COSMETIC TENSIONING COMPOSITION
20210386653 · 2021-12-16
Inventors
Cpc classification
A61K2800/5922
HUMAN NECESSITIES
International classification
Abstract
The present application relates to cosmetic compositions and in particular, to skintightening compositions and to compositions that improve the appearance of the skin by providing skin-tightening improvements to the skin, for treatment of, for example, eye bags, facial wrinkles and other skin imperfections, the cosmetic compositions comprising a polyvalent silicate; at least one film former, and a carboxylic acid wherein the pH of the composition is in the range 6.0 to 11.2 wherein the composition provides a tightening effect on application to the skin. The present invention provides a composition which provides an efficient tightening product yet with good natural skin shine but without the white residue appearance associated with known products.
Claims
1. A cosmetic composition comprising sodium silicate, pyrogenic silica, at least one film former, and a pH adjusting agent wherein the pH of the composition is in the range 6.0 to 11.2 wherein the composition provides a skin tightening effect after application to the skin.
2. A composition as claimed in claim 1 wherein the pH of the composition is in the range between 6.0 to 10.
3. (canceled)
4. A cosmetic composition as claimed in claim 1 wherein the composition provides a tightening effect after application to the skin, substantially without a white or ashy appearance on the skin.
5. A composition as claimed in claim 1 wherein the pyrogenic silica is present in an amount within the range 0.1-5% w/w of the composition, 0.6%-32% of the solids contents.
6-9. (canceled)
10. A composition as claimed in claim 1 wherein the sodium silicate comprises Na.sub.2O and SiO.sub.2 with a 3.22 weight ratio of SiO.sub.2:Na.sub.2O suspended in an aqueous solution.
11. A composition as claimed in claim 1 wherein the sodium silicate solution is in the range of 34-42% solids, and preferably, comprises 4-20% w/w of the total weight of the composition.
12. A composition as claimed in claim 1 wherein the composition also comprises a plasticiser.
13. A composition as claimed in claim 12 wherein the plasticiser is selected from the group consisting of glycerine, propylene glycol, butylene glycol and propanediol, and mixtures thereof.
14. (canceled)
15. A composition as claimed in claim 1 wherein the composition also comprises 0-2% xantham Gum to provide a transparent composition to allow for the stabilization of the film by significantly increasing the viscosity of the composition, preventing it from running off the area of skin to which it was applied.
16. A composition as claimed in claim 1 wherein the composition comprises a preservative.
17. A composition as claimed in claim 16 wherein the preservative is phenoxy ethanol.
18. (canceled)
19. A composition as claimed in claim 1 wherein the composition comprises an antimicrobial agent.
20. A composition as claimed in claim 19 wherein the antimicrobial agent is present in an amount in the range 0-2% by weight of the composition.
21. A composition as claimed in claim 1 wherein the acid comprises citric acid, present in an amount of 5-9% w/w 20% citric acid aqueous solution.
22-24. (canceled)
25. A composition as claimed in claim 1 comprising the following ingredients in an amount in the range indicated: (all amounts are in % w/w weight of the ingredient as total weight of the composition): Pyrogenic Silica 0.1-2% Sodium Silicate (38.6% water solution) 4-20% Citric Acid (20% water solution) 5-9% Polyurethane (41% water emulsion) 2-20%; and optionally: any one or more of the following: Xanthan 0-2% Polyhydric alcohol plasticizers 0.5-20%, optionally, the polyhydric alcohol plasticizers comprising 1,3 butylene glycol in an amount in the range 0.5-6% and Glycerin in an amount in the range 0.5-6%, Phenoxy Ethanol 0-2%; and 1,2 Hexanediol and Capryloyl glycol 0-2%.
