EP2026748A1

EP2026748A1 - Process to prepare free flowing potassiium nitrate for oral care

Info

Publication number: EP2026748A1
Application number: EP06760319A
Authority: EP
Inventors: Michael Fooken; Andreas Klingenberg; Romano Ruscelli
Original assignee: Honeywell International Inc
Current assignee: Honeywell International Inc
Priority date: 2006-05-23
Filing date: 2006-05-23
Publication date: 2009-02-25
Also published as: AU2006344090A1; JP2009538297A; CN101489521A; WO2007136381A1

Abstract

The invention relates to free flowing potassium nitrate compositions including anti-caking amounts of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate. The composition finds use in oral care compositions such as toothpastes. The composition which comprises an admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate. The oral care composition comprises an orally acceptable vehicle and a preformed admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

Description

PROCESS TO PREPARE FREE FLOWING POTASSIUM NITRATE FOR

ORAL CARE

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to free flowing potassium nitrate compositions including anti-caking amounts of dipotassium hydrogen phosphate and potassium dihydrogen phosphate. The composition finds use in oral care compositions such as toothpastes.

Description of the Related Art It is known in the art to produce potassium nitrate by the reaction of potassium hydroxide and nitric acid in water. The reaction water is partly evaporated to force the crystallization of the material in the remaining mother liquor. The crystals are separated and dried in a three-step process by vacuum, a combined vacuum and heat treatment step at 60 °C to 70⁹C and a cool down to below 30°C under vacuum.

It has been a problem in the art to store and ship potassium nitrate crystals since they tend to form large agglomerates during such storage and shipment, leading to difficult drum discharge operations for the customer. Proposed solutions to the agglomeration problem have been suggested in the art. Chinese patent application CN 1467156 teaches an antiblocking agent for potassium nitrate including a C_1O-Cj₄ alkylsulfonate (l-90wt.%), phosphoric acid (1-75) and water (0-90). The antiblocking potassium nitrate is prepared by adding the antiblocking agent before the potassium nitrate is crystallized, stirring, holding the temperature at 60-100 ⁰G for 30-60 minutes, cooling and crystallizing. Its advantages are high performance and effect, low cost, and no environmental pollution. U.S. patent '5,203,906 (=DE 68901948T2) relates to anti-clumping compositions for preventing the setting of solid of salts such as potassium nitrate. SU585144, JP50104796 and UD5286272 teach potassium phosphates as anti caking materials in fertilizers containing potassium nitrate.

However, these state of the art anti-caking proposals are not an option to overcome the problem for food and pharmaceutical applications of potassium nitrate since they do not comply with the European Pharmacopoeia and comparable worldwide regulations. Such compliance is required in order to use the potassium nitrate material in oral care applications as a desensitizing agent in toothpaste. A specific requirement is the pH-neutral behavior of the salt as described in the European Pharmacopoeia.

It has now been found that potassium nitrate can be maintained in a free flowing condition when it is admixed with an anti-caking amount of dipotassium hydrogen phosphate and potassium dihydrogen phosphate. It has also been found that an oral care composition, such as toothpaste, has a more uniform distribution of potassium nitrate when the potassium nitrate is preformed with an anti-caking amount of dipotassium hydrogen phosphate and potassium dihydrogen phosphate according to the invention. The resulting composition meets the requirements of the European Pharmacopoeia.

SUMMARY OF THE INVENTION

The invention provides a composition which comprises an admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

The invention also provides an oral care composition which comprises an orally acceptable vehicle and an admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

The invention further provides a method of preparing an oral care composition which comprises combining a pre-formed composition which comprises an admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate, with an orally acceptable vehicle.

The invention still further provides a method of preparing an oral care composition which comprises combining a pre-formed composition which comprises an admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate, with an orally acceptable vehicle.

DESCRIPTION OF THE INVENTION

A free flowing, anti-caking potassium nitrate composition comprises an admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate. The composition may be formed by admixing dry potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate. The potassium nitrate component is present in the composition in an amount of from about^' 99 wt.% or more. The dipotassium hydrogen phosphate component is usually present in the composition in an amount of from about 0.13 wt.% to about 0.25 wt.%. The potassium dihydrogen phosphate 5 component is usually present in the composition in an amount of from about 0.1 wt.% to about 0.19 wt.%. Both dipotassium hydrogen phosphate and potassium dihydrogen phosphate must be present with the potassium nitrate in order to achieve a neutral pH. Any balance comprises water. The admixture has a water content of from about 0.0 wt.% to about 0.5 wt.%. The mixture 0 always has a neutral pH value since the potassium dihydrogen phosphate and the dipotassium hydrogen phosphate form a buffer keeping the hydrogen cation concentration ate the same level even if some acid or base is added.

