Exceptional college sophomores and juniors majoring in chemistry and chemical engineering can apply for a prestigious 10-week internship through the SCI Scholars Program. Benefits include industrial experience, a generous stipend, scientific meeting travel award, and the chance to nominate a high school teacher of their choice for further benefits. Applications will be due Dec. 14, 2013.
Rabu, 04 Desember 2013
ACS Scholars
The American Chemical Society (ACS) offers renewable scholarships to underrepresented minority students who want to enter chemistry or related fields. Awards of up to $5,000 are given to qualified African American, Hispanic or American Indian students who are high school seniors or college freshman, sophomores, or juniors pursuing a college degree in the chemical sciences. Applications will be due March 1, 2014.
More information can be found at http://www.acs.org/content/acs/en/funding-and-awards/scholarships/acsscholars.html
More information can be found at http://www.acs.org/content/acs/en/funding-and-awards/scholarships/acsscholars.html
2014 Nebraska Summer Research Program
Nebraska’s summer program offers research opportunities in the science, technology, engineering, and mathematics fields in addition to a new interdisciplinary Minority Health Disparities program doing research in and around the social sciences. A complete listing of faculty mentors and research project descriptions can be found on our website at http://www.unl.edu/summerprogram. Students can also find information about program benefits including a competitive stipend, room and board, travel expenses, and more.
Summer 2014 programs include:
Algal Biofuels and Nanohybrid Materials
Applied Mathematics
Bioenergy Systems
Biomedical Engineering
Chemistry
Minority Health Disparities
Redox Biology
Virology
Water in the Earth System
During the Nebraska Summer Research Program, students receive first-hand exposure to research and the experience of graduate school. They work closely with faculty mentors and research teams of graduate students and other summer scholars. Students also have opportunities to participate in meaningful social and professional development activities outside of the laboratory.
Our online application makes it easy for students to apply. Priority review begins Friday, February 1 and all applications must be completed by Monday, February 17. Students historically underrepresented in graduate education and students from academic institutions where research programs are limited are especially encouraged to apply.
Summer 2014 programs include:
Algal Biofuels and Nanohybrid Materials
Applied Mathematics
Bioenergy Systems
Biomedical Engineering
Chemistry
Minority Health Disparities
Redox Biology
Virology
Water in the Earth System
During the Nebraska Summer Research Program, students receive first-hand exposure to research and the experience of graduate school. They work closely with faculty mentors and research teams of graduate students and other summer scholars. Students also have opportunities to participate in meaningful social and professional development activities outside of the laboratory.
Our online application makes it easy for students to apply. Priority review begins Friday, February 1 and all applications must be completed by Monday, February 17. Students historically underrepresented in graduate education and students from academic institutions where research programs are limited are especially encouraged to apply.
PathwaystoScience.Org
Paid Summer 2014 Undergrad Research Opportunities:
More than 650 programs – REU and other summer research opportunities for undergrads
Senin, 02 Desember 2013
What We Did, Monday, 12/2/13
Chemistry:
*Turned in PPs 3.5 and 3.6 (a) and (b)
1) Fake Pop Quiz: How many atoms are in a 79.0 g sample of neon? -- completed and discussed
2) Group activity: Moles Scavenger Hunt
Advanced Chemistry:
*Turned in Lab Reports: Specific Heat of an Unknown Metal
1) Notes 2.2/2.3
2) PPs 2.2/2.3 #1 (front only, add mass of 10.0 g to number 5).
*Turned in PPs 3.5 and 3.6 (a) and (b)
1) Fake Pop Quiz: How many atoms are in a 79.0 g sample of neon? -- completed and discussed
2) Group activity: Moles Scavenger Hunt
Advanced Chemistry:
*Turned in Lab Reports: Specific Heat of an Unknown Metal
1) Notes 2.2/2.3
2) PPs 2.2/2.3 #1 (front only, add mass of 10.0 g to number 5).
