What is a chromatogram?

Defining a Chromatogram.

A chromatogram is a graphic interpretation of information in relevance to time. The output is in the form of a chromatogram that we can get through the chromatography machine’s effective running. The results can be displayed on the hardcopy or even the electronic file. The type of output one hopes to get relies on the statistics and the information that is fed. Therefore, there can be many variations to the information one can get through the chromatogram. Due to their usefulness, these instruments are now functional in all sorts of laboratories to measure data in real-time. Some of the most common examples that can be given a GC run of a sample can be:

  • The identity of the sample
  • The physical information of the sample, such as its weight or concentration
  • A chart shows relevant peaks that form and the baseline; this baseline is also known as a trace.
  • The tabular display of the results can incorporate the raw data as well as the new information.

Though now automation is widely used to create chromatograms for various information purposes, this was not a very easy task to do in the past. It took a lot of time and effort to display information in this form.

How to read a chromatogram?

Through innovative and developed techniques, chromatogram reading has become a lot easier than it was. It is still essential to understand before what a chromatogram is before one can begin to read it. Some essential interpretation techniques even need interpretation. It is vital to check if the trace is perfect before any further assessment is done. If there is something wrong with it, moving forward can be all in vain. The checks that can be done on the trace are:

  • Checking if the baseline is all right means looking to see that it’s mainly flat and not too noisy
  • Checking if the formations of the peaks are symmetrical and sharp. It is also essential to check if they are on-scale as well.
  • Checking if the number of peaks is all right, and none of them are missing or faulty.
  • Check if all the retention times’ calculations correct and adequately identify the reference ones’ standard peaks.

Even though the data is easily in the display, it is the analyst’s responsibility to view this information, make a proper analysis of any errors that may be present, and then notify and amend those errors.

How was a chromatogram read before technological advancement?

Moreover, before implementing data integration in all forms of measuring tools became the standard procedure, the tedious method of using graph paper and scissors were widely used. A chart recording device was in link to the detection device to record the trace in those days. It was all done with the help of an ink pen. Now, to decipher the details from the path, the following techniques were commonly in practice:

The Counting squares technique.

In this process, a drawing with a pen and ruler helps make the best peak and the baseline. The analyst, after this procedure, would next count all the squares in every triangle. The sum was essential to find the sensor’s attenuation, and then calculations for the conformation of the sample were done.

The cutting and weighing technique

Now for the peaks that were in record, baselines would be made. Then the analyst would cut them out and weigh them together. The peak area being relational to the heaviness gave the paper’s wideness and told if the moisture content is uniform.

Additionally, actions like photocopying and zooming the trace were usually in use to surge accuracy.

But, in reality, these techniques were not as simple as written here, for they would have a lot of probability of errors. There were a lot of mistakes involved when there was an overlapping of peaks and diverse sampling. The likelihood of errors in these errors today is next to zero.


It is a very efficient instrument that is very popular today for different calculations related to the content’s reference with time. You can quickly get the output on an electronic file or even a piece of paper. The instrument’s efficiency has become profound with technology innovation when calculations would take days to complete in the older times, and now they can be done in mere seconds.  Now you know everything about what a chromatogram is. You will undoubtedly be more comfortable next time you will be using it.

About Rashid Faridi

I am Rashid Aziz Faridi ,Writer, Teacher and a Voracious Reader.
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