An oral care composition according to the invention comprises a combination 5 of an orally acceptable vehicle, and the admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate described above. Orally acceptable vehicles usually comprises water and/or ethanol and may comprise one or more of an anti-caries agent, a flavor, a sweetening agent, an anti-microbial agent, a surfactant, a gel, ethanol, an o abrasive,' colorants, an anti-tartar agent, an anti-plaque agent, anti-calculus agents, a gum, a wax, a gelling, agent, a humectant, a polishing agent, a . stabilizer, a preservative, a source of fluoride ions among others known in the art.

In one embodiment the anti-caking potassium nitrate composition may be employed in an oral care composition in an amount of from about 0.25% to about 10% by weight of the oral care composition, preferably from about 2% to about 10% and more preferably from about 3 to about 7% by weight of the oral care composition. The water and/or ethanol content of the oral care composition may be from about 3 to. about 80% by weight and more usually from about 3 to about 30 wt.% for a creamy, or visually transparent or translucent toothpaste in gel form.

Suitable anti-caries agents non-exclusively include a wide variety of fluoride ion-yielding materials as sources of soluble fluoride. Examples of suitable fluoride ion-yielding materials are found in U.S. patents 3,535,421 and 3,678,154. Preferred fluoride ion sources for use herein include sodium fluoride, stannous fluoride, potassium fluoride, potassium stannous fluoride, indium fluoride, zinc fluoride, ammonium fluoride, sodium monofluorophosphate and stannous chlorofluoride as well as mixtures thereof. Stannous fluoride and sodium fluoride, are particularly preferred. Preferably the oral care compositions have from about 50 ppm to 10,000 ppm, more preferably from about 100 to 3000 ppm, of fluoride ions in the oral care composition.

Suitable flavoring agents include oil of wintergreen, oil of peppermint, oil of spearmint, oil of sassafras, sage, eucalyptus, marjoram, cinnamon, lemon, orange, and oil of clove. Preferably the amount of flavoring agent in the oral care composition is from about 0.3 wt.% to about 1.2 wt.%. ' i

Sweetening agents which can be used in the oral care composition include sucrose, saccharin, dextrose, lactose, maltose, levulose, aspartame, D- tryptopnan, dihydrochalcones, acesulfame and sodium cyclamate. Flavoring agents are generally used in the oral care composition at amounts of from about 0.01 wt.% to 2 wt.% and sweetening agents at amounts of from about 0.05 wt.% to about 2 wt.% by weight of the oral care composition.

Typical surfactants include anionic, nonionic, cationic, zwitterionic and amphoteric surfactants of the types described more fully in U.S. patents 3,959,458 and 3,937,807. Anionic surfactants include the water-soluble salts of alkyl sulfates having from 10 to 18 carbon atoms in the alkyl radical and the water-soluble salts of sulfonated morioglycerides of fatty acids having from 10 to 18 carbon atoms. Sodium lauryl sulfate, and sodium coconut monoglyceride 5 sulfonates are examples of anionic surfactants of this type. Mixture of anionic surfactants can also be employed. The nonionic surfactants which can be used in the present invention can be produced by the condensation of alkylene oxide groups with an organic hydrophobic compound which may be aliphatic or alklaromatic in nature. Examples of suitable nonionic surfactants include the 0 Pluronics, polyethylene oxide condensates of alkyl phenols, products derived from the condensation of ethylene oxide with the reaction product of propylene oxide and ethylene diamine, ethylene oxide condensates of aliphatic alcohols, long chain tertiary amine oxides, long chain tertiary phosphine oxides, long chain dialkyl sulfoxides and mixtures of such materials. The 5 zwitterionic surfactants useful in the oral care compositions of the present invention can be derivatives of aliphatic quaternary ammonium, phosphonium, arid sulfonium compounds, in which the aliphatic radicals can be straight chain or branched, and wherein one of the aliphatic substituents contains from about 8 to 18 carbon atoms and one contains as anionic water-soϊubilizing group, o e.g., carboxy, sulfonate, sulfate, phosphate, or phosphonate. Cationic

