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Frequently Asked Questions (FAQs): Reference Standards

Reference Standards

Gas Reference Standards

Residual Solvent Gas Standards

What are the most important considerations when handling residual solvent gas standards?
Are there any important tools that should be used when handling these standards?
I’m experiencing poor reproducibility in my residual solvent gas standards. Where can I go for support?
Why was a free transfer vial not included in my residual solvent gas standard purchase?

If your question doesn’t appear on the list, please contact Restek's expert chemists.
(Remember to include your company name and complete mailing address.)

Reference Standards

1. How can I purchase a custom-formulated reference standard from Restek?

Because of the sheer number of compounds, solvents, and concentrations that can be uniquely combined into a reference standard, it is not uncommon for our customers to need a mix that we do not have readily available as a stock product. If you find yourself in that situation, simply submit a custom reference standard request using our easy online tool. Our reference standards group will evaluate your request for feasibility and pricing, assign a quote number, and deliver the finished quotation to you—typically within three business days. Once you receive a response, give your quote number to Restek Customer Service or your local Restek representative to place an order; we will generate a custom catalog number just for you and will prepare the formulation. Restek even offers standing orders (also known as "blanket orders") on our custom standards to drastically lower your cost!

2. Where can I find a Certificate of Analysis, Safety Data Sheet (SDS), or Data Pack for my stock or custom reference standard?

Use our reference standard documentation search tool to find certificates of analysis, safety data sheets (SDS), or data packs for your Restek reference standards, whether stock or custom. For stock products, simply enter the cat.# into our documentation search tool to access documentation for the most recently produced lots. For custom products or older lots of stock products, you must enter the cat.# and lot number into our documentation search tool.

If you cannot find a particular certificate, SDS, or data pack online, feel free to contact us.

3. Can you recertify or extend the expiration date of my reference standard?

Unfortunately, no. Restek conducts real-time stability studies and accelerated stress tests to establish reliable expiration dates. Use beyond the identified expiration date is neither recommended nor guaranteed.

4. Which pieces of documentation are available with my Certificate of Analysis (CofA)?

Restek offers three different types of Certificate of Analysis: gravimetric, chromatographic, and chromatographic plus. Each provides different pieces of documentation, which are outlined in the graphic below:

Nearly all our stock reference standards are provided with the highest level of documentation available—Certificate of Analysis (Chromatographic Plus)—and we provide all three options for most of our custom reference standards. Reference standards that fall within our ISO scopes of accreditation will be classified as certified reference materials (CRMs) regardless of documentation level.

Certificate of Analysis gravimetric includes all raw material information, lot numbers and purity, isomer ratios for isomeric compounds, and calculated concentration(s). Associated uncertainties are also included for Certified Reference Materials (CRMs).
Certificate of Analysis chromatographic includes all raw material information, lot numbers and purity, isomer ratios for isomeric compounds, and calculated concentration(s). Associated uncertainties are also included for Certified Reference Materials (CRMs). Additionally, a single sample is withdrawn from the packaged units and is tested via an appropriate technique to verify mixture composition. A chromatogram of the analyzed standard, with each peak identified, is included on the certificate.
Certificate of Analysis chromatographic plus includes all raw material information, lot numbers and purity, isomer ratios for isomeric compounds, and calculated concentration(s). Associated uncertainties are also included for Certified Reference Materials (CRMs). Additionally, a sample of the packaged units is analyzed in triplicate and the peak areas are statistically compared to a second lot—either a previous lot (if available) or a freshly produced independent second lot. A chromatogram of the analyzed standard, with each peak identified, is included on the certificate. Plus, a detailed data pack containing the product certificate, all quantitative assay data and statistics, and the Reference Material Batch Record are available at www.restek.com/documentation

For more information, see GNBR1845C-UNV.pdf

5. What is included in a Restek reference standard data pack?

Our detailed data packs are designed to provide an exhaustive compendium of data describing your reference standard and feature gravimetric documentation, all quantitative assay raw data, and statistics. At a minimum, the following data sets are included:

Chemical Standard Lot Sheet showing the lot number, purity, and exact gravimetric weight of each analyte as well as the volume of solvent used in formulating the product.
Acceptance Chromatogram(s) showing elution order and relative peak sizes.
Data Analysis Spreadsheet based on the chromatogram(s).
Certificate of Analysis (CofA).

