Quantitative estimation methods

This range is a confidence interval of the average of two values with a Student s t value of 2, which corresponds to a free degree of forty six with which the average coefficient of variation is known. So for benzene the only value of LD50 provided by Sax (3306 mg/kg) would lead to the following range  

Note that this large range contains the value 930 mg/kg, which comes from another source and would have justified application of code R22. This example thus illustrates the fact that one has to be careful in this particularly serious context of toxicity risk. This approach to estimation by range is another reason why the approach to estimation by regression as seen in paragraph 3.4 should be used. 

There are only two animals that are used in the search for criteria rat (intoxication by inhalation, skin and orally) and rabbit (by skin). The only means of penetration that can be used are inhalation, skin and orally. When a substance is not subjected to regulations, the absence of one or several animal/means of penetration combinations prevents the proposal of any level of danger for the substance labelling and also any suitable prevention measures. 

With the other risks the emphasis is placed on the importance of having available a quantitative evaluation method. Although it seems difficult, it would also be useful for toxicity. The following paragraph illustrates an approach, which used to be used in France by the old PUCK L This is followed by an introduction to the approach suggested in paragraph 3.6. 

Safety and risk factors evaluate approximately the speed at which a toxic substance reaches a toxic vapour concentration in air. An accurate way to do this would be to know the vapourisation speed for this substance and the air renewal rate of the room in which it is handled. This is why regulations recommend measurement of the vapourisation speed for a particular substance and include it in safety sheets. One can hardly use this figure since it is rarely mentioned. The only substances which were subjected to such measurements are the most commonly used although these figures only are remotely linked to the real conditions. So it was decided to suggest a method derived from the vapour pressure of the substance, which is a factor the vapourisation speed depends on precisely. 

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B29. Bush, I. E., Advances in direct scanning of paper chromatograms for quantitative estimations. Methods Biochem. Anal. 11, 149-209 (1963). 

The same method can clearly be applied to the quantitative saponifica- tion or hydrolysis of most esters. Hence it may equally well be used for the quantitative estimation of a known ester in a crude sample. 

In the previous section we described several internal methods of quality assessment that provide quantitative estimates of the systematic and random errors present in an analytical system. Now we turn our attention to how this numerical information is incorporated into the written directives of a complete quality assurance program. Two approaches to developing quality assurance programs have been described a prescriptive approach, in which an exact method of quality assessment is prescribed and a performance-based approach, in which any form of quality assessment is acceptable, provided that an acceptable level of statistical control can be demonstrated. 

Quantitative estimation of cyclohexane in the presence of benzene and aUphatic hydrocarbons may be accompHshed by a nitration-dehydrogenation method described in Reference 61. The mixture is nitrated with mixed acid and under conditions that induce formation of the soluble mononitroaromatic derivative. The original mixture of hydrocarbons then is dehydrogenated over a platinum catalyst and is nitrated again. The mononitro compounds of the original benzene and the benzene formed by dehydrogenation of the cyclohexane dissolve in the mixed acid. The aUphatic compound remains unattacked and undissolved. This reaction may be carried out on a micro scale. 

Several instmmental methods are available for quantitative estimation of from moderate to trace amounts of cerium in other materials. X-ray fluorescence is widely available, versatile, and suitable for deterrninations of Ce, and any other Ln, at percent levels and lower in minerals and purer materials. The uv-excited visible luminescence of cerium is characteristic and can be used to estimate Ce content, at ppm levels, in a nonluminescing host. X-ray excited optical luminescence (15), a technique especially appropriate for Ln elements including cerium, rehes on emissions in the visible, and also measures ppm values. Atomic emission spectrometry is appHcable to most lanthanides, including Ce (16). The precise lines used for quantitative measurement must be chosen with care, but once set-up the technique is suitable for routine analyses. 

There have been also found the quantitative characteristics of the methods. They are as follows for HPLC method the linearity is 0.1 ng to 2 ng the detecting limit is 0.1 ng the limit of the quantitative estimation makes up 0.0004 mg/kg a coefficient of variation is 2.74% for the chromatodensitometry method the linearity is 2 ng to 10 ng the detecting limit is 0.6 ng the coefficient of variation is 2.37%. The data obtained have been treated using a regressive analysis. 

