Total residue

Although every redox titrimetric method has its own unique considerations, the following description of the determination of total residual chlorine in water provides an instructive example of a typical procedure. 

Fig. 7. Toxicity of chlorine to aquatic organisms, (a) Time-dependent mortaUty (50%) of four example species in various levels of total residual chlorine in the laboratory, where for A, A.losa aestivalis and B, Salmogairdnerii r (correlation coefficient of the curve) = —0.96 and for C, P/euroneetesplatessa and D, Salmo trutta r = —0.98. (b) A summary of chlorine toxicity to freshwater species, indicating overall no-effect thresholds for acute and chronic exposures. Numbers indicate where more than one test yielded the same result. A different summary figure appHes to marine organisms because of differences in the...

Environment Tube side Sea water, 0.25 ppm total residual chlorine, continuous, 40-90°F (4-32°C), pH 7.5-8.5, pressure estimated 15-50 psig (103-345 kPa), tubes supported by support plates... 

The amount of residual sulfonate ester remaining after hydrolysis can be determined by a procedure proposed by Martinsson and Nilsson [129], similar to that used to determine total residual saponifiables in neutral oils. Neutrals, including alkanes, alkenes, secondary alcohols, and sultones, as well as the sulfonate esters in the AOS, are isolated by extraction from an aqueous alcoholic solution with petroleum ether. The sulfonate esters are separated from the sultones by chromatography on a silica gel column. Each eluent fraction is subjected to saponification and measured as active matter by MBAS determination measuring the extinction of the trichloromethane solution at 642 nra. (a) Sultones. Connor et al. [130] first reported, in 1975, a very small amount of skin sensitizer, l-unsaturated-l,3-sultone, and 2-chloroalkane-l,3-sultone in the anionic surfactant produced by the sulfation of ethoxylated fatty alcohol. These compounds can also be found in some AOS products consequently, methods of detection are essential. 

Neither endosulfan nor endosulfan sulfate was detected in surveys of the milk supply of the southern region of Ontario, Canada conducted in 1970-1971 and 1973 (Frank et al. 1975). In Burley tobacco, when the crop was harvested immediately after treatment with 0.5 pound/acre of endosulfan, the total endosulfan residue levels (isomers and sulfate) were reported to average 23.2 ppm after curing for 4 months. Average total residues decreased to 2.2 ppm when the time between treatment and harvest was increased to 28 days (Dorough et al. 1973). 

To satisfy the requirement of having a total residue of only a few micrograms, the sample cleanup must be very thorough (10). The procedure which we have used to accomplish this is the following. A 10-... 

Figure 10. TCDD recovery in 10 gram human milk to which 10 gram (0.1 ppb) TCDD was added. Each trace represents 8% of the total residue.

Stairs comments that this p value is strongly dependent on the temperature but his data have been criticised by Duffin and Tucker ", who prefer their method of observing the rate of formation of the adduct to that of estimating total residual oxidising power employed by Stairs, and they find p (25°) to be —2.32+0.10 as compared to a value of —2.20+0.07 at 40 °C. These values are considerably more negative than those found for chromic acid oxidation of diphenylmethanes (— 1.17) and toluenes (-1.12). 

The total residual sum of squares, taken over all elements of E, achieves its minimum when each column Cj separately has minimum sum of squares. The latter occurs if each (univariate) column of Y is fitted by X in the least-squares way. Consequently, the least-squares minimization of E is obtained if each separate dependent variable is fitted by multiple regression on X. In other words the multivariate regression analysis is essentially identical to a set of univariate regressions. Thus, from a methodological point of view nothing new is added and we may refer to Chapter 10 for a more thorough discussion of theory and application of multiple regression. 

NADA methods should be capable of reliably measuring an analyte (i.e., the marker residue) that has a defined quantifative relationship to the total residues of toxicological concern in the tissues of interest, namely the target tissue and muscle. The target tissue is generally the last tissue in which total residues deplete to the permitted maximum safe concentration. When the marker residue is at the tolerance, a defined unique concentration, the total residues have depleted to the respectively established safe concentrations in the target tissue and muscle. 

In those cases where the total residue in not represented by a single marker compound, a more complex residue definition is necessary. The hydrolytically unstable ester of bromoxynil octanoate is presented as an example here (Table 1). 

Calculate the total residue in terms of total pyraflufen-ethyl in plant, soil and water samples (mgkg or mgL ) using the following equation ... 

Pyraflufen-ethyl (ester type) and E-3 are quantitatively converted to E-2 by the sulfuric acid treatment, but not E-1 (free acid type) therefore, methylation of E-1 to E-15 (ester type) is a necessary step for accurate analysis of total residues. 

The skin exposure is first calculated by correcting the outer whole-body dosimeter residues by the penetration factor. The penetration factor is derived from dividing the total outer torso residues into the total residues on the combined tee-shirt and brief... 

