Clean glassware - a clear favourite

When striving for good laboratory practice, clean glassware is a must – here, Lee Marshall tells us how to win the battle with grime

A WIDE range of different glass, ceramic or plastic vessels are used in laboratories to perform experiments and analyses, to culture tissue, take specimens and many other applications. Ensuring that standards of apparatus cleanliness do not jeopardise the outcome of experiments is of paramount importance in laboratories and requires complex treatment processes and excellent efficiency.

Good laboratory practice demands clean glassware, because the most carefully executed piece of work may give a flawed result if dirty glassware is used. In all instances glassware must be physically clean, it must be chemically clean, and in many cases, it must be bacteriologically clean or sterile.

As the cleaning and drying standards required vary from one laboratory to the next, cleaning system requirements are also different, depending on the individual application. Treatment methods and machines have been developed which offer appropriate cleaning processes to suit individual applications, depending on the type and degree of soil, cleaning standards required and the load requirements.

Many laboratory professionals are faced with the task of how to effectively clean the interior of narrow-necked laboratory glassware, Erlenmeyer and volumetric flasks, BOD bottles, pipettes, autosampler vials and test tubes - all of which can all be a challenge to clean. Hand washing these items does not guarantee adequate cleaning, is labour intensive and more costly than an automated system in the long run.

Finding the right automated cleaning system to suit every application is the key to a successful cleaning regime. Effective cleaning of narrow-necked glassware in an automatic system is dependent on many factors: Direct injection baskets – Cleaning narrow-necked items such as volumetric or Erlenmeyer flasks require direct injection baskets for hard to reach interiors. When considering direct injection baskets it’s important to evaluate the following:

• Injectors should be provided in a variety of diameters and lengths for use with different sizes and types of glassware. • Individual injectors should be removable for customer configuration by the user. • Clips for holding glassware firmly at optimal height should be available. • Injector baskets should be interchangeable with other baskets, and injection capability should be possible on one or two levels. • Does the washer circulate water at a high enough rate to thoroughly clean for your application? • How many injectors are provided on each basket? • If the washer includes a forced air drying cycle can the air be blown through the injectors for drying of glassware interiors? Injector baskets from Miele have a radial design where water reaches the end of each injector with equal pressure. Some manufacturers use a grid like injector design, where water pressure may be inadequate on injectors which are farthest from the feed tube.

Temperature – In general, hotter water provides better cleaning and rinsing.  For this reason Miele ensures that wash and purified water, can be heated to 93ºC. Some automated cleaning systems will only heat the wash water to 55 or 65ºC, and most brands provide non-heated purified water heating capability which is not as effective.

Mechanical action – it is often assumed that high pressure must be used to provide good cleaning results. The problem is that higher pressure also means a greater chance of breaking delicate glassware. Choosing a machine with a high turnover rate (circulation) of water at a low discharge pressure provides the best results without risk of breakage. How often the water and detergent contact the surface to be cleaned is actually more important than how hard it hits. A high circulation rate ensures analytically clean results, reduces the wash time required, aids in energy efficiency, and allows for lower detergent usage.

Time – increasing the time of a wash cycle will improve the cleaning results.  Yet most labs can’t afford to spend time waiting for a washer to complete long cycles. Finding an automated system with high circulation rates is the key to faster cleaning, but another important factor is the time taken for water to heat up. Miele’s systems utilise only 9L of water per cycle which is heated by 6kw of power at 230v and 9kw for 400v.

Detergent – Selecting the proper detergent is an important step in achieving critically clean glassware and should be application specific. For example, cosmetic creams and lotions are typically thick non-water soluble emulsions that adhere to the surface of glassware. Pre-rinsing with hot water can be helpful prior to hand washing, but removal of the thin film that often remains can pose a problem. To overcome this, it is typical to try using a very strong alkaline detergent. Experience has shown that this will only compound the problem, by leaving a hard ‘skin’ that is even more difficult to clean. A mild detergent in combination with an emulsifier will, in fact, provide the best results. The mechanical effect of as much water as possible passing over the glassware surface is also critical.

Petroleum compounds, such as refined hydrocarbon distillates, are generally a difficult to clean, oily, molasses like substance. Traditionally, these compounds have been cleaned using hydrocarbon solvents such as diesel fuel. However, this process can be hazardous to personnel and create environmental disposal problems. Converting to an aqueous based method can eliminate these concerns and be less costly. For petroleum compound applications a liquid detergent has proven effective in combination with an acid neutraliser and an emulsifier, to aid in suspending hydrophobic hydrocarbons in solution. Consideration should also be given to using a machine fitted with silicone seals as petroleum compounds can degenerate rubber based components.

Cleaning glass plates used to hold DNA polyacrylamide sequencing gels can be a labour intensive task. Plates used in automated DNA sequencing systems are expensive due to the special nature of the glass, making breakage or chipping due to excessive handling costly. The plates are large and awkward to handle, especially in a crowded lab area around a sink.  Laying them out to dry after hand washing requires bench space, which is also inconvenient. Effective cleaning can be achieved in an automated lab washer by using powder detergent that has been specially formulated for biological work. This detergent contains complexing agents and chlorine for thorough cleaning without any interference from residues, fluorescing or otherwise. A liquid neutraliser can be used to restore the proper pH balance to the plates.

As research becomes more and more precise, the importance of perfectly clean glassware is paramount. As accuracy has increased so has the requirement for ‘proof’ that the research process itself is valid. As a result, organisations are faced with documenting and validating equipment and processes that were never questioned in the past. These days, an efficient analytical laboratory must use reliable and validated methods and must satisfy requirements for quality control for all methods and apparatus it uses. These include the repeatability of all results and procedures used. Those in industry and legislation demand state of-the-art analytical methods, either to meet legal regulations or to improve product and process quality. Included in these state of the art methods are highly sensitive detectors, which demonstrate the slightest contamination in a sample, therefore it is absolutely crucial to ensure that the glassware used is not a source of contamination, which could disturb the detection of analytes. For this reason it is necessary to test the applications-specific suitability of the reprocessing procedure.

Industries such as pharmaceutical, biotechnology and medical device manufacturing require strict documentation and verification to ensure that all equipment is installed, operating and performing according to specifications.

By Les Marshall, has worked as the Sales & Marketing Director for Miele Professional for the last 7 years. He has a long background in the industry, and has worked with commercial machines for over 25 years.