Technical Service - Frequently Asked Questions
AccuStandard is accredited to ISO Guide 34, ISO/IEC 17025 and certified to ISO 9001. Our quality system undergoes multiple audits each year and has become stronger and more robust with each review. We hold regular interdepartmental nonconformance meetings to determine the cause of each nonconformity and make the appropriate corrective actions in an effort to eliminate the possibility of repeat occurrences.
Although uncertainty relates to the general concept of doubt, uncertainty of measurement does not imply doubt about the validity of a measurement, but rather the confidence in the validity of a measurement result. Uncertainty takes the form of a range and should never be used to correct a measurement result. The value reported on the certificate should be used as a factor in the laboratory’s uncertainty assessment. The uncertainty values as stated on our Certificate of Analysis have been determined using the EURACHEM/CITAC Guide (Quantifying Uncertainty in Analytical Measurement). We have evaluated both Type A (based on a series of observations) and Type B (manufacturers specifications and calibration data) factors and report a combined expanded uncertainty. The expanded uncertainty provides an interval (or width of the margin) and a confidence level (how sure we are that the “true value” is within the margin).
Chemical Reference Materials, 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 and over twenty years of stability data. Based on this information, we assign a period ranging from three months to ten years.
Sometimes it is possible to extend the expiration period of a product. Our QC department will test a retain of the product and may extend the expiration date if it is still within specification. Contact our Technical Service department for additional information.
Most inorganic single-component standards have a shelf life of 3 years while most of the mixes have a shelf life of 12 to 18 months. Most organic standards have a shelf life of one year or more. Some organic standards are more thermally labile and last a shorter period of time. These products are marked with a snowflake icon in the catalog, and should be ordered with a cold pack to lessen the temperature effects during shipment. Ask the customer service representative for the actual remaining shelf life of the existing lots when you place your order.
Yes, when available, AccuStandard provides NIST traceability. The traceability reference is stated on the Certificate of 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.
Technical Mixtures, or tech mixes, can be mixtures of multiple chemicals or contain multiple isomers of the compound. Chromatograms of these products will have multiple peaks. These peaks are NOT impurities, but components of the product. The use of technical mixtures as reference materials is important for identity of substances (qualitative or quantitative), calibration, assessment of measurement and quality control. Contact our Technical Service Department for additional information.
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, light and pH. For example, aldehydes and ketones form adducts when methanol is used as the solvent, certain acids will form salts with bases such as amines, and anthracene will react with oxygen in the air to form anthraquinone. AccuStandard works to formulate the most stable solutions possible, but we cannot change the nature of the chemistry of unstable chemicals so some products will have a short expiration to reflect 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.
“Sonicate” is written on the label of products with high component concentrations or cold-temperature storage items because some of the analytes may begin to fall out of the solution under these conditions. This precipitation may be so slight that it cannot be detected visually, however, it could affect the outcome of the analysis. If sonication is recommended, the product should be warmed to room temperature and then the sealed ampule should be sonicated in an ultrasonic bath for at least fifteen minutes. Invert the ampule several times to achieve homogeneity and allow the sample to return to room temperature before using.
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.