Determination of sulfur forms in wine including free and total sulfur dioxide based on molecular absorption of carbon monosulfide in the air-acetylene flame

A new method for the determination of sulfur forms in wine, i.e., free SO2, total SO2, bound SO2, total S, and sulfate, is presented. The method is based on the measurement of the carbon monosulfide (CS) molecular absorption produced in a conventional air-acetylene flame using high-resolution continuum source absorption spectrometry. Individual sulfur forms can be distinguished because of the different sensitivities of the corresponding CS molecular absorption. The sensitivity of free SO2 is about three times higher than the value for bound SO2 and sulfate. The method makes use of procedures similar to those used in classic reference methods. Its performance is verified by analyzing six wine samples. Relative standard deviations are between 5 and 13% for free SO2 and between 1 and 3% for total SO2. For the validation of the accuracy of the new method, the results are compared with those of reference methods. The agreement of the values for total SO2 with values of the classic method is satisfactory: five out of six samples show deviations less than 16%. Due to the instability of free SO2 in wine and the known problems of the used reference method, serious deviations of the free SO2 results are found for three samples. The evaluation of the limits of detection focuses on the value for free SO2, which is the sulfur form having by far the lowest concentration in wine. Here, the achievable limit of detection is 1.8 mg L-1.