In May, I announced that CASSS organizes a discussion group about consulting.

Today, I would like to mention next discussion group focused on New directions/developments in Separation Science.

The meeting is taking place on September 15th, 2010 in Woodfin Suites in Emeryville, CA at 6 pm.

Personally, I am looking forward to attending this meeting. The topic as well as a list of panelist (see below) are very interesting. It will be nice to hear opinions about new directions in separation science from people with different background and experience.

I have to admit that my knowledge, interest, and predictions focus mainly on liquid chromatography (and monoliths, of course;)  so I am very curious about other topics, such as sample preparation, miniaturization and/or new materials in separations, which are possibly going to be part of the discussion too (I don’t know, just guessing;)

The information from CASSS website

Today’s sophisticated separation and analytical instruments and techniques bear scant resemblance to the “absorption analysis” technique reported by M.S. Tswett in 1903.  But that same drive for innovation and improvement is alive and well in 2010.

Join us for a lively discussion on the latest trends and technical innovations presented at the Pittcon, ASMS and HPLC conferences this year.  Question our expert panelists on where the trends might be taking the industry - and what to watch out for.

One thing is constant in this field … change.  From mergers and acquisitions to plenty of new products – stay abreast of the trends that will affect you most.

Invited panlists

• Tom Jupille, LC Resources
• O. David Sparkman, University of the Pacific, Stockton
• Robert Stevenson, R. Stevenson Consulting

Registration starts at 5:30 p.m., dinner at 6:00 p.m., and Panel discussion at 7:00 p.m.

The prize for registration before Wednesday, September 8 is $35 for Discussion only and $49 for Discussion and Dinner. On-site registration are not eligible for dinner. More info on CASSS website.

Future post

I will try to remember (ie. make notes of;) discussed topics and possible conclusions and bring them to you here on chromatographer.com soon after the meeting. Keep in touch.

PS: if you would like to be informed about new posts, you might consider subscribtion to RSS chanel or email newsletter in the right sidebar.

Recently, I was browsing amazon.com products related to the chromatography keyword. To my big surprise, the number ten (at least in my results) was a “16 oz. Double Wall Insulated Tumbler with chromatography column alone – Paper Insert”.

This is what I call a present for a chromatographer!

I waited until our next order (Harry Potter Playstation 3 game for my wife) and included the coffee tumbler in the order. Partly because I didn’t (want) understand, partly because of wishful thinking but I thought that the (chromatographic) paper is inserted in between the tumbler’s walls. It wasn’t. My bad. Instead, there was inserted paper with the picture of chromatographic column (ehmm, old fashioned burette). As advertised.

Anyway, I have decided to modify the tumbler to way I see it – original tea/coffee cup with the chromatographic separation on it. My only next condition was to avoid using any laboratory equipment.

So – if you are interested – you can very easily repeat the experiment in your kitchen and prepare your own original coffee cup.

To summarize, the aim of this small experiment is to perform thin layer chromatography of black office marker on a paper as stationary phase and use this paper as an original sign of a tea/coffee tumbler. No one else will touch it and everyone will ask about the way how to do it.

Ok, that’s plan.

A little bit of theory

The black markers usually contain more then a black color with several basic colors. Therefore, the black line traced on the filtration paper immersed with one side in the mobile phase is drifted towards the other side via capillary forces. During this journey the marker’s pigments are separated into the individual colors. Pretty much as a principle of thin layer chromatography ;-) Let’s start.

Materials

For our experiment we need: black marker as a sample, filtration paper as a stationary phase and some mobile phase. Further you might need a glass, cup or pot, pencil, scotch-tape, and scissors. That’s pretty it.

Preparation of a stationary phase

As a stationary phase I have used filtration paper from our lab. This is only one violation against my no lab staff condition. The filtration paper from the coffee machine can be successfully use too. We just don’t have any. The filtration paper I have had was smaller than the paper inserted in the tumbler, thus I used two of them and cut a right size and shape according the original paper.

Original tumbler and preparation of filtration paper as a stationary phase

The reaction vessel

An empty glass. Or a cup, pot; whatever fits your paper and purpose. Better if you can have one with a lid. With the lid, vapor of your mobile phase fills vessel and speed up and improve the separation. In my case, I have used an ordinary kitchen glass (made by ikea).

