.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/analytical/chromatography/plot_05_kovats_retention_index.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_api_gallery_analytical_chromatography_plot_05_kovats_retention_index.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_api_gallery_analytical_chromatography_plot_05_kovats_retention_index.py:


Kováts retention indices from an n-alkane ladder
===================================================

Under isothermal gas chromatography, :math:`\log t'` of the n-alkanes
rises linearly with carbon number. Kováts placed every other compound on
that ladder: :func:`~chemistrykit.analytical.kovats_retention_index`
interpolates :math:`\log t'` between the bracketing alkanes, giving an
index (n-octane = 800, n-nonane = 900, ...) that is far more
transferable between instruments than a raw retention time.

.. GENERATED FROM PYTHON SOURCE LINES 14-34

.. code-block:: Python

    import matplotlib.pyplot as plt
    import numpy as np

    from chemistrykit.analytical import kovats_retention_index

    t0 = 1.20  # dead time, min
    carbons = np.arange(6, 12)
    # Illustrative isothermal alkane retention times following log t' = a + b*n.
    t_alkanes = t0 + 0.035 * 2.05**carbons

    # Unknowns eluting between the alkanes (retention times in min, chosen to
    # give indices close to literature values on a nonpolar phase):
    unknowns = {"toluene": 9.57, "ethylbenzene": 17.40, "1-octanol": 71.8}

    for name, t_x in unknowns.items():
        n = int(np.searchsorted(t_alkanes, t_x)) - 1 + carbons[0]
        i = n - carbons[0]
        I = kovats_retention_index(t_x, t_alkanes[i], t_alkanes[i + 1], n=n, dead_time=t0)
        print(f"{name:13s}: t_R = {t_x:5.2f} min, between C{n} and C{n + 1} -> I = {I:.0f}")





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    toluene      : t_R =  9.57 min, between C7 and C8 -> I = 763
    ethylbenzene : t_R = 17.40 min, between C8 and C9 -> I = 855
    1-octanol    : t_R = 71.80 min, between C10 and C11 -> I = 1060




.. GENERATED FROM PYTHON SOURCE LINES 35-48

.. code-block:: Python

    fig, ax = plt.subplots(figsize=(7, 4.5))
    ax.plot(100 * carbons, np.log10(t_alkanes - t0), "o-", color="gray", label="n-alkanes (I = 100 n)")
    for name, t_x in unknowns.items():
        n = int(np.searchsorted(t_alkanes, t_x)) - 1 + carbons[0]
        i = n - carbons[0]
        I = kovats_retention_index(t_x, t_alkanes[i], t_alkanes[i + 1], n=n, dead_time=t0)
        ax.plot([I], [np.log10(t_x - t0)], "s", markersize=8, label=f"{name}: I = {I:.0f}")
    ax.set_xlabel("retention index I")
    ax.set_ylabel(r"$\log_{10} t'_R$ (adjusted retention time, min)")
    ax.set_title("Kováts index: interpolation on the alkane ladder")
    ax.legend()
    plt.tight_layout()
    plt.show()



.. image-sg:: /api/gallery/analytical/chromatography/images/sphx_glr_plot_05_kovats_retention_index_001.png
   :alt: Kováts index: interpolation on the alkane ladder
   :srcset: /api/gallery/analytical/chromatography/images/sphx_glr_plot_05_kovats_retention_index_001.png
   :class: sphx-glr-single-img






.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 0.048 seconds)


.. _sphx_glr_download_api_gallery_analytical_chromatography_plot_05_kovats_retention_index.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: plot_05_kovats_retention_index.ipynb <plot_05_kovats_retention_index.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: plot_05_kovats_retention_index.py <plot_05_kovats_retention_index.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: plot_05_kovats_retention_index.zip <plot_05_kovats_retention_index.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_