The essence of the methods is the dissolution of a certain mass of vegetable oil in a mixture of solvents, followed by titration of the available free fatty acids with an aqueous or alcoholic solution of potassium or sodium hydroxide.
Determination of the acid number of light and refined oils, including those obtained from unrefined cottonseed oil.
A sample of the tested oil is mixed well and filtered at 15-20°C.
3-5 g of oil are weighed into a conical flask with an error of not more than 0.01 g, 50 ml of a neutralized mixture of solvents are added and shaken.
If the oil does not dissolve, it is heated in a water bath, cooled to a temperature of 15-20°C.
alcohol-ether mixture prepared from two parts of diethyl ether and one part of ethyl alcohol with the addition of 5 drops of a solution of phenolphthalein per 50 ml of the mixture. The mixture is neutralized with 0.1 N. a solution of potassium hydroxide or sodium hydroxide to a barely noticeable pink color.
When using an alcohol-ether mixture, titration is carried out with an aqueous or alcoholic solution of hydroxide.
The resulting oil solution, with constant agitation, is quickly titrated with 0.1 N. with a solution of potassium or sodium hydroxide until a faint pink color is obtained, stable for 30 s.
When titrated with 0.1 N. with an aqueous solution of potassium or sodium hydroxide, the amount of alcohol taken together with ether or chloroform, in order to avoid hydrolysis of the oil solution, must be at least 5 times the amount of the consumed hydroxide solution.
When the acid number of the oil is over 6 mg KOH/g, take a sample of the oil with an error of not more than 0.01 g 1-2 g and dissolve it in 40 ml of a neutral mixture of solvents.
The acid number of the oil (X 1), mg KOH / g, is calculated by the formula
where 5.611 is a coefficient equal to the value of the calculated mass of KOH in 1 ml of 0.1 n. KOH solution, and when using NaOH, this coefficient is obtained by multiplying the calculated mass of NaOH in 1 ml of 0.1 N. solution (equal to 4.0) by 1.4 - the ratio of the molecular weights of KOH and NaOH;
K - correction to the titer 0.1 n. a solution of potassium hydroxide or sodium;
V - volume 0.1 n. potassium or sodium hydroxide solution used for titration, ml;
m is the mass of oil, g.
APPENDIX H
Determination of milk density
Taking measurements
The cylinder with the test sample is installed on a flat horizontal surface and the temperature of the sample i 1 is measured. The reading of the temperature readings is carried out no earlier than 2-4 minutes after the thermometer is lowered into the plug.
A dry and clean hydrometer is slowly lowered into the test sample, immersing it until 3-4 mm remains to the expected mark of the hydrometer scale, then leaving it in a free floating state. The hydrometer must not touch the walls of the cylinder.
The location of the cylinder with the stopper on a horizontal surface should be, in relation to the light source, convenient for reading readings on the density scale and the thermometer scale.
The first reading of the density p 1 is carried out visually from the scale of the hydrometer 3 minutes after setting it in a stationary position. After that, the hydrometer is carefully raised to a height to the level of the ballast in it and lowered again, leaving it in a free floating state. After establishing it in a stationary state, a second reading of the density p 2 is carried out. When reading the density reading, the eyes should be at the level of the meniscus. The readings are taken along the upper edge of the meniscus.
The determination of the acid number of an oil is based on the interaction of acids extracted from the oil with ethyl alcohol with caustic potash in the presence of an indicator of nitrazine yellow.
To carry out the analysis, pour 20 ml of an alcohol solution of the indicator into a measuring cylinder with a ground stopper with a capacity of 100 ml, then pour the test oil into the same cylinder using a syringe in the amount determined according to Table 1, depending on the maximum allowable acid number established for this type of oil.
After that, close the cylinder with a stopper and shake for 1 minute.
The green and blue color of the upper (alcohol) layer indicates that the acid number-oil does not exceed the permissible norm. The yellow color of the alcohol layer indicates that the acid number of the oil exceeds the norm.
It is necessary to find out the suitability of turbine oil for further operation. The acid number of this oil should not exceed 1 mg KOH per gram of oil.
From Table. 1 shows that for testing it is necessary to take 2 ml of oil. After shaking the oil sample with the indicator, the alcohol layer turned yellow, therefore, the acid number of the oil exceeds the norm.
