Tanaka Test


Chromatographic Characterization of Column Properties

Controlling the physical and chemical properties of stationary phases is important. However, only comprehensive chromatographic characterization ensures a consistently high level of reproducibility. Therefore, various approaches have been applied by leading HPLC scientists to characterize selectivity.

The Tanaka* Test is established worldwide as the industry standard for evaluating the selectivity and performance of different HPLC columns. These parameters not only simplify column comparison, but also facilitate the selection of the most suitable HPLC column for a particular separation.

A set of seven selected substances are used to describe capacity, hydrophobicity, steric selectivity, and silanophilic properties. The values of these parameters are outlined on the six axes of a hexagon, illustrating the quality of a sorbent at a glance.

The more symmetrical the hexagon appears and the larger its area, the more balanced the stationary phase is in the sum of its chromatographic properties.

* Prof. Tanaka, Kyoto Institute of Technology, J. of Chrom. Sci. 27, 725, 1989

Parameters According to Tanaka for the Characterization of Purospher® HPLC Sorbents

ParametersProperty of
stationary phase
Factors in preparation of
the stationary phase
k (Pentylbenzene)
80% Methanol
Retention
capacity (A)
Amount of alkyl chains Silica surface
Silica coverage
k (Pentylbenzene) /
k (Butylbenzene)
80% Methanol
Hydrophobicity (B) Hydrophobic capacity
(CH2-group selectivity)
Surface coverage
k (Triphenylene) /
k (o-Terphenyl)
80% Methanol
Steric selectivity (C) Steric (shape) selectivity Silane functionality
Surface coverage
k (Caffeine) / k (Phenol)
30% Methanol
Silanol capacity (D) Silanol capacity (content and type of silanols) Residual silanols
Endcapping
Surface coverage
k (Benzylamine) / k (Phenol)
30% Methanol /
70% Phosphate buffer pH 7.6
Ion exchange capacity (E) Ion exchange capacity at
pH 7
Residual silanols
Active sites at pH 7 
k (Benzylamine) / k (Phenol)
30% Methanol / 70% Phosphate buffer pH 2.7
Ion exchange capacity (F) Ion exchange capacity at
pH 3
Active sites at pH 3
Treatment of basic silica (metal impurities

Tanaka Tests for Purospher® STAR RP-18 Endcapped

Tanaka 1: Retention Capacity, Hydrophobicity, Steric Selectivity

The Tanaka 1 Test describes the retention capacity, the hydrophobicity, and the steric selectivity of RP-phases.

See details
Column Purospher® STAR RP-18 endcapped (5μm) LiChroCART® 150-4,6 HPLC column
Mobile Phase Methanol / Water 80:20
Flow rate 1.0 mL/min
Detection UV 254 nm
Temperature 30° C
Inj. Volume

10 μl

Sample 1. Uracil
2. Butylbenzene
3. o-Terphenyl
4. Pentylbenzene
5. Triphenylene
  Merck:/Freestyle/LE-Lab-Essentials/Chromatography/Diagrams/LE-Purospher-Tanaka 1-300x221-11182013.jpg

Tanaka 2: Silanol Capacity

The Tanaka 2 Test (Chromatogram A) illustrates the silanophilic properties of stationary phases. Chromatogram B is not part of the Tanaka 2 Test. The Phenol/Pyridine test measures silanol activities. 

See details
Column Purospher® STAR RP-18 endcapped (5μm) LiChroCART® 125-4 HPLC column
Mobile Phase A: Methanol / Water 30:70 (v/v)
B: Acetonitrile / Water 30:70 (v/v)
Flow rate 1.0 mL/min
Detection UV 254 nm
Sample A: Uracil (1), Caffeine (2), Phenol (3)
B: Pyridine (1), Phenol (2)
 

Tanaka 3 and 4: Ion Exchange Capacities

The results obtained from the Tanaka 3 Test (at low pH) demonstrate whether the deactivation of the residual silanol groups is complete. The Tanaka 4 Test (at high pH) indicates the complete absence of metal in the base sorbent. 

See details
Column Purospher® STAR RP-18 endcapped (5μm) LiChroCART® 125-4 HPLC column
Mobile Phase Methanol / 0.02 mol/L
Phosphoric acid 30:70 (v/v)
Flow rate 0.6 ml/min
Detection UV 254 nm
Sample 1. Uracil
2. Benzylamine
3. Phenol
 

Tanaka Test Results for Purospher® STAR RP-18 Endcapped

When compared with other brands of "high purity" RP-18 endcapped columns, Purospher® STAR RP-18 endcapped demonstrates the best overall selectivity, making it the column of choice for successful HPLC separations.

A. K (Pentylbenzene) 9.59
B. α (Pentyl-/ Butylbenzene) 1.51
C. α (Triphenylene/ o-Terphenyl) 1.63
D. α (Caffeine/ Phenol) 0.44
E. α (Benzylamine/ Phenol; pH 7.6) 0.23
F. α (Benzylamine/ Phenol; pH 2.7) 0.02
 
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