. surfactants useful in the oral care compositions of the present invention can be quaternary ammonium compounds having one long alkyl chain containing from about 8 to about 18 carbon atoms such as lauryl trimethylammonium chloride; cetyl pyridinium chloride; cetyl trimethylammonium bromide; di- 5 isob.utylphenoxyethoxyethyl-dimethylbenzylammonium chloride; coconutalkyltrimethylammonium nitrite; cetyl pyridinium fluoride; etc. Useful quarternary ammonium fluorides are described in U.S. patent 3,535,421. Amphoteric surfactants useful in the present invention can be derivatives of aliphatic secondary and tertiary amines in which the aliphatic radical can be Straight chain or branched and wherejn one of the aliphatic substituents contains from about 8 to about 18 carbon atoms and one contains an anionic water-solubilizing group, e.g., carbox'ylate, sulfonate, sulfate, phosphate, or phosphonate. The surfactant agent can be present in the oral care compositions of this invention in an amount from O.i% to 6% by weight of the total oral care composition.

Agglomerating agents which can be used in the practice of this invention include waxes and gelling agents. Suitable waxes are those which are non- toxic and have a hardness value of from about 0 to. about 65 (ASTM Test D 1321-65) and preferably from about 0 to 5. Examples of suitable waxes include carnauba wax, candelilla wax, purified montan wax, castor wax, paraffin, ceresin wax and bayberry wax. Preferred waxes have a melting point above 70 ⁰F. Waxes having these properties which can be used herein are disclosed in Soap & Chem. Specialties, Vol. 33, page 141 (1957). See also Industrial Waxes, Vol. I and II, H. Bennett, Chemical Publishing Co., Inc., New York, 1963, for a discussion of waxes and their properties.

Gelling agents for toothpaste vehicles are well _'known in the art. These are often high polymers (e.g., gums or other thickening agents) which are soluble or swellable in water or aqueous medium. Suitable gelling agents, or thickening agents, are those that form stable, firm gels which are non-toxic; hard enough to withstand conventional shear stresses when admixed in a dentifrice or extruded from the toothpaste tube; frangible enough to disintegrate into smaller particles at time of use to give no adverse mouth impression; light colored; innocuous in flavor and odor; and compatible with toothpaste ingredients. Gelling agents which can be used to form agglomerates of pigment particles include sodium carboxymethylcellulose, gum tragacanth, gum arabic, gum karaya, sodium alginate, hydroxyethyl cellulose, methyl Cellulose, ethyl cellulose, carrageen a,nd other polysaccharides, polyvinyl pyrollidones agar-agar, cassava starch, microcrystalline cellulose, complex magnesium aluminum silicate and high molecular weight carboxyvinyl polymers. The amount of thickening agent used in the practice of this invention is preferably sufficient to impart to the mixture the pasty consistency, body and the non-tacky nature which is characteristic of conventional dental creams or toothpastes. As is well known, dental creams are extrudable from ordinary collapsible toothpaste tubes to form a ribbon of substantial thickness (e.g., about 3/8 inch) which if left undisturbed, substantially retains its original thickness over a period of, say, one minute or more (and does not penetrate substantially into the bristles of a toothbrush when resting on the.ends of such bristles for a similar period); but which preferably offers no substantial resistance to brushing or to deformation when, for instance, one touches it lightly with a finger; and which has little tack, in that it does not tend to form a string when the finger is pulled away from the ribbon. The proportion of the thickening agent is often within the range of about 0;5 to 2%, such as about 0.8 to 1.5%, of the oral care composition.

Useful stabilizers for oral care composition include dicalcium phosphate dihydrate¹ and calcium pyrophosphate. A description of the method of preparation of dicalcium phosphate dihydrate and of its stabilization is found in U.S.. patent 3,169,096. See also "Cosmetic Science" Vol. 1 pub. 1972 (Wiley Interscience) edited by Balsam and Sagarin pages 477-479.