26. A composition as claimed in claim 1 comprising the following ingredients in the amounts indicated (all amounts are in % w/w weight of the ingredient as total weight of the composition): TABLE-US-00009 Raw Material Percentage % w/w Sodium silicate 6-12 (34-42%% water solution) Fumed Silica 0.1-2 Polyurethane Polymer 5-12 Citric Acid (20% water 5-9 solution)
27. A composition as claimed in claim 25 comprising the following additional ingredient in the amounts indicated (all amounts are in % w/w weight of the ingredient as total weight of the composition): TABLE-US-00010 Raw Material Percentage % w/w Deionised water 60-75
28. A composition as claimed in claim 26 comprising the following additional ingredient(s) in the amounts indicated (all amounts are in % w/w weight of the ingredient as total weight of the composition): TABLE-US-00011 Raw Material Percentage % w/w Xanthan Gum 0.3-0.8 1,3-butylene glycol 1.0-15% Glycerine 1.5-3.5 1,2-hexanediol and 0-2 Capryloyl glycol Phenoxy ethanol 0.0-2.0
29. A cosmetic composition comprising sodium silicate, pyrogenic silica, at least one film former, and a pH adjusting agent wherein the pH of the composition is in the range 6.0 to 11.2 wherein after application to the skin, the composition provides a skin tightening effect, substantially without a white or ashy appearance on the skin.
30. A method of preparation of the composition of claim 1 comprising the following steps: (a) mixing sodium silicate and pyrogenic silica in pre-determined amounts; (b) adding a film former to the mixture; and (c) after step (b), adding a pH adjusting agent to achieve a pH in the range of between 6.0 to 11.2
31-33. (canceled)
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The present application will now be described with reference to the accompanying drawings in which:
[0038]
[0039]
[0040]
[0041]
DETAILED DESCRIPTION OF THE INVENTION
[0042] Historically, anti-wrinkle cosmetic products have relied heavily on silica and polyvalent silicate film formers in order to produce their asserted skin-tightening effect to reduce wrinkles and puffiness. These prior art compositions usually have a pH range of around 10-12, as the silica itself is strongly alkaline and it is taught in the prior art that lower pH leads to the formation of a more brittle and less flexible film on the skin, which in turn resulted in cracking, whitening and other obvious visual drawbacks. However, even at higher pH, many current market products still result in a whitening effect of the area of the skin onto which the composition is applied.
[0043] The present invention provides a skin tightening composition comprising sodium silicate and pyrogenic fumed silica with a solid weight ratio of pyrogenic silica:sodium silicate of about 1:5 based on the solids level since the solids level of sodium silicate is in the range of between 34-42%, preferably, 35-40% and most preferably, 36-39% and most preferably, 38-39% The technical advantage of the composition of the present invention is that an enhanced skin-tightening effect is achieved which has been found to smooth facial wrinkles over a period of up to 8 hours while simultaneously reducing puffiness. A combination of pyrogenic fumed silica and sodium silicate has been found to be surprisingly effective. While the mechanism of combination is not known, it is thought that the skin tightening effect may arise due to the fact that unlike previous compositions disclosed by prior art the current composition is not chemically cross-linked but instead physically cross-linked. This results in a more pliant and flexible film that allows the facial muscles underneath the skin to move without resulting in film cracking and whitening. The synergistic effect is shown in the Examples shown in Table 1 below. In the absence of pyrogenic fumed silica, the efficient skin-tightening effects is not achieved, whereas even small amounts of pyrogenic fumed silica will contribute to significantly increased skin tightening properties.
[0044] All amounts are in % w/w (weight of ingredient to weight of total composition).
TABLE-US-00003 TABLE 1 Raw Material Raw Material Trade Name INCI Name CB8-5B1 CB8-5C1 CB8-5D1 CB8-5E1 DI water DI water 65.0 60.0 70.0 75.0 O Sodium sodium 6.0 12.0 10.0 8.0 Silicate silicate, water Baycusan C Polyurethane 12.0 12.0 8.0 5.0 1004/1 35, water Glycerin Glycerin 1.5 3.5 1.6 3.3 99.7% usp 1,3-butylene 1,3-butylene 3.5 3.5 1.5 3.1 glycol glycol Wacker HDK N20 silica 2.0 0.9 0.5 0.1 Keltrol CG-T Xanthan Gum 0.8 0.8 0.8 0.3 Citric Acid Citric acid, 9.0 6.5 7.0 5.0 (20% water water solution) Phenoxyethanol Phenoxyethanol 0.2 0.8 0.6 0.2 Total 100.0 100.0 100.0 100.0 Tightening feel significant moderate moderate slight Wrinkle significant moderate moderate slight smoothing effect Appearance Moisturized Moisturized Moisturized Moisturized natural skin natural skin natural skin natural skin pH 7.2 7.47 7.66 8.37 pH of the composition is in the range 6.0 to 11.2
[0045] The ranges of the materials are indicated below with the total adding up to 100% w/w
TABLE-US-00004 TABLE 2 Raw Material Percentage % w/w Deionised water 60-75 Sodium silicate 6-12 (38.6% water solution) Fumed Silica 0.1-2.sup. Polyurethane Polymer 5-12 (41% emulsion) Xanthan Gum 0.3-0.8 Citric Acid (20% water 5-9 solution) 1,3-butylene glycol 1.5-3.5 Glycerine 1.5-3.5 1,2-hexanediol and 0-2 Capryloyl glycol Phenoxy ethanol 0.0-2.0 Total 100.00
[0046] Examples in Table 1 and 2 are tested on the back of a hand at the dosage of 2 mg/cm using finger to apply. 32 mg sample was applied in the 4*4 cm.sup.2 area and allowed to dry for 3 minutes while the hand is laid flat, the stretch test was carried out by making a first which stretches the film that has formed on the skin from the application of the composition of the present invention. The result was observed as a visual test, without any instrument measurement.
