Difference between hypochlorous acid water and sodium hypochlorite

On May 29, the National Institute of Technology and Evaluation (NITE) issued an interim report stating that about “hypochlorous acid water” used for the purpose of disinfecting new coronavirus, “its effectiveness has not been confirmed at this time.”

In Japan these days, there are “hypochlorous acid atomizers” as countermeasures against new coronaviruses everywhere. Those who believed that it would be effective against the coronavirus in that space and purchased and used it would have been disappointed at the news. Aside from those who use it just to comfort their mind regardless of the effect.

 

Virus classification

Here is a review. Virus particles have the following three basic structures.

(A) A type in which virus particles do not have an envelope (outer membrane)

This type includes viruses such as polio virus, adenovirus, and norovirus.

 

(B) A type in which virus particles have an envelope (outer membrane), but proteins are not attached to nucleic acids

Herpes virus falls into this type.

 

(C) A type in which virus particles have an envelope (outer membrane) and nucleic acids have proteins

Influenza virus, coronavirus, measles virus, etc. are this type. The new coronavirus this time also falls into this type structurally.

 

 

In addition, there are two further categories.

(1) Virus whose nucleic acid is DNA

(2) Virus whose nucleic acid is NA

Influenza virus and norovirus are NA viruses. The new coronavirus this time is also an NA virus.

 

As you may have noticed here, the particle structures of the novel coronavirus and influenza virus are similar. Therefore, what is effective against influenza virus is also effective against the new coronavirus, and it is speculated that acidic electrolyzed water (hypochlorous acid water) will be effective, leading to the current situation.

 

Of course, based on that assumption, the Ministry of Economy, Trade and Industry selected the following three fields of products as disinfecting methods and products that could be effective against the new coronavirus, and outsourced the verification test to NITE.

  • Surfactant (Kitchen detergent, etc.)

  • Hypochlorous acid water (generated by electrolysis)

  • Quaternary ammonium salt

The result was the opening interim report on May 29. The effect of hypochlorous acid water could not be confirmed at this time.

 

 

The topical “hypochlorous acid water” (electrolyzed water) (HOCl) contains the bactericidal component “hypochlorous acid”, but the effect on the new coronavirus is not confirmed yet. Because it is effective against influenza virus and old type (?) coronavirus, it is used for disinfecting food and articles.

On the other hand, what we often see in your comments is “sodium hypochlorite (soda)” (NaClO). This is also active as a bleaching agent. Sodium hypochlorite solution is very alkaline. Sodium hypochlorite also contains a bactericidal component “hypochlorous acid.”

 

Difference between hypochlorous acid water and sodium hypochlorite

There are three differences between the two. I will explain each one.

1) Different pH

As I touched briefly in the previous chapter, hypochlorous acid water is weakly acidic, but sodium hypochlorite is a strong alkali.

It is a famous story that a skin is weakly acidic. Hypochlorous acid water has a pH close to that of a skin, so there is less damage to a skin.

The reason your hands are slimy when you touch something alkaline is that your skin is melting due to damage to it. Sodium hypochlorite causes this phenomenon, so application to a skin is strictly prohibited.

 

2) Different usage

Although hypochlorous acid water is used as it is, sodium hypochlorite is generally diluted before use.

Dilution example (stock solution 12% concentration)

Use Effective chlorine concentration Dilution ratio (example)
Disinfection of water (drinking water, pool, and drainage) Approximately 0.8 ppm Approximately 140,000 times(approximately 0.7 ml for 100 L of water)
Disinfection of tableware Approximately 100 ppm Approximately 1,200 times (approximately 75 ml for 100 L of water)
Disinfection of raw vegetables and fruits Approximately 100 ppm Approximately 1,200 times (approximately 75 ml for 100 L of water)
Disinfection of bathrooms, bathtubs, toilet bowls, etc. Approximately 600 ppm Approximately 200 times (450 ml for 100 L of water)
Stain removal/bleaching (liquor, fruit juice, ink, etc.) 600-2000 ppm 60-200 times (450 to 1,500 ml for 100 L of water)

 

3) Different form of bactericidal component

Free chlorine contained in hypochlorous acid water is contained in the form of unstable HClO. Therefore, although it has a bactericidal effect even at low concentrations, it decomposes immediately when it comes into contact with organic substances, so a large amount of hypochlorous acid water is required when sterilizing cookware and medical equipment. Even when applying it to your hands, it has been decomposed by the time you spread the hypochlorous acid water applied to your left hand to your right hand, so it is necessary to apply a large amount of hypochlorous acid water directly to both hands.