If it is necessary to determine the numerical value of the acid number, the analysis is carried out as follows:
Pour 20 ml of an alcohol solution of the indicator into the measuring cylinder. Then, using a syringe, inject the first dose of oil corresponding to the limit value of the acid number of the oil (see Table 1);
close the cylinder with a cork, shake the sample and examine the exfoliated alcohol layer. If the color of the layer has not changed, then add such an amount of oil to the cylinder that its volume in total with the first dose is equal to the volume corresponding to the next (lower) value of the acid number according to Table. 1. If the color of the alcohol layer has not changed this time, then add oil to the cylinder so that its entire volume in the cylinder is equal to the volume corresponding to the next value of the acid number, etc. method of successive approximations until the color of the indicator changes. When changing color - according to the table. 1 determine the numerical value of the acid number, taking into account the volume of oil taken.
MS-20 oil was obtained for analysis from the engine oil system. The maximum allowable acid number at which an oil change is necessary is 0.5 mg KOH per gram of oil. From Table. 1 shows that for the sample. you need 4 ml of oil.
After shaking the sample with the indicator, the color of the latter did not change. Pour another 1 ml of oil and so on until the color changes.
Assume that with 9 ml of oil in the cylinder, the alcohol layer turns yellow. So the acid number of the oil is 0.20 mg KOH / g of oil,
It is necessary to add oil in quantities that will comply with the intervals in oil volumes indicated in Table. 1. But for a more accurate determination, you can add 1 ml of oil constantly. In this case, the value of the acid number is calculated by interpolation.
Preparation of the indicator.
An alcohol solution of nitrazine yellow and potassium hydroxide is prepared as follows: 7-10 ml of a 0.5% aqueous solution of nitrazine yellow is added to 1 liter of 96% ethyl alcohol (0.5 g of nitrazine yellow is dissolved in 100 ml of water), after which the alcohol turns yellow-orange. Then 0.05 alcohol solution of caustic potash is added dropwise there.
Part of the resulting neutralized alcohol solution is poured into a 1 liter volumetric flask and an amount of 0.05 N potassium hydroxide solution is added there so that it contains 80 mg of potassium hydroxide (28.57 ml of 0.05 N solution of caustic potash) and topped up with the remaining alcohol to the 1 liter mark, shaking.
The indicator solution is packaged in 100 ml plastic bottles with a special cap.
APPS
GOST R 52110-2003
Group H69
STATE STANDARD OF THE RUSSIAN FEDERATION
VEGETABLE OILS
Methods for determining acid number
vegetable oils. Methods for determination of acid value
OKS 67.200.10
OKSTU 9109
Introduction date 2004-06-01
Foreword
1 DEVELOPED by the State Scientific Institution "All-Russian Research Institute of Fats" (VNIIZH)
INTRODUCED by the Technical Committee for Standardization TC 238 "Vegetable oils and products of their processing"
2 ADOPTED AND INTRODUCED BY Decree of the State Standard of Russia dated July 7, 2003 N 241-st
3 This standard is harmonized with the international standard ISO 660-96 "Animal and vegetable fats and oils. Determination of acid number and acidity" in parts of sections 4 and 5
4 TO REPLACE GOST R 50457-92 (ISO 660-83) regarding vegetable oils
1 area of use
1 area of use
This International Standard applies to vegetable oils and specifies methods for the determination of acid number.
2 Normative references
This standard uses references to the following standards:
GOST 12.1.007-76 Occupational safety standards system. Harmful substances. Classification and general safety requirements
GOST 12.1.019-79 Occupational safety standards system. Electrical safety. General requirements and nomenclature of types of protection
GOST 1770-74 Measuring laboratory glassware. Cylinders, beakers, flasks, test tubes. General specifications
GOST 4233-77 Sodium chloride. Specifications
GOST 4328-77 Sodium hydroxide. Specifications
GOST 5477-93 Vegetable oils. Methods for determining color
GOST 6709-72 Distilled water. Specifications
GOST 12026-76 Laboratory filter paper. Specifications
GOST 17299-78 Technical ethyl alcohol. Specifications
GOST 18300-87 Rectified technical ethyl alcohol. Specifications
GOST 20015-88 Chloroform. Specifications
GOST 24104-2001 Laboratory balance. General technical requirements
GOST 24363-80 Potassium hydroxide. Specifications
GOST 25336-82 Laboratory glassware and equipment. Types, basic parameters and dimensions
GOST 25794.1-83 Reagents. Methods for preparing titrated solutions for acid-base titration
GOST 25794.3-83 Reagents. Methods for preparing titration solutions for precipitation titration, non-aqueous titration and other methods
GOST 28498-90 Liquid glass thermometers. General specifications. Test Methods
GOST 29251-91 (ISO 385-1-84) Laboratory glassware. Burettes. Part 1. General requirements
GOST R 52062-2003 Vegetable oils. Acceptance rules and sampling methods
ISO 660-96 Animal and vegetable fats and oils. Determination of acid number and acidity
ISO 661-89 Animal oils and fats. Test sample preparation
ISO 5555-91 Animal and vegetable oils and fats. Sample selection
3 Measuring ranges and metrological characteristics of methods
3.1 Measurement ranges of acid number when determined by methods:
- titrimetric with visual indication 0.1-30.0 mg KOH/g;
- saline 1.0-30.0 mg KOH/g;
- using hot ethyl alcohol (or isopropyl alcohol without heating) 0.05-30.0 mg KOH/g;
- titrimetric with potentiometric indication 0.2-30.0 mg KOH/g.
