#marshtest

[forensicfield]

James Marsh and the Marsh Test

An important test used in early toxicology was developed in 1836 by chemist James Marsh (1794–1846). In 1832 John Bodle had been accused of poisoning his grandfather with arsenic placed in coffee. Marsh was asked by the prosecution to check the stomach contents of the victim. He used a hydrogen sulfide method and was able to produce a yellow solid consistent with the presence of arsenic. Unfortunately, the solid degraded between the time it was prepared and when it was presented to a jury. To Marsh’s dismay Bodle was acquitted.

Marsh went into his lab with one simple goal: develop a reliable and visually convincing method to detect arsenic in messy and complex samples like tissue and stomach contents. First, he turned to Scheele’s procedure in which arsenic was converted to arsine gas. Marsh knew that under the proper conditions compounds containing arsenic, such as arsine, could be manipulated to form arsenic metal. Magnus had demonstrated that conversion centuries earlier. Marsh realized that metallic arsenic is stable, and if he could capture the arsine gas, he could manipulate it so that metallic arsenic would form on a solid surface. This process is sometimes called “plating out.” This simple idea took Marsh four years to perfect, and the method became known as the Marsh test. This famous procedure was the first reliable analytical test for arsenic. For his efforts Marsh received wide acclaim and a gold medal from the Royal Society of Arts.

[josvandenbroek]

Vergif met een knoflookluchtje

Tegenwoordig is het een fluitje van een cent om arseen aan te tonen. Vroeger – eind 19de eeuw – kostte het heel wat meer moeite. Toch was er toen al een heel gevoelige methode die forensisch toxicologen toepasten bij een vermoeden van arseenvergiftiging: de marshtest, genoemd naar de Britse scheikundige James Marsh.

Tot de opkomst van deze test rond 1840 was rattengif in de vorm van wit arseen(III)oxide favoriet om je tegenstanders ongemerkt om te leggen. Het heeft geen smaak, je kunt het eenvoudig toevoegen aan levensmiddelen en bovenal kon je het moeilijk traceren.

De marshtest komt neer op de reductie van arseen(III)oxide met zink in sterk zuur milieu tot arsine of arsaan (arseenhydride). Dat is een gas met een knoflookachtige geur. De neus van de analytisch chemicus was dus een uiterst gevoelig instrument om arseen aan te tonen.

Het ontstane arseenhydride ontleedt bij verhitting, en laat vervolgend een zwartglanzende arseenspiegel achter op glas. Het woord 'spiegel' moet je hier dus letterlijk nemen. Je kon moeilijk een rechter aan een buisje met knoflook laten ruiken. De arseenspiegel – het buisje met daarom arseen neergeslagen – kon je wel als bewijsstuk meenemen naar de rechtszaal. Het is deze procedure die de Leidse hoogleraar artsenijbereidkunde Van den Burg als getuige-deskundige heeft toegepast in de zaak-Maria Swanenburg, geboren Van der Linden ('Goeie Mie').

[forensicfield]

Question- Who has developed the Marsh Test? Answer-  It was developed by the chemist James Marsh and first published in 1836. Question- Why is it used? Answer- Marsh test is a method for the detection of arsenic , so sensitive that it can be used to detect minute amounts of arsenic in foods (the residue of fruit spray) or in stomach contents. Question- What is the procedure for Marsh Test? Answer- First, add some zinc to the test tube. Then, the arsenic compound, and in this case, it's arsenious acid = As(OH)3. Then, place a stopper with a dripping funnel filled with hydrochloric acid onto the test tube. The reaction of zinc with the hydrochloric acid sets produces nascent hydrogen, which reacts with the arsenic compound to form arsine. The arsine bubbles through the hydrogen to the glass pipette. This arsine/hydrogen mixture is very flammable. Ignite it at the end of the pipette, which causes pure arsenic to be condensed out of the flame. Sensitivity- The lowest level of detection for this test is 1µg. --------------------------- #forensicfield #forensicbiology #forensicintro #forensicstudy #forensicscientist #forensiclab #forensic #forensics  #rigormortis #criminalistic #criminology #crimescene #crimesceneinvestigation #forensicscientist #forensicinvestigation #forensicmedicine #forensictechnology #forensictechniques #forensictechnic #bloodyprint #pathology #pathologist #deadtales #deadtalk #forensicpathology #Postmorteminterval #evidence #evidences #crimesceneevidence #arsenic #marshtest https://www.instagram.com/p/B60GS3Kpnkm/?igshid=lvqr8imc1461