Phar Lap's preserved hide, which is on display at Museum Victoria, Melbourne, Australia.
Their peer-reviewed work has just been published online, ahead of print, in the international edition of the journal, Angewandte Chemie.
Debate has raged over the circumstances around Phar Lap's mysterious death in 1932, just two weeks after winning the richest race on North American soil.
Speculation swirled that the horse may have been deliberately poisoned in a mobster hit, or had accidentally consumed insecticide on sprayed grass.
However, no conclusive reason for his fatal mystery illness was established.
The study by Kempson and Henry, entitled "Determination of Arsenic Poisoning and Metabolism in Hair by Synchrotron Radiation: The Case of Phar Lap", centred around the analysis of four mane hairs taken from Phar Lap, whose mounted hide is on display at the Melbourne Museum.
An arsenic based recipe for a horse tonic written by Phar Lap's trainer Harry Telford.
However, analysis work, including samples from two horse exhibits in Scotland of a similar era to Phar Lap, reveal key chemical differences between the arsenic used in hide preservation and that which Phar Lap ingested.
Aside from providing evidence of massive ingestion of arsensic, the pair also worked to show it did not form part of regular dosing with small amounts of arsenic - a common ingredients in horse tonics at the time.
Kempson and Henry described Phar Lap's demise as one of sport's most intriguing mysteries.
The researchers used a synchrotron X-ray fluorescence microprobe in the United States to test the mane samples.
Only hairs identified as being in a growth phase were used.
Analysis of Phar Lap's hair. An optical image shows the root end of one hair with the root sheath intact (a). The hair was analyzed with an X-ray microprobe that imaged the internal arsenic distribution (b). The longitudinal profile reflects the hair growing outwards as the arsenic is metabolized (c), while 2D XANES mapping reveals the variation in arsenic speciation ratios (d).
This map indicated low arsenic concentrations throughout the hair. However, in the hair region beneath the skin, an intense band existed in all hairs at the same location.
This band indicated a substantial increase in arsensic, followed by its subsequent decay as Phar Lap's body tried to metabolise it in the lead-up to his painful death.
Based on horse-hair growth patterns, the pair estimated Phar Lap received the arsenic dose 30 to 40 hours before his death.
The wide extent of arsenic distribution in the hairs showed Phar Lap's hide had been treated with an arsenic-based preservative. The pair's analysis work was able to show that the arsenic used in the preservation process of Phar Lap's hide behaved differently under a beam-induced photo-reduction process than that which had been ingested.
Kempson and Henry also tested hair samples from two horses from the early 20th century, held at the National Museum of Scotland.
That work showed that the arsenic used for hide preservation in Phar Lap and the two hide samples in Scotland rapidly photo-reduced from arsenate to arsenite, which the ingested arensic did not.
Micro X-ray fluorescence maps of sulfur and arsenic. Arsenic has a strong affinity for the sulfur-rich cuticle layer as well as within the cortex, and to a lesser extent the root sheath.
"While the reasons for this difference are unclear, the effect may be used to discriminate between the two modes of arsenic incorporation."
They continued: "At the time of Phar Lap's demise, he vomited blood and suffered from abdominal pain, high temperature, gastrointestinal inflammation, and ulcers, which are consistent with all cause-of-death theories proposed.
"A point of contention has been that he did not have diarrhoea. However, this symptom is not universally encountered in humans, horses, and cattle [in arsenic poisoning].
"Even in modern veterinary practice, the diagnosis of arsenic poisoning is not easy. There are several documented accounts of horses dying from arsenic poisoning; in one instance, if arsenic had not been identified in the animal's feed, then poisoning would have been indistinguishable from colitis."
The authors noted that arsenic concentrations in the organs of horses are typically around only 10 parts per million in fatal cases, if they can be detected at all.
"Small quantities of arsenic were measured in Phar Lap's vital organs," they wrote. "This result supports the poisoning argument, but was dismissed at the time as the concentrations were too low.
"The suggestion of a fatal dose of arsenic has been highly provocative, and has led to conspiracy theories that raise questions of foul play and involvement of gangsters and illegal racing syndicates.
"Other theories include a bad 'green feed' ... However, other horses had access to the same foliage but did not fall ill."
Kempson and Henry said their arsenic evidence did not necessarily point to a deliberate act of poisoning.
"An unfortunate case of misadventure or a simple dosing error provides another explanation," they said.
"Arsenic-based tonics were common in the racing industry for boosting the oxygen-carrying capacity of the blood, improving stamina, and stimulating appetite to improve an animal's ability.
"The tonic book of Harry Telford (Phar Lap's trainer), held by Museum Victoria, lists an arsenicalis-based tonic that is 'a great tonic for all horses'.
"Many complexities in the analysis (and interpretation of results) of arsenic in hair exist," they wrote, "yet the results presented here show arsenic distribution and chemistry consistent with ingestion of a large dose of arsenic just prior to death; a finding that is consistent with his symptoms and autopsy results.
"Many questions, such as the source of the arsenic, are beyond the scope of this work; it is likely that the events of Phar Lap's last days will remain entrenched in mystery."
Determination of Arsenic Poisoning and Metabolism in Hair by Synchrotron Radiation: The Case of Phar Lap.
Ivan M. Kempson, and Dermot A. Henry
Angew. Chem. Int. Ed. 2010, 49,