Table VIII. Proportionality of Concentration Ratios to Absorbance Ratios for Solid Alloy Samples' Sample R, = c N i / c c u RA = ANiIAcu RJRA 5.28 0.851 6.2 SS406 3.96 0.572 6.9 H 1168 0.625 0.0952 6.6 SAC 1576 0.000771 0.000116b 6.6 c 1100 0.000841 0.000136b 6.2 C 1115 a Copper measured at 324.7 nm and nickel measured at Acu is measured a t 224.4 nm and corrected 352.5nm. to 324.7 nm.
knowing the concentration of one constituent of a sample, to determine that of any other constituent without the need for a reference sample.
ACKNOWLEDGMENT The author thanks A. Walsh for suggesting this study and for his continued encouragement and interest, J. M. Floyd for supplying the analyzed copper slag samples, J. B. Willis for analyzing the nickel compounds and incorporating them into copper disks, and P. Hannaford for many valuable suggestions.
LITERATURE CITED
i
in the sputtering cell. If the constants in Equations 4 and 5 are known, it is possible to determine the concentration of any element relative to any other in the sample. The results in Table VI1 show that the absorbance ratios ANi/AcUand AFe/AcU for a copper disk specimen are not affected by changes in discharge current, voltage, or pressure over the ranges investigated. Furthermore, Table VI11 shows that for several very different alloys the ratio ANi/Acu for the sputtered vapor is directly proportional to the ratio of the concentrations, CNi/CCu, in the solid. The results shown in both these Tables indicate that preferential sputtering, ionization, and agglomeration, if present, remain constant over a wide range of conditions. This suggests that preferential effects do not occur at all in the type of discharge used in this investigation, and hence that Equation 5 is valid. Thus it may be possible,
(1) B. J. Russell and A. Walsh, Spectrochim. Acta, 15, 883 (1959). (2) B. M. Gatehouse and A. Walsh, Spectrochim. Acta, 16, 602 (1960). (3) A. Walsh, Proceedings of the Xth Colloquium Spectroscopicurn Internationale, Washington, 1962, p. 127 (4) D. S.Gough, P. Hannaford, and A. Walsh, Spectrochim. Acta, Part E, 28. 197 11973). (5) D:'S.G&gh, Anal. Chem., 48, 1926 (1976). (6) G. M. McCracken, Rep. Prog. Phys., 36, 241 (1975). (7) M. Dogan, K. Laqua, and H. Massrnan, Spectrochim. Acta, Parts, 26, 631 (1971). (8) P. Hannaford and D. C. McDonald, unpublished work. (9) H. Jager and F. Blurn, Spectrochim. Acta, Part B , 29, 73 (1974). (IO) J. M. Floyd, Institute of Fuels Conference, Adelaide, Australia, 1974. (11) K. Kimoto, Y. Kamiya, M. Nonoyarna, and R. Uyeda, Jpn. J. Appl. Pbys., 2, 702 (1963). (12) Yu. 1. Petrov, Opt. Spectrosc. (USSR),27, 359 (1969). (13) A. Walsh, Spectrochim. Acta, 7, 108 (1955).
RECEIVEDfor review February 22, 1977. Accepted May 10, 1977.
Laser-Vaporized Atomic Absorption Spectrometry of Solid Samples Toshio Ishlzuka, * Yoshinori Uwamino, and Hlroshi Sunahara' Government Industrial Research Institute, Nagoya 1- 1, Hirate-machi, Kita-ku, Nagoya, 462 Japan
A Q-switched ruby laser was used to produce the atomic vapor from the solid samples, such as brass, steel or aluminum alloy. The atomlc vapor produced wlth the laser beam was Introduced Into the absorption path by the flow of Ar gas. The absorption signals of AI, Cr, Cu, Fe, Mn, Mo, NI, and V were traced wlth an oscllloscope, and those elements were determlned wlth the peak-helght or integratlon method. Preclsbn (reiatlve standard devlatlon) was 2.1 to 10% for the peakhelght method, and 1.0 to 12% for the Integration method. The analytlcal curves prepared wlth both methods were hear for all the elements studled. The detectlon llmlts obtalned wlth the peak-helght method were lower than those obtalned wlth the Integration method.
