Page 63 - Application Handbook - Liquid Chromatography
P. 63

2-2. Instrument                                                                                                                                                   A        70 280nm, 4nm
                                                                                                                                                                                         mAU
            • Shimadzu CBM-20A controller                                                                                                                                              60                                        A
                                                                                                                                                                                       50                     t R2 =0.50  t R3=0.53  t R4 =0.54
            • Shimadzu LC-30AD dual-plunger parallel- ow pumps (D1-LC)                                                                                                                 40                  t R1 =0.49  t R5 =0.55
                                                                                                                                                                                       30                             t R6=0.60
            • Shimadzu DGU-20A5R degassing unit (D1-LC)                                                                                                                                20
                                                                                                                                                                                       10
            • Shimadzu LC-30AD dual-plunger parallel- ow pumps (D2-LC)                                                                                                                 0
                                                                                                                                                                                         65.3     65.4      65.5     65.6     65.7  min
            • Shimadzu DGU-20A3R degassing unit (D2-LC)
                                                                                                                                                                                        mAU
            • Shimadzu CTO-20AC column oven                                                                                                                                           30  280nm, 4nm        t R2 =0.48           B
            • Shimadzu SIL-30AC autosampler                                                                                                                                           25                 t R1=0.46  t R4 =0.53
                                                                                                                                                                                      20                      t R3=0.51
            • Shimadzu SPD-M30A photo diode array detector (1 µL  ow cell)                                                                                                            15                          t R5=0.54  t R6=0.58
                                                                                                                                                                                      10
            • Shimadzu LCMS-8030 (ESI source)                                                                                                                                          5
            For connecting the two dimensions: two electronically-controlled 2-po-                                                                                                     0  65.3     65.4     65.5     65.6    65.7  min
            sition, 6-port high pressure switching valves FCV-32AH (with two 20
                                                                        Fig. 3  Scheme of the LCxLC-Assist software                                                                     Fig. 5  Analysis of a red wine sample. A comparison of the
            µL empty loops).
                                                                                                                                                                                             second-dimension separation of the 65  fraction for both
                                                                                                                                                                                                                      th
                                                                                                                                                                              B              LC×LC plots shown in Fig. 4A–B.
            2-3. Software
                                                               4.
                                                                   Results and Discussion
                                                               4. Results and Discussion
            • Shimadzu LabSolutions (Version 5.60 SP2)                                                                                                                                An evaluation of the performance, in terms of peak capacity (n C ), of
                                                               In  an  LC×LC  system,  with  two  not  orthogonal  dimensions,  an                                                    the two different set-ups tested was carried out, considering both
                                                               LC×LC separation most likely results in peaks concentrated around                                                      theoretical and practical peak capacity. The theoretical peak capacity
            2-4. 2D Software                                   the main diagonal line of the separation area. A typical example is                                                    values, multiplicative of the individual values obtained for the two
                                                                                                                                                                                                  2
                                                                                                                                                                                               1
            • LCxLC-Assist                                     the LC×LC analysis of a red wine sample, illustrated in Fig. 4A, by                                                    dimensions ( n C  × n C ), yielded values as high as 690 and 570 for the
                                                               employing a Cyano column in the D1 and a C18 column in the D2                                                          full in fraction and for the shifted gradients, respectively.
            • ChromSquare (Version 2.0) from Chromaleont, Messina, Italy
                                                               using the conventional full-in-fraction approach.
