“Sodium hypochlorite”的意思、由来-开放百科全书

Sodium hypochlorite is most often encountered as a pale greenish-yellow dilute solution commonly known as liquid bleach or simply bleach, a household chemical widely used (since the 18th century) as a disinfectant or a bleaching agent. The compound in solution is unstable and easily decomposes, liberating chlorine, which is the active principle of such products. Indeed, sodium hypochlorite is the oldest and still most important chlorine-based bleach.^[2]^[3]

While sodium hypochlorite is non-toxic, its corrosive properties, common availability, and reaction products make it a significant safety risk. In particular, mixing liquid bleach with other cleaning products, such as acids or ammonia, may produce toxic fumes.^[10]

Chemistry

Stability of the solid

Anhydrous sodium hypochlorite can be prepared; however, like many hypochlorites, it is highly unstable and decomposes explosively on heating or friction.^[4] The decomposition is accelerated by carbon dioxide at atmospheric levels.^[5]^[10] It is a white solid with the orthorombic crystal structure.^[6]

Sodium hypochlorite can also be obtained as a crystalline pentahydrate {{chem|NaOCl}}·5{{chem|H|2|O}}, which is not explosive and is much more stable than the anhydrous compound.^[5]^[7] The formula is sometimes given as 2{{chem|NaOCl}}·10{{chem|H|2|O}}.{{citation needed|date=June 2018}} The transparent light greenish yellow orthorombic^[8]^[9] crystals contain 44% NaOCl by weight and melt at 25−27 °C. The compound decomposes rapidly at room temperature, so it must be kept under refrigeration. At lower temperatures, however, it is quite stable: reportedly only 1% decomposition after 360 days at 7 °C.^[10]^[11]

A 1966 US patent claims that stable solid sodium hypochlorite dihydrate {{chem|NaOCl}}·2{{chem|H|2|O}} can be obtained by carefully excluding chloride ions ({{chem|Cl|-}}), which are present in the output of common manufacturing processes and are said to catalyze the decomposition hypochlorite into chlorate ({{chem|Cl|O|3|-}}) and chloride. In one test, the dihydrate was claimed to show only 6% decomposition after 13.5 months storage at –25 °C. The patent also claims that the dihydrate can be reduced to the anhydrous form by vacuum drying at about 50 °C, yielding a solid that showed no decomposition after 64 hours at –25 °C.^[12]

Equilibria and stability of solutions

At typical ambient temperatures, sodium hypochlorite is more stable in dilute solutions that contain solvated {{chem|Na|+}} and {{chem|OCl|-}} ions. The density of the solution is 1.093 g/mL at 5% concentration,^[13] and 1.21 g/mL at 14%, 20 deg C.^[14] Stoichometric solutions are fairly alkaline, with pH 11 or more^[10] since hypochlorous acid is a weak acid:

The following species and equilibria are present in solutions of {{chem|NaOCl}}:^[15]

The second equilibrium equation above will be shifted to the right if the chlorine {{chem|Cl|2}} is allowed to escape as gas. The ratios of {{chem|Cl|2}}, HOCl, and {{chem|OCl|-}} in solution are also pH dependent. At pH below 2, the majority of the chlorine in the solution is in the form of dissolved elemental {{chem|Cl|2}}. At pH greater than 7.4, the majority is in the form of hypochlorous acid {{chem|HClO}}.^[2] The equilibrium can be shifted by adding acids (such as hydrochloric acid) or bases (such as sodium hydroxide) to the solution:

At a pH of about 4, such as obtained by the addition of strong acids like hydrochloric acid, the amount of undissociated (nonionized) HOCl is highest. The reaction can be written as:

Sodium hypochlorite solutions combined with acid evolve chlorine gas, particularly strongly at pH < 2, by the reactions:

At pH > 8, the chlorine is practically all in the form of hypochlorite anions ({{chem|OCl|-}}). The solutions are fairly stable at pH 11-12. Even so, one report claims that a conventional 13.6% NaOCl reagent solution lost 17% of its strength after being stored for 360 days at 7 °C.^[10] For this reason, in some applications one may use more stable chlorine-releasing compounds, such as calcium hypochlorite {{chem|Ca|(ClO)|2}} or trichloroisocyanuric acid {{chem|(CNClO)|3}}.

