Indicator tests, qualitative analysis

Qualitative analysis for the elements. This includes an examination of the effect of heat upon the substance—a test which inter alia will indicate the presence of inorganic elements—and quahtative analysis for nitrogen, halogens and sulphur and, if necessary, other inorganic elements. It is clear that the presence or absence of any or all of these elements would immediately exclude from consideration certain classes of organic compounds. 

Students usually identify the existence of anions such as carbonate, iodide and sul-fate(VI) by adding a barium/silver(I)/lead(II) solution to the unknown, followed by a dilute acid or vice-versa in qualitative analysis practical work sessions and examinations. Mat r students had difficulty understanding the roles of the bar-ium/silver(I)/lead(II) solution and the dilute acid in the tests for anions. For example, 20% believed that the addition of aqueous barium nitrate(V) followed by dilute nitric(V) acid was to test for sulfate(VI) only. Another 25% believed that to test for a carbonate, acid had to be added directly to the unknown sample, while 20% believed that the addition of barium nitrate(V) invalidated the test for carbonates. When the students were asked the purpose of adding dilute nitric(V) acid following die addition of silver nitrate(V) solution (in one question) and lead(II) nitrate(V in another question) to the unknown solutions, 22% and 35%, respectively, indicated... 

Qualitative Analysis.—The minium is treated with dilute nitric acid effervescence indicates carbonates in the solution the lead is precipitated by means of hydrogen sulphide, the filtrate being tested for zinc, iron, aluminium, calcium and magnesium by the ordinary methods. The brown residue insoluble in nitric acid is heated further with nitric add in presence of either sugar solution or hydrogen peroxide until the lead dioxide is completely dissolved any insoluble residue then remaining may contain lead sulphate, barium sulphate or clay, which may be identified in the usual way. 

Qualitatively, the presence of the nonulosaminic acids is best indicated by the brilliant-red coloration formed on addition of an acidic solution of p-dimethylaminobenzaldehyde (the so-called direct Ehrlich reaction ), and by the bright-purple coloration which develops upon boiling with Bial s reagent for several minutes at 100°. In addition, the nonulosaminic acids give a blue-violet coloration with Dische s diphenylamine reagent for deoxypentoses and a positive reaction in the tryptophan-perchloric acid test. Since no single one of these color reactions is absolutely specific for a nonulosaminic acid, it is advisable to carry out at least two of these for a qualitative analysis. For quantitative determinations, all four reactions have been employed, using either A/ -acetylneuraminic acid (m. p., 183-185° [a] —32.0°) or methoxyneuraminic acid [m. p., 200° (dec.) [a]o —55.0°] as colorimetric standards. 

A ruby laser pulsed irradiation of Ge/Si heterostructures with Ge nanoclusters (quantum dots) at the irradiation energy density near the melting threshold of Si surface has been studied by means of Raman spectroscopy and by numerical simulation of the laser-induced processes. Two types of the structures have been tested. They differ mainly in the depth of nanoclusters occurence (0.15 and 0.3 pm). From the RS analysis one may conclude that laser irradiation results in different changes of QD properties. The decrease of QD size dispersion is observed in the samples with QDs at 0.3 pm, this effect is not observed in the samples with QDs at 0.15 pm. The numerical simulation of laser heating shows that the QDs are in a molten state for the same time, but the induced temperatures of nanoclusters for the two depths differ by -100 K. This result indicates that qualitatively different effects of the laser irradiation may be connected with different temperatures of QDs during laser irradiation. 

Suitable mathematical expressions representing the fault tree entries may be developed using Boolean algebra. When more than one event on a chart can contribute to the same effect, the chart and the Boolean expression indicate whether the input events must all act in combination (and relationship) to produce the effect, or whether they may act singly or relationship). The probability of failure of each component or of the occurrence of each condition or listed event is then determined. These probabilities may be from actual failure rates vendors test data comparison with similar equipment, events, or conditions or experimental data obtained specifically for the system. Hie probabilities are then entered into the simplified Boolean expressions. The probability of occurrence of the undesirable event being investigated may then be determined by calculation. When an FTA is used for qualitative analysis, care is required in the description of each event to be sure it can be fitted with a suitable probability. 

