In today’s busy laboratories, technical staff are often subjected to intense time and work pressures as they monitor multiple analysis systems and evaluate results simultaneously. The automation of daily analyses can represent an important opportunity for valuable time savings.
The determination of dry mass and ash – one of the most important parameters in the analysis of many materials and substances – is an area in which automation can effectively increase sample throughput and reduce stress on technical staff. Moisture has a direct effect on the shelf life of foodstuffs, while ash content provides information about mineral content. Moisture and ash are thus parameters for the quality of foodstuffs, the determination of which is prescribed for all product groups in food registers.
For example, the ash content correlates with the extraction rate of grain and serves to directly typify flour. With meat products, moisture and ash content is included in the calculation of carbohydrates. For milk, “traditionally, ash determination is done … to verify it has not been watered down,” says Monika Roth-Blum of Precisa Gravimetrics’ application laboratory.
To determine the ash content manually, the sample is first weighed, burned in a muffle furnace or a microwave at approximately 550°C, cooled and weighed. This process is repeated until the values remain stable.
“Normally, this means several hours’ work, as every analysis step has to be done by hand,” says Roth-Blum. To prevent the samples from re-absorbing moisture before back weighing, they must be placed in a dessicator to cool off. The draining agent it contains generally ensures that moisture is not re-absorbed. Despite this, this cooling-down phase is prone to error so the draining agent must be changed regularly to ensure the samples really do not re-absorb moisture and falsify the result. Cooling-down times must also be precisely adhered to, which makes the parallel working with other analyses more difficult.
Although these analyses are important they do not count as highly qualified tasks. “Due to the time-consuming work steps, technical staff are tied up with these parameters for too long, so that the analysis costs are usually significantly higher than the calculated values,” says Roth-Blum.
To simplify and optimize processes for determining ash content, laboratory staff can have the determination of moisture and ash done by an analysis device. Precisa Gravimetrics’ prepASH® automatic ashing and drying system, for example, combines the function of a drying oven, a muffle furnace, an analysis scale and an evaluation unit in one system. It permits the determination of dry mass and ash in up to 29 samples at a time, depending on the model.
The West Yorkshire Analytical Services in the UK recently began working with a prepASH system in its food testing laboratory.
Moisture and ash determination form a part of one of the most common suites for nutritional and meat content analysis at the lab, says Dr Duncan Campbell, BSc, DPhil, MChemA, CChem, FRSC, registered analytical chemist, public analyst and agricultural analyst at West Yorkshire. He explains, “Our analysis is very wide ranging: foreign bodies, nutritional analysis, additives, contaminants, authenticity, health claims etc. We use a wide range of classical and instrumental techniques. Our instruments range from flame photometers and simple spectrophotometers, through cryoscopes, Dumas nitrogen analyzer, HPLC and GC to LS-MS-MS and PCR techniques.”
A temperature profile and process gases are specified in the method used by the lab. A built-in balance permits the recording of the weight progression for every sample, automatic end-point recognition and result calculation without the samples having to cool down. The device is set up on two levels. A muffle furnace and sample dish for 29 samples and reference crucible are built into the upper level and the analytical balance and all electronics are fitted in the lower level. For the analysis, the samples simply have to be weighed by laboratory staff.
“For this, a turntable moves into position and places the crucible on the balance. After precise weighing the dish rotates again and offers up the next crucible until all 29 samples have been weighed,” says Roth-Blum. The turntable on which the crucibles are arranged in two circles lowers itself for the weighing process and places every single sample on the balance. The balance can be moved so that all samples in both circles can be weighed.
After selecting the analysis method, all further steps run automatically. During drying and ash determination, the samples are repeatedly weighed until they all exhibit a stable weight. In addition, cooling phases in the dessicator are eliminated as the samples do not have to leave the device during the entire analysis. Handling the red-hot crucibles when they have to be removed from the furnace – as is done with the manual method – is also unnecessary. The results are displayed automatically after the analysis is finished and can either be printed out directly or further processed on a computer. Method settings, temperature and weight changes, relevant weighing values such as initial and back weighing as well as the calculated results (eg, moisture and ash content in %) are logged.
Unlike the manual method, the analysis processes are monitored and logged continuously, which is a prerequisite for making quality assurance possible in a certified laboratory.
“The device thus makes manual processes such as back weighing of the samples and sample handling (pre-ash determination, loading or removal from the drying cabinet, muffle furnace, dessicators) superfluous, and reduces time and effort by up to 80 percent,” says Roth-Blum.
Dr Campbell says the main factor for his lab choosing the prepASH was “its small amount of operator input.”
Beyond that, he also offers a perspective on today’s food safety testing: “During my career, the modernization of laboratories with an increase in automated sample-handling techniques and information technology means that we can analyze many more samples than even ten years ago,” he says. “However, particularly in my line of work, there is still a need to understand the chemistry behind what we do and to realize that a sophisticated hyphenated technique may not provide the answer to a problem which is best solved by careful observation, simple tests and expert use of an optical microscope.”
For more details, request # 17 online at www.labcanada.com/rsc.
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