Patai S., Rappoport Z. 1996 The chemistry of functional groups. The chemistry of amino, nitroso, nitro and related groups. Part 2 / 1041 1168

OAc

Me N+

Me Br−

Me

N

AcO

(214)

Field desorption MS proved to be the most effective MS technique for the detection and determination of bis(quaternary ammonium) molecules, such as the antibiotic drug ethonium (216)431,432.

The critical concentration for micelle formation (CMC) has been determined by various methods, including the use of membrane electrodes that are selective to specific ionic surfactants. Unfortunately, it is difficult to find materials suitable for producing the selective membranes. An alternative method is based on the drastic change in the mobility of the species occurring on micelle formation. This affects the liquid junction potential generated at the interface between two solutions of different concentration. The method was applied for determination of the CMC of alkylammonium nitrates of various chain lengths433. The structure of the air water interface layer of an aqueous solution of C18H37NMe3Br, at the CMC (3.1 ð 10 4 M at 33 °C), was investigated by surface tension and neutron reflectivity. The possible sources of systematic error in the neutron reflectivity measurements were taken into account for the improvement of analysis434. The effect of various factors on the aggregation number N of alkyltrimethylammonium micells was studied by small-angle neutron scattering. Thus, N was found to increase with concentration and chain length of the alkyl group, and to vary as follows for the various counter ions: OH − Cl < MeSO4 < Br < NO3 435 . The shape and thickness of the monolayer of cetrimide (197c) formed at the air water interface was determined by neutron reflection. The total thickness of the monolayer was estimated to be 2.1 š 0.2 nm, of which 1.0 nm is immersed in water; six water molecules are associated with each molecule of surfactant436. Similar studies were performed for various C10 to C18 alkyltrimethylammonium surfactants. Interpretation of the neutron reflection results included an estimate

of the molecular cross-section at the air liquid interface, surface roughness, molecular shape and chain orientation437.

The hydration numbers N of the quaternary ammonium alkanesulfonates (217) and alkylidene-˛,ω-disulfonates (218) were determined from the melting points of their saturated aqueous solutions. Both the N values and the melting poins were fairly high (217: N ³ 37, mp 13 19 °C; 218a: N ³ 52, mp 1 10 °C; 218b: N ³ 76, mp 13 18 °C). The water molecules probably assume a clathrate structure438.

The apparent standard rate constant ks for the transfer of tertiary and quaternary alkylammonium ions between water and nitrobenzene increased slightly when the ionic radius was increased from Me3HNC to Et4NC and then it decreased with further increase of the ionic radius until Pr4NC . The dependence of ks on the ionic radius suggests that with small ions the processes of desolvation and resolvation are involved in the ratedetermining step, while the effect of hydrodynamic drag is the prevalent one with the larger ions439.

The stability of the gel phase and the transitions of coagel and gel phases to liquid crystal in the dioctadecyldimethylammonium bromide water system were determined by differential scanning calorimetry (DSC)440.

VI. NITRO COMPOUNDS

A. General

The present section is organized following roughly the nature of the structural frame supporting the nitro groups (arene, hetaryl or alkyl C, N and O atoms) and the presence of other functional groups that may contribute additional analytical methods (phenols, anilines, etc.). Nitro compounds are important intermediates and end products of the chemical industry with a wide range of applications in organic synthesis, manufacturing industries, medicine, agriculture and engineering (civil and military). Table 5 lists nitro

TABLE 5. Examples of environmental, occupational and quality control protocols for industrial nitro compounds

(continued overleaf )

a Nomenclature may vary from source to source. See also Reference 69. bEntry number in Reference 70.

c Codes beginning with I and N denote FTIR spectra in Reference 71, NMR spectra in Reference 72, respectively.

d A code of two letters followed by seven digits is a reference to RTECS of NIOSH/OSHA; aŁ denotes a protocol for a different derivative of the same main compound. Standard samples are commercially available for compounds with reference to protocols of EPA and USP74.

e The compound has two or more nitro groups of the same type.

f Included among other pollutants listed by EPA in the Municipal Industrial Strategy for Abatement regulations of the Ontario Ministry of the Environment.

gA pesticide, see Reference 75.

compounds of commercial relevance possessing C NO2, O NO2 and N NO2 bonds with reference to environmental and occupational protocols.

A review appeared on the determination of nitroalkanes, polynitroalkanes, nitroalkenes, aromatic nitro and polynitro compounds, heterocyclic nitro derivatives and inactive compounds after nitration, by polarography, voltammetry and HPLC with electrochemical detection441.

