Solvent elimination

Programmed-temperature vaporizers are flexible sample-introduction devices offering a variety of modes of operation such as spHt/sphtless, cool-sample introduction, and solvent elimination. Usually the sample is introduced onto a cool injection port liner so that no sample discrimination occurs as in hot injections. After injection, the temperature is increased to vaporize the sample. 

Figure 9.9 Schesatic diagrans of flow-through cell. A, and solvent elimination interfar B, for SFC/FTIR. For A (1) polished stainless steel lig..v.pipe (2) zinc selenide window (3) PTFE spacer (4) viton rubber o-ring (5) graphitized Vespel nicroferrule (6) deactivated fused-silica capillary tubing (7) bolt with Allen nut (8) stainless steel end-fitting and (9) stainless steel body of flow cell.

The solvent elimination appro2K h is quite straightforward for supercritical fluids lAich are often gases at atmospheric pressure. Each chromatographic peedc is deposited fron the end of a restrictor, connected to the end of the column by a heated transfer line, onto a small area of infrared-transparent support [110,128,129,134]. The support can be moved manually to collect each peak at a n osition or stetq>ed continuously to record the... 

Both flow-cell and solvent elimination SFC-FTTR are useful, in particular for thermolabile components. This hyphenated technique requires a compromise between chromatographic and spectroscopic requirements. Its use... 

Consequently, the major experimental options for the analyst are packed or capillary SFC, mobile phase with/without modifier and off-line or on-line mode, namely direct deposition (DD-SFC-FUR) vs. flowcell. Both small-bore packed columns and narrow-bore open-tubular columns have been used for SFC-FTIR analysis using a pressure-stable, thermostated, flow-cell or solvent elimination interfaces. 

The problems discussed above may be circumvented by eliminating the mobile phase before measuring the spectra of the eluites, as first demonstrated by Shafer et al. [379] for pSFC-FTIR. Each eluite was deposited on a moving glass plate, on which a layer of powdered KC1 or KBr had been laid down from methanol slurry for diffuse reflectance spectroscopy (SFC-DRIFTS). Solvent elimination SFC-FTIR after deposition of the eluites on to a moving ZnSe substrate is quite straightforward the window is moved to the... 

Table 7.35 Main characteristics of solvent-elimination SFC-FTIR...

The solvent-elimination interface offers various advantages over the flow-cell approach ... 

In solvent-elimination LC-FTIR, basically three types of substrates and corresponding IR modes can be discerned, namely, powder substrates for diffuse reflectance (DRIFT) detection, metallic mirrors for reflection-absorption (R-A) spectrometry, and IR-transparent windows for transmission measurements [500]. The most favourable solvent-elimination LC-FTIR results have been obtained with IR-transparent deposition substrates that allow straightforward transmission measurements. Analyte morphology and/or transformation should always be taken into consideration during the interpretation of spectra obtained by solvent-elimination LC-FTIR. Dependent on the type of substrate and/or size of the deposited spots, often special optics such as a (diffuse) reflectance unit, a beam condenser or an FITR microscope are used to scan the deposited substances (typical diameter of the FITR beam, 20 pm). 

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. 

LC-FHR has been reviewed [204,507]. Various mobile-phase elimination designs were discussed by White [167]. Resolution of complex LC-FTIR spectroscopy data was described [508]. A general overview of flow-cell based IR detection and of early solvent-elimination interfaces for LC-FHR has recently appeared solvent-elimination RPLC-FHR interfaces have also been described [500]. 

Temperature-programmed packed capillary liquid chromatography (TP-CLC), coupled off-line to solvent elimination FTIR (LC Transform ) has recently been used for gradient separations of Irganox 1010/1076/3114 dissolved in DMF with LOD of about 40 ng [511]. Low... 

Hyphenation in capillary electrophoresis is still in its infancy. Critical aspects of CE hyphenation include the minute volumes of sample injected (typically a few nL) and small flow-rates (in the order of nLmin-1). Interfaces are not commercially available. CZE-UV can be used for the analysis of higher polyamide oligomers in HF1P solution [859]. A solvent elimination design with nebuliser has been described for CE-FTIR and CEC-FTIR coupling absolute detection limits are hundreds of pg [860]. An advantage of CE-FTIR is that analytes may be detected and identified without derivatisation. CE(C)-NMR [861-863] is advancing rapidly. 

The neat material is about three times as shock-sensitive as glyceryl nitrate, and should not be handled undiluted [1]. It exploded during vacuum distillation at 3.3 mbar from a bath at 140°C. Impact- and spark-sensitivities were determined, and autoignition occurred after 30 s at 107°C [2], An explosion occurred during distillation at a pot temperature of 80°C. Full handling precautions are detailed. Dilution of neat material with solvent eliminates shock-sensitivity [3],... 

Base-aprotic solvent elimination has also been reported for 1-hydroxyneodihydro-carveyl tosylate and for 1-hydroxyneocarvomenthyl tosylate (epoxide and allylic alcohol products). 

---