Determination of the Insecticide Promecarb by Fluorogenic Labelling with Dansyl Chloride

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ANALYST, AUGUST 1991, VOL. 116 851 Determination of the Insecticide Promecarb by Fluorogenic Labelling With Dansyl Chloride

F. Garcia Sanchez and C. Cruces Blanco Department of Analytical Chemistry, Faculty of Sciences, The University, 29071 Malaga, Spain

The use of spectrofluorimetry to determine the fluorescent derivative of the insecticide promecarb, following hydrolysis to the corresponding phenol in basic media and subsequent coupling with the labelling agent dansyl chloride, is described and discussed. A study of media of different basicity and of different temperatures for both reactions gave optimum conditions of 20 min for the hydrolysis reaction and 10 min for the labelling reaction at 55 "C in 0.05 mol dm-3 sodium hydrogen carbonate solution with a reagent to insecticide ratio of 12: 1. The effect of the solvent on the formation of the dansyl derivative and on the extraction process was studied using nine and seven solvents, respectively. The use of a mixture of acetone and water (50 + 50, v/v) and an extraction into cyclohexane gave the best results. The minimum detectable concentration of promecarb in the experimental assays was 100 ng ml-1. The error and relative standard deviation at a concentration level of 0.6 pg ml-1 were 9.7 and 10.9%, respectively. Air samples containing promecarb at different concentration levels were analysed. Keywords: Promecarb insecticide determination; air samples; dansyl chloride labelling; spectrofluorimetry

The N-methylcarbamate insecticide promecarb (3-isopropyl- Experimental 5-methylphenyl methylcarbamate) acts against many pests and is effective both as a contact and a stomach poison. The Apparatus risks associated with exposure to this type of insecticide are All spectrofluorimetric measurements were performed on a caused by the accumulation of endogenous acetylcholine in Perkin-Elmer Model MPF-43A fluorescence spectrophoto- human beings, due to the inhibition of cholinesterase. meter, equipped with an Osram XBO 150 W xenon lamp, For these reasons, and taking into account the paucity of excitation and emission grating monochromators, 1 X 1 cm analytical methods described in the literature for this insecti- quartz cells, a Hamamatsu R-777 photomultiplier and a cide,' simple and rapid assays are required. Carbamate Perkin-Elmer 023 recorder. Instrument sensitivity was adjus- pesticides have frequently been analysed by thin-layer2 or gas ted daily, using a Rhodamine B bar as a reference standard. A chromatography.3 These procedures, however, are not water-bath circulator (Frigiterm S-382) was used for tempera- entirely satisfactory in terms of the sensitivity normally ture control. An electric shaker (Selecta) was used for required for residue analysis. extraction procedures. Because promecarb does not show native fluorescence, the technique of spectrofluorimetry has not been previously Reagents applied to its determination. This difficulty has been over- come in the present work by introducing a highly fluorescent A stock solution (1 mg ml-1) of promecarb (>99% pure, moiety into the pesticide molecule. Such an approach, called Pestanal quality, Riedel-de Haen, Hannover, Germany) was fluorogenic labelling, has found much application in the field prepared in analytical-reagent grade acetone. A working of amino acid and peptide chemistry4 and also in pesticide standard solution of 60 pg ml-1 was prepared from this stock residue analysis.5-9 solution by dilution with acetone. The dansyl chloride used The reagent most often used in such labelling techniques is (Sigma, St. Louis, MO, USA) was prepared as solutions (1 dansyl chloride [5-(dimethylamino)naphthalene-l-sulphonyl mg ml-1 and 470 pg ml-1) in ACS spectrophotometric grade chloride], which reacts with primary and secondary amino acetone (Gold Label; Aldrich, Milwaukee, WI, USA). groups and phenolic hydroxy groups to form highly fluores- Sodium hydroxide, sodium carbonate and sodium hydrogen cent derivatives. The extensive application of dansyl chloride carbonate were of analytical-reagent grade (Merck, Darm- is due not only to its ability to react with compounds having an stadt, Germany); solutions of these salts were prepared in amine or phenol moiety but also to its ability to react with both de-ionized water. All of the solvents used were of analytical- the amine and phenol hydrolysis products of carbamates, reagent grade. All pesticides tested were of 99% purity or resulting in two derivatives suitable for the quantification of better and were used without further purification. carbamate residues in the low nanogram range. This procedure has permitted the determination of numerous carbamate Reaction Procedure insecticides, 1@12 organophosphate insecticides,*3,14 herbi- cides7.15 and fungicides.16 Similar procedures have been used Different volumes (30,21,15,9 and 3 pl) of the stock solution for determining amino acids,17?18 food additives such as of promecarb in acetone (1 mg ml-1) and 50, 40, 30, 20 and monosodium glutamatel9 or alkaloids in complex phar- 10 pl of the working standard solution of the same reagent in maceutical dosage forms.20.21 acetone (60 pg ml-1) were placed in 15 ml test-tubes. A 0.5 ml In the present work, the use of dansyl chloride as a volume of 0.1 mol dm-3 sodium hydrogen carbonate solution fluorogenic labelling reagent for the determination of the was added and the tubes were loosely stoppered and heated in carbamate insecticide promecarb is described. The reaction, a water-bath at 55 "C for 20 min. The tubes were then cooled based on the formation of a fluorescent derivative of the to room temperature and 0.5 ml of a solution of dansyl phenolic hydrolysis product of the carbamate, has been chloride in acetone (470 pg ml-1) was added. The tubes were studied in detail and can be carried out in less than 40 min. heated in the water-bath for a further 10 min at 55 "C and then 852 ANALYST, AUGUST 1991, VOL. 116 allowed to cool to room temperature. A 3 ml volume of cyclohexane was added and the tubes were shaken for 1 min. Immediately after sample preparation, when both layers were clearly separated, the fluorescence intensity of the organic layer was measured at an excitation wavelength of 340 nm and an emission wavelength of 485 nm against a reagent blank.

