Chromatography is certainly one of the standard tools of the analytical laboratories of the chemistry and pharmaceutical industry. In its various guises chromatography is the principal method within separations science for isolating individual components in complex mixtures. Chromatography of course has numerous "flavors" (LC, GC, SEC and so on) and has become the foundation of the tandem techniques for molecular identification (LC-MS, LC-MS/MS, LC-NMR etc.). It is also the primary screening tool during the scale up and manufacturing process for quality screening using methods developed for the identification of impurities and secondary products. As with most forms of analytical chemistry, computer systems and software developments have been an integral part of the technology development. Chromatography Data Systems (CDS) have been produced by a number of vendors with the general intent of allowing chromatographic data processing, visualization and databasing. Other than routine measurements for quality control, discovery chemists and the research and development environments focus a lot of their efforts into the resolution of components with direct attention paid to the actual resulting chemical structures. In this regard, one aspect of the CDS that has been ignored is the direct integration of the chromatogram with chemical structure information.
The development of chromatographic methods requires definition of the appropriate conditions by which a particular separation can be executed. The resulting method will include details regarding the column type, the solvents, the solvent gradient, buffers and so on. Generally at least a hard copy of the chromatogram will be filed with the method with each peak in the chromatogram annotated with a textual identifier of the related chemical structure or alternatively with a hand-drawn or copy-and-pasted structure. This approach to the management of method details is hardly sufficient in a global corporate environment where analytical details need to be exchanged between different laboratories. Similarly, even though millions of dollars are invested annually in the installation and maintenance of molecular structure databases, there have been few attempts to provide links between the thousands of chromatograms generated on an annual basis with the chemical structures identified within associated analytical laboratories. As a result, even though an abundance of information exists in regards to appropriate separations and methods related to particular classes of chemical structures, little of this is easily accessible and therefore of little use for future method development.
Chromatographers, like spectroscopists, utilize their technology to both separate and identify chemical structures. Spectroscopists assign their spectra in relation to chemical structures using fragmentation analysis in mass spectrometry, nucleus to peak assignments in NMR and vibrational bands to IR peaks for example. Commonly, spectroscopists have utilized the standard filing system of drawers full of spectra with an association of the file number with some textual identifier. The general level of spectral management has been limited to hand written notes in notebooks or sometimes text-searchable databases pointing to associated spectra. It is only during recent years that tools have become available to allow spectra to be databased in electronic format with associated chemical structures. Such tools include those of the industry leader, Advanced Chemistry Development, and Chemical Concepts. In this manner the spectroscopist has inherited the opportunity to search the database for related structures or substructures, or spectral features when performing fresh analyses. This approach allows the generation of a legacy database of multiple spectroscopy data thereby building a foundation for future analyses. The value residing in such tools is the time savings which result for the analysis of related chemicals and the exchange of information between different analytical laboratories within the same company. In theory, such an approach should not be isolated to spectroscopists.
For chromatography, tools now exist to allow the similar integration of chromatographic peaks and chemical structures. The software application described here is ACD/ChromManager. Differently than in spectroscopy however, a single peak in the chromatogram is associated with a single chemical structure, or multiple if species coelute.
The development of a toolkit to allow the association of chemical structures with a chromatogram and ultimately databasing of the resulting information requires a number of specific features. In particular, processing of an experimental chromatogram will require the standard tools for peak picking, noise removal, baseline correction, smoothing and peak integration as well as advanced tools such as deconvolution. Since there are many chromatography hardware system vendors the ability to read in raw formats or alternatively standard ASCII or AIA format data is necessary to allow laboratories with inhomogeneous environments to database their information in a consistent manner. Unfortunately a lot of important information can be lost during the export to standard format exports. As a result of this loss of information and the crucial need for maintaining GLP an GmP constraints required in many areas for Chromatography we have opted to integrate in such a way that ChromManager accesses the data system directly. The screenshot below shows the integration to Waters Millennium32.
Following direct import of the data, processing gives a resulting processed chromatogram as shown in the ChromManager interface below.
Following processing of the chromatogram to produce the appropriate result, this chromatogram should be available for printing as well as transfer to other tools for reporting (standard word processors and graphics programs etc.). In order to attach chemical structures to the chromatography report, the CDS should be integrated with a chemical structure drawing system. For the system described here ACD/ChemSketch1, a powerful application for generating molecular structures is directly integrated. This application also allows the import of standard file formats such as Molfile from other applications, again supporting inhomogeneous software environments. Following processing of the chromatogram a peak is selected and one or more structures are directly associated. Following this process across the whole chromatogram structures are attached one by one to appropriate peaks thereby integrating chemical connectivity. An example screen of the resulting file is shown below. Moving the cursor across each chromatographic peak will show each associated structure(s).
The resulting chromatogram with associated chemical structures carries valuable information for future applications. Such resulting files can be stored onto a centralized server and become a powerful means for dissemination of the chromatogram-structure connectivity information. For example, a copy of ACD/ChromProcessor (ChromManager without the databasing capability) can be distributed to each chemists or chromatographers desktop and access to the centralized server where textual methods and associated chromatogram-structure (ESP) files reside. This general approach can be expanded to a world wide web intranet approach whereby the methods are posted as individual HTML pages with hyperlinked ESP files. When the methods are searched textually the associated ESP file can be downloaded for viewing in the ChromProcessor helper application. A series of such information rich chromatograms forms a valuable basis for method development and rapid chromatographic condition identification. These approaches, though valuable, have the constraints associated with most CDS systems: searches are primarily text based.
However, the ACD/ChromManager application allows each chromatogram to be databased with associated chemical structures, thereby offering significantly enhanced capabilities over the common file systems used today in many laboratories. Prior to databasing of the chromatogram it is possible to edit and update the sample data, instrumental data, detector data, elution data and column parameters. The entry screen for these parameters is shown below.
Due to the capabilities of database technology of course there is enhanced searching capability over the standard filing cabinet system or text based databasing system. It is possible to search the resulting databases by structure, substructure, formula, molecular weight, chromatographic parameters or user data. Multiple databases can be searched at one time thereby allowing different databases to be constructed according to column, project name, individual user and so on. These multiple databases can also be distributed across different departments, divisions or even an entire corporation, simply by using the ability to point to databases located on mapped network drives. Other than the HPLC parameters for searching the association of individual searchable user data fields is of course invaluable, thereby allowing each chromatogram in the database to be associated with a project, a customer, an analyst or any other appropriate information such as associated Word reports as shown below.
The value of the approach outlined here should be obvious as the ability to integrate structural information with chromatograms into a database offers exciting benefits to the chromatographer and is an ideal solution for an environment where multiple chromatographers need to quickly determine appropriate conditions for separation of specific chemical structure classes. The additional benefit of this tool is that it is also fully integrated with a similar toolset for spectroscopy allowing similar structure-spectrum management for NMR, MS, UV-Vis, IR and Raman. Since the databasing tool is integrated to both the spectroscopy and chromatography applications it is possible for the first time to simultaneously search across the multiple technologies by both text, structure and substructure. An additional benefit of the package is its integration to an LC Simulator application which predicts a priori the chromatogram from the chemical structures alone, and then is calibrated with experimental data2. Optimization for the gradient program, pH, column length, and solvent mixture can be done quickly and interactively. Such interactions offer a complete solution for the Chromatography laboratory3.
Information
- The Chemsketch structure drawing package discussed here is freeware from http://www.acdlabs.com/download/.
- This program will be examined in a separate article.
- Details regarding the application outlined here can be found at http://www.acdlabs.com/products/chrom_lab/.