Kamis, 28 November 2013
What We Did, Tuesday, 11/26/13
Chemistry:
1) Work on PPs 3.5 and 3.6 b -- staple to PPs 3.5 and 3.6 a (due Monday upon return)
Advanced Chemistry:
1) LTA 2.1
2) Work on Lab/Clean Lab Stations
1) Work on PPs 3.5 and 3.6 b -- staple to PPs 3.5 and 3.6 a (due Monday upon return)
Advanced Chemistry:
1) LTA 2.1
2) Work on Lab/Clean Lab Stations
Rabu, 27 November 2013
Selection of the Stationary Phase in Liquid Chromatography (LC)
Once the LC modeand the type of column packing (porous, superficially porous) are selected, the choice of the stationary phase is determined by the requirements and the nature of the sample. In general, each stationary phase can have a unique selectivity towards sample components.
Selection of the Liquid-Solid Chromatography (LSC) Stationary Phase
Silica and alumina are the two most popular stationary phases (adsorbents). Silica is the preferred stationary phase mainly because of its availability, known performance and low cost. Silica has a lower reactivity, yields columns of better efficiency, and offers a higher linear capacity than alumina.
In general, silica and alumina are both used for the separation of the same type of compounds, although certain compounds tend to favor one over the other.
The following semiempirical relationships have been found by comparing the two adsorbents with regard to their selectivity for various functional groups:
- Moderately strong bases (pKb < 5) are preferentially adsorbed on silica
- Base-sensitive compounds should be separated on silica
- Acidic compounds are preferentially adsorbed on alumina
- Unsaturated molecules (olefins, aromatic) are preferentially adsorbed on alumina
- Halogen groups are preferentially adsorbed on alumina
Whisky Review: Slyrs Pedro Ximénez Finish
Slyrs is a whisky distillery in a region not traditionally associated with single malts: Bavaria
Founded in 1999 by Florian Stetter, a German brewer, the distillery was originally part of a brewery, but now occupies its own purpose-built space. Despite the fact that the distillery has been around for over a decade, all of their whiskies are still bottled between three and four years old and are bottled by vintage, much like Kilchoman.
This particular whisky was aged in new American oak barrels for three years, then transferred to ex-PX sherry butts for nine months. The whisky is then proofed down to 46% for bottling.
Thanks to Ian of PDXWhisky for picking up a bottle during his travels and letting me sample this whisky.
Slyrs PX Sherry Edition Nº 1
Nose: sweet raisins, very light malt, toasted grain, molasses, fruit cake/baking spices, creamy brown sugar. After adding a few drops of water, it becomes creamier and the raisins become less sweet, a lot more new make grain comes out, there's some lemongrass hand soap, and a touch of coffee/mocha.
Taste: malt and sherry have blended almost seamlessly, it's lightly sweet up front - fading to bittersweet across the palate, a bit floral at the back with some sour apples and very light oak. After dilution, there's a strong note of burnt sugar, the raisins become more bittersweet, the sour apple note becomes stronger, and there is some emerging pepper and honey.
Finish: light sherry and malt, raisins, sour apples, bittersweet tannins
This is what it is - a young single malt with an aggressive cask finish. The PX sherry, as it is wont to do, has almost completely dominated the malt. Given the new make notes that popped out with water, that might not be a bad thing, but you have to like that style of whisky for this one to do the trick. I can appreciate it to a degree, but it's not something I would want to drink a whole bottle of. Now if this had been lightly peated or smoked, it'd be another matter...
Founded in 1999 by Florian Stetter, a German brewer, the distillery was originally part of a brewery, but now occupies its own purpose-built space. Despite the fact that the distillery has been around for over a decade, all of their whiskies are still bottled between three and four years old and are bottled by vintage, much like Kilchoman.
This particular whisky was aged in new American oak barrels for three years, then transferred to ex-PX sherry butts for nine months. The whisky is then proofed down to 46% for bottling.
Thanks to Ian of PDXWhisky for picking up a bottle during his travels and letting me sample this whisky.
