Author Archives: Sven Kochmann

From a for atto to z for zepto

Todays detection limits are very low. Using various methods such as amperometric detection [1], surface plasmon resonance [2], and laser–induced fluorescence detection [3] it is possible to sense few attomolar (10-18 mol·L-1) concentrations of analytes.

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References

  1. W. Gao, H. Dong, J. Lei, H. Ji, and H. Ju, "Signal amplification of streptavidin–horseradish peroxidase functionalized carbon nanotubes for amperometric detection of attomolar DNA", Chemical Communications, vol. 47, pp. 5220, 2011. http://dx.doi.org/10.1039/C1CC10840A
  2. J. Ferreira, M.J.L. Santos, M.M. Rahman, A.G. Brolo, R. Gordon, D. Sinton, and E.M. Girotto, "Attomolar Protein Detection Using in-Hole Surface Plasmon Resonance", Journal of the American Chemical Society, vol. 131, pp. 436-437, 2009. http://dx.doi.org/10.1021/ja807704v
  3. D.B. Craig, J.C.Y. Wong, and N.J. Dovichi, "Detection of Attomolar Concentrations of Alkaline Phosphatase by Capillary Electrophoresis Using Laser-Induced Fluorescence Detection", Analytical Chemistry, vol. 68, pp. 697-700, 1996. http://dx.doi.org/10.1021/ac950650z

ICP-OES: Why spectral lines are true peaks and how this can fool the user.

ICP–OES is a common technique in analytical chemistry, which is characterized by simplicity, simultaneous multi-elemental determination capability, high sensitivity, linear dynamic range, low detection limits, and good precision [1]. It seems to be the perfect method for element analysis (esp. metals). However, sometimes it can fool the user.

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References

  1. K. Satyanarayana, and S. Durani, "Separation and inductively coupled plasma optical emission spectrometric (ICP-OES) determination of trace impurities in nuclear grade uranium oxide", Journal of Radioanalytical and Nuclear Chemistry, vol. 285, pp. 659-665, 2010. http://dx.doi.org/10.1007/s10967-010-0591-8

Software: Ancient Origin version (2.74)

Last friday, we needed an old 3.5″ floppy disk to backup an old system we wanted to replace. So, I was searching our offices and labs, and found an very old (but working) disk.

To my surprise, this disk contained a very old version of Origin, viz. 2.74 from 1991! It was packed in an old archive type (ARJ) to fit onto the disk (unpacked: 2.62 MB!). It still works on my Windows XP machine.

Of course, modern features such as project managment and context menus are missing. However, it also possesses features, which the current version lacks: fast start, no annoying copy protection, and a clear and simple GUI. Below, you can see a screenshot of it.

Figure 1. Screenshot of Origin 2.74.

Figure 1. Screenshot of Origin 2.74. Note the clear and simple GUI.

I wonder at which point the development created this huge multi-gigabyte monster of today?

Howto: Replacing axes in Origin without changing the data

Recently, my co-worker and me had to replace an axis of one of our plots in Origin [1]. We measured a signal over time and, actually, wanted to just add a little offset without changing the data. We didn’t want to go through the get-a-nice-matrix-out-of-your-data-for-3D-plotting-torture, again.

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References

  1. " OriginLab - Origin and OriginPro - Data Analysis and Graphing Software " http://www.originlab.com/

Software: QtiPlot

QtiPlot is a cross platform data analysis and scientific visualisation solution [1] similar to Origin [2]. The program is developed by Ion Vasilief, who also developed some other nice tools[3].

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References

  1. "Page Redirection", 2014. http://soft.proindependent.com/qtiplot.html
  2. " OriginLab - Origin and OriginPro - Data Analysis and Graphing Software " http://www.originlab.com/
  3. ProIndependent, "ProIndep Serv Srl" http://soft.proindependent.com/serv/projects.html

Howto: Fit sigmoid functions in OpenOffice Calc and Excel

Last week, I posted an article about sigmoid functions and how to use them. Nevertheless, it is hard to guess the parameters for a given problem. So, people use software such as Origin [1] or QtiPlot to fit.

Personally, I use Origin/QtiPlot only for plotting and Excel/OO–Calc for evaluation/calculation, because both programs are much more comfortable and powerful. However, both lack the possibility to fit sigmoid functions, automatically.

It is possible to do such fits for nearly any function using the solver, though, but only a few people I’ve met knew how to do this or that it is even possible. But, I think the solver is a very handy feature and, therefore, I want to give here a short introduction into using it for fitting a sigmoid function to a set of data.

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References

  1. " OriginLab - Origin and OriginPro - Data Analysis and Graphing Software " http://www.originlab.com/

Analysis: Sigmoid functions for data evaluation

Note: There was an error in the reverse formula (and maybe also with some of the values given). Frank pointed this out (see comments section below).

In analytical chemistry, linear regression or linear function is a common (maybe the most common) tool to describe the relationship between a measured signal and the concentration of an analyte. Even if the relationship is much more complex, one usually works in small ranges only where the assumption of linearity is convenient.

However, there are analytical problems, which cannot be solved with this simple approach. In this short article I want to introduce and present another useful function for data evaluation on the basis of a real example.

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