To obtain a data pack, visit www.restek.com/documentation. All raw material purity and identification results are available upon request.

6. Are your reference standards weight corrected for purity?

Yes! Raw material purity information is recorded on the certificate of analysis. Restek’s Quality Control (QC) lab confirms the chemical identity and purity of mixture components and solvents using two or more of the following techniques: GC-FID, HPLC, GC-ECD, GC-MS, LC-MS, refractive index, and melting point. Compounds with a listed purity of less than 99% have been weight corrected to compensate for the presence of extraneous impurities in the compound, inorganic moieties (salts, hydrates, etc.), and organic moieties (typically the functional group of a derivatized compound). To better illustrate these scenarios, the following examples will explain the process we apply:

Example 1 – Purity adjustment

Compound A is tested and found to contain a 2% impurity (compound B). That is, the purity of compound A is 98%. So, if 100 mg is weighed out, the material will contain 98 mg of compound A and 2 mg of compound B. Adding 100 mL of solvent will produce a concentration of 980 µg/mL for compound A, not the desired 1,000 µg/mL. To reach a concentration of 1,000 µg/mL for compound A, Restek chemists apply a correction factor of 0.98 to obtain the final concentration:

100 mg ÷ 0.98 = 102 mg

Using the following calculation will result in 100 mg of compound A being added to the solution and the desired concentration of 1,000 µg/mL:

(102 mg ÷ 100 mL) x 1,000 = 1,020 µg/mL x 0.98 = 1,000 µg/mL compound A

Example 2 – HCl adjustment

Compound A is the hydrochloride salt of an organic amine. If the molecular weight of compound A is 100 AMU, then the molecular weight of the parent compound (organic moiety) would be 63.5 AMU—molecular weight of compound A minus molecular weight of HCl. The ratio of organic moiety to inorganic moiety would be:

63.5 ÷ 100 = 0.635

If 100 mg is weighed out, the material will contain 63.5 mg of the parent compound and 36.5 mg of HCl. Adding 100 mL of solvent will produce a concentration of 635 µg/mL for the parent compound, not the desired 1,000 µg/mL. To reach a concentration of 1,000 µg/mL for the parent compound, Restek chemists apply a correction factor of 0.635 to obtain the final concentration:

100 mg ÷ 0.635 = 157.5 mg

Using the following calculation will result in 100 mg of compound A being added to the solution and the desired concentration of 1,000 µg/mL:

(157.5 mg ÷ 100 mL) x 1,000 = 1,575 µg/mL x 0.635 = 1,000 µg/mL parent compound

Example 3 – DNPH adjustment

Compound A is the dinitrophenylhydrazone (DNPH) derivative of a carbonyl compound. If the molecular weight of compound A is 250 AMU, then the molecular weight of the parent compound (carbonyl moiety) would be 70 AMU—molecular weight of compound A minus molecular weight of DNPH moiety. The ratio of carbonyl moiety to carbonyl DNPH moiety would be:

70 ÷ 250 = 0.28

If 100 mg is weighed out, the material will contain 28 mg of the parent compound and 72 mg of DNPH. Adding 100 mL of solvent will produce a concentration of 280 µg/mL for the parent compound, not the desired 1,000 µg/mL. To reach a concentration of 1,000 µg/mL for the parent compound, Restek chemists apply a correction factor of 0.28 to obtain the final concentration:

100 mg ÷ 0.28 = 357.1 mg

Using the following calculation will result in 100 mg of compound A being added to the solution and the desired concentration of 1,000 µg/mL:

(357.1 mg ÷ 100 mL) x 1,000 = 3,571 µg/mL x 0.28 = 1,000 µg/mL parent compound

7. What is the expiration date of my reference standard?

The expiration date of an unopened ampul, stored under the recommended storage conditions, is identified on your certificate of analysis. (If only the month and year are given, the standard expires on the last day of the month.) The expiration date is also printed on the ampul label. Once opened, the integrity of the standard is subject to handling and storage conditions, and it cannot be guaranteed.

8. How should I properly store my reference standards?

Restek’s reference standards are provided with documentation that states the recommended storage conditions needed to ensure the optimal stability of the components in that specific standard. Storage at lower-than-specified temperatures is acceptable unless otherwise noted on the certificate. (If the ampul is stored at lower temperatures, be sure to invert the ampul several times prior to opening. In the event of observable undissolved material, warm and sonicate the ampul before opening.)

