Evaluation of Monodisperse Silica for High Performance Liquid Chromatography using Van Deemter Plot
Norikazu Nagae, Tomoyasu Tsukamoto, Shun Kojima

ChromaNik Technologies Inc., 6-3-1 Namiyoke, Minato-ku, Osaka, Japanwww.chromanik.co.jp

Abstract

The feature of superficially porous particle used as a highly efficient material is existence of a core, a thin porous layer and narrow particle size distribution, which lead to higher efficiency than totally porous particle. On the otherhand, recently a monodisperse silica gel has been presented to be the almost same particle size distribution as a superficially porous silica and to be higher performance materials than a conventional totally porous silica. In this study,a monodisperse totally porous silica and a superficially porous silica were compared regarding theoretical plate and Van Deemter plot. As a result of a plate measurement, a monodisperse silica showed 16% higher theoretical plate
than a conventional totally porous silica, while a superficially porous silica indicated 50% higher. It was leaded by comparing with Van Deemter plot that only A term of Van Deemter Equation was decreased by effect of narrow particle
size distribution and both B and C terms were reduced by effect of a thickness of porous silica layer. It was elucidated that predominance of superficially porous silica over totally porous silica was leaded by not only low Eddy diffusion
due to narrow particle size distribution but also both low longitudinal diffusion and short mass transfer path due to a thin porous layer.

Some assumptions and the definition of Van Deemter Equation

Table 1. Parameter of each particle1) It is assumed by Plots in figure 3 that the ratio of B/Dm value of B term
between core shell and totally porous particles is 7/10.
B termA term2) The particle size distribution is narrowed, a coefficient (A) of A term
decreases. The coefficient (A) is also the same value in the case of the particle
size distribution is the same.

C termu

A term : Eddy diffusion(dp is particle diameter)
B term : Longitudinal diffusion (Dm is diffusion coefficient)C term : Mass transfer

3) C term value is in proportional to a particle size (dp) squared.
4) B·Dm is assumed to be 5 for a totally porous particle and 3.5 for a core shellparticle by plots in figure 2 and above (1) .

1. F. D. Antia and C. Horvath, J. Chromatogr., 435 (1988) 1-15.

Figure 1. Van Deemter equation

5) C/Dm of totally porous particle is assumed to be 0.044 by plots in figure 2.
The C term value of 1.8 μm totally porous particle is assumed to be as same asthat of 2.7 μm core shell particle.

Fully porous 3 um

12

Fully proous 1.8 um
HC=0.044x52u106) The coefficient A is assumed to be 1.33 and 1.00 for a conventional particle
and a narrow particle size distribution particle respectively by plots in figure 2and above (4) and (5).

CoreShell2.6
2.7 umum
SunShell(H=1.08u+6)1414

Totally porous 1.8 μm

12864

HB=5/u (H=5/u + 4)

400

14

4

68

10

HA=2.4
HC=0.14u
HB=5/u

4

68

10

1214

16

20Mobile Phase Velocity , u (mm/sec)

Figure 2. Comparison of plate height plots
Totally porous silica

Core shell silica

A solute diffuses both outside a particle and in a pore.

The ratio of the core for a cross section of the column is around 30%.

Cores block the path ofdiffusion of a solute.

0Figure 3. Difference of diffusion in column
Longitudinal direction

246810HA=3.6
HC=0.32u
HB=5/uu (mm/sec)

Table 2. Property and chromatographic data
PhotoParticle typeParticle size
distribution

Core shellparticle

2.78 μm

D90/D10=1.11

9 nm

N=20,500h=1.75

Monodisperse
totally porous
particle

2.81 μm

D90/D10=1.09

10 nm

N=16,000h=2.22

D90/D10=1.48

16% up12 nm

3.19 μm

Efficiencya,

Pore
Retention
diameter Reduced HETPa timeb

N=12,200h=2.57

7.8 min

47% up
9.6 min

9.8 mina: Stationary phase, C18; column dimension, 100 x 2.1 mm; mobile phase, acetonitrile/water (60/40); flow rate, 0.3 mL/min;column temperature, 25 oC; sample, butylbenzene.
b: Retention time of butylbenzene

Conclusion

50.044x2.72=0.32
0.14(Core shell)same as 1.8um particle(Core shell)

50.044x2.72=0.32(Totally porous)

18
162468

HA=2.7
HC=0.14uHB=3.5/u
10

Totally porous 5 μm

Totally porous 2.7 μm
Narrow particle size distribution（as same as core shell）

42046850% up

15% upTotally porous 2.7 μm
Totally porous 2.7 μm

8narrow particle size distribution

Core shell 2.7 μm
Totally porous 1.8 μm

462106801210

HA=2.7
HC=0.32u
HB=5/u

200u (mm/sec)

Figure 4. Van Deemter Plot

Averageparticle
size

Conventional
totally porous
particle

B term decreases to 70%.

01080.044x1.82=0.14141242(Conventionaldistribution)

6141053.5

1.33x2.7=3.6u (mm/sec)

60

1.00x2.7=2.70Conventional particle size distribution(C/Dm)·dp2(Totally porous)(Narrow distribution)2

Totally porous 2.7 μm

120

1.00x2.7=2.7

8u (mm/sec)

HB=3.5/u (H=3.5/u + 2.7)

2

2

B·Dm
(Totally porous)(Narrow distribution)

4

H (μm)

6Column: C18, 50 x 4.6 mm
Mobile phase:
Acetonitrile/water=(60/40)
Temperature: 25 oC
Sample: Naphthalene(Conventionaldistribution)

1028

1.33x1.8=2.4Core shell 2.7 μm
Narrow particle size distribution

12

Conventional particle size distribution

10H (μm)

Fully porous 5 um

14H (μm)

Plate Height, H (um)16H (μm)

18A·dpTotally porous
Conventional particle size distribution
1.8 μmTotally porous
Narrow particle size distribution
2.7 μmCore shell
Narrow particle size distribution
2.7 μmTotally porous
Conventional particle size distribution
2.7 μm

H (μm)

HParticle

246810U (mm/sec)

A monodispersie totally porous silica showed a narrow particle size distribution
as same as superficially porous silica.
A narrow particle size distribution made A term of Van Deemter Equation
decrease 25% to compare with a conventional particle size distribution particle.
The coefficient (A) became from 1.33 to 1.00. As the result, an efficiency
increased 15% to 16%.
Measurement value was almost corresponded the theoretically calculated value
including some assumptions.
A core shell silica showed ca. 50% higher theoretical plates than a conventional
totally porous silica because reducing of both B and C term values of VanDeemter Equation was added due to a thin porous layer of the particle.