ISSN:0003-2654    

DOI:10.1039/AN98611FX001

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALAO 111(1) 1-128 (1986)The AnalystJanuary 198613111519232937414549535761656973778187919597101105107The Analytical Journal of The Royal Society of ChemistryCONTENTSEditorial-P. G. W. CobbAutomated Potentiometric Titrations of Sulphides and Thiols in Petroleum Systems-S. W. Bateson, G. J. Moody,J. D. R. ThomasIndirect Determination of Cyanide in Waste Waters by Formaldehyde Chronopotentiometry-Jesus RodriguezProcopio, Jose-Maria Pinilla Macias, Lucas Hernandez HernandezSimultaneous Determination, by Hydride Generation and Inductively Coupled Plasma Atomic Emission Spectrometry,of Arsenic, Antimony, Selenium and Tellurium in Silicate Rocks Containing the Noble Metals and in SulphideOres-L. Halicz, G.M. RussellDetermination of Gallium in Phosphorus Flue Dust and Other Materials by Graphite Furnace Atomic AbsorptionSpectrometry-David C. Barron, Benjamin W. HaynesDetermination of Nitrogen-15 by Optical Emission Spectrometry Using an Atomic Absorption Spectrometer-MichaelH. Timperley, John C. PriscuStudies on the Determination of Mercury in Human Beard Shavings by Neutron-aaivation and y-Ray Analysis-J. G.Pritchard, S. 0. SaiedAutomated Determination of Fat, Crude Protein and Lactose in Ewe Milk by Infrared Spectrometry-Wendy M. HarrisUse of Orthogonal Polynomials for Unequal Intervals t o Eliminate Interference in Spectrophotometric Analysis.Simultaneous Determination of Ephedrine Hydrochloride and Diphenhydramine Hydrochloride in Two-component Mixtures-M.A. Korany, Mona Bedair, F. A. El-YazbiSpectrophotometric Determination of Some Anti-inflammatory Agents Using N-BromosuccinimideSonia T. Hassi b,Hany M. Safwat, Ramzeia I. El-BagrySilver(1) - Gelatin Interaction: Spectrophotometric Determination of Trace Amounts of Silver in Water-T. Pal, D. S.MaitySpectrophotometric Study of a Titanium (IV) - Peroxide - 1 -(2-Pyridylazo)-2-naphthol System in the Presence of aNon-ionic Surfactant-M. Llobat-Estelles, J. Medina-Escriche, A. Tomas-Primo, A. Sevillano-CabezaExtraction - Spectrophotometric Determination of Indium Using 4-(2-Pyridylazo)resorcinol-Yadvendra K. Agrawal,Vinay J. BhattRapid Spectrophotometric Determination of Chromium(ll1) with 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol inthe Presence of Benzoate and Sodium Dodecyl SulphateG.V. Rathaiah, M. C. EshwarSimultaneous Spectrophotometric Determination of Copper, Nickel and Palladium by Flow Injection Analysis-Ami nT. Haj-Hussein, Gary D. ChristianCatalytic Determination of Manganese at Ultra-trace Levels by Flow Injection Analysis-S. Maspoch, M. Blanco, V.CerdaDetermination of Trihalomethanes in Water Using Gas Syringe Injection of Headspace Vapours and Electron-captureGas Chromatography-Brian T. Croll, Margaret E. Sumner, David A. LeathardDetermination of Methoxy Groups in Soils by the Zeisel Method Combined with Gas - Liquid Chromatography-Alberto M. T. Magalhiies, Phillip M. ChalkAnalytical Reference Materials. Part V. Development of a Sediment Reference Material for Chlorobenzenes andHexachlorobutadieneHing-Biu Lee, Robert L.Hong-You, Alfred S. Y. ChauPorous Membrane-based Diffusion Scrubber for the Sampling of Atmospheric Gases-Purnendu K. Dasgupta, WilliamL. McDowell, Jae-Seong RheeSHORT PAPER§Simple and Precise High-performance Liquid Chromatographic Method for the Investigation of Carbodiimide-Elimination of Feed Additive Derived Interferences in the Assay for Avoparcin-H. L. Hatfield, A. ThomasSpectrophotometric Determination of Tetracycline with Sodium Molybdate-Salah M. SultanDetermination of Alkylnaphthalenes in Petroleum Fractions by Second-derivative Ultraviolet Spectrophotometry-Critical Comparison of X-ray Fluorescence and Combustion - Infrared Methods for the Determination of Sulphur inDetermination of 28 