Detectors compatibility

Other properties of solvents which need to be considered are boiling point, viscosity (lower viscosity generally gives greater chromatographic efficiency), detector compatibility, flammability, and toxicity. Many of the common solvents used in HPLC are flammable and some are toxic and it is therefore advisable for HPLC instrumentation to be used in a well-ventilated laboratory, if possible under an extraction duct or hood. 

Solvent venting WCOT 1 ppm (FID) Limitations in solvent detector compatibility... 

Miniaturised SEC uses small fused-silica packed-capillary columns (0.32-1 mm i.d., 30-200cm) instead of relatively large metal columns. Miniaturisation puts stringent requirements on the quality of SEC columns. Advantages of ptSEC are (i) much smaller amounts of (toxic, expensive) solvents (ii) smaller samples (iii) better and easier temperature control (iv) increased detector compatibility (e.g. MS) and (v) greatly reduced... 

For the cationic surfactants, the available HPLC detection methods involve direct UV (for cationics with chromophores, such as benzylalkyl-dimethyl ammonium salts) or for compounds that lack UV absorbance, indirect photometry in conjunction with a post-column addition of bromophenol blue or other anionic dye [49], refractive index [50,51], conductivity detection [47,52] and fluorescence combined with postcolumn addition of the ion-pair [53] were used. These modes of detection, limited to isocratic elution, are not totally satisfactory for the separation of quaternary compounds with a wide range of molecular weights. Thus, to overcome the limitation of other detection systems, the ELS detector has been introduced as a universal detector compatible with gradient elution [45]. 

C. The Choice of Column Diameter Sensitivity, Detector Compatibility, Bandspreading... 

Detector Compatibility A solvent must be carefully chosen to avoid interference with the detector. Most UV detectors monitor the column effluent at 254 nm. Any UV-absorbing solvent, such as benzene or olefins, would be unacceptable because of high background. Since refractometer detectors monitor the difference in refractive index between solvent and column effluent, a greater difference leads to greater ability to detect the solute. 

A limitation to the use of modifiers in SFC has been the detector compatibility of the specific modifier. For example, most modifiers (i.e. methanol) provide a flame ionization detector response preventing use at a large concentration. In SFE, however, this limitation does not exist since modifiers can be used in a mixed mode with CCb and the sample. Figure 1 (taken from reference 25) shows an example of the use or modifiers in SFE. Here the comparison of extraction efficiencies obtained using CO and CO2 modified with methanol is shown. The matrices extracted in these SFE experiments were an XAD-2 sorbent resin and soils. The target analytes were dibenzo[a,i]-carbazole, diuron, 2,3,7,8-tetrachorodibenzo-p-dioxin (TCDD) and linear alkylbenzenesulfonate (LAS) detergent. For each of these respective analytes the extraction efficiency increased dramatically with the use of C02/methanol modifier compared to pure CO2 only as the extracting fluid. This was even the case for the ionic compounds namely, the linear alkylbenzenesulfonates (LAS), which were quantitatively recovered. 

The development in the determination of many classes of nonvolatile nitrosamines depends on the development of detectors suitable for the trace analysis of ionizable, ionic, macromolecular, and thermally unstable A-nitroso compounds. In particular, the development of detectors compatible with reversed-phase liquid chromatographic conditions is receiving special attention. Among others, the electrochemical detectors are attractive because of their high sensitivity and their ability to operate in different aqueous and mixed aqueous-organic eluents. 

There are several factors to consider in selecting a stationary phase. General considerations include temperature limits of the stationary phase, column efficiency, and lifetime and detector compatibility. Since nonpolar phases generally give more efficient columns that also exhibit superior lifetimes, it is wise to use the least polar phase that provides satisfactory separation. Phases containing the specific element corresponding with element-selective detectors (e.g., cyanopropyl phases with an NPD detector trifluoro-propyl phases with an BCD detector) should be avoided where possible. These selective detectors will be substantially more sensitive to normal column bleed with such phases. 

LGCs use mainly capillary columns, while PGCs still use packed columns. PGC with capillary col-lunns is becoming more popular, but criteria such as detector compatibility, sample capacity, robustness, and temperature effects must be considered. 

Gradients result from the mixing of two or more different solvents. The following restrictions apply to isocratic solvents selectivity, safety, sample compatibility, column compatibility, detector compatibility, viscosity, corrosivity, purity, cost. The same restrictions apply to gradient solvents, as well as, miscibility, mutual compatibility, and insensitivity of detector for variations in composition. 

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