Care & Maintenance of Laboratory Glassware

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To obtain the maximum performance from your laboratory glassware correct handling is essential. The following information is a guide on the safe handling of glassware and tips on how you can optimise its performance and life span.

General Precautions

  • We recommend that all glassware is washed before it is first used.
  • Before using any piece of glassware, always take time to examine it carefully and ensure that it is in good condition. Do not use any glassware that is scratched, chipped, cracked or etched. Defects like these can seriously weaken the mechanical strength of the glass and cause it to break in use.
  • Borosilicate glass should under no circumstances be dispose of broken or defective glassware safely. Use a purpose-designed disposal bin that is puncture resistant and clearly labelled. Pyrex® glassware (or any other borosilicate glass) should under no circumstances be disposed of in a domestic glass recycling stream (e.g. bottle banks), as its high melting point makes it incompatible with other glass (soda-lime glass) for recycling. The correct method of disposal is to include it in the general waste in accordance with the relevant guidelines, provided that the glass is free from any harmful chemical contamination.
  • Never use excessive force to fit rubber bungs into the neck of a piece of glassware. Always ensure that you select the correct size of bung.
  • Many glass products are supplied with durable, easy to use plastic screw thread tubing connectors to allow the safe fitting of any flexible tubing. When attaching tubing, ensure that the screw thread connector is removed from the glassware, the tubing is lubricated and protective gloves are worn. Never use excessive force to connect the rubber hose or tubing.
  • Carrying or lifting large glass flasks, beakers or bottles, etc. by the neck or rim can be very dangerous. Always provide support from the base and sides.
  • When stirring solutions in glass vessels, avoid using stirring rods with sharp ends which can scratch the glassware causing it to become weakened.

Heating and Cooling

  • The maximum recommended working temperature for borosilicate glass is 500oC (for short periods only). However, once the temperature exceeds 150oC extra care must be taken to ensure that the heating and then cooling of the glassware is achieved in a slow and uniform manner.
  • Always heat glassware gently and gradually to avoid sudden temperature changes which may cause the glass to break due to thermal shock. Similarly, allow hot glassware to cool gradually and in a location away from cold draughts.
  • If you are using a hotplate, ensure that the top plate is larger than the base of the vessel to be heated. If the base of the vessel overhangs the hotplate top, hotspots can occur causing the base of the vessel to break. Also, never put cold glassware onto a pre-heated hotplate. Always warm up the glassware from ambient temperature.
  • If you are using a Bunsen burner, employ a soft flame and use a wire gauze with a ceramic centre to diffuse the flame. Never apply direct localised heat to a piece of glassware.
  • Borosilicate glass is microwave safe. However, as with any microwave vessel, ensure that it holds microwave absorbing material, before placing it in the oven. Many products utilise plastics screwcaps and connectors. These components are typically manufactured from polypropylene or PTFE, both of which are also microwave safe.
  • When autoclaving containers e.g. bottles with screwcaps, always loosen off the caps. Autoclaving glassware with a tightly screwed cap can result in pressure differences which will cause the container to break.

Vacuum and Pressure Use

Because working conditions can vary enormously, DWK Life Sciences cannot guarantee the performance of any of its glassware when used under vacuum or positive pressure. The application of positive pressures inside glass apparatus is particularly hazardous and should be avoided, if at all possible. Safety precautions should always be taken to protect personnel and a number of these are listed below:

  • Always use an adequate safety screen and/or protective cage when using glassware under vacuum or positive pressure.
  • Flat bottomed vessels such as Erlenmeyer flasks and bottles should not be used under vacuum as they are likely to implode. Exceptions are vessels with specially thickened walls such as Buchner filter flasks and desiccators.
  • Under no circumstances should glassware that is scratched, cracked or chipped be used. Any damage to the glassware will seriously impair its mechanical strength.
  • Never subject glassware to sudden pressure changes. Always apply and release pressure gradients and vacuums gradually.
  • Avoid stressing the glass by over-tightening clamps. Support glassware gently where possible.

Ground Glass Joints

To prevent joints leaking in use and to assist separation, lubricate the ground surfaces of the joint with a silicone-free laboratory grease. Apply a light coating completely around the upper part of the joint. Alternatively, a PTFE sleeve can be fitted between the cone and socket.

If ground glass joints do seize, we suggest the following remedies to separate the joint:

  • Always wear thick protective gloves and safety spectacles. Never use force.
  • Carefully rock the cone (inner joint) in the socket to achieve separation.
  • If the joint is dry, try to provide lubrication. Hold the joint upright and add penetrating oil to the top of the cone. Wait until the penetrating oil is well dispersed into the joint before trying to separate.
  • If the use of temperature is permissible e.g. no volatile substances are present, warm the outer socket under a running stream of hot tap water. Hold under the tap for a few minutes before trying to separate the joint.

Volumetric Glassware

  • Always ensure that volumetric glassware is kept scrupulously clean. Dirt, and especially grease, can distort the shape of the meniscus and can also cause droplets of liquid to adhere to the vessel walls. Both seriously impair accuracy. (Good cleanliness is indicated by uniform wetting of the glass surface with distilled water).
  • Never pipette by mouth. Always use a purpose designed pipette filler.
  • Autoclaving at 121oC and cleaning glassware in an automatic dishwasher will not affect the accuracy of volumetric products.
  • All items should be held in a vertical position when reading the meniscus. The meniscus should be at eye level to avoid parallax errors.
  • If using strong corrosive acids, etc. select volumetric products manufactured from chemically resistant borosilicate glass.
  • Never expose volumetric glassware to direct heat e.g. hotplates and Bunsen flames, as this will affect the accuracy.
  • This technical information is provided in good faith by DWK Life Sciences for the safety of its customers.

Please note that the advice given is for general laboratory applications and may not necessarily apply to all tests and procedures.

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