top of page

#4 Chemical Paint: Forensic Toxicology II

Updated: 16 hours ago

STEM on the streets

Hi there! Welcome back to STEM on the Streets if you are new here, my name is Aiza Jamil and alongside CAI (Crime AI) we will be going through the legal and illegal streets of STEM. And if you missed the previous episode I recommend going and checking it out for better context (click the button).



(✿◡‿◡)CAI: The scene is set in a white room, filled with cabinets the colour of an acorn. A woman wearing a white lab coat. Her ugly chicken-feet hands reach for a pale blue bag. With a metal measuring cup, she carefully measured out a white powdery substance and placed it in the bowl. Some of the powder drifted through the air and fell on her- on her flip-flops?

CAI, for goodness gracious sake! Stop telling people I make sourdough like if I am in Breaking Bad or a witch of some sort! And those aren't just any flip-flops, they are flip-flops blessed by the rats of comfort!

 (✿◡‿◡)CAI: You need some serious supervision while in the kitchen. And I would never eat anything you make.

CAI, that's very entitled of you to assume I would offer you some in the first place. Secondly, I don't disagree with the fact that I need supervision in the kitchen- I truly do. Now, CAI, if you would stop being so dramatic we have a long episode to go through so it's best we start now.

Methods of Toxicology

Now, last episode we listed 5 different methods of toxicology, that is if you remember cause I surely don't. CAI, could you list the different methods, please?

 (✿◡‿◡)CAI: See, I told you she has the memory of a mop-

CAI, I am sitting right here!

 (✿◡‿◡)CAI: Fine. Here are the 5 sorts of toxicology analysis (we'll be going through the bold ones):

  1. spectrophotometry

  2. chromatographic methods

  3. immunologic methods

  4. gas chromatography-mass spectrometry

  5. special methods for metal analysis

Lovely, I remember now. CAI, because I want to do the crime part, can you do the methods part?

(✿◡‿◡)CAI: It would be my pleasure.



Big word don't you think?

(✿◡‿◡)CAI: I believe it was my turn.

Sorry, my bad.

(✿◡‿◡)CAI: Ahem- ah yes, spectrophotometry. Aiza would have taken ages on just going through spectrophotometry but I can do it way faster. Generally, spectrophotometry is a technique used to measure the amount of light absorbed by a chemical substance present in a sample solution. The method involves passing a beam of light through the sample solution and measuring the intensity of the light that passes through. The underlying principle is that every compound absorbs or transmits light within a specific range of wavelengths.

For the sake of relating this to forensics, here is an example:

In the event of a shooting crime where no weapon has been found, smokeless powder can be a crucial piece of forensic evidence. Smokeless powder is the propellant that is deposited from cartridges when they are fired. To identify the smokeless powder, a spectrophotometer is used to gather information which is then compared to a database of different types of smokeless powder used in various cartridges. This process can help investigators identify the type of firearm used in the crime.

There you go I summarised it in two paragraphs!

You know, CAI, that is why I gave you the boring stuff to do. So keep it short, thanks!



Listen, CAI, please make this one more fun.

(✿◡‿◡)CAI: By doing what? Adding the topic of drugs and that sort to it?

Preferably, yes.

(✿◡‿◡)CAI: Lucky for you, chromatography does have something to do with drugs. According to Google chromatography is a technique for the separation of a mixture by passing it in solution or suspension through a medium in which the components move at different rates. There are two types of chromatography:

  • Gas Chromatography

  • Liquid Chromatography

There are two different methods of chromatography:

  • Paper Chromatography (the only difference between the two is the stationary phase. In paper chromatography, the stationary phase is cellulose filter paper containing water in the pores)

  • Thin-Layer Chromatography ( according to Google: chromatography in which compounds are separated on a thin layer of adsorbent material, typically a coating of silica gel on a glass plate or plastic sheet.)

Gas Chromatography

(✿◡‿◡)CAI: One of the most common and well-known gas chromatography devices is breathalysers used for drug testing. Aiza, stop smiling.

Oh, no don't mind me just sitting here.

