German to English Science Chemistry; Chem Sci/Eng NDA

I am at a loss as to what this sentence is trying to say. Hoping for an explanation of the meaning rather than a translation, but will happily accept either :)

***Die Konzentrationen der Faktoren sollen den in der Probe zu erwartenden Gehalt umschließen.***

Context: Preparation of calibration solutions:

Es werden mindestens fünf Kalibrierlösungen aus zwei unabhängig voneinander angesetzten Stammlösungen hergestellt. Die Konzentrationen der Faktoren sollen den in der Probe zu erwartenden Gehalt umschließen.

I assume, the translation should be "The concentrations of the factors should comprise the content to expected in the sample." However, I do not understand which factors are meant here (no prior mentioning) or the content of what is comprised. But then, I am by no means a chemistry expert, hopefully somebody with more expertise in this area can shed some light on this.