text.skipToContent text.skipToNavigation

Dr Ehrenstorfer Frequently Asked Questions


How can I prepare a standard solution from my Dr. Ehrenstorfer neat reference material?

Handling small quantities and semi-solid materials might be easier than you think.  We have prepared some steps that you may find useful to refer to.



How do I select an appropriate solvent to prepare my standards?

In the first instance, you should refer to your in-house procedure/SOP.  If you don’t have this or this is the first time you have used a particular compound, a number of factors can influence the choice of solvent, including solubility of the chemical, miscibility of different solvents and the application or technique you are using. There are a wide range of solvents to choose from and this can be quite overwhelming.  We have supplied a list of example solvents that are suitable for a range of compounds / analytes.  However please note, this list is a suggested list and other solvents can also be appropriate.  If you can't find what you need or require any further assistance please contact us askus@lgcstandards.com.


Are all Dr. Ehrenstorfer products provided with a Certificate of Analysis?

The vast majority of Dr. Ehrenstorfer products are provided with a Certificate of Analysis.  However, products with a part number pre-fix of DRE-E are not supplied with a Certificate of Analysis due to one of the following reasons:

  • only a very limited quantity of material is available
  • chromatographic analytical techniques are not applicable
  • the material is a technical grade / mixture of components for which the individual components are unavailable to characterise the material

Where products are provided without a Certificate of Analysis (DRE-E prefixed part numbers), the purity of the product is stated on the product container label, if available. Further details are not available or provided with the product.

We are constantly reviewing our processes and portfolio and as part of this process some new batches of DRE-E-prefixed products will convert into DRE-C products prefixed products, which are supplied with a Certificate of Analysis.


Are Dr. Ehrenstorfer Certificates of Analysis provided with chromatograms?

Example chromatograms are provided where possible, as part of the Certificate of Analysis. These are provided for information only.  Certificates of Analysis are not provided to demonstrate the purity of the product (e.g. peak purity). 

In some cases, a chromatogram is not supplied on the Certificate of Analysis.  It may not be possible to provide a chromatogram due to the analytical technique used (e.g. titration). In other cases a chromatogram from the analysis is not indicative to the purity of the product without supporting data to interpret the chromatogram supplied.


Why are different analytical methods used for different lots of the same product?

We are constantly reviewing and optimizing our procedures and analytical methods used in the production and certification process. Therefore the analytical method used for one particular lot may vary to the next lot for the same chemical.  Our aim is to provide the best available method at the time of testing.


Does the purity value provided on the Certificate of Analysis already account for water content?

The water content on the Certificate of Analysis of your neat material is provided for information only. We have taken the water content into account when calculating the purity value provided. Watch our video to find out more.



Why does the purity sometimes vary from batch to batch for the same product?

The purity provided on the Certificate of Analysis may differ from one batch to another. Different synthesis and purification processes may be used from batch to batch. Therefore the purity for each batch may differ.  In all cases we try to provide the highest purity possible together with a stated uncertainty value as low as possible. In order to achieve this, some products need to be stabilized by dilution. The identity and the amount of the stabilizer are mentioned on the Certificate of Analysis.



How does Dr. Ehrenstorfer demonstrate the traceability of its certified values?

Dr. Ehrenstorfer use a quality management system certified according to ISO 9001 and methodology accredited to ISO 17025 in order to manufacture our products.  Using accredited procedures, measurements of weight, volume and temperature are used to demonstrate traceability back to SI unit. 

An increasing range of products also are produced under our ISO Guide 34 scope of accreditation (lot numbers prefixed with the letter G or H).  As such, associated uncertainties and traceabilities obtained using valid reference measurement procedures, including chromatographic techniques, elemental analysis (CHN) and quantitative NMR are achieved.


How does Dr. Ehrenstorfer demonstrate the stability of its reference materials?

Dr. Ehrenstorfer has a long history in producing pesticides and other organic chemicals for the residues testing industry. We therefore have significant background information on the stability of many of the substances in the range.

Real time stability studies are undertaken on our products prior to release.  Products are not released for sale until a minimum of three months stability data is available.  They are then released with ‘short shelf life stability’ until additional stability data is collated.

Stability is assessed under the long term storage conditions that are described on the certificate. In addition short term storage conditions are also assessed.  All products are tested to be stable at ambient temperature for at least one week, unless otherwise stated on the Certificate of Analysis.


Are the expiry dates of lots / batches of Dr. Ehrenstorfer products reviewed and extended?

Expiry dates are valid for an unopened, originally sealed container and are lot are specific. The storage conditions given on the Certificate of Analysis are mandatory for the expiry date to be valid.
Expiry dates for lots / batches are not reviewed or extended. 


Can I store my product at a lower temperature than stated on the Certificate of Analysis?

For a neat material, storage or transportation at lower temperatures is not normally a problem, unless the melting point is between the actual storage temperature and ambient temperature.  In these cases the substance may freeze on storage. The substance must be allowed to melt before use.

For solutions, we do not recommend storage at temperatures lower than those specified on the Certificate of Analysis, as substances may precipitate and in some cases be difficult to re-dissolve. 


How should I store my product once it has been opened?

LGC can only guarantee integrity of our reference materials until first opening of the vial or ampoule. It is the responsibility of the user to ensure integrity afterwards by correct further storage and handling of the reference material. The recommended storage conditions for an opened container are the same as those for an unopened container. Please take care that the lid for an open bottle is closed tightly after use. If the product was supplied in an ampoule, the contents should be transferred to a suitable storage vial / bottle with a lid for storage. Check the Certificate of Analysis for additional information provided (e.g. store under suitable inert gas) as this will affect the stability of the product.


Why is the ratio of isomers or congeners on the not given on the Certificate of Analysis?

Where possible, the ratio of isomers or congeners is stated on the Certificate of Analysis.  For some products it is not possible to state the amount of the individual isomers or congeners within the required measurement uncertainty.


What does the term “technical mixture” mean? 

The term "technical mixture" is used for products when information on the quantity or identity of individual components is not available.  Information that is available is supplied on the Certificate of Analysis.



Refine your


Online Ordering made easy


Sign up to our email newsletter



Punchout session timeout warning

Your punchout session will expire in1 min59 sec.

Select "Continue session" to extend your session.