Anhydrous sodium hypochlorite is soluble in methanol, and solutions are stable.{{citation needed|date=June 2018}}

Decomposition to chlorate or oxygen

In solution, under certain conditions, the hypochlorite anion may also disproportionate (autoxidize) to chloride and chlorate:^[28]

In particular, this reaction occurs in sodium hypochlorite solutions at high temperatures, forming sodium chlorate and sodium chloride:^[16]^[17]

In hot sodium hypochlorite solutions, this reaction competes with chlorate formation, yielding sodium chloride and oxygen gas:^[16]

These two decomposition reactions of {{chem|NaClO}} solutions are maximized at pH around 6. The chlorate-producing reaction predominates at pH above 6, while the oxygen one becomes significant below that. For example, at 80 °C, with NaOCl and NaCl concentrations of 80 mM, and pH 6–6.5, the chlorate is produced with ∼95% efficiency. The oxygen pathway predominates at pH 10.^[16] This decomposition is affected by light^[17] and metal ion catalysts such as copper, nickel, cobalt,^[16] and iridium^[18] Catalysts like sodium dichromate {{chem|Na|2|Cr|2|O|7}} and sodium molybdate {{chem|Na|2|MoO|4}} may be added industrially to reduce the oxygen pathway, but a report claims that only the latter is effective.^[16]

Titration

According to one US patent, the stability of sodium hypochlorite content of solids or solutions can be determined by monitoring the infrared absorption due to the O-Cl bond. The characteristic wavelength is given as 140.25 μm for water solutions, 140.05 for the solid dihydrate NaOCl·2{{chem|H|2|O}}, and 139.08 μm for the anhydrous mixed salt {{chem|Na|2|(OCl)|(OH)}}.^[12]

Oxidation of organic compounds

Oxidation of starch by sodium hypochlorite, that adds carbonyl and carboxyl groups, is relevant to the production of modified starch products.^[19]

In the presence of a phase-transfer catalyst, alcohols are oxidized to the corresponding carbonyl compound (aldehyde or ketone).^[20]^[10] Sodium hypochlorite can also oxidize organic sulfides to sulfoxides or sulfones, disulfides or thiols to sulfonyl chlorides or bromides, imines to oxaziridines.^[10] It can also de-aromatize phenols.^[10]

Oxidation of metals and complexes

Heterogeneous reactions of sodium hypochlorite and metals such as zinc proceed slowly to give the metal oxide or hydroxide:

Homogeneous reactions with metal coordination complexes proceed somewhat faster. This has been exploited in the Jacobsen epoxidation.

Other reactions

If not properly stored in airtight containers, sodium hypochlorite reacts with carbon dioxide to form sodium carbonate:

Sodium hypochlorite reacts with most nitrogen compounds to form volatile chloramines, dichloramines, and nitrogen trichloride:

Neutralization

Production

Chlorination of soda

Hence, chlorine is simultaneously reduced and oxidized; this process is known as disproportionation.

The process is also used to prepare the pentahydrate {{chem|NaOCl}}·5{{chem|H|2|O}} for industrial and laboratory use. In a typical process, chlorine gas is added to a 45−48% NaOH solution. Some of the sodium chloride precipitates and is removed by filtration, and the pentahydrate is then obtained by cooling the filtrate to 12 °C .^[10]

From calcium hypochlorite

Another method involved by reaction of sodium carbonate ("washing soda") with chlorinated lime ("bleaching powder"), a mixture of calcium hypochlorite {{chem|Ca|(OCl)|2}}, calcium chloride {{chem|CaCl|2}}, and calcium hydroxide {{chem|Ca|(OH)|2}}:

This method was commonly used to produce hypochlorite solutions for use as a hospital antiseptic that was sold after World War I under the names "Eusol", an abbreviation for Edinburgh University Solution Of (chlorinated) Lime – a reference to the university's pathology department, where it was developed.^[24]

Electrolysis of brine

Near the end of the nineteenth century, E. S. Smith patented the chloralkali process: a method of producing sodium hypochlorite involving the electrolysis of brine to produce sodium hydroxide and chlorine gas, which then mixed to form sodium hypochlorite.^[25]^[23]^[26] The key reactions are:

Both electric power and brine solution were in cheap supply at the time, and various enterprising marketers took advantage of the situation to satisfy the market's demand for sodium hypochlorite. Bottled solutions of sodium hypochlorite were sold under numerous trade names.

