One of the compounds Kevorkian used in his assisted suicide machine was Potassium Chloride.
If you are eating a decent diet, you are already getting what you need, or most of it. A daily vitamin like Centrum can't hurt.
I would stay away from these supplements of selenium, chromium, etc. These are toxic metals except in very, very tiny amounts.
There are only about 3 vitamin manufacturers in the world. They supply the companies that distribute them or formulate them into multivitamins.
There is no difference between synthetic and natural vitamins. The natural vitamin may be formulated with some other compounds that may or may not be beneficial but the vitamins themselves are no different.
If you want your antioxidants, drink orange juice, tomato juice, cranberry juice, grape juice, raspberry juice or pomegranate juice. Or red wine. Make sure they don't have the evil high fructose corn syrup added.
Vitamin C and E are often added to foods for their preservative powers. The anti-oxidants in cranberries and raspberries are benzoic acid and sorbic acid, respectively. You see them all the time as sodium benzoate and potassium sorbate. But then, they are the evil preservatives that must be stamped out. There's actually more benzoic acid in cranberries than the FDA allows to be used as a preservative.
Since vitamin E is an oil it's used to preserve oils and oil-containing foods. The marketing guys hype it as being in there just for you.
Sugar is a great preservative and it's why many snack cakes don't require preservatives. Like Twinkies.
Likewise, your carotenoids, lycopenes, vitamin A, etc. have anti-oxidant powers as they themselves are easily oxidized. But if you eat too much of them you'll get carotenosis, or orange-colored skin. Ewwww. Tomatoes, peppers, squash, carrots.
Dark green leafy vegetables, the kind most people don't like, are high in the B vitamins and folic acid. Eat red and green leaf lettuce, kale, collards, cabbage, turnip greens, spinach and stay away from the tasteless iceberg lettuce.
Some famous dude once said "moderation in all things." Pretty good advice.
Warning: I am an organic chemist with a master's degree. I did Suzuki coupling reactions with boronate substituted isoxazoles, real exciting stuff.