Flames or graphite furnaces are normally used as an atomizer for solution samples in atomic absorption spectrometry (AAS). In the case of solid samples, they are converted into solution samples, and the analyses are performed. In order to analyze directly various elements in solid 'Present address, The Faculty of Engineering, Hiroshima University, Hiroshima, Japan.
samples, some methods for the atomization of solid samples have been investigated (1). Laser beam has been used as the atomizer for the atomic absorption of solid samples by several investigators (24). In these studies, the plumes produced on the sample surfaces by the laser beam were used as an absorption path. A xenon flash lamp (21, the continuum at the base of the laser plume (3), pulse-radiated hollow-cathode lamps ( 4 , 5), and dc-operated hollow-cathode lamps (6) were used as the primary light source for AAS. The instantaneous emission from the laser plume is significantly intense compared with the light from the hollow-cathode lamps of conventional light source for AAS. In the laser plume, the line spectra from excited atoms or ions and the continuous spectrum from bremsstrahlung of electrons are observed. When the laser plume is used as the absorption path in AAS, those emission spectra may interfere with atomic absorption measurement. Then compensation for background emission must be performed. The authors designed and constructed an atomizationabsorption cell in which the chamber for atomizing solid sample was separated from the absorption path. An atomic absorption spectrophotometer with conventional hollowcathode lamps and monochromator was used. Laser-vaporized ANALYTICAL CHEMISTRY, VOL. 49, NO. 9, AUGUST 1977
1339
TO VACUUM
Table I.
t
Element A1 Cr
LASER BEAM ABSORPTION CELL
GLASS WINDOW
cu
QUARTZ
Fe Mn Mo
fiwa
ATOMIZATION CELL (13mm i d , 1 5 m m I )
LIGHT
Ni
V
(9m; ~ d25. mm I )
Ar GAS
SAMPLE
Flgure 1. Schematic diagram of atomization-absorption cell. The cell is made up of stainless steel walls and quartz or glass windows. The scheme is represented in inside dimensions
U LASER BEAM
0 RECORDER
Flgure 2. Block diagram of measuring system atomic absorption spectrometry (LVAAS) of solid samples was studied with the atomization-absorption cell system. The oscillograms of absorption signals for several elements in metal samples, optimum operating conditions, precision, analytical curves, and detection limits are discussed.
EXPERIMENTAL Apparatus. A model JLR-O2A Giant Pulse Laser with a ruby rod 10 cm long and 10 mm in diameter (Japan Electron Optics Lab. Co., Ltd., Japan) was used as the atomizer for solid samples. The maximum peak power is about 70 MW; the maximum output energy, about 1.5 J; the pulse-width, less than 20 ns; and the reproducibility of laser energy, *5%. The laser energy increases with an increase of the capacitor voltage (CV) for the power scpply to the xenon flash lamp used to pump the laser rod. According to the test record offered by the maker, the laser energies at various CVs were approximately as follows: 0.4 J at 3800 V, 1.0 J at 4000 V, 1.2 J at 4200 V, and 1.3 J at 4400 V. The optical system of a model AA-1 Atomic Absorption Spectrophotometer (Nippon Jarrell-Ash Inc., Japan) was used in this study. The atomization-absorptioncell made up of stainless steel walls and quartz or glass windows was designed and constructed. Figure 1shows the schematic diagram represented in inside dimensions. The cell attached to the atomic absorption apparatus was connected to a vacuum line with a rotary oil vacuum pump (Hitachi Ltd., Japan, Model 4VP-C). The pressure inside the vacuum line was measured with a Pirani gauge (Daia Vacuum Engineering Co., Ltd., Japan, Model PT-S2OO). A needle valve (Edwards Vacuum Components, England, Model LBlB) was used for the controlled introduction of argon gas into the cell. The flow rate of argon gas (FRAG) was measured with rotameters (Ueshima Brooks, Japan). When a sample was mounted to the atomization cell, an O-ring was used to seal the sample. The atomic vapor produced from a sample by the laser beam stayed in the absorption cell for the time of millisecond order. The profile of the very rapid absorption signal by the atomic vapor 1340
