Sample solvents

When the sample solvent evaporates at the front end of the liquid, volatile compounds co-evaporate with the solvent and start moving through the main column. In this way, volatile components can be lost through the early vapour exit or, if venting is delayed, the most volatile compounds reach the detector even before the end of... 

The purge activation time (or the sample transfer time) depends on the sample solvent and carrier gas flow relative to the volume of the injection port liner and the boiling points of the sample components. For most applications, a purge activation time of 50-120 sec is better than 25-50 sec. Early activation results in the loss of sample, while late activation results in peak tailing. A more accurate method of determining purge activation time is to divide the volume of the injector liner by the flow rate (F) of the carrier gas and multiply this value by 1.5 or 2.0. (Do not use a packed liner.)... 

After the purge activation time (which can be optimized), the split mode is turned on and the solvent vapors are purged out of the split vent. If possible, choose a sample solvent that has a boiling point that is at least 20° below the boiling point of the first sample component (if known). 

Special solvents that are not components of the mobile phase, but are included in the sample to improve component solubility, will act as though they were solutes themselves. Each will produce a spurious peak somewhere on the chromatogram that must not be misinterpreted as a solute peak. Irrespective of the sample solvent, the solutes of interest must always be sufficiently soluble in the mobile phase to permit effective chromatographic development. 

The sample solvent or other constituents must neither affect the column performance, temporarily or permanently, or the column resolution. 

PLC of plant extracts is presented in Chapter 11, with sections on the choice of systems, sampling, choice of the sample solvent, detection, and development modes. These applications in the field of pharmacognosy play a key role in the investigation and understanding of the healing potential of the constituents of medicinal plants. 

HPnspot sizes are about l.fl mm, this corresponds to a sample volume of 100 to 200 nl. Pot conventional TLC plates sample volumes 5 to 10-fold greater an- /f acceptable. The sample solvent must be a good solvent for tlw sample to promote quantitative transfer from the saapl application device to the layer. Also, it must be of low viscosity, and sufficiently volatile to be easily evaporated from the plate. Further, it must wet the sorbent layer adequately otherwiaa ... 

Unfortunately, the preset split flow ratio is only an approximate indication of the sample split ratio. The latter depends in a complex way on many parameters, including the range of sample volatilities, sample solvent, volume of sample injected. 

The solvent in which a sample is dissolved can play a very important role in HPLC analysis. Immiscibility, precipitation, decomposition, and system peaks are all problems potentially caused by a sample solvent incompatible with the analysis. Ideally, the mobile phase should be identical to the reaction solvent. The addition of an internal standard permits a kinetic analysis to be conducted. 

Detector sensitivity Sample solvent Sample concentration Injection size Retention times ... 

On a laboratory scale, generally an ultrasonic probe (horn) and an ultrasonic cleaner are used. The ultrasonic field in an ultrasonic cleaner is not homogeneous. Sonication extraction uses ultrasonic frequencies to disrupt or detach the target analyte from the matrix. Horn type sonic probes operate at pulsed powers of 400-600 W in the sample solvent container. Ultrasonic extraction works by agitating the solution and producing cavitation in the... 

Extraction procedure Sample Solvents for additive extraction and PP oligomer precipitation Time (h)... 

The advent of high-resolution capillary gas chromatography (HR-CGC) with on-column injection has resulted in improved GC analysis of polymer additives [92-94]. The solution of the additive mixture is injected directly into the cold end of the capillary column by means of a cold injector. Thus, sample discrimination, the instantaneous evaporation of the sample solvent, is avoided. The nonvaporising, on-column injection combined with very high resolution of the capillary columns allows accurate separation, identification and quantification of additives of complex mixtures. With the solvent venting technique, the sample is introduced into the column without splitting and sample concentrations... 

---