Mark A Nussbaum

Two types of 3D printed devices for simultaneous mixing of small volumes (e.g., 50-500 mu L) of reactant solutions are described. One device (a "Flip-Lid") is a specially designed lid for commercially available 96-well plates, with which solutions in adjacent wells can be mixed by inversion. The other type ("Mix-Bricks") consists of two 3D printed parts: an interlocking "brick" that contains a selected number of wells of specified volume and a lid for mixing solutions in adjacent wells by inversion. In both cases, the lids contain transparent windows through which reactions can be visually monitored or recorded. The application of these devices to quantitative measurements was evaluated by use of an iodine clock reaction to quantify ascorbic acid in fruit juices and vitamin C tablets. A smartphone was used to record, via time-lapse video, the times at which color appeared as a function of ascorbic acid concentration, producing a linear calibration curve with time as the dependent variable. Up to 12 reactions, each involving four reactant solutions, were monitored simultaneously in a single device. Replicate measurements within a given device consistently yielded standard deviations of less than 5% RSD. Accuracy was evaluated by comparison of the vitamin C tablet results to those obtained by iodine titration and by HPLC-UV; all three methods were within 1.3% of the overall mean of 543 mg/tablet. These 3D printed devices thus show promise for simultaneous reaction monitoring in a wide variety of applications.

The interest in and use of microfluidic paper-based analytical devices (mu PADs) has grown exponentially over the last decade. Cellulose, and modified cellulose, has been used for centuries for making chemical measurements but devices made with this material traditionally suffered from either poor detection limits and/or limited ability to provide quantitative measurements. mu PADs address these problems by patterning paper to create microfluidic channel networks that can direct flow to different regions of the device without the need for external pumps used in most traditional microfluidic devices. Furthermore, because the devices are made from cellulose or modified cellulose using inexpensive manufacturing methods, the devices can be inexpensive and disposable. The ability to carry out multiplexed analysis without external pumps using inexpensive, disposable devices makes pPADs ideal for point-of-care (POC) analysis. The interest in pPADs has led to a number of excellent comprehensive reviews in the field; in this review, we do not attempt to reference the entire field but instead seek to highlight major developments as well as areas that will be important for future development of this field.

•Approaches for measuring and conveying mass balance.•Primary causes of mass imbalance with general approaches to mitigation.•The contribution of analytical variability to assessments of mass balance.•Importance of other reactants and stoichiometry in determinations of mass balance.•Examples of problems of mass balance associated with analytical methodology. Mass balance is an important concept in pharmaceutical development, but it often proves challenging to assess accurately. This article explores the various methods by which mass balance can and should be measured, expressed, and evaluated in conjunction with degradation chemistry. Causes of mass-balance issues and potential solutions are summarized, as are the advantages and the disadvantages of various detection strategies. The importance of reactants other than the parent drug, reaction stoichiometry, response factors, and assay variability are discussed, and recommendations for obtaining reliable and informative mass-balance information are provided.

We monitored benthic macroinvertebrates and adult caddisflies along an agricultural stream continuum upstream, within, and downstream of a small forested preserve. The habitat upstream of all sites was >60% disturbed by agricultural activities. The percentage of riparian disturbance was markedly lower adjacent to the sites inside the preserve than those outside. Water physicochemical factors did not exhibit clear changes among sites, except for nitrate concentration, which was highest upstream of the preserve. Biological diversity of adult caddisflies was significantly higher within the preserve. Biological diversity of benthic invertebrates exhibited similar results except for non-significance between the upstream and preserve sites. Pollution tolerance and percentage of filtering collector metrics were unchanged among sites for both assemblages. The percentage of adult caddisflies in the shredder functional group increased significantly within the preserve but remained small relative to that of pollution-tolerant filtering collectors. The small terrestrial preserve promoted a three-fold increase in species diversity, even without corresponding changes in water quality or trophic structure. Such an increase, however, may not be as detectable with traditional benthic biomonitoring techniques due to the difficulties of sampling benthic microhabitats representatively and identifying specimens to the species level.

Ultraviolet (UV) absorbance is the most widely used detection method for high-performance liquid chromatography (HPLC) separations. In pharmaceutical analysis, purity determinations often include quantitation of related impurities based on relative HPLC peak areas obtained at a specific wavelength. In order for this quantitation to accurately reflect weight percentages of impurities, the relative UV response factors (absorptivities) at the given wavelength must be known. In this work, we present a convenient method for determining relative UV response factors on-line, without isolation or purification of impurities, without standards, and without requiring known analyte concentrations. The procedure described makes use of a chemiluminescent nitrogen-specific HPLC detector (CLND) in conjunction with a UV detector. The CLND response is directly proportional to the number of moles of nitrogen in each eluting peak, and can, therefore, be used to determine relative amounts of each nitrogen-containing impurity present in the sample, provided the molecular formulas are known (e.g. from exact mass LC-MS). It is a simple matter, then, to determine the relative UV response factors from the UV area ratios obtained for the same sample. The feasibility and accuracy of this method is demonstrated for gradient HPLC separations of commercially available compounds of widely varying structures. Finally, the method's utility in obtaining accurate mass balance is demonstrated by application to photodegradation of nifedipine.

There are few methods available for the rapid and precise quantitation of non-covalent aggregation. The very methods used to measure the aggregation can easily disrupt the weak forces holding an aggregate together. This paper describes the novel application of free solution capillary electrophoresis (CE) for the quantitation of a biologically inactive non-covalent aggregate of C8GLIP (Des-amino-histidine-7-arginine-26 N ε-octanoyl-lysine-34-human glucagon-like insulinotropic peptide), an acylated peptide. The CE results are compared to a more traditional approach using size exclusion chromatography (SEC). Under the conditions explored in this paper, SEC showed a significantly slower apparent rate of aggregation than CE. This is due to the disruption of the aggregate during the SEC process. The cause of the disruption is complex and is potentially related to the separation process itself, on-column dilution effects, and/or interactions of the aggregate with the column packing or SEC components. Analysis times and dilution are greatly reduced by CE, and, because there is no potentially interactive stationary phase and because both the protein and the walls of the capillary are negatively charged, potential disaggregation due to surface interactions is reduced. Thus, CE is shown to be superior to SEC for this peptide in that disruption of the aggregate is minimized.