Editorial Note on Part 173
Editorial Note: Nomenclature changes to part 173 appear at 61 FR 14482, Apr. 2, 1996; 66 FR 56035, Nov. 6, 2001; 66 FR 66742, Dec. 27, 2001; and 81 FR 49896, July 29, 2016.

§ 173.25 Ion-exchange resins. Ion-exchange resins may be safely used in the treatment of food under the following prescribed conditions: ( a ) The ion-exchange resins are prepared in appropriate physical form, and consist of one or more of the following: ( 1 ) Sulfonated copolymer of styrene and divinylbenzene.
( 2 ) Sulfonated anthracite coal meeting the requirements of ASTM method D388-38, Class I, Group 2, “Standard Specifications for Classification of Coal by Rank,” which is incorporated by reference. Copies are available from University Microfilms International, 300 N. Zeeb Rd., Ann Arbor, MI 48106, or available for inspection at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202-741-6030, or go to: *http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html .*
( 3 ) Sulfite-modified cross-linked phenol-formaldehyde, with modification resulting in sulfonic acid groups on side chains.
( 4 ) Methacrylic acid-divinylbenzene copolymer.
( 5 ) Cross-linked polystyrene, first chloromethylated then aminated with trimethylamine, dimethylamine, di-ethylenetriamine, or dimethylethanol-amine.
( 6 ) Diethylenetriamine, triethylene-tetramine, or tetraethylenepentamine cross-linked with epichlorohydrin.
( 7 ) Cross-linked phenol-formaldehyde activated with one or both of the following: Triethylene tetramine and tetraethylenepentamine.
( 8 ) Reaction resin of formaldehyde, acetone, and tetraethylenepentamine.
( 9 ) Completely hydrolyzed copolymers of methyl acrylate and divinylbenzene.
( 10 ) Completely hydrolyzed terpolymers of methyl acrylate, divinylbenzene, and acrylonitrile.
( 11 ) Sulfonated terpolymers of styrene, divinylbenzene, and acrylonitrile or methyl acrylate.
( 12 ) Methyl acrylate-divinylbenzene copolymer containing not less than 2 percent by weight of divinylbenzene, aminolyzed with dimethylaminopro-pylamine.
( 13 ) Methyl acrylate-divinylbenzene copolymer containing not less than 3.5 percent by weight of divinylbenzene, aminolyzed with dimethylaminopro-pylamine.
( 14 ) Epichlorohydrin cross-linked with ammonia.
( 15 ) Sulfonated tetrapolymer of styrene, divinylbenzene, acrylonitrile, and methyl acrylate derived from a mixture of monomers containing not more than a total of 2 percent by weight of acrylonitrile and methyl acrylate.
( 16 ) Methyl acrylate-divinylbenzenediethylene glycol divinyl ether terpolymer containing not less than 3.5 percent by weight of divinylbenzene and not more than 0.6 percent by weight of diethylene glycol divinyl ether, aminolyzed with dimethylaminopropylamine.
( 17 ) Styrene-divinylbenzene cross-linked copolymer, first chloromethylated then aminated with dimethylamine and oxidized with hydrogen peroxide whereby the resin contains not more than 15 percent by weight of vinyl *N,N-*dimethylbenzylamine*-N-*oxide and not more than 6.5 percent by weight of nitrogen.
( 18 ) Methyl acrylate-divinylbenzene-diethylene glycol divinyl ether terpolymer containing not less than 7 percent by weight of divinylbenzene and not more than 2.3 percent by weight of diethylene glycol divinyl ether, aminolyzed with dimethylaminopropylamine and quaternized with methyl chloride.
( 19 ) Epichlorohydrin cross-linked with ammonia and then quaternized with methyl chloride to contain not more than 18 percent strong base capacity by weight of total exchange capacity [Chemical Abstracts Service name: Oxirane (chloromethyl)-, polymer with ammonia, reaction product with chloromethane; CAS Reg. No. 68036-99-7].
( 20 ) Regenerated cellulose, cross-linked and alkylated with epichlorohydrin and propylene oxide, then sulfonated whereby the amount of epichlorohydrin plus propylene oxide employed does not exceed 250 percent by weight of the starting quantity of cellulose.
