Analytical Ultracentrifugation of Polymers and Nanoparticles (eBook)

Preface 7
List of Symbols and Abbreviations 9
Table of Contents 11
1 Introduction 14
1.1 Historic Examples of Ultracentrifugation 15
1.2 Basic Theory of Ultracentrifugation 20
1.3 Basic Experiment Types of Ultracentrifugation 25
1.4 Closing Remarks 28
References 29
2 Analytical Ultracentrifugation, Instrumentation 30
2.1 Ultracentrifuges 31
2.2 Rotors 38
2.3 Measuring Cells 39
2.4 Detectors 42
2.5 Multiplexer 56
2.6 Auxiliary Measurements 56
References 59
3 Sedimentation Velocity 60
3.1 Introduction 60
3.2 Basic Example of Sedimentation Velocity 60
3.3 Advanced Theory of Sedimentation Velocity Runs 67
3.4 Sedimentation Velocity Runs of Macromolecules to Measure AverageMand 75
3.5 Sedimentation Velocity Runs on Particles to Measure Average dp and PSD 82
3.6 Synthetic Boundary Experiments 99
References 108
4 Density Gradients 110
4.1 Introduction 111
4.2 Static Density Gradients 114
4.3 Dynamic Density Gradients 133
4.4 Other Types of Density Gradients 138
References 142
5 Sedimentation Equilibrium 144
5.1 Introduction 144
5.2 Experimental Procedure 146
5.3 Data Analysis 151
5.4 Examples 164
5.5 Further AUCMethods to Measure Molar Masses 172
References 175
6 Practical Examples of Combination of Methods 176
6.1 Combination of Different AUC Methods 176
6.2 Combination of AUC with Other Techniques 202
6.3 Literature Examples: AUC and Nanoparticles 225
References 225
7 Recent Developments and Future Outlook 227
7.1 New AUC Instrumentation and Detectors 228
7.2 New AUC Methods 234
7.3 New AUC Data Analysis 240
References 245
8 Subject Index 247

7 Recent Developments and Future Outlook (p. 215-216)

In 1991, one of the authors of this bookwrote a paper about the future requirements formodern analytical ultracentrifuges [1]. The four most important requirements proposed in this paper were:

(i) multi-hole rotors,
(ii) multiple detecting systems,
(iii) automatic online data analysis, and
(iv) a new running technique with a variable rotor speed ?(t) during a run.

In a recent feature article about analytical ultracentrifugation of nanoparticles, Cölfen [2] wrote "it is amazing that small parts of these requirements were understood in only a few specialized laboratories, although their potential benefit is obvious".

Nevertheless, some of these proposed requirements are realized: eighthole rotors are standard, the Optima XL-A/I now has two simultaneous online detectors (absorption and interference), Laue [3] recently presented a powerful new fluorescence detector inside an XL-A/I, and the authors of this book together with coworkers presented a Schlieren optics detector (needed for density gradients, [4]).Additionally, there has been a dramatic improvement of data analysis due to new, fast and powerful computer programs described by Philo [5], Demeler [6], Schuck [7, 8], Stafford [9], Lechner [10], and Behlke [25], which are partly mentioned in the foregoing chapters.

To date, however, no 50-hole rotors, nor any triple or quadruple detectors have been developed. Nearly all detectors are still not fast enough, and the quality of their primary measuring data should be higher. Thus, the full power of the new data analysis cannot be used fully today. Furthermore, the benefits of the variable rotor speed ?(t) technique are used only rarely, although recent efforts are dedicated to using variable rotor speeds on the Optima XL-A/I [26, 27].

The authors of this book are optimistic that in the next two decades, the requirements proposed in 1991, but not yet developed, will be realized. Especially,we appeal to themanufacturers of analytical ultracentrifuges to attend to this business. Each laboratory working with GPC, liquid and size exclusion chromatography or field flow fractionation, i.e., each laboratory analyzing polymers, polyelectrolytes, colloids, emulsions or nanoparticles (and there are a lot of them!) is a potential user of AUC technology.

It has to be stressed here that a more user-friendly design of the AUC, especially of the measuring cells, is believed to directly increase the number of potential users. It is one major drawback of AUC technology that a relatively high expertise is needed to run an apparatus. In the following three sections, some details of the requirements remaining to be realized are repeated briefly. Additionally, some new ideas and possible improvements of the AUC technique are proposed. In Sect. 7.1, new instrumentation and detectors will be discussed, whereas Sect. 7.2 will deal with new AUC methods, and Sect. 7.3 with new data analysis.

7.1 New AUC Instrumentation and Detectors

The present standard AUC, the Optima XL-A/I of Beckman-Coulter, is a good basis for further improvements of the AUC technique. We hope Beckman-Coulter, or other manufacturers will carry this out, but it could also be a task for specialized scientific laboratories, because the XL-A/I is a compact modular instrument that has enough space inside the rotor chamber to introduce new detectors and other modifications. However, it is not easy to make use of this type of modularity, as well as of the space inside and below the rotor chamber, because of the associated safety and warranty loss aspects.