A useful preservative for the oral care composition may be sodium benzoate, methyl paraben, propyl paraben, phenyl mercuric nitrate, sodium bisulfite, disodium calcium EDTA, chlorobutanol, and mixtures thereof in amounts of from about 0.5 to about 15 percent by weight, based on the total weight of the oral care composition, Suitable anti-microbial agents include alcohols, formaldehyde preparations and compounds which liberate formaldehydes, hypochloride substances, iodine preparations, mercury preparations and phenolic compounds such as halogenated diphenyl ethers, halogenated salicylanilides, benzoic esters, halogenated carbanilides, phenol and its homologs, mono- and poly-alkyl and aralkyl halophenols, resorcinol and its derivatives, bisphenolic compounds; N¹ -(4-chlorobenzyl)-N⁵ -(2,4-dichlorobenzyl) biguanide; p-chlorophenyl biguanide; 4-chlorobenzyhydryl biguanide; 4-chlorobenzhydrylguanylurea; N-3-lauroxpropyl-N.sup.5 -p-chlorobenzylbiguanide; l-(lauryldimethylammonium)-8-(p-chlorobenzyldimethylammoήium) octane, dichloride; 5,6-dichloro-2-guanidinobenzimidazole; N¹ -p-chlorophenyl-N⁵- laurylbiguanide; 5-amino- 1 ,3-bis (2-ethylhexyl)-5-methylhexahydropyrirnidine cetyl pyridinium chloride and their non-toxic acid addition salts, particularly the fluorides and the dihydrogeri fluorides. l,6-di-(p- chlorophenylbiguanidohexarie) is particularly preferred. These agents may be used in amounts ranging from about 0.01 to 10 percent by weight of the oral care composition.

The oral care composition may contain a colorant such as a food grade pigment or dye. Pigment particles must be essentially color-fast, i.e., must. not leach a significant amount of color in the presence of water. Thus, water- soluble dyes per se are not preferred in the practice of this invention. Water- soluble dyes can be used to prepare pigment particles which will not leach - color. Other pigment particles which can be used to prepare colored oral care compositions include, for example,. non-toxic water-insoluble, inorganic pigments such as chromium oxide greens, carbon blacks, ultramarine blues and pinks, and ferric oxides; dyed cellulose particles such as dyed cotton linters and dyed wood pulp; and water- insoluble dye lakes prepared by extending calcium or aluminum salts, of FD&C water-soluble dyes on alumina, such as FD&C Green #1 lake, FD&C Blue #2 lake and FD&C Yellow #5 lake. The mean particle size of the pigment particle can range from about 5 to about 490 microns, and preferably from 10 to about 200 microns. Larger particles tend to feel gritty in the mouth and stick between the teeth. The particle sizes referred to herein can be determined for example by microscopic measurements using a calibrated eyepiece. The pigment particles can comprise from, about 10% to about 50% by Weight of the total oral care composition. Preferably, the pigment is used at a concentration in the range from about 30% to about 50% by weight of the total oral care composition.

Typical abrasives, or polishing agents, contemplated for use in the present invention can be any material which does not excessively abrade teeth. These may be water soluble, such as sodium bicarbonate, or water insoluble materials provided (hey do not remove tooth material but rather to removal of deposits on dental enamel from and polishing the teeth. These include, for example, sodium bicarbonate, calcium carbonate, sodium metaphosphate, potassium metaphosphate, dicalcium orthophosphate dihydrate, calcium pyrophosphate, tricalcium phosphate, calcium polymetaphosphate, insoluble sodium polymeta'phosphate, hydrated alumina, calcium phosphate dihydrate, anhydrous dicalcium phosphate, magnesium orthophosphate, trimagnesium phosphate, alumina trihydrate, aluminum silicate, zirconium silicate^ calcined alumina, bentonite,. silica gel, colloidal silica, complex amorphous alkali metal aluminosilicates and mixtures thereof, and resinous abrasive materials such as particulate condensation products of urea and formaldehyde, and other such as disclosed in U.S. patent 3,070,510.. Still other suitable polishing materials include the particulate thermosetting resins described in U.S. patent. 4,070,510, such as melamine-, phenolic-, and urea-formaldehydes, and crosslinked polyepoxides and polyesters. Mixtures of abrasives may also be iisecL Silica dental abrasives, of various types, can provide the unique benefits of exceptional dental cleaning and polishing performance without unduly abrading tooth enamel. The abrasive polishing materials useful herein, generally have an average particle size ranging between about 0.1 to 30 5 microns, preferably 5 and 15 microns. The silica abrasive can be precipitated silica or silica gels such as the silica xerogels as described in U.S. patents 3,538,230; 3,862,307 and 4,340,583. The abrasive in the compositions described herein is present in an amount of from about 6% to about 35%, preferably from about 15% to about 25% by weight of the oral care o composition.

