Skip to main content

Mass Spectrometer Working Principle

 Mass spectrometer :

Principle:

Mass spectrometer works on mass to charge ratio principle.

To know the Mass spectrometer, first we have to know what is Mass Number ?

Mass number is also called atomic mass number which is the total number of protons and neutrons in an atomic nucleus.

As carbon (C) has 6 protons and 6 neutrons so in carbon total mass number is (6+6 =12)

As CH4 (Methane) total mass is

Carbon mass is 12 and H mass is 1 then total mass is = 12+1 x 4 = 16

Mass to charge ratio is denoted by m/z or m/e, Mass to charge ratio of a cation is equal to mass of cation divided by charge of cation. Charge of cation in mass spectrometer is always +1. So mass-to-charge ratio of a cation is usually equal to the mass of the cation.

A mass spectrometer is a gas analyzer in which sample molecules are pulled into a vacuum system then ionized (using an electrical charge), which are then separated by mass-to-charge ratio by the quadrupole and the detector measures the equivalent ion current (quantitative) which is the analyzer output reading.

Parts of Mass Spectrometer:

Here we are discussing about Extrel Make, MAX 300 Model Mass Spectrometer

Inlet and outlet valves:

There are two rotary selector valves in which one rotary selector valve is used for sample gas and 2nd is used for calibration.

Each rotary valve has 16 ports each port has a separate outlet and there is a common outlet. In calibration, rotary selector valve outlet is plugged to avoid the mixing of gases.

At one time, only one inlet is connected with common port and left port is connected to outlet and its continuous vent. By continuous vent sample become dry and there is no deposition of condensate. The Inlet ports with the larger diameter fitting, contains a 2 micron filter and are labeled with an arrow pointing towards the valve body.  The Inlets are in the row closest to the common port for both the front loading and rear loading valves.

After the outlet of common parts, there are 2 types of inlets used.

Direct inlet
*Differentially pumped inlet
*The direct inlet is required for samples near 1atm and the differentially pumped inlet is used for low pressure applications.

After this sample goes in Ionizer
Ionizer main parts :

Filaments: filament is a part of the ionizer assembly. A filament is simply a resistor to which electrical power is applied and converted to heat the filaments. The filament’s temperature will rise until it loses free electrons at the rate the heat is generated. There are 2 filaments. One is always in line and second always is in auto made when first is fail then second automatic comes in line.

The main purpose of a filament is to produce free electrons (e–) which will then collide with a neutral atom in the ion volume to produce ions.

Lens:  A unique voltage is applied to each of the lens elements, as they help focus the positively charged ions toward the Quadrupole and the detector.  The ions, which have a positive charge, are attracted to a negative charge that is applied to a lens and repelled by a positive charge.

How ionizer works:  A current is continuously applied to the (active) filament to heat it up and emit electrons.  The capillary leaks a small amount of sample into the ionizer where it is bombarded by electrons to make positively charged ions. The positive charged ions are attracted towards the lens stack where there is a negative voltage potential. The ions are pulled out of the ionizer and directed into the quadrupole mass filter

Quadrupoles: The main heart of mass spectrometer is Quadrupoles. Quadrupoles are known as the “Mass Filter. , they are four  ¾ inch (19mm) stainless steel rods held together by two ceramic collars. The quadrupole separate ions according to their mass per charge ratio (m/z).  They deflect and attract the ions by an applied magnetic field, produced by voltages applied to the quadrupole.   The voltage applied to the quads changes continuously, which attracts and deflects each ion equally toward the detector If a positive voltage is applied to one set of rods and a negative voltage to the other set of rods, the rods with the negative voltage will attract the positive ions.  Eventually, the ions will hit the negatively charged rods and become neutralized.  The ion becomes neutralized when it collides with the negative rod, because the rod gives up an electron to the ion.

Summary Of Quadrupole working

*RF and DC voltage is applied to opposite rods
*Only ions of the right mass make it all the way down the quad
*Other masses are unstable and will strike the quad and be neutralized and pumped away
Detector:  For detection the positively charged ion we use a faraday plate. The faraday plate is a stainless steel flat disk on which ions are detected. After exiting the quadrupole, the positively charged ion will strike the stainless steel plate, producing a small current which is proportional to the gas concentration .that is sent to the preamplifier.



Vacuum Pump: Vacuum pump is used for pump out the collide or neutralized ions from quadrupole its outlet is connected with venting system.





Labels:

Comments

Post a Comment

Popular posts from this blog

PLC Program for Mixing Tank

 Create a ladder diagram for controlling a batch mixing process. Implement a PLC program for mixing tank or Mixing Process using PLC Ladder Logic. PLC Program for Mixing Tank Fig : Mixing tank A tank is used to mix two liquids. The required control circuit operates as follows: A. When the START button is pressed, solenoids A and B energize. This permits the two liquids to begin filling the tank. B. When the tank is filled, the float switch trips. This de-energizes solenoids A and B and starts the motor used to mix the liquids together. C. The motor is permitted to run for 1 minute. After 1 minute has elapsed, the motor turns off and solenoid C energizes to drain the tank. D. When the tank is empty, the float switch de- energizes solenoid C. E. A STOP button can be used to stop the process at any point. F. If the motor becomes overloaded, the action of the entire circuit will stop. G. Once the circuit has been energized, it will continue to operate until it is manually stopped. Solution...
1 comment
Read more

What is Relay? How it Works? Types, Applications, Testing

 We use relays for a wide range of applications such as home automation, cars and bikes (automobiles), industrial applications, DIY Projects, test and measurement equipment, and many more. But what is Relay? How a Relay Works? What are the Applications of Relays? Let us explore more about relays in this guide. What is a Relay? A Relay is a simple electromechanical switch. While we use normal switches to close or open a circuit manually, a Relay is also a switch that connects or disconnects two circuits. But instead of a manual operation, a relay uses an electrical signal to control an electromagnet, which in turn connects or disconnects another circuit. Relays can be of different types like electromechanical, solid state. Electromechanical relays are frequently used. Let us see the internal parts of this relay before knowing about it working. Although many different types of relay were present, their working is same. Every electromechanical relay consists of an consists of an Elect...
1 comment
Read more

Ferrules and Cross Ferruling

 Ferrules are identification labels provided for every wire terminations in an instrument, equipment, or electrical/instrumentation control panels. These tube-shaped sleeves can be inserted easily on each individual wire in a multi-core cable. In earlier days fixed digits/letters are used as ferrules, but now Instrumentation engineers/technicians prints out desired ferrules by using a ferrule printing machine. Typical Ferrule The numbers/ letters on the ferrules will be given as per the approved electrical hook up or loop diagrams. This helps technicians to easily identify a particular loop/wiring from a series of terminal blocks and to troubleshoot the desired terminal connection. Separate numbers on the ferrules distinguish the positive and negative polarities of wires, thus ensure the polarity protection of the instrument. Cross Ferruling  As a wire is connected on its both ends, it is quite useful to use a cross reference method for wire identification. Unlike normal ferru...
Post a Comment
Read more