Reference Standards Technical Tips
REFERENCE STANDARDS
Instructional Videos:
AccuStandard Inc. has posted a number of instructional videos to their YouTube Channel, please click on the following link to take you to their channel, where you can select any of the following short videos
• Easily & Safely Open a Reference Standard Ampule
• Transferring Neat Material from a Vial
• Additional notes:
• Make sure to remove the shrink wrap from the ampule before weighing it.
• To avoid cross contamination, do not touch the volumetric flask with the pipette.
• Sonicate a Reference Standard
• Additional note:
• If sonicating multiple ampules at the same time, separate them by using small beakers filled with DI water to the same level as the bath.
• Understanding Reference Standard Expiration
• How to Use AccuStandard's Two-Part Ampule Label
Contact Chromatographic Specialties Technical Support Team at 1-800-267-8103 / tech@chromspec.com for more advice on the handling and use of Analytical Standards
Preparing Calibration Curve Standards and Avoiding Sources of Error
Accurate calibration data is the foundation of all quantitation. But, behind every great calibration curve is a tremendous amount of work. Many sources of potential error are waiting at every turn, so it pays to be familiar with how to best ensure precision and accuracy. To avoid the frustration of failed calibration curves, project delays, and wasted time and resources, let’s explore some tips to help you prevent some of the pitfalls you can encounter when preparing calibration curve standards. While there are plenty of instrument issues that could cause an unacceptable calibration curve, this article focuses on standard preparation and storage.
Managing Unstable Reference Standards with Short Shelf Lives - Using Acrolein as an Example...
Environmental labs are familiar with calibration issues and inventory management challenges with acrolein standards. Acrolein, as listed in EPA Method 8316 (SW-846), is an aldehyde with poor stability under analytical conditions. When acrolein (an aldehyde) is combined with methanol (an alcohol), the formation of acrolein dimethyl acetal (3,3-Dimethoxy-1-propene) occurs as the methanol adds to the carbonyl site of the acrolein. This reaction begins quickly—despite Restek manufacturing the standards under strict processing conditions; packaging them in flame-sealed, amber glass, deactivated ampuls; and blanketing them with nitrogen. The result is a maximum shelf life of three months.
Below are two solutions to consider for keeping your instruments calibrated with reliable standards:
Set Up a Standing Order
Unstable compounds with a short shelf life make management of your standards quite challenging. In the case of acrolein, if your methods mandate methanol-based calibration standards, you can reduce your administrative cost and calibration challenges by placing a standing order (sometimes called as a "blanket order") with prescheduled deliveries of freshly made solutions. Restek manufactures and inventories two new independent batches of these standards monthly to help ensure you always have what you need, when you need it.
Consider Alternative Formulations
Restek’s talented chemists are continuously researching methods of stabilizing compounds and formulating stable solutions. When working with notoriously unstable compounds, consider evaluating alternative formulations if your methods permit flexibility. Looking back to acrolein as an example, although method SW-846 states “methanol is used as the solvent,” labs are not required to use methanol calibration standards and you may be able to use CRMs in water. Restek’s chemists have developed proprietary methods of stabilizing acrolein in water—achieving 18-month stability—to offer you an alternate way of relieving your challenges with methanol-based solutions.
Contact our Technical Support Team at 1-800-267-8103 or tech@chromspec.com to discuss solutions for any of your difficult reference materials.
Preparing to Use New Reference Standards
Included are several good laboratory practices for preparing new reference materials. Contact our Technical Support Team for more tips and tricks.
How to Sonicate Your Reference Standards
Depending on how your reference standards are stored, it’s possible some of the analytes may fall out of the solution. This will impact the analyte concentration, which can be particularly detrimental for reference standards containing long-chained alkanes such as Restek’s MOSH/MOAH Retention Time Standard. Sonication can be used to help redissolve these analytes into the solution at the proper concentration.
How Long are Standards Good After the Ampul is Opened?
It's not uncommon for analysts to ask: how long are reference standards stable after opening the ampul when stored and handled properly? Restek designed an open ampul stabiity study using the 200+ pesticides in their LC and GC multiresidue kits to answer this question.
Matrix Spiking – Terms and Technique
Matrix Spiking is a technique that is used to evaluate the performance of an analytical procedure when testing a specific sample (matrix) type.
• A matrix spike test helps answer the question “Are our tests results valid when using this this method to test for samples of? A “good” matrix spike result increases your confidence in the accuracy and validity of the sample test results.
• A Matrix Spike is generated by adding a known amount (the spike) of analyte to a sample, testing the spiked sample, and determining if the amount added has been recovered; this is sometimes referred as % recovery.
• In practice, two portions of the sample are prepared for testing. In the “matrix spike” portion, we add a known amount of standard (this increases the concentration by a known amount). When we test the sample and then the matrix spike, the matrix spike result should be higher by that known amount added. If the analytical procedure is not working well for your sample, the matrix spike result will be higher or lower than expected.
The Importance of CAS Numbers when Requesting Standards
Going through a long list of compounds for an analytical standard and adding a CAS number for every compound on the list is something nobody wishes to do. Unfortunately, it's become crucial for accurate processing of ever lengthening analyte lists, especially for international methods. Many drugs and pesticides have local variations on name or spelling while CAS numbers are constant throughout the world. CAS numbers are now the primary identifier for analytes in most, if not all, ISO 17034 Certified Reference Materials.
To let us help you find the best solutions for extensive analyte lists please:
• Include CAS numbers whenever you have them.
• Include a technical contact to clarify any oddities in a list when submitting a quote request.
• Let us know if you need us to add the CAS numbers for you. Otherwise we'll need to check if you have or can get them.
• If you need us to add CAS numbers, understand it will take us time to do so, and that you'll need to review and approve the CAS numbers and associated chemical names
before you order.
The following 2 sites are places where CAS numbers can be found:
• Common Chemistry (a CAS Solution)
• National Library of Medicine (PubChem)
Contact our Technical Team for further assistance.
How to handle, open, and not store volatiles standards
Ensuring the integrity of your volatile gas reference standards starts with having the proper tools and skillset for best practices in handling and use.