In order to find the Vitamin C content you will need to use a process called titration which, according to the Columbia Electronic Encyclopedia, is when you add a chemicals to a liquid in order to create a reaction which can determine the content of a substance inside the liquid. This is how you will find the Vitamin C content of different juices. Iodine will be added to the juice, which will create a reaction that can help determine the Vitamin C content. To start, pour 30 milliliters (mL) of Lugol’s solution into a 500 ml graduated cylinder. Add enough distilled water to bring the level of fluid to 300 mL.
Slowly pour the diluted solution into the amber glass bottles, using a funnel. Store the bottles in a dark place, keeping the bottles tightly sealed. Rinse and dry the 500 ml graduated cylinder. Next, you need to make a starch indicator solution, to add to the juices. This will help find the Vitamin C content by determining when the titration is complete. When the Lugol’s lodine is added to the juices and they react, the starch indicator will turn the juice a different color, once the Lugol’s lodine and the Vitamin C in the juice complete their reaction.
To make the starch indicator, heat 200 mL of distilled water in a pot on the stove. When it is near boiling, add 1 gram (which is 1/4 teaspoon) of soluble starch powder to the pot. The exact amount of starch is not extremely important. Stir to dissolve the starch, making sure the water is close to boiling point. The starch may take 4-5 minutes to fully dissolve. After the starch is dissolved in the water, turn off the heat and let the solution cool. When the starch solution has cooled, store the solution in a tightly sealed glass jar.
Next you will need to make a fresh vitamin C standard solution (at a concentration of 1 milligram [mg] per milliliter, or 1 mg/mL). This solution will “standardize” your iodine titration solution. You will find how much Lugol’s lodine Solution is needed to titrate a known amount of Vitamin C. Then, you can use the Lugol’s lodine Solution to determine the amount of Vitamin C in the produce juices. To make the Vitamin C standard solution, crush a 250 mg vitamin C tablet with a knife and cutting board. Take the powder and put it in a bowl.
Dissolve the powder in 100 mL of distilled water. Pour the dissolved Vitamin C into the clean 500 ml graduated cylinder and add distilled water until it reaches a level of 250 mL. Next, set up the 50 mL buret on the ring stand. To do this, screw the metal rod into the black metal base. Screw the buret clamp on the top of the ring stand’s metal rod. Finally, slide the buret into the clamp. After setting up the buret, measure out 20 mL of vitamin C standard solution. Then, pour this into the 50 mL Erlenmeyer flask.
To begin the titration process add 10 drops of starch indicator solution to the Erlenmeyer flask. Make sure the bottom of the buret is turned to the closed position. This is done by turning the red stopper to the horizontal position. Next, use the funnel to carefully fill the buret with the diluted Lugol’s iodine solution. Fill it somewhere between the 5 mL and 35 mL marks on the buret. The position does not, as long as the Lugol’s Solution is between 5 and 35 ml. To make sure your measurements are accurate, make sure the tip if full of Lugol’s lodine Solution and it is free of large air bubbles.
To do this, put the extra beaker below the buret and turn the red stopper at the bottom of the buret to let a few drops of Lugol’s lodine solution flow into the tip of the buret. Make sure the buret stopper is closed and put the Erlenmeyer flask under the tip of the buret. Next, write down the initial level of the Lugol’s iodine solution in the buret. Now, turn the red stopper at the bottom of the buret until one drop of the iodine solution drips out into the flask below it. Then close the buret again.
After a few drops are added, swirl the flask to mix in the juice and the iodine together. Carefully continue adding the iodine solution, making sure to swirl the flask, until the iodine creates a blueback color throughout the solution that lasts for longer than 20 seconds. Once this happens the titration is done. Record the final level of the iodine solution remaining in the buret, after titration. The difference between the initial level and the final level is the amount of iodine titration solution needed to create a reaction with the vitamin C.
Rinse out and dry the Erlenmeyer flask. Repeat step 17-26 three times with the Vitamin C standard solution. You should get results that are within about 0. 5 mL of each other. If you do not, repeat this step until you have three results that are within about 0. 5 mL of each other. Be sure to check the level of the iodine solution in the buret before each trial. Remember, if the level is below the 35 ml mark, carefully add more iodine solution to the buret (until it is between the 5 mL and 35 mL marks). Record the new level. Prepare juice from each fruit or vegetable for testing.
Use the juicer to extract 60 mL juice from each food tested. Remove any stems or seeds from each of the types of produce. You need 20 mL of juice per titration, and you should do at least three titrations per food, so you will need at least 60 ml total. Filter the juice through a strainer to remove any pulp and seeds. Titrate the juices you just prepared by repeating step 17-24, but this time, use 20 mL of each juice in the Erlenmeyer flask instead of 20 mL of the vitamin C solution. Be sure to check the level of the iodine solution in the buret before each trial.
In step 23, the titration is complete when the iodine creates a distinct color change in the juice/starch solution. This color change will be harder to see than with the vitamin C solution, since the juice starts out in a different color. For example, when testing an orange, the color will change from orange to grayish brown when the endpoint is reached. If you continue to add iodine, the color will darken further, but you want to note the volume of iodine added when the color first changes. Remember to record the final level of the iodine solution in the buret, as done in step 24.
The difference between the initial level and the final level is the amount of iodine titration solution needed to oxidize the vitamin C in each juice Repeat the titration process for each juice a total of three times. You should get results that are within about 0. 5 mL of each other. Remember that for each food being tested repeat the previous steps for finding Vitamin C exactly the same, but three times for each food. Once the difference in iodine levels for each test is collected, use the following equation to find the Vitamin C content. Equation to find Vitamin C in Produce: odine1 is the amount of iodine (in mL) needed to titrate the vitamin C standard solution.
Vitamin C1 is the amount of vitamin C in the standard solution (in mg). This number should be 20 mg, if 20 ml of Vitamin C standard solution was tested. lodine2 is the average amount of iodine (in mL) needed to titrate the produce juice sample. Vitamin C2 is the amount of vitamin C in the produce juice sample (in mg). Record and compare the total amount of Vitamin C in each type of produce in order to determine which type of produce has the most Vitamin C.