/u/adbaba or /u/abdada i always forget

I hope I have discussed all important papers about heat degradation of sucralose interesting for vaping now. After examining all of them my conclusion is, there were no alarming amounts of toxic compounds found yet. Considering vaping involving much lower amounts of sucralose and shorter times of exposure to heat than usually used in these studies I predict the amounts of toxic compounds will be much smaller for vaping conditions - but not zero. Analytic techniques available in nowadays are able to detect extremely small amounts of analytes, so small that it is often questionable, which relevance regarding realistic hazard estimations this implies.

Of course research is never really complete or final, so there are always possibilities something important will be found in future studies or studies available having some unknown errors.

Most interesting for me is still the Bannach paper and the Hutchinson review regarding direct HCl elimination from sucralose and the instantaneous evolution of primary products and amounts thereof. In the near future I will try doing some simple experiments involving pH measurement of sucralose VG and PG solutions especially at short heating durations. This is not very complicated and I'm able to do this. Of course everyone having the ability and skills needed, is invited to do the same as well as things I didn't think about yet.

If there is any critique, something is remaining unclear or there are any other questions, don't bother and just ask!

I initially used pure sucralose, but found that my vision was getting blurry (not joking), when I stopped using it, vision returned after about a week. I won't use it again - I now mix 90% VG which is sweet enough (IMHO).

Paul

https://www.reddit.com/r/Deeper_DIY/comments/3uvw8c/safety_of_sucralose_that_has_been_heated/

wow its been 5 months? time flies.

It does level some worthy concerns, particularly for high wattage stainless steel. It's not just sucralose either, other artificial sweeteners have shown similar issues with heat stability in research I've read (if my memory serves me well stevia - http://publik.tuwien.ac.at/files/PubDat_190293.pdf had issues as well). Tried reaching out to Dr. F months ago about it but never heard anything back.

To name some of the few things to consider when using sucralose if you still do decide to use it -

Do you vape super high wattage, what type of coils you have, how clean they are (oxides facilitate production of the nasty stuff), do your diy mix contain acids that could contribute to degradation of the sweetener (citric acid for example).

Examining the glycerol paper in detail. "Thermal degradation of sucralose and its potential in generating chloropropanols in the presence of glycerol." by Anja Rahn and Varoujan A. Yaylayan.

First of all I want to show you, how it's possible to have juice components longer at the coil than usually thought to be a single firing period. Imagine (or propably you have already done it) a drop of menthol juice at the coil previously used with a non menthol juice. Continue vaping as usual and use another non menthol juice afterwards. How long can you smell the single drop menthol? I think it's very surprising how long that can be! In chemistry that's called https://en.wikipedia.org/wiki/Residence_time_%28fluid_dynamics%29 and https://en.wikipedia.org/wiki/Residence_time_distribution

Although most molecules leave the coil relatively fast, in reality there is always a distribution of residence times. Imagine you have some resting times between your draws. During this time molecules can exchange and diffuse throughout all the space available, which is the liquid continuum.

Now paper no 2:

The authors made the experiments as follows: A 1:1 mixture sucralose and glycerol was heated 20 s at 250 °C and left there for additional 100 s without heating. 20 s heating time isn't miles away from vaping conditions.

Different cases were examined: Helium atmosphere (inert), air (oxidizing), two different amounts of water (hydrolyzing). Helium and air conditions gave about the same results while the water examples gave lower amounts but at a very similar order of magnitude. Products of concern were 3-MCPD as the major compound, followed by 1,3-DCP and 1,2-DCP as the minor compounds.

What about amounts?

This is not completely trivial in table 2. It reads "Normalized relative formation efficiency" "based on area/mole of sucralose (x 10^10)"

If the vaules are shown as multiplied by 10^10 the meaning might be we have to divide the values by 10^10. I think it's parts per mole of sucralose then. The value '105.2' for 3-MCPD in the first row of table 2 results in:

105.2 * 10^(-10) * 100 % = 1.052 * 10^(-6) % or 10.52 ppb

ppb (parts per billion) referrs to the proportion of amount of molecules 3-MCDP / sucralose. It's not the weight proportion!

