When test results are used to assess compliance, i.e. to decide whether specifications or regulations are met, the measurement uncertainty of the test results has to be taken into account. Assessment of compliance for cases i and v in the Figure below is clear – the measurement results including the uncertainty interval are clearly above or below the limit value. In the other cases the decision is not clear since the uncertainty interval overlaps the limit value. The Eurachem/CITAC guide [1] gives guidance on cases ii, iii and iv.&nbsp;<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Eurachem_Upper_control_limit_9366d8f597.jpg" alt="Eurachem: Upper control limit" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Eurachem_Upper_control_limit_9366d8f597.jpg 245w," sizes="100vw" width="1536" height="585"><h4>We need acceptance &amp; rejection zones&nbsp;</h4>In order to judge whether the results in cases ii, iii, and iv comply with the limit value we need a decision rule, based on the risks associated with making a wrong decision. This decision rule enables a guard band, g, to be calculated which defines an acceptance zone and a rejection zone. If the measurement value is within the acceptance zone the specifications are met and we can conclude compliance. If the measured value is in the rejection zone, we can conclude non-compliance. The intersection between these two zones is called the decision limit. A guard band is normally chosen so that for a measured value in the acceptance zone the probability of correct acceptance is more than or equal to a defined confidence value α. Note that a guard band, g = 0 can also be used. This is called simple acceptance.&nbsp;<h4>Decision rule&nbsp;</h4>A decision rule should have a well-documented method of determining the location of acceptance and rejection zones, ideally including acceptable levels of probability, P, that the value of the measurand 1) lies within the specification limit, high confidence of correct acceptance (low probability of false acceptance) or 2) lies outside the specification limit, high confidence of correct rejection (low probability of false rejection).<h4>Information needed for assessing compliance&nbsp;</h4>The following information is needed:&nbsp;<ul><li>measurand clearly specified;&nbsp;</li><li>specification stating upper or lower limit or both;&nbsp;</li><li>decision rule;&nbsp;</li><li>measured value:&nbsp;</li><li>measurement uncertainty for a measured value at the limit(s).</li></ul><h4>Example focusing on correct acceptance&nbsp;</h4><ul><li>Measurand: Mass fraction of nickel, Ni in a batch of steel delivered to a customer.&nbsp;</li><li>Uncertainty: U = 0.2 % Ni, k = 2 (95 %). Standard uncertainty, u = 0.1 % Ni. This uncertainty includes both sampling uncertainty for the batch and analytical uncertainty.&nbsp;</li><li>Specification: The specification zone is from the lower limit 16.0 % Ni to the upper limit 18.0 % Ni.&nbsp;</li><li>Decision rule High confidence of correct acceptance: The acceptance range is the mass fraction where it can be decided with a confidence level of approximately 95 % (α = 0.05) that the batch has a mass fraction above the lower limit and below the upper limit.&nbsp;</li><li>Guard band: Each guard band is calculated as 1.64u ≈ 0.17 % (rounded upward for safety) with k value 1.64 from the one-tailed upper 95 % quantile of the normal distribution.&nbsp;</li><li>Acceptance zone: 16.2 % Ni to 17.8 % Ni , after rounding to one decimal place.&nbsp;</li><li>Measured value: 16.1 % Ni</li></ul><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Eurachem_Guard_bands_g_and_acceptance_and_a_rejection_zones_based_on_a_lower_and_upper_bedc4769b3.jpg" alt="Eurachem: Guard bands (g), and acceptance and a rejection zones based on a lower and upper limit and a decision rule stating high confidence of correct acceptance" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Eurachem_Guard_bands_g_and_acceptance_and_a_rejection_zones_based_on_a_lower_and_upper_bedc4769b3.jpg 245w," sizes="100vw" width="1091" height="447">The measured value, 16.1 % Ni, is below the lower acceptance limit of 16.2 %; that is, in the rejection zone. The batch is non-compliant.&nbsp;<blockquote>Note – if the decision rule stated simple acceptance the acceptance zone would be 16.0 % to 18.0 % and the batch would be compliant.&nbsp;</blockquote><h4>Example focusing on correct rejection&nbsp;</h4><ul><li>Measurand: Mass fraction of a banned substance in a sample.&nbsp;</li><li>Uncertainty: The relative standard uncertainty urel is 35 %.&nbsp;</li><li>Specification: Upper limit is 2 ng/g.&nbsp;</li><li>Decision rule High confidence of correct rejection: The concentration of the banned substance will be deemed to be above the limit if the probability of the value of the concentration being greater than the limit is 95 % or greater.</li><li>Guard band: The guard band g for correct rejection is 1.6 ng/g assuming a lognormal distribution (due to the high relative uncertainty – see further Guide Annex A, Case 4 [1]).&nbsp;</li><li>Acceptance limit: 3.6 ng/g&nbsp;</li><li>Measured value: 3.3 ng/g&nbsp;</li></ul><img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Eurachem_Guard_band_g_and_acceptance_and_a_rejection_zones_based_f0f8f140db.jpg" alt="Eurachem: Guard band (g), and acceptance and a rejection zones based on a decision rule stating high confidence of correct rejection" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Eurachem_Guard_band_g_and_acceptance_and_a_rejection_zones_based_f0f8f140db.jpg 245w," sizes="100vw" width="883" height="392">The measured value, 3.3 ng/g, is below the acceptance limit of 3.6 ng/g; that is, in the acceptance zone. The sample is compliant. Note that the assumption of the type of distribution is crucial. If assuming a normal distribution in this case the acceptance limit would be 3.2 ng/g and the sample would not be compliant.