Fluorescent cellulose triacetate membranes were prepared by incorporation of pyrenebutyric acid (219), and were applied to in situ detection of ground water contamination by explosives, based on fluorescence quenching by the nitro groups; LOD 2 mg/L of DNT (220) and TNT (221) and 10 mg/L for RDX (276); the response follows the Stern Volmer law for DNT and TNT442.

CH2 CH2 CH2 CO2 H

The nitrogen camera is an instrument based on detection of -rays in the multiscalar mode, after irradiation of a target pixel by a beam from a 50 MeV electron racetrak microtron. An image consisting of 180 2 ð 2 cm2 pixels can be produced in about 7 s. This technique is capable of imaging nitrogen concentrations with surface densities and amounts typical of concealed conventional explosives. The sole interfering signal from 13C can be disentangled443.

A novel technique for sensing trace vapors of nitro compounds is based on photolysis of the target molecule using a laser operating at 226 nm. The same beam can be used to detect the characteristic NO fragment formed from a rapid predissociation of NO2, by resonanceenchanced multiphoton ionization and by LIF using the A2 C X2 (0,0) transition. The analytical utility of this technique was demonstrated on a number of compounds, including TNT (221), RDX (276), dimethylnitramine, nitromethane and nitrobenzene, employing molecular beam sampling444.

B. Aromatic Nitro Compounds

1. General

A comparison of active (using pumps) and passive (relying on diffusion) sampling techniques for the determination of nitrobenzene, benzene and aniline in air was mentioned in Section IV.A77. Several LLE methods for nitroaromatic compounds dissolved in water were evaluated. High recoveries were achieved with discontinuous or continuous extraction with dichloromethane, adsorption on a 1:1:1 mixture of Amberlite XAD-2, -4 and -8 resins and elution with dichloromethane445.

Polynitroaromatic compounds are used as explosives. They are toxic and might cause liver damage, methemoglobinemia and uncoupling of the oxidative phosphorylation process. Trace analyses of polynitroaromatic residues in groundwater, surface water, rainwater

1126 Jacob Zabicky and Shmuel Bittner

runoff, soil and sediments are important because these compounds become absorbed through the skin446.

It is possible to quantify individual nitroaromatic compounds present in commercial nitroglycerine-based explosives without prior separation, by using 500 MHz 1H NMR. Patterns within the quantitative data provide a good degree of sample batch characterization447.

Mutagenicity tests and gas chromatographic analyses of motor oils exposed to NO2 indicated the presence of many mutagenic nitroaromatic compounds. Comparison of motor oil nitrated with NO2 and used automobile oil show similar behavior448.

A new dual-electrode electrochemical detector for LC was designed utilizing two series of generator/detector electrodes, having a larger electrode area and higher electrolytic efficiency and sensitivity, as compared with the commercial ones. Analytes are reduced at the upstream electrode and the products are then detected by oxidation at the downstream electrode. This eliminates the influence of dissolved oxygen and trace amounts of heavy metals in the mobile phase and sample, and exhaustive removal of dissolved oxygen before injection is not required. The method can be easily automated449.

A semiconductor sensor-based instrument was described for determination of the composition and concentrations of vapors of organic nitro compounds and nitrogen dioxide in the atmosphere. Four organic semiconductor sensors [e.g. aluminum phthalocyanine fluoride (222a)] were tested in conjunction with platinized platinum preconcentrators; sensitivity is to ppm levels of nitrobenzene450.

N N

N

N

(a) M = AlF N M N (b) M = Co

(c) M = Fe

N

N N

(222)

LOD and LOQ were measured to assess the sensitivity of the FID, ECD and TSD detectors for GC analysis of various nitroaromatic compounds. A parallel connection of the three detectors at the end of a single narrow-bore capillary column enabled direct comparison of the chromatograms. Structural effects on the response were evaluated and detection mechanisms were discussed. Recommendations were made for identification purposes and for analysis of environmental samples of nitroand chloro-nitro-benzenes in a wide range of concentrations451.

2. Monocyclic arenes

This section also includes nitrated monocyclic arenes with halogen atoms directly attached to the benzene ring.

Sampling on Tenax TA followed by thermal desorption and GC affords a simple method for the determination of nitrobenzene in the workplace air. Recoveries were quantitative in the mass range 0.04 10 mg452.