3.2 The metrological characteristics of the methods at a confidence level of 0.95 are set out in Table 1.
Table 1
Acid interval | Borders | Repeatability limit | Reproducibility limit |
|||
absolute- | relative | absolute- | relative | absolute- | relative |
|
1 Titrimetric methods with visual indication |
||||||
Up to 0.2 incl. | ||||||
St. 0.2 to 0.4 incl. | ||||||
For cotton unrefined oil (thymolphthalein indicator) | ||||||
2 Salt method |
||||||
St. 1 to 30 incl. | ||||||
3 Titrimetric method with potentiometric display |
||||||
St. 0.2 to 1 incl. | ||||||
St. 1 to 30 inclusive: | ||||||
for light oils | ||||||
for dark oils | ||||||
4 Method using hot ethanol and an indicator (or isopropyl alcohol without heating) |
||||||
St. 0.05 to 1 incl. | ||||||
4 Definitions
For the purposes of this standard, the following term is used with the appropriate definition:
acid number: A physical quantity equal to the mass of potassium hydroxide, mg, required to neutralize free fatty acids and other substances that are neutralized by alkali, associated with triglycerides, contained in 1 g of oil.
The acid number is expressed in mg KOH/g.
5 Essence of methods
The essence of all methods given in this standard is the dissolution of a certain mass of vegetable oil in solvents or a mixture of solvents, followed by titration of the free fatty acids present with an aqueous or alcoholic solution of potassium hydroxide or sodium hydroxide.
6 Sampling
6.1 Sampling - according to GOST R 52062-2003.
For export-import deliveries - according to ISO 5555.
7 Titrimetric method with visual indication
7.1 Measuring the acid value of light and refined oils
7.1.1 Measuring instruments, auxiliary devices, reagents:
Laboratory scales according to GOST 24104
Laboratory drying cabinet with a thermostat that maintains the temperature (50±2) °C.
Bath water.
Stopwatch.
Cylinders 1(3)-50; 1(3)-100 or 1-500 according to GOST 1770.
Flasks Kn-2-250-34 (40, 50) THS according to GOST 25336.
Burettes 1-1(2, 3)-1(2)-1(2, 5, 10, 25, 50)-0.01(0.02, 0.05, 0.1) according to GOST 29251.
Glasses V(N)-1(2)-400 according to GOST 25336.
Liquid glass thermometer in accordance with GOST 28498, which allows you to measure the temperature in the range from 50 ° C to 100 ° C with a division value of 1 ° C-2 ° C.
Glass stick.
GOST 12026.
Potassium hydroxide according to GOST 24363, chemically pure or analytical grade, aqueous or alcoholic solution of molar concentration (KOH)=0.1 mol/dm (0.1 N), prepared according to GOST 25794.1 (2.2) and GOST 25794.3 (2.4).
Sodium hydroxide according to GOST 4328 chemically pure or analytical grade, aqueous or alcoholic solution (NaOH)=0.1 mol/dm, prepared according to GOST 25794.1 (2.2) and GOST 25794.3 (2.4).
GOST 17299 GOST 18300.
Chloroform technical according to GOST 20015.
Distilled water according to GOST 6709.
Solvent mixture: alcohol-ether or alcohol-chloroform, prepared in accordance with 7.1.2.1.
It is allowed to use other measuring instruments with metrological characteristics and equipment with technical characteristics not worse, as well as reagents in quality not lower than those indicated.
