Lib Search: Cleaning Up Workspace and Temporary HLM Files in NIST26clean up

Keep Your NIST Workspace Clean by Managing HLM History Files

When performing library searches in NIST MS Search Version 4 (NIST 26), whether for EI GC-MS or MS/MS LC-MS data, the software automatically generates several temporary files to store search results and search history. These files make it easy to revisit previous library searches without repeating the analysis, but over time they can accumulate, clutter the workspace, and consume unnecessary disk space.

This guide explains how NIST stores library search history, what HLM files are used for, and how to remove them manually or automatically to keep your software organized.

👉You can download PDF Handout for this guide HERE

Temporary Files Are Created for Both EI and MS/MS Searches

Although the examples in the demonstration use an MS/MS chromatogram, the workflow is identical for EI GC-MS library searching.

Every time spectra are submitted to the NIST library search engine, the software creates temporary files that preserve the search history. Regardless of the acquisition technique, the same housekeeping procedures apply.

Running a Library Search

To perform a library search on multiple spectra:

1. Open the chromatogram in NIST MS Search.
2. Select the spectra to search.
   • Click the first spectrum.
   • Hold the Shift key.
   • Click the last spectrum to select the entire range.
3. Right-click the selected spectra.
4. Choose Library Search.

The software processes each selected spectrum and displays the search results. Depending on the number of spectra, the search typically requires only 10–15 seconds.

Reviewing Previous Search Results

After the search is complete, NIST automatically saves every search result as part of its history.

Normally, selecting a result displays:

• The unknown spectrum at the top.
• The best library match underneath.

Because every search is stored, users can return to any previous search result without repeating the library search. Simply selecting an earlier entry in the history list immediately restores the corresponding comparison.

Although many users simply perform a new search because it is very fast, the history feature can be useful when reviewing previous identifications or comparing earlier results.

What Are HLM Files?

Search history is stored in files known as HLM files.

These files are created automatically within the main NIST MS Search installation directory whenever library searches are performed.

As routine data processing continues, the number of HLM files gradually increases.

While these files are relatively small, they can eventually accumulate and make the software workspace more difficult to navigate.

Manually Clearing Search History

Once library searching has been completed, there is usually little reason to retain every temporary history file.

To remove the stored search history:

1. Open the search history window.
2. Click Clear History.
3. Confirm the deletion.

The HLM history files are removed, leaving the workspace clean for future analyses.

This simple housekeeping step helps reduce unnecessary file accumulation.

Automatically Delete History on Exit

Users who prefer not to manage history manually can configure NIST MS Search to automatically remove temporary history every time the program closes.

To enable this option:

1. Right-click inside the search results window.
2. Select Properties.
3. Open the Hit List settings.
4. Enable Clear History on Exit.
5. Click OK.

If desired, these settings can be saved as part of the software configuration.

Once enabled, NIST automatically deletes history files whenever the application closes, eliminating the need for manual cleanup.

Cleaning the Spectrum List

In addition to HLM history files, the temporary spectra that were submitted for searching also remain in the spectrum list.

Removing these entries helps keep the workspace organized.

To clear the temporary spectra:

1. Select the first spectrum.
2. Hold the Shift key.
3. Select the last spectrum.
4. Choose Cut.

This removes the temporary entries from the workspace without affecting the original analytical data.

Benefits of Regular Housekeeping

Although the generated files are temporary, periodically cleaning them provides several advantages:

• Reduces clutter within the NIST interface.
• Makes navigating the spectrum list easier.
• Prevents accumulation of unnecessary HLM history files.
• Saves a small amount of hard drive space.
• Keeps the workspace organized for future analyses.

For users who process large numbers of samples every day, enabling Clear History on Exit is often the simplest solution.

Best Practices

To maintain an organized NIST MS Search workspace:

• Use the search history when you need to revisit previous library matches.
• Delete HLM history files after completing an analysis if they are no longer needed.
• Enable Clear History on Exit to automate housekeeping.
• Remove temporary spectra from the spectrum list after searching.
• Periodically review your workspace to avoid unnecessary accumulation of temporary files.

Conclusion

NIST MS Search automatically creates HLM history files and temporary spectrum entries during every EI or MS/MS library search. While these files provide a convenient way to review previous search results, they are generally not needed once an analysis is complete. By clearing history manually—or enabling automatic deletion on program exit—you can maintain a cleaner workspace, simplify navigation, and prevent unnecessary file accumulation without affecting your original analytical data.