Sample

As a sample I have used black Expo Vis-à-vis wet erase marker. I have tested two different markers: Expo and Sharpie. The reason why I used the Expo is that with Sharpie I didn’t get a nice separation.

Hint #1: you better try the separation before the one you want to use in your tumbler. In this case, you can select the marker you like the most.

From analytical point of view, this can be used to indentify unknown marker: just compare their traces.

Mobile phase

That’s my favorite part. As a mobile phase I have used vodka. I told you: no lab staff ;-) You can probably use any distilled brandy. I would prefer the transparent one since I am not sure about the color of (evaporated) whisky on the stationary phase paper. Since the vodka (or any kind of home made brandy) is in the range of 40 – 50% the further dilution is not necessary. In lab I would use acetonitrile : water mixture (70 : 30 or 80 : 20 ratio). The concentration composition of this mobile phase can vary depending on the desired speed and resolution of separation.

Home-made thin layer chromatography

Ok, all stuff is ready. Let’s go. First, I labeled the paper with the marker. The length of your line is up to you. You would prefer either the long line through the width of the paper or short line covering only small part of the paper. I made a 5 cm (2”) long line roughly 2.5 cm (1”) from the edge of paper. This side (under the line) is then going to be immersed in the mobile phase.

Hit #2: To help paper fits the glass I curled the paper and used hairpins to hold it. Use new ones. Otherwise you can very easily get dirty paper.

Finally, to hold the paper in a vertical position I have used a pencil. You should have avoided any touch of the paper and glass wall. The mobile phase then flows equally without any restrictions, dispersions or speed ups.

Development of the separation (togerther with a test trace comparing two different markers - top left)

After immersing the paper in your favorite mobile phase, the liquid starts to rise via capillary forces and takes a sample with it. The low retained colors are faster than the more retained ones and “run” towards the opposite end of the paper faster. In our case you can see almost immediately after a start quick separation of four colors: black, yellow, red, and blue. As separation continues, the colors are separated more and more and later on you can notice total separation of least retained blue color from other colors. When the mobile phase reaches the other end of the paper, the separation is done. To cover only specific space of the paper, you might wish to stop the run sooner. All you need to do is then remove paper from the glass.

Happy chromatographer with a final product ;-)

When the separation is finished, move the paper to other glass and let it dry. Your original sign of chromatographic society membership is ready for use.

Have fun and enjoy your coffee, tea or any kind of tasteful mobile phase.

As I mentioned several weeks ago, there was an international symposium on the separation science – HPLC 2010 – held in Boston last week. It was my second North American conference (together with San Francisco 2006) and third in total (plus Stockholm 2005).

Allow me to summarize my remarks I made during the lectures I have attended. Fortunately, I have the opportunity to see majority of my pre-selected talks as a volunteer with the microphone in presentation halls.

This post is quite long. However, I didn’t want to chop it in several different posts rather to place all the information together. One more note: your selection (and conclusions) of talks can be completely different, I was mainly visiting sessions focusing on the new columns material, columns characterization and multidimensional techniques as well as monolithic stationary phases.

Sunday

Peter Carr in his plenary lecture awarded with a Martin Gold Medal of The Chromatographic Society described the advantages of the fast second dimension in two-dimensional comprehensive liquid chromatography (2D-LC). He compared time of 2D-LC analysis in 1990 (6 hours) with the current analysis time of twenty-thirty minutes with very fast second dimension (20 seconds!). The combination of perfluorated column together with zirconia type of the stationary phase seems to be satisfactory for several different applications of real samples from corn extract to Starbucks coffee or Minnesota’s red wine.

Short time travel: Peter’s lecture was next day followed by a 2D-LC tutorial led by Dwight R. Stoll. He focused on the necessity of the 2D-LC (is it really necessary and/or better?), column selection for multidimensional techniques and the biggest problem in the field of 2D-LC: lack of 2D instruments with very low gradient delay volume. He also focused on the fraction transfer and second dimension analysis time (why the 20 s looks like good compromise).

In the second plenary lecture, George M. Whitesides describes his efforts in preparation of no or low cost diagnostic tools. Nice talk. Why are we developing separation methods with the highest selectivity, capacity, retention, efficiency … when we are not able to provide their results for majority of people? I am sure symposium such as HPLC (2010) can significantly attribute to discussion like this.