Suitable anti-tartar agents, non-exclusively include an alkali metal polyphosphate or a phosphono anti-tartar agent. The polyphosphates may be ^' any of various water soluble polyphosphates, including alkali metal 5 pyrophosphates, such as tetrapotassium pyrophosphate, trisodium pyrophospate, dipotassium pyrophosphate, tetrasodium pyrophosphate and disodium pyrophosphate, with the sodium salts being preferred. Instead of the pyrophosphates, the tripolyphosphates and other polyphosphates, such as the hexametaphosphates, may be substituted, at least in part. The pyrophosphates o are considered to be superior as anti-tartar agents that help to desensitize the teeth. A most preferred pyrophosphate is tetrasodium pyrophosphate, but the corresponding tetrapotassium pyrophosphate or tri, -di and mono sodium and potassium pyrophosphates may also be used, at least in part. The anti-tartar agent may be a phosphono compound such as azacyloalkane-2,2- diphosphosphonic acid, preferably azacycloheptane-2,2-diphosphonic acid, phosphonopropane tricarboxylic acid, phosphono butane- 1,2,4-tricarboxylic acid and ethanedihydroxy diphosphonic acid and water soluble salts thereof. The anti-tartar agent is employed in an effective anti-tartar amount which is generally about 0.1 to 10% by weight of the oral care composition, preferably about 0.8 to 7%.

Suitable anti-calculus agents may be known phosphorus-containing anti- calculus agents such as disodium ethane- 1 -hydroxy- 1, 1-diphosphonate which are described in U.S. patent 3,488,419. Suitable anti-plaque agents include bis-biguanide compounds such as cholorhexidine (l,6-bis[N⁵ -p-chlorophenyl- N¹ -biguanido]hexane), the soluble and insoluble salts thereof and related materials such as l,2-bis-(N⁵ -p-tri-fluoromethylphenyl-N¹ -biguanido)ethane as described in U.S: patents 3,934,002 and 3,937,807.

A humectant component of the oral care composition serves to keep the toothpaste compositions, from hardening upon exposure to air. Suitable humectants for use in this invention include edible polyhydric alcohols such as glycerine,' sorbitol, xylitol, glycerol, polyethylene glycol, propylene glycol and polypropylene glycols. A normal range of molecular weights for the polyethylene glycol humectants is 200 to 1,000, preferably 400 to 600 or 800, e.g., about 600. The humectant content is usually from about 10% to about 80%, preferably from about 20% to about 70%,_' and more preferably from about 30% to 65%, by weight of the oral care compositions herein.

It has been found that the oral care composition, such as a toothpaste, has a more uniform distribution of potassium nitrate when the potassium nitrate is preformed with an anti-caking amount of dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

The oral care compositions of the invention, when in the form of toothpaste compositions, are used in conventional manner. The toothpaste compositions or slurries thereof are brushed, onto dental surfaces and subsequently rinsed away. During use of the toothpaste herein in* conventional manner, pastes or slurries generally contact dental surfaces for at least about 30 seconds. More

1 - ' preferably such pastes or slurries contact dental surfaces for at least about 60 seconds.

The following non-limiting example serves to illustrate the invention.

EXAMPLE

To prepare 4000 kg of free flowing potassium nitrate, 3900 1 of potassium hydroxide solution 45% by weight is pumped into a vessel containing 3500 1 de-ionized water. 3500 1 nitric acid 60% are added while maintaining the temperature below 85°C. After adjusting the pH value to 1-2, 10 1 hydrogen peroxide are added. The reaction is allowed to complete while stirring the solution for one hour. In the next step the pH is adjusted with potassium hydroxide solution 45% to pH 7-8. De-ionized water is used to adjust the potassium nitrate content in the solution to approximately 30%. The solution has a temperature of 35-45°C, and is then filtrated using 0.6 micron membrane filters. 7000 1 water are then evaporated from the solution by using vacuum and maintaining the temperature at 50 °C. Residual water is evaporated to reach a temperature of below 25°C. A centrifuge is then used to reduce the water content further. The final moisture content is reached by drying the material in a tumble dryer under vacuum while maintaining a temperature of 60-70°C. 0.13% K₂HPO₄ and 0.1% KH₂PO₄ by weight are added. Then a tumble dryer is used to homogenize the material by operating it for another three hours. The free flowing material is filled into bags via a 5 mm mesh sieve. ^■While the present invention has been particularly shown and described with reference to preferred embodiments, it will be readily appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the claims be interpreted to cover the disclosed embodiment, those alternatives which have been discussed above and all equivalents thereto.