7.1.2 Preparation for measurement
7.1.2.1 Preparation of the solvent mixture
An ethereal mixture is prepared by volume from two parts of ethyl ether and one part of ethyl alcohol with the addition of five drops of a solution of phenolphthalein per 50 cm3 of the mixture.
An alcohol-chloroform mixture is prepared from equal parts of chloroform and ethyl alcohol with the addition of five drops of a phenolphthalein solution per 50 cm of the mixture.
Alcohol-ether and alcohol-chloroform mixtures are neutralized with a solution of potassium hydroxide or sodium hydroxide of molar concentration (KOH or NaOH)=0.1 mol/dm to a barely noticeable pink color.
7.1.2.2 Sample preparation
Transparent, unhardened vegetable oil is well mixed before taking a sample for analysis. In the presence of turbidity or sediment in liquid oil, as well as in the analysis of solidified oils, a part of the laboratory sample (50 g) is placed in an oven, in which the temperature is maintained at (50 ± 2) ° C, and heated to the same temperature. The oil is then stirred. If after that the oil does not become transparent, it is filtered in a cabinet at a temperature of 50 °C.
7.1.3 Taking a measurement
In a conical flask with a capacity of 250 cm3 weigh a sample weighing 3-5 g with an accuracy of 0.01 g. Then 50 cm3 of an alcohol-ether or alcohol-chloroform neutralized mixture is poured into the sample. The contents of the flask are mixed by shaking. If the oil does not dissolve in this case, it is heated in a water bath heated to (50 ± 2) ° C, then cooled to 15 ° C-20 ° C. A few drops of phenolphthalein are added to the solution. The resulting oil solution, with constant agitation, is rapidly titrated with a solution of potassium hydroxide or sodium hydroxide of a molar concentration (KOH or NaOH) = 0.1 mol / dm3 until a faint pink color is obtained, stable for 30 s.
When titrating with an aqueous solution of potassium hydroxide or sodium hydroxide of a molar concentration (KOH or NaOH) = 0.1 mol / dm, the amount of alcohol used together with ether or chloroform, in order to avoid hydrolysis of the soap solution, must be at least five times the amount of the spent solution of potassium hydroxide or sodium hydroxide.
When the acid number of the oil is more than 6 mg KOH/g, take a sample of oil weighing 1-2 g with an accuracy of 0.01 g and dissolve it in 40 cm 3 of a neutralized solvent mixture.
When the acid number of the oil is less than 4 mg KOH/g, titration is carried out from a microburette.
7.2 Measurement of the acid number of dark oils (unrefined cottonseed and others) with thymolphthalein
7.2.1 Measuring instruments, accessories, reagents
To carry out the determination, in addition to those specified in 7.1.1, the following must be applied:
- conical flasks with a side outlet tube with a capacity of 250 ml (Figure 1);
- thymolphthalein, alcohol solution of mass fractions of 1%;
- solvent mixture: alcohol-ether or alcohol-chloroform, prepared in accordance with 7.2.2.1,
- Lovibond tintometer with a set of glass filters and a cuvette for a layer of oil 10 mm thick.
Figure 1 - Conical flask with outlet tube
7.2.2 Preparation for measurement
7.2.2.1 Preparation of the solvent mixture
An ethereal mixture is prepared from two parts of ethyl ether and one part of ethyl alcohol with the addition of 1 cm3 of thymolphthalein solution per 50 cm3 of the mixture.
An alcohol-chloroform mixture is prepared from equal parts of ethanol and chloroform with the addition of 1 cm3 of thymolphthalein solution per 50 cm3 of the mixture.
Alcohol-ether and alcohol-chloroform mixtures are neutralized with a solution of potassium hydroxide or sodium hydroxide of molar concentration (KOH or NaOH)=0.1 mol/dm (0.1 N) until a blue color appears.
When using an alcohol-ether mixture, titration is carried out with an aqueous or alcoholic solution of potassium hydroxide or sodium hydroxide; when using an alcohol-chloroform mixture - an alcohol solution of potassium hydroxide or sodium hydroxide.
7.2.2.2 Sample preparation
To determine the weight of the sample, the color of the oil is determined according to GOST 5477 with a Lovibond tintometer in a cuvette for a 10 mm thick oil layer.
