Log

October 10th 2011

Research Topic:
I'd like to do my topic on the use of microemulsion electrokinetic chromatography (MEEKC) for chiral separations. In particular, I'd want to focus on chiral surfactants and/or oils. I do not want to look into cyclodextrins.
[That sounds good - there have been chromatography essays in prior years but not on this specifically JCB]

Chemical for 5 properties assignment:
(I still need to complete links)
propiophenone

Melting Points
17-18 degrees C. Mean Value: 17.5 degrees C. 290.15 K: Alfa Aesar
18 degrees C. 291.15 K. MSDS
21 degrees C. 294.15 K PubChem
18.6 degrees C: 291.75 K Wikipedia
18.4-18.5 degrees C. Corrected value: 18.3 Degrees C: 291.45 K Reaxys Article

Density
1.009 g/ml : 1.009 g/cm^3 Sigma Aldrich
1.008 g/ml: 1.008 g/cm^3 Alfa Aesar
1.01 g/ml: 1.01 g/cm^3 MSDS
1.0087 g/ml: 1.0087 g/cm33 Wikipedia
1.0092 g/ml: 1.0092 g/cm^3 Reacys Article

Boiling Point
218 degrees C. 491.15 K Sigma Aldrich
214-218 degrees C. Mean Value: 216 degrees C. 489.15 K. Chemicalland
218-219 degrees C. Mean Value: 218.5 degrees C. 491.65 K JECFAfao.org (good scents company)
217-218 degrees C, Mean Value: 217.5 degrees C. 490.65 K. Alfa Aesar
217.999 degrees C. 491.149 K. ChemSpider Theoretical Value


Flash Point
98.89 degrees C. 372.04 K JECFAfao.org (the good scents company)
88 degrees C. 361.15 K MSDS
87 degrees C. 360.15 K Alfa Aesar
87.78 degrees C. 360.93 K Wolfram Alpha
87.4 degrees C: 360.55 K Cas.chemnet.com

Refractive Index n20
1.526: Sigma Aldrich
1.5258: Alfa Aesar
1.5269: PubChem
1.507: ChemSpider Theoretical Value
1.527: Fluka

Finished in google spreadsheet: 11/2/2011

Propiori_image.JPG
Densitypropiofile.jpg
MeltingPointpropiofile.jpg
MeltingPointpubchempropio.jpg
Propiorefractiveindexsigma.JPG


Review of Article Assignment
Rapid Separation of Pharmaceutical Enantiomers using Electrokinetic Chromatography with a Novel Chiral Microemulsion
Pascoe, Robert. Foley, Joe. The Analyst. 2002, 127, 710-714 Article
[Full Marks JCB]

Summary/Abstract Paragraph
Dodecoxycarbonylvaline (DDCV) is used for an electrokinetic chromatography (EKC) microemulsion separation. Elution range was more than double and enantioselectivity was higher than a similar, more popular micellar system. Certain parameters in the microemulsion, such as oil selection, buffer choice, and surfactant concentration, allowed for low conuctivity and higher voltage runs. This made the separations much faster. This allowed for the optimization of a DDCV, ethyl acetate, 1-butanol, and ACES pH 7 buffer, as listed.

Page 1, Paragraph 1 Introduction
The pharmaceutical industry uses a wide range of compounds that have enantiomeric properties. Electrokinetic chromatography (EKC) techniques use additives to separate the enantiomers while being fast, easy, and needing low volume amounts. The current industry standard is HPLC.

Page 1 Paragraph 2
Dodecoxycarbonylvaline (DDCV) is a readily available R or S additive surfactant that can be used in EKC for enantiomeric separation. Using either R or S DDCV would reverse elution order of analytes. DDCV consists of a C12 hydrocarbon chain, a chiral center, and a polar group.

Page 1 Paragraph 3
DDCV has low solubility below pH 7 and a small elution range at neutral or basic pH. Therefore, DDCV has some limitations in use for typical EKC media, although manipulation of these problems could theoretically increase resolution.