Monday

Nobuo Tanaka introduced next generation of silica-based monolithic columns. Connecting several columns together (1 – 2 m) it is possible to achieve efficiency of several hundreds to million of plates. Moreover, the separation can be done at linear velocity as high as 11mm/s.

My colleague Stuart Chambers talked about the modification of the methacrylate-based monolithic columns with carbon nanotubes or methacrylate modified fullerenes. Surface modification significantly enhanced the column efficiency and values such as 80 000 tp/m for small molecule (benzene) can be achieved using this type of modification.

Ulrich Tallarek described mathematical approach towards the characterization of 3D structure of stationary phases. From my point of view, I am really looking forward to seeing such a model for organic polymer-based monoliths (taking into account their heterogeneity).

Fabrice Gritti discussed why the shell particles are so good and if there is still space for improvement? He described the mass transfer in these particles and compared several different types of the core-shell particles.

Tuesday

Wolfgang Lindner introduced new zwitterionic type of chiral stationary phase which can be used for both weak anion and strong cation exchange chromatography only by tuning the composition of the mobile phase.

Paola Dugo mentioned recent progress in comprehensive LC in the separation of small molecules (flavonoids) as well as larger ones (peptides).

My former boss from Pardubice, Czech Republic Pavel Jandera showed how to optimize gradients in 2D-LC. The gradients in the second dimension can be described as full in fraction (0 – 100%), segment in fraction (x – y%) and continuous shifting with separate run of gradient in second dimension. Optimization of the gradient in second dimension can be described as optimization of three separated steps – isocratic (dwell volume) – gradient – and isocratic again.

Matthew Lindford presented nanodiamond modified stationary phases. The diamond (nanoparticles) was attached to the impervious core using layer by layer addition using polyaminoallyl. These column show enhanced stability, as well as decent efficiency (55 000 tp/m).

Mary Wirth described submicron colloidal crystals nanoparticles packed in capillary format with submicron plate heights. This can be one of the new/next steps in the future of liquid chromatography – packing with ultra small particles and achieving ultrahigh column efficiency. However, the whole process has to be studied more deeply.

Gert Desmed asked where is ultrahigh pressure needed and if. The first part of his talk focused on the application of several connected column to provide the desired efficiency, whereas second one discussed the possibility of the gradients at constant pressure, which significantly speed up the separations (roughly about 10 – 20%).

Susan Olesik presented probably only one talk about the thin layer separations. She described the application of electrospinned polymer as stationary phase in TLC.

Peter Schoenmakers in his first talk (substituing his student Elena) introduced application of regular HPLC column for fast size-exclusion separation of polymers in UPLC mode in less than 1 min. In this case, the extracolumn volumes play very significant role and has to be minimize as much as possible.

Wednesday

Georges Guiochon has begun his talk with historical summary of core-shell type of the particles. Their superior performance is due to the reduced heat effect, short diffusion path and subsequently low contribution of A and C terms of van Deemter equation. The columns are getting smaller and smaller and therefore the role of the instrument is more and more important (why are you using highly efficient column if you are loosing all its performance in the extracolumn connections?). On the end of his talk Georges Guiochon pointed out the importance of column packing method and its quality.

Magdalena Titrici showed the possibility of the surface modification with either NIPAM or PEG-methacrylate based monomer to achieve a thermoresponsive stationary phase. With this kind of polymers the surface can be changed from highly hydrophilic to hydrophobic one.

I missed the beginning of talk of Marja-Liisa Riekkola, however on the very end of her talk she spoke about the capillary packed with very low density lipoproteins (VLDL) “particles”. I have to check this idea again because it looks very originally.

Jesse Omamogho described the new types of core-shell particles prepared using the seeded growth method. Using this technique they are able to control both the diameter of inner core as well as the thickness of the porous layer independently. The pore size of the particles is about 90 A with surface area from 80 to 200 m2/g. On the very end of the HPLC symposium, this talk won a first prize of the Csaba Horvath Award.

Charles Lucy discussed the influence of the stationary phase hydrophilicity on the retention and selectivity of the inorganic ions.

Uwe Neue described the selectivity of the new type of the stationary phases with controlled surface charge. He introduced plots/ways how to characterize column selectivity and how to compare it with other types of the columns.

