The Benefits of Machine Washing Laboratory Glassware Versus Hand Washing

If the aim of the laboratory is to be cost-efficient and provide consistent results, hand washing should not be the process of choice for cleaning laboratory glassware. Hand washing not only presents inherent safety risks for employees, but is also not a repeatable process and produces variable results. Automating the washing process is one step that can be taken that will help modernize the laboratory by making it a safer and greener work environment, streamlining the operation and providing a huge cost savings in the long run.

Lacking standards

The first problem with hand washing laboratory glassware is that there is no standard operating procedure (SOP) for the process. A quick search on the Internet for standard methods to clean chemical laboratory glassware will uncover a host of solutions. At Frostberg Education’s General Chemistry Online,1 for example, one reader writes in for some guidelines on cleaning glassware and is instructed to use 20 g ammonium peroxydisulfate in 1 L of 98% sulfuric acid and soak for 30 min. “This is the cleaning solution from hell but it’s not as bad as the chromic acid witch’s brew chemists used to use—which is corrosive and a carcinogen.”

Unfortunately, what this author refers to as “witch’s brew” is still being suggested by many sources. At,2 for example, chromic acid is suggested for use when glassware is just too dirty to be cleaned by hand washing alone. Another Web site,,3 provides instructions on traditional chromic acid cleaning and how to prepare the solution using sodium dichromate dehydrate and sulfuric acid. It cautions that the dichromate should be added to the acid slowly because the mixture can heat and spatter. It also mentions that there are reports on how to regenerate the spent chromic acid to reduce disposal quantities, since it is no longer considered appropriate to pour it down the drain! Another suggestion is to use physical abrasion methods, such as sand, pumice, glass spheres, or walnut shell chips.

Chemistry.about.com4 recommends the use of acetone or ethanol for cleaning water-insoluble debris. This is a typical approach that many laboratory technicians use since a solvent or alcohol has the ability to dissolve water-insoluble residues. This leads many to believe that water-based cleaning will simply not work. In reality, hot water combined with the correct detergent and proper mechanical cleaning action can remove water-insoluble residues from glassware. It does this not by dissolving the residue the way acetone or ethanol would, but rather by physically removing it from the surface of the glassware and suspending it.

The University of Rochester Web site5 recommends several possibilities for “aggressive cleaning,” including soaking in a 6 M HCl solution, aqua regia, acidic peroxide solution, chromic acid, or hydrofluoric acid. These recommendations come with strong warnings for students such as: “Extreme caution must be used when working with aqua regia because it generates Cl2 and NOx gases in addition to causing severe tissue damage.” Acetone rinses and acid washes using nitric, aqua regia, HCl, and dichromate soaks are common procedures to be routinely performed for general cleaning, according to various sources. Even the Standard Methods Handbook for the Examination of Water and Wastewater6 gives a procedure.

While the Standard Methods Handbook attempts to provide direct washing instructions for specific tests, such as acid washing glassware for metal analysis, the directions are still lacking. In Section 3500-A3 (Iron, Introduction, Sampling and Storage), the author directs laboratory personnel to clean sample containers with acid and rinse with reagent water. There is no direction on what type of acid to use, how long to clean, or how to determine when an item is “clean.” Nor does it mention how long the container should soak, or if the acid should be poured into the container and immediately poured out. Other sections are a bit more detailed, but still leave much room for interpretation.

In the Handbook’s Section 3500-AL (B2B for Aluminum Determination by the Eriochrome Cyanine R Method), the author states: “Treat all glassware with warm 1 + 1 HCl, and rinse with aluminum free DI water to avoid errors due to materials absorbed on the glass. Rinse sufficiently to remove all acid.” There are no details given on how warm the water should be, and, if this is a soak, how long it should soak and if all glassware should be treated the same.

Other methods follow this same pattern of leaving important cleaning variables unspecified. Some of the questions typically left unanswered by these standards are: How long should the item soak? What is the exact acid solution or concentration? How long should the glassware be subjected to a DI rinse? How many DI rinses should take place? What are the proper temperatures for the soaking and DI rinsing steps to obtain the best results?

Clearly, the need for an SOP is essential if adopting a hand washing program in a laboratory, yet even the establishment of an SOP for washing glassware will not translate into consistent cleaning results. An SOP will help in attaining a higher level of consistency, but is still subject to human judgment, variations, and limitations. That leads to some questions about the effectiveness of the hand washing system in general, and the health hazards involved with the handling of these chemicals, especially since laboratory work involves unavoidable exposure to hazards in the daily routine.

Variable results

Hand washing provides variable results for a variety of reasons. First, the task is inefficient because there is no control of the quality of the process. It is a manual job performed by a human who is subject to a great deal of variation. Different people clean to varying degrees. Some scrub harder or rinse more thoroughly, and respond differently to hot temperatures; indeed, the hottest water temperatures for best cleaning cannot even be used because the lab technician will get burned. Thus, the temperature of the water is determined by the hand washer’s tolerance for heat, not by the intensity of cleaning needed.

Consistency is also not guaranteed. If 10 laboratory technicians follow a given washing procedure, they will not all wash the glassware in exactly the same way. Even if they do have a set procedure, for example, initial rinse for 2 min, scrub for 1 min, and final rinse for 2 min, are they timing it exactly? When faced with hundreds of dirty test tubes, does the technician wash and rinse each one in exactly the same manner? The tools used to perform the washing procedure are also precarious variables. For example, the brushes being used can become worn out and can scratch the glass surface and ruin the glassware. The amount of detergent used is also variable and will differ from item to item.

