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Testing the Accuracy of Nicotine Concentration

          When we first started mixing nicotine we based our calculations on pure math.  This seems theoretically logical in assumption if all methodology is accurate in implementation.  So the idea was to prove or disprove just this.  In essence we set out to self regulate our methods and procedures to ensure that we were producing an accurate concentration of nicotine in every product.  To do so we purchased a nicotine concentration test kit on the internet which we found on ECF.  It seemed simple enough, but how did we know if this test was giving accurate results?  So first we started out to "test the test".

Testing the Test

Detail:

            The test consists of measuring nicotine concentration using a simple reagent called Bromothymol Blue to titrate the nicotine solution to a pH level of 6.  What does this mean?  Bromothymol Blue has a pH sensitivity of 6 to 7.6.  At 7.6 or above the solution is blue.  As it hits 7.6 and decreases in pH the color changes to a blue green and then to a yellow when it hits its bottom limit of sensitivity of 6.0.  Nicotine by nature has a pH of around 10.2.  So when diluted with vegetable glycerin or propylene glycol the pH of the solution is still above 7.6.  So a solution of .12N Sulfuric Acid (H₂SO₄) can be used to titrate the sample to a pH of 6.  The amount of Sulfuric Acid used can then be calculated, when multiplied with a constant, to mathematically measure the mg concentration of the nicotine.  The constant (19.47) we used was from the test kit.

Defining the Test:

            Start with a 1 mL sample of VG or PG nicotine in a graduated cylinder.  Then add 2 drops of Bromothymol Blue, and then topped off with distilled water to make a 3 mL solution.  (If testing a nicotine sample over 30 mg use 4 drops of Bromothymol Blue.  If testing a nicotine sample over 100 mg use 8 drops of Bromothymol Blue.)  Then add small amounts of .12N Sulfuric Acid with stirring until the color of the solution starts to change.  Continue until the solution is a golden yellow.  As the solution nears the end of the test and gets closer to the desired color change decrease the amount of Sulfuric Acid to just a drop at a time to ensure you don't move past the end titration point.  Measure the final volume of the solution and subtract out the original 3 mL to give you the resulting volume of Sulfuric Acid used.

            So our first step was to break down the test to see if any one variable would change the outcome of the test.  This was broken down into the following areas.

1. Amount of distilled water used.
2. Volume of sample used.
3. Number of drops of Bromothymol Blue used.
4. Type of Bromothymol Blue used.
5. Testing with a pH meter.

After This Seris of Tests our Initial Conclusions are –

• Make sure your measuring equipment is accurate. 
• The amount of distilled water is not a factor but can make mixing the solution easier if you use 3 to 4 mL with a 1 ml sample of VG nicotine and more so if you are using 2 or 3 mL. 
• No matter how much distilled water you use, top to an even increment on the graduated cylinder preferably on an even number.
• The larger the sample of nicotine tested, the more accurate the test.  It just reduces the human error in reaching the end of the titration but uses 2 or 3 times the Sulfuric Acid over a 1 mL sample size.
• The number of drops of Bromothymol Blue does not change the results of the test but 4 drops is easier to see than 2.  If you are testing higher concentrations over 100 mg, use 8 drops.
• Both amber and blue Bromothymol Blue can be used for the test.
• A pH meter will increase accuracy of the test because it removes having to visually evaluate when you have reached the end of the titration.

The results were too lengthy to include in the newsletter in whole.  To See the full results of the testing we did click here.