Ascorbic acid (vitamin C) testing is as easy as 1, 2, 3!
Vitamin C besides being an essential nutrient is also used in a variety of applications. Luckily, ascorbic acid concentration can be determined photometrically without a hassle!
What is Ascorbic Acid?
Most people know ascorbic acid as Vitamin C. Vitamin C occurs naturally in a variety of fruits and vegetables and is essential for a person to be healthy. The exact amount of vitamin C needed per day varies by age and medical conditions, however, it is undisputed that some vitamin C is needed daily. It is an antioxidant that aids in bolstering the body against oxidizers, and plays a critical role in the production of things such as neurotransmitters.
Is Ascorbic Acid More Than Just A Vitamin? Why yes, yes it is! When researching vitamin C, we were quite surprised by the myriad of uses for vitamin C across a wide number of industries.
Which Industries Test for Ascorbic Acid?
Food and Beverage
Uses of ascorbic acid in the food and beverage industry are pretty diverse. Not only can vitamin C be found in some foods naturally; fortification of foods with vitamin C is also common. Not only is this a way to incorporate more vitamin c into the average diet, but it can also play a key role in food quality and safety. Vitamin C can be used as a flavor enhancer as well as a preservative. It is commonly used as a preservative in items such as jams, jellies, bread (gluten enhancing), preserved meats, ground meat (reduces oxidation), and more! Why is it used? Well, it is safe for consumption and is a great pH adjuster. The pH of foods and beverages (such as wine and beer) can be adjusted to preserve the flavor as well as the integrity of a product. The pH adjustment can mean the difference between an item being shelf-stable, or spoiling.
Cosmetics and Skincare
Vitamin C can be found in all sorts of lotions, creams, balms, toners, scrubs, and cosmetics. Ascorbic acid aids the body in working against free radicals and pollution in the environment. In facial care, vitamin C has proven effective in smoothing fine lines and wrinkles. Had a bit too much sun? Vitamin C can help heal photodamage, and it can lighten dark spots. It also aids the body in producing collagen and adsorbing it. In the long term, this can result in more youthful-looking skin.
Ascorbic acid can be used in water treatment plants and at home as a dechlorinator. Chlorine is commonly used as a sanitizer to make water safe for drinking, bathing, and swimming. Dechlorination does happen naturally if the water is allowed to stand in air and UV light (sunlight) long enough. This is useful in small batches (ie. a gallon or two of water for an aquarium), but if a larger amount of water has to be dechlorinated, that method is a bit costly in terms of time and space. Using ascorbic acid to dechlorinate water allows treatment plants to put water back out into the environment. On a smaller scale, people at home can use ascorbic acid to dechlorinate water coming out of their taps and showerheads (there are attachments preloaded with vitamin c on the market).
A few more examples would include in research (i.e. cell cultures, pH adjuster, purification of water), pharmaceuticals (i.e. vitamin production), agriculture (i.e. aids with disease defense, pH adjustment of growth medium), photography (picture development), and manufacturing (i.e.plastics).
Potentiometric vs. Photometric Titrations
To determine the concentration of ascorbic acid in samples, we recommend titration (either potentiometrically or photometrically.
To titrate for vitamin c potentiometrically, one must utilize a redox (oxidation-reduction) titration. These titrations require a titrator (or ORP Meter), an ORP electrode, iodine, sulfuric acid, and potassium iodide. One of the issues with this method is the fact that the redox reaction accounts for all reducing agents in a sample. This can potentially result in artificially high results.
Photometrically titrating for ascorbic acid is safe and easy. This method has the added bonuses of abiding by standard methods and avoiding some of the issues associated with titrating for vitamin C potentiometrically. Instead of measuring a mV change in the sample, the photometric method has a color-change endpoint. To run a photometric titration automatically, you need to have a photometric electrode with the correct wavelength, oxalic acid, 2,6-dichloroindophenol, and deionized water (in addition to the automatic titrator).
|Differences at a Glance|
|Titrant||Stabilized Iodine||2, 6-dichloroindophenol|
|Electrode||ORP||525 nm Photometric|
|Reagents Needed||Sulfuric Acid, Potassim Iodide||Oxalic Acid, Deionized Water|
|Titration Apparatus||Automatic Titrator||Automatic Titrator|
|Interferences||Reducing Agents||Highly Colored Samples|
|Industry Standard Methods||Adapted From||Yes|
Photometric Titration for Vitamin C
0.00086M ,6-Dichloroindophenol (DPIP)
2% Oxalic Acid Solution
Class A Volumetric Pipettes
150 mL Beakers
Standard Operation Procedure
Set up your automatic titrator and select the method.
Choose your sample size in accordance with ISO 6557-2 Determination of Ascorbic Acid Content – Part 2: Routine Methods.
Using Class-A glassware, transfer an exact amount of oxalic acid at 1 to 5 times that of the sample.
Bring the sample up to volume with deionized water (to the 75mL mark on the beaker).
Place the beaker under the stirrer assembly and lower it to immerse the electrode and stirrer. Ensure that the sensor portion of the electrode is 5-6 mm below the surface. NOTE: The dispensing tip should be in contact with the surface of the sample (slightly submerged).
Press “Start”. The titrator will start the analysis.
At the end of titration, when the equivalence points are reached, ‘titration complete’ will appear with the results expressed as ascorbic acid in g/L.
Remove the electrode and stirrer from the sample and rinse them thoroughly.
Record the result.
A Trio of Testing Tips
If your samples for titrating involve fresh or frozen fruits and vegetables, it can be necessary to remove seeds and seed cavity walls. Then, thoroughly mix the sample to homogenize it. Filter the sample, and then you can titrate. Too much debris in the sample can make titrating more complicated.
Frozen samples? In order to titrate them, allow the frozen samples to thaw in a closed vessel. Once thawed, make sure you do not forget to mix in the liquid formed while defrosting.
If your sample is chunky, or has suspended solids, those solids can interfere with titrations. Suspended solids can be removed or separated out via filtering or centrifuging.
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Allison graduated from Bryant University with a Master’s Degree in Global Environmental Studies. She is passionate about nature, and how science is connected to the world around us. At Hanna, she provides an array of content and support to customers through the Hanna Blog, SOPs, and Data Sets.
Allison may be reached at email@example.com.