Promecarb Hydrolysed Standard Procedure for Air Samples promecarb Air samples were collected in a workroom environment (dry A temperature, 29 "C; humidity temperature, 16 "C; relative humidity, 52%) of 40.5 m2 (4.5 x 9.0 m) with 37 mm three-body filter cassettes equipped with mixed cellulose ester OH membrane filters of 0.8 pm pore size [Mine Safety Applicans Co. (MSA), Pittsburgh, PA, USA]. Battery-powered per- sonal sampling pumps (Model Fixt-Flo, MSA) with the capacity to operate at between 1 and 2 1 min-1 were calibrated at flow rates of 1.00 1 min-1 over a period of 24 h. Each filter so2 I sample was treated with 25 ml of acetone. After the mixture 0 had been shaken for 30 min at 25 "C and 160 rev min-1, the Dansyl chloride I acetone extract was transferred into a round-bottomed glass funnel and evaporated to incipient dryness in a rotary evaporator at 45 "C. The dry residue was then dissolved in acetone and taken to a final volume of 10 ml with the same solvent. An aliquot of this solution (100 p1) was then treated as described under Reaction Procedure.

Results and Discussion Unless indicated otherwise, the conditions employed in the S03H optimization experiments were the same as those employed in Sulphonic acid the Experimental section. From earlier work in the field of carbamate pesticide B analysis,7~"~14~*2~23it is known that the labelling reaction with Fig. 1 Over-all reaction scheme for A, the hydrolysis; and B, the dansyl chloride involves two distinct steps: (a) hydrolysis of dansylation of promecarb the carbamate; and (b) coupling of the hydrolysis product with dansyl chloride. The coupling reaction proceeds faster than either the hydrolysis of the carbamate or the hydrolysis of the reagent to It can be seen that solvents that are immiscible with water the corresponding sulphonic acid. As the rate of hydrolysis of (such as chloroform and isobutyl methyl ketone) give no dansyl chloride is constant at a constant pH or temperature, fluorescence, indicating that dansylation has not taken place. only the rate of hydrolysis of the carbamate will govern the Solvents with high relative permittivities and hydrogen yield of the dansyl derivative. A reaction scheme is shown in bonding capacity (such as water, ethanol and methanol) give Fig. 1 for the formation of the derivative of the N-methyl- high fluorescence both in the analyte and reagent blank, carbarnate, promecarb. because of the absence of hydrolysis of the excess of dansyl Several reaction procedures were attempted for the hydroly- chloride to the corresponding sulphonic acid. The fluor- sis of the insecticide to the corresponding phenol. Different escence emission occurs also at longer wavelengths in highly concentrations (0.02, 0.04, 0.06, 0.08 and 0.10 mol dm-3) of polar solvents as reported previously.26 As the extent of the sodium hydroxide, sodium hydrogen carbonate and sodium solute-solvent interaction increases, the emission is shifted to carbonate were tried using a heating time of 30 min (hydrolysis shorter wavelengths. reaction) and 20 min (dansylation reaction) at 45 "C. 1,4-Dioxane, despite having a low relative permittivity, is The fluorescence intensity of the organic layer (benzene) miscible with water and gives, together with acetonitrile and was compared with that of a blank signal. The