Laboratory Tips on the Measurement, Steeping, and Storage of eLiquids 06/10/2014
In this article, we will be reviewing our laboratory practices here at Nude Nicotine for the manufacture of eliquids from 100mg/mL nicotine base. However, we will write this article with the home DIY user in mind with respect to skill level and equipment available:
Measurement tools for PG/VG/Nicotine/Flavoring:
Here at Nude Nicotine, we utilize a variety of glassware, polypropylene containers, graduated cylinders, syringes, serological pipettes, and many other tools for our measurements. Here we will review some tools at our disposal that are not outrageously expensive and can be realistically obtained for the home DIY user.
Transfer pipettes, or pasteur pipettes, are commonly seen in plastic or glass with detachable rubber bulbs. Transfer pipettes are a VERY inexpensive and easy solution for the transfer of small amounts of eliquids when graduated measurements are not necessary. Commonly plastic transfer pipettes are molded with plastic graduations but most are uncalibrated and very difficult to read a meniscus in.
Syringes are a great way to utilize a high powered suction action for the transfer and measurement of viscous eliquids, commonly high in VG content. Most, if not all syringes with graduations are required to be calibrated, so you can be assured that the volume you are measuring is indeed true. Syringes are fairly inexpensive and a must-have tool for any DIY formulator in 1mL, 2.5mL, 5mL, 10mL, 20mL, and 60mL sizes. Most syringes are disposable if not constructed of glass. We also recommend the use of serological pipette tips (or syringes) to be used for the measurement of nicotine, as these tools minimize the probability of spills in comparison to pouring from a graduated cylinder.
Serological pipettes are a vacuum and gravity/pressure-operated measurement tool for non-viscous fluids. A disposable pipette tip is inserted into the unit, which provides suction of the liquid up the pipette tip, as well as the proper flow, or pressure, to expel the liquid. Flavorings, PG, and nicotine are very easily and quickly measured using serological pipettes, however closed-tip designs are too restrictive for the flow of viscous VG. We also recommend the use of serological pipette tips (or syringes) to be used for the measurement of nicotine, as these tools minimize the probability of spills in comparison to pouring from a graduated cylinder. Common sizes for serological pipette tips are 1mL, 5mL, 10mL, 25mL, 50mL, and 100mL. While the electrical units range from $150-400, manual models can be had for $50-100 and pipette tips are a great alternative expense-wise to syringes.
Everyone knows these! They are a very easy tool to read graduated measurements. They are inexpensive, reusable if washed clean with distilled water, and a great tool for the DIY home formulator. However, it is critical to be sure all liquid is evacuated from the cylinder to ensure a proper dispense. Viscous liquids like VG will take some time to extract from a graduated cylinder, and it is advised for smaller measurements, stick to a more controlled measurement solution such as a serological pipette or syringe. One additional piece of advice – VG’s viscosity also lends itself to its adhesiveness, which can prove a problem in the lengthy dispense times from borosilicate glass graduated cylinders. (While for PG, this is less of a problem). Therefore we recommend polpypropylene (PP) graduated cylinders for the measurement of VG, while borosilicate glass should be used for the majority of other measurements.
Techniques and Machinery for Mixing and Steeping:
Most mixing for the DIY home formulator can be performed by hand. Nicotine is very non-viscous and disperses well in solution, along with a wide selection of flavorings. The only real problem arises in mixing volumes of eliquids with VG. Due to its viscosity, VG makes obtaining a well-mixed solution difficult. However, persistent hand-shaking will eventually obtain a well-mixed solution. IF you require some assistance, hobby-based paint bottle shakers work excellent for mixing bottles of eliquids. Here at the laboratory, we use a pneumatic-powered apparatus similar to a paint can shaker, but this is obviously overkill for most IDY home formulation scenarios. A quick confirmation can be done by visualizing an even dispersion of bubbles throughout the solution after thorough mixing, as well as the absence of any visible nicotine ‘pockets,’ evident as very transparent ‘whips’ in solution.
As for steeping, three variables are critical to shortening your steep time, while not endangering the chemical integrity of the eliquid. Avoiding heat, excess UV light, and to provide ample agitation. Our goal is to oxidize flavoring molecules and ensure they are adequately solvated by the PG/VG solvents without oxidizing the nicotine:
AVOID excessive heat at all costs! Heat will only accelerate the oxidation of nicotine. While it will also accelerate the oxidation of the flavorings, the activation energy to do so is much lower than required. Within our laboratory, we have concluded that a room-temperature after bath between 20-30C is ideal for maintaining a stable steep temperature.
Agitation is key in achieving adequate dispersal of your flavoring in solution. Constant agitation would be ideal, but unless you have access to a shaker, this might not be attainable. However, this is not needed in most cases. Another way to assist in agitation is through the use of sonication. By pulsing sound waves through the eliquid, all molecules in solution are further agitated and dispersed, all while in the absence of added heat. This is why sonication is a great method for agitation and won’t accelerate oxidation of your nicotine. A frequency of ~600Hz should provide adequate agitation but remain under the activation energy required to accelerate the oxidation of nicotine further. These sonicators are obviously intended for the laboratory, but a common home jewelry cleaner can work wonders as well. Make sure the bath is filled with distilled water to prevent buildup of mineral deposits on the interior of your sonicator, and have at it! Common sonication times range from 3-10 minutes per session. Give your liquid some time to settle in between sonications.
Oxygen is helpful in the steeping process, especially to accelerate the oxidation of flavoring molecules. If kept at room temperature and away from UV light, eliquid will be at the optimum ‘steeping’ conditions, avoiding the unwanted oxidation of nicotine in solution. Feel free to steep with your caps open! It can help to evaporate excess ethanol in solution from flavorings, and in combination with ample shaking/sonication, is an excellent approach to accelerating the steeping of eliquids.
Storage of 100mg/mL Nicotine Base and Flavored (Diluted) eLiquids:
For 100mg/mL nicotine base, we recommend storage in a freezer capable of temperatures between -10-20C. For short-term storage under months, PET bottles are more than adequate. However for longer storage times, we recommend the use of glass bottles and storage under argon gas. By minimizing the damage done from our three enemies heat, light (hidden in the freezer), and oxygen (argon displaces atmospheric oxygen sealed inside the storage bottle), we can lengthen the expiration of our nicotine base to its maximum potential.
As for diluted eliquids <36mg/mL (3.6%), storage in a cool (<40C), dry place away from light is an ideal short-term storage environment. However, for longer-term storage, we advise using a refridgerator in the ange of 2-8C. These storage guidelines can also be applied to flavor concentrates as well