Slyrs PX Sherry Edition Nº 1
Nose: sweet raisins, very light malt, toasted grain, molasses, fruit cake/baking spices, creamy brown sugar. After adding a few drops of water, it becomes creamier and the raisins become less sweet, a lot more new make grain comes out, there's some lemongrass hand soap, and a touch of coffee/mocha.
Taste: malt and sherry have blended almost seamlessly, it's lightly sweet up front - fading to bittersweet across the palate, a bit floral at the back with some sour apples and very light oak. After dilution, there's a strong note of burnt sugar, the raisins become more bittersweet, the sour apple note becomes stronger, and there is some emerging pepper and honey.
Finish: light sherry and malt, raisins, sour apples, bittersweet tannins
This is what it is - a young single malt with an aggressive cask finish. The PX sherry, as it is wont to do, has almost completely dominated the malt. Given the new make notes that popped out with water, that might not be a bad thing, but you have to like that style of whisky for this one to do the trick. I can appreciate it to a degree, but it's not something I would want to drink a whole bottle of. Now if this had been lightly peated or smoked, it'd be another matter...
Selasa, 26 November 2013
Gradient Elution in Liquid Chromatography
Gradient elution is used in chromatography (mainly in reversed-phase but with other modes such as ion-exchange) to modify the separations achieved in a column. It involves a continuous change in the composition of the mobile phase to achieve separation of sample components of widely varying affinities for the stationary phase.
The separation in a chromatographic column can be changed by changing the polarity of either the column (stationary phase) or the mobile phase. Generally, it is easier and cheaper to change the composition of the mobile phase (solvent).
The method used more often to modify the separation is to change the difference in polarity between the stationary phase and the mobile phase.
The following is observed for the polarity difference of these phases:
- Increasing the difference in polarities between the stationary and the mobile phase makes compounds elute slower – they adsorbed more efficiently on the column.
- Making the solvent polarity more like the column polarity makes compounds elute faster
For example:
On a nonpolar column running in acetonitrile if we could switch to a more polar mobile phase (by adding a known percentage of water –which is very polar- to the acetonitrile solution) then the compounds will be retained longer in the stationary phase and they will have more time to separate.
We could also start with a mobile phase containing a large percentage of water to make nonpolar compounds stick to the top of the column and then gradually increase the amount of acetonitrile to elute them (Fig. 1).
 |
| Fig.1: Gradient elution of seven compounds showing the effect on peak resolution using as a mobile phase H2O - acetonitrile (A) linear, 0-100% acetonitrile (B) convex, 30-100% acetonitrile |
What We Did, Monday, 11/25/13
Chemistry:
1) Finish notes 3.6 (copy from a friend)
2) Finish PPs 3.5 and 3.6 a
Advanced:
Last day to work on Lab
1) Finish notes 3.6 (copy from a friend)
2) Finish PPs 3.5 and 3.6 a
Advanced:
Last day to work on Lab
Senin, 25 November 2013
Scotland 2013: Bowmore Distillery Tour and Loch Indaal
I once again woke bright and early - I didn't have a ton of miles to cover before my first appointment in Bowmore, but I didn't want to dawdle either. I ate breakfast and said goodbye to Joy before leaving the Askernish, then headed north.
The bulk of the Port Ellen maltings was hard to miss on my way out of town. It's unmistakably an industrial site now - the remnants of the old distillery are completely dwarfed by the maltings.
Though I had never tried a Port Ellen before, the almost constant talk about the place meant that viewing it still produced a certain cognitive dissonance. The place is apparently very special, yet there's little if anything romantic about it as it currently exists.
In the interest of time, I took the more direct A-road route to Bowmore. It was a lovely ride, since the sun was out and the wind wasn't blowing too hard. I had heard from locals that it was a bit of a wavy road, since it was built across an enormous peat bog, so the road has a tendency to sink in places. This was less noticeable on a bike than on a car, but it could still be seen from certain points. While I didn't get to see any peat cutting in progress, I did see areas that had been cut before.
