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* We had 5 µg of Cayman's leptomycin, lot # 194542-1, analyzed within one hour after its arrival.  We found it to have two impurities totaling 6% or more.

** Our prices are lower than other vendors', but there is no compromise in quality.  Read how we are able to accomplish this:  Product Quality Discussion.

*** Biorbyt is selling leptomycin B in a dried-down, solvent-free form.  The original report describing leptomycin B stated quite clearly that leptomycin B is unstable as a solid and cannot be dried down and then successfully used at its expected potency.  For example, we tested a sample of dried-down leptomycin B from a different vendor by treating it with methanol, an excellent leptomycin B solvent, and then doing an HPLC assay.  The result was a nice, clean-looking peak that showed high purity.  HOWEVER, THIS IS VERY MISLEADING -- IT WAS A NICE CLEAN PEAK, BUT WHEN CAREFULLY QUANTITATED, IT CONTAINED LESS THAN 40% OF THE EXPECTED AMOUNT OF LEPTOMYCIN B.  This indicates that drying leptomycin B down to a solid probably results in partial polymerization to a highly insoluble material that cannot be redissolved.  So, we are not showing prices for these vendors' dried-down leptomycin products because the expected recovery of actual leptomycin from dried-down material is far less than what is claimed on their labels, and thus not equivalent to leptomycin in solution.

NOTES:
1.  The purpose of our competitor price comparison tables is to enable our visitors to compare the prices and purities of products of nominally equivalent quality, for vendors whose price and purity claims are openly available from a website or catalog (without a need for the customer to contact the vendor and request a quotation in order to obtain a price and purity for a standard product size).  However, the quality comparisons in these tables are not absolute:  although our product purities are uniformly very high and are established by careful testing of every lot in our laboratories, we cannot and do not vouch for the purities claimed by other vendors in these competitor price comparison tables.  (We do carry out occasional testing of other vendors' products -- see below --  and we have found many instances where vendors' product purities are far below their claimed levels.)  Effective April 1, 2011, our price comparison tables only include products where a purity commitment is found together with sizes and prices on at least one page of the vendor's web site.

2.  Researching and compiling sizes and prices for the >140 competitive vendors and more than 135 products is an expensive and tedious task for our small company.  Thus, we typically only perform revisions of these tables annually or less frequently.  The date and source of each competitive vendor's prices is indicated at the bottom of this page.  Obviously, we make no guarantee that competitive vendor prices will remain unchanged in the interval between our annual revisions.  We may occasionally update individual competitive vendor information and add new competitive vendors as we locate them.

3.  In some circumstances we permanently remove vendors from our price comparison tables.  Circumstances that lead to permanent removal are: 

A.  If a vendor does not honor its advertised price (ignoring small price increases) for one or more products when an order is attempted.  Example:  a vendor listed a compound at $808 for 10 grams on its website price list, but quoted $4,500 per 10 grams upon our inquiry.  That vendor has been permanently removed from our price comparison tables.

B.  If, on a product-by-product basis, our analyses of a vendor's product show purities more than a few percent below the vendor's advertised purities.  Example:  a vendor advertises a purity for 97% for a compound, but repeated elemental analyses show a minimum of 9% inorganic material present, beyond any salt counterion.  Another example: an HPLC analysis at a relevant UV detector wavelength shows 92% purity for a vendor's product for which 98% purity is claimed.  We realize of course that UV absorbances for impurities can be higher than for the main compound, but our products meet our purity commitment of typically >99% irrespective of absorbance factors for impurities, and we apply that standard to products from other vendors.

C.  Again on a product-by-product basis, if a vendor makes no purity claim for a given product, then their product is not shown on that product table.

D.  If we find that, as a pattern, several of a competitive vendor's products fail to meet their advertised purity commitments by significant margins, then that vendor is permanently removed from all of our competitor price tables.

E.  Finally, if we determine that a vendor has provided fraudulent information on its website, in its literature or on a certificate of analysis, that vendor is permanently removed from all of our price comparison tables.

4.  IMPORTANT:  The presence of a competitive vendor entry in our price comparison tables does not necessarily mean that we have analyzed any of that vendor's products for purity; indeed, in most cases we have not.

5.  Please note:  where necessary, competitor prices are rounded to the nearest whole dollar.

To the best of our knowledge, the prices listed above for our competitors' products were correct as of the dates listed below for the sources of our annual price information update process.

Pricing Sources and Dates:  LC Labs - Current, Calbiochem - website - Dec 2011, Sigma - website - Jan 2012, MPBio - website - Dec 2011, Enzo - website - Dec 2011, AG Scientific - website - Jan 2012, Axxora - website - Dec 2011, Alomone - website - Dec 2011, LKT Labs - website - Dec 2011, Santa Cruz Biotech - website - Jan 2012, Cayman Chemical - website - Dec 2011, US Biological - website - Jan 2012, BioVision - website - Dec 2011, BioShop Canada - website - Dec 2011, GenDepot - website - Dec 2011, International Laboratory - website - Dec 2011, Alfa Aesar - website - Dec 2011, Cambridge BioScience - website - Dec 2011, AppliChem - website - Jan 2012, Advanced Technology - website - Dec 2011, biorbyt.com - website - Jan 2012, Abcam - website - Feb 2012.