Documentation of chromatograms

All modifications recommended in The European Pharmacopoeia 4th edition (English) 2002 with respect to the work method in TLC were also recommended on a European level but with a time delay. For the first time the documentation of chromatograms is required with photographs and/or data files. 

So little experience has been accumulated about the use of these two types of paper for documentation of chromatograms, that then-value in this field cannot be estimated. 

This method of chromatogram preservation has lost a great deal of its importance with the increasing perfection of photographic methods, particularly since true-colored, instant, paper and slide positives have become available. Photography is the more rapid method of documentation if suitable photographic equipment is available. 

The required exposure times are difficult to estimate. They are best found by trial and error. Documentation of fluorescence quenching at A = 254 nm usually only requires one trial. The exposure time found to be adequate here is normally suitable for all following exposures of fluorescence quenching if the exposure conditions are maintained constant (camera type, film type, distance of objective and lamp, aperture etc.). The exposure time required for fluorescent chromatograms is primarily dependent on the intensity of the fluorescence and, therefore, has to be optimized for each chromatogram. It is best to operate with a range of exposure times, e.g. aperture 8 with exposures of 15,30,60,120 and 240 seconds. Experience has shown that one exposure is always optimal. 

The unusual feature of the programs is the automatic processing based on sample class. The operator provides the relevant parameters to the system of programs using the program SETUP, which contains several fill-in-the-form screens. These parameters Include the "class" of the specimen and the required automatic processing, as described below, and other pertinent information such as Mark-Houwink parameters, vial number, injection number, and documentation of the experimental conditions under which the chromatogram is to be measured. 

The GC data system performs the tasks of recording, handling, evaluation, and documentation of the chromatogram. In a modem gas chromatographic system, these can be performed by means of a computer with specialized software. Nowadays, software for calculating the quantitative results and for the method validation is available. 

During the investigation of a biotransformation pathway of a lead drug compound, many different types of data accumulate, such as documents, images, chromatograms, mass spectra, NMR spectra, structures, substructures, generic structures, and result tables. A study editor module serves as the main user interface for the... 

Special care is necessary in TLC when working with light-sensitive samples. As special precautions must be taken when dealing with these throughout all stages of the work from receipt of the material to the documentation of the chromatogram, a special chapter is devoted to sensitive samples (see Section 10.2 Substances Sensitive to TLC ). 

Modular systems of the latest type for the production of images and documentation of thin-layer chromatograms consist of four components. 

In today s industry, digital cameras have replaced most video systems. All information about the illumination system, data processing equipment and image output system given in Section 7.3 also apply here. Only the current software determines how to achieve a qualitative and/or quantitative evaluation of chromatograms. For the topic Digital Camera see Documentation , Section 8.5. 

The main theme of this Chapter is the documentation of a TLC plate, i.e. the capture and storage of the result with the object of being able to reconstruct it. Methods used can range from simple descriptions of chromatograms to modem recording systems based on electronic data processing. 

To illustrate this theme, the cartoon below shows a young man somewhat laboriously tracing thin-layer chromatograms, while the girl is using modern video equipment for the documentation of a TLC plate. 

The result is documented by placing a cross against the relevant parameter. This raw data sheet does not show whether the checker has actually seen the completed chromatogram or whether the formal documentation of this work has simply been authenticated ... 

This form fulfills all the GMP/GLP requirements for the documentation of thin-layer chromatograms, and has been found to be highly satisfactory over the years, especially in method development. It is advisable to fill out this sheet before starting to apply samples to a plate. 

Hahn-Deinstrop, E. The Documentation of Thin-Layer Chromatograms by Non-Densitometric Methods , J. Planar Chromatogr., Vol. 4,154-157,1991... 

Figure 98. Documentation of thin-layer chromatograms with a video system (in contrast to a simple description of the chromatogram)...

It has been almost seven years since the publication of the first English Edition of my book on TEC The following improvements in technology over the years have made it necessary for me to update the first edition new precoated layers for both existing and new fields of applications, a new generation of equipment for safe operations and reproducible results, new devices such as the Diode Array Detector and Bioluminescence Analyzer, new methods of interface between TEC and analysis methods, especially the use of digital cameras for the documentation of thin layer chromatograms. For the reader s benefit, I have updated my description of available products on the market. 

Figure 1.10 Effect of column length on the resolution. Chromatograms obtained with a GC instrument illustrating that by doubling the length of the capillary column, the resolution is multiplied by 1.41 or. ffl (adapted from a document of SGE Int. Ltd).

The software supplied with commercial equipment often also supports the documentation of the sample evaluation. Identified peaks of a chromatogram can be stored in a table, and if a chromatogram needs to be looked at later, these data can be retrieved quickly. Because of the high measurement sensitivity of mass spectrometric detectors, carry-over of highly concentrated components such as dihydrocodeine can falsify the results from subsequent samples. To prevent this kind of unpleasant surprise, chromatograms should at least be evaluated in the chronological order of the samples. Blank runs or methanol injections after analyzing samples of this type minimize the risk of false positive results. 

Documentation of a TLC chromatogram as an image is conveniently possible. Traditionally photographs have been taken but the availability of electronic devices such as flatbed scanners or digital cameras have simplified the process. The principal advantage of electronic images is their durability. Added benefit is the possibility of qualitative and quantitative densitometric evaluation. 

The biggest initial gain in the transition from paper-based to electronic documentation can be achieved by laboratories that take the decision to convert a paper-intensive process step into an electronic form. That means many companies opt for a gradual implementation in the form that the paper printouts of chromatograms are replaced by PDF/A-1 files. So step by step, the single documentation steps are converted from paper to electronic format and in the end will form an integrated solution that deserves the labeling electronic documentation. ... 

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