James Jorgenson, father of ultra high pressure chromatography, spoke about the columns packed with 1 – 1.5 porous and non porous particles used at very high pressure. He studied the influence of the packing slurry solvent on the quality of the column. In the following discussion, Georges Guiochon compared chromatographic particle to the city: there are cities with a lot of gates and streets which make them very easy to enter. On the other hand, there are towns with only one gate and main street. Those are difficult to enter. The particles inside the column have a same “behavior” – either it is easy to enter them (core-shell) or it is difficult (e.g. fully porous).

Anthony Edge described the usage of graphitic column at high temperature with water as mobile phase.

David McCalley focused on the relationship between the applied pressure and compound retention together with molecular structure. Main influence of the analysis pressure on the retention can be observed for ionizable compounds.

Tivadar Farkas compared the influence of the extracolumn volume on the chromatographic behavior of core-shell highly efficient columns. He claimed that with current instrumentation we are not able to fully exploit potential of such columns.

Thursday

Kazuki Nakanishi described the preparation of silica-based monoliths with improved homogeneity of stationary phases enabling high efficient separations at low back pressure. Columns prepared according a new protocol contain only 5% of solid material. However, the disadvantage is their mechanical stability. Such column can be applied either in solid phase extraction or bioreactors.

Emily Hilder presented monoliths in planar format for dried blood spot sampling.

Brett Paul introduced the organic polymer monoliths prepared inside a 1 mm ID titan tubing. He described optimization of preparation together with first results. The column provide efficiency of 50 000 tp/m. Such column can be used at high analysis temperature, e.g. 180 °C.

Peter Schoenmakers continued with the ultra pressure size-exclusion chromatography topic. He focused on the degradation of very large polystyrene standards (> 7 MDa) at ultra high pressure. Further, he described separation of branched polymers using molecular topology fraction inside the monolithic stationary phases with very narrow flow-through pores. Peter correctly pointed out selectivity is one of the main property we should focus on. With very high and specific selectivity it is not necessary to require high efficiency, especially in case of very specific and tailored separations.

Robert Kennedy described in his plenary lecture segmented flow methods for hyphenation of LC and detection techniques, as well as their application in sample handling and tailored injection.

My current boss Frantisek Svec summarized the work of our group. He mentioned hypercrosslinking modification of organic polymer-based monoliths suitable for separation of small molecules (my work), as well as results of my colleagues with modification of the monolithic surface with carbon nanotubes (Stuart Chambers), gold (Yan Xu) and hydroxyapatite (Jana Krenkova) nanoparticles.

Atilla Felinger focused on the description of the thernodynamics and kinetics of solute transfer in HPLC. His very last talk at HPLC 2010 was “spiced” with the sudden technical problem with microphone. Fortunately, the organization team worked quickly and efficiently. As a very good chromatographic column ;-)

Conclusions

So, there are my HPLC 2010 flashbacks. In summary, my feelings are that the future of HPLC separation lies between superficially porous core-shell particles for fast and highly efficient separations and multidimensional techniques for complex samples. The monolithic stationary phases can still play significant role, especially 2nd generation of monoliths with tailored surface modification providing high selectivity for compound(s) of interest. Due to their thermal stability they can be also used at very high temperatures.

I would be more than happy to read your opinion either about HPLC 2010 or my notes.

Thanks for reading.

PS: and as a very last note: the poster of my wife about pressurized electrochromatography and electrophoresis on the thin layer monolithic plates for separation of peptides and oligonucleotides was awarded with the first prize in poster competition.

I am flying tomorrow to the Czech Republic. Two weeks of holiday. So, although I wasn’t updating this website frequently, I will have even less time now.  Shortly after my holiday starts the most important chromatographic conference of a year – HPLC 2010 in Boston.

Let’s meet at the HPLC 2010 in Boston

I have the nice opportunity to be part of the volunteers team at this conference and I would be more than happy to meet you, my readers. If you are attending the conference and willing to meet me – just do it. Tug on my sleeve and stop me. Use secret password: chromatographer.com ;-)

Attending HPLC 2010? Tug on my sleeve and stop me

We can discuss the beauty of our chromatographic life or just chat about your or mine latest results.

Anyway, number of my poster is P-1501-M and I have been assigned to the Poster Session on Monday (June 21st) from 2:45 to 4:30pm.

I will be showing results of fast and efficient separation of small molecules on hypercrosslinked monolithic stationary phases.

