystallizing point apparatus. Calculation of the content from the water content of the test sample and the crystallizing point of the complex. The relation between crystallizing point and m-cresol content of m-cresol/urea mixtures is given in a table. ISO 1897/9 replaces ISO Recommendation R 1911-1971.

Specifies a volumetric method, after distillation, for determining of neutral oils, and a titrimetric method, after distillation, for determining of pyridine bases. The principle is based on distillation from an aqueous alkaline solution of a test portion. Measurement of the volume of neutral oils collected. Titration of the bases present in the aqueous distillate and in the oils with standard volumetric hydrochloric acid solution using methyl orange and xylene cyanol FF as indicator. An assembled distillation apparatus is shown in a figure.

This method is the best available at the present time. It was primarily intended for samples containing 40 % (m/m) or more but has been extended to lower ranges. The principle is based on dehydration of a quantity of the test sample. Formation of a complex between o-cresol and cineole (having a crystallizing point not lower than 1,2 °C) by addition of excess cineole to a test portion of the dehydrated sample. Determination of the crystallizing point of the complex in a crystallizing point apparatus. Calculation of the content from the water content of the test sample and the crystallizing point of the complex. The relation between crystallizing point and o-cresol content of o-cresol/cineole mixtures is given in a table. ISO 1897/8 replaces ISO Recommendation R 1910-1971.

The principle of the method is based on distillation of a test portion in the presence of an appropriate solvent, in a Dean and Stark apparatus. Determination of the volume of condensate collected in the receiver tube, brought to ambient temperature, assuming this liquid to be water. An appropriate solvent is xylene, solvent naphtha or alternatively, toluene. ISO 1897-2 replaces ISO/R 1898-1971.

simple test which cannot be used to obtain quantitative results. The principle of the method is based on formation of a brown colour on lead acetate paper due to reaction with any hydrogen sulphide present in a test portion. ISO 1897/6 replaces ISO Recommendation R 1908-1971.

Conversion of the iron in a test portion to iron(III) sulphate by evaporation to dryness in the presence of sulphuric acid. Dissolution in nitrid acid, reduction of the trivalent iron in the solution thus obtained by hydroxylammonium chloride. Photometric measurement of the coloured complex iron(II)-2,2' -dipyridyl. Applicable to products having Fe contents in the range 0,1 to 2 mg/kg.

Applicable to products having inorganic chlorides contents in the range 0,0005 to 0,5 % (m/m). Comparison of the turbidity, obtained by the addition of silver nitrate to a solution prepared from a test portion, with that similarly obtained from a standard chloride solution.

Gives general instructions relating to methods of test, especially for sampling. ISO/R 731 has been subdivised into seven parts. ISO 731/1 replaces clauses 1, 2 and 7 of ISO Recommendation R 731-1968.

The principle consists in a quantitative oxidation of the formic acid in a test portion with excess mercury(II) oxide. Potentiometric titration of the residual acids with standard volumetric sodium hydroxide solution. The method is applicable to products containing 0,5 to 6,0 % (m/m) of other acids, expressed as acetic acid. ISO/R 731 has been subdivised into seven parts. ISO 731/3 replaces clause 4 of ISO Recommendation R 731-1968.

The principle consists in a decomposition of most of the formic acid in a test portion by sulphuric acid an of the remainder by chromic acid. Steam distillation of acetic acid and/or other volatile acids and titration of the distillate with standard volumetric sodium hydroxide solution in the presence of phenolphthalein as indicator. The method is applicable to products containing less than 0,5 % (m/m) of other volatile acids, expressed as acetic acid. The ISO Recommendation R 1913-1971 was review and has been changed to ISO 731/7. ISO 731/7 replaces ISO/R 1913-1971, to which it is technically identical.

The principle consists in a titration of a test portion with a standard volumetric sodium hydroxide solution, using phenolphthalein as indicator. ISO/R 731 has been subdivised into seven parts. ISO 731/2 replaces clause 3 of ISO Recommendation R 731-1968.

The principle consists in a comparison of the turbidity, obtained by the addition of barium chloride to a solution prepared from a test portion in the presence of hydrochloric acid, with that similarly obtained from a standard sulphate solution. The method is a applicable to products having inorganic sulphates contents, expressed as sulphate (SO42-), in the range 0,001 to 0,1 % (m/m).