Solvent injection

Another important factor is the composition of the injection solvent that involves a compromise between good solubilities of sample carotenoids, compatibility with... 

A mixed-mode method called liquid chromatography under limited conditions of adsorption has been described and applied to analyzing co-polymer composition of poly(styrene)-co-(methylmethacrylate).41 The polymer, dissolved in a good solvent, was injected onto a GPC column and eluted with a poor solvent. The polymer partially adsorbed to the column, allowing the plug of injection solvent to catch up with the adsorbed polymer and desorb it. 

On-line SFE-SFC modes present several distinct advantages that are beyond reach of either technique when used separately (Table 7.13). An obvious advantage of SFE is that it is an ideal way to introduce a sample into an SFC system. Because the injection-solvent is the same as the mobile phase, in this respect the criteria for a successful coupling of different techniques are fulfilled [94], i.e. the output characteristics from the first instrument and the input characteristics of the second instrument are compatible. Supercritical fluid techniques can separate high-MW compounds are significantly faster than classical Soxhlet extractions and require less heat and solvent. SFE-SFC techniques are versatile,... 

Non-column Failures too large an increase in injection volume inadvertent change to strongly eluting injection solvent inadvertent overloading of column... 

Erythromycin, a macrolide antibiotic, lacks a significant chromophore. Detection sensitivity was enhanced by using a wavelength of 200 nm and selecting an injection solvent of lower conductivity than the BGE. In order to facilitate the separation of erythromycin and its related substances, 35% (v/v) ethanol was incorporated into a 150 mM phosphate buffer pH 7.5. Resolution of all of the compounds was achieved in approximately 45 min. The method was employed as an assay method for erythromycin and for impurity determination. Peptide antibiotics, such as colistin and polymyxin, are mixtures of many closely related compounds. A validated CZE method for impurity analysis of polymyxin B was described, employing 130 mM triethanolamine-phosphate buffer at pH 2.5 to reduce the adsorption of analyte onto the capillary wall. Methyl-/l-cyclodextrin (M-/1-CD) and 2-propanol were found to be necessary for selectivity enhancement. Using similar buffer additives, the same group developed and validated a method for colistin analysis. ... 

Effect of Injected Solvent. It was eventually determined that the mobile phase injected from the first SEC (i.e., pure THF) affected the separation in the second SEC. This is dreunatically demonstrated in Figure 13 which shows the result of injecting a narrow molecular weight distribution polystyrene sample directly into the second SBC. Mobile phase was of constant composition throughout (63.8% n-heptane in THF). However, the solvent used to dissolve the polystyrene was varied from 0% n-heptane in THF to 50% and plotted on the abscissa versus peak retention time on the ordinate. Peak retention time varied from 915 seconds at 0% n-heptane to 960 seconds at 50%. 

The consequences of this effect of injected solvent are as follows ( ) ... 

Figure 13 Effect of injected solvent composition on polystyrene retention in SBC 2. (Reproduced from Ref. 6. Copyright 1983, American Chemical Society.)...

J.L. Manzoori, A. Miyazaki, Indirect inductively coupled plasma atomic emission determination of fluoride in water samples by flow injection solvent extraction. Anal. Chem. 62 (1990) 2457-2460. 

Because column performance decreases with age, it is important to keep good records of its performance. Entries useful to keep track of are chromatogram number, sample identification number, amount injected, volume injected, solvents used (A and B components), column characteristics (ID number, packing, size), back pressure, flow rate, detector setting (UV, absorbance units full scale at given wavelength), gradient conditions, results (retention time of desired product), remarks (baseline shifts, unusual wash profile, etc.), and date. 

Injection solvent 50% (v/v) HPLC-grade acetonitrile in water Reference standard solutions (see recipe)... 

Add 5.0 ml injection solvent (50% acetonitrile) to each 4-dram vial and tighten the Teflon-lined screw cap. Vortex the sample vials every 10 to 15 min until no residue is found on the wall of the vials ( l hr). 

Pipet 5.0, 10.0,30.0, and 50.0 ml of each 1.0 mg/ml stock solution into fourdifferent 100-ml volumetric flasks. Dilute to volume with injection solvent (50% acetonitrile) and mix well. Store up to 6 months at room temperature. 

If the injection solvent is of comparable solvent strength to that of the mobile phase, up to 30 ml may be used as the sample injection volume however, if the injection solvent is more lipophilic than the mobile phase, the injection volume is limited to 10 ml. 

Eluent or injection solvent % Composition Solubility of /3-carotene (mg/100 ml)... 

The operating conditions range from an excitation wavelength of 360-365 nm and an emission wavelength 425-435 nm. The intensity of aflatoxin fluorescence depends strongly on the injected solvent, with a higher response if the sample is injected in the mobile phase (usually a ternary mixture of methanol/acetonitrile/water) and a lower one if injected in the methanol or acetonitrile only. 

Method A 50 /jl (ca 250 ng) of the stock solution or of the purified extract is transferred into a reaction tube. One ml of boron trifluoride is added to the methanol, the cap is closed, and the tube is kept on a block heater (80°C) for 10 min. Two ml of water and 2 ml of -hexane are added. After thorough mixing, the layers are left to separate. Using disposable glass Pasteur pipettes, the upper layer is transferred to a clean, small vial. The extraction is repeated another two times with 2-ml portions of n-hexane. The hexane extracts are taken to dryness with a nitrogen stream, and the residue is dissolved in 1 -2 ml of injection solvent. Ochratoxin A is confirmed by the presence of an OA-methyl ester peak at delayed retention time and the disappearance of the OA peak (62). 

Non-ionic polymer gel, swollen with dielectric solvent, can be extremely deformed as is the case for non-ionic polymer plasticised with non-ionic plasticiser. Instead of the charge-injected solvent drag as a mechanism of the gel actuation, the principle is based on local asymmetrical charge distribution at the surface of the gel18. The mechanism can also be applied to non-ionic elastomers in which the motion of the polymer chain is relatively free. In spite of their many difficulties for practical actuators, polyelectrolyte gels and related materials are the most interesting electroactive polymer materials. 

Initial separation of compounds for subsequent identification was performed with a Symmetry (Waters) C18 column (250 x 4.6 mm). A 100-mL sample volume was injected. Solvent A contained 5% formic acid in water, and solvent B consisted of HPLC-grade methanol. The gradient program was initiated with 98 2 solvent Atsolvent B and linearly decreased to 40 60 solvent A solvent B over 60 min. Compounds were monitored at 280,320, 360, and 510 nm. 

Mac-Nod HPLC Column Companion, Section 10 Injection Solvent Effects, http //www.mac-nod.com/cc/cc-10.html (August 1, 2002). 

Doring (39) has shown that infinite dilution relative volatilities can be evaluated through GLC. He prepared a special column for each solvent under consideration, a tedious project. A year later Sheets and Marchello (38) showed that separation factors increase with increased amounts of injected solvent. Later Tassios (35) found out the same to... 

Ideally, samples should be dissolved in the eluent prior to injection. However, if the sample has low solubility, it is sometimes necessary to use a more powerful solvent and in such cases only small injection volumes should be used otherwise broad peaks with shoulders can arise. Injection solvents of lower elution strength than the eluent can be useful for dilute samples, as the material concentrates on the top of the column during the injection. Neverftieless, lai e injections of any liquid other Hum eluent can cause serious detector distmlxmces. 

E. Looser and P. Drumm, Using strong injection solvents with 100% aqneons mobile phases in RP-LC,/. Sep. Sci. (2006), accepted for pnblication. 

---