Nicotine is a toxic substance and is highly addictive. It can be absorbed through the skin and the mucous membranes of the body.
Most nicotine liquids for use with e-liquids can come in a variety of different strengths but are usually listed as mg/ml. That's milligrams per milliliter. So, this means that if you have one milliliter of 100mg/ml strength liquid, you have 100mg of nicotine dissolved in that liquid. that is enough for a fatal dose depending on how it's taken into the body and the size of the person affected.
When you have nicotine liquids to mix with, most people tend to go with 100mg/ml as it is usually the most cost effective... However, some vendors will sell the liquids at varying strengths but rarely ever exceed 100mg/ml as depending on the country they reside in there can be licensing regulations needed for handling and selling that strength to the average consumer.
It must be said, however, that unless you are properly trained and have the right facilities, it is extremely unwise to get pure nicotine crystals to dissolve into your own liquids. These are usually done by trained professionals with the right certification and licensing requirements and usually in a well equipped facility that is designed explicitly with the handling of hazzardous materials in mind.
When handling nicotine the safest way to do so is to wear gloves that are impermeable such as latex or nitrile gloves. Porous gloves such as fabric or leather are not advised.
In the event of a spill be sure to clean up the spill with an absorbant material and be sure to wash the affected area with soap and water. Nicotine can stain porous materials and over time those affected areas might become stained a brown colour and may emit an unpleasant odour. So, when handling it is advised to use in a clean environment that is easily cleaned.
In the event of nicotine being spilled or exposed to skin, immidiately wash the affected area with warm soap and water thoroughly. Depending on the amount this may require calling a poison control center for advice and possible treatment however most little spills of a drop or two may not require you to contact poison control if you are able to wash off the affected area immidiately and remove any stained clothing that may have been exposed.
In the event of nicotine liquid getting into your eyes, thoroughly flush the affected area with water and contact a poison control center immidiately. Nicotine can burn and eyes are very sensitive organs.
In the evdent of ingesting nicotine liquid, contact a poison control center in your area immidiately and follow their directions.
Nicotine poisoning is potentially life-threatening. So, treat the raw materials with the utmost of care and protect yourself appropriately.
Nicotine can oxidize over time. This will usually result in the liquid that it's in taking on a yellowish-brown colour depending on how much oxidation has occurred. There are many users that report that this does not affect the availability of nicotine as it's used for e-liquids however we're still looking for research that would either confirm or deny that as being true. If you have a link to a study that goes over the properties of the oxidized nicotine liquids, please consider contributing. Also, oxidation doesn't seem to impart any significant change in the flavour of the liquids being made however if you have a bottle of nicotine liquid that is murky brown it may be time to consider investing in a fresh bottle.