Obtaining control commodities

As with any residue method, a method used in an LSMBS method should include analysis of control commodities to demonstrate adequate selectivity and analysis of fortified control samples to demonstrate recovery. These aspects present a particular challenge in every food-based market basket survey, because, unlike field residue studies, control samples of known provenance are not available. 

In a field residue study, commodities are grown on control plots located near the plots used to produce commodities treated with test substance. Care is taken to ensure that the only difference between control and treated commodities is that the former does not receive application of the pesticide and the latter does. Crop variety and growing conditions (including geographical location, soil, time of year, weather, etc.) are essentially identical for the control and the treated commodities. 

A market basket survey, however, is unique in that untreated control commodities, as the term is normally used in residue studies, cannot be obtained. In a market basket survey, food commodities are collected at the consumer level and not from controlled field tests. By design, the cultural and treatment details for the collected commodities are expected to differ from sample to sample. This factor enables the collected commodities to represent the spectrum of conditions under which crops are supplied for human consumption. 

A second problem was that some lots of control commodities contained one or more extractable interferences, i.e., co-extractives that interfered with one or more of the analytes for the particular commodity and could not be removed during cleanup. This problem was addressed by either using controls from different sources for specific analytes or by blending controls to obtain a matrix with a sufficiently low level of interference to allow accurate determination of recovery. 

---

Apart from butter or butter oil most fats that are used in biscuits are defined in terms of their physical and chemical properties. Fat suppliers are skilled at producing products with controlled physical and chemical properties from a range of raw materials. The baker can either buy fat on a physical and chemical specification, e.g. solid fat index, slip melting point, and not to contain lauric fat, or on an origin basis, e.g. to be coconut oil. The advantage of the botanical specification is that the item is a commodity and can be obtained from numerous sources. The disadvantage of this approach is that the product is tailored for a particular use. 

Osmosis has other important uses. In some parts of the world, potable water is a precious commodity. It can be obtained much more economically by desalinizing brackish waters, through a process called reverse osmosis, than by distillation. When an ionic solution in contact with a semipermeable membrane has a pressure applied to it that exceeds its osmotic pressure, water of quite high purity passes through. Reverse osmosis is also used to control water pollution. 

The solubility of the reactants and products are shown in Figure 1.20. Again in this type of process mixing is crucial in obtaining a homogenous supersaturation profile. Precipitation is important in the manufacture of a variety of materials. TPA, which is an organic commodity chemical used in the manufacture of polymers, is made from the oxidation of p-xylene in an acetic acid water mixture. The product has a very low solubility in the solvent system and rapidly precipitates out. Control of the supersaturation in a precipitation process is difficult because it involves control of the mixing of the reactants and or the reaction rate. 

Viewed from the perspective of ethylene oxide, these reactions are competitive by contrast, from the perspective of the amines, they are consecutive. Consider a research scale batch reactor operating at 60°C and 20 bar to maintain all species in the liquid phase. Actual production of these commodity products on a large scale would be conducted in flow reactors, as described in Illustration 9.5. The rate laws are of the mixed second-order form (first-order in each reactant), with hypothetical rate constants ki, k2, and equal to 1,0.4, and 0.1 L-moCV min, respectively. MEA and DEA are both high-volume chemicals, while TEA is less in demand. The distribution of alkanolamine products obtained under the specified conditions can be influenced by controlling the initial mole ratio of EO to A and the time of reaction. 

The extension of these principles to molecules and macromolecules based on renewable resources has been applied to polymer chemistry and technology, mostly in two areas requiring viscous materials, namely (i) the preparation of liquid polyols to be used in the manufacture of polyurethanes, and (ii) the synthesis of macromol-ecular rheology modifiers. A typical polyol for the synthesis of polyurethane foams is obtained industrially from the oxypropylation of sorbitol, [3] whereas hydroxypropyl cellulose represents a major commodity for the rheological control of paints, foodstuff, cosmetics, etc. [4]. 

Hydrochloric acid may be purchased or produced internally. It is a widely available commodity, easily obtained in good quality. HCl is available in the anhydrous form as well as in the form of aqueous acid (up to 23° Be or about 37% HCl). The use of aqueous acid is standard in the chlor-alkali industry, and we do not discuss anhydrous HCl here. Byproduct acids are available, sometimes at lower prices, and may be suitable for use in the chlor-alkali process. Their quality should be checked carefully, and testing may be advisable before use. When HCl is produced from chlorine liquefaction tail gas, the absorbing water is the most likely source of impurities. Demineralized water is the standard source when producing acid for use in a membrane-cell chlorine plant. A certain amount of chlorine tends to be present in burner acid. This can be minimized by process control, and a small bed packed with activated carbon (Section 7.5.9.3B) is a useful safeguard. Usually only the acid intended for use in the ion-exchange system need be treated in this way. 

Polylactides (PLA) may have many potential applications for an important set of products but some of their properties should be improved to obtain similar performance to petroleum-based commodities. One of the most important current applications of PLA is food packaging, in particular for short-shelf-life products with common applications such as rigid containers, drinking cups, over-wrap and lamination films. PLA production and consumption are expected to increase therefore research into the variation of PLA mechanical and barrier properties is currently very active. The control of barrier properties in PLA films is possible by modification of the polymer network through the formation of intramolecular and inter-molecular covalent crosslinking, for example by applying thermal treatment, or by modifying the chemical composition. Another method is to incorporate fillers, in particular layered nanoclays, and this will be the subject of this chapter. 

Although metallocene-produced polyolefins can compete with commodity polyolefins synthesized with conventional Ziegler-Natta catalysts, they wiU probably not be restricted to the pol)uner commodity market. Because of the better pol3uner microstructure control obtained with metallocene catalysts, it will be possible to produce specialty polyolefins to compete with nonolefinic polymers, thus opening an entire new market for polyolefin applications. 

---