Vapor Dynamix advises that persons who have 3 months or less experience of electronic cigarette/liquid use should not attempt to DIY with e-liquid, as neither the background knowledge nor an appreciation of the safety issues may not exist. It is best to wait until sufficient knowledge is acquired.
It is recommended to use DIY e-liquid only if you can answer the following questions immediately after asking:
To work safely with liquids that contain poisons requires some knowledge. It is not safe to work with potentially dangerous materials without the required knowledge. Anyone who does not know the answers to these and similar questions should only buy commercial e-liquid.
The highest strength normally available is 36mg, though some suppliers sell 24mg or 30mg as their maximum strength.
48mg is available from some suppliers, but this should not be used without the advice of an expert. It should only be consumed by those with severe cravings while using 36mg, combined with high tolerance to nicotine. There is a very good argument that WTA e-liquids should be investigated first.
Any strength higher than this should not be used by anyone for the purpose of consumption in an e-cigarette, it is specifically for mixing and thus dilution only. For example 60mg can be used for dilution to produce 30mg by diluting it with an equal volume of zero-nicotine liquid.
54mg, 60mg and 100mg liquid (in either PG, VG or PEG-400) is used only for mixing. Some strengths higher than this may be available but they are best avoided except by commercial labs.
It is diluted down to 36mg or below, for consumption. There is no need to buy any liquid stronger than those above unless you are a commercial manufacturer of e-liquids and have a full-facility lab. Vapor Dynamix advises that you do not engage in any DIY involving the use of bulk e-liquid base unless you have training, and have the correct facilities. Commercial manufacture requires the supervision of a chemist, for several reasons.
Pure nicotine, of 99% purity, should not be purchased or used under any circumstances, except by licensed laboratories with a fume cabinet and hazmat facilities. It is a highly dangerous poison in this form, and a small spillage on the skin is likely to be lethal.
Nicotine was used as an insecticide, and when used to fumigate a greenhouse for example it will kill anything living - including any humans unfortunate enough to be inside. 99% nicotine has a strength of 990mg, or 990mg/ml, and is almost ten times stronger than 100mg, normally the strongest e-liquid base sold for mixing, which itself is dangerous enough.
It is as dangerous as pure potassium cyanide.
Note that pure nicotine is far more dangerous than high-strength e-liquid because it will be rapidly absorbed into the bloodstream if there is a spill on the skin. This is not normally the case with e-liquid because the nicotine seems to be bound or 'locked' by PG and/or VG, and there appears to be a time window in which the liquid may be rinsed off. This will not be the case with pure nicotine.
Simply opening a bottle of it can result in a room filling with toxic fumes - it should only be handled in a fume cabinet. If you don't have a fume cabinet then DON'T BUY IT.