results (Fig. 2) acetone, a good signal-to-noise ratio. It is deduced from this indicated that, by using sodium hydrogen carbonate solution study that a change in the polarity of the reaction medium for the hydrolysis process, stable analytical measurements and modifies, to a great extent, the characteristics of the labelling a good signal-to-noise ratio were obtained with a constant pH reaction. In order to obtain a good signal-to-noise ratio, the of 9 in the reaction mixture (1 pg ml-1 of promecarb). excess of dansyl chloride has to be completely converted into The dansylation reaction is usually performed in a mixture the corresponding sulphonic acid, which is more polar and of water and acetone at pH 9-11.15 This method proved to be remains in the aqueous phase instead of passing into the favourable with respect to the competitive kinetic rates of the organic layer. labelling reaction and the hydrolysis of dansyl chloride .24,25 After acetone had been chosen as the solvent for the The effect of the solvent on the dansylation reaction was reaction procedure, the ratio of water (buffer) to acetone in investigated. For these experiments, 15 pl of the stock solution the reaction mixture was studied at values of between 20 and of promecarb in acetone (1 mg ml-1) and 0.5 ml of 0.1 90%. The ratio was found not to be critical, as reported mol dm-3 sodium hydrogen carbonate solution were placed in previously.15.27 It was decided to use a mixture of 50% acetone 15 ml test-tubes and the solution was heated in a water-bath at (dansyl chloride solution) and 50% water (buffer solution) for 45 "C for 30 min. Then, 0.5 ml of each pure solvent and 50 pl of further work. The reaction eliminates HCl but the pH is kept dansyl chloride in acetone (1 mg ml-1) were added and the constant by the presence of 0.05 mol dm-3 sodium hydrogen mixture was heated for a further 20 min at 45 "C. The carbonate as buffer. fluorescence of the organic (cyclohexane) layer was measured Owing to the partial hydrolysis of the dansyl chloride and the results obtained are summarized in Table 1. reagent by the buffer or its consumption as a result of the ANALYST, AUGUST 1991, VOL. 116 853

Table 1 Effect of the solvent on the dansylation reaction

Relative RFI? permittivity Solvent at 25 "C h,,/nm h,,/nm Ah*/nm Analyte Blank A RFIf 1,4-Dioxane 2.2 338 480 142 83 4 79 Chloroform 4.8 345 485 140 5 2 3 Isobutyl methyl ketone 13.1 345 490 145 1 1 0 Ethanol 20.5 345 495 150 140 128 12 Acetone 20.7 340 485 145 100 4 96 Methanol 32.7 345 500 155 164 164 0 Acetonitrile 35.5 343 492 149 71 4 67 Dimethylformamide 36.7 338 488 150 10 9 1 Water 78.5 350 495 140 25 3 22 * Stokes shift = he, - hex. ? RFI = Relative fluorescence intensity. $ ARFI = RFI analyte - RFIblank-

0 0.02 0.04 0.06 0.08 0.1 0.12 [NaOH]/mol dm-3

2 6 10 14 18 Dansyl chloride: analyte

- Fig. 3 Effect of the amount of dansyl chloride on the formation of 60 the phenol derivative of 5 pg ml-1 of promecarb (shaded area shows a, the working zone) v) 2 the hydrolysis product. Fig. 4(a) shows the rates of hydrolysis at different temperatures. These were determined by forming the dansyl derivative of the liberated phenol in the hydrolysis mixture of the carbamate. The amount of dansyl derivative formed is directly proportional to the extent of carbamate

