dreaming spirals http://www.dreamingspirals.com/ Blog description en-us Nucleus CMS v3.23 Weblog http://backend.userland.com/rss http://www.dreamingspirals.com//nucleus/nucleus2.gif dreaming spirals http://www.dreamingspirals.com/ <![CDATA[ Column Cleaning and HPLC Peak Splitting]]> http://www.dreamingspirals.com/index.php?itemid=124


]]> HPLC http://www.dreamingspirals.com/index.php?itemid=124 Sun, 13 Jul 2008 09:23:35 -0400 <![CDATA[The Good, The Bad and The Solvent Effect]]> http://www.dreamingspirals.com/index.php?itemid=123
Solvent
Boiling Point
Acetone 56.5°C
Acetonitrile 82°C

The GC method in use, is one using splitless injection with an injector temperature of 250°C and an initial oven temperature of 70°C. Based on the boiling points we can see that there will be solvent effects from both acetone and acetonitrile. In the following chromatograms the concentration of acetone is increased while the concentration of acetonitrile is decreased and the concentration of the analytes is held constant. In effect this creates multiple solvent effects at the head of the column, resulting in the greatest peak distortion when the ratios are around 50:50. We can see that increasing acetone concentration decreases the amount of peak distortion until sharp peaks are obtained at a concentration of 90% acetone.









]]> GC-MS http://www.dreamingspirals.com/index.php?itemid=123 Mon, 30 Jun 2008 21:46:11 -0400 <![CDATA[It's alive!]]> http://www.dreamingspirals.com/index.php?itemid=122

]]> General http://www.dreamingspirals.com/index.php?itemid=122 Sun, 29 Jun 2008 09:47:40 -0400 <![CDATA[Vial Fill and Injection Reproducibility in GC/MS]]> http://www.dreamingspirals.com/index.php?itemid=120

]]> GC-MS http://www.dreamingspirals.com/index.php?itemid=120 Sun, 3 Dec 2006 10:50:00 -0500 <![CDATA[Minimizing the delay volume on the Agilent 1100.]]> http://www.dreamingspirals.com/index.php?itemid=119 here. The method was modified with an injector program to switch the valve to bypass at one minute into the run. This is before the gradient starts so switching back to main-pass before during the next injection will not effect the retention times or the second sample. As you can see the elution time of the last peak decreased significantly.

This decrease and setting the autosampler to pre-fetch the net vial saves about 50 seconds per sample. This can add up fast when you have 20 or more samples to run. ]]> HPLC http://www.dreamingspirals.com/index.php?itemid=119 Wed, 29 Nov 2006 19:54:36 -0500 <![CDATA[Inlet temperature optimization]]> http://www.dreamingspirals.com/index.php?itemid=118

The sample being analyzed is a PFBOA derivative dissolved in acetonitrile. The inlet liner is an SGE tapered focus liner. Pulsed splitless mode was used with a pulse pressure of 14psi for 0.5min. Purge flow was active at 0.04min with a flow of 25mL/min. As you can see the peak area increases as the inlet temperature increases up to 175°C and then starts decreasing with increasing temperature. In this particular case we are seeing sample degradation as opposed to back flash.

]]> GC-MS http://www.dreamingspirals.com/index.php?itemid=118 Tue, 21 Nov 2006 19:10:16 -0500 <![CDATA[Reference Wavelengths]]> http://www.dreamingspirals.com/index.php?itemid=117

The sample in question contains multiple compounds that absorb through the entire UV and into the visible. Here is the spectrum of one of the peaks with the reference highlighted.


When compounds elute that absorb in the reference range (310nm to 410nm) Chemstation offsets the absorbance at 210nm accordingly. This is obviously an extreme example, but demonstrates the need of the analyst to be on guard for cases where the impact of incorrect reference is less apparent.
]]> HPLC http://www.dreamingspirals.com/index.php?itemid=117 Sun, 12 Nov 2006 14:58:49 -0500 <![CDATA[Server Status]]> http://www.dreamingspirals.com/index.php?itemid=116 Dear Faithful DS Readers,

You may have noticed that DS was off-line for approximately 72 hours. The cause of this is not clear, but this is the second time in three months that my host, Vizaweb, has left me and many others hanging for over twenty-four hours. There were rumors that the owners had cut and run. Vizaweb was unreachable by email, phone or even fax. Well it looks like they're back, at least for now. Currently, I am in the process of backing up all content (I store a lot of research in the protected DS vault) and moving to a new host. I will continue to post new content here and on the new host. When I have all the bugs worked out on the new server, I will point dreamingspirals.com to the new ip address.

Sincerely,
George (lostcosmos) ]]> General http://www.dreamingspirals.com/index.php?itemid=116 Fri, 10 Nov 2006 17:24:10 -0500 <![CDATA[Troubleshooting High Pressure Ripple: Part 2]]> http://www.dreamingspirals.com/index.php?itemid=115 Here is an example of pressure ripple in a binary pump. Purging the pump did not reduce the pressure ripple as it did in "Troubleshooting High Pressure Ripple Part 1". A little more work is required this time. As with most flow processes, we can segment the system step wise to find the source of the problem. Isolating the origin of the ripple starts with:
  1. Installing a restriction capillary
    In order to effectively troubleshoot we need to keep the pressure above 50bar, but also want to eliminate having to equilibrate the column after each step. A restriction capillary is ideal for the purpose.
  2. Run 100% A:

    After changing to 100% A the pressure ripple is gone. This eliminates the A channel from the list of possible sources. This also eliminates all the flow path components that the A and B channels share.
  3. Run 100% B:

    We can see that the pressure ripple is isolated to the B channel.
  4. Run 100% B2:
    This eliminates the pistons and seals as the cause of the ripple. (Note that the initial pressure drop is air being purged from the B2 channel.) We now know that the cause of the pressure ripple is on the B side of the pump and specific to the B1 channel. There are three remaining suspects: the solvent selection valve, the inlet filter or the B1 mobile phase. Changing the inlet filter is the easiest so that's a good place to start.
  5. New Inlet Filter:
    From ripple to stable in only four steps. This final graphic was squished to show all the steps in one and the ripple looks a little higher than it is. A closer view shows no more than pressure noise:
]]> HPLC http://www.dreamingspirals.com/index.php?itemid=115 Tue, 7 Nov 2006 19:38:34 -0500 <![CDATA[My Great, Great, Great Grandfather's Scale]]> http://www.dreamingspirals.com/index.php?itemid=114 Apothecary. This was his scale. It stays on the self most of the time, collecting dust, but I can't help but imagine the potions that pasted over it from Apothecary to patient.

]]> General http://www.dreamingspirals.com/index.php?itemid=114 Mon, 6 Nov 2006 19:00:10 -0500