Looking forward to meeting you in Boston ;-)

I have to admit that this information is mainly interested for chromatographers located in California (especially Bay Area). The CASSS (An International Separation Science Society) organizes the Discussion group focused on the Keys to Successful Consulting.

Maybe you dont know it yet. Maybe your future job is a consulting.

Following information are from a Discussion group website:

If you’re serious about becoming a consultant (or even if you daydream about telling your boss to “take this job and shove it”), this course is a required investment in your future. While most scientists and engineers have traditionally sought full-time, long-term employment in industry, academia and government, many have found rewarding, flexible and dynamic careers as full- or part-time consultants.

This Workshop will be taught by Bob Stevenson, a successful consultant with a 20-year track record, “Keys to Consulting Success” takes you through the entire start up process. Consulting is a business – and successful businesses require serious commitment and planning. If you’re considering a consulting career or want to improve your existing business, join us for Keys to Consulting Success.

For complete meeting details and registration please visit: Discussion group website at www.casss.org

PS: Registration does close this Friday (May 28th).

Before the last CASSS Discussion group debate on difference between high temperature and high pressure liquid chromatography started, there was a welcome slide projected on the wall. There was only one sentece (paraphrase):

Meet other people who like and understand what you do

I highlighted the most important part (for me), because I have always problems to explain what I am doing. I would like to ask you all for your thoughts.

• How do you define chromatography?
• Do you have problems to interpret chromatography to other people who don’t understand the chemistry at all?

How do you define chromatography?

In my case, I am always trying to use words as analysing what is inside a sample, separation of complex mixtures, etc. On the very end (when I see that the listener has no clue at all), I am always using examples such as “when you are visiting doctors, they can determine the level of your cholesterol in a blood with chromatography” or “it can be used for a quality control of gasoline in your car”.

Usually, people just answer “ahaa”. And I know, that they still don’t know what I am talking about.

Once I have read the definition of the chromatography as a running race. On the beginning there is a group of a runners and as time flows (mobile phase?;) the group is separated to a groups of the runners with a same speed (retention). On the end of the run, the winner is a non retained compound and the others are individual parts of the mixture. I am not using this expression often, though. But maybe I will.

On the end of the day – as the saying goes – if I am not able to explain what I am doing to my grandparents, then I dont know what I do.

What are your experience and expressions how to define chromatographic separations?

Your comments and suggestions are more than welcome.

The last CASSS Discussion group focused on the possible advantages and disadvantages of high temperature and/or high pressure in a liquid chromatography. The Discussion group was hold as a debate – two experts against each other. The high temperature approach was defended by Nebojsa M. Djordevic (SANO CRO) and Michael W. Dong (Genetech) advocated the use of ultra high pressure in HPLC.

High temperature or High pressure?

High temperature in liquid chromatography

The first speaker was Nebojsa Djordevic. First of all, he started with short introduction of the influence of the temperature on the separation in HPLC. The most important equation in the liquid chromatography – the resolution equation – is temperature dependent. Change in the temperature causes change in all three parts of the equation: efficiency, selectivity and retention.

The higher temperature also decreases the mobile phase viscosity. With lower viscosity of the mobile phase, the pressure of the system decreases and then we can use higher flow rates (= faster analysis). At elevated analysis temperature the solubility of the samples increases and it is not necessary to use high concentration of the organic modifier in the mobile phase. Thus, high temperature liquid chromatography is another step to green chemistry.

Using a high temperature liquid chromatography one has to consider also some limitations. The secondary equilibrium (pH) changes, the kinetics varies (chiral separations) and the conformational changes of the sample can occur.

Using a high temperature is not only “heating” a column. The instrumental demands have to be also considered. The heater itself can form radial and axial temperature gradients, the solvent needs to be preheated; unheated detection cell can causes the precipitation of the sample, etc. Last but not least, the column and sample stability can change significantly using a high temperature.

The main advantage of high temperature HPLC is possible control of the elution selectivity. The high temperature can switch the elution order of (critical) peak pair and help to separate compounds which are not separated at ambient temperature. As Nebojsa Djordevic rightly mentioned ‘you don’t need a hundred thousands of plates if you have good selectivity’.