I1I 1 I I I hydrolysis. Although the rate of hydrolysis is increased on 0 0.02 0.04 0.06 0.08 0.1 0.12 increasing the temperature from 25 to 55 "C, prolonged [Na2C031/moldm-3 heating at 65 "C leads to decomposition of the products. Also, 30 (c) the fluorescence signal was found to be fairly stable for heating I times of between 5 and 20 min at 55 "C, but for heating times longer than 20 rnin the signal started to increase. A heating time of 20 min was considered sufficient for complete hydrolysis of the carbarnate, thereby avoiding problems of decomposition. In order to unify the temperatures for the hydrolysis and dansylation reactions, a study of the effect of temperature on A I T ,-B the latter was carried out. Fig. 4(b) indicates that at 45 "C,35 0 0.02 0.04 0.06 0.08 0.1 0.12 rnin are required for complete stabilization of the fluorescence [NaHC031/moldm-3 measured, whereas only 10 rnin are necessary at 55 "C. As a Fig. 2 Influence of (a) NaOH, (b) Na2C03 and (c) NaHC03 result, the working conditions chosen for the over-all reaction concentrations on the hydrolysis reaction and fluorescence intensity of were 20 rnin for the hydrolysis reaction and 10 rnin for the A, promecarb; and B, a reagent blank dansylation reaction at 55 "C. These reaction times are considerably shorter than those formation of side-products, the amount of dansyl chloride normally employed by other workers for the determination of added to the reaction mixture could influence the results. Fig. similar compounds with dansyl chloride (between 45 and 90 3 shows the effect of varying the dansyl chloride concentration rnin); hence the optimization of the experimental variables has on the yield of the dansyl derivative for a final promecarb permitted a rapid method for the determination of promecarb concentration in the reaction medium of 5 pg ml-1. A gradual (30 min), which is suitable for routine analysis. increase in fluorescence intensity on increasing the dansyl chloride to analyte concentration ratio up to 10 : 1 is observed. Fluorescence Phenomena A minimum of an 8-fold concentration excess of dansyl chloride over the carbamate is required. Use of a larger excess The spectra of the dansylated promecarb hydrolysis products, of dansyl chloride does not affect the results. extracted into cyclohexane, are shown in Fig. 5. The excitation The rate of hydrolysis of the carbamate increased at higher and emission maxima were found to be 340 and 485 nm, temperatures as did the rate of the reaction of the reagent with respectively. In order to check that the excess of dansyl 854 ANALYST, AUGUST 1991, VOL. 116 chloride is hydrolysed and that the hydrolysis products remain methane), and an increase in the blank signal. Solvents such as in the aqueous phase, a blank test was performed without benzene and cyclohexane gave the best signal-to-noise ratio. promecarb, and the organic phase was analysed by measuring Cyclohexane was chosen for further work as it is 30 times less the fluorescence intensity in the same wavelength range. As toxic than benzene. can be seen in Fig. 5, no significant signal was found. The The reaction proved to be reproducible from one day to the formation of the intensely fluorescent hydrolysis product (the next although fresh standards were always carried through the sulphonic acid) makes it necessary to isolate this compound reaction procedure. The dansylated derivatives were very from the derivative of the hydrolysed promecarb. This stable, showing the same fluorescence intensity after storage isolation is usually carried out by solvent extraction into in a refrigerator for 21 d. This is particularly useful for residue non-polar solvents such as benzene or hexane. The organic analysis as samples cannot always be extracted and analysed phase is then used for fluorescence measurements. Maximum on the same day. emission of dansyl derivatives occurs between 450 and 580 nm, depending on the type of solvent used. The effect of the solvent on the extraction process was Calibration Graph and Repeatability Experiments studied using seven solvents. All the solvents were of low The relative fluorescence intensity of a 3 ml volume of the polarity and had low relative permittivities and also low organic phase, obtained as described under Reaction Pro- solubility in water. Table 2 indicates that an increase in the cedure, was found to be a linear function of the promecarb relative permittivity causes a bathochromic shift of the concentration over the range 0.2-10.0 pg ml-1. The precision emission maxima (485 nm, cyclohexane; 504 nm, dichloro- is good, as shown by the regression coefficient of 0.9980. The equation for this graph is: relative fluorescence intensity = 0.06 [promecarb] -2.70 for the range 0.2-10.0 pg ml-1. The minimum detectable concentration or detection limit, cL, and the lower limit of the dynamic range, cQ, defined by 120 IUPAC28 as CL = 3sB/rn and CQ = 10s~/rn[where SB is the relative standard deviation (RSD) of the blank signal and 100 rn