[0047] With reference to Table 1, it can be seen that the composition tightening feel and wrinkle smoothing effect increase with the amount of pyrogenic silica.
[0048] It can be seen from the above Table 1 that providing a composition comprising sodium silicate, pyrogenic silica, citric acid, and polyurethane plays a vital role in the efficacy of the resulting composition. If pyrogenic fumed silica and citric acid are not used, it has been found that the tightening effect is reduced. The skin tightening effect provided by the composition of the present invention comprising pyrogenic silica, sodium silicate, citric acid and polyurethane is of commercial importance and valuable because it is far less visible on the skin than alternative market products when applied to the skin; this is likely due to the fact that polyurethane wet the surface of dry particles such as silica to prevent the white chalky look after the product is completely dried and in addition polyurethane also offers great adhesion on skin and improved flexibility to minimize cracking due to skin movement. The lack of or diminishment of the whitening effect that is known to occur when the prior art compositions are used on the skin, is a significant advantage of the present invention.
[0049] In addition to the skin-tightening benefits that the current invention achieves, the novel composition also has an additional technical effect of reducing the puffiness under the eyes, a common side effect of ageing along with wrinkle formation. This combination of effects is not disclosed in any of the prior art, and to our knowledge, there exists no single formulation that would alleviate both wrinkles and puffiness with a single topical treatment.
[0050] Additionally, the tolerance of skin tightening products for other cosmetic compositions has never been high, and indeed, as evidence of this, the use of other cosmetic products such as toner and foundation in conjunction with the compositions disclosed in prior art is discouraged. However, in the current composition, the use of cosmetics such as toner, foundation, while reducing the effect of the skin-tightening and puffiness reduction, does not prevent the current invention from fulfilling its described technical purpose.
[0051] Prior to the skin tightening composition of the present invention, most of the prior art skin-tightening products have had pH ranges of 10-12, which is close to being classified as ‘corrosive’ for the skin. Generally, lower pH values are not recommended as the use of sodium silicate in acidic media resulted in higher viscosity and gelation of the formulation. In this present invention, one embodiment is disclosed in which citric acid is included in the composition as well as a self-emulsified polymer, such as Polyurethane-35 (commercially available such as under the trade name, BAYCUSAN C1004, a commercially available product from Covestro AG (formerly Bayer Material Science AG), Leverkusen). This polyurethane product comprises 2-20% by weight of the composition of the present invention, such as in the range of 5˜12% by weight of the composition.
[0052] In another aspect, the present invention also relates to a method of preparation of a skin tightening a composition wherein the method comprises the step of adding citric acid in the presence of thickener and self-emulsified polyurethane-35 to maintain the stability of the formula. The citric acid reduced the pH of the solution to the range of 6-10, such as in the range 6.5-8.5. This improvement over the prior art results in a less alkaline composition that is more compatible with skin and less aggressive as compared with known cosmetic skin care products.
[0053] In some embodiments, silica is present in an amount within the range 0.1-5% w/w of the composition, 0.6%-32% of the solid contents, such as 0.2-2% w/w of the composition and 1.3-13% of the solids contents.
[0054] For citric acid, in some embodiments, 20% citric acid solution is present in an amount within the range of 1-10% of the composition and present in an amount with the range of 1.3-13% of the solids contents, such as present in a range of 5-9% and present in an range of 6.5-11.7% of the solid contents.
