How like sarin is a sarin-like substance?

The OPCW has analysed samples from Khan Sheikhoun in April containing what they have identified as ‘sarin or a sarin-like substance’. They know that much, even if they are not sure how it got there or who is responsible.

But how much actually is that? Throughout the OPCW report we find the cumbersome expression sarin or a sarin-like substance.  Why not just sarin, pure and simple?

All a non-chemist like me can understand from this is that we are dealing with some nasty stuff, but there is no definite confirmation it is sarin pure and simple. Of course, a non-chemist also has no idea how impure a sample or how different a molecule would need to be to count as merely of a substance like sarin; nor would we know how much more impure or different it could be before becoming unlike sarin.  So we non-chemists could easily be bamboozled in these matters.

One thing we do know is that the sarin the Syrian government produced and gave up for destruction in 2013 was referred to by all concerned as sarin, pure and simple. To produce sarin with military grade purity is not easy.  To produce improvised versions, however, is within the capacity of insurgents in Syria.

Given that there are already open questions about motive, means and opportunity, as I indicated in my previous blog, then if there is doubt about even the weapon as well, the case for blaming Assad looks decidedly uncertain. In fact, regarding the weapon, as I mentioned in the blog before last, the OPCW could not ascertain the method of delivery or therefore the ‘hardware’ used. So it becomes crucial for those who would prosecute a case against Assad to say that the chemical was one the opposition could not have had access to.  So crucial has it become that the UK’s Ambassador Adams has said it: ‘There is no evidence to suggest that any party to the conflict in Syria, other than the Syrian Government, has access to a complex nerve agent such as sarin.’

Still, just saying it does not make it true if the report you are relying on does not say it is true. And – it bears repeating – the OPCW does not say anything that clearly rules out the possibility of opposition responsibility for the incident.

It bears repeating because to accept the unsubstantiated claim as a pretext for sending more bombs, death and destruction against the people of Syria would be a heinous act. Anybody who pronounces on the matter without striving to be scrupulously honest and clear about what they are saying will be complicit in that act.



This entry was posted in disinformation, journalism, propaganda, Syria, UK Government, Uncategorized, war. Bookmark the permalink.

11 Responses to How like sarin is a sarin-like substance?

  1. Paul McKeigue says:


    The rather odd phrase “sarin, or a sarin-like substance” has come up repeatedly in OPCW reports, and caused some puzzlement.

    Close reading of OPCW reports shows that this phrase is used as a pedantic way of reporting a positive result for sarin in the “fluoride regeneration” test that is used on blood samples. When sarin binds to its receptor, the sarin molecule loses a fluoride ion. In the fluoride regeneration test, fluoride is added in excess to the sample to reverse this reaction and regenerate sarin which can then be detected by mass spectrometry. It is theoretically possible that this test could be positive for sarin if the original molecule had some other atom or group, such as a chlorine atom or cyanide group, as the “leaving group” instead of a fluorine atom. This isn’t relevant as there would be no advantage in trying to synthesize such a molecule as it would be no easier to produce than sarin, and less useful either as a CW agent or for purposes of blaming the Syrian government.

    Three lines of evidence were available to the UK government in 2013 to suggest that the opposition had sarin:

    1. A report by Mokhtar Lamani, then the UN Special Representative in Damascus, investigating the Khan-al-Assal attack in March 2013, that the Nusra Front was bringing what appeared to be a nerve agent into Syria from Turkey.

    2. The prosecutors’ report on the Nusra team arrested in Turkey in May 2013, with phone intercepts showing that they were buying sarin precursors in large quantities

    3. The report of Russia’s OPCW-designated Laboratory of Chemical and Analytical Control in July 2013 that the sarin recovered from Khan-al-Assal was “home-made” and “not synthesized in an industrial environment”. This report was circulated to the other four governments of the UNSC P5. As at this time both the UK and French CW detection laboratories (Porton Down and Le Bouchet) had their own samples from alleged chemical attacks in Syria, they could easily have rebutted the Russian findings if their own analyses had failed to replicate them.

    • Neil Broatch says:

      Hi, I was wondering, given your expertise, if you thought the OPCW results would be consistent with the scenario some have put forward, where a conventional munition struck a depot containing chemicals such as fertilizers, or pesticides and that secondary explosions occured spreading a poisonous cloud?

      This report concerning March/April 2013 incidents seems to suggest this is possible.

      “Another person familiar with the issue, who asked not to be further identified because of its sensitivity, said that only a minuscule trace of a “byproduct”– a toxic residue left behind after use of a nerve agent, and which he did not identify – had been found in a soil sample.

      “They found trace amounts of a byproduct in soil, but there are also fertilizers that give out the same byproduct,” the person said. “It’s far from conclusive.””

  2. DDTea says:

    Hi Paul,

    I have qualms about Russia’s conclusions regarding the Khan Al-Assal attack and wish that we could see their report. They mentioned that Sarin was mixed with diisopropyl fluorophosphate (DIFP) and dispersed by hexogen (another name for RDX). To them, this is “homemade sarin” made in “cottage industry” conditions. This is not necessarily so. It could simply reflect priority being given to ease of manufacture rather than an unnecessarily pure material. My conjecture on the manufacturing process would explain the mixture of side products (see note at bottom, rehashed more succinctly from earlier discussions). This may well be the signature of SSRC sarin.