80 A B 60 > .z 40 aC 4- .G 20 0, C $0 a 4 110 r- .-P 100 -4- 90

60 290 330 370 410 450 490 530 570 610 50-_ Wnm 0 5 10 15 20 25 30 35 tlmin Fig. 5 Fluorescence spectra of the dansylated phenol moiety of promecarb (solid line) and a reagent blank (broken line) under the Fig. 4 Influence of time and temperature on (a) the hydrolysis and same conditions. Promecarb concentration, 5 pg ml- l; acetone-water (b) the dansylation of 5 pg ml-1 of promecarb with a 12-fold excess of (50 + 50, vlv); and a 12-fold excess of dansyl chloride. A, Excitation; dansyl chloride. A, 55; B, 45; C, 65; and D, 25 "C and B, emission

Table 2 Effect of the solvent on the extraction process

Dipole Relative RFIS moment at permittivity Solubility TLV-t hexlhem Solvent 25 "CPD at 25 "C in water* lpg ml-1 lnm Analyte Blank ARFIP Benzene 0 2.3 0.18 10 3451490 96 10 86 Cyclohexane 0 2.0 0.01 300 3381485 116 10 106 Hexane 0.1 1.9 0.001 100 3381490 74 5 69 Toluene 0.3 2.4 0.051 200 3451490 91 18 73 Dichloromethane 1.1 8.9 1.60 500 3451504 90 32 58 Chloroform 1.1 4.8 0.815 25 345/500 87 22 65 Ethyl acetate 1.9 6.0 8.70 400 3301490 77 102 -25 *Solubility in water expressed in % dm. 7 TLV = Threshold limit values. $ RFI = Relative fluorescence intensity. 8 ARFI = RFIanalyte - RFIblank. ANALYST, AUGUST 1991, VOL. 116 855

Table 3 Characteristics of the proposed spectrofluorimetric method for the determination of promecarb

