Acid bath cleaning of Laboratory Plasticware

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Some qualities of Plastic labware

Cleaning laboratory plasticware depends on the type and properties of the plastic.
Temperature in the form of extreme heat or cold affect flexability and strength.

Chemicals such as lubricants and oil cause cracking, and prolonged use of oxidizing agents cause brittleness and breakage.

Laboratory ware made with glass, quartz, polyethylene and polypropylene are subject to interaction between container and sample,
or with reagents and standards and can give incorrect results.

However, polyolefins and fluorinated hydrocarbons have excellent resistance to high temperatures and chemical attack.
They have wettable surfaces and are easy to clean.

PFA Hydrocarbons

PFA is best for making laboratory plasticware. It can be formed by injection blow moulding. It therefore has high transparency and smoothe surfaces that do not interact with analytes, reagents or standards. It has excellent resistance to conc acids, alcohols, bases, aliphatic/aromatic/halogenated hydrocarbons, ketones, mineral and vegetable oils. It is ideal for trace analysis in low concentration of ng/g and pg/g.

Cleaning methods

ACID BATH

An acid bath is a container containing acid in which the plasticware is placed and kept for some time until clean. The container should be made of moulded plastic or pyrex glass with a loose fitting lid. The size and shape may vary according to wash load and need.
Immerse plasticware into a 1M nitric acid and allow to soak overnight for mild contamination. Keep in bath for about one week for heavy contamination. The cleaned plasticware is then taken out off the bath and rinsed with distilled water and put to air dry. A rinse with acetone or placement in a glassware dryer at lowest temperature can be used. D o not use oven or furnace to dry plastics because high temperatures will deform the plastic.
Note: Plastics tend to float when put into the cleaning solution and can be sunk to the bottom using a pair of tongs.

Polyolefins and Fluorinated hydrocarbons
LPDE, HPDE, PP, PMP(TXP) and
PTFE, PFA, FEP, ETFE, E-CTFE
Slight contamination: Use a chemically neutral (pH 7) cleaning agent.
Heavy contamination: Remove using an alkaline (pH 12) cleaning agent.

Polycarbonate
Use only pH 7 neutral cleaning agents. Do not use alkaline cleaning agents.

Polystyrene
Use neutral cleaning agents only. Do not autoclave under any condition.
Note: Use only alcohols as solvent to remove greese and oils from PC and PS. Other solvents attack these plastics.

Polysulphonate
Never use cleaning agents containing tensiles (tween) for PSU.

Trace analysis

Soak in a 1:1 HCl acid bath for about 3 hours. Remove and then immerse for another 3 hours in a 1:1 nitric acid bath. Take out and rinse with distilled or deionized water. Dry as necessary.

Autoclave

Certain chemical contaminants on plasticware can be baked onto the plastic at autoclave temperatures. Rinse thoroughly with distilled water before autoclaving.
Autoclave within the tolerated temperature range of the plastic being sterilized. Remove any stoppers, caps or fittings before autoclaving.
Plastic containers such as vials, sample tubes and bottles should be autoclaved with their closures disengaged to avoid deformation.
Note: Nylon, polyurethane, polystyrene, polyvinyl chloride (PVC), Acrylic, LPDE and HPDE must not be autoclaved under any condition.



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