Analyzer
Content
Q1. What are the main differences between High Performance Liquid
Chromatography and Gas Chromatography?
In HPLC the mobile phase is a liquid whereas in Gas Chromatography the
mobile phase or carrier is a gas.
HPLC is useful for analysis of samples which are liable to decompose at
higher temperatures. GC involves high temperatures so compounds are
stable at such temperatures.
Gas Chromatography is applied for analysis of volatile compounds whereas
non volatile compounds can be easily analyzed on HPLC
Gas Chromatography cannot be used for analysis of high molecular weight
molecules whereas HPLC has applications for separation and identification of
very high molecular weight compounds
HPLC requires higher operating pressures than GC because liquids require
higher pressures than gases for transport through the system
HPLC columns are short and wide in comparison to GC columns
Q2. Which type of GC detector is most commonly used? Explain its working
principle and what are its limitations?Ans. The most commonly used detector
is the flame ionize detector. The sample is combusted with the help of fuel gas and
oxidant in the detector body. Combustible sample components burn and produce
ions and electrons which can conduct electricity through the flame. A large potential
difference is applied at the burner tip and the collector electrode located above the
flame and the current between the electrodes is measured. The detector is mass
sensitive and response is not affected by carrier gas flow rate changes. However,
the detector is not responsive to inorganic gases such as CO, O2, NH3, N2, CS2,
CO2, etc.
Q3. What are the commonly used carrier gases in GC analysis when using
FID detector?Ans. Inert gases commonly used in analysis when using FID detector
are Nitrogen and Helium. Nitrogen is more commonly used as it is less expensive
than Helium. Purity of carrier gas should be more than 99.995% and on-line traps
should be used to prevent residual moisture or other impurities from entering the
system.
Q4. What are the desirable characteristics of a GC detector ? The detector
chosen for particular analysis should :
Give reproducible response to changes in concentration of eluting
compounds in the carrier gas stream.
Should provide a large linear dynamic range
Should have high sensitivity
Should have small internal volume to give narrow peaks and also facilitate
flushing of previous sample traces
Should preferably be non-destructive
Q5. What do you understand by specificity of a detector?
Ans. Detectors falls into three categories depending upon response to the eluting
compounds:
Non-selective – Respond to all component in the gas stream except for the
carrier gas
Selective – Respond to a particular class of compounds with common
physical or chemical properties
Specific – Respond to a single specific compound only in the carrier gas
stream
Q6. What are the commonly used types of capillary columns? Capillary
columns are generally 10 – 100m long tubes having an internal diameter ranging
from 0.1 – 0.5mm made of flexible material such as fused silica. Common types of
capillary columns are
Wall coated open tubular (WCOT) – Internal wall is coated with a very fine
film of adsorbing liquid
Surface coated open tubular (SCOT) – Inner wall is lined with a layer of solid
support on to which the liquid phase is absorbed.
The columns are flexible and wound into several turn coils supported on a SS cage
inside the column oven
Q7. What do you understand by column efficiency and how it is
expressed? On continuous use a column gradually loses its original resolution
power. Column efficiency is expressed on the basis of plate theory concept. Each
component under separation spends a finite time in each theoretical plate. Smaller
the plate height the larger the number of plates (N) and better is the column
efficiency.
where N = Number of theoretical plate
tr = Retention time of a peak
w = Peak width at base
N can also be expressed as
where w1/2 is peak width at half peak height
Column efficiency is expressed in terms of Height Equivalent to a Theoretical Plate
(HETP)
HETP = L/N
where, L = Length of column in terms of mm
Small value of HETP signifies greater column efficiency
Q8. What do you understand by temperature programming in GC analysis?
Ans. Temperature programming means change of temperature of the column at a
rate predetermined rate during the analytical run. This has the same influence on
elution time of separated components as gradient programming in HPLC analysis.
Temperature programming helps reduce analysis time by permitting early elution of
less volatile components.
Q9. When is isothermal operation useful?
Ans. Isothermal operation is useful when high resolution is required for separating
compounds having narrow boiling range. Temperature is set to around mid range of
boiling points of constituents. This results in good resolution of low boiling
components but band broadening of higher boiling components can result due to
their longer retention in the column.
Q10. What measures you would adopt to extend useful life of a column?
Ans.
Condition a column before first use or after long time storage
Take care not to exceed upper temperature limit specified by the
manufacturer
Avoid injection of solutions which are strongly acidic or basic in nature
Rinse columns by injection with blank solvents such as methanol, methylene
chloride or hexane to remove contamination of column after excessive usage
zriconium oxide SENSOR and paramagenetic are for oxygen i.e. flue
thermal conductivity is for hydrogen .. confirm
purging..... to introduce, n2 or instrument air into the analyzer box to prevent the
sparks causing any
trouble as we are in hazardous zones.
A validation process ensures that the components of a system function together to
meet the need
or intent of a customer or regulating body. The aim of validation is to ensure that
the components of a
system work together to produce the intended result for which the system was
designed.
Whereas verification focuses on the right operation of a process (or product) itself,
validation tends to
focus on the right output of the process.
Calibration is performed at the factory. It establishes the relationship between
flow and signal produced by the sensor.
Validation confirms flow performance by comparing a primary flow standard to the
sensor.
Verification establishes confidence in performance by analysis of the secondary
variables associated
with flow. Many times these terms are used interchangeably. Also, frequently
calibration or validation
is done when only verification is needed.
flue gas analyser enable you to measure the concentrations of the pollutants
present and to
adjust your burners for optimal combustion
Chromatography and Gas Chromatography?