I'm very tired today and will continue this later on. Please ask questions if something is incomprehensible.

Examining paper no 1, "Polychlorinated dibenzo-p-dioxins and dibenzofurans formed from sucralose at high temperatures" by Shujun Dong, Guorui Liu, Jicheng Hu & Minghui Zheng.

It's about decomposition of pure sucralose in the presence of metals and metal oxides. The idea might be derived from the question how cooking utensils like metal pots might affect decomposition of sucralose. All non noble metals have some oxide coat on their surface, but there are basically more or less oxides possible, dependent on the amount of oxidation that has happend.

Temperatures investigated were between 200 and 400 °C and oxides investigated were Al2O3, Fe2O3, or CuO. However in polished untensils (extremely low amount of oxides) no PCDD/Fs were found with one exeption, which was stainless steel showing toxic chemicals at and above 350 °C. For the former this doesn't mean there was nothing there, this means everthing there was below the detection limit. Every analytical instrument has its specific detection limit for different analytes.

Chemical reactions usualy speed up by applying higher temperatures. This is also the case here. Amounts found were 25 times higher at 400 °C compared to experiments performed at 350 °C.

A rule of thumb in chemistry says, for every 10 °C temperature elevation, the reaction speed doubles. The rule applied here predicts 32 x speed. (2^50/10 ). So 32 x compared to 25 x is not completely different.

But now, the authors have found the following results:

They couldn't detect any PCDD/Fs when sucralose was heated together with metal oxides up to 300°C. This is why they continued mentioning the 350 and 400 °C experiments only.

This means there were so few toxic chemicals, they couldn't detect them. This is good news.

Detection limits were as follows:

PCDD/Fs (polychlorinated dibenzo-p-dioxins and dibenzofurans): 0.01–0.4 pg / g

PAHs (polycyclic aromatic hydrocarbons): 4–30 pg / g

CBzs (chlorobenzenes): 4–15 pg / g

Predicting results which might be realistic at 300 °C would lie between 32 x and 25 x lower amount of toxic chemicals than found at 350 °C. For 250 °C the same game again: (25 x)² = 625 x up to (32 x)² = 1024 x lower amount of toxic chemicals.

EDIT: Totally forgot using Mr. Dadas 1% dilution. The amount of PCDD/Fs below the detection limit therefor has to be multiplied by 1 % -> 0.01 pg / g * 1 % = 0.1 fg / g and 0.4 pg / g * 1 % = 4 fg / g.

0.1–4 fg / g.

fg means femtogram and is 10^−15 g.

Now I want to introduce another paper which was just briefly mentioned in paper no 1. I will call it the 'Bannach paper' published in 2009. This is the oldest paper I've seen so far which raises serious concerns about sucralose stability at relatively low temperatures, namely at 119 °C and above. This paper is especially interesting because paper no 3 (2015) in my OP looks like a direct follow-up in low temperature stability research of sucralose.

"Thermal stability and thermal decomposition of sucralose." by Gilbert Bannach, Rafael R. Almeida, Luis. G. Lacerda, Egon Schnitzler, Massao Ionashiro.

http://www.scielo.br/pdf/eq/v34n4/a02v34n4.pdf

In this study a very simple but cool method was used. The mass loss is monitored while a sample is heated up 10 °C / min over a wide temperature range. This method makes it possible to see at which temperatures something happens, i.e. weight loss occurs. Two other methods were used, differential thermal analysis (TG-DTA) and differential scanning calorimetry (DSC) to counter check results and make some energy balances for the different events of weight loss. This is very smart because chemical changes are not overlooked so easily.

