Degassing, mobile phase

For pump blending or gradient applications, thorough mobile phase degassing is critical. 

Procedure (See Chromatography, Appendix BA.) Use a suitable high-performance liquid chromatograph equipped with differential refractometer, autosampler injection unit, mobile-phase degasser, column heating block or oven, and a computing integrator. The column is Lichrosorb RP-18 250-mm x 4.5 mm (id) (GL Science, Inc., or equivalent) and YMC-Pack ODA-A A-303 250-mm x 4.5 mm (id) (YMC Company, Ltd., or equivalent) connected in a series, or equivalent, maintained at 50°. Use 80 20 acetone acetonitrile as the eluent, at a flow rate of 2 mL/min. 

Mobile-phase degassing is an important step in the LC/MS experiment and can be accomplished via on-line membrane or vacuum devices, sonication, helium sparging or as part of the mobile-phase filtration step. Degassing will eliminate pump cavitation, ensure reproducible retention times and minimize possible sputtering from the ion source. 

A noisy baseline of an RI detector can be caused by inadequate mobile phase degassing or temperature thermostatting. However, low light energy can also be caused by a contaminated detector flow cell or high UV absorbance of the mobile phase (Figure 10.7d). 

Spikes on baseline Spikes on baseline (Figure 10.7c) are caused by air bubbles out-gassing in the detector flow cell. They can be eliminated by mobile phase degassing and/or by placing a pressure restrictor in the detector outlet (e.g., with 50-psi back pressure). Spikes can also be caused by poor signal wire connections (loose or damaged wiring) or malfunction of the detector or the data system. 

Contamination of mobile-phase reservoirs can often become a possible source of problems such as blocked frits, irregular pump performance, extra peaks, or noise in the chromatogram. Mobile phase degassing by helimn sparging, sonication, and vacuum or heating (mostly in case of electrochemical detection) prior to, or dming, use prevents air bubble formation. 

Shimadzu liquid chromatograph model SCL lOAvP containing a multichannel mobile phase degasser (DGU-14A), a column heater (CTOlOASvp), and three pumps (two LCIOAD pumps and one LClOADvp pump Shimadzu, Columbia, MD)... 

The effect of the mobile-phase composition on the operation of the different interfaces is an important consideration which will be discussed in the appropriate chapter of this book but mobile-phase parameters which affect the operation of the interface include its boiling point, surface tension and conductivity. The importance of degassing solvents to prevent the formation of bubbles within the LC-MS interface must be stressed. 

The mobile phase consisted degassed distilled water containing 1.0 grams/liter of Aeorosol(B)-OT and varying amounts of sodium nitrate, NaNOj. The detector was a DuPont Model 840 UV photometer with a fixed wavelength of 254 nm. 

Degasser for high-performance liquid chromatography (HPLC) mobile phase... 

Although the method is simple and straightforward, there are a few important points to consider. First, since 200 pL are being injected on to a 2-mm diameter HPLC column, compatible solvents must be injected on to the column and the amount of acetonitrile used in the prepared samples should be exactly as directed. Second, the temperature of the column and the use of a degassing system for the mobile phase are critical components required to guarantee reproducible chromatography. In addition, the standards should be stored in a refrigerator when not in use. 

Mixture-design, aobile phase optiaization (LC) 480 Mobile phase (GC) flow control 232 aodifiers 43 pressure control 232 purification 232 selection 4i velocity 44 viscosity 43 Mobile phase (LC) classification 460 degassing 553 gradient elution 485 ideal properties 458 aixed solvents 465 reservoirs 553... 

Figure 5.2 A, valve, column and flow cell asseidily of a ainiaturized liquid chromatograph for use with small bore columns (Reproduced with permission from ref. 14) and B, mobile phase reservoir designed for solvent degassing by heat and helium sparging (Reproduced with permission from ref. 34. Copyright Elsevier Scientific Publishing Co.)...

Quenching Impurities in the mobile phase, particularly oxygen, may entirely quench the signal from low concentrations of fluorescent compounds (see solvent degassing). 

Figure 14 Separation of 1,2/1,4 ketal with and without protection from oxidative degradation. Chromatographic conditions were column 25 cm x 4.6 mm Zorbax C8 (5-pm) column mobile phase 100 mM KH2P04 (pH 6.5) acetonitrile (50 50) flow rate 1.0 ml/min column temperature 35°C detector wavelength 220 nm. (A) Acetonitrile degassed. (B) Acetonitrile not degassed.

Method 3 was modified to an internal standard method into Method 5 by changing the bonded phase and the mobile phase composition. Biphenyl was used as an internal standard added into the reaction. Aliquots were withdrawn, diluted with degassed acetonitrile, and analyzed according to Method 5. This internal standard method, Method 5, was helpful in the optimization of the desired ris-1,2/1,4 product of the key step of the LANA reaction (scheme 5). 

Mobile phase Prepare a filtered and degassed mixture of methanol and 1-penta-nesulfonate sodium solution (60 40). Make adjustments if necessary (see system suitability under Chromatography <621 >). 

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