Презентация на тему Comparison of Competitors’ Evaporative Light Scattering Detectors

consequently determines size of particle
Evaporation
Efficiency to remove

solvent
Light source
Intensity
Wavelength

Liquid flow --------------- Increases droplet size
Increase Liquid viscosity --------

Increases droplet size

Ideally, you need the largest droplet size possible, but not too large that it can’t be fully evaporated in the drift tube.

Hence, the efficiency of your evaporation step is critical to the performance of an ELSD.

ELSD manufacturers has increased considerably.

Current ELSD manufacturers are:
Alltech
Sedere
Waters
SofTA
Schambeck
ESA
Polymer Labs

Current

Manufacturers of ELS Detectors

diode
Detector element: Silicon photodiode
Temperature range: Ambient to 110°C
Nebulizer gas:

Up to 3.0L/min,
Gas inlet pressure: 15–90psi (1.0–6.0 Bar)
Typical operating range: 1.0-3.0L/min
Mobile phase flow rate: 1–5.0mL/min
Analog outputs: 1V or 10mV full scale

diode
Detector element: Silicon photodiode
Temperature range: Ambient to 120°C
Nebulizer gas:

Up to 4.0L/min (MFC controlled)
Gas inlet pressure: 60–80psi
Typical operating range: 1.0-3.0L/min
Low temperature operation
The optical and electronic components have been redesigned to minimize background noise and increase sensitivity.

diode
Silicon photodiode detector
Temperature range: Ambient to 120°C
Nebulizer gas: Up

to 4.0L/min (MFC controlled)
Gas inlet pressure: 60–80psi
Typical operating range: 1.0-3.0L/min
Low temperature operation
The optical and electronic components have been redesigned to minimize background noise and increase sensitivity.

temperature control
Evaporation
Temperature setting dependent on solvent properties
Impactor

removes the large droplets at low temperatures -limits to how low in temperature can go
Detection
Laser source @ 650-670nm - scattering efficiency is lower at higher wavelengths but this is compensated by 30mW LASER
Silicon photodiode detector - optimum sensitivity to red light

Design Features of Alltech’s ELSDs

flow controller
Remote power-down
Automatic gas shut-off
SEDEX 75 LT-ELSD
Tungsten halogen

lamp
Coiled drift tube
No mass flow controller
Different nebulizers for different flow rates

Design Features of Sedere’s ELSDs

nebulize solvents under standard conditions
Large volume nebulizer chamber

with a bend removes large droplets
Nebulizer not temperature controlled
cannot connect to SFC systems without modification
Different size nebulizers for different flow rates

Design Features of Sedere’s ELSDs

centrifugal force and provides laminar flow - potential increase

in band broadening
Longer drift tube means the temperature can be lower, compared to a short tube, for a given solvent
Longer tubes have greater equilibration times for heating and cooling
Detection
SEDEX 75 Halogen lamp produces a broad range of wavelengths, but low intensity
SEDEX 85 uses a blue LED, same as PL-ELS 2100
PMT gain adjustable

Design Features of Sedere’s ELSDs

Lamp
Detector Element: PMT
Temperature Range: Ambient to 100°C

(?)
Nebulizer Gas: adjustable 3-60psi,
Nebulizer set at 0-100% of Drift tube temp
Gas Inlet Pressure: 65psi min
High and Low flow nebulizers
0.050-3ml/min
2 Analog Outputs: 2V full scale
Digital Output

Waters

rate
Sharp peak shape (1.2 - 1.5sec)
Stackable
Digital Output

Waters

of drift tube temp)
Gas pressure/flow set according to solvent

Evaporation
Coiled drift tube
No design features included to operate at low temperatures
Detection
Halogen lamp – high power, but produces a wide range of wavelengths (mean wavelength ca. 900nm)
PMT – detector type not optimized for light source
Heated optics, to prevent condensation onto optical lenses (same as PL-ELS 2100)

Design Features of Waters’ ELSDs

element: Photodiode
Temperature range: Ambient to 120°C
Gas inlet pressure

50psi
Nebulizer chamber 0-80°C
Analog Output: 0-1V full scale
Digital Output
Heated/Cooled Nebulizer Chamber (Thermosplit)

SofTA

phases, or high flow rates, the nebulizer chamber walls

are cooled
By making the walls suitably cold, 99+% of an aqueous stream can be diverted away from the evaporative zone
Nebulizer gas pressure set according to solvent type (no MFC)
Evaporation
Heated drift tube (coiled ??) no form of impactor or diffuser
Detection
LASER diode – same as Alltech
Photodiode detector

Design Features of SofTA’s ELSDs

Detector element: Photomultiplier
Temperature range: Ambient to 70°C

Nebulizer gas flow: <1L/min
Drying gas: <2L/min
Analog output: 0-1V full scale
Digital output

Schambeck

or high flow rates, the nebulizer chamber walls are

cooled
By making the walls suitably cold, 99+% of an aqueous stream can be diverted away from the evaporative zone
Nebulizer gas pressure set according to solvent type (no MFC)
Evaporation
Heated glass drift tube no form of impactor or diffuser
Detection
Tungsten Halogen Lamp (av. wavelength ca. 900nm)
Photomultiplier tube - not optimized for light source

Design Features of Schambeck’s ELSDs

Photomultiplier
Temperature range:
Nebulizer: Up to 70°C by

1°C increments
Evaporator: Up to 150°C by 1°C increments
Gas inlet pressure: 0.5 to 3.9 bars (1 to 4 L/min) Helium or Nitrogen
Mobile phase flow rate: 50µl/min to 4 ml/min
Digital outputs: RS232

ESA

design to SEDEX 75
No special design features for

low temperature operation
Detection
Tungsten-Halogen lamp (wavelength ca. 900nm)
Photomultiplier tube - not optimized for light source

Design Features of ESA’s ELSDs

nitrogen, before passing into a heated drift tube.
The droplets

are dried to remove mobile phase, producing analyte particles.
Dried particles are mixed with a secondary stream of positively charged nitrogen as it passes a high-voltage, platinum corona wire.
This charged gas subsequently imparts a charge onto the stream of analyte particles.   
These streams of charged particles then pass through a charge collector where the magnitude of the imparted charge is measured by a electrometer.
A signal is generated which is proportional to the quantity of analyte present.

Charged Aerosol Detector (CAD)

not bound by scattering laws.

Small particles, which would be

missed by ELSD, will be charged and detected by CAD.
Charging the particles produces a wider dynamic range.
In principle, the LOD should be better (not necessarily).
Produce more uniform response between compounds as it is not dependent on particle size.
Nebulization is not critical, as droplet size is irrelevant, therefore, nebulizer can set to produce smaller particles that will dry more easily.

CAD vs ELSD

stages.

It is gradient sensitive - the response will change

as solvent composition changes.
Change in solvent composition makes the technique difficult to apply to unknowns.
Highly volatile compounds will be lost through evaporation.
It is not a linear technique (but is slightly better than ELSD), so unknown quantification is difficult.
Some buffers, such as TEA, can cause problems.
Not all compounds charge easily, so LOD is still compound dependent.

CAD vs ELSD

1000-1500 units/year

PL shares
ca. 25% of the market
80%

PL-ELS 2100
20% PL-ELS 1000

Main Competitors
Sedere
Alltech
ESA/Eurosep
Waters