Today, an improved version of this method, known as the Hooker process (named after Hooker Chemicals, acquired by Occidental Petroleum), is the only large-scale industrial method of sodium hypochlorite production. In the process, sodium hypochlorite (NaClO) and sodium chloride (NaCl) are formed when chlorine is passed into cold dilute sodium hydroxide solution. The chlorine is prepared industrially by electrolysis with minimal separation between the anode and the cathode. The solution must be kept below 40 °C (by cooling coils) to prevent the undesired formation of sodium chlorate.

Commercial solutions always contain significant amounts of sodium chloride (common salt) as the main by-product, as seen in the equation above.

From hypochlorous acid and soda

A 1966 patent describes the production of solid stable dihydrate {{chem|NaOCl}}·2{{chem|H|2|O}} by reacting a chloride-free solution of hypochlorous acid {{chem|HClO}} (such as prepared from chlorine monoxide {{chem|Cl|O}} and water), with a concentrated solution of sodium hydroxide. In a typical preparation, 255 mL of a solution with 118 g/L {{chem|HClO}} is slowly added with stirring to a solution of 40 g of NaOH in water 0 °C. Some sodium chloride precipitates and is removed by fitration. The solution is vacuum evaporated at 40-50 °C and 1-2 mmHg until the dihydrate crystallizes out. The crystals are vacuum-dried to produce a free-flowing crystalline powder.^[12]

The same principle was used in another 1991 patent to produce concentrated slurries of the pentahydrate NaClO·5{{chem|H|2|O}}. Typically, a 35% solution (by weight) of HClO is combined with sodium hydroxide at about or below 25 °C. The resulting slurry contains about 35% NaClO, and are relatively stable due to the low concentration of chloride.^[27]

From ozone and salt

Sodium hypochlorite can be easily produced for research purposes by reacting ozone with salt.

This reaction happens at room temperature and can be helpful for oxidizing alcohols.

Packaging and sale

Household bleach sold for use in laundering clothes is a 3–8% solution of sodium hypochlorite at the time of manufacture. Strength varies from one formulation to another and gradually decreases with long storage. Sodium hydroxide is usually added in small amounts to household bleach to slow down the decomposition of NaClO.^[2]

A 10–25% solution of sodium hypochlorite is, according to Univar's safety sheet, supplied with synonyms or trade names bleach, Hypo, Everchlor, Chloros, Hispec, Bridos, Bleacol, or Vo-redox 9110.^[28]

A 12% solution is widely used in waterworks for the chlorination of water, and a 15% solution is more commonly^[29] used for disinfection of waste water in treatment plants. Sodium hypochlorite can also be used for point-of-use disinfection of drinking water.^[30]

Dilute solutions (50 ppm to 1.5%) are found in disinfecting sprays and wipes used on hard surfaces.^[31]^[32]

Uses

Bleaching

Household bleach is, in general, a solution containing 3–8% sodium hypochlorite, by weight, and 0.01–0.05% sodium hydroxide; the sodium hydroxide is used to slow the decomposition of sodium hypochlorite into sodium chloride and sodium chlorate.^[33]

Cleaning

Sodium hypochlorite has destaining properties.^[62] Among other applications, it can be used to remove mold stains, dental stains caused by fluorosis,^[34] and stains on crockery, especially those caused by the tannins in tea. It has also been used in laundry detergents and as a surface cleaner.

Its bleaching, cleaning, deodorizing and caustic effects are due to oxidation and hydrolysis (saponification). Organic dirt exposed to hypochlorite becomes water-soluble and non-volatile, which reduces its odor and facilitates its removal.

Disinfection

Sodium hypochlorite in solution exhibits broad spectrum anti-microbial activity and is widely used in healthcare facilities in a variety of settings.^[35] It is usually diluted in water depending on its intended use. "Strong chlorine solution" is a 0.5% solution of hypochlorite (containing approximately 5000 ppm free chlorine) used for disinfecting areas contaminated with body fluids, including large blood spills (the area is first cleaned with detergent before being disinfected).^[35]^[36] It may be made by diluting household bleach as appropriate (normally 1 part bleach to 9 parts water).^[37] Such solutions have been demonstrated to inactivate both C. difficile^[35] and HPV.^[38] "Weak chlorine solution" is a 0.05% solution of hypochlorite used for washing hands, but is normally prepared with calcium hypochlorite granules.^[36]

"Dakin's Solution" is a disinfectant solution containing low concentration of sodium hypochlorite and some boric acid or sodium bicarbonate to stabilize the pH. It has been found to be effective with NaOCl concentrations as low as 0.025%.^[39]

US government regulations allow food processing equipment and food contact surfaces to be sanitized with solutions containing bleach, provided that the solution is allowed to drain adequately before contact with food, and that the solutions do not exceed 200 parts per million (ppm) available chlorine (for example, one tablespoon of typical household bleach containing 5.25% sodium hypochlorite, per gallon of water).^[40] If higher concentrations are used, the surface must be rinsed with potable water after sanitizing.