7.2.2.3 Taking a measurement
Weigh a sample of oil weighing 1-5 g to the nearest 0.01 g, depending on the color determined in 7.2.2.2, in accordance with Table 2, into a conical flask with a drain tube.
table 2
Oil color, red units | Oil weight, g |
From 21" 30 | |
Pour 50 ml of the neutralized mixture into a weighed flask and shake until the oil dissolves. 2 ml of thymolphthalein solution is added to the mixture and rapidly titrated with a solution of potassium hydroxide or sodium hydroxide of molar concentration (KOH or NaOH)=0.1 mol/dm with constant stirring of the contents of the flask.
Stirring is carried out so that the liquid is mixed in the outlet tube of the flask.
Observe the color change of the oil solution during the titration in a thin layer located in the outlet tube of the flask.
Titration is carried out until the color of the solution changes from yellow or reddish to greenish-brown or light blue.
It is allowed to measure the acid number in dark oils according to 7.1.
8 Salt method
8.1 Acid number measurement of unrefined cottonseed oil
8.1.1 Measuring instruments, accessories, reagents
Laboratory scales in accordance with GOST 24104 with a maximum permissible absolute error of not more than ±0.02 g.
Flasks Kn-1-250-29/32 ТХС according to GOST 25336 or special flasks for titration with a capacity of 200 cm3 (Figure 2).
Figure 2 - Flask special for titration
GOST 29251.
Laboratory filter paper according to GOST 12026.
Potassium hydroxide according to GOST 24363, chemically pure or h.d.a. molar concentration (KOH) = 0.25 mol / dm (0.25 N.), aqueous or alcoholic solution or sodium hydroxide according to GOST 4328, chemically pure. or h.d.a. molar concentration (NaOH) = 0.25 mmol / dm (0.25 N.), aqueous or alcoholic solution, prepared according to GOST 25794.1.
Sodium chloride according to GOST 4233, 35-36% aqueous solution.
Technical ethyl alcohol (hydrolysis) in accordance with GOST 17299 or rectified technical ethyl alcohol in accordance with GOST 18300.
Phenolphthalein, alcohol solution, mass fractions 1%.
Distilled water according to GOST 6709.
It is allowed to use other measuring instruments with metrological characteristics and equipment with other technical characteristics not worse, as well as reagents in quality not lower than the above.
8.1.2 Preparing for measurements
Sample preparation according to 7.1.2.2.
8.1.3 Taking measurements
A 10 g sample of oil is weighed into a titration flask with an accuracy of 0.01, 50 cm 35% -36% neutralized sodium chloride solution and 0.5 cm phenolphthalein solution are poured. The flask is stoppered and the contents are shaken, then titrated with an aqueous solution of potassium hydroxide or sodium hydroxide of molar concentration (KOH or NaOH)=0.25 mol/dm. When the acid number of the oil is less than 4 mg KOH / g, it is allowed to use a solution of potassium hydroxide or sodium hydroxide with a molar concentration (KOH or NaOH) = 0.1 mol / dm.
During titration, shaking is repeated each time after adding 4-5 drops of potassium hydroxide or sodium hydroxide until the color of the lower layer of the liquid disappears.
When the color of the lower layer begins to slowly disappear, the flask is shaken after adding 1-2 drops of a solution of potassium hydroxide or sodium hydroxide.
Titration is carried out until a stable pink color of the lower liquid layer appears.
9 Titrimetric method with potentiometric display
The method is applied to all types of vegetable oils.
9.1 Measuring instruments, accessories, reagents
Laboratory scales in accordance with GOST 24104 with a maximum permissible absolute error of not more than ±0.02 g.
Laboratory pH meters (ionomers) with a measurement range of 0-14 pH units and a scale division of 0.01 or 0.05 pH units, equipped with glass and silver chloride electrodes.
Glasses V (N) -1 (2) - (100) according to GOST 25336.
Burettes 1-1(2, 3)-1(2)-5(25, 50) - 0.02(0.05, 0.1) according to GOST 29251.
The stirrer is magnetic.
Filter paper according to GOST 12026.
Potassium hydroxide according to GOST 24363, chemically pure or analytical grade, molar concentration (KOH) = 0.1 mol / dm (0.1 N), aqueous or alcoholic solution or sodium hydroxide according to GOST 4328, chemically pure. or h.d.a. molar concentration (NaOH)=0.1 mol/dm (0.1 N.), aqueous according to GOST 25794.1 or alcohol according to GOST 25794.3 solutions.
Technical ethyl alcohol (hydrolysis) in accordance with GOST 17299 or rectified technical ethyl alcohol in accordance with GOST 18300.
Chloroform technical according to GOST 20015.
Purified ethyl ether or medical ether.