Use of uncertainty in compliance

<h3>Keep Your NIST Workspace Clean by Managing HLM History Files</h3>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.<blockquote>👉<a target="_blank" rel="noopener noreferrer" href="https://gcms.labrulez.com/labrulez-bucket-strapi-h3hsga3/clean_up_workspace_hlm_files_2eef9909c8.pdf">You can download PDF Handout for this guide HERE</a></blockquote><h4>Temporary Files Are Created for Both EI and MS/MS Searches</h4>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.<h4>Running a Library Search</h4>To perform a library search on multiple spectra:<ol><li>Open the chromatogram in NIST MS Search.</li><li>Select the spectra to search.<ul><li>Click the first spectrum.</li><li>Hold the Shift key.</li><li>Click the last spectrum to select the entire range.</li></ul></li><li>Right-click the selected spectra.</li><li>Choose Library Search.</li></ol>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.<h4>Reviewing Previous Search Results</h4>After the search is complete, NIST automatically saves every search result as part of its history.Normally, selecting a result displays:<ul><li>The unknown spectrum at the top.</li><li>The best library match underneath.</li></ul>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.<h4>What Are HLM Files?</h4>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.<h4>Manually Clearing Search History</h4>Once library searching has been completed, there is usually little reason to retain every temporary history file.To remove the stored search history:<ol><li>Open the search history window.</li><li>Click Clear History.</li><li>Confirm the deletion.</li></ol>The HLM history files are removed, leaving the workspace clean for future analyses.This simple housekeeping step helps reduce unnecessary file accumulation.<h4>Automatically Delete History on Exit</h4>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:<ol><li>Right-click inside the search results window.</li><li>Select Properties.</li><li>Open the Hit List settings.</li><li>Enable Clear History on Exit.</li><li>Click OK.</li></ol>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.<h4>Cleaning the Spectrum List</h4>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:<ol><li>Select the first spectrum.</li><li>Hold the Shift key.</li><li>Select the last spectrum.</li><li>Choose Cut.</li></ol>This removes the temporary entries from the workspace without affecting the original analytical data.<h4>Benefits of Regular Housekeeping</h4>Although the generated files are temporary, periodically cleaning them provides several advantages:<ul><li>Reduces clutter within the NIST interface.</li><li>Makes navigating the spectrum list easier.</li><li>Prevents accumulation of unnecessary HLM history files.</li><li>Saves a small amount of hard drive space.</li><li>Keeps the workspace organized for future analyses.</li></ul>For users who process large numbers of samples every day, enabling Clear History on Exit is often the simplest solution.<h4>Best Practices</h4>To maintain an organized NIST MS Search workspace:<ul><li>Use the search history when you need to revisit previous library matches.</li><li>Delete HLM history files after completing an analysis if they are no longer needed.</li><li>Enable Clear History on Exit to automate housekeeping.</li><li>Remove temporary spectra from the spectrum list after searching.</li><li>Periodically review your workspace to avoid unnecessary accumulation of temporary files.</li></ul><h4>Conclusion</h4>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.

