Technical Service - Frequently Asked Questions
AccuStandard is accredited to ISO Guide 34, ISO/IEC 17025 and certified to 9001. Our quality system undergoes multiple audits each year and has become stronger and more robust with each review. We hold regular interdepartmental Non-Conformance meetings, in accordance with our ISO work instructions. The failure analysis determines the root cause and the appropriate corrective action for each non-conformance.
There are many different ways of describing uncertainty, or ranges that are reported on certified values. The uncertainty value discussed above is one of the more useful. Other wording you may encounter on certificates include: The uncertainty is expressed as the “expanded uncertainty”. Reporting expanded uncertainty allows the uncertainty to be expressed so that it encompasses a larger interval around the value, typically an expanded uncertainty is reported as being at the 95% confidence interval. To obtain the expanded uncertainty, a coverage factor is used. A coverage fact is typically between 2 and 3. Therefore, if the original uncertainty calculation shows an uncertainty of 2%, but you want to report this value in the 95% confidence interval, you must multiply it by 2 to get an expanded uncertainty of 4%. The expanded uncertainty often results in a number that appears to be very large, however, statistically it is the preferred manner of reporting uncertainty. This product is guaranteed accurate to ± x% of the certified value. This means that the manufacturer is confident enough to certify that their preparation methods, analysis, and history with this product will provide a certified value in a range of ± x% of the certificate value. This statement is generally more generic than the uncertainty, and is NOT independent or contradictory of uncertainty. It is a guarantee of the confidence of the manufacturer to support their product. Tolerance of the weighing procedure and dilution error add a maximum of ± 0.5%. This is very similar to the above. It is basically a statement of the tolerance of their internal procedures. Uncertainty based upon balance and glassware accuracy. A statement like this means that an uncertainty calculation was done, but rather than assessing ALL the possible sources of uncertainty (such as purity, repeatability, moisture, etc.), they are only using the items stated. This will generally give a better-looking number, but may not encompass the full scope of contributing factors. The most important part of the uncertainty is that you understand how it fits into your laboratories’ analysis and work accordingly from there.
It means you may be able to use that expired standard instead of paying for a new one. Here's how it works: Customers call daily asking if a particular expired lot can get re-certified for a longer expiration period. Our QC Department will review the data, including re-analyzing the retain for that lot if necessary. A high percentage of the time we can re-certify the product for additional time. In those cases we send new labels and Certificates of Analysis (free of charge!). That's the value to our customers of the AccuStandard "On-Going Stability Program".
Chemical Reference Standards, like all chemicals, can undergo changes or decomposition under certain thermal conditions or as a result of interactions with air, moisture, and other chemicals and solvents. The likelihood and extent to which this happens is dependent on the specific chemical structure, and can be predicted based on experience and an extensive knowledge of the behavior of the particular chemical. Most Standards manufacturers state Expiration Dates and Storage Conditions on their products. For the chemist who uses the product, understanding the way these dates are generated will allow them to choose products with the best accuracy and reliability. AccuStandard uses the “On-Going Stability Program” data to determine Expiration Periods (over 21 years of data on over 35,000 chemical products). We compare data from the latest lot of a given product to historical data. Based on this information, we assign a period ranging from three months to three years to each product. If a customer has product left at the end of its expiration period, our QC Department may re-analyze the product and may extend the expiration period if it is still within specification. This saves money, especially on specials, and reduces your facility's waste stream, which is good for the environment.
Most Inorganic Single Standards have a shelf life of 3 years while most mixes have a shelf life of 12-18 months. Most Organic Standards have shelf life of a year or more. Some Organic Standards are more thermally labile and last a shorter period. These are marked with a snowflake icon in the catalog, and they should be ordered with a cold pack to lessen the temperature effects during shipment. The other way to know is to ask the AccuStandard CSR for the actual remaining shelf life of existing lots before you place the order.
Yes, when available, AccuStandard provides NIST traceability. The traceability link is stated on the Certificateof Analysis that is provided with the Standard.