Phenolphthalein, alcohol solution, mass fractions 1%.
Distilled water according to GOST 6709.
A mixture of solvents, alcohol-ether or alcohol-chloroform, prepared according to 7.1.2.1.
9.2 Preparing to take measurements
Sample preparation - see 7.1.2.2.
9.3 Taking measurements
A sample of oil weighing 2-3 g is weighed into a glass and 40 cm3 of a neutralized mixture of solvents are poured. The beaker is placed on a magnetic stirrer, turned on, and then the electrodes of the pH meter are lowered into the beaker so that they are immersed to a depth of at least 3 cm.
Potentiometric titration of the oil solution is carried out in accordance with the instructions attached to the device, to an equivalent point in the pH range of 11-13. At the equivalence point, the arrow instantly registers a "potential jump" (a sharp shift along the scale). or rectified technical ethyl alcohol (0.5 N.), prepared according to
Thymolphthalein, in the case of dark-colored oils - an alcohol solution with a mass fraction of 2%.
It is allowed to use other measuring instruments with metrological characteristics and equipment with technical characteristics not worse, as well as reagents in quality not lower than the above.
10.2 Sample preparation for measurement
Prepare the test sample in accordance with 7.1.2.2 or ISO 661.
10.3 Taking a measurement
Take two conical flasks. Weigh into one flask with an accuracy of 0.01 g a portion of the test oil sample with the mass indicated in Table 3, depending on the expected value of the acid number. The mass of the test sample and the concentration of the titrating solution should be such that the volume of the solution used for titration does not exceed 10 cm3; depending on the color of the oil (light or dark), an indicator is selected.
Table 3
Expected value of acid number, | Mass of the test sample, g |
From 1 to 4 incl. | |
From 4 to 15 incl. | |
From 15 to 75 incl. | |
Over 75 |
In the second flask add 50 ml of ethyl alcohol, 0.5 ml of phenolphthalein and heat in a water bath to a boil. Then, immediately, while the temperature of the alcohol is above 70 ° C, it is carefully neutralized with a solution of potassium hydroxide with a molar concentration (KOH) = 0.1 mol / dm3 until a slight but noticeable color change to pink, stable for 15 s. Next, the contents of the second flask are poured into the first (with a sample), mixed thoroughly, brought to a boil and quickly titrated with a solution of potassium hydroxide or sodium hydroxide, stirring thoroughly during the titration. The alkali concentration is chosen depending on the expected value of the acid number of the test sample.
When using isopropyl alcohol instead of ethyl alcohol, it is not necessary to heat the test sample solution. Applied indicators: phenolphthalein - for light oils, thymolphthalein - for dark oils.
NOTE For dark-colored oils, large volumes of ethanol and indicator may be required, which are experimentally determined to provide optimal conditions for establishing the end of the titration. The ratios between alcohol and phenolphthalein should be those used for light oils (100:1).
11 Processing results
11.1 Oil acid number, mg KOH/g, is calculated by the formula
where 5.611 is the mass of KOH in 1 cm3 of a solution of molar concentration (KOH) = 0.1 mol / dm (0.1 N), mg, when using NaOH; obtained by multiplying the calculated mass of NaOH in 1 cm3 of a solution of molar concentration (NaOH)=0.1 mol/dm (0.1 N.), equal to 4.0, by 1.4 - the ratio of the molecular weights of KOH and NaOH;
- the ratio of the actual concentration of a solution of potassium hydroxide or sodium hydroxide to the nominal;
- the volume of a solution of potassium hydroxide or sodium hydroxide of molar concentration (KOH or NaOH)=0.1 mol/dm, used for titration, cm;
- weight of the sample, g.
12 Presentation of measurement results
12.1 For the final result of the determination, the arithmetic mean of the results of two parallel determinations is taken, the discrepancy between which should not exceed the values given in Table 1.
In case of disagreement in the assessment of product quality, the result of the determination is taken as the arithmetic mean of the results of at least four parallel determinations obtained by titrimetric methods with visual or potentiometric indication.
12.2 Calculations are performed to the second decimal place, followed by rounding the results to the first decimal place.
13 Safety requirements
13.1 When performing measurements, it is necessary to comply with safety requirements when working with chemical reagents in accordance with GOST 12.1.007.
13.2 The room in which measurements are taken must be equipped with supply and exhaust ventilation. Work must be carried out in a fume hood.
13.3 It is necessary to comply with the safety requirements when working with electrical appliances in accordance with GOST 12.1.019.