Short-term exposures (≤ seven total days) to higher temperatures is acceptable and should not, based on our studies, negatively affect the long-term stability of your product. For specific statements and claims on product uncertainty as a result of short-term exposures to elevated temperatures, refer to the certified uncertainty value notes on each product’s certificate.

Please note that once the product is opened, the integrity of the standard is subject to handling and storage conditions, and it cannot be guaranteed.

For more information about reference standard storage, review our technical video on How to Store Reference Standards.

9. What are certified reference materials (CRMs)?

A CRM from Restek is in an exclusive subset of reference standards that meets the following set of strict criteria defined under ISO 17034 and ISO/IEC 17025:

Made of raw materials characterized via qualified methods on qualified instruments.
Produced in an ISO-accredited lab under documented procedures.
Falls under the manufacturer’s scopes of accreditation.

To learn more about Restek’s ISO quality credentials and to view our certificates (including scopes of accreditation), visit www.restek.com/iso

10. How do I know whether the reference standard I purchased from Restek is a certified reference material (CRM) as defined by ISO?

Before you purchase, you can check at www.restek.com/iso to see if your standard falls within our scope of accreditation. You can also ask Restek Customer Service or your local Restek representative.
After you purchase, you can easily confirm that your standard is a CRM by looking at your certificate of analysis (CofA). For a standard to be considered a CRM, it must be both manufactured and tested in an ISO-accredited lab. Every certified reference material we sell will have A2LA/ILAC logos in the upper right-hand corner of its CofA, signifying that it was both manufactured and tested under our ISO 17034 and ISO/IEC 17025 accreditations. The CofA will also state "Certified Reference Material" at the top.

Please note that our gas reference standards are not within our scope of accreditation, so they are not certified reference materials (CRMs).

11. Why do the shipping conditions on my Certificate of Analysis (CofA) differ from the storage conditions?

Storage conditions and shipping conditions are identified at the top of the Certificate of Analysis for your reference standard.

The storage field refers to the temperature that the product should be stored at once you receive it to guarantee its uncertainty, concentration, and expiration. This does not mean the ampul must remain at or below this temperature during shipment from Restek to you.

The shipping field refers to the packaging conditions that the product can be shipped in and still maintain stability. Most—approximately 98%—of our reference standards will remain stable when shipped under “Ambient” conditions. The remaining 2% of our reference standards require “On ice” packaging.

If your shipment was in transit for more than seven days and you have reason to believe it was exposed to extreme temperature conditions, contact Restek Technical Service at www.restek.com/contact-us for recommendations.

For more information about uncertainty, storage, and shipping, review our "Understanding Uncertainty on Your Restek Reference Standard Certificate of Analysis" article.

12. What is an expanded uncertainty value?

Our Certificates of Analysis (CofAs) include a certified expanded uncertainty value. In reference standards, “uncertainty” is a quantitative measurement that determines the quality of a standard. It’s used to provide a margin of error that could potentially apply to the product. It’s important to note, however, that unless your analysis results require the presentation of uncertainty, it may not be necessary for you to use the uncertainty value provided on your CofA.

Visit our "Understanding Uncertainty on Your Restek Reference Standard Certificate of Analysis" article to learn more about expanded uncertainty values.

13. Why does Restek include an expanded uncertainty value on its Certificates of Analysis (CofAs)?

Restek is an ISO 17034 accredited manufacturer of certified refence standards. Our ISO 17034 accreditation requires us to provide uncertainty values to our customers.

Visit www.restek.com/ISO to learn more about Restek’s ISO quality credentials.

14. Are my certified reference materials (CRMs) NIST* traceable?

Yes! Reference standards manufactured within our scopes of our accreditation (i.e., CRMs) are traceable as follows:

All analytical balances are verified at seven mass levels daily using NIST traceable weights and are also calibrated yearly by an ISO/IEC 17025–accredited provider to guarantee accurate measurement.
Volume is assured by using Class A volumetric flasks and/or Class A pipettes.
Raw materials are characterized to confirm identity and purity using two or more of the following techniques: GC-FID, HPLC, GC-ECD, GC-MS, LC-MS, refractive index, and melting point.
Only the purest materials available are used; any material with purity less than 99% is weight corrected.