Claims

What is claimed is:

1. A composition which comprises an admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

5

2. The. composition of claim 1 which comprises from about 99 wt.% or more of potassium nitrate.

3. The composition of claim 1 which comprises from about 0.13 wt.% to about o 0.25 wt.% of dipotassium hydrogen phosphate.

4. The composition of claim 1 which comprises from about 0.1 wt.% to about 0.19 wt.% of potassium dihydrogen phosphate.

5 5.¹ The composition of claim 1 which comprises from about 99 wt.% or more of potassium nitrate, from about 0.13 wt.% to about 0.25 wt.% of dipotassium hydrogen phosphate, and from about 0.1 wt.% to about 0.19 wt.% of potassium dihydrogen phosphate.

6. An oral care composition which comprises an orally acceptable vehicle and an admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

7. The oral care composition of claim 6 wherein the admixture comprises from about 99 wt.% or more of potassium nitrate by weight of the admixture.

8. The oral care composition of claim 6 wherein the admixture comprises from about 0.13 wt.% to about 0.25 wt.% of dipotassium hydrogen phosphate by weight of the admixture.

9. The oral care composition of claim 6 wherein the admixture comprises from about 0.1 wt.% to about 0,19 wf.% of potassium dihydrogen phosphate by weight of the admixture.

10. The oral care composition of claim 6 wherein the admixture comprises from about 99 wt.% or more of potassium nitrate by weight of the admixture, and from about 0.13 wt.% to about θ.25 wt.% of dipotassium hydrogen phosphate by weight of the admixture, and from about 0.1 wt.% to about 0.19 wt.% of potassium dihydrogen phosphate by weight of the admixture.

11. The oral care composition of claim 6 wherein the orally acceptable vehicle comprises one or more of an anti-caries, agent, a flavor, a sweetening agent, an anti-microbial, a surfactant, a gel, sodium bicarbonate, ethanol, an abrasive, a thickening agent, an anti-tartar agent, a gum, an alkali metal carboxymethyl cellulose, a gelling agent, a humectant, a polishing agent, a stabilizer, a preservative, a source of fluoride ions, and a water soluble fluoride.

12._. The oral care composition of claim 6 which is a toothpaste.

13. The oral care composition of claim 11 which is a toothpaste.

14. A method for preparing a composition which comprises dry mixing potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

15. The method of claim 14 which comprises admixing from about 99 wt.% or more of potassium nitrate. ¹Io. The method of claim 14, which comprises admixing from about 0.13 wt.% to about 0.25 wt.% of dipotassium hydrogen phosphate.

17. The method of claim 14 which comprises admixing from about 0.1 wt.% 5 to about 0.19 wt.% of potassium dihydrogen phosphate.

18. The method of claim 15 which comprises admixing from about 99 wt.% or more of potassium nitrate, from about 0.13 wt.% to about 0.25 wt.% of dipotassium hydrogen phosphate, and from about 0.1 wt.% to about 0.19 wt.% 0 of potassium dihydrogen phosphate.

19. A method of preparing an oral care composition which comprises combining a pre-formed composition which comprises an admixture of potassium nitrate, dipotassium hydrogen phosphate and potassium dihydrogen 5 phosphate, with an orally acceptable vehicle.

20. The method of claim 19 wherein the orally acceptable vehicle comprises one or more of water, an anti-caries agent, a flavor, a sweetening agent, antimicrobial agents, a surfactant, a gel, ethanol, an abrasive, colorants, an anti- o tartar agent, an anti-plaque agent, an anti-calculus agent, a gum, a wax, a gelling agent, a humectant, a polishing agent, a stabilizer, a preservative, a source of fluoride ions.