Cleaning Detergents Should Be Mildy Alkaline

The Australian Standards AS/NZS 4815-2001 & AS/NZS 4187-2003 recommend the use of mild alkaline detergents (pH 8.0-10.8) for cleaning. Alkaline detergents are recommended because they clean better than neutral or acidic detergents.

Why alkaline detergents clean better

  • Surfaces: Alkalinity helps keep soil particles suspended in the cleaning solution. This prevents “clumping” and re-deposition of soil onto the cleaned surface.
  • Fatty Acids: Alkalinity converts insoluble fatty acids into their more soluble salts, making them easier to wash away.
  • Proteins: Alkalinity helps to increase the solubility of proteins.
  • Hard Water: Alkaline builders help remove calcium and magnesium (soften the water) which improves the performance of surfactants in the detergent.
  • Metal: Alkaline builders help prevent the corrosion of metal. Some alkaline ingredients have anti-corrosion properties. Corrosion of steel is at a minimum in mild alkaline solutions (pH 8.5-10) compared to neutral or mild acid solutions where corrosion can be more significant.

Hard Surfaces and Particulates.

Alkaline solutions produce a negative charge on surfaces & suspended soil. Particulates with a negative charge will repel each other, and prevent “clumping”. Instrument surfaces will also be negatively charged and repel the particulates – reducing the re-deposition of soils onto the cleaned surfaces.

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These advantages also apply to enzyme-containing detergents, with an added advantage. Most protease
enzymes used in detergents are alkaline proteases – meaning they function best in alkaline solutions

Acids and Bases – Alkalinity and pH

To understand the significance of alkalinity in the cleaning process it is useful to be familiar with the meaning of alkalinity and pH, and the chemical properties of the main components of biologically derived soils.

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Acids and Bases – Alkalinity and pH –

Acids and bases are a regular part of our daily life, vinegar and lemon juice are acidic while sodium bicarbonate (baking soda) and ammonia are basic (alkaline). The acidity or alkalinity of an aqueous solution is measured using the pH scale (Figure 1.1). On the pH scale, pure water is considered neutral with a pH = 7.0. Acids have pH values less than 7.0 and alkaline solutions have pH values greater
than 7.0. Acidic solutions have an increasing concentration of positive ions (+H3O) as the strength of the acid increases. For alkaline solutions, the concentration of hydroxide ions (-OH) increases with the strength of the base.

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