Elements in American Cigarette Tobacco by Neutron-activation Analysis-Felib Y.Iskander,mediated Peptide Synthesis-Marek Slebioda, Aleksander M. KotodziejczykLalji Dixit, Siya Ram, R. 6. Gupta, H. C. Chandola, Pradeep KumarBiological Matrices-Nathan W. Bower, Ernest S. Gladney, Roger W. FerenbaughThomas L. Bauer, Dale E. Kleincontinued inside backcoverElectronically typeset and printed by Heffers Primers Ltd, Cambridge, Englan111 Releasing Effect of Iron(ll1) and Other Oxidants on the Interference from Nickel in the Determination of Selenium by115 Rapid Determination of Tungsten in Alloys, Ores and Concentrates by Atomic Absorption Spectrometry-Sarala119 Titrimetric Determination of A2-Pyrazol-5-ones and A3-Pyrazol-5-ones via Bromination-Darwish Amin, Red ha I.Hydride Generation Atomic Absorption Spectrometry-Ragnar ByeRaoot, S.V. Athavale, T. H. RaoAl-Bayati121 BOOK REVIEWS125 INSTRUCTIONS TO AUTHORSThe Periodic Tableof the ElementsThe Royal Society of Chemistry has produced acolourful wall chart measuring 125cm x 75cmcovering the first 105 elements as they exist today.Each group is pictured against the same tintedbackground and each element, where possiblephotographed in colour and discussed with regardto its position in the hierarchy of matter. Additionalinformation for each element includes chemicalsymbol, atomic number, atomic weight and orbitsof electrons.The chart is particularly useful for both teachersand students and would make a worthwhileaddition to any establishment.Price: Non-RSC Members f3.00 including VATRSC Members f2.00 including VATTeacher Members f 12.00 for 10 including VATRSC members should send their orders to: TheRoyal Society of Chemistry, The MembershipOfficer, 30 Russell Square, London WClB 5DT.Non-RSC members should send their orders to:The Royal Society of Chemistry, DistributionCentre, Blackhorse Road, Letchworth, HertsSG6 IHN.Please contactBUREAU OF ANALYSEO SAMPLES LTOfor a copy of their list ofOVERSEASREFERENCE MATERIALSproduced byALCAN (Canada)BAM (W. Germany)CANMET (Canada)CKD (Czechoslovakia)CTIF (France)IRSID (France)NBS (USA)SABS (S. Africa)JERNKONTORET (Sweden)Please write, telephone or telex to:BAS Ltd., Newham Hall, Newby,Middlesbrough, Cleveland, TS8 9EATelephone: Middlesbrough (0642) 317216Telex: 587765 BASRIDr201 for further information. See page iv

ISSN:0003-2654    

DOI:10.1039/AN98611BX003

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, JANUARY 1986, VOL. 111 11 Indirect Determination of Cyanide in Waste Waters by Formaldehyde Chronopotentiometry Jesus Rodriguez Procopio, Jose-Maria Pinilla Macias and Lucas Hernandez Hernandez* Facultad de Ciencias, Departamento de Quimica Analitica, Universidad Autonoma de Madrid, 28049 Madrid, Spain An indirect method for the determination of cyanide at concentrations between 0.01 and 0.1 pg ml-1 is described. The method is based on the displacement observed in the quarter-wave potential of the chronopotentiometric graph of formaldehyde, in 0.1 M NaOH using a gold electrode, on increasing the concentration of cyanide. The method exhibits a relative error of 2% and a relative standard deviation of 1%. It has been applied to the determination of cyanide in waste waters.Keywords: Cyanide determination; chronopotentiometry; waste waters Previously1 we have studied the chronopotentiometry of formaldehyde with a gold electrode in a basic medium and the effects on the potential- time graph of species that are adsorbed on gold, including cyanide, bromide and tetraethyl- ammonium. It was observed that increasing the concentration of cyanide, produced a displacement of the chronopoten- tiometric graph of formaldehyde to a less negative potential. Van Effen and Evans2 examined this effect in studies of the cyclic voltammetry of benzaldehyde with a gold electrode, observing a displacement of peak