For certain products, AccuStandard can prepare a second standard if only one lot is available. Ask the Customer Service Representative if this is an option.
Products which are “Technical Mixtures”, known by a variety of names such as “Tech Mix”, “Technical Product”, and other names, are not pure chemicals, but are very necessary in analytical chemistry. Hence, they are available as Reference Standards. They are mixtures of multiple chemicals, so chromatograms of Tech Mixes will have multiple peaks. None of the peaks are “impurities”, rather they are all components important as ingredients in the product. How does a chemist know a particular Reference Standard is a single component or a mixture? First, chemists universally understand that certain compounds, such as Aroclors and gasoline, are actually mixtures of multiple chemicals rather than a single chemical. Second, any trade name, such as Aroclor (trademarked by Monsanto), and some pesticides, are formulations of multiple chemicals that have been combined for a specific purpose. So the name itself can be an indication. Thirdly, there may be different isomers of a given chemical, and these isomers (such as cis- and trans-) exist in various proportions. Similarly, when the letters “iso” appear in a chemical name, that may be an indication that there are multiple compounds in that mixture. To help clarify this situation for the non-chemist, AccuStandard has taken the lead in the Standards industry and now shows on its web site and to an increasing degree in its catalogs, which products are “Technical Mixtures”.
Like most Organic Chemical Reference Material manufacturers, AccuStandard uses ampules. There are many positive reasons for using ampules.One of the most important is that once sealed, they provide a long term, air tight and relatively inert environment that protects the product for long term storage. Ampules preserve the concentration of the analytes since neither the analytes nor the solvent can escape. Ampules do have some inconveniences associated with them, such as snapping them without breaking them and not being able to use a pipette in the neck of the ampule. When snapping ampules, we suggest using an AccuSnap to protect your hands. Alternatively, a folded paper towel, or thick gloves can also provide protection. To transfer from an ampule to another container we suggest either using a clean narrow tipped disposable Pasteur pipette. Once the transfer has been made, the designated portion of the AccuStandard label can be removed from the ampule and attached onto the transfer container for easy identification. To dilute the standard directly from the ampule, we suggest using a CLEAN glass syringe.
Certain chemicals, due to their structure, are more likely to react than others. The conditions that increase this reactivity are: time, temperature, solvent, other analytes present, air and/or light, and pH. Here is a brief list of some problem products:• Many Pesticides, such as Tetraethyl Pyrophiosphate (TEPP)• Trinitrotoluene (TNT) solutions• Aldehydes and Ketones (ex. Acrolein and Methylethyl ketone that form adducts with methanol as a solvent)• Acids (Phenols and Carboxylic acids) that can form salts with bases such as amines• Anthracene which will react with the oxygen in the air above the solution (if it is not purged with nitrogen between usage) to form anthraquinone - keeping the solution dark will help prevent this from happening. AccuStandard works to formulate the most stable solutions possible, but we cannot change the nature of the chemistry of these unstable items. Therefore, we assign an expiration date that reasonably reflects their anticipated usable shelf-life.
Certain of the Chemical Reference Standards are thermally labile. This means they are highly susceptible to change at room temperature or above. For this reason, AccuStandard states the storage conditions on the label. In some of these cases, AccuStandard also recommends that the product ship in a “Cold PAK”, which is a styrofoam container that has an ice pack in it. The purpose of the Cold Pak is to delay the exposure of the product to higher temperatures. The purpose is NOT to keep the product frozen. The product will not immediately go out of specifications when the Cold PAK melts or when the product reaches room temperature. Temperature related effects would begin to exhibit themselves at various times (up to many months) after this happens. The Cold Pak simply delays exposure to higher temperatures. When a product is shipped with a Cold Pak, the customer should also consider requesting next-day delivery (where available) and should avoid having the shipment sent on a Friday unless it is approved for Saturday Delivery.
