LC Detection Systems (1)
3
Created with MindGenius Business Created with MindGenius Business 2005 2005® LC Detection Systems (1) LC Detection Systems (1) Generally the most expensive part of the instrument Depends on analyte properties, and required sensitivity (and money) Choice may be assisted by obtaining spectra on traditional instruments A) Ultraviolet/Visible absorption (may extend to IR) Most commonly used, Mass LOD = 100pg-1ng (1pg), 0.1-1mg for IR Three major types: The simplest (and cheapest) uses a mercury source & can only detect 254nm and 280nm Tungsten and Deuterium sources used, together with interference filters The best (and most expensive) uses a diode array to monitor the spectrum of the eluent over a wide range of wavelengths B) Fluorescence Mass LOD = 1 -10pg (10fg) Monitors emission at specific wavelengths, in response to excitation with a specific wavelength
description
LC Detection Systems (1). Generally the most expensive part of the instrument Depends on analyte properties, and required sensitivity (and money) Choice may be assisted by obtaining spectra on traditional instruments A) Ultraviolet/Visible absorption (may extend to IR) - PowerPoint PPT Presentation
Transcript of LC Detection Systems (1)
Created with MindGenius Business 2005Created with MindGenius Business 2005®®
LC Detection Systems (1) LC Detection Systems (1) Generally the most expensive part of the instrument Depends on analyte properties, and required sensitivity (and money) Choice may be assisted by obtaining spectra on traditional instruments A) Ultraviolet/Visible absorption (may extend to IR) Most commonly used, Mass LOD = 100pg-1ng (1pg), 0.1-1mg for IR Three major types:
The simplest (and cheapest) uses a mercury source & can only detect 254nm and 280nm
Tungsten and Deuterium sources used, together with interference filters
The best (and most expensive) uses a diode array to monitor the spectrum of the eluent over a wide range of wavelengths
B) FluorescenceMass LOD = 1 -10pg (10fg)Monitors emission at specific wavelengths, in response to excitation with a specific wavelength
Created with MindGenius Business 2005Created with MindGenius Business 2005®®
LC Detection Systems (2)LC Detection Systems (2)C) Refractive Index Mass LOD = 100ng-1mg (10ng) Monitors changes in the refractive index of the solvent, caused by the
presence of analytes Universal, but non-specific, not very sensitive
D) Mass Spectrometric Mass LOD = 100pg-1ng (1pg) Often found as a tandem or “hyphenated” technique
E) Nuclear Magnetic Resonance Spectroscopic A recent innovation in tandem techniques
F) Electrochemical Mass LOD = 10pg-1ng (100fg) May be potentiometric, conductometric or amperometric Most common is conductivity (esp for ion exchange and capillary
electrophoresis) – see over
Created with MindGenius Business 2005Created with MindGenius Business 2005®®
LC Detection Systems (3)LC Detection Systems (3)Conductivity: Simple cheap robust but……need to solve the problem of detecting analyte ion in presence of large quantities of other ions (eluent)
Suppressor Column Ion exchange column of the opposite type to the analytical column Converts eluent ions (but not analyte) to a non-charged (non-conductive) form
Anion exchangeThe eluent is often sodium carbonate (Na2CO3), and the suppressor column is a strong acid type cation resin.2Na+
(aq) + CO32-
(aq) + 2Resin-H+(s) 2Resin-Na+
(s) + H2CO3(aq)
Charged Neutral
Cation ExchangeThe eluent is often hydrochloric acid (HCl), and the suppressor column is a strong base type anion resin. H+
(aq) + Cl-(aq) + Resin+OH-(s) Resin+Cl-(s) + H2O
Charged Neutral