If an appreciable amount of residue remains, note its colour. Add a few drops of water and test the solution (or suspension) with htmus or with Universal indicator paper. Then add a httle dilute hydrochloric acid and observe whether efiervesceiice occurs and the residue dissolves. Apply a flame test with a platinum wire on the hydrochloric acid solution to determine the metal present. (In rare cases, it may be necessary to subject a solution of the residue to the methods of qualitative inorganic analysis to identify the metal or metals present.) If the flame test indicates sodium, repeat the ignition of the substance on platinum foil. 

Selection of a suitable analytical method can be made once the reason for carrying out the analysis is well understood. Analytical methods may be (a) qualitative or (b) quantitative or semi-quantitative. The former usually pose few problems if only an indication is required as to whether a particular analyte is present or not - certainly not how much with a value having a small uncertainty. If a negative result is required (i.e. confirmation of absence from the product), then one has only to worry about the limit of detection of the test used. Many tests to confirm the absence of impurities in pharmaceutical products fall into this category. Equally, rapid tests for positive confirmation are often made on unknown substances. These may subsequently be confirmed by other, quantitative tests. Quantitative methods are used in a variety of situations and a variety of different methods can be employed. What you must always remember is that the method used must be fit for the purpose. 

The problem of toxic subjects detection in the tested objects can be solved by two options chemical analysis, for revealing separate toxics, or their products, and biotesting with the result of the tested samples toxicity degree indication without identification of the agent. Qualitative and quantitative chrmical/analytical methods allow with the higher accuracy and, in some cases, rapidly detect presence of the separate toxics or their products in the tested objects. It is important for the regular detection of the different pollutions of any agents in the tested objects. 

Even if quantitative results are more often expected for wastewater quality measurement, qualitative information is of great interest, as is the case for other applications of the analytical sciences (in the health sector, the use of test kits and biodiagnostic systems leads to quick and useful information, often far from a classical analytical result). In fact, quantitative analysis gives the concentration not only of one substance, but also of a group of comparable substances (surfactants, PAH,...), and even the value of a specific (TOC, TKN,...) or aggregate (BOD, COD, toxicity,...) parameter. In this context, total indices are often proposed as parameters complementary to classical analytical results [1]. 

If the two-factor cases considered here were known to originate (at least approximately) from a normal population, the standard randomized block experiment approach would be admissible for testing the significance of the block effect. A detailed discussion of this technique, widely documented in the statistical textbook literature, is omitted. Table 10 indicates the possibility of drawing qualitatively identical inferences from nonparametric and conventional analysis of variance, even if only one of the two is correct, in principle. 

Analysis. Be can be quantitatively determined by colorimetry down to 40 ppb using eriochrome cyanine R or acetylacetone. The sensitivity may be improved by electrothermal absorption spectroscopy (ETAS) to 1 ppb and to 0.1 ppb by inductively-coupled plasma emission spectroscopy (ICPES) or inductively-coupled plasma mass spectroscopy (ICPMS). A simple spot test for qualitative detection of Be is one with quinalizarin in alcoholic NaOH which can detect 3 ppm. The color is produced by both Be and Mg. If the color persists after the addition of Br2 water. Be is present. If the color is bleached. Mg is indicated. 

Coupling chromatographic procedures with immunochemical techniques can also provide a very sensitive and specific analytical system for either determinative or confirmatory analysis. If the antibody used is very specific for the analyte of interest and the antibody reactivity is known to be sensitive to small variations in the structure of the analyte tested, positive reactions with the method are strongly indicative that an analyte of defined structural characteristics is present in the sample. Full rigorous confirmation, however, would depend on further analysis by mass spectrometry, which is the method of choice in confirmatory analysis. Mass spectrometry gives specific information on the identity and structure of the compound of interest. Coupled with chromatographic techniques it becomes a very powerful confirmatory tool for both quantitative and qualitative assessment of drug residues in foods. 

Using the LTF scheme, the study of effluent discharge situations at 16 Ontario pulp and paper mills has illustrated predominantly moderate to strong qualitative relationships between toxicity tests and ecosystem indicators (fish populations and benthic invertebrate communities). Ceriodaphnia- to-benthos, Selenastrum-to-benthos and fathead-to-fish survey relationships were qualitatively rated strong or moderate in 94%, 75% and 60% of the sixteen studies, respectively. Regression analysis of LTF scores has revealed that the relationship between the Ceriodaphnia reproduction test and benthic invertebrate field survey measurements was significant (p < 0.001, r = 0.79). However, there were not sufficient data to determine if this can be used as a predictive tool (Borgmann et al., 2004). 

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