Mark Bosley, Technical Manager of Purite Ltd, discusses the importance of glassware washing in laboratories.

A consistent supply of high quality water is crucial for the cleaning and decontamination of laboratory glassware apparatus, including beakers, measuring cylinders, dispensing pipettes, flasks, volumetric flasks and test tubes. Water performs two major functions: it acts as a carrier for detergents and is a rinsing agent for the removal of residual traces of dirt which may otherwise be redeposited on clean surfaces.

A wide range of glassware is used for general wet chemistry techniques such as buffer make up, standard preparations, titritmetric and gravimetric analyses, as well as quantitative and qualitative analyses.

The process of glassware washing for these wet chemistry techniques, especially in smaller laboratories, is normally straightforward and frequently not automated. This typically only requires a pure water feed plus the addition of an appropriate chemical cleaning agent. The glassware is generally left to soak during the working day and is then given a succession of water rinses until the glassware is clear and free from any residual cleaning agent .

For critical techniques such as AAS, IC, ISE and ICPMS, a more sophisticated approach to washing glassware is required, using pure water in conjunction with automatic washing systems. These systems have considerable capacity, numerous wash cycles depending on the level and nature of the contamination on the glassware, and use a range of chemical cleaners.

These washers are also capable of removing heavy solids, metallic salts and precipitates that may have formed on the glassware as a by-product of the previous use, or organic residues that have resulted from evaporation.

In addition, some of these automatic systems are capable of washing and rinsing the glassware in water at elevated temperatures which has the added advantage of giving microbiological control.

Water used for these specially designed washing systems has to be pretreated to ensure the absence of Calcium and Magnesium salts. If these remain present, even in minor amounts, they can create unsightly watermarks on the glassware. In addition, lime scale can build up and contaminate heating elements and block the fine water jet spray nozzles of cleaning systems leading to a dramatic loss in efficiency and increase in running costs.

The presence of contaminants on glassware is also undesirable as they may alter the chemical properties of the solution, either temporarily or permanently, which can influence the outcome of any results.

This is, of course, unacceptable in a laboratory where the glass must be contaminant free in order to preserve the integrity of contents, and this illustrates why it is imperative that glass washing be carried out with the correct grade of water.

In addition, the same need for purified water applies in laboratories that are situated in both hard and soft water areas. Although hard water results in larger deposits of lime scale, and the creation of soap scum - the most obvious of contaminants - soft water still contains minerals and salts, dissolved organics and iron complexes that are capable of forming residues or contaminating glassware.

Glass equipment that has undergone thorough cleaning should be aesthetically pleasing to the eye and, therefore be completely free of watermarks, residue and stains. This provides the reassurance that the glass equipment is free of any contamination and is safe to use.

Ensuring the optical quality of the glassware is not only necessary for aesthetic reasons, but also for use in techniques that involve measuring light absorption or transmission through a Cuvette, such as Spectrophotometry. In such cases, the presence of residues on the glass can have a severe impact on the results recorded and invalidate the entire procedure. The use of control methods may not highlight this discrepancy in the results, as if the control Cuvette was washed in the same water, the same contaminants would be present.

Standard potable tap water is generally unsuitable for glass washing, due to the fact it contains a variety of chemical and microbial contaminants that can affect the sterility of laboratory equipment, or, as previously noted, block the internal workings of the washing system.

Regardless of size, laboratories, therefore need a dependable and consistent supply of pure water on demand, whenever and wherever technicians require it. Depending on the size of the laboratory and the type of analytic work being carried out, different grades of pure water are usually required.

Pure water Provision

Although traditionally distilled water has often been used in laboratories for glassware cleaning purposes, it is no longer seen as cost efficient due to the high energy costs involved. The process has been superseded by membrane filtration techniques, such as Reverse Osmosis (RO), which remove up to 98% of inorganic ions in addition to virtually all the colloids, microorganisms, endotoxins and other macromolecules present.

The RO process involves feeding pretreated water under pressure into a module that contains a semi permeable membrane. When the applied pressure exceeds the natural osmotic pressure of the impure water it causes the direction of the osmotic flow to reverse, and this results in a proportion of the feedwater passing through the membrane, which strips the impurities from the water to form the permeate. The residual concentrate collects the removed impurities and is continuously bled to drain.

The process can generate varying qualities and types of water. BS EN ISO 3696 details standards for general laboratory use: Grade III water is generated using Reverse Osmosis (RO) only and has a conductivity of lower than 5 µS/cm , Grade II water is generated using RO and additional deionisation, using ion exchange resins or electrodeionisation. Its resistivity ranges from 1-10 Megohm-cm and such water is ideal for glassware rinsing, buffer, stain and media preparation, and reagent make-up. Grade I water has a resistivity of above 10 Megohm-cm and would typically be used for spectrophotometry and other analytical techniques .

System Solutions

There is a wide range of cost effective solutions for the provision of pure water for glassware washing. For smaller laboratories a variety of options of easy to install and maintain stand alone units are available that offer a simple and cost effective means of providing purified water direct from a mains water supply.

For example, units such as the Purewater 300 unit from Purite have been specially designed to provide purified water for laboratory glassware washing machines. Compact in design, combining the tank and purification equipment into one unit, these units can be bench or wall mounted making them ideal for use where space is at a premium.

In the case of larger laboratories - with requirements typically above 100 litres per day - a centralised reverse osmosis system usually provides the most economical method of creating a constant supply of pure water quickly and efficiently. This is due to the fact that the quantities and grades of water required can vary greatly from one department to another, and also that for ease of access, pure water must be fed to a number of points of use that can be spread over various floors within a building. Localised treatment units can then be added if higher quality water is required for specific applications.

One of the major benefits of a centralised water purification plant is that it can be easily upgraded as and when demand or water requirements change, or in the event of new departments being added. Purified water systems providers, such as Purite, can design bespoke systems based on the exact requirements of the individual laboratory and support it with 24/7 service contract and full consumables package.

It is imperative that the importance of proper washing and sterilisation of glass instruments should not be overlooked, as the effects of contamination can be far reaching and long lasting. However, with the range of pure water provision solutions available, and the flexibility of designs and also of support and maintenance, laboratories of all sizes can choose a solution that suits them.