Anal. Chem. 1986, 58, 102R-108R
Functional Group Analysis Walter T. Smith, Jr.,* a n d John M. Patterson Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055
The analytical methods discussed in this review have been selected from the literature that has become available to the reviewers from December 1983 through November 1985.
reaction shows possibilities for the kinetic optical resolution of racemic alcohols as well as potential for the estimation of enantiomeric content. In the specific example illustrating the method, racemic 2,2-dimethyl- 1-phenyl-1-propanol was oxidized selectively to the corresponding ketone at a lead dioxide electrode coated doubly with polypyrrole and poly(L-valine). In this way 43% of the optically pure S'-(-) enantiomer was recovered unoxidized when half of the starting alcohol was oxidized (15). Enantiomers of some sugar alcohols (arabinitol, fucitol, and mannitol, as well as some 2-aminoalkanes) have been separated as trifluoroacetyl derivatives on capillary glass and fused-silica gas chromatography columns coated with XE-60-~-valine-(R)-c-phenylethylamide and its diastereomer (16). A study of methods for determining the hydroxyl content of commercial liquid butadiene and nitrile rubbers found that the method using the acetylation of the hydroxyl groups with acetic anhydride [p-toluenesulfonic acid catalyst] was simpler than either the phthalic anhydride-pyridine method or the isocyanate method using toluene (diisocyanate dioctyltin dilaurate catalyst) (17). The time required for the determination of hydroxyl groups in various polymer polyols has been cut from 2 h to 15 min by the addition of imidazole as a catalyst (18). For distinguishing primary hydroxyl content of olyols, two NMR methods have been evaluated. Both the F NMR of trifluoroacetates and the 13C NMR of CH, and CH groups serve to distinguish primary from secondary alcohols and ethylene oxide from propylene oxide units in the chain. The 19Fmethod is more precise but is less accurate for samples consisting of blends, such as the blend poly(ethy1ene glycol)-poly(propy1ene glycol) (19). Near-infrared reflectance analysis has been recommended for the rapid determination of hydroxyl number in polymers of ethylene oxide and propylene oxide (20). The method can also be applied to the determination of ethylene oxide units and water in these polymers. The method is rapid but does require a lengthy calibration process. Hydroxyl functions in asphaltenes and acidic extracts of petroleum oils have been determined by I9F and 29SiNMR spectroscopy after treatment with trifluoroacetic anhydride or hexamethyldisilazane (21). Non-hydroxyl oxygens were determined by difference between the oxygen determined by NMR and the total oxygen as determined by elemental analysis. Fourier transform infrared and solid-state 13CNMR have been used for the determination of hydroxyl groups in coal (22). It is necessary to derivatize the sample, either via acetylation for the infrared studies or by methylation for the NMR studies. 13C NMR spectroscopy has also been used for estimating the ratio of primary, secondary, and phenolic hydroxyls per methoxy in milled wood lignin and other wood derivatives (23). An improved periodate-selective electrode has been used for a kinetic determination of glycerol using the periodate method for vicinal glycols (24). The color reaction of benzyl alcohol with sulfuric acid has been used as the basis of a method for determining the alcohol in air (25).
ACIDS The determination of fatty acid mixtures (as methyl esters) using gas chromatography and chemical ionization mass spectrometry has been reviewed (1). The procedure of Sturrock (2) in which the pH difference between the 25% and 75% points on a titration curve is used to distinguish between mono- and dibasic acids has been extended to aliphatic carboxylic acids (3). Procedures for the chromatographic determination of carboxylic acids involve derivatization followed by the use of liquid or gas chromatography. In one method, acids in water are simultaneously extracted and derivatized by use of the macroreticular resin XAD-2 impregnated with benzyl or pentafluorobenzyl bromide (4) while in another the acids are treated with phenacyl bromide (5) prior to analysis by highperformance liquid chromatography. Aldonic acids (ribonic, xylonic, mannonic, gluconic, galactonic acids) were converted into amides by treatment with an alkylamine and then acetylated prior to gas chromatographic analysis (6). The peracetylated amides were thermally stable. Pyrolytic decarboxylation has been used to determine the carboxylic acid content of partially oxidized cellulose. The volume of CO, was measured in an azotometer (7). The isotopic analysis of aromatic carboxylic acids, aromatic dicarboxylic acids, and heterocyclic carboxylic acids was accomplished by use of the pyrolytic decarboxylation method a t 550' (8). The application of the BaC1,-triethanolamine reagent to the determination of carboxyl groups in low-rank coals has been critically examined (9). Reliable analyses are obtained when an excess of acid is used to liberate barium from the coal. The excess acid is determined titrimetrically.