Now, the authors found a relatively large weight drop of 18 % to occur between 119 °C and 137°C and assigned it to the loss of two molecules of water and one molecule of hydrogen chloride. The conclusion is, the two water molecules were constitution water and hydrogen chloride was eliminated from sucralose molecules. Constitution water means, there are two water molecules for each sucralose molecule part of the original sucralose crystals. The crystal formula is therefor sucralose x 2 H2O. Unfortunately decomposition doesn't stop after the loss of these three molecules, but increases in two steps from 160-370°C and 370-550°C further in a nearly linear manner. They are assigned to exothermic oxidation processes of [sucralose minus HCl].

In earlier studies the activity at ~130 °C was attributed to the melting point of sucralose. This seems now disproven and it's shown just to be loss of crystal water and HCl.

Here I have three questions I think are very interesting:

1. What is the taste of sucralose after it has lost that one HCl. Still sweet?

2. The fumes of the weight loss around 130 °C were checked for pH and it was pH 1 -> very sour. Thinking about vaping, what happens if a small sample of juice is taken from a used e-cigarette with a q-tip and checked for its pH with an universal indicator? Sour or not?

3. Are there any differences in the formation of HCl from sucralose whether it is crystalline or dissolved in glycerol?

EDIT: Now I have a nice series of experiments in mind. A tempered oil bath where I can put in vials with sucralose-glycerol mixtures at different temperatures for different periods of time. After that a pH measurement will reveal if HCl was liberated.

EDIT2: Question 1 might be answered by vaping a diluted sample of sucralose which was previously heated to ca. 125 °C for some minutes. From the paper it's clear, if the decomposition has happened between 119 and 138 °C with a heating rate of 10 °C / min, this takes about two minutes.

Paper no 3: "Thermal degradation of sucralose: a combination of analytical methods to determine stability and chlorinated byproducts" by Diogo N. de Oliveira, Maico de Menezes, Rodrigo R. Catharino.

In the future I will try to have a look at all the other papers about heat stability of sucralose, so this won't be the last literature source I will examine here. I want to have the picture of the state of the art research on sucralose as complete as possible.

As described before this study used the same technique as described in the Bannach paper. Thermogravimetric analysis, DSC, and TGA but some other methods too, which are IR spectroscopy, hot-stage microscopy (HSM) (looking for crystal structure and color changes during heating) and high-resolution mass spectrometry (HRMS) (identifing degradation compounds) in order to have a closer look at the compounds being formed during sucralose heating. Two technically pure samples of sucralose from two different manufacturers were used.

The findings from Bannach et al. about water and HCl loss beginning at 119 °C were confirmed. The weight loss around 125 °C was 17,94% which is very similar to the findings of Bannach et al. (18%). These graphs from DSC/TGA experiments look pretty much the same: http://www.nature.com/articles/srep09598/figures/1

The HSM (hot-stage microscopy) is a method to accurately assign different temperatures to a video (supplementary materials) taken through a microscope. They provide the video and three screenshots (figure 2) which show melting and a decomposition (caramelization) process. Unfortunately I can't find the temperature assignments belonging to the video or the screenshots. That's unfortunate, I thought this to be the important part of the method. Anyhow...

They took the same temperature range (25 °C - 250 °C) and the same heating ramp 10°C/min like in the DSC/TGA experiments. If you watch the video, you see the browning and darkening to occur just in the very end. What we see in the video is hopefully the whole 22.5 min in time lapse:

225°C / 10 °C / min = 22.5 min

The video is 12 s long and I can see no darkening until 10-11 s. 1 s is ~1.9 min, so there is no darkening until 19-21 min or 190-210 °C. However, this is not very accurate for sure but I will keep in mind the possible darkening of sucralose at and above those temperatures.

Fourier-transform Infrared Spectroscopy (FTIR):

After 11 min of heating, a FTIR spectrum was done on both manufacturer samples. 11 min is where the weight drop of ~ 18% occurs. They tried to compare newly observed peaks with literature databases and report to have found similiarities to: water, carbon dioxide, hydrogen chloride, and chloroacetaldehyde. This is qualitative only, so no amounts are known and there is no 100% proof the assignments are really correct.