Linear Mean dynamic concentration SA/ CLl rangel found/ Error? RSDS

SS* yg ml-l ygml-l pgml-I ygml-I (Yo) (Yo) 4.0 0.1 O.l§ O.l$-lO.O 0.6 9.7 10.9 * Expressed in units of relative fluorescence intensity. ? Relative error = 100ts/Xn+. $ RSD = Relative standard deviation. § Values calculated from the expressions: XB + 3sB/m and xB + 10sB/m, respectively. the slope of the calibration graph] and the sensitivity, sA,8 of Table 4 Interference study. Analysis of synthetic mixtures the determination, together with other analytical characteristics, are summarized in Table 3. Concentration of Repeatability assays were carried out by performing the promecarb Recovery Interferent * foundlyg ml- k SD? (%) hydrolysis reaction, and the subsequent dansylation, simul- taneously on seven separate carbamate samples of two Chlortoluron (25) 5.4 101 t 5 107 k 4 different concentrations (0.6 and pg ml-1). The RSD Fenitrothion (5) 5.3 5 Propham (50) 4.3 86 f 3 (1OOs/X) and the relative error (100stlVnX) are a measure of Methyl parathion (25) 4.2 83 k 3 the precision and accuracy of the analytical determination, l-Naphthaleneacetic acid, NAA respectively, where s is the standard deviation (50) 5.6 114 k 8 (%‘X(x - X)2/n - 1) for n = 7, X the mean value of seven Dimethoate (50) 5.3 107 k 5 samples containing 0.6 or 5 pg ml-1 of carbamate and t the l-Naphthol(50) 4.6 92 k 2 Student’s t value for a 95% confidence limit. An RSD of 5.4% Chlortoluron (25) + 1-naphthol and an error of 4.8% were obtained at the higher concentra- (25) 5.2 104 k 5 Propham (50) + NAA (25) 4.7 95 t 5 tion level of 5 yg ml-1. At lower concentrations (0.6 yg mi-*), Dimethoate (50) + chlortoluron both the RSD (10.9%0) and the error (9.7%) increased. (25) 5.5 110 k 7 The inherent error in the dansylation step was determined Propham (25) + dimethoate (25) by analysing a set of seven replicate samples containing 5 + chlortoluron (25) 4.7 95 * 4 pg ml- 1 of promecarb and prepared from the same hydrolysed Propham (50) + fenitrothion (5) 5.6 112 k 4 solution. In order to evaluate the inherent error in the Dimethoate (25) + fenitrothion hydrolysis reaction, seven aliquots of a 5 pg ml-1 sample from (5)+ NAA(5) 5.5 109 * 5 individual hydrolysed solutions were analysed. Chlortoluron (25) + l-naphthol The first step evaluates the intra-assay precision, whereas (25)+ NAA(25) 4.6 92 f 2 Carbaryl(2.5) 5.5 110 5 the second gives the inter-assay precision of the proposed method. The intra-assay RSD and error were 6.8 and 6.l%, * Promecarb concentration added: 5 pg ml-I. Values in parentheses respectively, whereas values of 5.4 and 4.8%, respectively, are the concentrations of the interferents in pg ml-I. ‘r Mean value of three determinations. were obtained for the inter-assay precision. This indicates that the higher percentage of error is caused by the dansylation reaction, as in other types of labelling reactions. The between-day precision was determined by analysing samples The criterion for evaluation of interference was a deviation containing 5 pg ml-1 of labelled promecarb (hydrolysis of the fluorescence intensity of ;F k 3s,, where X is the mean products) over a period of seven consecutive days. The RSD concentration value found after a repeatability assay of and error obtained were 5.8 and 5.2%, respectively. samples (n = 7) containing 5 yg ml-1 of promecarb and s, is the standard deviation of these measurements. This criterion permits a confidence limit for the concentration measurements of between 4.2 and 5.8 yg ml-1, which is equivalent to a Specificity of Promecarb Determination confidence of 83.7-116.3% recovery. Results are shown in Table 4. Low recoveries are obtained if the ratio of the Owing to the wide applicability of the dansylation procedure labelling reagent to the synthetic mixture to be analysed is for pesticide analysis,10-16 it was considered of particular below 12. interest to determine the selectivity of the proposed method The values shown in Table 4 indicate that the concentration for the determination of promecarb in the presence of other ratio for propham, 1-naphthaleneacetic acid, dimethoate and pesticides that are susceptible to derivatization with this 1-naphthol is 10 : 1, for chlortoluron the ratio is 5 : 1 and for labelling reagent. fenitrothion it is 1 : 1. Carbaryl and methyl parathion, both of The specificity of the proposed spectrofluorimetric method which formed derivatives with dansyl chloride, gave a positive was determined with different concentrations of several interference; hence these compounds must first be separated pesticides having a chemical structure that made them by chromatographic techniques. The maximum ratio tested susceptible to derivatization with dansyl chloride, with or for these pesticides was a 10-fold m/m ratio of interferent to without a previous hydrolysis reaction. The compounds used promecarb. were the insecticides carbaryl, chlortoluron, fenitrothion, methyl parathion, dimethoate and l-naphthol, the herbicide propham and the plant growth regulator 1-naphthaleneacetic Analysis of Air Samples acid. Because of their benefits, pesticides have become increasingly Various volumes of stock solutions of the different potential important in agricultural production; however, their prolifera- interferents in acetone (1 mg ml-1) were added to 15 ml tion in the environment is causing concern for human health test-tubes together with 15 yl of the stock solution of and because of their effect on other components such as soil, promecarb (1 mg ml-1) in order to obtain different interferent sediment, water, air, animals and vegetation. to analyte ratios in the final solution. The solutions were then In an attempt to measure the amount of environmental treated as described under Reaction Procedure. contamination related directly to the application of promecarb 856 ANALYST, AUGUST 1991, VOL. 116