Page 1 Paragraph 4
This paper deals with a novel microemulsion consisting of the chiral selector surfactant DDCV. Microemulsions consist of a surfactant, co-surfactant, and oil present in a specified ratio in buffer. The microemulsion system has a large number of adjustable variables in comparison to other EKC techniques (micelles) and is typically larger in size. Microemulsions have been used in a wide variety of ways, including but not limited to pesticides and pharmaceuticals. It is thought that, in general, microemulsion electrokinetic chromatography (MEEKC) has greater resolving power, separation capability, and lower retention time than micellar electrokinetic chromatography (MEKC).

Page 1 Paragraph 5
While MEEKC and MEKC are considered similar techniques; MEEKC has had only one publication dealing with enantiomeric separation. That separation consisted of chiral selector oil (2R, 3R) di-n-butyl tartrate, while this paper will focus on a chiral selector surfactant.

Page 1 Paragraph 6
The cosurfactant in this study will be 1-butanol and the oil will be ethyl acetate. The buffer will be the zwitterionic ACES. The zwitterion will allow for a higher separation voltage. Ethyl acetate, a low surface tension oil, will allow the microemulsion to be made with less surfactant. The low conductivity will lead to shorter analysis times. The following chemicals are used as analytes: indapamide, atenolol, norphenylephrine, ephedrine, octopamine, metoprolol, pseudoephedrine, synephrine, methyl pseudoephedrine.

Page 2 Paragraph 1 Instrumentation
Detailed instructions, which include length and diameter of capillary, run voltage, injection parameters, and system requirements were mentioned in this paragraph. Also, the use of micellar DDCV experiments outside the realm of the paper was mentioned.Page 2 Paragraph 2 ReagentsThe reagents used in the paper (DDCV, ethyl acetate, 1 butanol, ACES, and TPAH (tetrapropyl ammonium hydroxide) were discussed briefly to indicate purchaser information

Page 2 Paragraph 3 Microemulsion Preparation
Microemulsions were prepared using 1% (w/v) DDCV dissolved in water with 50 mM ACES pH adjusted to 7. Ethyl acetate and 1-butanol were added in specific ratios and the entire system was sonicated for 30 minutes until clear. This method was determined by trial and error.

Page 2 Paragraph 4 Calculations
Certain parameters were calculated, such as electroosmotic flow (EOF) and electrophoretic mobilities of the analyte and microemulsions. The retention factor was also calculated using the equation show in the text. Enantioselectivity, or the relationship between the retention factors of each enantiomer, was also calculated. Alkylphenones were used to determine the elution time of the microemulsion. Resolution was calculated using Chemstation Software.

Page 2 Paragraph 5 Results and Discussion, Selection of Buffer
The reason behind choosing a zwitterionic buffer was discussed. Inorganic buffers tend to give rise to Joule heating and high running currents, which cause problems in retention and temperature fluctuations. Ohm’s Law plots, or plots of the voltage versus the current, give a good estimation of the break from linearity and the potential start of Joule Heating (usually around 1.5 watts per meter). This can help determine the best running voltage. This paper utilized 18 kV.

Page 2 Paragraph 6
Peak tailing was present with a running buffer pH adjusted with LiOH. This was because of the lithium ion, which had a higher mobility than the analyte ion. TPAH was used instead, since this phenomenon did not occur with this ion. Also, ephedrine was used initially since its high resolution was apparent even with minimal optimization. Exact differences between LiOH and TPAH were discussed in terms of efficiency.

Page 2 Paragraph 7 (finishes page 3) Elution Range
DDCV’s narrow elution range in MEKC is a major problem for that particular system. Microemulsions increase the elution range. Equations are shown with tabular data to support this claim.

