Total residue, determination

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 ... 

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. 

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. 

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. 

The purified sulfuric acid (i.e., preheated the commercial ultrapure grade H2SO4 at 200°C for 24 hr under vacuo to remove its decarboxylating contaminants and subsequently cooled to ambient temperature), 0.5 ml, was added to the bottom well of the decarboxylation flask and subsequently placed under vacuo. A known amount of a GC-standard (640 mm of 100 ppm C2Hg in He) was introduced into the flask for the total CO2 determination. The acid was then allowed to dissolve the photodegraded residual film on the side of the flask by tilting. The acid solution was left standing for 20 minutes at room temperature. 

The total-chlorine method for residues of the chlorinated hydrocarbons has also been applied to animal tissues, milk, and dairy products (9). As in the spray-residue determinations, the method does not differentiate between the insecticide and metabolites. 

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. 

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. 

A 10 g sample is roasted at 650°C and decomposed with hydrochloric acid/hydrogen peroxide. The Pt and Pd in the solution is pre-concentrated using adsorbent materials which are composed of active charcoal and anion resin. The adsorbent materials are washed sequentially with 2% ammonium bifluoride, 5% hydrochloric acid and distilled water, and subsequently ashed in a muffle furnace at 650°C. The total residue of ca. 0.25 mg is dissolved with 2 ml fresh aqua regia, then diluted to 5ml using 10% hydrochloric solution, and determined using ICP-MS, which has a detection limit of 0.2 ppb for Pt and Pd. The residue can also be mixed with a spectral buffer, and determined by DC-arc ES, which has detection limits of 0.3 ppb for Pt and 0.2 ppb for Pd. 

Conceptually, SPMD data fills a gap between exposure assessments based on direct analytical measurement of total residues in water and air, and the analysis of residues present in biomonitoring organisms. SPMDs provide a biomimetic approach (i.e., processes in simple media that mimic more complex biological processes) for determining ambient HOC concentrations, sources, and gradients. Residues accumulated in SPMDs are representative of their environmental bioavailability (see Section 1.1.) in water and air and the encounter-volume rate as defined by Landrum et al. (1994) is expected to be proportional to the uptake rate. SPMD-based estimates of water concentrations can be readily compared to aquatic toxicity data (generally based on dissolved phase concentrations) and SPMD extracts can be used to screen for toxic concentrations of HOCs using bioassays or biomarker tests. 

The amount of total residues is generally determined by study with radiolabeled drugs and is expressed as the parent drug equivalent in milligrams per kilogram of the food. Bound metabolites can be measured as the difference between the total and extractable residue. Microbiological assays measure the parent molecule and its bioactive metabolites immunochemical assays measure the parent molecule and closely chemically related metabolites. 

Having determined the target tissue, the parent drug and/or one or more of the metabolites in the target tissue are chosen to be the marker residue. The proportion of the marker residue to total residues is obtained at the point on the total residue depletion curve where this line crosses its permitted safe concentration. The level of the marker residue at that point represents the tolerance since it is specified in the Code of Federal Regulations, Title 21, Part 556. 

The rates of dissociation of Gd3+ chelates used or proposed as CAs are generally low at pH = 7.4. The complexes dissociate much faster in acidic solutions, when the proton-assisted dissociation predominates. In order to compare the kinetic stabilities of complexes, some authors suggest use of the first-order rate constants (kobs) obtained in 0.1 M HCl or HC104 solution. Wedeking et al. compared the acid-assisted dissociation rates (kobs) of several acyclic and cyclic Gd3+ complexes with the long term (14 days) deposition of Gd in the whole body of mice [ 15]. They found an inverse proportionality between the dissociation rates (kobs) and the total residual Gd, i.e. the lower the dissociation rate, the less the residual Gd found in the bodies of the mice [15]. The (kobs) values determined by Wedeking et al. and other authors for several Gd3+ and Y3+ complexes are shown in Table 1. 

The determination of which chemical entities are to be included in the tolerance will depend on their toxicolgical significance, their relative proportion of the total residue, and whether analytical methods are available to detect the entity. 

This paper establishes toxicologically-safe levels for total residues of parathion, azinphosmethyl, methidathion and their oxons on tree foliage and reports these levels in terms of absorbance units as determined by the rapid field method. Safe levels for a new insecticide, chlorthiophos, are also proposed based on preliminary residue data. Chemical structures of the four insecticides mentioned above are shown in figures 1, 2, 3 and 6. 

Figures IB, 2B and 3B, drawn using the data from Figures 1A, 2A and 3A, give the dissipation curves for the total residues (thion + oxon) of parathion, azinphosmethyl and methidathion. These dissipation curves are similar to the curves obtained when OP residues are determined by the rapid field method as shown by the extensive studies conducted by Gunther et al. (5) which compare gas chromatographic values for thion + oxon with RFM values for total OP residues.

Drugs that have a radioactive isotope incorporated into their structures are invariably used in studies to establish safe withdrawal periods. The presence of the radioactive isotope is harmless to the animal, but offers a highly sensitive means of determining the biological half-life of the drug and the total residue concentrations in different tissues in different animals. 

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