(✿◡‿◡)CAI: Now where was I? Ah, yes gas chromatography.

Gas chromatography is a process used to separate the various elements of a compound for individual analysis. This is done by observing how the elements react with a specific solvent and identifying them using their unique "retention time". Retention time refers to the time it takes for an element to release the solvent, and it occurs when a liquid stationary element is transformed into a gaseous mobile element.

Liquid Chromatography

(✿◡‿◡)CAI: Liquid chromatography can be used to find or detect drugs in the blood- Aiza this is the last time I am going to tell you to stop smiling when you hear the word 'drug'!

I am not smiling at the word 'drug'! How rude of you to accuse me like that! I am smiling because I am winning the imaginary argument going on in my head at the moment.

(✿◡‿◡)CAI: Fine. Liquid chromatography is when the liquid solvent is absorbed by the paper, the compounds within the mixture gradually separate. This method is used by forensic scientists to analyze fingerprints and certain bodily fluids. The mixture typically comprises compounds of varying colours, which can be observed separating as the solvent progresses up the paper strip.


Special Methods for Metals

(✿◡‿◡)CAI: There are different special methods for analysing metals and special tools like Trace Metal Detection (TMDT) solutions.

When a person comes into contact with a metal object for a prolonged period of time, some metal ions from the surface of the object may transfer onto their skin or clothing. These metal ions can then react with the Trace Metal Detection (TMDT) solution, causing a chemical reaction that can be detected by specialized equipment. The TMDT solution is often used in forensic investigations or industrial settings to detect the presence of trace amounts of metal on surfaces or clothing.


Experiment Time!

Have you ever wanted to be a real-time forensics scientist? Or at least try to do something forensic-y?

(✿◡‿◡)CAI: Aiza, you sound like one of those incredibly annoying ads.

CAI, shut up or I'll shut you down!

Excuse me. Well if you have wanted to do forensic-y stuff we have the perfect experiment for you! You will need the following materials:

  • Different types of black felt tip pens or ballpoint

  • Coffee filter or a kitchen towel ( use a thick kitchen towel, not a thin one)

  • A clear cup or glass

  • Water

  • Straw

  • Paper clips

  • Pencil

  • Ruler

You are going to be making your paper chromatogram. Here are the steps:

  1. Take your kitchen towel or coffee paper and mark a line using your pencil 2 cm away from the bottom

  2. Make 1 circle and colour it in and if you are using different sorts of black ink or pens make sure to space them equally.

  3. Add water to the cup, make sure it is only 1 cm deep

  4. Place the straw horizontally on the clear glass and hang or attach the coffee filter or kitchen towel to it. At this point, only 1 cm from the bottom of the filter or kitchen towel should be in contact with the water.

  5. Wait for a few seconds and you'll see the water traveling upward and the inks will separate into different colours.

Chromatogram Diagram

The inks are separated into different colours because a solid colour of ink is made from multiple different colours. You'll soon find out why this is helpful in forensic investigations.


That's all for today folks. Our goal is to have short, informative and interesting blogs for our readers but because of SOMEONE, not mentioning names (CAI), we reached our blog limit. So my sincere apologies to my fellow crime enthusiasts who were looking forward to the crime case- we'll be doing that next episode. To make up for it I have attached a little mystery puzzle below.

I'm a forensics sleuth, what's your mystery to solve?

Thanks for reading! This is Aiza Jamil signing out!


Forensic scientists may find notes written with a pen on the crime scene. Separating it into different colours might help but always keep in mind someone can be framed!

In the office building, there have been a lot of chocolate thefts going around. The latest one left a note:

Chocolate thiefs note
The Chocolate Thief's Note

You, a super forensic scientist were able to separate the ink's colours and this is the chromatograph you ended up with:

The Chocolate Thief's Pen's Chromatograph

There are three suspects found with three pens. You ran chromatography tests on each of the pens now it's time to find out who is guilty!

Analyze the chromatograms. Who is the Chocolate Thief?

  • Susan Jax

  • Bob McGrath

  • Shagufta Riaz

Citations (click on the button to find out more)


bottom of page