There are two widely-available grades of iodine: "crude" and "resublimed," the latter of which is crude iodine that has been further refined via a vaporization/crystalization process. ACS-grade iodine is resublimed iodine which satisfies the ACS requirements. The following quotations are included to support these statements:
Commercial-grade crude iodine normally has a minimum purity of 99.5% I2: the main impurities are water, sulfuric acid, iron, and insoluble materials (Lyday 1999 [see excerpt below]). Specifications of the U.S. Pharmacopoeia [USP] XVII call for crude iodine to be not less than 99.8% I2. Resublimed iodine is usually 99.9% pure, and American Chemical Society (ACS) specifications call for not more than 0.005% total bromine and 0.020% nonvolatile materials (Anon. 1971).
from Industrial Minerals & Rocks, 7th edition, By Jessica Elzea Kogel p 549
Commercial crude iodine normally has a minimum purity of 99.5%. Impurities are chiefly water, sulfuric acid, iron, and insoluble materials. The USP XVII specifies iodine content of not less than 99.8%. The Committee on Analytical Reagents of the American Chemical Society allows a maximum of 0.005% total bromine and chlorine and 0.010% nonvolatile matter.
from Iodine By Phyllis A. Lyday
So, there's really only one grade of non-crude, refined ("resublimed") iodine which is widely available, and that is ACS-grade. After a batch is refined, it is tested for compliance to the ACS specification , which limits total impurities to 0.01%, or 100 ppm, implying a purity requirement of 99.99%. Considering that the quantity used for dietary purposes is on the order of 5 mg per day typically, total impurities would be on the order of 500 nanograms, or 0.5 micrograms. You probably get more in the air you breathe on a daily basis.
Besides water and iodine, Lugol's solution contains potassium iodide, and the ACS grade is typically used. The spec for Potassium Iodide, ACS includes a list of impurities and the maximum permissible level for each. Those that aren't listed specifically would fall into the category of "insoluble matter," which is limited to 0.005%, i.e. 50 parts per million. Soluble matter would have been removed by the manufacturing process, so the spec covers everything that could be present, including residues of chemicals used in the manufacturing process. My main concerns would be the heavy metals, which are low to begin with (again, in the single-digit nanogram range), and which Lugol's solution helps the body to expel.
Putting "USP grade" into context
USP-grade ingredients, which are typically ACS (or lower) grade ingredients which have passed certain tests related to their suitability to be used in or on the human body, are also available. In order to legally sell Lugol's solution for human consumption, the ingredients must pass these USP-mandated tests, and certain USP-approved manufacturing standards must be met. I gather that the designation "lab grade Lugol's solution" is Lugol's solution that was made with ACS-grade materials and wasn't subjected to the USP tests. However, I would check the manufacturer's specification to be certain that ACS-grade materials were used.
It is my understanding that J Crow's (http://www.jcrow.com
), one of the major suppliers of USP-grade Lugol's solution to consumers, uses ACS grade ingredients. They indicate that their product is "USP grade or higher," which is true of anything that exceeds the relevant USP requirements. Considering the high purity of ASC-grade materials, it would seem that the USP testing is a formality which must be performed in order to be absolutely certain that a product is safe for human consumption. However, CHANCES ARE that "lab grade" Lugol's solution made from ACS-grade materials by a reputable company (such as those who manufacture aquarium chemicals) would be essentially identical to the typical USP-grade Lugol's solution.
Considering A) the purity of the widely-used ACS-grade ingredients; B) the simplicity of manufacturing Lugol's solution; C) the fact that manufacturers and resellers probably make reasonable efforts to ensure that they don't contaminate their product (because the purer it is, the better it will work for lab procedures); D) the fact that Lugol's solution is a germicidal; and E) that it helps the body to rid itself of various toxic substances such as heavy metals, I would be willing to use the lab-grade version if it is made of ACS-grade ingredients and manufactured and rebottled by reputable companies. As of this writing, I had been using Clarkson Labs' non-USP Lugol's solution for about two years, and I hadn't noticed any ill effects. Most "lab grade Lugol's solution" is probably quite similar. (Unfortunately, Clarkson's no longer sells to individuals due to the new DEA regulations, which require anyone who purchases more than one ounce at a time to be registered with the DEA. This status is not available to individuals, and even if it were, it would be absurd to register just to save a few bucks on Lugol's solution.)