potential and a decrease in peak height with increasing the concentration of cyanide. This peak disappeared when the cyanide concentration reached 10-4 M.The concentration of cyanide present in solution necessary to cause a displacement of the potential - time graph was very small. The aim of this work was to develop an indirect method for the determination of cyanide at concentrations less than 0.1 pg ml-l using the chronopotentiometric behaviour of formaldehyde. The optimum formaldehyde concentration and pH have been studied and a calibration graph was constructed and the precision and accuracy of method were established. The method was applied to the determination of cyanide in waste waters. Experimental Apparatus A constant-current coulostat (Amel 381) was used as the current supplier and the chronopotentiograms were recorded on a potentiometric recorder (Mettler DKlO/GA13). A gold electrode with a projected area of 0.785 cm2 was inlaid in a PTFE tube, which provided a shield around the electrode surface with an upward orientation for obtaining a greater stability of id/C (where i is the applied current, t the transition time and C the bulk concentration).The contact was established by pushing a copper wire, protected by a Pyrex tube, against the rear side of the gold disc. This contact was replaced periodically. The counter electrode was a platinum wire introduced into a compartment separated from the main cell by a sintered-glass disc. This compartment was filled with a portion of the solution under investigation. The reference electrode was a saturated calomel electrode. A coulostat (Metrohm E 524) was used to supply a constant potential of -1.4 V in order to obtain an electrode with an oxide-free surface.The temperature was fixed at 25 rt 0.1 "C with a Tamson Tee 3/150 thermostat. A suitable distillation apparatus, des- cribed previously,3 was used to isolate the cyanide ion from the sample. ~~ ~~~ ~ * To whom correspondence should be addressed. Reagents All chemicals were of analytical-reagent grade. Formaldehyde solutions were prepared from formaldehyde solution (Merck) without further purification and titrated by the Tollens method.4 The presence of 10% of methanol as a stabiliser in commercial formaldehyde did not interfere in the measure- ments. Cyanide working standard solutions were prepared by accurate dilution of a 100 pg ml-1 NaCN stock solution standardised by a silver titration. Procedure From 500 ml of sample, made free of sulphide by the addition of a cadmium salt, cyanide was distilled into 50 ml of 1.0 M NaOH solution.375 The contents of the alkaline trap were transferred into a 100-ml calibrated flask and diluted to the mark.Next, 20 ml of this solution and 5 ml of 0.01 M formaldehyde solution were pipetted into a 100-ml calibrated flask and made up to the mark with cyanide-free doubly distilled water. (If the total cyanide content was expected to be between 0.1 and 1.0 mg ml-1 only 2 ml of cyanide solution were pipetted and 9 ml of 1.0 M NaOH solution were added to the calibrated flask before addition of the formaldehyde.) The solution obtained was transferred into the cell and a constant potential of -1.4 V vs. S.C.E. was applied to the working electrode for 5 min and at the same time a stream of nitrogen was passed through the solution.The potential was then removed and the nitrogen was passed through the shield of the electrode for 1 min. Between 1 and 2 rnin were allowed for the solution to become quiescent and then a constant current was applied to the working electrode in order to obtain a transition time of 30 s. The chronopotentiogram was recorded and the quarter-wave potential was determined. The measurements were made in duplicate. For the preparation of the calibration graph, a 0.0-10.0 ml volume of a cyanide working standard solution (1 pg ml-I), 