F
ACID HALIDES Acid halides have been determined by an indirect method in which the acid halide is treated with an excess of NaN3 in aqueous acetone (10). The unreacted azide is converted to its red FeN:+ complex and measured spectrophotometrically. Phosgene at the 10-40 mg/mL levels can be determined with a relative standard deviation of 3.3-7.3% by conversion to a heterocyclic derivative using o-aminophenol or metoprolol (11). The heterocyclic derivative is detected by gas chromatography using a nitrogen-selective detector.
ACTIVE HYDROGEN Active hydrogen functional groups (alcohols, phenols, carboxylic acids, amines, and thiols) can be converted to p-fluorobenzoyl derivatives by reaction with p-fluorobenzoyl chloride. The resulting compounds can be characterized by fluorine-19 NMR (12).
ALCOHOLS
ALDEHYDES AND KETONES
Several methods relating to enantiomers have been reported. The enantiomeric purity of glycols of the type RCHOHCH,OH has been determined by conversion of the glycol to a pair of epimeric 1,3-dioxolanes by cyclic acetal formation with benzaldehyde and subsequently observing the benzylic hydrogen by NMR in the presence of a chiral shift reagent (13). The same type of glycols has also been converted to dioxolanes by reaction with (S)-(+)-Zpro lcyclohexanone. In this case the products were studied by C NMR and/or HPLC (14). An electrochemical enantiomer-differentiating
The oxidation of o-phenylenediamine by H,02 is promoted by glutaraldehyde. The nature of this reaction has been studied and the reaction has been made the basis for the catalytic detection and determination of aldehyde groups in aminosilanes which have been modified by glutaraldehyde (26).
1,3-Cyclohexanedione, a more water-soluble analogue of dimedone, has been adapted for precolumn fluorigenic labeling in a HPLC method for determining trace amounts of aldehydes (27). Low molecular weight aldehydes and acetone in
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1986 American Chemical Society
FUNCTIONAL GROUP ANALYSIS
ethers which are extracted into chloroform. The absorbance of the chloroform solutions is measured at 4 M 0 2 nm (34).
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1-I
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The formation of colored Meisenheimer complexes of trinitrobenzene in Me2S0 with aliphatic, aromatic, and heterocyclic amines permits the spectrophotometric determination of these compounds (35). The cleavage of pyridine and pyrimidine rings by dicyclohexylcarhodiimide to form glutaconaldehyde and malonaldehvde. resoectivelv. forms the basis of colorimetric determination of these Gmpounds. The colored species results from the reartion of the aldehydes with dimethylbarhituric acid reagent ( 3 6 ) ~ Factors affecting the stability of fluorescent isoindole derivatives formed by reaction of primary amines, phthalic anhydride, and 2-mercaptoethanol have been studied. Excess phthalic anhydride has a deleterious effect on compound formation while increasing bulk and substitution increases stability. 3-Mercapto-1-propanol was a better thiol in the formation of the isoindoles (37). Descriptions of several different gas chromatographic methods for the trace analysis of amines have been published (38). ~ . ~ , .
In a as chromategaphic analysis of primary amines as their Schiff ases, furfural was found to give better results than benzaldehyde in the derivatization reaction (39). By the use of 2,2,2-trichloro-l.l-dimethylethylchloroformate as derivatizing agent, hydrophilic amines can be determined at concentrations below M using thermionic or electron-capture detectors. 2,4,6-Tribromophenyl chloroformate was used to derivatize a hydrophobic amine (40). In a comparison of two indicator systems used in end point detection in a nonaqueous catalytic thermometric titration of 14 representative bases, there was found no significant differences in relative standard derivation or titration error. The indicator reagents studied were e-methylstyrene and mixtures of acetic anhydride and hydroxy compounds (42). Certain bases such as aniline and benzylamine cannot be determined by use of the acetic anhydride indicator system. It has been found that aniline facilitates the transfer of protons across an aqueous-nitrobenzene interface. With cyclic voltammetry, the peak current can be related to concentration of aniline in the nitrobenzene (42). Tertiary amines in the presence of amine oxides have been determined by a rapid nonaqueous potentiometric titration procedure (43). Reverse-phase high-performance liquid chromatography was used to determine normal alkvlamines after derivatization with 2,2-diphenyl-l-oxa-3-oxonia"-2-boratanaphthalene. The derivatives were detected fluorometrically (44). Aromatic amines, phenols, and other active hydrogen compounds that couple with diazonium salts have been determined by a titrimetric procedure using an ion-selective electrode. The most widely applicable titrant was 4-bromo-lnaphthalenediazonium chloride (45). A back-titration procedure using sodium tetraphenylborate or 2,4-diaminotoluene to determine the excem diazonium salt was recommended for the analysis of slowly reacting compounds (46).