* National Institute of Standards and Technology

15. Where can I find more information about Restek reference standards?

Restek’s website: www.restek.com/standards
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Gas Reference Standards

1. What do I do with my empty reusable gas cylinders?

Local regulations can vary greatly. If you wish to dispose of or recycle empty cylinders, be sure to do so according to local regulations. Some cylinders can be returned to the manufacturer; for more information, directly contact Linde Gases (1-800-932-0624) or Airgas (1-800-331-4953).

2. Can my gas standard be recertified?

Recertification is available for gas standards. Gas standards can be expensive and tend to be stored in the lab for months, if not years, so it is wise to have the composition recertified by a qualified vendor. For gas standards purchased from Restek, request recertification directly from Linde Gases (1-800-932-0624) or Airgas (1-800-331-4953). For gas standards purchased from vendors other than Restek, it is necessary to contact the vendor who manufactured the mixture.

3. What regulator should I use with my gas standard?

We offer six regulators for our gas standards. Specifications are summarized below:

DCG Partnership Cylinders:

Size: 7.6 x 24 cm

CGA-170/110 connection

U.S. DOT Specs: DOT-4B-240ET

Please note: This cylinder is not approved for use in Canada.

Recommended regulator:
cat.# 22032

Airgas 14 L:

Contents: 14 liters

Pressure: 240 psig (17 bar)

Outlet Fitting: CGA 160

Weight: 1.5 lb/0.7 kg

Dimensions:
3" diameter x 11" height
(7.6 x 28 cm)

DOT Specifications: 4B240

Please note: This cylinder is not approved for use in Canada.

Recommended regulator:
cat.# 22690

Linde 104 L:

Aluminum construction

Size: 8 x 24 cm

Volume/Pressure:
104 liters of gas @ 1,800 psi

CGA-180 outlet fitting

Weight: 1.5 lb/0.7 kg

Recommended regulator:
cat.# 21572, 21572-R100, 26371, or 26372

Airgas 48 L:

Contents: 48 liters

Pressure: 300 psig (21 bar)

Outlet Fitting: CGA 165

Weight: 1.75 lb/0.8 kg

Dimensions:
4" diameter x 16 ¼" height
(10.2 x 41 cm)

DOT Specifications: 39 NRC

Please note: This cylinder is not approved for use in Canada.

Recommended regulator:
cat.# 22691

Airgas 124 L:

Aluminum construction

Size: 8.3 x 30 cm

Volume/Pressure:
124 liters of gas @ 1,800 psi

CGA-180 outlet fitting

Weight: 2.3 lb/1 kg

Recommended regulator:
cat.# 26371, 26372, 21572, or 21572-R100

4. How can I troubleshoot pressure problems in my gas standard?

The most common problem encountered with gas standards is the absence of a pressure reading at the regulator. To check your regulator, remove it from the cylinder, and connect it to a cylinder that you are sure has pressure. If the regulator registers a reading on the “good” cylinder, the problem is likely that the cylinder in question is empty. If the regulator does not register a reading on the “good” cylinder, then the problem is the regulator and it must be repaired or replaced.

Residual Solvent Gas Standards

1. What are the most important considerations when handling residual solvent gas standards?

Because these standards are very volatile and are more sensitive to temperature and agitation than nonvolatile standards, rigorous mixing and agitation should be avoided. Additionally, it is important to allow the standard to equilibrate to room temperature organically without heating the ampul to avoid evaporative loss of the standard.

2. Are there any important tools that should be used when handling these standards?

We recommend using gas-tight syringes for transfer of your volatile gas standards.

3. I’m experiencing poor reproducibility in my residual solvent gas standards. Where can I go for support?

Because residual solvent gases are extremely volatile, proper care and handling of these standards is especially important to ensure their integrity. We recommend utilizing the tips and tools in our Volatile Gases Handling Guide to help guarantee the accuracy and reproducibility you need in these standards. For additional support or questions, please contact Restek Technical Service.

4. Why was a free transfer vial not included in my residual solvent gas standard purchase?

Due to the extreme volatility of our residual solvent gas standards, we do not recommend saving the unused content of opened ampules for later use.

GNOT3397E-UNV