Automation delivers consistency

Simply stated, a high-quality laboratory glassware washer eliminates these variables and delivers the accuracy that is imperative in the research world. By carefully balancing time, temperature, chemical dispensing, and mechanical action, the laboratory glassware washer provides effective, repeatable cleaning results without long wash times. By using hotter water combined with the proper cleaning agents, and rinsing with the aid of acid neutralizers, glassware can be cleaned in a shorter amount of time. The balance of these factors results in a wash that is more rigorous than hand washing—it is more controlled, more repeatable, and safer for laboratory technicians.

Unlike many spray-type washers that rely on pressure to blast off contamination (like many home dishwashers), a well-designed laboratory glassware washer cleans by creating a high water flow over a surface. The circulation pump turns over more water per minute under low to medium pressure. This will provide proper cleaning without the risk of breaking small or delicate items. These machines are programmable and can heat water to a designated temperature, measure the actual temperature, and control it to a set point. There are also built-in safety features on the machines, which are crucial to achieving consistent results. A wash cycle will only run to completion if all parameters are carried out correctly. If not, an error display is revealed to alert the operator that the unit is not functioning. For example, if temperature is not reached, the proper amount of detergent is not dispensed, or there is a lack of water flow, a high-quality laboratory glassware washer will alert the user to these conditions. This technology allows laboratory washers to provide repeatable, documented, and valid cleaning results.

Proven and tested

Various tests have been conducted that verify and document the effectiveness of automated glassware washers. In one test, conducted by Paul Bowers, John George, and Jerry Thoma of Environmental Health Laboratories (South Bend, IN), acid washing by hand was compared to machine washing, with favorable results.7 In another, conducted by Katrin Georgi and Karl-Siegfried Boos of the Institute of Clinical Chemistry, University Hospital (Munich, Germany), the cleaning ability was tested by using two very different contaminants, one hydrophobic and the other hydrophilic, to show that the contaminant need not be dissolved in the wash solution, but simply taken off the surface of the glassware and not redeposited as the cycle proceeds.8 Other tests demonstrate the cleaning capacity with respect to detergent residue removal.7 Most importantly, end users report good results using laboratory glassware washers and eliminating acid washing by hand. One major environmental testing laboratory uses all automated wash systems. They report that even the glassware used for orthophosphate testing does not give them any problems since they eliminated acid washing by hand. These results prove that laboratory glassware washers are effective, even for residues that many researchers assume must be cleaned by hand with solvents, alcohols, or acids.

The cost of not automating

There is no getting around the fact that the original outlay for a laboratory glassware washer will be a sizable capital expenditure. However, it is necessary to analyze the purchase beyond the initial cost of the machine: The price for not automating will be considerably higher in the long run. A repeatable process is being created—a machine that will deliver consistently clean glassware every day, with results that cannot be duplicated by any hand washing method. Additional gains include a greener laboratory and reduced labor costs associated with the hours needed to wash glassware by hand. Laboratory technicians have more free time for other tasks. A quick look at the return on investment (ROI) based on labor alone reveals that if someone is being paid $12 per hour for hand washing 25 hr per month, a $9000 washer would pay for itself in 30 months. Labor is only one avenue for savings; calculating total hand washing costs is very difficult because other variables, such as how long water is left running, glassware breakage, and amount of detergent used, are tricky to calculate correctly. There are costs associated with those variables that are virtually eliminated with the use of an automated system. Laboratory glassware washers use detergents with monitored dispensing; thus there is a reduced cost in detergents, brushes, and gloves. Since no solvents or alcohols are being used, cost is reduced in their purchase and disposal. Because water fills are set and programmable, deionized (DI) water costs are reduced and can be easily calculated. While manual labor costs are not eliminated with an automated washer, they are significantly reduced, enabling technicians to spend time on other tasks. Although it is difficult to assign a dollar value to the faster turnaround in getting clean glassware back on the shelf for reuse, most would agree that this time savings is very valuable. Chemical test setup and the carrying out of those tests are far less likely to be delayed because of time spent preparing and organizing the glassware.


There are both tangible and intangible benefits to automating the laboratory glassware washing process. Labor savings, a greener laboratory, time savings, and reproducible results are benefits that will differ significantly from laboratory to laboratory; however, all laboratories stand to gain in the end. Good, solid test results that can be trusted are the greatest advantage. Obtaining those results in less time and with fewer materials results in an overall gain in productivity. Higher laboratory efficiency invariably leads to a better work environment and higher overall satisfaction in the laboratory, in turn, often leading to greater accomplishments in the laboratory.


  6. Standard Methods Handbook for the Examination of Water and Wastewater; APHA, AWWA, WEF: Baltimore, Maryland; 20th Ed.
  7. Bowers, P.E.; George, J.E.; Thoma, J.J. Evaluation of the Miele Laboratory Glassware Washing System for the Cleaning of Sample Containers for Reuse, Environmental Health Laboratories, A Div. of MAS Technologies, South Bend, IN, 1993.
  8. Georgi, K.; Boos, K.S. Investigating the cleaning efficiency of a laboratory glassware washer when using tandem mass spectrometry. Am. Lab. News 2004, 36(19) 34–6.