Question

1. Describe the biochemical process of vinegar production. Include in your description the biological agents involved, steps of the biochemical change and possible byproducts of the vinegar formation. 2. Find the following: a. The molecular formula, formula weight, density and boiling points of acetic acid, formaldehyde, acetaldehyde, and acetone b. Explain the proper procedure to avoid the evaporation of volatile compounds during the preparation of the calibration standards. 3. Based on the above-mentioned information: a. Design a gradient elution method for the analytes on a JW-Wax or Carbowax column (plot it as a GC-Gradient chart). Use figure 4 of the instrument standard operating procedure (SOP’s) as a guide b. Predict the elution order of the analytes under your proposed conditions. NOTE: Visit www.agilent.com or www.sigmaaldrich.com to check the stationary phase properties. Search on the web to device an isothermal and gradient method suitable for the analysis of the sample. Remember that you need a resolution greater than 1.0 and 1.5 for qualitative and quantitative determinations respectively 4. Using references from the literature explain what is the Homologous Series Method and how it is used to estimate the tm in GC-FID? What is the relation between the number of carbons of the analyte and its retention time? 5. Which method is more precise, a standard addition or a direct calibration? Justify your answer.

Answer 1

1. Vinegar is the product made from the conversion of ethyl alcohol to acetic acid by a genus of bacteria, Acetobacter and is known as Vinegar bacteria or acetic acid bacteria (AAB). AAB are characterised by
   their ability to convert ethyl alcohol (C₂H₅OH) into acetic acid(CH₃COOH) by oxidation. The biochemical process involved are:
   CH2CH2OH +(0) Ethyl alcohol oxygen CHẶCHO +H,0 CH3CHO+H,0 Acetaldedyde Water CH2CH + (OH)2 Hydrated acetaldehyde CH2CH(OH)2+(0) (Aldehyde) + Dehydrogenase CH3COOH+H,0 Acetic acid