Hollow-Cathode Lamp Settings
ANALYTICAL CHEMISTRY, VOL. 49, NO. 9, AUGUST 1977
Analytical line, nm 396.2 429.0 324.7 372.0 279.5 or 403.1 313.3 352.5 318.4
Lamp current, mA 10 10 8
10 10
12 10
12
could not be directly recorded by a conventional strip chart recorder. Therefore, absorption signals were measured by means of the measuring system shown in Figure 2. The absorption signal (percent absorption) from a photomultiplier (Hamamatsu TV, Japan, Model R-106) was transformed into the logarithm (absorbance) by a logarithmic amplifier (Teledyne Philbrick, U.S.A., Model 4363). The output signal from the logarithmic amplifier followed into a peak holder or a integrator through FET switches (Teledyne, U.S.A., Model 2110BE). The FET switches were turned ON by the gate pulse generated from an oscilloscope (Matsushita Communication Industrial Co., Ltd., Model VP5410.4). The oscilloscope was triggered by the pulse-radiation from the xenon flash lamp used to pump the laser rod. The peak holder and integrator using 0.01-pF polystyrene capacitors were arranged with operational amplifiers (Teledyne Philbrick, U.S.A., Model 1026). The peak holder was used for measuring the peak value of the absorption signal profile (peak absorbance). The integrator was used for measuring the area of the profile (integrated absorbance). The value of integrated absorbance is expressed in the product of absorbance and time (ms). The signals stored in the peak holder or integrator were recorded by a two-pen strip chart recorder (Matsushita Communication Industrial Co., Ltd., Japan, Model VP-654A). Samples. Metal samples were used as solid samples in this study. The metals were as follows: brasses (the National Bureau of Standards, U.S.A., C1103-Cl105); carbon steels (the Bureau of Analysed Samples, Ltd., England, SS431-SS435); alloy steels (the Iron and Steel Institute of Japan, Japan, 152-154); and aluminum alloys (Alcoa Research Laboratories,U.S.A., KA-213-B, KA-356-E, KB-356-B, KC-356-E, and SS-138-R). Procedure. The flat and smooth surfaces of samples were obtained by polishing with a 400-mesh silicon carbide paper. The samples with the polished surfaces were washed with distilled water and ethyl alcohol, and dried with hot air. A sample was mounted on the atomization cell. A laser beam was directed downward by a 45' quartz prism and focused on the sample surface by using a 10-cmfocal length lens. The diameter of the laser beam was about 1 mm on the sample surface. A plume was produced from the sample by the laser beam. The atomic vapor in the laser plume was introduced into the absorption cell by the flow of argon gas. The absorption signal from the atomic vapor was traced by the oscilloscope and measured by means of the measuring system shown in Figure 2. The laser beam was shot on the sample at 30-s intervals. The following elements in each sample were determined: iron and nickel in brass; aluminum, chromium, copper, manganese, molybdenum, and nickel in carbon steel; vanadium in alloy steel; and copper, iron, and manganese in aluminum alloy. The concentrations of most of the above elements were too high to use the most sensitive analytical lines. Less sensitive lines were used for most of the elements. Table I shows the wavelengths of analytical lines and the lamp currents for each element used in this study.