A readily available form of Lugol's solution is "lab grade" product for aquariums. Kent Marine's product appears to be the most prevalent of these, and according to their Material Safety Data Sheet, it, unlike some lab-grade "Lugol's solution," contains the proper 5% iodine/10% potassium iodide mixture required to be considered genuine full-strength Lugol's solution. (However, I haven't investigated all of the available brands of "lab grade" LS for aquariums - it's possible that they all have this desirable balance of ingredients.) Considering their emphasis on maintaining water purity, I assume that their Lugol's solution consists of ACS-grade materials. (As far as I know, the only ingredients readily available for use in chemical mixtures are ACS-grade. I suppose they could use crude iodine, or go out of their way to find resublimed iodine that doesn't quite meet the ACS spec, but it's highly doubtful.) However, I don't know what grade they use, and I doubt that Kent Marine will supply the documentation required to prove it one way or the other. But because they have a competitor (Warner Marine Research) who touts their product as USP-grade, I'd be willing to bet that they do use ACS-grade materials. If KM's Lugol's solution were made of inferior ingredients, this competitor could steal the market by performing an analysis of the KM product and publicizing it, which I doubt Kent Marine would want to risk. They would also be risking their reputation and the rest of their business. The fact that the competitor hasn't done this might mean that both products are made of ACS-grade materials, so the only advantage the competitor has is the aura of greater purity by means of USP certification. The bottom line is that I would be willing to risk using KM's product, but you will have to evaluate the information and decide whether to take the risk before using it as a dietary supplement.
On their website as of 12/29/07, Warner Marine (WM) made the following claim about their Lugol's solution: "ReefPure Lugol's Solution is the original Iodine tool for the aquarists' toolbox. It is produced entirely from Pharmaceutical Grade (U.S.P.) Potassium Iodide and Iodine Crystals, the highest quality raw material in the hobby. Inferior competing products are produced using poor quality raw materials containing up to 10x the heavy metals and impurities compared to Warner Marine products." However, in light of the information I have provided above, this sounds like sales hype. If they had any data, they would probably present it. But it is a way to get reasonably-priced Lugol's solution, USP, and if it's available locally, it would be the logical choice.
You might be able to find suitable Lugol's solution at laboratory supply outlets that are willing to sell to private individuals and to provide details on their product. I found a couple of such places through Yahoo Shopping, but upon examination of the relevant Material Safety Data Sheets, I realized that their products do not contain the proper proportion of ingredients, or are so loosely specified that the specs are useless.
Conclusion and disclaimer
So, as far as I can tell, "lab grade Lugol's solution," (assuming it's made with ACS ingredients by a reputable manufacturer, and rebottled by a reputable reseller) is fine to consume, just as Lewis Ford claims in his article Iodide/Iodine (also posted below). But I'm not an expert, and I might have missed something, so I cannot guarantee that it is. It's up to you to determine whether I've covered all the bases, to weigh the evidence, (including the fact that the manufacturing facilities and process, and the rebottling facilities, are not USP-certified), and decide whether you want to take the risk of consuming it. If you get sick from it, you will have only yourself to blame. If you die from it, you won't even be able to blame yourself. But if Warner Marine's Lugol's solution, USP is available locally and competitively priced, it's the logical choice, although if you were to analyze the various brands used for aquaria, I suspect they'd all yield similar results.
Was: Considering the high purity of ASC-grade materials, it would seem that the USP testing is a formality which must be performed in order to guarantee that a product is safe for human consumption. With modern test gear, these tests are probably easy to perform.
Is: Considering the high purity of ASC-grade materials, it would seem that the USP testing is a formality which must be performed in order to be absolutely certain that a product is safe for human consumption. However, CHANCES ARE that "lab grade" Lugol's solution made from ACS-grade materials by a reputable company (such as those who manufacture aquarium chemicals) would be essentially identical to the typical USP-grade Lugol's solution.