Monier-Williams procedure

Determination of sulfite - Part 1 Optimized Monier Williams procedure... 

Acid-induced decomposition is the basis of many methods of determining the presence of sulfite in foodstuffs. One of the best known methods is the Monier-Williams procedure, in which the sample is refluxed with HC1, and the S02 driven off is estimated iodometrically. 

It is important to note, however, that sulfonic acids formed by the addition of bisulfite to a double bond do not decompose on heating with acid, i.e., the Monier-Williams procedure will not assess sulfite bound in this form. 

Roughly 10 years ago, an ion-pair HPLC was introduced for the determination of sulfites in foods (32). The method combined the chemical approach of the Monier-Williams technique for liberating the sulfite from the matrix with ion chromatography. The ion chromatographic procedure... 

In one study, a modified Monier-Williams method has been utilized as a preparative procedure to obtain both the free and bound sulfite fractions. The two fractions were analyzed by HPLC with indirect photometric detection using a 250 X 4.6-mm LC-SAX column eluted with potassium hydrogen phtalate (0.15 g/L, pH 5.7) and detected at 280 nm. Levels of 5-10 ppm of S02 in foods, corresponding to 30 - 60 ng injected, were reliably detected by this method. The results confirmed that the chromatographic method, unlike the Monier-Williams method, is able to avoid the potential interference of volatile substances derived from matrices or utilized chemicals (36). The HPLC conditions are summarized in Table 3. 

A long-established procedure for the determination of sulfur dioxide is the Monier-Williams method in which sulfur dioxide is distilled from an acidified solution and the vapor passes through U-tubes containing hydrogen peroxide which oxidizes it to sulfuric acid. The acidity produced is then titrated with dilute standard alkali. This procedure is preferred to an iodimetric titration when volatile sulfur compounds are present as in mustard, onion, and horseradish. Sulfur dioxide may also be... 

Monier Williams in an investigation on the determination of lead in foodstuffs, critically reviewed the methods available and suggested a combination of that by Allport and Skrimshire using wet oxidation with sulphuric and nitric acids and that by Francis, Harvey and Buchan, in which the dithizone-extracted lead is precipitated as sulphate. The latter procedure eliminates bismuth and the colour developed with ammonia from nitric acid digestion. Finally, the lead sulphate is dissolved in ammonium acetate and the lead determined colorimetrically as sulphide. The method is as follows ... 

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