It didn't take too long to roll into Bowmore, where I found myself with some time to kill. Though the wind made it a bit chilly, it was still very nice to just sit outside and soak up the sun.
The tasting sessions at Bowmore are at 12:15, which is a little inconvenient since I wasn't quite hungry enough to have lunch beforehand. So I dived into an hour of whisky tasting (notes later).
After the tasting wrapped up, I went on a tour of the distillery. Katrina first led us into the malt barns, where Bowmore produces about 40% of the malt it uses. Bowmore contracts with a dedicated set of 16 farms for their malt, with the other 60% being malted by a commercial malting plant. The maltsters own the farms, which ensures traceability - if something is wrong with a batch of malt, it can be more easily traced to either something wrong with the maltings or a particular farm. This gives them more control over their malting process than distillers that simply buy malt on spec.
The malt was being turned while we were there, which looked like an arduous process, even with an electric malt aerator, which needs to be done every four hours, over three floors, for four to seven days.
From there we walked up to the kiln, where a batch of malt was being dried with hot air. The peating had already been done for this batch, which takes about fifteen hours, then hot air is used to finish it off over forty-five hours, giving malt that has about 25 PPM phenol content. Bowmore used to use about eight tons of peat a week for their maltings, but now consumes two to three tons.
Bowmore's kiln has a device, which can be seen at the back, which periodically turns the drying malt so that it is evenly heated. I'm sure the employees appreciate not having to do it by hand, especially when the malt is being peated.
From there we passed by the mash tun, which is a single large copper-topped affair. The large wooden cylinder above is the grist bin, where ground malt is stored before being fed into the mash tun.
Next was the room with Bowmore's washbacks. These are all traditional Oregon pine. A first while I was on Islay, the room actually smelled very, very good - honey, wood, yeast, spicy, caramel, and maple syrup. It was quite striking and rather surprising.
The fermentation is fairly short, at about 50 hours, with the wash coming out at 7.5-8% ABV. This is then pumped into the still room next door. Each 40k liter washback is split evenly between the two 31k liter wash stills, giving a fairly low charge.
Through a quirk of architecture, one of Bowmore's stills is actually situated outside, which means that the flow of water has to be adjusted more frequently to account for the weather (temperature, wind, rain) affecting the amount of cooling.
Bowmore's spirit is filled mostly into first- and second-fill ex-bourbon casks, with a smaller number going into ex-sherry, ex-port, and other ex-wine casks. All of the distillery's output goes into single malts - none is sold for blending.
We got to peek at the warehouse, but not actually go inside. There was also a fill your own cask, which sounded tasty, but the price was just too steep for me.
I left Bowmore with some of the same feelings with which I left Laphroaig. Bowmore is caught between the old ways of doing things, as exemplified by their floor maltings, and the new ways, which will be necessary if they want to continue expanding production. They currently operate five days a week and are considering moving to seven. However, they already use all of the output from their floor maltings, so any more will have to come from the commercial supplier, diluting whatever special character the floor maltings give them.
After the tour had wrapped up, I discovered that I had made a bit of a mistake: between the tasting and the tour, I had passed lunch time and the restaurants in town had mostly closed down for the lull between lunch and dinner. I wasn't in a dire state, but I also knew that I needed to get the rest of the way around Loch Indaal before nightfall. While it was a fairly short hop to Bruichladdich, where I would be staying the night, I needed to overshoot the mark a bit to go to Port Charlotte, where I was hoping to find facilities to do some laundry. So, as I would do all too often, I ate a granola bar, gritted my teeth, and kept moving.
The ride around Loch Indaal was simply beautiful. The terrain was mostly flat, there wasn't a ton of traffic, and the water was very pretty. I made pretty good time, despite the lack of food. Luckily the Anchorage B&B, where I was going to stay the night, was right on the main road. The owners were out when I stopped by earlier in the afternoon, so I pressed on to Port Charlotte. It was only a couple more miles down the road from Bruichladdich. I got a bit confused looking for the Port Mor Centre, but eventually found my way there. It is a combination community center and camp ground, which also happens to have publicly accessible laundry facilities. I eventually worked out what I needed to do and plonked down to get some clean clothes. If I had been smart, I would have eaten while I was there, but I was so focused on getting the laundry done that I didn't think about it.