Page 3 Paragraph 1
Electroosmotic flow and electrophoretic mobility calculations show that EOF was lower in the microemulsion than in the micellar system. The small amount of the cosurfactant (1-butanol) and the oil (ethyl acetate) can lower the EOF. Organic modifiers are known for dropping EOF levels in EKC methods. The exact mathematical reasons are expressed, with focus on the effects of zeta potential and viscosity changes.

Page 3 Paragraph 2
Electrophoretic mobilities were not as drastically different between the microemulsion and the micellar systems. More surfactant was used in the microemulsion system, so the effect of the much larger microemulsion droplet was counterbalanced. In general, the smaller micelle has the higher electrophoretic mobility. However, the diminished EOF and the slightly smaller electrophoretic mobility of the microemulsion aids in defending the large elution range present.

Page 3 Paragraph 3 Enantioselectivity, retention, and efficiency
If the retention factor stays within the optimal range and the efficiency and selectivity are constant, the increase in the elution range for the microemulsion will improve the resolution capabilities of the system. The table presented with this paragraph shows the values associated with each analyte tested for enantioselectivity, efficiency, efficiency per unit time, resolution, and resolution per unit time.

Page 3 Paragraph 4
The retention factors for the microemulsion remained in the optimal range while the retention factors for the micellar system tended to fall outside of the range. An explanation for the two resolutions in the table, one that includes all values and one that rejects any compound outside of the range, is explained.

Page 3 Paragraph 5
The enantioselectivities of the microemulsion were slightly greater than the enantioselectivities of the micellar system, but reasons were not known at publication. This showed that elution range did not sacrifice enantioselectivity. Those compounds with multiple chiral centers (ephedrine, pseudoephedrine, and methyl pseudoephedrine) showed greater enantioselectivity than those without. The remainder of the analytes studied were separated into groups by their enantioselectivity: one chiral center with an aromatic, phenolic substitutions, and neutral compounds.

Page 4 Paragraph 1
The microemulsion had a lower efficiency on average than the micellar system. While the writer cannot discertain reasons for the lower efficiency, they have ruled out the following: sample introduction, detection, excessive Joule heat, electromigration dispersion, and mass transfer. Reasonings, including the constant length of capillary, counter ion exchange, and viscosity corrections were discussed.

Page 4 Paragraph 2
The following were not ruled out as zone broadening problems: stationary phase mass transfer, polydispersity, and solute wall interactions. Wall interactions (the most probable interaction) can normally be resolved by additives, but microemulsions tend to be incompatible with these additions. Other methods were not explored.

Page 4 Paragraph 3 Resolution and analysis time
Resolution, overall, was comparable between the microemulsion and the micellar system. Therefore, the positives (increased elution range) and negatives (decreased efficiency) of microemulsion presented earlier seem to counterbalance each other in terms of resolution

Page 4 Paragraph 4
Analysis time was significantly reduced, by 3 fold, in microemulsions. This is due to low conductivity and lower retention. Reduced analysis time can be very profitable, especially if other issues can be resolved

Page 4 Paragraph 5 Fast separation of chiral pharmaceuticals
A separation of ephedrine and methyl pseudoephedrine (and their enantiomers) is shown as being complete in less than four minutes with baseline resolution. The separation’s time is less than half of most other EKC techniques described to date of publication.

Page 4 Paragraph 6
The elution order of the previously mentioned separation can be switched by changing R DDCV to S DDCV. This can allow for the quantitation of the peaks to be optimized. Resolution can also be improved by lengthening the capillary.

Page 5 Paragraph 1 Conclusion
The conclusions to the article state that DDCV based microemulsions had a greater elution range and increased enantioselectivity. The analysis time is also greatly reduced and the elution order can be switched by changing the R or S form of the surfactant used.

Research Project: November 18th 2011
Outline for Paper:
CE Theory and background
EKC theory and background
Types of EKC, to not be main focus: micellar, CD, polymers
Microemulsion EKC
Applications
Optimization of MEEKC
Chiral Microemulsion EKC
Optimization of Chiral MEEKC
Types of Chiral MEEKC

Erin.jpg