St. John's University Chemistry

“It’s freezing in the NMR room!” – A Crash Course In Superconductivity

Joe Ocando — Tue, 21 Aug 2012 17:54:35 +0000

It does get pretty cold in there. Although don’t be tempted to shut the A/C in the NMR room. Keep a sweatshirt in your lab and bring it with you when running a sample. That baby needs to be kept cool.

NMR’s major hardware consists of an electromagnet, a coiled wire made of nobium and tin/titanium with tons of current running through it. This creates an electromagnetic field (remember right hand rule?) which aligns protons in your sample as you plop it down in the middle of the coil according to a specific resonating frequency. Protons emit their own tiny magnetic field changing the resonating frequency slightly depending on electron cloud environment (shielding). After the computer conducts a Fourier transform, voilà, you can now see these changes/chemical shifts in a nice clean spectrum. Resolution is directly proportional to the external magnetic field strength so superconductivity, or an electrical resistance of zero, is a must to ramp up the magnet into the 1-20 Tesla range. Since resistivity decreases with temperature, maintaining superconductivity at temps close to absolute zero can be quite costly.

Niobium makes for a terrific superconductor. It has a high critical temperature compared to other elements on the periodic table at 9.25K. That means at that temperature its resistivity is exactly zero, so you can pump ‘er up with lots of current to increase magnetic field strength. Nb is bonded with tin or titanium (to make Nb₃Sn or NbTi wire) to increase durability.

Here’s where the A/C comes in. The superconductor is kept cool in liquid helium at 4K and the liquid helium is kept cool with liquid nitrogen at 77K. If the liquid helium evaporates the wire loses its superconductivity, becomes resistive and generates lots of heat. This is called a quench. To bring the magnet back up to field typically costs $18,000. That’s why the room should be kept cool with the door closed. Time to make an Old Navy run for that sweatshirt, eh?

photo credit to Connections digital education ecosystem

How To Review HPLC Chromatograms in Empower

Joe Ocando — Mon, 09 Apr 2012 18:17:57 +0000

Here is a brief video on how to quickly navigate through empower to review and process your acquired HPLC data. This can also be done in real time. (Be sure to watch in 720p HD).

How To Set Up an HPLC Run

Joe Ocando — Sun, 08 Apr 2012 03:11:53 +0000

Empower is by far the most commonly used HPLC/UPLC software. Here is a brief video on how to set up and start an automated run.

How To Check For Gas Leaks

Joe Ocando — Fri, 30 Mar 2012 14:57:16 +0000

Here’s a quick and cheap way to save money, especially if you’re running lots of NMR and GC samples. After each tank change simply spray soapy water on all joints leading to and from the regulator. If any bubbles appear then there is a leak and the connection needs to be re-fitted. Pictured below is a recent change of Helium carrier gas on the GC/MS. Note the leaking of gas in the second pic. Beware of overtightening. A “wrench tight” connection will prevent stripping of the threads.

How To Install a GC Column

Joe Ocando — Tue, 27 Mar 2012 18:53:18 +0000

Taking care of a GC column will help to extend its life. Of course, this means it needs to be installed correctly. Agilent put together a video with some great tips to get the most out of a column including carrier gas traps to prevent oxidation, a leading cause of column damage.

GC 101

Joe Ocando — Tue, 27 Mar 2012 18:38:37 +0000

The Royal Society of Chemistry posted a terrific tutorial on the basics of gas chromatography. The video shows an operator separating methanol and toluene step by step using a flame ionization detector (FID). Towards the end of the video, the GC is connected to a mass spectrometer detector similar our Shimadzu QP5050A.

It just takes a second…

Joe Ocando — Wed, 11 Jan 2012 22:35:02 +0000

..to be safe. This reminder is especially useful during routine tasks. Indeed, safety has been a hot topic lately in the chemistry blogosphere. It is abuzz about recent charges brought against UCLA over the tragic death of a research assistant in an organic chemistry laboratory. According to C&ENews, the young chemist was using tert-butyllithium when it spilled and autoignited. This tragedy has become a teachable moment for chemistry labs everywhere. Subscribe to The Safety Zone at CENtral Science for the latest chemical safety news and tips.

New IR Makes Sample Prep a Cinch

Joe Ocando — Fri, 30 Sep 2011 00:09:45 +0000

Say goodbye to the elusive art of KBr pellet making and messy NaCl plates (along with the variability they introduce) with the department’s new FT-IR spectrometer and ATR accessory. The PerkinElmer Spectrum Two is the gold standard for rapid IR measurements and the ATR zinc selenide crystal is perfect for generation of an evanescent wave that penetrates any sample (pH range 5-9).

Apply just enough pressure on the clamp to ensure a 1 micrometer intimacy and you’re on your way to spectral heaven. There’s even a nifty preview feature in the software which allows you to optimize contact before scanning to prevent scratching. An installed humidity sensor detects the best time to change desiccants, perfect for the rainy seasons we’ve been having (a.k.a. optics killers). Still curious about how this incredible technology works? The vid below depicts the S2 in action. (Click here to learn more about IR spectroscopy with correlation table.)

Supercharged GC/MS

Joe Ocando — Thu, 18 Aug 2011 21:20:45 +0000

Recently, an overhaul was conducted on our Shimadzu GC/MS. Both source and trap filaments were replaced inside the ion source box, the heart of the system. This is where your sample gets zapped by an electron beam turning it into fragments. The two filaments (doohickeys that produce the beam) were barely alive and have since been put out of their misery. Additionally, the ion source box was scrubbed from top to bottom, ridding it of extraneous ions produced from the blasts.

A helium purifier has also been replaced which scrubs our carrier gas. This provides a smoother baseline when injecting into the GC port.

Bottom line – the unit is fully optimized for its nanogram range detection limit. Here are some tips to keep it that way:

1) Begin with 1uL of sample for GC or a “spec” of solid for direct insertion. More than that may contaminate the system for the next person.

2) Remember to set the detector no greater than 1.10 kV. It’s an electron multiplier that won’t give you better data if you ramp it up. You’ll only be shortening its life.

3) Any questions contact Joe at the info provided on the instrument. He will be more than happy to assist.

HPLC 101

Joe Ocando — Mon, 13 Jun 2011 21:48:09 +0000

This Royal Society of Chemistry vid is the best I’ve seen to describe chromatographic principles within the context of HPLC. According to the standard handbook, the money currently spent annually on HPLC exceeds that of any other analytical technique.