[0055] In some embodiments, the sodium silicate solution comprises Na.sub.2O and SiO.sub.2 with a 3.22 weight ratio of SiO.sub.2:Na.sub.2O suspended in a 34-42% water solution. For example, the sodium silicate solution comprises 4-20% of the total weight of the composition, such as 6-12%.
[0056] In addition to the pyrogenic fumed silica and sodium silicate, other additives may be included in the formulation of the present invention to form an effective skin tightening product.
[0057] The composition may also contain 0-2% xantham Gum, such as Keltrol CG-T, to provide a transparent composition. Xantham gum allows for the stabilization of the resultant film by significantly increasing the viscosity of the composition, preventing it from running off the area of skin to which it was applied.
[0058] In some embodiments, the composition also comprises 0.5-6% 0.5-20% 1,3-butylene glycol that similarly to Xanthan Gum acts as an anti-freeze agent to stabilize the formation of the film.
[0059] The composition may also comprise 0.5-6% glycerine, which is used in skincare to promote the smoothness and moisture content of the skin. This hydration can also help chronically reduce wrinkle visibility by making the skin more pliant.
[0060] Preservatives and stabilisers make up 0-2% of the total weight of the formulation and is used as a preservative and a stabilizer. Preservatives such as phenoxyethanol, Chlorophenesin, parabens can be used in the formulation.
[0061] An additional additive may comprise a film former, such as a high molecular weight polyurethane. Preferred polyurethane is Polyurethane-35 such as commercially available under the trade name BAYCUSAN C1004/1, a commercial product from Covestro AG (formerly, Bayer Material Science AG), Leverkusen. The polyurethane film former comprises 2-20% by weight of the formulation, such as in the range of 5-12%.
[0062] Water based PU usually demonstrates good affinity to dry pigment/particles, therefore water-based PU helps to wet/disperse the dry particle to minimize the matt/dry particle look. However, if a lot of PU is used, it can promote a glossy look which is undesirable. For this application, the ratio of PU used must be controlled since too much could result in interference with the sodium silicate polymer structure to weaken the skin tightening effect. Of course, it is to be understood that other polymers could wet dry pigment or particles as well such as polyester, etc. However, for the composition of the present invention, PU can be the plasticiser because of its great adhesion on the skin and elastic shape recovery capability, which are also beneficial properties to help with durability of the skin tightening effect.
[0063] The remaining weight percent is made up by deionised (DI) water.
[0064] It will be understood by those skilled in the art that some of the above additives are not necessary to achieve the desired technical skin-tightening effect. Compounds that promote skin health and/or that exhibit antimicrobial activity are not necessary for skin-tightening but do act in concert with the skin-tightening compounds to improve the overall appearance and health of the skin.
[0065] The resulting composition should then be applied to the skin in a regular and homogenous layer according to conventional manner. In some embodiments, the composition can be applied to a layer of clean, dry skin that is free of excessive oils. It should be applied in a single layer and allowed to dry.
EXAMPLES
Method of Preparation of the Skin Tightening Composition of the Present Invention
Example 1
[0066] The preparation method for the present invention will now be described with reference to Table 3 below.
[0067] Initially, deionised (DI) Water, O Sodium Silicate and Fumed Silica are combined in the amounts and ratios indicated in Table 3 below and the ingredients were mixed at a medium speed, such as about 800 to about 1500 rpm, for 5-10 minutes until a uniform/homogenous mixture is obtained. An overhead mixer and propeller blade were used, in this particular Example, IKA® RW 20 with prop/propeller blade was used for stirring until homogeneous. Of course, this is only one method and apparatus that can be used.
[0068] This mixing stage followed by the addition of polyurethane, continuously mixing the composition at a medium speed, such as about 800 to about 1500 rpm, until homogenous.
[0069] Simultaneously, pre-wet xanthan gum, Glycerine and 1,3-butylene glycol are mixed in a separate container before being added to the main composition. This leads to a significant increase in the viscosity of the composition. The composition is mixed at a higher rate until no further increases in viscosity occur.
[0070] Finally, 20% citric acid in water as well as a preservative such as phenoxy ethanol are added at high speed, such as about 1000 rpm to about 2000 rpm according to the viscosity changes to ensure that the composition is emulsified uniformly.
