Automating Sample Preparation in the Metals Laboratory

Preparing samples for analysis is an extremely time-consuming task. In fact, sample preparation steps can easily take up more time in the laboratory than the actual analysis. With autosamplers on analytical instrumentation, inductively coupled plasma (ICP) and ICP-MS systems can analyze samples throughout the night when analysts leave the laboratory. As laboratories continue to look for ways to save time and money, the sample preparation process is the next logical task to automate.

A yearly goal for every laboratory is to try to save money while maintaining high-quality standards and obtaining the most accurate sample results possible. One way to do this is to stay at the forefront of the latest technological advancements. This often means that laboratories not only must change processes, but also make new equipment purchases. When deciding to buy a new piece of equipment, the question becomes whether the purchase will provide a good return on investment for the laboratory, i.e., does it make sense from a business standpoint?

A common misconception often seen in the laboratory is that it is the actual analysis of samples that determines the quality and length of time of the overall analysis of a sample, not the sample preparation steps. Because of this perception, many laboratories do not deem it worthwhile to invest in sample preparation. Without accurate sample preparation, however, the analytical step is worthless, and the preparation process has to be done all over again, potentially causing the late reporting of results. If the laboratory is spending more time preparing samples than analyzing them or dealing with the quality of work issues within the sample preparation process, it becomes evident that sample preparation is what can make or break the laboratory. Automating the sample preparation process to change the balance of time in the laboratory is always a good investment.

Figure 1 - The AutoBlock accurately adds concentrated acids and heats and cools samples in a HEPA-filtered environment.

In traditional metals digestions, there are several steps that need to be done before a raw sample is ready to be analyzed for metals. Steps include washing and drying beakers, watch glasses, and volumetric flasks; adding acids and reagents to all of the samples; heating up the hotplate; checking the temperature of the hotplate; monitoring the samples during the digestion process; transferring the samples to a separate storage container; and then filtering them prior to analysis. Traditionally this has been done manually by laboratory personnel. This has been addressed with the development of the AutoBlock™ for automated metals digestion (Environmental Express, Inc., Mt. Pleasant, SC) (Figure 1). With the AutoBlock, the analyst simply selects or programs a method or methods, loads the samples, and walks away.

Figure 2 - The touchscreen controller with Windows® XP® software (Microsoft Corp., Redmond, WA) provides easy, intuitive operation.

The AutoBlock either completely eliminates the manual work in metals sample preparation or greatly reduces the time one spends doing it. It uses a controller with preprogrammed U.S. EPA methods stored in permanent memory to add the necessary acids and reagents to metals samples and to control the heating and cooling of the samples automatically (Figure 2). The controller can also be easily programmed with custom methods to meet an individual laboratory’s needs. There is an automatic purge of each reagent after every addition step to ensure contaminant-free reagent addition (Figure 3).

Figure 3 - With the AutoBlock, reagent additions and digestion times are timed automatically and performed on schedule.

The AutoBlock can run up to three different digestion methods of the same temperature at once, giving the laboratory flexibility in running multiple methods. It accomplishes this by employing three independent racking systems of 18 samples each. The thermocouple reads and records sample temperature, and the data are stored along with the data from every step in the digestion process for good record-keeping practices. The instrument performs digestions in a benchtop, HEPA-filtered environment, freeing up much-needed laboratory hood space, and utilizes the 54-well, 50-mL-volume Teflon® (DuPont, Wilmington, DE)-coated graphite block (HotBlock™) (Environmental Express) as the digestion heat source.

The AutoBlock uses disposable polypropylene tubes as the digestion vessels, eliminating the need to wash glassware and removing most chances of carryover contamination from one digestion to the next. These graduated, screw-cap digestion cups can also be used as a storage container, eliminating transfer steps and the need for a second storage vessel. Samples can even be filtered within the same digestion cup using the FilterMate™ filtration system (Environmental Express).

The AutoBlock’s heater mat provides uniform heat distribution to all samples throughout the digestion process; thus samples that start the digestion process together finish together. It is no longer necessary to continually watch samples and move glassware around on the hotplate. All digestion blocks are made from Teflon-coated graphite and KYDEX® (KYDEX LLC, Bloomsberg, PA) materials; therefore they will not corrode in the harsh acid environment of the hood.

Automating the sample preparation area of the laboratory reduces the time spent in this area and frees up personnel. In turn, results can be achieved more quickly and efficiently. The AutoBlock is a significant advance in laboratory automation.

Mr. Boyd is Technical Specialist, Environmental Express, Inc., 490 Wando Park Blvd., Mt. Pleasant, SC 29464, U.S.A.; tel.: 800-343-5319/843-881-6560; e-mail: [email protected].  

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