A similar concentration of bleach in warm water is used to sanitize surfaces prior to brewing of beer or wine. Surfaces must be rinsed with sterilized (boiled) water to avoid imparting flavors to the brew; the chlorinated byproducts of sanitizing surfaces are also harmful. The mode of disinfectant action of sodium hypochlorite is similar to that of hypochlorous acid.

Solutions containing more than 500 ppm available chlorine are corrosive to some metals, alloys and many thermoplastics (such as acetal resin) and need to be thoroughly removed afterwards, so the bleach disinfection is sometimes followed by an ethanol disinfection. Liquids containing sodium hypochlorite as the main active component are also used for household cleaning and disinfection, for example toilet cleaners.^[41] Some cleaners are formulated to be thick so as not to drain quickly from vertical surfaces, such as the inside of a toilet bowl.

The undissociated (nonionized) hypochlorous acid is believed to react with and inactivate bacterial and viral enzymes.

Neutrophils of the human immune system produce small amounts of hypochlorite inside phagosomes, which digest bacteria and viruses.

Deodorizing

Sodium hypochlorite has deodorizing properties, which go hand in hand with its cleaning properties.^[42]

Waste water treatment

Sodium hypochlorite solutions have been used to treat dilute cyanide waste water, such as electroplating wastes. In batch treatment operations, sodium hypochlorite has been used to treat more concentrated cyanide wastes, such as silver cyanide plating solutions. Toxic cyanide is oxidized to cyanate (OCN⁻) that is not toxic, idealized as follows:

Sodium hypochlorite is commonly used as a biocide in industrial applications to control slime and bacteria formation in water systems used at power plants, pulp and paper mills, etc., in solutions typically of 10–15% by weight.

Endodontics

Sodium hypochlorite is the medicament of choice due to its efficacy against pathogenic organisms and pulp digestion in endodontic therapy. Its concentration for use varies from 0.5% to 5.25%. At low concentrations it dissolves mainly necrotic tissue; at higher concentrations it also dissolves vital tissue and additional bacterial species. One study has shown that Enterococcus faecalis was still present in the dentin after 40 minutes of exposure of 1.3% and 2.5% sodium hypochlorite, whereas 40 minutes at a concentration of 5.25% was effective in E. faecalis removal.^[43] In addition to higher concentrations of sodium hypochlorite, longer time exposure and warming the solution (60 °C) also increases its effectiveness in removing soft tissue and bacteria within the root canal chamber.^[43] 2% is a common concentration as there is less risk of an iatrogenic hypochlorite incident.^[44] A hypochlorite incident is an immediate reaction of severe pain, followed by edema, haematoma, and ecchymosis as a consequence of the solution escaping the confines of the tooth and entering the periapical space. This may be caused by binding or excessive pressure on the irrigant syringe, or it may occur if the tooth has an unusually large apical foramen.^[45]

Nerve agent neutralization

At the various nerve agent (chemical warfare nerve gas) destruction facilities throughout the United States, 50% sodium hypochlorite is used to remove all traces of nerve agent or blister agent from Personal Protection Equipment after an entry is made by personnel into toxic areas. 50% sodium hypochlorite is also used to neutralize any accidental releases of nerve agent in the toxic areas. Lesser concentrations of sodium hypochlorite are used in similar fashion in the Pollution Abatement System to ensure that no nerve agent is released in furnace flue gas.

Reduction of skin damage

Safety

It is estimated that there are about 3300 accidents needing hospital treatment caused by sodium hypochlorite solutions each year in British homes (RoSPA, 2002).

