Special methods of solvent analysis

1 USE OF BREATH MONITORING TO ASSESS EXPOSURES TO VOLATILE ORGANIC SOLVENTS 

Hazardous Materials Laboratory, Department of Toxic Substances Control, California Environmental Protection Agency, Berkeley, CA, USA 

There should be adequate information on the absorption, distribution, biotransformation, metabolism and elimination of the chemical in the body. This type of information will indicate what tissues to sample, for what compound (parent chemical or a metabolite) and at what time. The latter issue is very important with chemicals that are eliminated rapidly (i.e., those with short half-lives). 

The coneentration of the ehemical (or its metabolite) to be measured in the selected medium (breath, blood, urine) must be in equilibrium with the concentration of the chemieal at the target organ. 

The assay has to be sensitive, in order to detect low levels of the compound before any adverse effeets take place speeific, in order to link exposure to dose and accurate and preeise, in order to be reliable. 

---

The second part of this handbook (Chapters 14-25) is devoted more to the industrial use of solvents. Formulating with solvents applied in a broad range of industrial areas such as biotechnology, dry cleaning, electronic industry, food industry, paints and coatings, petroleum refining industry, pharmaceutical industry, textile industry, to mention only a few, is extensively described in Chapter 14. Standard and special methods of solvent detection and solvent analysis as well as the problem of residual solvents in various products, particularly in pharmaceutical ones, are the topics of Chapters 15 and 16. 

It is possible in some cases to obtain analytically piure dyes. This is most successful with the vat dyes, which can frequently be crystallized from a high boiling solvent such as chlorobenzene or nitrobenzene, or from glacial acetic acid or pyridine. Tetrabromoindigo (Ciba blue 2B), for example, can easily be obtained analytically pure from dichlorobenzene, as can other vat dyes of the type of indanthrene blue. With these dyes, quantitative chemical analysis is often of great value. Other special methods of analysis can also be employed, such as the Zeisel determination of alkoxyl groups. 

As any method of anion analysis may be applied if isolation techniques such as evaporation, precipitation, ion exchange, or solvent extraction are employed, we shall limit the discussion to direct methods and admit isolation techniques only if they are simple and rapid. The methods apparently best suited to the direct analysis of trace amounts of anions therefore are limited to selective membrane potentiometric, atomic absorption, fluorescence, and spectrophotometric methods following oxidation-reduction or complexometric reactions, or solvent extraction. Most of the traditional analytical methods—gravimetric, titrimetric, emission spectrometric, and electrical methods involving oxidation and reduction are less suitable, as are most radioactive procedures including neutron activation analysis, except in special cases. 

In Table 1.3.2 a method for the analysis of nitrates and nitrites for a wide variety of samples is given Aqueous nitrate ions are converted to nitrobenzene by reaction with benzene in the presence of concentrated sulfuric acid as catalyst. The special methods for the different materials are described. To stabilize samples against bacterial action, which can reduce nitrate concentrations, phenylmercuric acetate is added after collection ° Other inorganic compounds in the trace levels for gas-chromatographic determination are, for example, water and carbon monoxide, which were determined in organic solvents or air in the ppb-range ... 

A coated fused silica fibre is directly introduced in the liquid sample or in the headspace above the sample. Respective ingredients from the sample material are absorbed onto the fibre material until equilibrium is reached. The fibre is removed from the sample and directly applied into the injection system of the GC. The absorbed compounds are thermally desorbed into the GC column for analysis. The method is solvent-free and requires no special additional equipment. It is used for the analysis of special groups of compounds, depending on the enrichment based on the type of fibre used/52-567. 

Laser ablation can be carried out on any material without special sample preparation. The laser beam can be directed onto a defined spot of the sample or moved to different parts to analyse over a defined area. It can be moved in an XYZ plane using a stepper motor and driven in translational motions on which the cell is mounted and with more expensive models can be turned for analysis in other parts of the sample. Lasers can operate in UV, visible, and IR regions of the spectrum and a recent development in laser technology uses neodymium yttrium aluminium garnet (Nd YAG) which gives high repetition rate at a comparatively low power. This method of analysis is suited to bulk analysis of solid materials and the amount of volatility varies from sample to sample. The size of the laser spot can vary from 10 to 250 pm and little or no sample preparation is required. Errors are greatly reduced because of the simple sample preparation, and the fact that no solvents are required reduces interferences. 

Due to the rapidly growing importance of capillary columns in bioanalytical applications, special attention will now be devoted to sampling techniques associated with capillary GC. Small samples are typical for this type of chromatography and, consequently, a direct introduction of such samples is an apparent technological problem. In most biochemically interesting applications (typically, trace analysis problems), there is no general discrepancy between the demands of such analysis and the performance and sensitivity of capillary separation techniques. However, the manipulation of samples presents difficulties, as reliable methods for measurement, disposal, and introduction of nanoliter volumes are not readily available. Ironically, in many capillary GC applications, the solvent serves only as a sample vehicle we... 

The various problems connected with the use of infrared spectroscopy in pesticide research have been reviewed by Frehse (1963). The paper dealt with qualitative and quantitative analysis, determinations of residues, and special problems such as methods of extraction, cells, solvents, and measuring attachments to be used. Frehse has given many references to the literature concerning the infrared spectroscopic analysis of various food crops for pesticides, e.g., aldrin, alodan, chlorbenside, DDT, dieldrin, endrin, ethion, lindane, malathion, tedion, endosulfan, biphenyl, captan, pentachloronitrobenzene, 2,4-DB, MCPB, and methylisothiocyanate. The infrared band(s) used for the determinations have also been given. 

---