RESULTS AND DISCUSSION Oscillograms of Absorption Signals. The signals from the photomultiplier followed directly into the oscilloscope. The absorption signals for each element were traced with the oscilloscope. The profiles of absorption signals were affected by FRAG (i.e., pressure in cell) and CV (i.e., laser energy). In the oscillograms for several elements, emission signals were
Flgure 3. Oscillograms of the absorption signals for copper in brass and aluminum in aluminum alloy. (A) Cu (61.3%) in brass: analytical line, 324.7 nm; time scale, 2 ms/div. (B) AI (92.3%) in AI alloy; analytical line, 396.2 nm; time scale, 1 ms/div. FRAG, 200 mL/min. CV, 4100
V
observed first, followed by absorption signals under conditions of FRAG up to 100 mL/min (2.5 Torr). The emission intensities decreased with an increase of FRAG, and increased with an increase of CV. The oscillograms of absorption signals were taken under conditions of FRAG from 20 to 1000 mL/min (0.9 to 40 Torr) and of CV from 3800 to 4400 V (0.4 to 1.3 J). The effects of FRAG and CV on the absorptions for several elements are quantitatively discussed in successive sections. In this section, the oscillogramsobtained under the optimum conditions of FRAG of 200 mL/min (5 Torr) and of CV of 4100 V (1.1J) are presented. The absorption signals for copper in brass, iron in steel, and aluminum in aluminum alloy were traced with the oscilloscope. Figure 3 shows the oscillograms of absorption signals for copper and aluminum. In the oscillograms, emission signals were observed prior to absorption signals. In the oscillogram for copper, the light of 324.7 nm from the copper hollowcathode lamp was fully absorbed by copper vapor introduced into the absorption cell. The oscillogram for iron was similar to that for copper in Figure 3. The emission signal in the oscillogram for aluminum was significantly intense compared with those for copper or iron. The lifetime of atomic vapor of aluminum was appreciably shorter than those of copper or iron. The shorter lifetime of aluminum atoms is concluded to be due to the immediate combination of aluminum atoms with oxygen as an impurity in argon gas. A check for scattered radiation was made using the nonabsorbing line at 352.1 nm from neon of filler gas in a hollow-cathode lamp and with a deuterium hollow-cathodelamp. Neither of the oscillograms obtained with the samples of brass, steel, and aluminum alloy represented absorption signals. The absorption signals for each element of minor concentrations in brass, steel, and aluminum alloy were traced with the oscilloscope. Figure 4 shows the oscillograms of absorption signals for iron (0.26%) in brass, manganese (0.37%) in steel, and copper (0.055%)in aluminum alloy under conditions of FRAG of 200 mL/min and of CV of 4100 V. The absorption profiles for manganese in steel and copper in aluminum alloy were simple. That for iron in brass showed a shoulder after peak absorption occurred. The shoulder was observed also in the oscillogram for nickel in brass. However, the shoulder was not observed in the oscillograms for iron in aluminum alloy and nickel in steel. The shoulder may be related to the fact that brass is composed of the two matrix elements of copper and zinc. In the atomic vapor produced from brass by the laser beam, the lifetime of zinc atoms was
Figure 4. Oscillograms of the absorption signals for several elements. (A) Fe (0.26%) In brass; analytical line, 372.0 nm. (B) Mn (0.37%) in steel;anaiytical line, 403.1 nm. (C) Cu (0.055%)in AI alloy; analytical
line, 324.7 nm. FRAG, 200 mL/min. CV, 4100 V. Time scale, 1 ms/div
02
8 c
a
1 0
-
2
z
0 Ar FLOW RATE ( m l l r n i n )
Flgure 5. Effect of flow rate of argon gas on the peak and integrated absorbance for copper in steel. Cu concn, 0.046%. Analytical line, 324.7 nm. CV, 4100 V
