Residue samples, separation

Suitable inlets commonly used for liquids or solutions can be separated into three major classes, two of which are discussed in Parts A and C (Chapters 15 and 17). The most common method of introducing the solutions uses the nebulizer/desolvation inlet discussed here. For greater detail on types and operation of nebulizers, refer to Chapter 19. Note that, for all samples that have been previously dissolved in a liquid (dissolution of sample in acid, alkali, or solvent), it is important that high-purity liquids be used if cross-contamination of sample is to be avoided. Once the liquid has been vaporized prior to introduction of residual sample into the plasma flame, any nonvolatile impurities in the liquid will have been mixed with the sample itself, and these impurities will appear in the results of analysis. The problem can be partially circumvented by use of blanks, viz., the separate examination of levels of residues left by solvents in the absence of any sample. 

A sample to be examined by electrospray is passed as a solution in a solvent (made up separately or issuing from a liquid chromatographic column) through a capillary tube held at high electrical potential, so the solution emerges as a spray or mist of small droplets (i.e., it is nebulized). As the droplets evaporate, residual sample ions are extracted into a mass spectrometer for analysis. 

Analytical-Scale HPLC Separations. Reverse-phase HPLC chromatography favors the distribution of the semi- and nonpolar constituents of a sample of residue organics, whereas normal-phase HPLC chromatography favors the distribution of semipolar constituents (32). This approach is illustrated in Figure 2 by the chromatograms of residue organics from a waste water sample separated by both reverse-... 

Gel permeation chromatography (GPC), also called size-exclusion chromatography, is the most widely used cleanup technique for pesticides in fatty foods. It is the method of choice for rapid cleanup of biological extracts, especially from high-fat samples, to determine pesticide residues, since separation occurs on the basis of molecular size (7). 

Orthophosphate and condensed phosphate are a measure of inorganic phosphoms. The latter is also termed as acid-hydrolyzable phosphate. However, during mild acid hydrolysis, a small amount of phosphoms from organic phosphoms compounds may be released. To determine suspended and dissolved forms of phosphoms, the sample should be filtered through a 0.45 pm membrane filter, and the filtrate and the residue analyzed separately. 

Water samples collected in February, March, June, and August from a small spring near the Hood River orchard were analyzed, and the results are shown in Table IV. The analyses were performed so as to reveal the total pesticide present, that in solution as well as that suspended. In a few cases the residues were separated into filterable and nonfilterable portions. In these cases about 75% of the pesticide appeared in the suspended form. 

Determination of Response Factors. Speciflc response factors were obtained by injecting known concentrations of saturates and aromatics fractions obtained by clay-gel chromatographic separation of various gas oil fractions as well as residua boiling above 510°C. All of the clay-gel saturates fractions showed the presence of some aromatic impurities (2-20%) by HPLC. This was particularly true of the saturates obtained from the 510°C residue samples. Also, the aromatics fractions showed the presence of some saturates (2-3%) by HPLC. The response factors for these saturates and aromatics fractions are listed in Table II. Based on the values shown in Table II, the response for the aromatics was about 1.7 times that for the saturates. The ratio of the response factors for the gas oil fractions differs from the ratio for the residuum samples by about 6%, relative. 

Once the lyophilization was completed, the residue was separated from the trays, weighed and placed into aluminium containers. The residue was weighted in each cycle, obtaining a total amount of 7.2 kg and 14.3 kg of blank and sample residue respectively. An average yield of 80% was obtained. The contents of the aluminium containers with pesticides-enriched material were put into a polyethylene container and homogenised in a turbo mixer for 30 minutes. The material was sieved (> 0.250 mm) to eliminate salt lumps. Finally, the sieved material was homogenised in a turbo mixer for two hours. 

Chlorinated insecticides The analysis of chlorinated pesticides in residue samples in complicated by the fact that they usually occur along with polychlorinated biphenyls (PCBs). The latter compounds occur widely in the environment due to their use as plasticizers, dye stuff additives and hydraulic oils, and both chlorinated pesticides and polychlorinated biphenyls are persistent in the environment. Since both compound classes include non-polar aromatic molecules, adsorption chromatography has been the mode of choice for the HPLC separation of these compounds. 

FIGURE 11.6 Pyrograms of PLC samples pyrolyzed at 400°C in the presence of TMAH, (a) control sample, (b) residual sample recovered after enzymatic degradation test for 36 h. Sample weight 0.05 mg reagent 3pl of 25 wt% TMAH solution in methanol separation column metal capillary (30 m x 0.25 mm i.d.) coated with 0.25 pm of polydimethylsUoxane (Frontier Lab, Ultra ALLOY PY-1) column temp 40 C (5 min)-300°C at 5°C/min. 

The residues are not as uniform within the different product groups as the temperatures T. Regarding the group of vacuum residues (bitumens, samples 1-13) the data of samples 6, 7, 10, and 11 stand out distinctly. Statistical evaluation of these samples separately results in a considerable higher mean ... 

Fig. 4-22 shows the distillation curves of the atmospheric residues (samples 14-17). Approximately 40 or 50 wt% of this samples may still be separated by means of a vacuum distillation. 

In Fig. 4-23 the distillation curves of samples from conversion processes are shown. The fully distilled residues from a cat-cracker (sample 20) and from a thermal cracker (sample 22) do not contain any substances separable by distillation, but do contain approximately 40-50 wt% crackable substances. From the visbreaker residues (samples 19 and 21) about 20 wt% may still be separated by vacuum distillation. Obviously the residue of a thermal cracker (sample 18) has undergone only atmospheric distillation. Approximately 5 wt% may still be gained from that sample by atmospheric distillation, and an additional 65 wt% by vacuum distillation. 

The vacuum residues and bitumens (samples 1-13) no longer contain portions, which can separated by atmospheric distillation, i. e. SAR = 100 wt%, except sample 1. The four atmospheric residues (samples 14-17) possess between 92.8 and 95.25 wt% SAR. 

An alternative approach to separating volatile compounds from liquid and solid samples is distillation, Simple distillation can accomplish the isolation of a volatile analyte from a nonvolatile residue, or separate multiple sample constituents with widely differing boiling points. A further application is separation of a sample into fractions with different boiling ranges. 

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