[0071] The final composition is then mixed at high speed, such as about 1500 to about 3000 rpm speeds, for 10-20 minutes to ensure a homogenous emulsion. The emulsion is an oil in water emulsion where the internal oil phase is the polyurethane in an external aqueous phase.
[0072] It was found that when citric acid is added into the system with water fumed silica, sodium silicate and Polyurethane-35 (Baycusan C1004/1) the system would gel up and insoluble small, sand-sized particles appear. The particles cannot be broken down in the later steps. This is not only an indication of non-uniform/unstable system, it is also very hard to break the sandy particles during application process and the product loses some visual appeal. For formula 87B3P, the Baycusan C1004/1 was not added until after the citric acid, and a similar phenomenon is observed. This demonstrates that the sandy particles are not because of the Baycusan C1004, which is polyurethane. Therefore, the inventor believes it is because of the reaction between the alkaline Sodium silicate with citric acid.
[0073] The following is the formula used in Example 1 with the process steps set out to allow the final composition of the finished system to have a uniform/stable phase.
TABLE-US-00005 TABLE 3 Order of Raw Material Raw Material Addition Trade Name INCI Name 97B2-suC Phase A: Weigh and add A1, A2 and A3 in sequence into the container while mixing A1 DI water DI water 67.7 A2 O Sodium sodium 8 Silicate silicate A3 (Pyrogenic Fumed silica 1.2 Silica - Fumed Silica) Wacker HDK N20 Mix at medium speed, such as 800 to 1500 rpm, for 5~10 minutes until uniform Phase B: Weigh and add B into the system while mixing, B1 Baycusan Polyurethane 10 C 1004 35 Mix at medium speed, such as 800 to 1500 rpm, for 5~10 minutes until uniform Weigh and premix Cs into a separate container to pre-wet Xanthan Gum into the liquid Add C mixture into the system while mixing, system viscosity will increase, increase speed accordingly C1 Keltrol CG-T Xanthan Gum 0.5 C2 Glycerin 99.7% Glycerin 2.4 usp C3 1,3-butylene 1,3-butylene 2.3 glycol glycol Mix at (medium speed), such as about 1000 to about 1500 rpm depending on viscosity increase for 10 minutes or until xanthan gum is completely activated, and the viscosity does not have any further drastic increase. Add Ds at high speed, such about 1500 to about 2000 rpm. D1 Phenoxy Phenoxy 0.9 ethanol ethanol D2 Citric Acid Citric 7 (20% water Acid, water solution) Mix at high speed, such as about 1500 to about 3000 rpm for 10-20 minutes; and the system looks like a uniform serum. Total 100
[0074] The following description sets forth other experiments which were carried out in which phase separation occurred and these experiments are included here for comparison and for reference.
[0075] From formula 87B2P, it was found that when citric acid is added into the system with water fumed silica, sodium silicate and Baycusan C1004, system gels up and non-compatible sand sized particles appears, and the particle cannot be broken down in the later steps. This is not only an indication of non-uniform/unstable system, it is also very hard to break the sandy particles during application process and the product does not have an appealing appearance. For formula 87B3P, the Baycusan C1004/1 was not included in the composition before adding the citric acid, and a similar phenomenon of phase separation was observed. This demonstrates that the sandy particle is not because of the Baycusan C1004/polyurethane. Therefore, the inventor believes it is because of the reaction between the alkaline Sodium silicate with citric acid.
Example 2
[0076] The preparation method for the present invention will now be described with reference to Table 4 below. The process steps as set out in Example 1 were followed as set out in Example 1 above.
[0077] Initially, deionised (DI) Water, O Sodium Silicate and Fumed Silica are combined in the amounts and ratios indicated in Table 4 below and the ingredients were mixed at medium speed, such as about 800 to about 1500 rpm, for 5-10 minutes until a uniform/homogenous mixture is obtained.
[0078] This mixing stage followed by the addition of polyurethane-35, continuously mixing the composition at medium speed, such as about 800 to about 1500 rpm, until homogenous.
[0079] Process: Raw materials were added in the order of the sequence as listed from top to bottom of the table. The composition was mixed for about 10 minutes between each addition.
