Observations on Vitamin analysis:
Odor: The only one with an odor is B1 (Thiamine), and that’s due to an ever-present miniscule breakdown product of the odorless parent molecule. Bulk Retinol concentrate has a faint creamy rose odor, possibly from tiny amounts of diterpene breakdown products.
Color: The water soluble vitamins are all white powders, with 2 exceptions (Riboflavin & B12 in all its various forms, due to the cobalt at the center of the molecule). B12 is structurally related to hemoglobin and chlorophyll (porphyrins or tetrapyrroles). Riboflavin has a rich dark orange yellow color, even when highly dilute; it’s also strongly fluorescent. There was an incident of shredded wheat cereal that had an unsightly appearance from unevenly distributed, sprayed-on riboflavin and reduced iron. Of the fat soluble vitamins, only the Carotenes have color (carrots, tomatoes, watermelon, cantaloupe, sweet potatoes).
The main fat-soluble vitamins (A, D, E): Beta-Carotene and the other carotenoids are 40 carbon tetra-terpenes, and are unrelated to keratin (a protein). Bulk Retinol concentrate (a 20 carbon di-terpene) is an oily liquid that might have a faint yellow coloring. Some but not all Beta-carotene is converted in the body to retinol (Vitamin A), while other carotenoids (lycopene, lutein) have no provitamin A activity. The carotenoids are very good antioxidants in the plants as well as in stored food and in the human body; retinol is not as powerful an anti-oxidant as the carotenes. The vitamin E Tocopherols ( (27, 28 and 29 carbon tri-terpene derivatives) are viscous oily liquids without much color. They also are good anti-oxidants in the food and in the body The D vitamins also are triterpene derivatives (with 27 and 28 carbons), nearly identical to the cholesterol molecule. D2 and D3 are white powders. Vitamin K as well comes from the terpene/isoprenoid pathway.
This is based on personal observation of USP (& other) reference standards used for quantifying vitamins with LC (HPLC). I spent time on all the vitamins except K.
GC-MS, limited use: The tocopherols and niacin are the only vitamins where GC & GC-MS can be used easily, and their unmistakable peaks always provide valuable markers when analyzing food of any type. The tocopherols are among the latest eluters (have the highest boiling point) in normal GC conditions, and this makes them even easier to recognize, when their molecular weights are shown with the mass spec. Retinol and D2/D3 seem like good candidates for GC separation, except they suffer thermal degradation in the hot injection port without ever reaching the separating column intact. Cool on-column injection was successful but is impractical for a workhorse instrument, and the extra time for a 2nd run provides small return value during busy routine multi-residue analysis (not to mention gunking up the front opening of the capillary column).
The earlier classical spectrophotometric assays were largely replaced with the more specific LC separations, except when a large number of samples had to be turned around quickly. Titrimetric assays were also no longer needed.
Measuring the large amounts present in vitamin tablets was much easier than measuring minute levels in foods (with all the additional matrix interferences compared to the concentrated tablets).
Several of the vitamins have native fluorescence in the visible or UV range (without needing derivatization).
During food production, both under-fortification and over-fortification are concerns. The 3 main fat-soluble vitamins (A, D, E) can be toxic because the body doesn’t excrete them as quickly as water-soluble vitamins. Excessive Niacin can cause a rapid onset allergic-like reaction similar to that of histamine (from certain fish, especially tuna, mackerel, mahi-mahi). There have been incidents in large batches of fortified rice having concentrated pockets of unevenly mixed vitamin powder.
Dan Harring (54) 