Pharmaceutical and biotechnology research requires instrumentation to be both functional and versatile. In the HTS and Drug Discovery environments, microplate-based assays are developed to make determinations on large numbers of samples. Regardless of the assay protocol, the end result is the measurement by some sort of detection device. Towards that end, BioTek has developed Synergy HT Multi-D...

Failure to account for fluorescein absorbance changes with pH may be responsible for some of the apparent non-conservative behaviour of this easily detectable tracer compound. While it is possible to calculate an accurate absorptivity value for fluorescein at every pH, this calculation is not necessary if the sample pH is increased above pH 9 before measuring the absorbance. Intense sunlight de...

The absorbance of the organic water tracer compound fluorescein is known to be pH dependent but differences between the reported pK a values make it difficult to predict these absorbance changes. A new pK a determination method, which incorporated activity corrections, was used to calculate the pK a values of fluorescein. Several published pK a values were re-evaluated and were in agreement onc...

Episulfides were determined by a simple colorimetric assay using 4-(p-nitrobenzyl)-pyridine, which has been used previously for the detection and analysis of epoxides, organophosphates, and other alkylating agents. With episulfides, absorbance was directly proportional to concentration up to an absorbance of at least 1.0. No interference was observed with a variety of non-episulfide sulfur-cont...

We determine optical absorption cross sections of single-wall carbon nanotubes for visible light copolarized and cross polarized with respect to the nanotube axis. The need for perfectly aligned ensembles in absorbance measurements is eliminated by using Raman scattering to measure the nematic order parameter in magnetically aligned nanotube suspensions. The absorbance data allow the first quan...

The high-potential 4Fe-4S* center ofAzotobacter vinelandii ferredoxin I has been titrated potentiometrically by a reductive procedure. The absorbance decrease at 510 nm accompanying the reduction of the high-potential center titrated with an Em of 320 mV (n = 1). The low-potential 4Fe-4S* center was titrated by using the absorbance decrease at 410 nm to monitor its reduction. This center exhibi...

The dye reagent is buffered by M/10 phosphate salts at pH 7.4 and is prepared by dissolving 12.07 gm. anhydrous disodium hydrogen phosphate powder, 2.04 gm. potassium dihydrogen phosphate crystals, 2.60 gm. sodium arsenite powder, and 2.10 gm. sodium fluoride powder in 1 L. of distilled water. Sufficient 2,6-dichlorobenzenoneindophenol sodium is added to bring the absorbance of the solution to ...

The UV-visible diode array spectrophotometer is a work-horse instrument for many laboratories. This article provides simple data acquisition and control routines in Microsoft QuickBasic for a HP-8452A diode array spectrophotometer interfaced to an IBM PC/XT/AT, or compatible, microcomputer. These allow capture of full spectra and measure absorbance at one or several wavelengths at preset time i...

In this Laboratory Exercise, we will determine the amount of active ingredient in a commercial face wash; Sodium Salicylate. We will accomplish this by conducting a spectrophotometric analysis of the preparation at the wavelength of maximal absorbance for this compound when complexed with Fe 3+ . The resulting absorbance measurement will be correlated against calibration standards, using Beer’s...

Nicotinium dichromate (NDC) oxidation of pentaamminecobalt (III) complexes of ∝ hydroxy acids in micellar medium yielding nearly 100% of keto acid complex is ultimate product. The decrease in UV-Visible absorbance at 502 nm for Co(III) complex corresponds to nearly 0% reduction of the initial absorbance. The stoichiometry of unbound ligand and cobalt(III) complex is accounting for no reduction ...