Mass Spectrometry (HRMS):

Ok then, there is not much to say here. The mass spectrometry revealed three interesting masses, which were assigned to compounds similiar to degradation products known for example from sugar chemistry and its pyrolysis. The compounds and the spectra are shown here:

http://www.nature.com/articles/srep09598/figures/4

No temperature information is provided and quantities were not determined (the method is not suitable for measuring amounts).

Without knowing any amounts of toxic substances generated, I don't consider this study very useful for us, compared to the other studies that provided amounts and revealed how small they were.

Of course future studies will have a look at those amounts based on the claims made here. Step after step...

Here are some additional papers covering the heated sucralose issue.

"Stability and degradation of the high‐intensity sweeteners: Aspartame, Alitame, and Sucralose." by Sheryl A. Hutchinson, Gregory S. Ho, Chi‐Tang Ho, 1999.

http://www.tandfonline.com/doi/abs/10.1080/87559129909541189

"Formation of polychlorinated naphthalenes during the heating of cooking oil in the presence of high amounts of sucralose." by Shujun Dong, Guorui Liu, Bing Zhang, Lirong Gao, Minghui Zheng, 2013.

http://www.sciencedirect.com/science/article/pii/S0956713512005956

"Unintentionally produced dioxin-like polychlorinated biphenyls during cooking." by Shujun Dong, Jiajia Wu, Guorui Liu, Bing Zhang, Minghui Zheng, 2011.

http://www.sciencedirect.com/science/article/pii/S0956713511001617

"Thermal decomposition of sucralose." Lu, X., Chen, Z., She, J., Hong, L., 2015.

https://www.researchgate.net/publication/282681782_Thermal_decomposition_of_sucralose

or http://xuebao.sysu.edu.cn/Jweb_zrb/EN/Y2015/V54/I1/37

Unfortunately I didn't find any free access yet, but I've already obtained paper 1-3.

"A chart illustrating how much dioxin the average American consumes per day. (Note: pg = picogram, or one trillionth of a gram, or 10^−12 g)" :

https://en.wikipedia.org/wiki/Polychlorinated_dibenzodioxins#/media/File:Dioxin_chart.png

Main page:

https://en.wikipedia.org/wiki/Polychlorinated_dibenzodioxins

Having had a look at the Hutchinson paper from 1999.

"Stability and degradation of the high‐intensity sweeteners: Aspartame, Alitame, and Sucralose." by Sheryl A. Hutchinson, Gregory S. Ho, Chi‐Tang Ho.

It's a review about the temperature stability of many different artificial sweeteners.

The first series of experiments is about heating aqueous solutions of sucralose at different pH (3, 5, 7) to 100°C for 2 h. 98 % sucralose was recovered in all cases. After 2 h it was on the average a double amout of sucralose gone. The highest degradation found was 4 % at pH 7.

Another expanded series of experiments was conducted at different pH (3, 7, 11) buffer solutions for 1 h at different temperatures (100, 140, 180 °C). After 1 h at 180 °C sucralose was completely gone no matter at which pH. For the other temperatures sucralose was found to be most stable at pH 3 and least stable at pH 11 with pH 7 in between.

The fate of sucralose was found to be decomposition into 4-chlorogalactose and 1,6-dichlorofructose. Under basic conditions (pH > 7) 3',6'-anhydro-4,1 '-dichlorogalactosucrose was found as an intermediate product.

Another publication is mentioned where no degradation products of sucralose were found in different baking goods at 180 °C for 25 min, 210 °C for 8 min, and 300 °C for 4 min baking time. Source: R. L. Barndt and G. Jackson, Food Technol., 44(1), 62 (1990).