6 Seitz, W. R., CRC Crit. Rev. Anal. Chem., 1980, 8, 367. Table 5 Analysis of environmental air samples 7 Lawrence, J. F., and Laver, G. W., J. Assoc. Off. Anal. Chem., 1974,597, 1022. Promecarb 8 Garcia Sanchez, F., and Cruces Blanco, C., Anal. Chem., 1986, content k SDt/ 58, 73. Sample No. Volume*/l mg m-3 9 Garcia Sanchez, F., Cruces Blanco, C., Hernandez Lopez, M., 1 21.3 6+1 Marquez Gomez, J. C., and Carnero, C., Anal. Chim. Acta, 2 18.9 4.5 + 0.3 1988,205, 149. 3 21.3 6.2 -t- 0.8 10 Lawrence, J. F., and Frei, R. W., Anal. Chem., 1972,44,2046. 4 20.2 6.4 ? 0.9 11 Frei, R. W., and Lawrence, J. F., J. Chromatogr., 1972,67,87. 5 22.5 8-cl 12 Lawrence, J. F., and Leduc, R., J. Chromatogr., 1978,152,507. 6 19.5 5.2 + 0.4 13 Lawrence, J. F., Renault, C., andFrei, R. W., J. Chromatogr., * Volume of air sampled. 1976,121, 343. t Mean value of three determinations. 14 Frei, R. W., Lawrence, J. F., and LeGay, D. S., Analyst, 1973, 98, 9. 15 Frei-Hausler, M., Frei, R. W., and Hutzinger, O., J. Chromat- to different crops (potato, citrus fruits and fruit trees) by ogr., 1973, 79, 209. dusting, the analysis of air samples by the proposed spectro- 16 Traore, S., and Aaron, J. J., Talanta, 1981, 28,765. fluorimetric method was carried out. 17 Bayer, E., Grom, E., Kaltenegger, B., and Uhmann, R., Anal. Chem., 1976,48, 1106. Six air samples were collected from different areas of a 18 Greco, B., J. Chromatogr., 1983, 255, 67. workroom environment permeated with promecarb at similar 19 Rhys Williams, A. T., and Winfield, S. A., Analyst, 1982, 107, flow rates. After a sampling time of 15 min, total air volumes 1092. of between 18 and 23 1 were obtained. The results, expressed 20 Nachtmann, F., Spitzy, H., and Frei, R. W., Anal. Chim. Acta, in milligrams per cubic metre of promecarb in the environ- 1975, 76, 57. ment, and given as the mean values of three replicates of each 21 Frei, R. W., Santi, W., and Thomas, M., J. Chromatogr., 1976, environmental sample, are presented in Table 5. 16, 365. 22 Frei, R. W., and Lawrence, J. F., J. Chromatogr., 1971,61,174. This investigation was supported financially by The Direccion 23 Lawrence, J. F., and Frei, R. W., J. Chromatogr., 1972,66,93. 24 Seiler, N., and Niechmann, M., Fresenius 2. Anal. Chem., General de Investigacion Cientifica y Tecnica (Project PB86- 1966, 220, 109. 0247). 25 Seiler, N., J. Chromatogr., 1971, 63, 97. 26 Chen, R. F., Arch. Biochem. Biophys., 1967, 120,609. References 27 Seiler, N., and Wienchmann, M., Progress in Thin-layer Chromatography and Related Methods, eds. Niedenvieser, A., Gunew, D. S., in Analytical Methods for Pesticides and Plant and Pataki, G., Ann Arbor Science Publishers, Ann Arbor, MI, Growth Regulators, eds. Zweig, G., and Sherma, J., Academic 1970, vol. I, p. 133. Press, New York, 1980, vol. XI, p. 141. 28 IUPAC, Guidelines for Data Acquisition and Data Quality Mendoza, C. E., and Shields, J. B., J. Chrornatogr., 1970, 50, Evaluation in Environmental Chemistry, Anal. Chem., 1980, 92. 52, 2242. Katz, S. E., and Strusz, R. E., J. Agric. Food Chem., 1969,17, 29 Sommer, L., Langova, M., and Kuban, V., Scr. Fac. Sci. Nat. 1409. Ujep Brun. Chem., 1978, 8, 13. Pataki, G., Techniques of Thin-layer Chromatography in Amino Acid and Peptide Chemistry, Ann Arbor Science Publishers, Ann Arbor, MI, 1968. Paper 8104298E Fink, D. W., TrAC, Trends Anal. Chem. (Pers. Ed.),1982, 1, Received October 28th, 1988 254. Accepted March 7th, 1991