longer than that of copper atoms. It is expected that a part of the atomic vapor of iron or nickel reacts with the zinc vapor. The absorption profiles for other elements in steel or aluminum alloy were similar to those for manganese and copper shown in Figure 4. The memory effect in the cell was not observed for all the elements studied. The absorption profiles for various elements obtained with the oscilloscopewere discussed in this section. In successive sections, the results obtained by means of the measuring system shown in Figure 2 are discussed. Effect of Flow Rate of Argon Gas. The peak and integrated absorbance for several elements were measured by varying FRAG from 20 to 1000 mL/min under conditions of CV of 4100 V. The elements measured were chromium in steel, copper in steel or aluminum alloy, and iro? in brass or aluminum alloy. The same point on a sample surface was shot five times by the laser beam. The average value of five data obtained with each laser shot was taken as the value at the point. Figure 5 shows the effect of FRAG on the peak and integrated absorbance for copper in steel. Each plot is the average of values obtained at two points on the sample. The two ends of the vertical line on each plot represent the values obtained a t the two points. The peak and integrated abANALYTICAL CHEMISTRY, VOL. 49, NO. 9, AUGUST 1977 * 1341
Table 11. Precision Dataa
Sample Brass
Relative standard deviation, % Peak- Integraheight tion 9.1 1.0 4.3 2.3 2.7 3.5 8.0 1.4 2.6 7.6
Element Fe (0.088%) Fe (0.26%) Ni (0.07%) Ni (0.16%) Steel A1 (0.026%) A1 (0.070%) 10 5.0 Cr (0.13%) 2.2 2.1 Cr (0.21%) 2.5 2.3 Mo (0.039%) 2.1 3.4 M o (0.085%) 5.1 6.6 v (0.11%) 6.1 7.1 v (0.22%) 2.8 4.5 A1 alloy Cu (0.055%) 6.1 2.9 c u (0.20%) 4.5 4.1 Mn (0.22%) 3.8 12 Mn (0.30%) 4.6 4.2 a The precision was evaluated from the data obtained at the five points which were shot every five times with the laser beam. Table 111. Concentration Ranges of Elements Studied for the Preparation of Analytical Curves Analytical line, Concentration Element Sample nm range, % 396.2 0.012-0.070 A1 Steel 429.0 0.13 -0.21 Cr Steel 324.7 0.017-0.062 cu Steel 324.7 0.055-0.20 cu A1 alloy 372.0 0.044-0.26 Fe Brass Fe A1 alloy 372.0 0.075-0.48 403.1 0.37 -0.95 Mn Steel 279.5 0.13 -0.30 Mn A1 alloy 313.3 0.015-0.085 Mo Steel 352.5 0.043-0.16 Ni Brass Ni Steel 352.5 0.069-0.24 318.4 0.11 -0.33 V Steel
sorbance increased with an increase of FRAG up to 200 mL/min. Those decreased with an increase of FRAG over 200 mL/min. The effect of FRAG on both absorbances for chromium in steel was similar to that for copper in steel. For iron in brass, both absorbances increased with an increase of FRAG in the range from 20 to lo00 mL/min. For copper and iron in aluminum alloy, both absorbances increased with an increase of FRAG up to 200 mL/min. Those slightly increased with an increase of FRAG over 200 mL/min. Judging from the results obtained above and the functions of the rotary oil vacuum pump used, FRAG of 200 mL/min was selected as optimum conditions. Effect of Capacitor Voltage. The effect of CV on the peak and integrated absorbance for the same elements as described in the preceding section was studied by varying CV from 3800 to 4400 V under conditions of FRAG of 200 mL/min. The peak and integrated absorbance were measured in the same way as mentioned in the preceding section. Both absorbances for the elements studied were low at CV of 3800 V near the threshold voltage for the Q-switched ruby laser used in this study. Both absorbances highly increased with an increase of CV from 3800 to 4000 V. Those increased little by little with an increase of CV from 4000 to 4400 V. From the results obtained above, 4100 or 4200 V was selected as the suitable CV for all elements studied. Precision. A method for data treatment to get as high precision as possible was studied, and the following method was employed as most suitable in this study. The same point on a sample surface was shot several times (five times in this study) with the