Questions related to Analytical Instruments

What is Chromatography?
Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of which is stationary (stationary phase) while the other (the mobile phase) moves in a definite direction. Chromatography may be preparative or analytical.

What is a Chromatogram?
A chromatogram is he visual output of the chromatograph in case of an optiomal separation, different peaks or patterns on the chromatogram corresponds to different components of the separated mixture. It is a graph relating concentration of solute leaving a chromatographic column, against time.

What does HPLC means?
HPLC stands for “High Performance Liquid Chromatograph”. Previously it stands for High Pressure Liquid Chromatograph.

What is the difference between Gas Chromatograph (GC) and Liquid Chromatograph (HPLC)?
The mobile phase carries in GC is a Gas whereas it is Liquid (Solvent/Water) in HPLC.

What is a ‘Mass Spectrum’?
A Mass Spectrum is intensity Vs m/z (mass-to-charge ratio) plot representing a chemical analysis. Hence, the mass spectrum of a sample is a pattern representing the distribution of components (atoms or molecules) by mass (more correctly mass to charge ratio) in a sample. It is usually acquired using an instrument called a mass spectrometer.

What do you mean by Reverse Phase Chromatograph?
Reversed phase HPLC (RPHPLC) consists of a non-polar stationary phase and a moderately polar mobile phase.

What do you mean by Normal Phase Chromatograph?
Normal Phase HPLC uses a polar stationary phase and a non-polar mobile phase, and is used when the analyte of interest is fairly polar in nature.

Name some polar solvents?
Methanol, Acetonitril etc. are the polar solvents.

Name some non-polar solvents?
Hexane, Dichloromethane, Benzene etc. are some non-polar solvents.

What do you mean by Isocratic HPLC?
HPLC system with only one solvent pump is called isocratic HPLC.

What do you mean by Binary HPLC?
HPLC system with two solvent pumps is called Binary HPLC.

What is FID detector?
A Flame Ionization Detector (FID) consists of a hydrogen (H2)/air flame and a collector plate. The effluent from the GC column passes through the flame, which breaks down organic molecules and produces ions. The ions are collected on a biased electrode and produce an electrical signal.

What is FPD detector?
The Flame Photometric Detector (FPD) allows sensitive and selective measurements of volatile sulphur and phosphorus compounds. The detection principle is the formation of excited sulphur (S2) and HPO species in a reducing flame. A photo-multiplier tube measure the characteristic chemiluminescent emission from these species. The optical fibre can be changed to allow the photo-multiplier to view light of 394 nm for sulphur measurement or 526 nm for phosphorus.

What is full form of ECD detector?
It’s ‘Electron Capture Detector’.

What is full form of NPD detector?
It’s ‘Nitrogen & Phosphorus Detector’.

What is m/z ratio?
m/z ratio denote the quantity formed by dividing the mass of an ion by the unified atomic mass unit and by its charge number (positive absolute value). This has been referred to as a mass-to-charge ratio, although it does not fit this description.

What is UV detector?
Ultra Violet (UV) detectors measure the ability of a sample to absorb light. This can be accomplished at one or several wavelengths.

What is Fluorescence detector?
Fluorescence detector measures the ability of a compound to absorb then re-emit light at given wavelength. Each compound has a characteristic fluorescence. The excitation source passes through the flow-cell to a photo detector while a mono-chromator measures the emission wavelengths.

What is Electrochemical detector?
Electrochemical detector measure compounds that undergo oxidation or reduction reaction. Usually accomplished by measuring gain or loss of electrons from migrating samples as they pass between electrodes at a given difference in electrical potential.

What is RT?
Retention Time (RT) is the characteristic time it takes for a particulars analyte to pass through the system (from the column in let to the detector) under set conditions.