For the spectrophotometric method, the evolved carbon disulfide is reacted with copper acetate and diethylamine to form a yellow copper complex which can be measured at 435 nm." The recoveries range between 70 and 90%. Reproducibility of this method was improved by reducing the time and the mode of sample pretreatment. Since all alkylenebis(dithiocarbamates) decompose to carbon disulfide by acid degradation, the above analytical methods are not selective. The result is the measured total residues of all alkylenebis(dithiocarbamates) related products. However, this method is recommended as standard method S15 for alkylenebis(dithiocarbamates) by the German Research Association. ... 

Organic solvent extraction. Two analytical methods for acetamiprid have been developed One method is for the parent only and the other determines the total residue of the parent and its metabolites (lM-1-2, lM-1-4 and lC-0). Air-dried soil (20-g equivalent dry soil) is weighed into a centrifuge tube and imidacloprid residue is extracted with 100 mL of methanol-0.1M ammonium chloride (4 1, v/v) using a mechanical shaker for about 30 min. After shaking, the tube is centrifuged at 8000 rpm for 2 min. The supernatant is filtered and the analysis of the soil residue is carried out in the same manner as described above for the parent compound. 

In the GC method, the recoveries of acetamiprid and its degradation products in soil are >95% by the individual method for the parent compound (parent determination method). On the other hand, the recovery ranged from 74 to 96% by the total residue determination method with a limit of detection of 0.01 mg kg ... 

A distinction has been drawn (1) between harvest and ultimate residues. The former term is being defined as the surface or penetrated residue of insecticide at the time of harvest, whereas the latter designation refers to the residues in or on the foodstuff, whether fresh or processed, at the time of consumption. Thus, there exist harvest surface and penetration or harvest total residues, as well as ultimate surface, penetration, and total residues. Where necessary, component parts of the foodstuff may be specified to delimit this concept further. 

The second stage of treatment is assumed to follow an exponential decrease in removal rates. Applying the approach of Kuo, this stage is divided into two time intervals, T2A and T2 2, representing the successive removal of equivalent amounts of toluene, Miem2A = Mrem2 2 = 2.3151. The initial theoretical concentration in the gas phase for the time interval T2A is equal to the vapor pressure of toluene, Ca = 109 mg/L. The final vapor concentration for this interval Ca f can be calculated from the total residual concentration Ctf and the phase distribution equations 5 and 7-9 in Table 14.3 ... 

The data presented in Table 3, which includes the amino acid composition of baker s yeast and Candida krusei cytochrome c for comparison, show that Ustilago and Neurospora cytochrome c contain the same number of total residues. In seven instances, the number of residues of a particular amino acid/mole are identical. Thus, even in the absence of a sequence for the Ustilago cytochrome it can be concluded that this protein, unlike the siderochromes, has suffered little alteration in the progression from the Ascomycetes to the Basidiomycetes. This can be ascribed to the varying function of the two types of molecules. Cytochrome c must fit into a relatively specific slot bounded by a reductase and an oxidase and it has hence evolved much more slowly than the more freely acting transport agents where the specificity constraints are less demanding. 

Although the amperometric titrimetric method has been accepted as a standard method for the determination of total residual chlorine in chlorinated effluents [2], recent reports [3,4] have suggested that in the case of chlorinated waters, significant errors may occur if certain precautions are not taken. Furthermore, somewhat opposing views were presented in these reports on what the optimal procedure might be. 

In the amperometric titration for the determination of total residual chlorine in seawater, tri-iodide ions are generated by the reaction between hypochlorite and/or hypobromite with excess iodide pH 4 (reactions (4.3) and (4.4)). The pH is buffered by adding a pH 4 acetic acid-sodium acetate buffer to the sample. 

Thus an apparent loss in total residual chlorine may be observed. 

In the sodium borate solution containing bromide, when the pH 4 buffer is added before the potassium iodate solution, titrations give low total residual chlorine concentrations. This loss increases with the amount of stirring time between the addition of the reagents. Even for a stirring time of 10 seconds, there is a loss of about 17% of the total residual chlorine. If the solution were stirred for 30 min, 85% of the chlorine would have disappeared. The concentration of total residual chlorine determined by the reference methods does not change throughout the experiment. This implies that this loss of chlorine does not occur in the reaction vessel, but in the titration cell as a result of the analytical procedure. 

Wong [10,11] has studied this in further detail and found that carrying out the titration at pH 2 yields a true concentration of total residual chlorine after correction for naturally occurring iodate. The effectiveness of sulfamic acid in this method for removal of the nitrite interference is shown in Fig. 4.1. In this experiment, all the solutions contained 30 pmol/1 nitrite, and about 0.5 pmol/1 of iodate. The absorbance of the solution at 353 nm decreased with increasing amounts of added sulphamic acid. A constant absorbance was recorded when 3 ml or more of 1% (w/v) sulphamic acid was added to the solution, and this absorbance was identical with that in a sample containing the same amount of iodate and no nitrite. A concentration of nitrite of 30 pmol/l is unlikely to occur in estuarine water and seawater ... 

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