Gaschromatograph

Gas chromatography is an analytical method to separate and detect a mixture of substances in a column. The separation is based on different levels of interaction between the column and the analytes.
Professional GC are very expensive (5000$) and not affordable for schools or the private basement lab.
With this GC-Column it is possible to separate and analyse LPG or other low molecular weight alkanes (C1-C5) which can be found in lighter gas.
The packend column of this GC is made of an PVC 1,5m infusionssystem filled with Silika gel.

Step 1: General Structure of GC

A typical gaschromatograph consists of different components.

1. Temperaturen-controlled oven containing the column.
2. The column in where the sample is separated on the stationary phase.
3. A carrier Gas (Helium, Hydrogen, Nitrogen) that transports the sample through the column.
4. A detektor to dedicate the different components of the sample. Mostly are flame Ionisation or thermal conductivity detektors are used.
5. Interface or integrator to translate data into a chromatogram.
6. Injektionunit for injecting the sample onto the column.

The sample (for example a mixture of Butane and Propane) is injectet into the column. The two components stays different long in the column and can be determined qualitatively over the retention time.
The Area below the peak is proportional to the concentration of the analyts.

Step 2: Hardware

•5V diaphragm pump
•silicon tubing
•clamp for the pump
•Switch
•CARESITE® Positive Displacement Needleless Connectors
•Arduino UNO
•TGS-813 Gassensor
•push button to reset program
•three way valve
•breadboard
•10k Resistor
•Jumper wires




https://m.youtube.com/watch?v=nDdQ6vMInPI

Step 3: Arduino Gas Detection Unit

Sketch is from another sensorprogram, some parts arent´t nessesary for the GC, but it works verry well.

To plot the chromatogram in excel you have to download PLX DAQ, its a plotting macro for MS excel.

It is also possible to use the serial plotter


Sketch:

float vp = 1.7;
float r1 = 100000;
float r2 = 10000;
float ts = 0;

void setup() {

Serial.begin(9600);
Serial.println("CLEARDATA");
Serial.println("LABEL");
Serial.println("RESETTIMER");

Serial.println((int) (vp / (r2 / (r1 + r2))));

delay(1000);
}
void loop() {
float v = (analogRead (0) * vp) / 1024.0;
float v2 = ((v / (r2 / (r1 + r2))*10)+1); // here you can calibrate the sensor
if (v2 <2) {
v2 = 0.00;

}
Serial.print("DATA,TIME,TIMER,");
Serial.println(v2);
delay (1000);
}

Step 4: How to Fill the Column

To pack the column you need silica gel 60 for column chromatography grain size 0,03-0.2mm. Bigger Grain size is also possible, but not bigger than 0,5mm.

For one column you need:
•10g Silica gel 60 (Carl Roth Sigma Aldrich)
•30ml Petroleum Ether 40-60 pharmazeutical purity (buy in your local Pharmacie)
•1g high-viscosity paraffin pharmazeutical purity
•200ml beaker
•glasrod
•oven
•1,5m infusion system with Luer-Lock joint. (Intrafix Braun)
•Balance


Solve the paraffin in petrolether and add the Silica Gel. Leave it by good ventilation until solvent is evaporated.
Dry the silica gel by 120°C (30 minutes) and fill it in the infusionsystem.
connect to the pump an rinse the column until you get a constant baseline.

Your column is now ready to use.

Step 5: Connection Between Column and Sensor

The distance between column and sensor have to be as small as possible so that the flow velocity does not change. Big distance leads in wide peaks and tailing.
For the fitting you can use a syringe.