13.4 Ethyl ether is flammable, flammable, and narcotic.
13.5 Chloroform is non-flammable, has a general toxic and narcotic effect.
APPENDIX A (informative). Bibliography
APPENDIX A
(reference)
TU 25-1819.0021-90 Stopwatches
TU 75-96804-97-90 Purified ethyl ether
State Pharmacopoeia, X ed. Ether medical
TU 6-09-5360-88 Phenolphthalein
TU 6-09-07-1610-87 Timolphthalein
TU 6-09-502655-95 Isopropyl alcohol
The text of the document is verified by:
official publication
M.: IPK Standards Publishing House, 2003
Vegetable oils are one of the types of widely used edible fats for the production of cosmetics and biologically active food supplements in contract manufacturing. "KorolevPharm".
The raw materials used for the manufacture of vegetable oils are the fruits of various oilseeds and seeds of cereals. In oilseeds, fatty oils can accumulate in such large quantities that it becomes possible to process the seeds on an industrial scale to obtain oils. The large group of oil plants includes mainly cultivated plants, of which there are more than 100. In the global production of vegetable oils, seeds of sunflower, soybean, cotton, rapeseed, flax, peanut, sesame, mustard, etc. are used. The pulp of various fruits is also used: nuts, olives, hazel, coconut and oil palms. Technologies for the use of waste products from the food industry are used: these are the germs of seeds of corn, wheat, oats and many other crops. Valuable oils for the cosmetic industry are obtained from stone fruits: apricots, plums, cherries, etc.
Valuable vegetable oils in a wide range are used for production of cosmetics And dietary supplements to food at the contract manufacturing KorolevPharm.
The appearance of defects and ways to prevent them.
Over time, during storage in vegetable oils, processes occur that lead to a significant decrease in their quality indicators. The ongoing processes are evidenced by one of the controlled quality indicators - the acid number. The depth of these processes depends on many factors, the main ones being the storage conditions of vegetable oils: the temperature and relative humidity of the air maintained in the warehouse, access to atmospheric oxygen, as well as exposure to light. One of the determining values is the initial quality of the oils that are stored for storage - the presence of various impurities, the condition of the container and the material from which it is made.
Under unfavorable and inappropriate storage conditions for oils, under the influence of atmospheric oxygen and intense light flux, at elevated storage temperatures in warehouses, vegetable oils undergo various changes that lead to a decrease in the quality indicators of oils and even to their deterioration, resulting in the formation of substances that have a negative effect on the human body.
During the hydrolysis of vegetable fats, the accumulation of intermediate and final decomposition products is possible. As a result of oxidation in fats, the accumulation of peroxides, aldehydes and other compounds occurs. The determination of these substances in the product indicates that deep decomposition of fat occurs in it. As a result of these processes - hydrolysis and oxidation, fats acquire an unpleasant rancid or greasy taste.
There are substances that have properties to slow down the oxidation process, for example: tocopherol (vitamin E), from the group of retinols (vitamin A), and from the group of phosphatides, lecithin is the most effective. These substances are also called natural antioxidants, the presence of antioxidants in oils can significantly slow down the oxidation process. 
This is the main indicator of the quality of oils and fats, as it characterizes the degree of lipid hydrolysis, since the amount of free acids in natural oils and fats is insignificant. Hydrolysis occurs during storage with the access of oxygen and is accompanied by oxidation primarily of fatty acids.
The lower the acid number, the less likely the formation of carcinogens in the oil under inappropriate storage conditions.
In accordance with ND, different oils have different acid number.
The acid number is defined as a physical quantity. It is equal to the amount of potassium hydroxide (measured in mg) that is necessary to carry out the neutralization of free fatty acids, as well as substances associated with triglycerides, which can be neutralized with alkali and are contained in 1 gram of vegetable oil.
What follows, the higher acid number, the more potassium hydroxide is used for neutralization.
In the physico-chemical laboratory of contract manufacturing KorolevPharm, the definition acid number carried out in accordance with GOST: GOST R 50457-92 Vegetable oils.
Definition acid number and acidity.
The essence of the definition method acid number. A certain mass of vegetable oil is dissolved in a solvent or in a mixture of certain solvents with further titration of free fatty acids with a hydroxide solution.
