Convex gradient

Radial-PAK cartridge containing C18 5 pm Convex gradient of EtOH/H20 (90 10) to EtOH/hexane (90 10) UV 254 nm... 

The pattern of the variation of retention with composition in LC is affected by the choice of both the stationary and the mobile phase. The optimum shape of the gradient for unknown wide range samples is dictated by the phase system. Linear or slightly convex gradients are optimal for RPLC. Concave gradients are optimal for LSC. 

Finally, the two lowest chromatograms show the effect of the shape (curvature) of the gradient on separation. With a convex gradient shape (A) the earlier-eluted peaks are more bunched together than the later-eluted ones, whereas the opposite effect is observed with a concave gradient (B). 

Fig. 1.29. Optimised normal-phase gradienl-clution separation of 30 lower oligoslyiencs on two Scparon SGX Cis. 7 pm, silica gel columns in series (150 x mm i.d. each), using the optimised linear and convex gradients of dioxanc in n-hcptanc. Flow rate 1 ml/min. Normalised response relates to the original concenlralions of the oligomers in the sample, to.

Synthesis in Solution Purified Dts>Tyr(tBu)-Gly-Gly-Phe-Leu-OH (4.5 (jmol) was fully dissolved in a mixture (1 mL) of 2-sulfanylethanol/DIPEA (0.5 M 0.5 M) in CHjCb, which was maintained at 25 °C for 5 min following which solvents and most of the reagents were removed by rotary evaporation at 25 °C, at 1 Torr, 15 min (coevaporated 3 x with CH2CI2). The resulting film was then immediately passed through a MPLC column (convex gradient formed from 175 mL each of 1 19 and 3 2 mixtures of MeCN and 0.1% TEA in HjO to provide pure peptide) FAB-MS w/z 634 [M- -Na]+. 

Fig. 3. Chromatograms of five poly-L-lysine samples eluted with three continuous convex gradients. Preparative details ...

Step 3. Increase the rate at the beginning as needed. This is called a convex gradient. 

Mobile phase Gradient. MeOH water from 15 85 to 60 40 over 10 min. (Convex gradient where MeOH% = -0.46exp(-x/1.18) + 0.6 where x = time in min.)... 

Mobile phase Gradient. MeOH 10 mM pH 6.9 ammonium acetate from 10 90 to 100 0 over 50 min (Waters No. 5 convex gradient). 

Figure 3.175 Gradient separation of polygalacturonic acid. Separator column lonPac AS11 eluent NaOH gradient 20-86 mmol/L in 20 min, convex gradient curve 3 flow rate 2 mlVmin detection suppressed conductivity sample polygalacturonic acid.

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