After everything was clean and dry, I packed up again and poked down the road looking for somewhere to eat. It was getting late-ish, so I was lucky enough to find a reasonably priced restaurant that was still open. I tucked in a very filling bowl of mac & cheese, which went a long way towards making me feel restored. After settling my bill, I made my way back to Bruichladdich in the fading light and finally checked in to the B&B. After a shower I tucked into bed early, knowing that I had a full day ahead of me. Little did I know that my plans weren't going to work out quite the way I hoped they would.
 |
| The gorgeous view from my room in Port Ellen |
Though I had never tried a Port Ellen before, the almost constant talk about the place meant that viewing it still produced a certain cognitive dissonance. The place is apparently very special, yet there's little if anything romantic about it as it currently exists.
In the interest of time, I took the more direct A-road route to Bowmore. It was a lovely ride, since the sun was out and the wind wasn't blowing too hard. I had heard from locals that it was a bit of a wavy road, since it was built across an enormous peat bog, so the road has a tendency to sink in places. This was less noticeable on a bike than on a car, but it could still be seen from certain points. While I didn't get to see any peat cutting in progress, I did see areas that had been cut before.
It didn't take too long to roll into Bowmore, where I found myself with some time to kill. Though the wind made it a bit chilly, it was still very nice to just sit outside and soak up the sun.
The tasting sessions at Bowmore are at 12:15, which is a little inconvenient since I wasn't quite hungry enough to have lunch beforehand. So I dived into an hour of whisky tasting (notes later).
After the tasting wrapped up, I went on a tour of the distillery. Katrina first led us into the malt barns, where Bowmore produces about 40% of the malt it uses. Bowmore contracts with a dedicated set of 16 farms for their malt, with the other 60% being malted by a commercial malting plant. The maltsters own the farms, which ensures traceability - if something is wrong with a batch of malt, it can be more easily traced to either something wrong with the maltings or a particular farm. This gives them more control over their malting process than distillers that simply buy malt on spec.
The malt was being turned while we were there, which looked like an arduous process, even with an electric malt aerator, which needs to be done every four hours, over three floors, for four to seven days.
From there we walked up to the kiln, where a batch of malt was being dried with hot air. The peating had already been done for this batch, which takes about fifteen hours, then hot air is used to finish it off over forty-five hours, giving malt that has about 25 PPM phenol content. Bowmore used to use about eight tons of peat a week for their maltings, but now consumes two to three tons.
Bowmore's kiln has a device, which can be seen at the back, which periodically turns the drying malt so that it is evenly heated. I'm sure the employees appreciate not having to do it by hand, especially when the malt is being peated.
From there we passed by the mash tun, which is a single large copper-topped affair. The large wooden cylinder above is the grist bin, where ground malt is stored before being fed into the mash tun.
Next was the room with Bowmore's washbacks. These are all traditional Oregon pine. A first while I was on Islay, the room actually smelled very, very good - honey, wood, yeast, spicy, caramel, and maple syrup. It was quite striking and rather surprising.
The fermentation is fairly short, at about 50 hours, with the wash coming out at 7.5-8% ABV. This is then pumped into the still room next door. Each 40k liter washback is split evenly between the two 31k liter wash stills, giving a fairly low charge.
 |
| Note the lyne arm going through the roof |
Bowmore's wash stills are fairly standard, with flat lyne arms. This gives them a fairly neutral profile, though the lower charge will increase copper contact. The spirit stills are relatively narrow and tall, with slightly (5º and 10º, respectively) rising lyne arms. This will generate more reflux and give more copper contact, producing a lighter spirit. However, the 14.7k liter stills are charged almost to capacity, which will reduce copper contact. Combined with Bowmore's lower peating levels, the new make spirit is lighter and more delicate than that produced at the Kildalton distilleries.