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aqueous samples have been determined by ion chromatography after conversion to their bisulfite addition productn (28). A study show that the modified pararosaniline method for formaldehyde in air is not afferted by the presence of phenol whereas the chromotropic acid method is seriouslv inhibited by comparable excesses of phenol (29).
AMIDES T h e dehydration of amides to nitriles by treatment with
trifluoroacetic anhydride has been used in the gas chroma. tographic determination of amides (30).
AMINES A number of spectrophotometric methods have been developd for the determination of amines. They differ primarily in the way the absorbing species is produced. Primary and secondary aliphatic amines form 1:l colored products with p-benzoquinone in ethanol. Average recoveries of 98.5% without interference from tertiary amines, ammonia, amides, imides, anilides. hydrazines, and o-amino arids were observed (31). Various alinhatir amines were detected in the ranre of -~ 0.2-4.0g/mL by converting them into a complex with barium ion and crowned dinitrophenylazophenol (1) (32). ~~
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AMINO ACIDS
I
Aromatic and aliphatic primary, secondary, and tertiary amines react with chloranil to form blue to purple comdetermined spectrophotometrically. pounds and can Phenol, oxiranes, alkynes, and non-amine nitrogen compounds do not interfere (33). Primary amines with three or more carbons form complexes with Metanil Yellow (Ill and 18-cmwn-6 or dibeml8.rown-6
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For determination of both D and L isomers of aspartic acid in amino acid mixtures, the isomers are derivatized with a chiral fluorogen before high-performance liquid chromatography on a reversephase column. The derivatization is done with 0-phthalaldehyde and N-acetyl-L-cysteine in a manner analogous to that using o-phthalaldehyde and the achiral 2-mercaptoethanol. The method permits the detection of 5 pmol of D-aspartate in a 100-fold excess of L-aspartate (47). The separation of D and L isomers of some amino acids and their derivatives has been accomplished by chromatography on silica gel modified with BOC-L-valine (48). A thin-layer chromatography method for separation of dansyl amino acid enantiomers uses reversed-phase plates, pretreated with a Cu(I1) complex of N,N-dipropyl-L-alanine (49). ANALYTICAL CHEMISTRY, VOL. 58. NO. 5, APRIL 1988
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FUNCTIONAL GROUP ANALYSIS
Cysteine and cystine have been separated on a stainless steel column packed with LiChrosorb RP-18 and detected polarographically (50). A high speed (30 min) chromatographic system for amino acids using a 6-pm cation-exchange resin uses a postcolumn reaction with o-phthalaldehyde and sodium hypochlorite (51).
ANHYDRIDES Two rapid and precise methods for the determination of carboxylic anhydrides have been developed. In one, the anhydride is treated with an excess of 4-aminophenol followed by a photometric titration of the N-acyl-4-aminophenol produced with 2-iodylbenzoate.
In the second method, excess sulfanilamide is added to the anhydride followed by a back-titration with chloramine-T to a methyl red end point (52). The spectrophotometric azide method described above for the determination of acid halides has been successfully used in the analysis of aliphatic anhydrides (10).
orcinol-hydrochloric acid reaction (66).
CHLORAMINES Cyclic voltammetry of aqueous solutions of organic and inorganic chloramines has been studied at various pH levels (67). Chloramines in aqueous solution form N-alkyl-5-dimethylamino- 1-naphthalenesulfonamides which can be detected a t concentrations as low as lo-’ M using high-performance liquid chromatography and a fluorescence detector (68).
ESTERS A coated piezoelectric quartz crystal device has been developed for the detection of propylene glycol dinitrate at levels lower than 0.05 ppm in air (69). Triglycerides at microgram levels may be determined spectroscopically by first conversion to the fatty acid hydrazide followed by formation of the N-isopropylidene alkanolhydrazide on reaction with acetone (70).
ETHERS Azabicyclic pol ethers (cryptands) have been determined down to 1.0 x 10-BM using lead(I1) perchlorate as titrant (71).
