METHOD OF DETECTING LACTIC ACID VAPOUR IN AROMA OF TRUE MILK SOLUTION Russian patent published in 2009 - IPC G01N33/04 

FIELD: physics; measurement.

SUBSTANCE: present invention relates to the food industry. The method involves preparation and taking a sample, preparation of the detecting device for operation, putting the sample into a cell, and registration of the analytical signal. The detecting device used is a cell with a piezo-quartz resonator, the electrodes of which are pre-modified by depositing a sorbent-solution of sulphosalicylic acid in acetone on them such that, the mass of the film after removal of solvent in a drying chamber for 30 minutes at 40°C remains at 10-20 mcg. Samples of equilibrium gaseous phase are removed using a plastic syringe from the glass weighing bottle and put into the cell for detection through a hermetic seal. The analytical signal is registered after every 5 s until establishment of equilibrium in the sorption system. From the difference F_F of frequency of oscillation of the piezo-resonator, modified by the film of sulphosalicylic acid, and Fs -frequency of oscillation of the piezo resonator during sorption of the lactic acid vapour, the sensor response ΔF (Hz) is calculated, which is the maximum change in frequency of oscillation of the sensor during sorption, and a calibrating graph is plotted of ΔF versus concentration of lactic acid vapour in the region of small values (s, mg/m³), and concentration s, of lactic acid is calculated from equation: ΔF=4.5·s.

EFFECT: provision for elimination of the sample preparation stage, increased number of determinations without replacing the sorbent and use of complex and long-term equipment.

2 tbl, 2 ex