Not all waters are created equal

In our day-to-day world, water basically means life for you and me. Nothing flourishes, nothing grows without this liquid. Water is important for scientists too — as an ultrapure distillate for taking high-precision measurements. Ultimately, water with even the slightest impurities can have long-term effects on the results of analytical experiments.

In such cases, the level of quality required depends for the most part on the complexity of the scientific task being performed. Many experiments even require ultrapure water. But how is this purity actually defined these days? “There is no single, standard type of lab water; there are various degrees of purity for different applications, such as analyses,” says Oliver Mell, who oversees Lab Essentials marketing at Merck Millipore.

The road to the lab water of today was a long one. “Up until 1880, most of the analyses were qualitative, detecting what substances were present. Today quantitative analyses are more common, in other words, precise determinations of how much of a certain substance is present... Back then, the standards for lab water were not as high as they are today — and it was not even possible to achieve today’s standards because of the state of technology,” adds Mell.

The quantitative and qualitative analyses are mutually interdependent, because determining the quantity of a substance is only possible when it is known what substance it is. So the qualitative analysis always comes first, followed by the quantitative. Many substances identified by qualitative analysis may be harmless in small quantities but harmful when present in larger amounts. It is therefore important to be able to determine the exact quantity of a substance, in other words, to perform the quantitative analysis.

In former times, each laboratory created its own “pure” water, and scientists consequently often arrived at different results when conducting the same experiments. In the chemistry of the first half of the 19th century, many criteria of measurement and analysis were still being developed. Scientists were still far from the sterile methods for the production of pharmaceuticals, liquid crystals, and electrochemicals that have been required ever since the second half of the 20th century.

In 1830, Emanuel Merck experienced what it means to have neither standards nor generally established methods of verification: The “Société de Pharmacie” in Paris was searching for methods that could be used in forensic medicine to detect the presence of alkaloids with certainty. Although Merck’s efforts were applauded, his results could not be reproduced.

Later, the chemist Justus von Liebig found out why different results were attained in Paris. “I have repeated Mr. Merck’s experiments for the most part and found them quite correct,” he said. “One can therefore presume that the differing purity of the substances the commission used to conduct its experiments was the only factor that caused its results to diverge from those of Mr. Merck.”

Establishing the quality of a substance or a process thus requires that standards be set, that norms be introduced, and that testing methods be available. These standards did not exist in Merck’s day. Nevertheless, his products were still deemed to be some of the best of his age, and they earned him numerous national and international awards. Even the Parisian manufacturers, otherwise leaders in this sector at the time, bought from Merck — not only because the quality of the products was unique, but also because they heeded the preferences of their customers.

In 1888, Carl Krauch published The Testing of Chemical Reagents for Purity (“Die Prüfung der chemischen Reagentien auf Reinheit”), a definitive work that was to set the standard in analytical chemistry. The text grew from 60 pages in the year 1888 to almost 700 pages in 1939. In the year of the first edition of the work, Merck committed itself to selling only reagents that had been tested according to the criteria published by Krauch.

Beginning in December 1888, these were marketed as “guaranteed pure reagents” with the tag pro analysi (meaning “for analysis” in Latin, i.e., sufficiently pure for analytical purposes). These products subsequently led to generally accepted purity standards in the world of chemistry.