Determination of Saponification Value in Carnuba Wax by USP/NF Residual Titration Method <541> ()
1. Introduction
The word wax comes from the Old English weax meaning “material of the honeycomb” carnuba wax. Copernica Cerifera Wax, also called Carnuba Wax, is obtained the leaves of the Brazilian tropical palm tree Copernica [1] . Copernica cerifera, and Rhus Succedanea Fruit Wax, also called Japan wax, is obtained from the berries of the sumac Rhus succedanea, which grows in Japan and Chine. Carnuba wax is the hardest of the commercial vegetable waxes. It is tough, amorphous, iustrous wax that varies in color from dirty yellow to brown, green or white. Japan wax is a tough malleable, sticky substance. There is no formula for carnuba wax [2] . Carnuba Wax consists chiefly of myricyl cerotate and small quantities of free cerotic acid and myricyl alcohol. A major component of carnuba wax coating on the leaves of Brazilian Palm and formula is CH3(CH2)30COO(CH2)23CH3 [3] .
Carnuba Wax is moderately coarse powder or flaxes, possessing a characteristic bland odor, and free from rancidity. Specific gravity is about 0.99. Insoluble in water, free soluble in warm benzene; soluble in warm chloroform and in warm toluene; slightly soluble in boiling alcohol [4] .
A complex mixture of several chemical compounds, predominantly esters, aliphatic esters (strait-chain acids with even-numbered carbon chains from C30 to C34, Alpha-hydroxy esters (straight-chain hydroxyl acids) with even-numbered carbon chains from C22 to C28, straight-chain acids with even-numbered chains from C24 to C28, straight-chain monohyric alcohols and dihydric alcohols with even-numbered carbon chains from C24 to C34, cinnamic aliphatic diesters (p-methoxy cinnamic acids and dihydric alcohols) with even-numbered carbon chains from C24 to C34 also contain free acids, free alcohols, hydrocarbons and resins.
In this study, a test for saponification value has been successfully determined in carnuba wax. This is in contradistinction to the U.S. Pharmacopeia/National Formulary (USP/NF) Method.
Carnuba wax is used in the pharmaceutical industry for tablet coatings and binding. Carnuba wax primarily consists of fatty acid esters. Coating tablets with the wax enables easier swallowing of the tablet. Carnuba wax has many other uses, including uses from car wax to dental floss. Carnuba wax is a safe, non-toxic and inert ingredient [5] [6] .
Carnuba wax is widely used in cosmetics, certain foods, and pharmaceutical formulations. Cosmetically, carnuba wax is commonly used in lip balms [7] .
Carnuba wax is the hardest and highest-melting of the waxes commonly used in pharmaceutical formulations and is used primarily as a 10% w/v aqueous emulsion to polish sugar-coated tablets. Aqueous emulsions may be prepared by mixing carnuba wax with an ethanolamine compound and oleic acid.
Carnuba wax (10% - 50% w/w) is also used alone or with other excipients such as hypromellose, hydroxypropyl cellulose, alginate/pectin-gelatin, Eudragit, and stearyl alcohol to produce sustained-release solid-dosage formulations [8] - [15] .
2. Materials
2.1. Equipment
Burettes;
Analytical balance, having a sensitivity of 0.1 mg;
Graduated cylinder, 50 mL;
Volumetric flasks;
Volumetric pipettes, 50 mL;
Electric hot plate and reflux condenser;
Round bottom flask, 3 arm (24/40) 250 mL, preferably of Pyrex;
250˚C thermometer in one-hole rubber stopper wrapped in Teflon type;
Cargille boiling chips;
Glass stirring rod.
2.2. Chemicals
Carnuba (Cera carnuba) pale yellow wax;
Ethyl alcohol, (Pharmco-Aaper, 95%, HPLC Grade);
Purified water: Water was purified with a Milli Q System (Millipore, Milford, MA). Hydrochloric acid, concentrated, Pharmco-Aaper, 36.6% - 38.0%.