Since the sodium hypochlorite aqueous solution is alkaline, it contains a large amount of free chlorine in the form of stable ClO-. Being stable, it requires a higher concentration than hypochlorous acid water to produce a bactericidal effect. On the other hand, since it is stable, it has a long-lasting sterilizing effect, so it is used for sterilization such as wiping.

 

 

Bonus

I briefly summarized the difference between hypochlorous acid water and sodium hypochlorite, but there is also “calcium hypochlorite.” It is a solid and is weakly alkaline when dissolved in water.

I think some people in Japan remember that a teacher threw white tablets called “kalki” into a school pool a long time ago. This white tablet is “calcium hypochlorite.”

Kalki is made by absorbing chlorine in calcium hydroxide (lime). This chlorine played a role in suppressing the growth of various bacteria in a pool.

Nowadays, sodium hypochlorite, which is a liquid and easy to manage, has become the mainstream. It is also used for sterilization of tap water. Unlike solid calcium hypochlorite, sodium hypochlorite is a liquid, so it is easy to dissolve in water and its concentration can be adjusted easily.

About disinfection of tap water

Water Supply Act in Japan stipulates that “basically, chlorine should be used to disinfect water.” For tap water, Japan has approved the use of especially 3 substances: “sodium hypochlorite,” “calcium hypochlorite,” and “liquefied chlorine.” Sodium hypochlorite is currently used to sterilize tap water.

 

Conclusion

The effect of hypochlorous acid water on the new coronavirus is not confirmed yet, but what about sodium hypochlorite? To answer this question, it is stated in the Ministry of Health, Labor and Welfare documents that sodium hypochlorite is effective against the new coronavirus. (Visit the URL below)

https://www.mhlw.go.jp/content/000617981.pdf

However, since it is a strong alkali, it cannot be either applied to a skin or used for hand disinfection. There is also a note on the link above, as you should wear gloves when disinfecting. In addition, it may corrode metals, so I think it is better to use sodium hypochlorite and alcohol properly for disinfection.

 

 

 

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Comments for this article

  • 四方輝夫 より:

    7/30日の時点では、すでに次亜塩素酸水の有効性がNITEの検証によって認められているのですが、コロナ禍の中、いつまでも誤った中間報告をぶら下げていられる情報弱者ぶりがすごいですね。

    そしていま、次亜塩素酸水について効果なしとの結果を出した唯一の検証機関である北里でデータ改ざん疑惑が持ち上がっています。

    「次亜塩素酸水という常識が公に認められると困る人は、報道をみてさぞやがっかりされたことでしょう」
    と書かれる日が、すぐそこまで来ているのではないでしょうか。

    • sankyo管理者 より:

      >>四方輝夫様

      コメントありがとうございます。
      申し訳ありません、当記事は6月上旬に更新した記事なのですが
      サーバーのアップデートにより記事が消えてしまい、7/30に再度掲載した記事になります。その旨の記載を漏らしてしまい混乱させてしまい申し訳ありません。
      次亜塩素酸水そのものに効果が見込めないわけではありません。
      ただ噴霧などの少量では効果が期待できず、水道水で手を洗うような感覚で次亜塩素酸水を大量にかければ効果はございます。

  • 高尾幸江 より:

    記事読みました。お世話になります。

    お忙しいところ、すみませんが、次亜塩素酸水(HClO)の生成(電気分解)について教えてください。

    市販されている生成機には、希塩酸(HCl)(出荷時200ppm程度)がセットされていて、これを塩(NaCl)と水(H2O)で電気分解するようですが、化学式がわかりません。

    製品は次のようなものです。

    https://paypaymall.yahoo.co.jp/store/rush-mall/item/asmaker001/?sc_i=shp_pc_search_itemlist_shsrg_img

    https://store.shopping.yahoo.co.jp/papillonyshop/jokinchan500bt-500pac-set.html?sc_i=shp_pc_search_itemlist_shsrg_img

    HClOが精製されたあとは水に戻ると書いてありますが、Naはどうなるのでしょうか?
    電離させるためにNaClをくわえるのかな?と考えていますが・・・。
    次亜塩素酸ナトリウム(NaClO)の生成方法は全く別と考えて合っていますか?

    また、1993年製Nationalの製造機は塩と酢を入れたようですが、酢酸は触媒でしょうか?

    中学生レベルの質問でお恥ずかしいのですが、回答いただければ幸いです。

    • sankyo管理者 より:

      >>高尾幸江様

      コメントありがとうございます。
      Naはナトリウムイオンの状態で電解した後の液体に入っています。
      電解すると出てくるのがマイナス極から水素、プラス極から塩素が出て、そのほかのものに関しては中に残ったままになります。

      酢酸や希塩酸は水素イオンの供給源です。
      電気分解した後の溶液を酸性状態に保つために入っています。

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