A weight of oil weighed with a certain accuracy is placed in a conical flask. After that, the neutralized mixture is added to the flask and stirring is carried out until the vegetable oil is completely dissolved. Next, an indicator is added to the mixture, which is capable of changing the color of the solution under certain conditions, and the titration is quickly carried out with a hydroxide solution, while constantly stirring the contents of the flask.
The titration process is carried out until the solution changes its color from yellow or reddish to greenish-brown or light blue. To achieve accuracy, measurements are carried out several times and the result is taken as the arithmetic mean of the data obtained.
The acid number is calculated by the formula: 
Where: 56.1 - the mass of KOH in 1 cm3. solution of molar concentration (KOH - potassium hydroxide) = 1 mol / dm. cube (1 N), mg, when using NaOH - sodium hydroxide; obtained by an arithmetic operation - multiplying the calculated mass of sodium hydroxide (NaOH) in 1 cm3. molar concentration solution (NaOH) = 1 mol/dm. cube (0.1 N.), equal to 4.0 to 1.4 - the ratio of the molecular weights of NaOH and KOH.
K - denotes the ratio of the actual concentration of solutions of potassium hydroxide (KOH) or sodium hydroxide (NaOH) to the nominal.
V is the volume of sodium hydroxide (NaOH) or a solution of potassium hydroxide (KOH) of molar concentration (KOH or NaOH) = 1 mol/dm. cube used for titration, see cube;
m - weight of sample.
Work is carried out in compliance with safety regulations, carefully and carefully.
To extend the shelf life of oils and prevent rapid oxidation in the contract manufacturing warehouse complex of KorolevPharm, vegetable oils are placed in containers pumped with nitrogen, which prevents contact with air.
Acid number, or acidity of fat - the number of milligrams of potassium hydroxide required to neutralize all the free fatty acids contained in one gram of fat. Acid number is a very important indicator of the properties and condition of fat, since it can easily increase during storage, both fat and fat-rich foods. It is an indicator of hydrolytic spoilage.
Fats almost always contain free fatty acids, and their concentration in vegetable fats is usually higher than in animal fats.
In the process of seed maturation, the content of free fatty acids decreases. Therefore, the acid number is used to assess the degree of seed maturity. At the first stages of seed ripening, the acid number is usually 30-40 mg KOH per 1 g of oil, which indicates a low rate of fat synthesis. By the end of seed ripening, the acid number decreases to 1.5-2.5. in addition, the content of acids increases sharply during seed germination due to the hydrolysis of fats.
The principle of the method. It consists in titration with a 0.1 N solution of potassium hydroxide of fat dissolved in a neutralized mixture of alcohol and ether (1: 2): RCOOH + KOH ® RCOOK + H 2 O.
By the amount of alkali solution used to neutralize acids, the value of the acid number is judged.
Equipment, reagents. 1) Water bath. 2) Refrigerator reverse. 3) Vegetable oil. 4) Burettes. 5) Ethyl alcohol. 6) Medical ether. 7) Potassium hydroxide, 0.1 N solution. 8) Phenolphthalein, 1% solution. 9) Thymolphthalein, 1% solution.
Progress
Place 3-5 g of vegetable oil into a clean dry conical flask with a capacity of 250 ml, add 30 ml of a mixture of alcohol and ether (1:2), previously neutralized according to the indicator used for titration. 1 ml of a 1% alcoholic solution of phenolphthalein is poured into the resulting solution and titrated with 0.1 N aqueous potassium hydroxide solution until a faint pink color appears.
In the study of dark-colored fats, a 1% solution of thymolphthalein is used as an indicator, which in an alkaline medium becomes blue.
Calculation of results. The acid number of fat X (in mg KOH per 1 g of fat) is calculated by the formula:
where V is the volume of 0.1 n potassium hydroxide solution used for
titration, ml;
K - conversion factor for exact 0.1 N hydroxide solution
m is the mass of the studied fat, g;
5.61 - the amount of potassium hydroxide corresponding to 1 ml of 0.1 n
potassium hydroxide solution, mg.
The arithmetic mean of the results of two parallel determinations is taken as the final result.
The content of fatty acids in oil can also be expressed not by the acid number, but by the amount of free acids as a percentage of the weight of the oil. Conventionally, calculations are based on free oleic acid, which is one of the most common acids included in most vegetable oils. To do this, the acid number is multiplied by a factor of 0.503. This coefficient is obtained from the following equation:
% acid number = 
,
where 282.3 is the molecular weight of oleic acid;
56.11 is the molecular weight of KOH;
100 - conversion to percentage;
1000 - conversion of milligrams to grams.