                                                                                                                                                                                      As  expected,  due  to  the  partial  correlation  of  the  two  dimensions,
                                                               As a matter of fact, a clear correlation of the D1 and D2 and a small                                                  “practical”  peak  capacity  values,  corrected  for  both  undersampling
            3. LC×LC-MS Conditions                             peak-distribution area were observed because the separation mech-                                                      (number of fractions effectively transferred from the D1 to the D2) and
                                                               anisms in the two dimensions were similar. The analytes eluted early                                                   orthogonality  (separation  space  effectively  covered  by  sample
                        First dimension (D1) separations       in the D1 were only weakly retained in the D2; the analytes eluted                                                     compounds), were signi¦cantly lower at 75 and 216. The set-up with
             Column     : Ascentis Cyano                       in the middle of the D1 were eluted in the middle of the D2 and the                                                    the  use  of  the  shifted  second  dimension  gradients  was  the  most
             Flow rate   : 20 µL/min
             Mobile phases  :   ( A) 0.1% acetic acid in water (pH around 3);  analytes eluted late in the D1 were strongly retained in the D2.   Fig. 4  Separation of a red wine sample by using the FIF (A) and the  ef¦cient  one  since  it  less suffered  from  the  correlation  of  the  two
                         (B) acetonitrile 0.1% acetic acid.                                                                              shifted gradient (B) approaches              dimensions tested (Table 1).
             Gradient elution :  0.01 min, 2% B; 10 min, 2% B; 60 min, 50% B; 75 min,  To overcome such a limitation, we used a narrower organic solvent
                         100% B; 100 min, 100% B.              span changing the gradient program according to the elution prop-                                                      Selected ion extracted chromatograms for some target compounds
             Backpressure (at analysis start) = 40 bar         erties. The shifted gradient program, led to a greater coverage of                                                     occurring in the red wine sample along the relative mass spectra are
             Injection volume :  5  mL
                                                               the separation space (Fig. 4B). The blue line is the program of the                                                    illustrated in Fig. 6.
                       Second dimension (D2) separations       D1 run and the red line is that of the D2 run. The D2 gradient cov-
             Column     : Ascentis Express C18                 ered  a  narrow  organic  solvent  range,  which  varied  continuously                                                  Table 1  Relative performances, in terms of peak capacity, n C , of the
             Flow rate   : 2.5 mL/min                          during the LC×LC run. The gradient program started with 0% ace-                                                               two set-up investigated
             Mobile phases  :   ( A) 0.1% acetic acid in water (pH around 3);
                         (B) acetonitrile 0.1% acetic acid.    tonitrile and rose to 20% ACN over 0.75 min; at the end of the                                                                          Full in fraction gradient  Shifted gradient
             Gradient elution :                                analysis, the gradient program in the D2 starts at 10% acetonitrile
                FIF, full in fraction: 0.01 min, 0% B; 0.10 min, 0% B; 0.75 min,   and rose to 50% acetonitrile. At the end of the analysis, the higher                                      1 n C          15              15
                         50% B; 1.00 min, 0% B.
                SG, Shifted gradient: illustrated in Fig. 3    percentage of organic solvent made possible the ef¦cient elution of                                                           2 n C          46              38
             Backpressure (at analysis start) = 170 bar        the strongly retained compounds.                                                                                          Theoretical D2 n C  690           570
             Modulation time of the switching valves : 1 min.
                                                               As can be seen from Fig. 4B regarding the red wine sample analyzed                                                         Practical D2 n C  75             216
                                                               with LC×LC with a shifted gradient in the D2, a signi¦cant improve-
            MS conditions
                                                               ment in the retention space was attained (Fig. 5). In fact, the use of
            MS acquisition performed using the ESI interface operating in negative   a shifted gradient with a gradual increase of the proportion of or-
            ionization mode:
                                                               ganic solvent gave better separation in the D2 with a less typical di-
            mass spectral range: 100–800 m/z; event time: 0.1 sec; scan speed:
                                                               agonal-line distribution. In addition, because of the narrower sol-
            7500 u/s; nebulizing gas (N 2 )  ow: 2 L/min; drying gas (N 2 )  ow: 15   vent range, the backpressure was much smoother and steadier.
            L/min; Heat block temperature: 250 °C; desolvation line (DL) tempera-
            ture: 250 °C; Interface voltage: 3.5 kV; detector voltage: 1.80 kV; The
             ow eluting from the second column was splitted before the MS in-
            strument (approximately 0.4 mL/min to the MS).

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