Reconstitutable Solutions
In the interest of bringing more isotopically labeled standards to our customers, we are sometimes faced with standards that do not store well in the various solvents we use. One way to provide a known amount of standard that can be kept for more than a few weeks or months is to dry down a known volume of fresh solution for future reconstitution.
What should you do when your reference standard is not stable in solution? Make your standard solution fresh from precisely measured dry reference standards. Commonly used in applications such as neonatal screening, dry standards are becoming more common in environmental applications. Dry reference standards are preferred for compounds which have low stability in solution. The longer shelf life of the dry reference standard means it can be kept until needed then reconstituted to make the reference solution on site.
CIL has extensive experience in dry reference standards. Currently, thousands of neonatal screening kits are sold by CIL each year. The kits (NSK-A and NSK-B) contain a dry mixture of 12 and 10 amino acids and carnitines at specific concentrations. This mixture is typically dissolved in water and methanol by the customer and used within a month.
Many environmental standards are also available in the dry form. They are typically sold in 0.05 mg to 0.10 mg (50-100 μg) amounts; the certified weight assures an accurate concentration when you add a specified amount of solvent. No need to weigh out the material – it is already done for you and the microgram amount means it is more economical as well. The GS-MS analysis of five reconstituted vials of endrin ketone is shown in the graph. The dry standard (50 μg of endrin ketone) was dissolved in methylene chloride using an internal standard to verify the recovery of compound in the reconstituted solution with RSD of 2.6% as shown.
Dry reference standards from CIL arrive in special conical vials. Keep the vials until ready for use, and then add solvent. The vials contain the precisely measured dry standard and have a capacity for 2 mL of solvent. Economical, easy to store and use, dry standards should be your standard for reliable results when solution stability problems arise.
