Maximum Detection Sensitivity Research Articles

General method for the separation of cyanogen bromide digests of proteins by high-performance liquid chromatography : Rabbit skeletal troponin I

In this study, we have demonstrated the necessity for a combination of size-exclusion, exclusion, ion-exchange and reversed-phase high-performance liquid-chromatography to resolve completely a protein digest. Our approach minimizes the number of steps, and the column order provides the maximum information about the properties of the fragments. The order is: (1) size-exclusion (Bio-Rad TSK-250 column), (2) strong cation-exchange (Synchopak S300 column), and finally (3) reversed-phase chromatography (Ulrapore C3). It was desirable for the first step of the procedure to be size-exclusion chromatography to produce the least of fractions. The volatile eluent used in size-exclusion eliminated the need for subsequent sample desalting. Volatile buffers were not necessary for the ion-exchange chromatography, since the fractions were both desalted and purified in the final reversed-phase step. All column effluents were compatible with adsorbance measurements at 210 nm to provide maximum sensitivity for peptide detection. The results obtained in this study strongly suggest that the combined use of three methods of separation, which utilize different selectivities (size, charge, hydrophobicity), can provide excellent resolving power for peptide separations. We believe this fast, efficient procedure should be generally applicable to other protein digests.

A quarantine protocol for analysis of returned extraterrestrial samples

A quarantine protocol is presented for analysis of samples of extraterrestrial material that might be returned from space to an Earth-orbiting quarantine facility. The protocol is designed to detect biologically active agents in extraterrestrial soil. Its goal is either to certify the sample safe to return to a terrestrial containment facility where extensive biological, chemical, geological and physical investigations can be conducted, or to detect “biological effects” thus dictating second order testing. The protocol requires 46 grams of a one kilogram returned sample plus 54 grams to be reserved for second order testing should that become necessary. The protocol operates at two levels. First, it seeks to detect the presence of any replicating organisms or toxic substances using chemical analyses, microscopy, metabolic tests, and microbiological culturing techniques. The second level involves hazard evaluation by adding any agents found at the first level (or the extraterrestrial soil) to challenge cultures of terrestrial species. The specific types of experiments and the means of executing them were chosen by participants in an American Society for Engineering Education Summer Systems Design Group to provide maximum life detection sensitivity, yet are compatible with a small crew operating behind biological barriers in a condition of weightlessness.

Infrared surveillance 2: Continuous-time signal processors

A number of infrared passive surveillance receivers are analyzed with the theory developed in a previous paper. The specific problem of interest is the detection of low-contrast point source targets against high-contrast structured backgrounds. A new and promising approach to signal processing is proposed for minimizing background-induced false alarms while retaining maximum target detection sensitivity. We show that time-delay and integration detector technology may afford us excess detector sensitivity that we can intentionally sacrifice in the interest of enhanced performance against structured scenes.

Air pollution measurement by Fourier transform spectroscopy

The use of infrared methods in pollution measurement has been hampered by sensitivity limitations and by interferences from water vapor. Fourier transform spectrometer systems reduce these limitations by their high optical efficiency and their ability to manipulate spectra for removal of interfering bands. At the Environmental Protection Agency we have sought to further increase the sensitivity of the infrared technique by evolving optimal long path cell designs and sample concentration techniques. Reactive pollutants such as O(3), H(2)O(2), HNO(3), HNO(2), H(2)CO, HCOOH, PAN, HCl, NH(3), NO, and NO(2) are best measured in the open atmosphere. In this case one strives toward large absorption cells with the paths as long as practical. Our largest cell is being used to measure pollutants in the smog at Riverside, California. This cell uses an eight-mirror system for multiple-passing radiation along a 23-m base path, yielding total paths measured in kilometers. Reactive gases at levels of just a few ppb have been measured. For measuring nonreactive pollutants, such as hydrocarbons and halocarbons, maximum detection sensitivity is achieved with small folded-path cells rather than with large cells. In this case a pollutant concentrate is prepared and introduced into a miniaturized multiple-pass cell designed for maximum path-to-volume ratio. Cryogenic trapping to separate the pollutants from the major constituents of the air has yielded concentration factors as high as one million. The smallest multiple-pass cell we have built to date encloses a 115-cm light path within a volume of 3 cm(3). This cell when used with the FTS spectrometer and mercury-cadmium-telluride detector permits the detection of nanogram quantities of pollutant gases. Measurements have been made of trace gases in the air at mixing ratios as low as 2 x 10(-11).

Linear elution adsorption chromatography : VII. gradient elution theory

The fundamental correlational equations previously developed for normal, linear elution from alumina, silica, and Florisil have been extended to include the technique of gradient elution. It has been shown that in general the eluent gradient should be of the linear strength form. The theoretical advantages of linear strength gradient elution include: (I) approximately equal spacing of solute peaks according to increasing solute adsorption energy,providing maximum resolution between both weakly and strongly adsorbing solutes with minimum separation time; (2) approximately equal band widths for maximum detection sensitivity; (3) no band splitting with development of spurious double peaks; (4) easily calculable retention volumes for solutes whose adsorption parameters have been measured or can be estimated. For some sample types a mildly convex eluent strength gradient is predicted to give a better separation system, although the advantage over the corresponding linear strength case will normally be small. The use in gradient elution of solvents of widely differing strengths can lead to displacement, rather than elution. with resulting loss of resolution for weakly adsorbing. The expermental condition required for displacement to occor are discussed, as is the avoidance of this phenomenon through various means including the use of ternary solvent mixtures. The theoretical stregnth of such ternary eluent has been derived as a function of the eluent composition and the stregnth of the pure constituent solvent.

Industrial radiography and the linear accelerator

To obtain maximum sensitivity of flaw detection in the radiographic examination of thick specimens encountered in heavy engineering, several aspects of the X-ray equipment must be considered. The most important factors are the energy of the radiation and the size of the source, while in order to obtain reasonably short exposure times a large X-ray output is required.The paper shows that, due to the complex process involved, the absorption of radiation at first decreases as energy is increased, but reaches a minimum and thereafter rises to some asymptotic value. The energy for minimum absorption depends on the absorbing substance, but for the materials used in engineering it will be some few MeV. Since the inherent unsharpness of the photographic image increases with energy, it can be shown that optimum results may be expected with equipment operating at an energy of the order of 4 MeV.The development of the travelling wave linear accelerator, which is briefly described, has made possible compact equipments to operate at such an energy, and the results of investigations into the suitability of such equipments for industrial radiography are given.