The phrase "a single sample of" is correct and usable in written English.
It can be used when referring to one instance or example of something, often in scientific or analytical contexts.
Example: "In the study, we collected a single sample of the water to test for contaminants."
Alternatives: "one specimen of" or "a lone example of".
There are further reasons why it may be pointless to analyse a single sample of breastmilk.
All analyses in this paper were performed on a single sample of each spleen.
Because automated controls are more reliable, only a single sample of an activity may need to be tested.
Today, I used tweezers to pick roughly 300 insects out of a single sample of swept-up and bagged vegetation.
A single sample of stem cells could, he reckons, yield 20,000 tonnes of "cultured beef".
While few details were available late Tuesday, agency officials said they had discovered melamine at trace levels in a single sample of infant formula.
In this paper we describe a single sample of nineteenth and twentieth century bows and arrows of the Ovambo, Namibia.
Governor Knowles also said a new study of discharges by large cruise ships, conducted by the state and the Coast Guard, found that "not a single sample of the sewage discharges fully complied with existing state and federal standards".
At the switch-on time instant, the length 2 FIR filter has a single sample of state that is still zero (instead of its steady-state value which is the previous input sinewave sample).
A single sample of stem cells could produce 20,000 tonnes of "cultured beef", enough to make 175m quarter-pounders that would otherwise require 440,000 cattle to be slaughtered.
An alternative top-down approach was developed to define composition in Vibrio cholerae biofilms and relied on an extensive panel of NMR measurements to tease out specific carbon pools from a single sample of the intact extracellular matrix.