laser beam. The average or sum of five values obtained with each laser shot was treated as the value at the point. This method was particularly effective for the measurements of copper, iron, and manganese in aluminum alloy. Because the surface of aluminum alloy was unevenly sputtered with each laser shot, the values obtained varied widely with each laser shot. However, with the method for the treatment of data mentioned above, the values obtained at each point did not mutually vary widely. Table I1 shows the precision data for the peak and integrated values obtained for various elements in brass, steel, and aluminum alloy. The precision (relative standard deviation) in Table I1 was evaluated from the data obtained a t
Table IV. Detection Limits for Various Elements in Brass, Steel, and Aluminum Alloy Detection limit Peak-height method Integration method Analytical line, Concn Concn, Weight, g Element Sample nma (ppm) Weight, g PPm A1 Steel 396.2 11 1.0 x lo-" 39 3.5 x lo-" (2.3 X l o - ' ' ) (309.3) (7.3) (6.7 x 10-l2) (26) 8.8 x 10-'I 98 Cr Steel 429.0 20 1.8 X lo-" (1.2 x 10-11) (357.9) (2.7) (2.4 X (13) 3.0 X lo-" 33 cu Steel 324.7 7.2 6.5 X 120 9.6 X lo-" 2.6 X 10-l' A1 alloy 324.7 32 29 2.9 X lo-'' Fe Brass 372.0 17 1.7 X lo-" (6.4) (6.4 X lo-'') (248.3) (1.9) (1.9 x 10-12) 2.6 X lo-'' A1 alloy 372.0 100 8.0 X lo-" 330 (3.0 X 10-l') (8.9 X 10-l') (37) (248.3) (11) 8.4 X 10'" 3.3 x lo-" 93 Mn Steel 403.1 37 (6.7 X l o - ' * ) (1.9 x 10-12) (7.4) (279.5) (2.1) 3.4 x lo-'' 1.6 X l o - ' ' 42 A1 alloy 279.5 20 2.2 x Mo Steel 313.3 10 9.0 x 10-l2 24 Ni Brass 352.5 24 2.4 X lo-'' 38 3.8 X lo-" (7.5 x 10-12) (4.7 x 10-12) (7.5) (232.0) (4.7) 5.6 X lo-" 2.6 X lo-" 62 Steel 362.5 29 (1.1x 10-11) (5.1 X lo-'') (12) (232.0) (5.7) 2.7 X 10'" 2.0 x lo-" 30 V Steel 318.4 22 (1.9 x 10-11) (318.5) (16) (1.4 X l o - ' ' ) (21) a
The values calculated for the most sensitive lines are shown in parentheses.
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ANALYTICAL CHEMISTRY, VOL. 49, NO. 9, AUGUST 1977
Figure 6. Analytical curves for molybdenum in steel. Analytical line, 313.3 nm. FRAG, 200 mL/min. CV, 4200 V
the five points on a sample. The precision was 2.1 to 10% for the peak-height method, and 1.0 to 12% for the integration method. No differences in precision for the peak-height and integration methods were found from the results shown in Table 11. Analytical Curves. The analytical curves for various elements were prepared with the peak-height and integration methods. Table I11 shows the concentration ranges of elements studied for the preparation of analytical curves. Figure 6 shows the analytical curves for molybdenum in steel. Each plot in Figure 6 represents the average of the values obtained a t the five points. The vertical lines on each plot represent the standard deviations. The analytical curves for molybdenum in steel were linear for both the peak-height and integration methods. The analytical curves for other elements also were linear for both methods. Detection Limits. Detection limits were determined by use of the samples containing the lowest concentrations of each element. The detection limit was defined as the concentration or weight of element which gives a signal equal to twice the standard deviation of the background level. The weight of the detection limit was calculated from the concentration of the detection limit and the weight of the sample sputtered with the laser shot. The weights of brass, steel, and aluminum alloy sputtered with one laser shot were about 1.0,O.g and 0.8 pg, respectively. In this study, the most sensitive analytical lines for most elements were not used for the determination of the detection limits. By multiplying the detection limits