AROMATIC HYDROCARBONS A review describing the detection of polynuclear hydrocarbons by laser-excited fluorescence, photoacoustic, and photoionization methods has been published (53). Electrochemical detection of polynuclear aromatic hydrocarbons in gradient high-performance liquid chromatography becomes feasible when a newly developed large volume wall-jet detector is used (54). Ultraviolet resonance Raman spectroscopy has been proposed as a means to detect trace levels (20 ppb) of polynuclear aromatic hydrocarbons in complex matrices (55). Additional methods for the detection of polynuclear aromatic hydrocarbons include the use of the preexponential factor of the fluorescence decay curve (56),high-resolution Shpol’skii spectrometry in a matrix (57),tunable-dye laser excited Shpol’skii spectrometry (58),and active nitrogen-induced chemiluminescence (59). In the Florisil and silica gel cleanup of polynuclear aromatic hydrocarbon samples, oxidative losses of sample occur when ethyl ether containing peroxides is the solvent (60).
AZO COMPOUNDS Azo compounds were determined by conversion to elemental nitrogen with either chromic acid or with bromine from bromide-bromate. The nitrogen was detected by gas chromatography. The bromide-bromate method gave low results with some compounds (61). CARBOHYDRATES Some pyranose anomers of mono- and disaccharides have been separated by low-temperature HPLC using amino columns in acidic eluents (62). The fluorescence detection of reducing sugars by the cyanoacetamide reaction after chromatographic separation has been greatly improved by the simple expedient of increasing the temperature of the reaction from 105’ to 135’. The improvement is fivefold with ribose and tenfold with glucose (63). A chemically modified electrode in which glucose oxidase
is covalently attached to the surface of reticulated vitreous carbon has been described. The hydrogen peroxide formed in the enzymic reaction is consumed a t the electrode surface. The current varies nonlinearly with the glucose concentration over most of the range from to 10-1 M but is approximately linear over the range 2.5-10 mM. The properties of the electrode make it attractive for possible use in flow systems (64). In the alkaline copper method for reducing sugars, both boric acid and chloride have been reported to suppress the reducing power of glucose and maltose. Chloride can affect the linearity of the absorbance vs. concentration curves (65). The color reaction between pentoses and indole in hydrochloric acid is reported to be twice as sensitive as the similar 104R
ANALYTICAL CHEMISTRY, VOL. 58, NO. 5, APRIL 1986
A two-phase titration procedure has been developed for the determination of poly(oxyethy1ene) nonionic surfactants in which the surfactant as a sodium tetraphenylborate complex is extracted into the nonaqueous layer. The complex is titrated with tetradecyldimethylbenzylammonium chloride (72). The poly(oxyethy1ene) nonionic surfactants were also determined in a two-phase system by titration with sodium tetrakis(4-fluoropheny1)borate (73) or by spectrophotometry after conversion to a red complex by reaction with Fe(SCN), (74). The cleavage of carboxymethyl ether groups with HI followed by the determination of the acetic acid produced by liquid chromatography allows the analysis of carboxymethyl ether groups in the presence of other cellulose ether substituents (75). Carbon-13 NMR has been used to determine the oxygen ether content of coals (76) and humic substances (77). A trapping system for collecting methyl tert-butyl ether in the presence of gasoline vapors has been described. The ether is determined by gas chromatography (78). The quantity of free poly(ethy1ene glycol) in the presence of esterified fatty acids can be determined by proton NMR in the presence of sodium dodecyl sulfate (79). Poly(ethy1ene glycol) bonded to Sepharose 6B through 1,4-bis(2,3-epoxypropoxy)butane can be cleaved quantitatively at the ether bonds with BBr,. The cleavage products are determined by gas chromatography (80).
HALOGEN COMPOUNDS Analysis by gas chromatography coupled with sensitive detectors is the most common method for determination of halogen compounds. In one detection system, a rapid scanning microwave-induced plasma emission detector is used (81)while in another, detection is based on atmospheric pressure ionization mass spectroscopy (82). An enrichment procedure has been developed for the determination of polychlorinated dibenzofurans and related compounds. Components of the enriched sample are determined by gas chromatograph-mass spectrometry or by gas chromatography with an electron capture detector (83).
HYDRAZINES Analysis of hydrazine derivatives has been accomplished by titration with phenyliodosoacetate, PhI(OAc)2, using a methyl red indicator or by an indirect method where the excess
FUNCTIONAL GROUP ANALYSIS
of phenyliodosoacetate is determined iodometrically (84). Electrochemically generated iodine has been used in the coulometric titration of hydrazines with an error of _
