Polychromatic detection

Polychromatic detection. The most sophisticated detectors (e.g. DAD diode-array detectors) either allow the wavelength to be changed during the course of the analysis or simultaneously record the absorbance at several wavelengths. These detectors can be used not only to record the chromatogram but also to provide spectral information that can be used to identify the compounds. This is called specific detection (cf. 11.14). 

Ninhydrin-enpric nitrate for amino acids (polychromatic detection). 

The success of separation of colored compounds is usually monitored visually. Such compounds absorb a particular portion of the polychromatic (white) light in the visible wavelength range. The remaining radiation (complementary radiation) is reflected and detected by the eye it determines the color of the substance zone. Table 1 correlates the wavelengths, colors and complementary colors. 

Figure 1-8 shows log-log curves calculated from Barkla s absorption-coefficient data. (A log-log plot shows most clearly what Barkla discovered.) For carbon, the wavelength distribution is virtually unchanged from that of the incident polychromatic beam, mainly scattered x-rays being detected the situation is reminiscent of Figure 1-5. The curve for calcium, on the other hand, begins with a straight line that shows the presence in the scattered beam of a relatively intense component for which k is large and sensibly constant. The curve for tin shows two such components. Barkla realized that these components are emitted, and he eventually called them K and L spectra.22 He...

In recent years, the evolution of the technological components required for IR sensor systems has been denoted by a significant miniaturisation of light sources, optics and detectors. Essentially, an IR sensor consists of (i) a polychromatic or monochromatic radiation source, (ii) a sensor head and (iii) a spectral analyser with a detector. As sensors where all optical elements can be included in the sensor head are the exception rather than the rule, also various optics, waveguides and filters may form essential parts of IR-optical chemical sensors. Another important building block, in particular when aiming at sensors capable of detecting trace levels, are modifications of the sensor element itself. 

An ELSD converts the HPLC eluent into a particle stream and measures the scattered radiation. It offers universal detection for nonvolatile or semivolatile compounds and has higher sensitivity than the RI detector (in the low ng range) in addition to being compatible with gradient analysis. ELSD is routinely used in combinatorial screening. Response factors are less variable than that of other detectors. An ELSD consists of a nebulizer equipped with a constant temperature drift tube where a counter-current of heated air or nitrogen reduces the HPLC eluent into a fine stream of analyte particles. A laser or a polychromatic beam intersects the particle stream, and the scattered radiation is amplified by a photomultiplier. Manufacturers include Alltech, Polymer Laboratories, Shimadzu, Waters, Sedere, and ESA. 

The in vivo micronucleus test is used for the detection of damage to chromosomes as well as the mitotic apparatus in bone marrow or peripheral blood cells of rodents. The assay system has been well standardized.14-17 The basic features of the test system are (1) the effect of the test chemical is observed in anucleated polychromatic erythrocytes (PCEs) (2) PCEs have a relatively short lifespan, so that any micronuclei they contain must have been generated as a result of recently induced chromosome damage (3) micronuclei are readily identifiable and their distribution is well defined and (4) the frequency of induced micronuclei in PCEs is dependent on sampling times. 

Genotoxic effects have been reported in animals treated with 3,3 -dichlorobenzidine. A single dose of 3,3 -dichlorobenzidine (1,000 mg/kg) administered to male and pregnant female mice induced micronuclei in polychromatic erythrocytes in the bone marrow of the males and in the liver of the fetuses, but not in bone marrow of the dams (Cihak and Vontorkova 1987). A micronucleus test is performed to detect a chemical s ability to induce chromosomal aberrations. However, the relevance of micronuclei formation to human health is not known. The reason for the lack of effect of 3,3 -dichlorobenzidine on bone marrow micronuclei formation in the mothers is unclear, but it may be related to deficiencies in the metabolic activation of 3,3 -dichlorobenzidine in female mice. The relative importance of pregnancy is unknown since the study did not evaluate nonpregnant females. In another study, an increase in unscheduled deoxyribonucleic acid synthesis (UDS) was observed in cultured liver cells from male mice previously pretreated orally with single doses of 500 mg/kg 3,3 -dichlorobenzidine no response was observed at a dose of 200 mg/kg (Ashby and Mohammed 1988). 

Animals, usually rodents, are exposed to the test substance by an appropriate route, usually by gavage or by intraperitoneal injection. Each treated and control group must include at least five animals per sex. Positive controls should produce micronuclei in vivo at exposure levels expected to give a detectable increase over background. No standard treatment schedule (i.e., 1, 2, or more treatments at 24-h intervals) has been recommended. Three dose levels are generally used these should cover a range from the maximum to little or no toxicity. The erythrocytes are sampled from the bone marrow and/or peripheral blood of the animals. If bone marrow is used, the animals are sacrificed at appropriate times after treatment, the bone marrow extracted, and preparations made and stained. When peripheral blood is used, the blood is collected at appropriate times after treatment and smear preparations are made and stained. Preparations are analyzed for the presence of micronuclei. An increase in the frequency of micronucleated polychromatic erythrocytes in treated animals is an indication of induced chromosome damage. 

The test is used for the detection of cytogenetic damage to the chromosomes or the mitotic apparatus of erythroblasts by analysis of erythrocytes for formation of micronuclei (small nuclei, separate from and additional to the main nuclei of cells, produced during the telophase of mitosis (meiosis) by lagging chromosome fragments or whole chromosomes). When a bone marrow erythroblast develops into a polychromatic erythrocyte (immature erythrocyte), the main nucleus is extruded any micronucleus that has been formed may remain behind in the otherwise anucleated cytoplasm. 

The photolysis of 1,3-dichlorotetrafluoroacetone has been studied by Bowles et al.,64 using the 3130 A. line from a medium pressure mercury vapor arc, and by Haszeldine and Nyman46 using a polychromatic source. The products of photolysis, as detected by gas chromatography and mass spectrometry, are given in Table III. 

Only few small angle scattering experiments have been performed with this techniquehowever, which is due to the potential deterioration of organic material in the polychromatic beam and the count rate limitation of the detection system. Current applications of this method ly mainly in the area of special environment experiments, e.g. under high pressure and for small structures. 

---