obtained with less sensitive lines by the relative sensitive factors for each analytical line, the detection limits for the most sensitive lines were obtained for most elements. Table IV shows the detection limits obtained with the less sensitive lines and those calculated for the most sensitive lines. The detection limits for the most sensitive lines ranged from 1.9 ppm (1.9 X 10-l' g) of iron in brass to 32 ppm (2.6 X 10-l' g) of copper in aluminum alloy with the peak-height method. Those ranged from 6.4 ppm (6.4 X lo-'' g) of iron in brass to 120 ppm (9.6 X g) of copper in aluminum alloy with the integration method. As the time for measuring the integrated value was about one order of magnitude over that for measuring the peak value, the fluctuation of light from the hollow-cathode lamps affected the integrated value more than the peak value. Therefore, the detection limits obtained with the peak-height method were lower than those obtained with the integration method. Because the copper hollow-cathode lamp used picked up a ripple of 60 Hz derived from the power supply, the background level fluctuated. The detection limit for copper was poorer than that predicted. The detection limits for copper, iron, and manganese in aluminum alloy were poorer than those in brass or steel. As mentioned previously, the atomic vapor of aluminum disappeared most rapidly in the atomic vapors of copper, iron, and aluminum of the matrix elements. The aluminum of the matrix element is assumed to affect the behavior of elements coexisting in the aluminum alloy. Therefore, the detection limits for the elements in the aluminum alloy were poorer than those in brass or steel. The atomization-absorption cell used in this study does not always have the optimum geometry. If the diameter of the absorption cell is reduced, higher sensitivity might be brought about by the improved geometry, and the detection limits can be lowered considerably.
LITERATURE CITED (1) H. Massmann, "Flame Emission and Atomic Absorption Spectrometry", J. A. Dean and T. C. Rains, Ed., Marcel Dekker, New York, 1971, Vol. 2, Chapter 4. (2) V. G. Mossotti, K. Laqua, and W. D. Hagenah, Spectrochim. Acta, Part 8, 23, 197 (1967). (3) A. V. Karyakin and V. A. Kaigorodov, Zh.Anal. Khim., 23,930 (1968). (4) E. K. Vul'fson, A. V. Karyakin, and A. I. Shidlovskii, Zavod. Lab., 40, 945 (1974). (5) D. E. Osten and E. H. Piepmeier, Appl. Spectrosc., 27, 165 (1973). (6) J. P. Matousek and B. J. Orr, Spectrochim. Acta, Part 8,31, 475 (1976).
RECEIVED for review January 17,1977. Accepted May 12,1977.
Spectrophotometric Determination of Vitamin K Compounds J-C Vir6 and G. J. Patriarche Institut de Pharmacie, Universitg Libre de Bruxelles, Campus Plaine, 205/
1 Bruxelles, Belgium
Robert J. Nowak and Harry B. Mark, Jr." Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 4522 1
A spectrophotometricmethod for the determination of Vitamin K (naphthoquinones) compounds has been developed. TItanium (111) is employed to reduce naphthoqulnone to its corresponding naphthohydroquinone which subsequently forms a highly colored complex with TI(1V). Complex formation as a function of time, sulfuric acid concentration, and Ti(II1) and Ti( I V ) concentration is reported. The method yields highly linear calibration data In the region of lo-' M.
Menadione (vitamin K3) and analogues (naphthoquinones)
are of considerable importance because of their role in blood coagulation processes. Thus, trace analytical techniques for these compounds are necessary for the study of their biological actions as well as in pharmacologicaland toxicological studies. Previously, these compounds were determined spectrophotometrically (1-3) and spot titanium(1V) tests for the identification of naphthoquinones as characteristic complexes had been reported ( 4 ) . Also, similar phenolic type compounds such as chromotropic acid (5), sodium 1,3-dihydroxybenzene3,5-disulfonate (6) and thymol (7) had been employed as spectrophotometric reagents for the determination of titanium. ANALYTICAL CHEMISTRY, VOL. 49, NO. 9, AUGUST 1977
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