A selective procedure for attomole detection of nitrobenzene and o-nitrotoluene vapors at sub-ppm levels has been developed using resonance-enhanced multiphoton ionization MS. The TOF-MS spectra of these nitroaromatic molecules show a prominent NOC ion signal (m/z 30) together with a characteristic pattern of hydrocarbon fragment ions. In the wavelength range studied, 224 260 nm, generation of NOC is strongly dependent on the laser wavelength, with maximum intensity at 226.3 nm. At this particular wavelength NOC ion signals have been detected with <1 amol (<10 18 mol) of nitrobenzene vapor present in the laser beam453. The same analytes were detected in trace concentrations in gas mixtures at atmospheric pressure in a simple unity-gain ionization chamber. They could be distinguished by observing their different laser-induced MS and the wavelength dependence of their fragmentation454.

Nitrobenzene, 2,4-dinitrotoluene and 2,6-dinitrotoluene were determined in water by GC-EC or GC-CLD thermal energy analyzer (TEA) and by EI-MS, CI-MS and NICIMS455, after solid-phase microextraction (SPME) with polydimethylsiloxane coated fiber. SPME is a technique to concentrate organic compounds dissolved in an aqueous matrix by adsorption on a solid stationary phase immobilized on a fused silica fiber. The analytes were thermally desorbed directly into the GC injector; LOD was 9 mg/L for nitrobenzene and 15 mg/L for the dinitrotoluenes456.

The recently reviewed EPA method 8330 uses RP-HPLC-UVD for determination of polynitroaromatics and other explosives at ppb concentration levels446. Very low concentrations of TNT (221), DNT (220) and some nitramines (Section VI.G) in water were determined by isothermal equilibrium adsorption on a porous film, color development with o-toluidine and Griess’ reagent and colorimetric measurements using diffuse reflected light457. Nitroaromatics and nitramines have been determined in drinking water by GC-ECD, using a DB-1301 wide-bore fused-silica capillary column, at low concentration levels never previously achieved; LOD was 0.003 mg/L for 2,6- dinitrotoluene, 0.04 mg/L for DNT and 0.06 mg/L for TNT458. Mononitrotoluenes, dinitrotoluenes, TNT and nitrotoluidines have been found in concentrations ranging from 0.1 to 20 mg/L in brooks and ponds in former ammunition production areas in Germany. The method consisted of SPE with Amberlite XAD 2/4/8, elution with dichloromethane and RP-HPLC-UVD with a photodiode array at their optimum wavelength; LOD was ca 50 ng/L with 85 105% recoveries, depending on the compound445. Good separations were achieved with methanol water gradient and a methanol water gradient containing 2% of THF, with different elution orders for nitrated benzenes, nitrated toluenes and nitrated toluidines459.

A method with LOQ at ppt levels was developed based on LLE followed by GC-AFID for the determination of trace concentrations of nitrobenzene, 1-chloro-2-nitrobenzene and synthetic fragrances such as musk xylene (223) and musk ketone (224). The method was applied to study the distribution of these compounds in environmental samples of North Sea waters460. GC with atomic emission detection (AED) has been successfully applied to the determination of nitro musks in human adipose tissues, at ppb concentration levels. A clean-up procedure for nonpolar substances and element-specific detection with AED enabled for the first time target screening analysis for lipophilic nitro aromatic compounds. The lack of sensitivity of AED was compensated by higher concentrations of the extracts

and injection of larger sample volumes, performed with cold programmed temperature vaporization in the solvent split mode461.

A sensitive ELISA procedure was developed for the determination of TNT (221) and other nitroaromatic compounds. TNT can be detected within the range of 0.02 20 ng/L in water samples462. A simplified immunofiltration prepacked portable device for field screening tests of TNT in water and soil was also developed. A quantitative color response to concentrations of TNT in the range 1 30 ng/L in water and 50 1000 pg/g in soil was demonstrated463.

A sensitive HPLC method for the determination of 5-(4-nitrophenyl)-2-furoic acid (225), a dantrolene (226) metabolite, in blood plasma and urine was developed464.

O

(225)

O

NH

O

O

(226)

Adsorptive stripping square-wave polarography and differential-pulse polarography methods were developed for the determination of 4-nitrobiphenyl (227a). The best adsorption conditions on a hanging mercury dropping electrode in aqueous solution with Britton Robinson buffer were pH 3, accumulation potential of 10 mV (vs Ag/AgCl electrode) and accumulation time of 100 s465. Optimum conditions were found for the determination of 227a by fast scan differential pulse voltammetry at a hanging mercury drop electrode in the concentration range 1 ð 10 5 to 2 ð 10 7 M. A further increase in sensitivity was attained by adsorptive accumulation of this substance on the surface of the working electrode466.

