There is one brand I used-hucog, its pre-mixed. The excipients and preservatives listed are: Disodium Hydrogen Phosphate Dihydrate, Benzyl Alcohol, Sucrose, Poloxamer 188,Methionine, Phosphoric Acid.
I prefer it because, considering the fact I only use 300 iu EOD, having it in a vial reduces the amount of oxygen it comes into contact with and-I am purely assuming here-its formulated in a solution that enhances its mixed shelf life.
As for your stuff not registering on a pregnancy test and your source saying its because of the preservatives-I call bullshit. Pregnancy tests are meant to detect HCG in the URINE of pregnant women, urine that has a whole lot of different reactive biological chemicals in it. Also, the test is designed to react to hcg and only hcg. If there was a chemical extremely similar to hcg in it, I could see a false positive. But a chemical that causes a false negative....i dont know if that is very likely.
If a chemical they are putting in it is causing it to appear negative despite them really putting hcg in it-this is assuming that they are not full of it-then that probably implies that the preservative destroyed the hcg.
Its kind of like how junkies put bleach in their cup of urine to pass a drug test-its not to bleach the test strip, its to destroy the chemicals the test strip is meant to detect.
I hope this helps.