Yes on Erowid there is this article in which many people who had experienced LSD from various street sources tried some 100% pure, sealed Sandoz from 1951 and could tell no difference:
This is a very very lofty subject. There are many factors to take into consideration, a person's own set and setting being but one small (albeit important) part. LSD can illicit innumerable forms of what we now call psychedelic experience which makes it very hard to try to figure out how pure a certain sample is. It's not like cocaine where you get the same reaction every single time at a certain purity level. One can't look at it on any real analytical level unless they have the crystalline form, which is pretty rare. Even then small amounts of substances in the atmosphere can alter the *appearance* of the crystal.
Even more problems present themselves when we enter into the realm of the laboratory. We know that LSD-25 is produced in solution with a number of other isomers of LSD before the final step in production--cleaning of the solution--is carried out. Now to be sure, one could drink the uncleaned LSD solution and trip. At this stage you either have produced LSD-25 floating around with a few of its isomer pals or a glass of water. No question about it. However, if one is to assume that purity is, as Bruce Eisner writes, "next to godliness" this last step is the most crucial. The purification technique is called "chromatography" and it is here where the perfectly good LSD-25 is turned into what would be called "pharmaceutical grade" LSD-25.
Of the many isomers and proteins present in the solution of pre-cleaned LSD-25 two seem to be the focus of purists--iso-LSD and lumi-LSD. Both of these compounds have been rumored to be the cause of "bad trips" or "fuzzy visuals" since at least the 70's. It has been theorized that these compounds and others could act as "blocks" on the receptor sites to which LSD binds, but there have been no scientific studies to conclusively prove this.
So then in order to ensure purity a cook must run his final solution through the chromatograph many times before it reaches the state of a white, translucent fluffy crystal (considered the highest purity possible). According to Owsley, at 99% purity the compound ceases to purify further unless considerable heat is added, at which point the LSD would probably be lost.
Now these other isomers and proteins present in the final solution are fractions upon fractions of molecules inside a molecule that is active at a fractional dose. The real question is: how potent could a fraction of molecules be when taken in a dose that is in the microgram range? Well, many people think that because LSD is active at such low doses then it is possible that its isomers are as well.
So you see from this long sprawling explanation, there is just no real way of knowing how purity figures into the equation. But I will go so far as to say that I would bet that if someone is going through the trouble of attaining these highly scheduled substances and investing 3-5 days in the making of such a substances then that person would most-likely not decide to skimp on the cleaning process. After all, a lot of these blokes are making it for themselves and their friends--that's probably why they got in it in the first place. A lot of cooks take pride in the purity and methods of their process. There are definitely a few exceptions, however, as the nature of clandestine production of an illicit substance is inherently risky and if the cook involved is a novice or unconcerned with purity then they may speed things up on the purification end so as to get their batch out faster and avoid cops.
But there is no such thing as "bad acid"--either LSD-25 is produced in the reaction or it's water--and impurities are entirely debatable. There's no killer acid out there that's guaranteed to give you a bum trip every time. Unfortunately the same can't be said for the myriad of Research Chemicals flooding America.
It has helped some... perhaps SWIY/M could discuss some of the potentially active isomers that are produced and eventually removed... some are active, right?