pH changes/extremes doesn't "clod your blood". It may be painful to inject though.
Heroin in solution does hydrolyse to some extent, being more rapid at higher temperatures and more alkaline pH. In general it decomposes first to 6-monoacetylmorphine, which is the active metabolite of heroin formed in the body, before becoming morphine. One study claimed a half life of at least 2 weeks if kept in a mildly acidic solution (which heroin HCl should be, anyway), another claimed total conversion of heroin to 6-MAM in 24 hours was between 4 and 13%. If stored as cold as possible without freezing, the half life should be extended even longer. In the presence of blood/serum it will decompose quickly though, due to enzymes in the blood.
So basically, if you want to prepare a syringe for use later, keep it cold and keep blood contamination out of it. It will be fine for a day or so, maybe 3 maximum if you are
really pushing it and keep it in a cold fridge.
Electron-capture gas-liquid chromatography was used to study the spontaneous hydrolysis of heroin in phosphate buffer (pH 6.4 and pH 7.4) at 23 degrees C. Aliquots of solution were taken over a 24-h period. After extraction at pH 8.9 into propan-2-ol (10%)-ethyl acetate, deacetylated products...
www.ncbi.nlm.nih.gov
onlinelibrary.wiley.com
Incorrect, fentanyl will not hydrolyse in aqueous solution. Carfentanyl may though, but it will behave differently than heroin in terms of hydrolysis rate, and would need to be measured before we knew for sure.