He was primarily known as a chemist and discoverer of the chemical element ruthenium, which he named after his homeland of Russia,[2][3] but also as one of the first scientists who applied quantitative methods in botany.

Although he had not received formal education, at age 21, Claus managed to pass the State exam in the pharmacy at the Military Medical Academy of St. Petersburg, becoming the youngest pharmacist in Russia at that time.

[4] In 1827, Claus became involved, as an assistant of Eduard Friedrich Eversmann, in the botanical research of the steppes of the rivers Ural and Volga.

[7] In 1834, while still studying at the University of Tartu, Claus went into another botanic trip to the trans-Volga steppes – this time with chemistry professor Gebel.

He graduated in 1835, and in 1837, defended his PhD thesis on analytical phytochemistry ("Grundzüge der Analytischen Phytochemie") at the University of Tartu.

In the same year, he applied at the St. Petersburg Medical-Surgical Academy for an academic position and obtained a post of the head of chemical laboratory at Kazan State University.

He noted the similarity of the chemical properties of ruthenium, rhodium, palladium and platinum and meticulously documented his results.