The next study has it's focus on chloride ion release of aqueous sucralose at different temperatures (80, 100, 120, 140, 160 °C) and pH buffer solutions (3, 7, 11), therefor chloride ion concentrations were measured. Unfortunately duration of heating is not reported and the literature source is Hutchinson's Ph.D. dissertation from 1996 which is not available easily. However, chloride release was found only prominent at 140 °C and above. Unfortunately the chloride concentrations are reported in ppm but the initial sucralose concentration is not reported. Therefor it makes only sense to compare the different cases in a qualitative manner. At pH 3 and 11 the chloride concentrations were about the same at 140, 160 and 180 °C, whereas at pH 7 the chloride concentration at 160 °C was about the half amount and at 180 °C it was similar again.

In the last chapter the focus is on formation of volatile compounds of aqueous sucralose solutions heated for 1 h at 180 °C. Interstingly the pH of the solution was found altered, it was around 5.0 before heating and decreased to about 1.7 after 1 h. So it went sour! The following volatile compounds were found: Cyclopentanone, Furfural, 2-Butanone, 2-Acetylfuran, 2,5-Hexanedione, 5-Methyl-2-furanone, 5-Methyl-2-furfural, 3-Methyl-2-furanone, 2-Hydroxy-3-methyl-2-cyclopenten-1-one, Ethyl levulinate, Methyl furoate, Levulinic acid, and 5-Hydroxymethyl-2-furfural. It is concluded that dehydrochlorination, the elimination of HCl, is involved in the formation of those compounds. No chlorinated compounds were found. Many of these are known from sugar decomposition and are also known as flavour compounds.

I think especially the pH and HCl release will be most interesting for vaping conditions. So my questions raised here: https://www.reddit.com/r/DIY_eJuice/comments/4ib7tg/possible_hazards_from_sucralose/d34qyam are still to be answered.

EDIT: HCl might also be able to corrode the heating coil, so there is a possiblility metal chlorides will form which might be further converted into rusts by water, setting free HCl again. I don't think this is a major issue, but I want to document it, just in case anyone makes such observations and has no explanation. HCl is also an irritant and the exposure limit is set to 5 ppm by OSHA and NIOSH, but immediate danger is at a much higher level: 50 ppm. https://en.wikipedia.org/wiki/Hydrogen_chloride#Safety I think HCl will surely be recognized, because HCl smells very biting and has a very low odor threshold: 0.25 ppm. https://www.indsci.com/products/hydrogen-chloride/

I will comment on the following two papers left only shortly, because I don't think the scenarios investigated are fitting to what vapers might be interested in.

"Unintentionally produced dioxin-like polychlorinated biphenyls during cooking." by Shujun Dong, Jiajia Wu, Guorui Liu, Bing Zhang, Minghui Zheng, 2011. http://www.sciencedirect.com/science/article/pii/S0956713511001617

This is about cooking beef with and without different amounts of sucralose added and analysis of dioxine-like polychlorinated biphenyl content before and after cooking for 12 different biphenyls in soi bean oil fumes analyzed.

I think cooking beef is not easily comparable to vaping. Furthermore it seems like amounts of biphenyls was lower after cooking than before. Another unit to measure the hazards used is WHO-TEQ (WHO toxic equivalents) which is based on amounts as well as toxicity of the actual bipehyl distribution. This was also lower for cooked beef than for uncooked beef. Not sure if I missed something, but I won't comment this any further.

"Formation of polychlorinated naphthalenes during the heating of cooking oil in the presence of high amounts of sucralose." by Shujun Dong, Guorui Liu, Bing Zhang, Lirong Gao, Minghui Zheng, 2013. http://www.sciencedirect.com/science/article/pii/S0956713512005956

This is about investigating amounts of another class of toxic compounds, polychlorinated naphthalenes, formed by heating peanut oil or olive oil sucralose mixtures at two different temperatures (200, 245 °C).

A high ratio of sucralose had to be mixed with oil (5 g / 50 g) in order to generate detectable amounts of polychlorinated naphthalenes after 15 min of heating. At 200 °C nothing was found while at 245 °C some amounts were found (total amount 200 for peanut oil and 98 pg / g for olive oil). As oil is thought to be the source of the naphthalene backbones and sucralose is thought to be the chlorinating agent, I think the question remaining is if this works without oils at all.