    I want to know what evidence led them to conclude that hexogen was used as the bursting explosive. Was it, perhaps, hexamine residues? Because hexamine is neither a significant impurity in nor a known decomposition product of RDX. However, hexamine appears at every single Sarin attack site in Syria; the French Intelligence Report mentions that hexamine was found in a recovered Sarin grenade that was allegedly dropped from a helicopter, suggesting it has some purpose in the context of sarin; and Syria declared 80 tons of hexamine as part of its chemical warfare program.

    If the rebels had a motive to use sarin on regime troops in Khan Al-Assal, it would have been *during* the fight to capture the police academy, not after the rebels had already captured it. On the contrary, the loss of the police academy was a setback for the regime, which may have precipitated their decision to deploy chemical weapons. Also, I don’t think it’s a coincidence that in both Khan Al-Assal and Khan Sheikhoun, airstrikes occurred in the chemical target area immediately after the agent was dispersed. My theory: the government does this to break up windows and fortifications, allowing the agent to diffuse into the target area better.


    To reiterate (in formula form):

    1. DMMP + PCl5 (excess) –> “DC” + POCl3 + PCl5 (“Mixture A”)
    2. [Mixture A”] + NaF (or HF gas) –> “DF” + POF3 + hexafluorophosphate . (“Mixture B”)
    3. [“Mixture B”] + isopropanol –(hexamine)–> Sarin, DIFP, DPP, DIMP, TIPP, hexafluorophosphate

    Isopropanol may contain ethanol and water. This would account for EIMP and pyroester residues seen at chemical attack sites. Sarin, DIFP, and sarin pyroester are all lethal nerve agents. TIPP was recently detected in samples from Khan Sheikhoun.

    • DDTea says:

      *DPP is a typo and should not be there. DIFP is referred to as DIPF in the OPCW report on Khan Sheikhoun.

    • Paul McKeigue says:


      As I’m sure you know better than I do, there has been a lot of work on “chemical signature attribution” for CW agents since 2010 See for instance the seminar at the American Chemical Society on 3 April this year on “Investigations of Alleged Use & Source Attribution of Chemical Weapons”.

      A leading researcher in this field is Carlos Fraga at Pacific Northwest National Laboratory, This is one of his group’s most relevant publications.
      Impurity Profiling to Match a Nerve Agent to Its Precursor Source for Chemical Forensics Applications. Carlos G. Fraga, Gabriel A. Pérez Acosta, Michael D. Crenshaw, Krys Wallace, Gary M. Mong, and Heather A Colburn. Anal. Chem., 2011, 83 (24), pp 9564–9572

      They showed that a sample of sarin can be matched not just to its source but to the batches of chemical precursors that it was produced from. They found 947 impurity peaks by GC/MS of which they used 43 for attribution by partial least-squares discriminant analysis.

      I think it’s clear from this that no serious investigator would base chemical forensics on a single molecule like hexamine.

      We know that both OPCW and the US Army’s Edgewood Chemical Biological Center have the results of GC/MS profiling of the Syrian military stocks of DF that were destroyed on the Cape Ray in 2014. We now know also that OPCW, Porton Down and Le Bouchet all have environmental samples of sarin from Khan Sheikhoun, and other alleged chemical attacks in Syria, and have profiled these samples by GC/MS. It should therefore be straightforward to establish whether or not the chemical signatures of the sarin recovered from these alleged attacks used in these alleged chemical attacks matches Syrian military stocks. As the mandate from the UN Security Council for the UN-OPCW Joint Investigative Mechanism established in 2015 requires it to identify “individuals, entities, groups, or governments involved in the use of chemicals as weapons” in Syria, with no time limit, it is difficult to understand why this has not been done, or if it has been done why it has not been reported.

      • Marko says:

        Yes , the trail left by those GC-MS signatures would seem like the obvious one to follow , which makes one suspicious by their refusal to do so , at least in public view.

        What if many , if not every , of the various sarin attacks yielded samples that showed a GC-MS signature suggesting a different source – this time Syrian , the next Libyan ,then “kitchen” , then Iraqi , maybe even American , French , Israeli , or British? Yet they all show the “telltale” hexamine residues. Oops ! Someone would sure have some ‘splainin’ to do.

        Hexamine makes for a nice , simple story that the public can easily grasp.Those confusing and confounding GC-MS traces will never – ever – see the light of day , unless they’re leaked. Wikileaks should put out a call……

  3. Pingback: How like sarin is a sarin-like substance? |  SHOAH

  4. timhayward says:

    Thanks Paul and Marko, these comments really go to underline how helpless we the general public are in front of misleading and deliberately incomplete information. If only more scientists would be prepared to engage in public education in these matters!

  5. Pingback: Khan Sheikhoun Chemical Attack: Guest Blog Featuring Paul McKeigue’s Reassessment | Tim Hayward

  6. Gaetano says:

    Sarin, cyclosarin, chlorosarin etc. all leave the same biomarkers and degradation products. Sarin itself is highly volatile and therefore does not hang around in the environment very long before degrading into simpler compounds. Those compounds are what is actually left behind in soil, blood, urine, etc.. For all practical purposes, these are all Schedule 1 organophosphate chemical weapon agents. Don’t make too much of the ambiguity.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s