Solutions
Alcoholic potassium hydroxide KOH, 0.5 M Volumetric Solution (VS) is prepared 17.0 g of KOH in 500 mL 96% ethyl alcohol.
Aqueous hydrochloric acid, 0.5 M Volumetric Solution (VS): Prepared by diluting 40 mL of concentrated HCl to 1 L with deionized water. Standardized vs Na2CO3.
Ethanol, neutralized against phenolphthalein.
Phenolphthalein Test Solution (TS).
3. Procedure
Place 1.5 - 2.0 g of the carnuba wax substance in a tared, 250-mL flask, weigh accurately. Prepare and conduct blank determinations simultaneously with the sample. Add to it 25.0 mL of 0.5 N alcoholic potassium hydroxide. Connect the air condenser and boil gently, but steadily, until saponified. This reflux usually requires about 30 min, frequently rotating the content. Reflux time can be up to 90 min to ensure complete saponification, depending on the type of ester to be tested.
After the flask and condenser have cooled somewhat, but not sufficiently to form a jell, wash down the inside of the condenser with a small quantity of distilled water. Disconnect the condenser, add about 1 mL of phenolphthalein indicator and titrate with 0.5 N HCl until the pink color just disappears. Record the volume of 0.5 N HCL required for the titration. The end point is very easily distinguished, of carnuba wax when this method was used. Perform a blank determination under the same conditions Titrimetry <541>, Residual Titrations [4] .
Calculate the Saponification Value:
Mw = molecular weight of potassium hydroxide, 56.11;
VB = volume of 0.5 N hydrochloric acid consumed in the blank test (mL);
VT = volume of 0.5 N hydrochloric acid consumed in the actual test (mL);
N = exact normality of the hydrochloric acid;
W = weight of the substance taken for the test (g).
If the oil has been saturated with carbon dioxide for the purpose of preservation, expose it in a shallow dish in a vacuum desiccator for 24 h before weighing the test specimen [4] .
4. Result and Discussion
The chemical properties of waxes are amongst the most important properties that determine the present condition of the wax. When heating the yellow carnuba wax with alcoholic potassium hydroxide volumetric solution, 0.5 N, solution turns from clear to straw to brown tea color. With excessive heating (i.e. 235˚C for 30 min), solution turns black coffee color, but then too much KOH is consumed, with the result that the saponification value exceeds the acceptable range of 78 - 95 mg KOH/g sample. Solution was completely clear at 185˚C, indicating that all wax sample has been saponified. Addition of water to cooled sample results in acidified soap, and with stirring resembles coffee with cream because of the color. The blank, on the other hand, remains clear even upon addition of water. A characteristic smell (like Murphy furniture soap) accompanies the solution after heating to 185˚C, both for sample and for blank, which in indicates a component of the ethanoic KOH and carnuba wax are responsible for the smell and for the color.
Notes: [Caution]: Potassium hydroxide, like all alkalies, can burn skin, eyes, respiratory tract severely. Wear heavy rubber gloves. Alkalies are extremely exothermic when mixed with water. Ethyl alcohol is flammable. Use fume hood when heating or evaporation this solvent. Substract the total determination reading from the blank reading and calculate the saponification value.
5. Conclusion
In this study, a test for saponification value has been successfully determined in carnuba wax.
The results obtained from mg KOH/g content of yellow carnuba wax. Expected saponification value for yellow carnuba wax is between 78 and 95 mg KOH/g sample. The saponification value has been found 90.1 mg KOH/g for sample A, and 91.6 mg KOH/g sample for the sample B as duplicate). In Table 1, %RPD is 1.65% and the result meets the saponification.
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Table 1. Result for Saponification value.
Acknowledgements
The authors are thankful to Dr. Krassi Lazarova, Head of the Science Department of the Centenary University to give us the opportunity to complete this research work.