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

<h3><a target="_blank" rel="noopener noreferrer" href="https://www.isc2026.org/">ISC 2026</a></h3>The <a target="_blank" rel="noopener noreferrer" href="https://lcms.labrulez.com/companies/314">International Symposium on Chromatography (ISC)</a> represents the oldest conference series on separation science. ISC symposia have been organised since 1956 in each even year. ISC is one of the premier meetings series for discussion of all modes of chromatography and separation science with a broad coverage of techniques and applications.<h4>35th International Symposium on Chromatography</h4>📆6. - 10. September 2026📍Prague, Czech Republic<h3>REGISTRATION</h3><blockquote>👉<a target="_blank" rel="noopener noreferrer" href="https://www.czech-in.org/cmPortalV15/Account/Login?ReturnUrl=%2FcmPortalV15%2FPortal%2FISC26%2Fnormal">Register HERE for the ISC 2026</a>Late Registration until 25 August 2026</blockquote><h3>ABSTRACT SUBMISSION</h3>There is still an opportunity to share your latest results at ISC 2026!&nbsp;<blockquote>👉<a target="_blank" rel="noopener noreferrer" href="https://www.czech-in.org/cmPortalV15/Account/Login?ReturnUrl=%2FcmPortalV15%2FPortal%2FISC26%2Fnormal">Submit your Abstract HERE</a><ul><li>Deadline for late-breaking poster abstract submission: July 30, 2026&nbsp;</li><li>Please note that late-breaking posters cannot compete for the Best Poster Award.&nbsp;</li></ul></blockquote><h3>ISC TUBE 2026</h3>Since its launch in 2019, Tube has become a beloved highlight of chromatography conferences — offering scientists a fun, creative outlet to express their passion for separation science. At ISC 2026, the excitement continues in Prague, and the top three videos will be awarded. Open to individuals and groups of all ages, the winners will be determined live by electronic audience voting.&nbsp;We invite you to create a short video (up to 1 minute) showing why you love chromatography! No need for fancy editing — just grab your phone and let your imagination flow. Be funny, be inspiring, be dramatic — but most importantly, be yourself! This is not a scientific presentation — it’s a science show! Your mission is to bring chromatography closer to the ISC audience in an engaging and entertaining way.<blockquote>👉<a target="_blank" rel="noopener noreferrer" href="https://files.c-in.eu/s/S7ekt8FYygFBNEW">UPLOAD YOUR VIDEO HERE</a></blockquote><h4>Rules for Participation</h4><ol><li>Format: Typical video formats, such as MP4, MPG, AVI, and others.&nbsp;</li><li>The theme is broad, but here are a few ideas to spark your creativity:</li></ol><ul><li>Infomercial: Combine science and storytelling — sell us your chromatography as if it’s changing the world!&nbsp;</li><li>Sports Highlights: Recreate your lab’s “winning moment” — a slam dunk analysis or record-breaking run time.&nbsp;</li><li>Movie Trailer: Turn your chromatography into a blockbuster — dramatic voiceovers encouraged!</li></ul><ol><li>Content: Make your video engaging, persuasive, and visually appealing. Showcase your research and chromatographic practice with flair.&nbsp;</li><li>Creativity: Think about what captivates you — a sports replay, a movie trailer, or even a teleshopping ad. Now channel that energy into your chromatography story!&nbsp;</li><li>Deadline: Upload your video via <a target="_blank" rel="noopener noreferrer" href="https://files.c-in.eu/s/S7ekt8FYygFBNEW">file upload</a> by July 31st 2026. In case you have questions please refer to plachkka@faf.cuni.cz.</li></ol><h4>Evaluation Criteria</h4><ul><li>Winners will be selected via live electronic audience voting</li><li>Judging will be based on scientific relevance, creativity, entertainment value, and technical quality</li><li>Entries containing discriminatory or offensive content will be excluded</li></ul><h4>Who Can Participate?</h4><ul><li>Eligibility: Scientists (academic or industrial) of any age registered for the ISC 2026 and working on chromatography-related projects — before, during, or after the separation step</li><li>Submissions: Individual and group entries are welcome&nbsp;</li><li>Content: Videos must be based on the participant’s own work&nbsp;</li><li>Selection: A shortlist of top videos will be chosen for the live finals at ISC 2026, which will be held on Tuesday 8 September, 18:30 – 19:30&nbsp;</li></ul>

ISC 2026 - ISC Tube & Late-Breaking Poster Deadline

Article

Events

Academy

Video

Software

Eurachem is a European network promoting international traceability of chemical measurements and good analytical practice. It provides expert guidance, supports method validation, uncertainty evaluation, proficiency testing, and facilitates discussion on technical and policy issues in analytical quality.

Eurachem

The International Symposium on Chromatography (ISC) represents the oldest conference series focussing on separation science. ISC symposia have been organised since 1956 in each even year. ISC is internationally recognised as one of the premier meeting series for discussion of all modes of chromatography and separation science with a broad coverage of techniques and applications.

International Symposium on Chromatography - (ISC)

My main interest is the identification of organic compounds by mass spectrometry in organic mixtures.

Related content

ISC 2026 - ISC Tube & Late-Breaking Poster Deadline

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

Use of uncertainty in compliance