purified gas that has an impurity concentration below the minimum detection limit (MDL) of the analytical instrument, pure gas not containing the component to be measured, and as similar to the matrix of the measured sample as possible, used in establishing the zero, or no response, adjustment of an instrument, puhastatud gaas, milles lisandite kontsentratsioon on väiksem kui analüüsiseadme minimaalne avastamispiir (MDL)