( b ) Ion-exchange resins are used in the purification of foods, including potable water, to remove undesirable ions or to replace less desirable ions with one or more of the following: bicarbonate, calcium, carbonate, chloride, hydrogen, hydroxyl, magnesium, potassium, sodium, and sulfate except that: The ion-exchange resin identified in paragraph (a)(12) of this section is used only in accordance with paragraph (b)(1) of this section, the ion-exchange resin identified in paragraph (a)(13) of this section is used only in accordance with paragraph (b)(2) of this section, the resin identified in paragraph (a)(16) of this section is used only in accordance with paragraph (b)(1) or (b)(2) of this section, the ion-exchange resin identified in paragraph (a)(17) of this section is used only in accordance with paragraph (b)(3) of this section, the ion-exchange resin identified in paragraph (a)(18) of this section is used only in accordance with paragraph (b)(4) of this section, and the ion-exchange resin identified in paragraph (a)(20) of this section is used only in accordance with paragraphs (b)(5) and (d) of this section. ( 1 ) The ion-exchange resins identified in paragraphs (a)(12) and (16) of this section are used to treat water for use in the manufacture of distilled alcoholic beverages, subject to the following conditions: ( i ) The water is subjected to treatment through a mixed bed consisting of one of the resins identified in paragraph (a)(12) or (16) of this section and one of the strongly acidic cation-exchange resins in the hydrogen form identified in paragraphs (a)(1), (2), and (11) of this section; or
( ii ) The water is first subjected to one of the resins identified in paragraph (a)(12) or (16) of this section and is subsequently subjected to treatment through a bed of activated carbon or one of the strongly acidic cation-exchange resins in the hydrogen form identified in paragraphs (a)(1), (2), and (11) of this section.
( iii ) The temperature of the water passing through the resin beds identified in paragraphs (b)(1)(i) and (ii) of this section is maintained at 30 °C or less, and the flow rate of the water passing through the beds is not less than 2 gallons per cubic foot per minute.
( iv ) The ion-exchange resins identified in paragraph (a)(12) or (16) of this section are exempted from the requirements of paragraph (c)(4) of this section, but the strongly acidic cation-exchange resins referred to in paragraphs (b)(1)(i) and (ii) of this section used in the process meet the requirements of paragraph (c)(4) of this section, except for the exemption described in paragraph (d) of this section.
( 2 ) The ion-exchange resins identified in paragraphs (a)(13) and (16) of this section are used to treat water and aqueous food only of the types identified under Categories I, II, and VI-B in table 1 of § 176.170(c) of this chapter: *Provided,* That the temperature of the water or food passing through the resin beds is maintained at 50 °C or less and the flow rate of the water or food passing through the beds is not less than 0.5 gallon per cubic foot per minute. ( i ) The ion-exchange resin identified in paragraph (a)(13) of this section is used to treat water and aqueous food only of the types identified under categories I, II, and VI-B in Table 1 of § 176.170(c) of this chapter: *Provided,* That the temperature of the water or food passing through the resin bed is maintained at 50 °C or less and the flow rate of the water or food passing through the bed is not less than 0.5 gallon per cubic foot per minute.
( ii ) The ion-exchange resin identified in paragraph (a)(16) of this section is used to treat water and aqueous food only of the types identified under categories I, II, and VI-B in Table 1 of § 176.170(c) of this chapter, *Provided,* that either: ( A ) The temperature of the water or food passing through the resin bed is maintained at 50 °C or less and the flow rate of the water or food passing through the bed is not less than 0.5 gallon per cubic foot per minute; or
( B ) Extracts of the resin will be found to contain no more than 1 milligram/kilogram dimethylaminopropylamine in each of the food simulants, distilled water and 10 percent ethanol, when, following washing and pretreatment of the resin in accordance with § 173.25(c)(1), the resin is subjected to the following test under conditions simulating the actual temperature and flow rate of use: “The Determination of 3-Dimethylaminopropylamine in Food Simulating Extracts of Ion Exchange Resins,” February 4, 1998, which is incorporated by reference in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies are available from the Office of Food Additive Safety (HFS-200), Center for Food Safety and Applied Nutrition, Food and Drug Administration, 5001 Campus Dr., College Park, MD 20740, 240-402-1200, or may be examined at the Dockets Management Staff (HFA-305), Food and Drug Administration, 5630 Fishers Lane, Rm. 1061, Rockville, MD 20852, 240-402-7500, between 9 a.m. and 4 p.m., Monday through Friday, or at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202-741-6030, or go to: *http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html .*
( 3 ) The ion-exchange resin identified in paragraph (a)(17) of this section is used only for industrial application to treat bulk quantities of aqueous food, including potable water, or for treatment of municipal water supplies, subject to the condition that the temperature of the food or water passing through the resin bed is maintained at 25 °C or less and the flow rate of the food or water passing through the bed is not less than 2 gallons per cubic foot per minute.
( 4 ) The ion-exchange resin identified in paragraph (a)(18) of this section is used to treat aqueous sugar solutions subject to the condition that the temperature of the sugar solution passing through the resin bed is maintained at 82 °C (179.6 °F) or less and the flow rate of the sugar solution passing through the bed is not less than 46.8 liters per cubic meter (0.35 gallon per cubic foot) of resin bed volume per minute.
( 5 ) The ion-exchange resin identified in paragraph (a)(20) of this section is limited to use in aqueous process streams for the isolation and purification of protein concentrates and isolates under the following conditions: ( i ) For resins that comply with the requirements in paragraph (d)(2)(i) of this section, the pH range for the resin shall be no less than 3.5 and no more than 9, and the temperatures of water and food passing through the resin bed shall not exceed 25 °C.