The mechanism of the global 4-electron electrochemical reduction of aromatic nitro compounds to hydroxylamines in aqueous medium shown in reaction 37 was investigated by polarography and cyclic voltametry. The nitro group is converted first to a dihydroxylamine, that on dehydration yields a nitroso group; the latter is further reduced to a

NO2

X

(a) X = H; (b) X = 4′-NO2

(227)

hydroxylamino group. The mechanism proposed for the process consists of a 9-membered square scheme involving protonations and electron transfer steps for each one of the equilibria shown in reaction 37467 471. The electrochemical processes may be complicated to some extent by the presence of other moieties; for example, a nitro group may reductively condense with nearby cyano or ester functions to yield products such as 174 and 175, as discussed in Section IV.H.

3. Polycyclic aromatic hydrocarbons (PAH)

Nitro-substituted PAH have received increased attention as an important class of environmental pollutants. They have been detected in an ample variety of sources, including automobile exhaust fumes, wood and cigarette smoke, kerosene heater flue, emissions of coal-driven power stations and grilled meat. These subjects have been reviewed472,473.

The effect of solvent polarity on the injection conditions for the determination of nitroPAH by capillary GC with splitless injection was investigated; LOD was 129 pg of 2-methyl-1-nitronaphthalene (228), at SNR 2, RSD 1.8 6.7% when measuring by peak area using FID474.

NO2

CH3

(228)

Mutagens in the semivolatile phase of airborne particulate matter of diesel and gasoline engine emissions were investigated using chemical and biological assays. Various modifications of a method for determination of nitro-PAH, such as 1-nitropyrene (229a) and 2-nitrofluorene (230), were described, consisting mainly of a reduction step followed by derivatization and chromatographic end analysis. In one instance the nitro group was reduced to an amino group by Zn or sodium hydrosulfide, derivatized with heptaflourobutyric anhydride and determined by GC-MS. The method was used for air samples collected in workplaces associated with the use of diesel engines, chassis dynamometer studies and others475. An HPLC-FLD method was developed, including an on-line reduction step for the determination of 229a and its nitroso analog. Chemical reduction on a zinc column was more efficient than electrochemical reduction LOD 20 30 fmol for SNR 3476. The method was applied to the determination of 229a at low pg levels in a variety of matrices:

The incubation mixture of a mutagenecity test using Salmonella typhimurium YG1021476, extracts from diesel particulate emissions477 and leaves of roadside trees478. Nitropyrenes 229a d found in sooty emissions of diesel and gasoline emissions were determined by HPLC-CLD, after conversion to the corresponding amines 43a d by refluxing samples in the presence of sodium hydrosulfide147.

A sensitive method was developed for determination of nitropyrenes 229a d in airborne particulates and in emission particulates from diesel and gasoline engine vehicles by on-line reduction and RP-HPLC-CLD. Chemiluminescence was according to reaction 24 (Section IV.G) using the oxalate 42. Urban air showed matutine and vespertine peaks; concentrations were higher in autumn and winter than in spring and summer. Mean con-

centrations of 229a d: 0.70 š 0.28 pmol/m3; 2.19 š 0.81 fmol/m3; 4.03 š 1.52 fmol/m3; 3.63 š 1.40 fmol/m3, respectively479 481.

Nitro-PAH were determined by capillary GC-MC, after reduction to amines and conversion to pentafluoropropionamides. This made it possible to prove the presence of 229a, 230 and 3-nitrofluoranthene (231a) in most samples of airborne particular matter taken in

Nitro-PAH were determined in air particulate matter by RP-HPLC with reductive electrochemical detection; sensitivity of 3 0.3 ng injected483.

6H-Dibenzo[b,d]pyran-6-one (232a) and its nitro derivatives at positions 2, 3, 4 and 8 (232b e) were characterized by their 1H-NMR spectra, mass spectra and GC retention indexes, to allow their analysis in ambient samples484. The 2-nitro isomer (232b) was found to be a significant contributor of ambient air particle and gas-phase mutagenicity, as assayed with a microsuspension modification of the standard Ames Salmonella plate, incorporating test strain Salmonella typhimurium TA98 without activation. Both 232b and 232d were quantified in diesel particulate emissions and in ambient air samples collected in