Through a quirk of architecture, one of Bowmore's stills is actually situated outside, which means that the flow of water has to be adjusted more frequently to account for the weather (temperature, wind, rain) affecting the amount of cooling.
Bowmore's spirit is filled mostly into first- and second-fill ex-bourbon casks, with a smaller number going into ex-sherry, ex-port, and other ex-wine casks. All of the distillery's output goes into single malts - none is sold for blending.
We got to peek at the warehouse, but not actually go inside. There was also a fill your own cask, which sounded tasty, but the price was just too steep for me.
I left Bowmore with some of the same feelings with which I left Laphroaig. Bowmore is caught between the old ways of doing things, as exemplified by their floor maltings, and the new ways, which will be necessary if they want to continue expanding production. They currently operate five days a week and are considering moving to seven. However, they already use all of the output from their floor maltings, so any more will have to come from the commercial supplier, diluting whatever special character the floor maltings give them.
After the tour had wrapped up, I discovered that I had made a bit of a mistake: between the tasting and the tour, I had passed lunch time and the restaurants in town had mostly closed down for the lull between lunch and dinner. I wasn't in a dire state, but I also knew that I needed to get the rest of the way around Loch Indaal before nightfall. While it was a fairly short hop to Bruichladdich, where I would be staying the night, I needed to overshoot the mark a bit to go to Port Charlotte, where I was hoping to find facilities to do some laundry. So, as I would do all too often, I ate a granola bar, gritted my teeth, and kept moving.
 |
| The Paps of Jura, visible from across the north end of Loch Indaal |
After everything was clean and dry, I packed up again and poked down the road looking for somewhere to eat. It was getting late-ish, so I was lucky enough to find a reasonably priced restaurant that was still open. I tucked in a very filling bowl of mac & cheese, which went a long way towards making me feel restored. After settling my bill, I made my way back to Bruichladdich in the fading light and finally checked in to the B&B. After a shower I tucked into bed early, knowing that I had a full day ahead of me. Little did I know that my plans weren't going to work out quite the way I hoped they would.
Sabtu, 23 November 2013
What We Did, Friday, 11/22/13
Chemistry:
1) LTA 3.4 -- Average Atomic Mass
2) Notes 3.6 part a -- must copy from a friend or from slides on Edmodo
3) PPs 3.5 and 3.6 a -- on Edmodo (hard copy is in Friday folder) -- due Monday
Advanced Chemistry:
Specific Heat of an Unknown Metal Lab
1) LTA 3.4 -- Average Atomic Mass
2) Notes 3.6 part a -- must copy from a friend or from slides on Edmodo
3) PPs 3.5 and 3.6 a -- on Edmodo (hard copy is in Friday folder) -- due Monday
Advanced Chemistry:
Specific Heat of an Unknown Metal Lab
Normal phase liquid chromatography (LC) / HPLC?
In normal-phase chromatography a polar stationary phase is used in conjunction with a less polar mobile phase for elution of the analytes (in contrast to reversed phase chromatography where a nonpolar stationary phase is used with a more polar mobile phase). Neutral solutes in the mobile phase are separated on the basis of their polarity. The more polar the solute the more it is retained on the stationary phase. The mobile phase that it is used is normally less polar than the stationary phase. If the polarity of the mobile phase continuously increases (in a gradient elution scheme) the solute retention is decreased.
The stationary phases used in normal phase chromatography are usually silica or alumina and they are polar as a result of hydroxyl groups (-OH) (Fig. 1). The surface hydroxyl groups interact with the functional groups on the solute molecules and depending on the strength of this interaction preferentially absorb one solute relative to another (absorb the more polar compound relative to the less polar). In case the solute is a neutral molecule that has a permanent dipole or if a dipole can be induced on it, then it will be attracted by dipole-dipole interaction to the stationary phase.