This technique provides quantitative information about tautomeric equilibria in the gas phase. The results are often complementary to those obtained by mass spectrometry (Section VII,E). In principle, gas-phase proton affinities, as determined by ICR, should provide quantitative data on tautomeric equilibria. The problem is the need to correct the measured values for the model compounds, generally methyl derivatives, by the so-called N-, 0-, or S-methylation effect. Since the difference in stability between tautomers is generally not too large (otherwise determination of the most stable tautomer is trivial) and since the methylation effects are difficult to calculate, the result is that proton affinity measurements allow only semi-quantitative estimates of individual tautomer stabilities. This is a problem similar to but more severe than that encountered in the method using solution basicities (76AHCS1, p. 20). 

Acetylation.—Gitronellal may be quantitatively estimated by the ordinary acetylation process i when the aldehyde is quantitatively converted into isopulegyl acetate, which is then determined by saponification with potash in the ordinary way. Dupont and Labaume have attempted to base a method for the separation of geraniol from citronellal in citron-ella oils on the fact that the citronellal oxime formed by shaking with hydroxylamine solution at the ordinary temperature is not converted into an ester by subsequent acetylation, but into the nitrile of citronellic acid which is stable towards" alkali during the saponification process. 

In as far as other analytical methods are concerned, many specific reactions have been elaborated for the quantitative determination of 2-deoxy aldoses. 2-Deoxy-D-ribose (2-deoxy-D-erythro-pentose), a compound which was recognized early as playing an important role in biological systems, has been of particular interest. Overend and Stacey (43) have given a critical review of the methods available until 1952 for the estimation of 2-deoxy pentoses. A recent summary of specific methods for the identification and quantitative estimation of the different classes of deoxy sugars has been prepared by Dische (13). 

To obtain reliable, accurate, and reproducible methods for quantitative estimation of deoxy sugars, certain conditions must be fulfilled. Thus, it is necessary that the chromogen be formed quantitatively from the sugar. The chromogen must then react quantitatively with the compound used for color formation, and lastly, the dye, once formed, should be stable and have a well defined molar extinction coefficient. In methods in which all of these conditions are not or cannot be fulfilled, recourse must be had to simultaneous determinations with suitable standard substances, a requirement not always easy to fulfil. 

The problems involved in quantitative analysis using NMR spectroscopy, have been discussed by several authors and it is evident that it still causes a lot of problems as especially pointed out by Hays55 in his excellent review on the subject. Thus in liquid state NMR spectroscopy the quantitative estimation of atoms and groups involves the use of normal analytical method. In the case of solid state NMR spectroscopy, however, the application of the cross-polarization technique results in signal enhancements and allows repetition rates faster than those allowed by the carbon C-13 Tl. Therefore, the distortion of relative spectral intensities must always be considered a possibility, and hence quantitative spectra will not always be obtained. 

Quantitative estimates are available for the amoiint of hordenine in malt roots as well as in dried malt (23) For gramine, only a quantitative estimate for the amount found in acrospires is available (2U). Because non-specific colorimetric methods were used to determine the amounts of these alkaloids in malt, the quantitative data can only be considered approximate. 

There are three main methods for quantitative estimation of an analyte after isolation on thin-layer chromatoplates ... 

The zone elution method has been used for quantitative estimation or recovery of heavy metals in plants and vegetable juices [29], mercury (11) in river and waste waters [52], zinc in different environmental samples [46], nickel and copper in alloys [53], zirconium in Mg-Al alloys [22], cobalt, zinc, nickel, and copper in natural water and alloy samples [54], thiocyanate in spiked photogenic waste water [55], and aluminum in bauxite ores [42],... 

Quantitative estimates of microbial and community structure by means of analysis of the phospholipid fraction have been performed on. sediments, water (135), and dust (136) as well as. soil (137-141). The method is applicable to the study of mixed populations of varying degrees of complexity and is relatively straightforward to perform. A selection of studies involving the analysis of fatty acid profiles of environmental samples are outlined in Table 6. 

Organotin stabilisers in PVC compositions were determined by means of TLC [518]. The determination of inorganic species (down to ppb range) by TLC has been reviewed on several occasions [519,520]. Instrumental methods successful in the quantitative estimation of inorganic TLC zones directly on the plate are densitometry, fluorimetry, radiometry, planimetry and visual methods. In the framework of recycling studies, in particular as to metal stabilisers in PVC, Braun and Richter... 

Although widely used, colorimetric methods for determining total ur-onic acid and hexosamine are now regarded as providing, at best, only semi-quantitative estimates of heparin.42 Colorimetric reactions in a strong acid, such as the carbazole reaction for the uronic acids48 and the Morgan-Elson reaction for the hexosamines,49 are not specific for hepa-... 

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