( ii ) For resins that comply with the requirements in paragraph (d)(2)(ii) of this section, the pH range for the resin shall be no less than 2 and no more than 10, and the temperatures of water and food passing through the resin shall not exceed 50 °C.
( c ) To insure safe use of ion-exchange resins, each ion-exchange resin will be: ( 1 ) Subjected to pre-use treatment by the manufacturer and/or the user in accordance with the manufacturer's directions prescribed on the label or labeling accompanying the resins, to guarantee a food-grade purity of ion-exchange resins, in accordance with good manufacturing practice.
( 2 ) Accompanied by label or labeling to include directions for use consistent with the intended functional purpose of the resin.
( 3 ) Used in compliance with the label or labeling required by paragraph (c)(2) of this section.
( 4 ) Found to result in no more than 1 part per million of organic extractives obtained with each of the named solvents, distilled water, 15 percent alcohol, and 5 percent acetic acid when, having been washed and otherwise treated in accordance with the manufacturer's directions for preparing them for use with food, the ion-exchange resin is subjected to the following test: Using a separate ion-exchange column for each solvent, prepare columns using 50 milliliters of the ready to use ion-exchange resin that is to be tested. While maintaining the highest temperature that will be encountered in use pass through these beds at the rate of 350-450 milliliters per hour the three test solvents distilled water, 15 percent (by volume) ethyl alcohol, and 5 percent (by weight) acetic acid. The first liter of effluent from each solvent is discarded, then the next 2 liters are used to determine organic extractives. The 2-liter sample is carefully evaporated to constant weight at 105 °C; this is total extractives. This residue is fired in a muffle furnace at 850 °C to constant weight; this is ash. Total extractives, minus ash equals the organic extractives. If the organic extractives are greater than 1 part per million of the solvent used, a blank should be run on the solvent and a correction should be made by subtracting the total extractives obtained with the blank from the total extractives obtained in the resin test. The solvents used are to be made as follows: Distilled water (de-ionized water is distilled). 15 percent ethyl alcohol made by mixing 15 volumes of absolute ethyl alcohol A.C.S. reagent grade, with 85 volumes of distilled de-ionized water. 5 percent acetic acid made by mixing 5 parts by weight of A.C.S. reagent grade glacial acetic acid with 95 parts by weight of distilled de-ionized water.
In addition to the organic extractives limitation prescribed in this paragraph, the ion-exchange resin identified in paragraph (a)(17) of this section, when extracted with each of the named solvents, distilled water, 50 percent alcohol, and 5 percent acetic acid, will be found to result in not more than 7 parts per million of nitrogen extractives (calculated as nitrogen) when the resin in the free-base form is subjected to the following test immediately before each use: Using a separate 1-inch diameter glass ion-exchange column for each solvent, prepare each column using 100 milliliters of ready to use ion-exchange resin that is to be tested. With the bottom outlet closed, fill each ion-exchange column with one of the three solvents at a temperature of 25 °C until the solvent level is even with the top of the resin bed. Seal each column at the top and bottom and store in a vertical position at a temperature of 25 °C. After 96 hours, open the top of each column, drain the solvent into a collection vessel, and analyze each drained solvent and a solvent blank for nitrogen by a standard micro-Kjeldahl method.
( d ) ( 1 ) The ion-exchange resins identified in paragraphs (a)(1), (a)(2), (a)(11), and (a)(15) of this section are exempted from the acetic acid extraction requirement of paragraph (c)(4) of this section.
( 2 ) The ion-exchange resin identified in paragraph (a)(20) of this section shall comply either with: ( i ) The extraction requirement in paragraph (c)(4) of this section by using dilute sulfuric acid, pH 3.5 as a substitute for acetic acid; or
( ii ) The extraction requirement in paragraph (c)(4) of this section by using reagent grade hydrochloric acid, diluted to pH 2, as a substitute for acetic acid. The resin shall be found to result in no more than 25 parts per million of organic extractives obtained with each of the following solvents: Distilled water; 15 percent alcohol; and hydrochloric acid, pH 2. Blanks should be run for each of the solvents, and corrections should be made by subtracting the total extractives obtained with the blank from the total extractives obtained in the resin test.
( e ) Acrylonitrile copolymers identified in this section shall comply with the provisions of § 180.22 of this chapter.
[42 FR 14526, Mar. 15, 1977, as amended at 46 FR 40181, Aug. 7, 1981; 46 FR 57033, Nov. 20, 1981; 49 FR 28830, July 17, 1984; 56 FR 16268, Apr. 22, 1991; 62 FR 7679, Feb. 20, 1997; 64 FR 14609, Mar. 26, 1999; 64 FR 56173, Oct. 18, 1999; 78 FR 14665, Mar. 7, 2013; 81 FR 5592, Feb. 3, 2016; 88 FR 17722, Mar. 24, 2023]