A mechanism that describes the adsorption process in normal phase liquid chromatography is shown in Fig. 1.
 | ||
| Fig. 1: The mechanism of retention of the solute Ph-OH is shown in a typical normal phase chromatography separation. An equilibrium is established between the charged and the protonated form of the solute. The charged form binds to the surface of the polar stationary phase and competes for the same positions with solvent molecules. If the polarity of the solvent is increased then more solvent molecules bind to the surface of the stationary phase and the solute (PhOH) elutes faster since it remains relatively unretained. |
Silica is the preferred stationary phase mainly because its availability, known performance and low cost. For basic compounds such as amines, which are very strongly retained on silica, alumina can be used as an alternative. In addition to the above stationary phases, a variety of polar bonded phases are used with functional groups such as cyano [-(CH2)3CN], amino [-(CH2)nNH2], diol, bonded to the silica stationary phase.
The mobile phases used in normal phase chromatography are nonpolar hydrocarbons such as hexane, heptane, octane (Table 1) to which is added a small amount of a more polar solvent such as 2-propanol.
Solvent selectivity is controlled by the nature of the added solvent. For example:
- solvents that are good proton donors such as water and chloroform interact preferentially with basic solutes such as amines
- solvents that are good proton acceptors such as alcohols, ethers and amines tent to interact best with acids and phenols
- solvents with large dipole moments such as methylene chloride interact preferentially with solutes that have large dipole moments such as nitriles, amines, sulfoxides and nitro compounds.
Mobile Phases used in Normal Phase Chromatography | |||
Solvent strength ε○ | |||
Solvent | Silica | Alumina | Solvent Properties |
n-hexane | 0.01 | 0.01 | nonpolar |
n-heptane | 0.01 | 0.01 | nonpolar |
isooctane | 0.01 | 0.01 | nonpolar |
chloroform | 0.26 | 0.40 | proton acceptor |
methylene chloride | 0.32 | 0.42 | large dipole |
ethyl acetate | 0.38 | 0.58 | proton donor |
THF | 0.44 | 0.57 | proton acceptor |
propylamine | ~0.5 | - | proton acceptor |
acetonitrile | 0.5 | 0.65 | dipole |
methanol | ~0.7 | 0.95 | proton acceptor |
Table 1: Solvents that are used as mobile phase in normal phase chromatography. The solvent strength parameter ε○ defines the strength of the solvent. In normal phase chromatography a solvent with a low ε○ is chosen and quantities of a second solvent with a greater ε○ is added until the desired separation is achieved.
In general, the order of elution for species separated by normal phase chromatography is the following:
Saturated hydrocarbons < olefins < aromatic hydrocarbons ≈ organic halides < sulfides < ethers < nitro compounds < esters, aldehydes, ketones < alcohols , amines < sulfones < amides < carboxylic acids.
The more polar compounds are retained longer than the nonpolar compounds such as satutated hydrocarbons.
Normal phase chromatography is mainly applied to the analysis of samples that are soluble in non-polar solvents. Amongst them isomeric and multifunctional compounds are best separated by this method. It is also possible to separate species on the basis of the number of electronegative atoms such as oxygen or nitrogen. Fat and water-soluble vitamins, pesticides and hydrocarbons have all been separated using hexane as the mobile phase.
The major disadvantages of normal phase chromatography are the following:- Lack of selectivity of the stationary phase (all compounds are eluted in the same order regardless of the stationary phase selected. The mobile phase is therefore used to achieve any change in selectivity).
- Absorption of water (water absorbed from the atmosphere is adsorbed onto the strongest adsorption sites on the stationary phase leading to a decrease in solute retention – deactivation of the stationary phase).
References
1) L.R. Snyder. J.J. Kirkland, “Introduction to Modern Liquid Chromatography”, 2nd edition, Wiley, 1979
2) A. Weston and P. Brown, “HPLC and CE Principles and Practice”, Academic Press, 1997
3) A. Braithwaite and F.J. Smith, “Chromatographic Methods”, 4thEd., Chapman & Hall, 1990
Langganan:
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