Oxidation and corrosion

Sodium hypochlorite is a strong oxidizer. Oxidation reactions are corrosive. Solutions burn the skin and cause eye damage, especially when used in concentrated forms. As recognized by the NFPA, however, only solutions containing more than 40% sodium hypochlorite by weight are considered hazardous oxidizers. Solutions less than 40% are classified as a moderate oxidizing hazard (NFPA 430, 2000).

Household bleach and pool chlorinator solutions are typically stabilized by a significant concentration of lye (caustic soda, NaOH) as part of the manufacturing reaction. This additive will by itself cause caustic irritation or burns due to defatting and saponification of skin oils and destruction of tissue. The slippery feel of bleach on skin is due to this process.

Storage hazards

Contact of sodium hypochlorite solutions with metals may evolve flammable hydrogen gas. Containers may explode when heated due to release of chlorine gas.^[49]

Hypochlorite solutions are corrosive to common container materials such as stainless steel^[10] and aluminium. The few compatible metals include titanium (which however is not compatible with dry chlorine) and tantalum.^[2] Glass containers are safe.^[10] Some plastics and rubbers are affected too; safe choices include polyethylene (PE), high density polyethylene (HDPE, PE-HD), polypropylene (PP),^[10] some chlorinated and fluorinated polymers such as polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF); as well as ethylene propylene rubber, and Viton.^[2]

Containers must allow venting of oxygen produced by decomposition over time, otherwise they may burst.^[4]

Reactions with other common products

Sodium hypochlorite solutions, such as liquid bleach, may release toxic chlorine gas when heated above 35 °C^[49] or mixed with an acid, such as muriatic acid or vinegar.

A 2008 study indicated that sodium hypochlorite and organic chemicals (e.g., surfactants, fragrances) contained in several household cleaning products can react to generate chlorinated volatile organic compounds (VOCs).^[50] These chlorinated compounds are emitted during cleaning applications, some of which are toxic and probable human carcinogens. The study showed that indoor air concentrations significantly increase (8–52 times for chloroform and 1–1170 times for carbon tetrachloride, respectively, above baseline quantities in the household) during the use of bleach containing products. The increase in chlorinated volatile organic compound concentrations was the lowest for plain bleach and the highest for the products in the form of "thick liquid and gel." The significant increases observed in indoor air concentrations of several chlorinated VOCs (especially carbon tetrachloride and chloroform) indicate that the bleach use may be a source that could be important in terms of inhalation exposure to these compounds. The authors suggested that using these cleaning products may significantly increase the cancer risk.^[50]

In particular, mixing hypochlorite bleaches with amines (for example, cleaning products that contain or release ammonia, ammonium salts, urea, or related compounds and biological materials such as urine) produces chloramines and nitrogen trichloride.^[51]^[49] These gaseous products can cause acute lung injury. Chronic exposure, for example, from the air at swimming pools where chlorine is used as the disinfectant, can lead to the development of atopic asthma.^[52]

Explosive reactions or byproducts can also occur in industrial and laboratory settings when sodium hypochlorite is mixed with formic acid, phenylacetonitrile, aziridine, and methanol.^[49]

Limitations in health care

The UK's National Institute for Health and Care Excellence in October 2008 recommended that Dakin's solution should not be used in routine wound care.^[53]

Environmental impact

In spite of its strong biocidal action, sodium hypochlorite per se has limited environmental impact, since the hypochlorite ion rapidly degrades before it can be absorbed by living beings.^[54]

However, one major concern arising from sodium hypochlorite use is that it tends to form persistent chlorinated organic compounds, including known carcinogens, that can be absorbed by organisms and enter the food chain. These compounds may be formed during household storage and use as well during industrial use.^[33] For example, when household bleach and wastewater were mixed, 1–2% of the available chlorine was observed to form organic compounds.^[33] As of 1994, not all the byproducts had been identified, but identified compounds include chloroform and carbon tetrachloride.^[33] The estimated exposure to these chemicals from use is estimated to be within occupational exposure limits.^[33]