TABLE-US-00006 TABLE 4 Raw Material Raw Material Trade Name INCI Name 87B2p Observed 87B3p Observed DI water DI water 66.9 67 (Pyrogenic Silica - Fume silica 1.2 1.2 Fumed Silica) Wacker HDK N20 O Sodium Silicate sodium silicate 8.0 8.0 Baycusan C 1004 Baycusan C 1004 10.7 Citric Acid (20% Citric Acid (20% 7 PH~8gel up, 7 PH~8 gel up, water solution) water solution) sandy particles sandy particles appears (phase appears (phase separation) separation, stop the batch here Baycusan C 1004 Polyurethane 35 10.7 Keltrol CG-T Xanthan Gum 0.5 viscosity increase Phenoxy ethanol Phenoxy ethanol 1 viscosity 1 increase Glycerine 99.7% usp Glycerine 2.4 viscosity 2.4 decrease 1,3-butylene glycol 1,3-butylene glycol 2.4 viscosity 2.4 decrease Keltrol CG-T Xanthan Gum viscosity 0.4 increase Citric Acid (20% Citric Acid (20% water solution) water solution) Total 100 PH~8gel up 100 with sandy particles
pH Study
[0080] In order to study how pH affects the efficacy of the present invention, two variations of the described composition were neutralized to two different pH levels, 8.6 and 6 as shown in Table 5 below. Both formula retained the desired viscosity, consistency and tightening effect. The in vivo test shows that the formulation with a pH of 6 was more prone to drying out and cracking, which resulted in a more obvious whitening of the area of the skin onto which the composition had been applied. Since citric acid is a white powder, it is assumed that too much acidic additive will result in the composition drying out more rapidly, resulting in the above described whitening effect. Consequently, further tests were carried out using formulations having a pH of 8.6 although there is potential for compositions with lower pH to be investigated for potential benefits.
[0081] It is understood that the optimum pH is at a pH of between 6 and 8.6, such as at 6.5-8.5.
TABLE-US-00007 TABLE 5 Raw Material Raw Material Trade Name INCI Name 93B 94A DI water DI water 67.0 66.1 (Pyrogenic Fume silica 1.2 1.2 Silica - Fumed Silica) Wacker HDK N20 O Sodium sodium 8.0 7.9 Silicate silicate Keltrol CG-T Xanthan Gum 0.4 0.4 Phenoxy Phenoxy 1.0 1.0 ethanol ethanol Glycerin Glycerin 2.4 2.3 99.7% usp 1,3-butylene 1,3-butylene 2.4 2.3 glycol glycol Baycusan C Polyurethane 10.7 10.6 1004/1 35 Citric Acid Citric Acid, 7.0 8.2 (20% water water solution) 100.0 100.0 pH 8.6 6
Examples 3 and 4
[0082] In some embodiments, fumed Silica is Wacker HDK N20; Polyurethane Polymer is Baycusan C 1004; xantham Gum is Keltrol CG-T and 1,2-hexanediol and capryloyl glycol are provided as Symdiol 68. Other acidic additives can also be included.
TABLE-US-00008 Raw Material Raw Material Trade Name INCI Name 93B 96A DI water DI water 67.0 70.1 (Pyrogenic Fume silica 1.2 1.2 Silica - Fumed Silica) Wacker HDK N20 O Sodium sodium 8.0 8.4 Silicate silicate Keltrol CG-T Xanthan Gum 0.4 0.4 Phenoxy Phenoxy 1.0 1.0 ethanol ethanol Glycerin Glycerin 2.4 2.5 99.7% usp 1,3-butylene 1,3-butylene 2.4 2.5 glycol glycol Baycusan C polyurethane 10.7 11.2 1004/1 35 Citric Acid Citric Acid, 7.0 (20% water water solution) Lactic acid Lectic acid 2.7 Total 100 100
[0083] A liquid acid, lactic acid was tested by adding to system 96A directly without dilution in water. Compared to sample 93B, sample 96A was more viscous, still tightens well, the composition is very stable with no water separation. Sample 93B showed some water separation for some batches and the inventor believes that this might due to the water added in the last step with citric acid solution and there was not enough sheer to bring the water into the system. When lactic acid is used without water at the last step, the resulting stable system confirms this assumption as to the reason for the water separation in some instances. Therefore, longer sheer time/mixing time is provided at the last step of preparing the standard formula comprising citric acid.