Ultra high pressure liquid chromatography

The next speaker, Michael W. Dong focused on the ultra high pressure liquid chromatography. His presentation was devoted mainly on the instrumental aspect of high pressure in HPLC. According M. Dong, high pressure instruments together with a low dispersion are new platform of HPLC. Currently, all main chromatography manufacturers offer the UPLC systems with pressure limit around 80 – 130 MPa (12 – 19 000 psi).

The UPLC allows fast and selective separation with high resolution for complex mixtures, enhanced peak capacity and fast method development. On the other hand, one has to take special care about injection precision, detector sensitivity (column bleeding) and method portability. Another issues rise from the high pressure safety, viscous heating of the mobile phase and system costs.

The main application of the UPLC system is connected with the high throughput, repeatability and speed, e.g. pharmaceutical industry. On the end of his presentation, M. Dong mentioned, that HPLC systems will be fully replaced by the UPLC instrumentation.

Discussion

In the following discussion the pros and cons of both high temperature and high pressure systems were compared. While the high pressure allows only increase in the efficiency (and the increase in pressure is still more the penalty we have pay with using small particles), the elevated temperature changes also selectivity and retention of the separation. And if you are able to control the selectivity (the peak resolution) you don’t need (super) high efficiency.

The significant argument for the temperature is financial expenses. The implementation of the high temperature in HPLC instrumentation can be done easily and cheaply then in the case of the high pressure application.

To conclude, the elevated temperature in liquid chromatography was slightly forgotten during last couple of years. With proper implementation, however, the high temperature can bring significant improvement of current and future separations. Cheaply.

What do you think?

The recent progress in the column development brought to the market new type of highly efficient columns. These columns can be use either with standard HPLC instruments or with the instruments allowing separations at ultra high pressure (900 MPa). The conventional size of the column (150 x 4.6 mm) has been decreased significantly. The typical size of column for ultra high pressure liquid chromatography (UPLC) is 50 x 2.1 mm with sub 2 μm ID particles.

Reduction of the extra-column volume of instruments

The decrease in the column size increases the significance of the extra column volumes – the volume of the liners between the injector and column, as well as column and detector, injector itself and detection cell. The contribution of the extracolumn volumes can be almost neglected using the conventional size of the column (150 x 4.6 mm) and flow rate as high as 1 mL/min (ok, almost neglected;). On the other hand, if we are using the identical instrument with small columns (50 x 2.1 mm) the influence of the extracolumn contribution is much higher and can devastate our efficiency and separation.

In recent paper, F. Gritti et al. compared several currently commercially available HPLC instruments in terms of the influence of the extracolumn volumes on their separation power. They found, that the only optimization of the extracolumn volume in standard Agilent 1100 HPLC system from 15.2 μl to 3.8 μl, together with the change in the volume of detection cell (13 μl to 1.7 μl) dramatically improve the columns efficiency. The average increases in the average column efficiencies were 28, 41, and 278% for the 100 x 4.6 mm, the 50 x 4.6 mm, and the 50 x 2.1 mm I.D. Kinetex columns, respectively.

Using this very simple and almost costless modification of the current instruments, the full performance of large diameter column can be achieved. However, other approach has to be applied in case of the resolution power of small diameter columns.

Sample focusing with weak solvent

In the same article, authors showed the possibility of column efficiency improvement with the injection of the weak solvent plug after the sample. After the sample injection, the weak solvent (water in reversed-phase chromatography) is injected and if there is no retention of this weak solvent on the stationary phase, the width of the sample band adsorbed at the column inlet can be reduced by diluting the sample with the weak solvent. Following picture (adapted from the discussed article) describes the whole idea.

Sample focusing with weak solvent

With this approach, the sample dispersion on the column inlet is almost eliminated and it is possible to achieve apparent column efficiency close to the maximum possible for most columns currently available, including the short 2.1 mm I.D. columns packed with 2.6 μm superficially porous particles.

These examples show that it is possible to improve the HPLC instrument performance using very simple and costless approaches. However, the further improvement in the instrumentation (especially decrease in the instrumental extracolumn volumes) is necessary to be able to reach the full possible performance of the new, highly efficient, columns.

Georges Guiochon pointed out in his excelent reivew about monolithic stationary phases four directions from which we can expect a serious improvement in (monolithic) columns performance.