See also

References

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2. ^¹²³⁴{{cite web|title=OxyChem Sodium Hypochlorite Handbook|url=http://www.oxy.com/OurBusinesses/Chemicals/Products/Documents/sodiumhypochlorite/bleach.pdf|website=oxy.com|publisher=OxyChem}}
3. ^{{cite web|title=Pamphlet 96, The Sodium Hypochorite Manual |url=https://bookstore.chlorineinstitute.org/mm5/merchant.mvc?Session_ID=85fbe8684bca6b6014d4def834848a2d&Store_Code=ci2store&Screen=PROD&Product_Code=SPHP0096-HC&|website=www.chlorineinstitute.org|publisher=The Chlorine Institute}}
4. ^¹²Peter Urben, editor (2006), Bretherick's Handbook of Reactive Chemical Hazards. 4th edition, p. 984; 7th Edition; vol. 1, pg 1433. {{ISBN|9780123725639}}, 9780080523408
5. ^¹²Arihiro Hamano (1997): "The formation and decomposition of sodium hypochlorite anhydrous salt and its pentahydrate". Science and Technology of Energetic Materials, volume 58, issue 4, pages 152-155.
6. ^¹²Carl L. Yaws (2015): The Yaws Handbook of Physical Properties for Hydrocarbons and Chemicals, 2nd edition, page 734. Gulf Professional Publishing. {{ISBN|0128011467}}, 9780128011461.
7. ^¹Malcolm Percival Applebey (1919): "Sodium hypochlorite". Journal of the Chemical Society, Transactions, volume 115, article XCVI, pages 1106-1109. {{doi|10.1039/CT9191501106}}
8. ^"Sodium Hypochlorite Pentahydrate, {{chem|NaOCl}}·5{{chem|H|2|O}}". MatWeb Material Property Data website. Accessed on 2018-07-12.
9. ^¹"[https://studfiles.net/preview/409824/page:2/ Sodium Hypochlorite]". Web page at StudFiles, accessed on 2018-06-14.
10. ^¹²³⁴⁵⁶⁷⁸⁹¹⁰Masayuki Kirihara, Tomohide Okada, Yukihiro Sugiyama, Miyako Akiyoshi, Takehiro Matsunaga, and Yoshikazu Kimura (2017): "Sodium Hypochlorite Pentahydrate Crystals (NaOCl·5H2O): A Convenient and Environmentally Benign Oxidant for Organic Synthesis". Organochemistry Process Research and Development, volume 21, pages 1925–1937. {{doi|10.1021/acs.oprd.7b00288}}
11. ^Tomohide Okada, Tomotake Asawa, Yukihiro Sugiyama, Toshiaki Iwai, Masayuki Kirihara, Yoshikazu Kimura (2016): "Sodium hypochlorite pentahydrate (NaOCl·5H2O) crystals; An effective re-oxidant for TEMPO oxidation". Tetrahedron, volume 72, issue 22, pages 2818-2827. {{doi|10.1016/j.tet.2016.03.064}}
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16. ^¹²³⁴⁵Staffan Sandin, Rasmus K. B. Karlsson, and Ann Cornell (2015): "Catalyzed and Uncatalyzed Decomposition of Hypochlorite in Dilute Solutions". Industrial Engineering Chemical Research, volume 54, issue 15, pages 3767–3774. {{doi|10.1021/ie504890a}}
17. ^¹Arihiro Hamano and Akie Ikeda (1995): "The pH effect on the photodecomposition of sodium hypochlorite solution". Science and Technology of Energetic Materials, volume 56, issue 2, pages 59-63.
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33. ^¹²³⁴Smith WT. (1994). Human and Environmental Safety of Hypochlorite. In: [https://books.google.com/books?id=Pbr2HJ1X_DkC Proceedings of the 3rd World Conference on Detergents: Global Perspectives], pp. 183–5.
34. ^{{cite journal |last1=Cárdenas Flores |first1=A |last2=Flores Reyes |first2=H |last3=Gordillo Moscoso |first3=A |last4=Castanedo Cázares |first4=JP |last5=Pozos Guillén Ade |first5=J |title= Clinical efficacy of 5% sodium hypochlorite for removal of stains caused by dental fluorosis |journal= The Journal of Clinical Pediatric Dentistry |volume= 33 |issue= 3 |pages= 187–91 |year= 2009 |pmid= 19476089 |doi=10.17796/jcpd.33.3.c6282t1054584157}}
35. ^¹²{{Cite web|url=https://www.cdc.gov/infectioncontrol/pdf/guidelines/disinfection-guidelines.pdf|title=Guideline for Disinfection and Sterilization in Healthcare Facilities|last=Rutala|first=William A.|last2=Weber|first2=David J.|date=15 February 2017|website=www.cdc.gov|orig-year=2008|access-date=2017-08-29}}
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40. ^21 CFR Part 178
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