Solvent disposal

The amount of gas employed in a GC analysis is not usually important, particularly where open tubular columns are used. In LC, however, solvent use presupposes a solvent disposal difficulty if not a toxicity problem and, thus, solvent consumption can be extremely important. 

Generally, size exclusion chromatography is carried out using columns with an internal diameter of 7.8 mm. However, some SEC applications require the use of expensive solvents. For this purpose, size exclusion columns with a smaller internal diameter (4.6 mm) have been developed. Of course one should use proportionally lower flow rates with narrow-bore columns. If the standard column size uses a flow rate of 1 ml/min, then the smaller 4.6-mm columns should be used at a flow rate of 0.35 ml/min. This provides the same linear velocity as 1 ml/min on 7.8-mm columns. The decreased flow rate reduces solvent consumption and solvent disposal cost. The performance of the smaller diameter columns is not compromised if properly optimized instrumentation is used. 

The mobile phase is interesting in that the water is buffered appropriately to complement the dissociation constants of the solutes. A mixture of methanol and acetonitrile is employed, the acetonitrile being used to increase the dispersive interactions in the mobile phase. The reason for the particular solvent mixture is not clear and it would appear that the separation might be achieved equally well by using a stronger solution of methanol alone or a more dilute solution acetonitrile alone. There is no particular advantage to one solvent mixture over another except for the fact that waste acetonitrile produces greater solvent disposal problems than methanol. 

Planters Lifesavers Company (former solvent disposal area), Suffolk, Virginia (D13727J, p. 2). The PetroClean bioremediation system treated 2,800,000 gal of groundwater (in situ) at a total project cost of 400,000 ( 67 per ton of treated material) (D10107L, pp. 19-20). 

Between 1993 and 1994, UVB technology was demonstrated at a solvent disposal site on the DOD s March Air Force Base in California. The capital cost for one UVB well was approximately 180,000. First and second year O M costs were approximately 75,000 and 42,000, respectively. The treatment costs for the trichloroethene-(TCE)-contamination was approximately 260 per 1000 gal of treated groundwater. The UVB well was designed to treat 1,000,000 gal per year (D188709, p. 9). 

The safety of the solvent, which is important for food and pharmaceutical-based processes, where compliance with safety and solvent-disposal legislation will be a major consideration. 

SFC provides complementary quantitative data to the structural information afforded by mass spectrometry. Thermally label materials such as isocyanates can be easily analyzed with minimal sample preparation. Supercritical carbon dioxide is nontoxic and can be obtained in high purity as measured by FID. The easy coupling of SFE with SFC makes the selective isolation and quantification of targeted analytes possible. Furthermore, we are in an age of increased environmental awareness. Solvent disposal is discouraged and has become very expensive. The waste disposal costs associated with supercritical carbon dioxide are negligible when compared to the solvent disposal costs generated by traditional Soxhlet methods. 

This analysis illustrates the utility of supercritical fluids for rapid selective extraction with no expensive solvent disposal problems, K IDS for molecular weight information, and the usage of on-line databases to assist in data interpretation. 

Place in nonhalogenated solvent disposal container for recycling or disposal by burning.21... 

Wear PVA or Viton gloves,18 laboratory coat, and eye protection. Avoid breathing vapor. Recycle by distillation (in a fume hood) or place waste in halogenated solvent-disposal container for disposal by burning. Dissolve the compound in a nonchlorinated flammable solvent and spray into a furnace with afterburner and scrubber.20,21... 

Waste quantities can be recovered for reuse by distillation. Otherwise, place in a solvent disposal container for disposal by burning in a chemical incinerator equipped with afterburner and scrubber.6,8... 

In the fume hood, behind a shield, decompose by slowly and cautiously adding a greater-than-stoichiometric amount of acetic acid. Place in solvent disposal container. (Generally, diazomethane has completely reacted when loss of yellow color of the solution is observed.)11... 

One of the major advantages of SPME is that it is a solventless sample preparation procedure, so solvent disposal is eliminated [68,131], SPME is a relatively simple, straightforward procedure involving only sorption and desorption [132], SPME is compatible with chromatographic analytical systems, and the process is easily automated [131,133], SPME sampling devices are portable, thereby enabling their use in field monitoring. 

The primary considerations which need to be addressed during or after the process development cycle with respect to environmental issues are (1) disposal of spent packing, (2) solvent disposal, (3) solvent recovery. (4) obtaining the air permits for the solvent systems in use, (5) systems in place to meet OSHA and EPA guidelines, and (6) the DOT classification. Environment guidelines and regulations are not within the scope of this chapter. 

The amount of solvent lost to the atmosphere and the amount of fresh feed per solvent disposed of in the sludge for the system without vapor recovery is therefore... 

General guidelines for initial disposal (D, dilute with water neutralize, if necessary, with an appropriate inorganic acid or base and flush down drain C, chlorinated solvent disposal NC, non-chlorinated solvent disposal S, solid disposal in accredited landfill site or burned in a chemical incinerator R, refer to local safety officer)... 

Figure 5.1. (a) Solvent cycletainer (b) Justrite solvent disposal can with secondary containment. Bottom photo in (b) courtesy of Joe Grills of Purdue Pharma. 

In this introduction, we have presented an overview of the benefits of applying the technique of SFE to the area of food analysis. There are substantially reduced costs derived from use of SFE versus traditional extraction in the areas of solvent purchase costs, solvent disposal costs, reduced labour charges, and even less need to repeat experiments due to reduced human errors in the overall analytical scheme. Moreover, productivity can be improved and the use of environmentally-unfriendly solvents is greatly reduced. In the rest of this chapter we will explore the fundamental principles of SFE in more detail, discuss some of the aspects of current SFE instrumentation, present a number of examples of applying SFE to food samples, and briefly summarise some hints for methods development. 

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