High temperature chromatography

High temperature chromatography, which causes a reduction in the viscosity of the mobile phase. So far, monolithic stationary phases have not yet been used at high temperatures but this is only a matter of time. High temperature liquid chromatography currently pioneered by Peter Carr and his group is going to be one of the major research areas in analytical chemistry for the next ten years. A significant reduction of analyses times by a factor between 3 and 4 is quite likely.

Increase in the pressure

An increase in the maximum pressure available to the analyst. Most commercial instruments can operate at inlet pressures of up to 40 – 50 MPa. A few of them can reach inlet pressures of 100 – 120 MPa and pumps able to reach 900 MPa are available. The use of high pressures requires far more caution than chromatographers are used to apply. This may create new, some times unexpected, safety hazards against which analysts should be forewarned. One advantage of monolithic columns is that extremely efficient columns, able to generate one or even several millions of theoretical plates could be operated with conventional HPLC instruments if long enough columns could be prepared.

Optimize the structure

A decrease in the minimum value of the height equivalent to theoretical plate (HETP) of the columns used. This will come from a reduction of the heterogeneity of the radial distribution of the flow-through pore sizes, also from a reduction of the average size of the domains of the monolithic column used and from a reduction in the variance of the domain sizes.

We have to be able to control (and suppress) monolith heterogeneity. My small prediction: one who is able to prepare the (monolithic) stationary phase with no or limited heterogeneity will be able to achieve unimaginable efficiency and column performance. Like for example homogeneous pillars.

Higher column permeability

Internal heterogeneity of organic polymer monolith

An increase in the column permeability. This requires an increase in the average flow-through pore size. Since this size is included in the domain size, this requirement is in conflict with the previous one. Both can be achieved only by decreasing the average size of the porons, which would increase the external and total column porosity at the expense of the internal column porosity and the total surface area of adsorbent in the column. There is no clear limit here but it does not seem that much can be gained. Most probably, a reduction in the variance of the domain size accompanied by an increase in the degree of radial homogeneity of the monoliths constitute the most promising avenues for the monolith designers and makers.

Solutions?

One of the possible ways how to connect these last two conflicting requirements can be preparation and optimization of hypercrosslinked monolithic stationary phases. The porous structure (flow through pores) can be optimized independently on the structure of the thin hypercrosslinked layer prepared on the surface of the monolith (micro- and mesopores). Firstly, the generic monolith is prepared (flow through pores) and then the surface of the stationary phase is modified with the hypercrosslinking reaction and thin layer of small pores is formed.  Then, only the general models connecting the preparation and modification of the hypercrossllinked monoliths with their chromatographic properties have to be developed and understand.

What do you think about these suggestions?

PS: if you haven’t done yet – look at the review written by Georges Guiochon. There is all you need to know about monoliths but were afraid to ask.

Analyst 1957, 77, 964 - 969.

Although the monolithic stationary phases suitable for separations were introduced in the 1990s [1,2,3], the idea of using a “continuous block of the porous gel structure” as stationary phase was discussed in Analyst by R. L. M. Synge, A. J. P. Martin, and A. Tiselius as longs ago as in 1952.

Both equilibrium and kinetic aspects of the molecular-sieve properties of zeolites have been studied in detail by Barrer, and it is clear that these equilibria could be used for the separation of small molecules on chromatographic columns of zeolites. Zeolites could not be used with larger molecules, as the spaces in them are too small. However, from dialysis and ultrafiltration studies enough is known of the properties of membranes and gel structures to suggest that these, though their pores could not be expected to possess the regularity of those of zeolites, could nevertheless be used for more refined separations than have hitherto proved possible. If used as powders in ordinary chromatograms, however, these substances would exhibit the disadvantages already discussed, namely that adsorption, increasing with molecular weight, would work in the opposite sense to molecular-sieve effects. An alternative possibility, suggested in discussions between Dr. A. J. P. Martin, Prof. A. Tiselius and one of us (R.L.M.S.), is to use electro-endosmosis to move a solution through a continuous block of porous gel structure. In this way the equivalent of movement of liquid through a very thick ultrafiltration membrane is attained without the necessity of great hydrostatic pressures, which would destroy the membrane structure. Here adsorption and molecular-sieve or frictional effects would all act in the same sense, tending to retard more the larger molecules.

And conclusions?

1. Smart people have smart ideas.
2. Each idea we are reading today in scientific journals may have a huge impact in comming years. At least in same way, as monoliths have changed the chromatography.