Identification limits

As the vast majority of LC separations are carried out by means of gradient-elution RPLC, solvent-elimination RPLC-FUR interfaces suitable for the elimination of aqueous eluent contents are of considerable use. RPLC-FTTR systems based on TSP, PB and ultrasonic nebulisa-tion can handle relatively high flows of aqueous eluents (0.3-1 ml.min 1) and allow the use of conventional-size LC. However, due to diffuse spray characteristics and poor efficiency of analyte transfer to the substrate, their applicability is limited, with moderate (100 ng) to unfavourable (l-10pg) identification limits (mass injected). Better results (0.5-5 ng injected) are obtained with pneumatic and electrospray nebulisers, especially in combination with ZnSe substrates. Pneumatic LC-FI1R interfaces combine rapid solvent elimination with a relatively narrow spray. This allows deposition of analytes in narrow spots, so that FUR transmission microscopy achieves mass sensitivities in the low- or even sub-ng range. The flow-rates that can be handled directly by these systems are 2-50 pLmin-1, which means that micro- or narrow-bore LC (i.d. 0.2-1 mm) has to be applied. 

Principles and Characteristics Many of the planar chromatography methods rely on fluorescence detection to achieve the required identification limits exploitation of sensitive and selective derivatisation reactions is of considerable importance. Most TLC scanning densitometers can be operated in the fluorescence mode and are able to record in situ excitation spectra of TLC... 

To improve the performance of TLC-FTIR coupling, optimised sorbent layers are required which allow substantial reduction in identification limits. The full... 

Interface type LC flow-rate ( l/min) Substrate Infrared mode Identification limit Ref. 

Ojanpera, I., Pihlainen, K., and Vuori, E., Identification limits for volatile organic compounds in the blood by purge-and-trap GC-FTIR, J. Anal. Toxicol., 22, 290-295, 1998. 

Determination online-HPLC-DAD recovery above 80% and limits of identification of 20 to 40 ng/g for 1.5% organic matter for 3.5% organic matter identification limits of 30 to 50 ng/g... 

Pharmaceutical Chemical Analysis Methods for Identification Limit Tests... 

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