Sometimes precipitation or crystallization may appear in a product. This can occur with products that are close to saturation and have gotten cold. If this happens, the solution should be warmed to room temperature and then the sealed ampule should be sonicated for approximately fifteen minutes. Invert the ampule several times and allow the sample to return to room temperature. The standard is now ready for use. If the sealed product has crystals at the top of the outside of the ampule, it may indicate a pinhole break in the seal. In this case, please call AccuStandard Customer Service for assistance.
If AccuStandard has a product with known or suspected solubility problems that can be corrected by sonication, “sonicate” is written on the label. An example of when this could happen is with products that may precipitate out of solution when they get cold. During shipment we cannot control the temperature of the products, and some of the less soluble analytes may start to precipitate out. This precipitation may be so slight that it cannot be detected visually, however, it could affect the outcome of the analysis. If you receive a product that says sonicate, the solution should be warmed to room temperature and then the sealed ampule should be sonicated in an ultrasonic bath for approximately fifteen minutes. Invert the ampule several times to achieve homogeneity, allow the sample to return to room temperature, and then the standard is ready for use.
Even though it doesn’t look like the product is in there, it is. Small amounts (5-10 mg) of powder often are spread over the surface of the vial and cap. If the chemical is a liquid it may coat the walls as a thin layer invisible to the eye.To recover all of the contents contained in a vial of neat material please use the procedure described below:
- Wipe the outside of the vial (containing the Standard) clean and dry (including the cap).
- Weigh the entire unit on an analytical balance. Record the weight to the nearest 0.1 mg.
- Carefully transfer the contents to a volumetric flask using a suitable solvent. Rinse the cap and vial several times to assure a complete transfer.
- Dry inside and outside of the vial and cap with mild heat or inert gas.
- Weigh the empty dry vial on the same analytical balance to the nearest 0.1 mg and calculate by difference the amount of material transferred.
Volatile Analytes, especially gases, can be troublesome to analyze. To provide the best possible standard we suggest the following procedures:
- Keep the ampules cool (follow the storage conditions on the label).
- Prior to use, invert the ampule several times to ensure the gases are in the solution, not in the headspace. Mixing too vigorously can cause the gases to be lost as well.
- Use freshly opened ampules whenever possible.
- When transferring, take care to avoid losses of the very volatile components. For example, holding the barrel of a syringe in your hand can warm it enough to lose some of the most volatile components.
- If using the purge and trap (PT) system is giving questionable results, try a direct liquid injection. If the results are not as expected, there may be a problem with the PT apparatus.
Poor recoveries on these analytes can result from an injector port problem. Try cleaning the port or replacing the liner. Most times this will correct the problem. Removing the first few inches of a capillary column can also help. Since elevated temperatures contribute to the breakdown problem, using cool on-column injection method scan be used to avoid this issue.
Since Phenols and Nitrosamines can react with the active sites on a column, they can sometimes give inconsistent results from run to run. By saturating these sites, the problem should go away. To do this, run a standard that is between 2 to 5 times higher than your highest calibration point. This can be repeated if necessary until the problem is alleviated. Alternatively silylation can be performed on the column (contact column manufacturer for more details).
AccuStandard has found that mixes that contain both Nitrate and Nitrite are not stable over long periods of time. Typically, the Nitrite oxidizes to Nitrate. This creates a problem for long-term storage of these solutions. Therefore, in order to provide the most stable solution, AccuStandard supplies the Nitrite as a separate solution. Diluting the two solutions together just prior to use will ensure the most accurate values for these standards.
Mercury has unique properties that make it not very stable in the presence of other analytes. Some of these properties are: Mercury can easily be reduced to the metallic state, tends to volatilize easily, can precipitate in the presence of even minute amounts of halogens (such as HCl fumes), and can plate onto some surfaces. As a result of these properties Mercury is provided as a separate solution, and if required, can be mixed with the other elements just before analysis.
AccuStandard sells only the 1000 µg/mL concentrations of the Uranium and Thorium. These products are made from naturally occurring Uranium and Thorium and have been tested and fall below the IATA 0.002 µCi/g limit for radioactive materials. AccuStandard cannot guarantee the exact isotopic distribution in either of these products.