In HPLC the mobile phase is a liquid whereas in Gas Chromatography the
mobile phase or carrier is a gas.
HPLC is useful for analysis of samples which are liable to decompose at
higher temperatures. GC involves high temperatures so compounds are
stable at such temperatures.
Gas Chromatography is applied for analysis of volatile compounds whereas
non volatile compounds can be easily analyzed on HPLC
Gas Chromatography cannot be used for analysis of high molecular weight
molecules whereas HPLC has applications for separation and identification of
very high molecular weight compounds
HPLC requires higher operating pressures than GC because liquids require
higher pressures than gases for transport through the system
HPLC columns are short and wide in comparison to GC columns
Q2. Which type of GC detector is most commonly used? Explain its working
principle and what are its limitations?Ans. The most commonly used detector
is the flame ionize detector. The sample is combusted with the help of fuel gas and
oxidant in the detector body. Combustible sample components burn and produce
ions and electrons which can conduct electricity through the flame. A large potential
difference is applied at the burner tip and the collector electrode located above the
flame and the current between the electrodes is measured. The detector is mass
sensitive and response is not affected by carrier gas flow rate changes. However,
the detector is not responsive to inorganic gases such as CO, O2, NH3, N2, CS2,
CO2, etc.
Q3. What are the commonly used carrier gases in GC analysis when using
FID detector?Ans. Inert gases commonly used in analysis when using FID detector
are Nitrogen and Helium. Nitrogen is more commonly used as it is less expensive
than Helium. Purity of carrier gas should be more than 99.995% and on-line traps
should be used to prevent residual moisture or other impurities from entering the
system.
Q4. What are the desirable characteristics of a GC detector ? The detector
chosen for particular analysis should :
Give reproducible response to changes in concentration of eluting
compounds in the carrier gas stream.
Should provide a large linear dynamic range
Should have high sensitivity
Should have small internal volume to give narrow peaks and also facilitate
flushing of previous sample traces
Should preferably be non-destructive
Q5. What do you understand by specificity of a detector?
Ans. Detectors falls into three categories depending upon response to the eluting
compounds:
Non-selective – Respond to all component in the gas stream except for the
carrier gas
Selective – Respond to a particular class of compounds with common
physical or chemical properties
Specific – Respond to a single specific compound only in the carrier gas
stream
Q6. What are the commonly used types of capillary columns? Capillary
columns are generally 10 – 100m long tubes having an internal diameter ranging
from 0.1 – 0.5mm made of flexible material such as fused silica. Common types of
capillary columns are
Wall coated open tubular (WCOT) – Internal wall is coated with a very fine
film of adsorbing liquid
Surface coated open tubular (SCOT) – Inner wall is lined with a layer of solid
support on to which the liquid phase is absorbed.
The columns are flexible and wound into several turn coils supported on a SS cage
inside the column oven
Q7. What do you understand by column efficiency and how it is
expressed? On continuous use a column gradually loses its original resolution
power. Column efficiency is expressed on the basis of plate theory concept. Each
component under separation spends a finite time in each theoretical plate. Smaller
the plate height the larger the number of plates (N) and better is the column
efficiency.
where N = Number of theoretical plate
tr = Retention time of a peak
w = Peak width at base
N can also be expressed as
where w1/2 is peak width at half peak height
Column efficiency is expressed in terms of Height Equivalent to a Theoretical Plate
(HETP)
HETP = L/N
where, L = Length of column in terms of mm
Small value of HETP signifies greater column efficiency
Q8. What do you understand by temperature programming in GC analysis?
Ans. Temperature programming means change of temperature of the column at a
rate predetermined rate during the analytical run. This has the same influence on
elution time of separated components as gradient programming in HPLC analysis.
Temperature programming helps reduce analysis time by permitting early elution of
less volatile components.
Q9. When is isothermal operation useful?
Ans. Isothermal operation is useful when high resolution is required for separating
compounds having narrow boiling range. Temperature is set to around mid range of
boiling points of constituents. This results in good resolution of low boiling
components but band broadening of higher boiling components can result due to
their longer retention in the column.
Q10. What measures you would adopt to extend useful life of a column?
Ans.
Condition a column before first use or after long time storage
Take care not to exceed upper temperature limit specified by the
manufacturer
Avoid injection of solutions which are strongly acidic or basic in nature
Rinse columns by injection with blank solvents such as methanol, methylene
chloride or hexane to remove contamination of column after excessive usage
zriconium oxide SENSOR and paramagenetic are for oxygen i.e. flue
thermal conductivity is for hydrogen .. confirm
purging..... to introduce, n2 or instrument air into the analyzer box to prevent the
sparks causing any
trouble as we are in hazardous zones.
A validation process ensures that the components of a system function together to
meet the need
or intent of a customer or regulating body. The aim of validation is to ensure that
the components of a
system work together to produce the intended result for which the system was
designed.
Whereas verification focuses on the right operation of a process (or product) itself,
validation tends to
focus on the right output of the process.
Calibration is performed at the factory. It establishes the relationship between
flow and signal produced by the sensor.
Validation confirms flow performance by comparing a primary flow standard to the
sensor.
Verification establishes confidence in performance by analysis of the secondary
variables associated
with flow. Many times these terms are used interchangeably. Also, frequently
calibration or validation
is done when only verification is needed.
flue gas analyser enable you to measure the concentrations of the pollutants
present and to
adjust your burners for optimal combustion
