Analytical mass load

CE presents potential advantages in forensic science to carry out the analysis of opium alkaloids, as it can be in the different applications being published. Nevertheless, the lack of the sensitivity required for this type of analysis is always a great problem. One of the most basic approach for sensitivity enhancement is based on increasing analyte mass loading via online sample preconcentration techniques. The most widely employed in the analysis of major alkaloids is FASI that basically consists in a mismatch between the electric conductivity of the sample and that of the miming buffer. It is achieved by injecting the sample diluted in a solvent of lower conductivity than that of the carrier electrolyte. Upon the application of the... 

The loading capacity of SEC columns is quite modest compared to interactive modes of chromatography. A rule of thumb dictates that the sample volume capacity is about 2% of the column volume. A typical analytical SEC column with dimensions of 8 x 300 mm has a VM of 10 to 11 ml, providing a sample volume limit of about 200 pi. The mass loading limit for such a column is about 1 to 2 mg. Above these volume and mass limits, resolution will be compromised. Sample capacity will scale in proportion to column volumes for different column lengths and diameters. 

Nevertheless, these methods all result in a filter that captures the atmospheric particles. The mass loading can be large, the deposit uniform, and the filter reasonably stable under transport to a central analytical laboratory. Numerous papers have treated analysis of such filters, so this information is not repeated. This chapter focuses on the problems of chemical analyses of impactor substrates, for which the problems are more serious and the solutions elusive. 

Surface mass changes can result from sorptive interactions (i.e., adsorption or absorption) or chemical reactions between analyte and coating, and can be used for sensing applications in bodi liquid and gas phases. Although the absolute mass sensitivity of the uncoated sensor depends on the nature of the piezoelectric substrate, device dimensions, frequoicy of operation, and the acoustic mode that is utilized, a linear dependence is predicted in all cases. This allows a very general description of the working relationship between mass-loading and frequency shift, A/ , for AW devices to be written ... 

The relative importance of the mass-loading and viscoelastic contributions to the observed acoustic sensor response is an issue that has yet to be resolved. Capitalizing on these effects to improve chemical selectivity and detection sensitivity requires further characterization of sensor response, in terms of both velocity and attenuation changes, in addition to more accurate models describing how coating-analyte interactions affect relevant film properties. 

In the somewhat rare instance that the coating (even when loaded with analyte), remains highly elastic, mass loading may be the only operative interaction mechanism. In this case, as the total coating-plus-anaiyte thickness reaches and exceeds several percent of one acoustic wavelength, the mass sensitivity deviates significantly from that derived from perturbation analyses for acoustically thin films, and is difficult to predict. 

In addition to receptor-type proteins, bilayer lipid membranes (BLMs) have been investigated for the detection of species of biochemical interest [221, 231,232]. The lipid film can be used alone, or chemical receptor agents can be incorporated into the membrane to enhance selectivity for inorganic ions or organic compounds/ions. Responses for BLM-coated devices are related to the mass loading of the analyte in/on the lipid film and to changes in interfacial conditions, e.g., elastic and viscous coupling effects [53,221-223]. 

All scaling of all parameters of the separation should be in proportion to the column volume. The sample load, in terms of both mass load and volume load, should be scaled in proportion to the column volume. Also, flow rates should be scaled in proportion to the column volume, at least when the scaling column and the preparative column contain the same particle size. Unfortunately, this is not always possible. Chromatographic instruments designed for preparative chromatography usually have a lower pressure capability than analytical instruments. In this case, a reduced flow rate is used, and one simply needs to accept the longer run times. Even if the flow rate cannot be scaled in proportion to the column volume, the load should still be scaled in proportion to the volume. 

We have developed a proprietary acoustic wave device which permits the detection of a specific analyte in a flowing system. By coupling specific chemistry (Protein A) to the surface of the device, the mass loading of the device by the target analyte (Human IgG) was detected as a shift in phase which was measured in real time. Using conditions which mimic a bioprocess separation for IgG, we were able to separate and detect Human IgG at 1 mg/ml and 100 ug/ml in the absence and presence of 10% Fetal Bovine Serum. Such a detector has the potential to increase productivity in process chromatography in biopharmaceutical applications. 

---