gas flows were equivalent, the circular capillary burner gives a greater emission signal in all instances. Burner heads may be readily constructed from stainless steel capillary tubing on which stable laminar flames may be maintained. These burners are safer in operation than conventional burners, even with the nitrous oxide-acetylene flame. The method of construction may be used for flame or inert gas shields for these burners.
very lean flame, rapid closure of the fuel valve produced no flashback. However, if the flame is left running for any length of time under these reduced flow conditions, localized overheating may cause damage to the burner. The 50-mm long-path nitrous oxide-acetylene flame shows a very stable CN emission region for some 20 mm above the burner head. Inert gas sheathing again extends the size and shape of this reducing region. The stability and intensity of the CN emission was measured just above the primary reaction cones with the circular burner, The results with and without nitrogen separation are shown in Figure 2 in comparison with a typical “circular slot” burner (2). Emission intensities for a restricted range of elements, from those which are readily atomized (e.g., sodium) to those which form refractory oxides (e.g., aluminium), were compared for the circular capillary and the circular slot burners operated both with and without flame separation (Table 11). Although both the burner heads were of the same diameter and the
ACKNOWLEDGMENT
We thank Perkin-Elmer (Beaconsfield, U.K.) Ltd. for technical assistance with some of this work. We thank the Science Research Council for the CAPS research studentship held by one of us (R.F.B.) and I.C.€,, Agricultural Division (Billingham, U.K.) for the research grant to K.M.A. RECEIVED for review December 5, 1969. Accepted March 6, 1970.
Fluorometric Determination of Microgram Amounts of Meperidine Leo A. Dal Cortivo, Mary M. De Mayo, and Sidney B. Weinberg Ofice of’the Medical Examiner, Suffolk County, Hauppauge, N . Y .
INTHE COURSE of experimental work involving the fluorescence behavior of various drugs, we discovered that a characteristic fluorophore is produced when crystalline meperidine hydrochloride is incubated at elevated temperatures in a mixture of formaldehyde and concentrated sulfuric acid. This observation provided the basis for the development of a method for detecting and determining the synthetic narcotic in biologic specimens suspected to contain the drug. EXPERIMENTAL
Apparatus. All spectra in this investigation were obtained using the Farrand MK-1 Spectrofluorometer equipped with a modified Heath strip chart recorder. The entrance slit of the exciter monochromator was of 20-nm bandpass; that of the analyzer monochromator was of 10-nm bandpass. The exit slits on both monochromators were of 5-nm band width. Reagents. Unless otherwise specified, Reagent Grade materials are used. A solution containing 1 mg of paraformaldehyde powder (purified) per milliliter of concentrated sulfuric acid is prepared and refrigerated for 12 hours prior to use. Procedure. One milliliter of the urine or plasma specimen is alkalized with 2 drops of concentrated ammonium hydroxide and shaken in a centrifuge tube for about 30 seconds with 5 ml of spectral quality chloroform. After centrifugation, the aqueous layer is aspirated and discarded. The organic phase is filtered through Whatman No. 1 paper to remove residual water. A 3-ml aliquot of the filtrate is transferred to a dry test tube, a micro drop of acetic acid added to prevent volatilization, and the solvent evaporated just to dryness in a heating block set at 90 “C. The residue is treated with 0.2 ml of the reagent and the mixture permitted to stand at room temperature for 5 minutes. It is then in-
cubated at 100 “C for 10 minutes, after which it is chilled in an ice bath for 5 minutes. Three milliliters of water are added and the contents of the tube mixed thoroughly. The emission is recorded over the period 350 nm to 500 nm with the exciter monochromator set at 275 nm. A calibration curve is constructed in the range 0 to 5 pg of the compound by evaporating appropriate dilutions of a reference methanolic solution of authentic meperidine hydrochloride and treating the residues identically to the unknowns. RESULTS AND DISCUSSION
The excitation spectrum of the fluorophore consists of a strong peak at 275 nm with two minor peaks at 385 nm and 405 nm. The emission curve is characterized by twin maxima at 425 nm and 440 nm. The uncorrected, instrumental spectra are shown in Figure 1, A rectilinear relationship exists between log intensity at 440 nm (or 425 nm) and log concentration up to 5 pg of the drug. Reproducibility of the method was established by assaying replicate 5-pg standards. Six such analyses furnished a mean peak height of 42.0 with an average deviation of 1.5. The fluorophore is stable for at least 1 hour at room temperature, exhibiting no diminution of fluorescence intensity during that period. The reagent is stable for at least 2 weeks when stored in the cold. Fluorescence intensity increases with increasing reagent strength, reaching a maximum at a concentration of 1 mg of paraformaldehyde per milliliter of sulfuric acid. Thereafter, the curve is a flat plateau. A similar relationship between intensity and volume of reagent is observed, the maximum occurring when 0.2 ml is used. ANALYTICAL CHEMISTRY, VOL. 42, NO. 8, JULY 1970
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tract of 1 ml of the same specimen to which 5 pg of meperidine hydrochloride was added. Note the low background contributed by normally occurring extractives a t 425 nm and 440 nm. The limit of detectability for the compound when extracted from urine or plasma is around 300 ng per milliliter. Recovery of meperidine added to urine and plasma lies in the vicinity of 65 %. The method has been applied successfully to the analysis of human tissues obtained at autopsy from decedents who had been administered the drug prior to death. In these instances, the compound was isolated from the biologic matrix by the alkaline-ether extraction procedure described by Goldbaum and Domanski (1). The method fails in the presence of quinine, quinidine, and methapyrilene, all of which give rise to products that fluoresce in the 425-nm to 440-nm region. Phenothiazines, benzodiazepines, dibenzazepines, and opiates d o not interfere.
RECEIVED for review March 19, 1970. Accepted May 8, 1970. (1) L. R. Goldbaum and T. J. Domanski in “Progress in Chemical Toxicology,” Volume 2, A. Stolman, Ed., Academic Press, New York, 1965, p 222.
Figure 1. Uncorrected excitation ( A ) and emission ( B ) spectra for meperidine fluorophore (b)
Correction Analysis of Polyimide Dielectric Coatings Using Attenuated Total Reflectance In this article by R. J. McGowan [ANAL.CHEM., 41, 2074 (1969)l there are errors both in Table I and Figure 3. The correct versions appear below. Table I. Relationship Between Curing Time and Per Cent Absorption Absorbance Spectrum Curing @ 12.5 no. time in mins micron Crazing 0.15 V. severe 2 15 Moderate 3 30 0.22 Slight 4 45 0.24 V. slight 5 60 0.37
-
L
425 440
425 440
NANOMETERS
Figure 2. Fluorescence spectra of extracts from ( A ) urine negative for meperidine and ( B ) urine containing 5 pg meperidine per milliliter Intensity of emission is enhanced steadily with increasing incubation time up to a maximum between 8 and 12 minutes. Further heating results in substantial decrements of fluorescence. Figure 2 shows the emission spectra of ( A ) the extract of 1 ml of a urine which was negative for the drug, and ( B ) the ex942
rn
ANALYTICAL CHEMISTRY, VOL. 42, NO. 8, JULY 1970
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11
Spectrum No.
A bsorbon ce
2. Cured 15 M i n
015
3. Cured 3 0 M i n
0.22
4. Cured 45 M i n
0.24
5. Cured 60 Min
0.37
12 13 14 MICRONS
Figure 3. ATR spectra of samples showing increasing absorbance with curing time