10 ml of 1.0 M NaOH solution and 5 ml of 0.01 M formaldehyde solution were pipetted into a 100-ml calibrated flask and the resulting solution was made up to the mark with distilled water.The procedure was continued as for a sample, measurements being taken in duplicate. A new calibration graph was plotted periodically, because it is dependent on the condition of the electrode surface. Results and Discussion Variation of the Quarter-wave Potential with Cyanide Concen- tration A study of quarter-wave potential variation, ET,4, as a function of cyanide concentration was made. The results are shown in12 ANALYST, JANUARY 1986, VOL. 111 . -0.4 - u! s d $ -0.3 - up -0.2 } \ 0.2 0.4 0.6 0.8 Cyanide concentration/pg ml-1 I -0.4 4 c! v) -0.2 d 5 0.0 0.2 10 s - Fig. 1. Variation of uarter-wave otential with cyanide concentra- tion in 0.54 mM formjdehyde and l.l M NaOH solution Time - -0.6 4 c! m 2 -0.4 a u; -0.2 I I I I 12 12.5 13 13.5 PH Fig.2. Variation of Na2C03 - NaH2P04 bufqer and 0.54 mM formaldehyde solution uarter-wave potential with pH in 0.1 M Table 1. Accuracy and precision for the determination of cyanide. Each result is the average of ten determinations Cyanide concentratiodyg ml-1 ~ ~~ Taken Found 0.019 0.020 0.037 0.039 0.056 0.054 0.075 0.073 0.093 0.094 Relative Relative standard error, YO deviation, % 1.61 0.81 1.80 1.05 1.25 1 .oo 0.46 0.89 0.61 0.42 Fig. 1. Two zones were observed for which ET,4 was linear with cyanide concentration, the first at concentrations between 0.01 and 0.1 pg ml-1 and the second at concentrations between 0.1 and 0.5 pg ml-1. The more sensitive first zone provides a method for the determination of cyanide at concentrations of less than 0.1 pg ml-1.Effect of Formaldehyde Concentration To determine the optimum formaldehyde concentration, a study of the minimum cyanide concentration that produces an observable displacement of potential - time graphs for several formaldehyde concentrations was made. From the results, it was concluded that the optimum formaldehyde concentration was between 0.4 and 0.6 mM. At this concentration it was Fig. 3. Typical chronopotentio rams of standards of NaCN in 0.1 M NaOH and 0.54 mM formaldehyfie solution. [NaCN]: (1) 0; (2) 0.019; (3) 0.037; (4) 0.056; (5) 0.075 and (6) 0.093 pg ml-1 Table 2. Comparison of the results of the determination of cyanide by a direct spectrophotometric method and indirectly by formaldehyde chronopotentiometry (IDFC) Cyanide found/pg ml-'* Sample Spectrophotometry IDFC I t 2 t 3$ 4$ 5$ 0.02 0.03 0.16 0.05 0.11 * Each result is the average of ten determinations. t River water (polluted by industrial effluents).$ Precious metal refining waste water. 0.01 0.03 0.17 0.05 0.11 possible to determine cyanide at concentrations down to 0.01 pg ml-1. A pre-treatment time of 5 min was chosen to obtain a constant potential of -1.4 V vs. S.C.E., in order to produce an oxide-free electrode surface, which gives a better repro- ducibility in transition times and quarter-wave potentials, as was observed in the chronopotentiometric study. 1 Also a greater constancy for EZI4 was attained on using a current intensity that produced a transition time of about 30 s, decreasing the double-layer capacity and convection prob- lems.Effect of pH on the Sensitivity A greater sensitivity was observed when the quarter-wave potential of formaldehyde alone was more negative. Fig. 2 shows the variation of quarter-wave potential with pH, in 0.1 M Na2C03 - NaH2P04 buffer solution. On increasing the pH, the quarter-wave potential was shifted to more negative potential. These results indicate a greater sensitivity at a pH greater than 13. Also a study of the reproducibility of Et/4 was performed at different pH values. It was observed that a greater reproduci- bility can be obtained at a pH higher than 13. From the results a 0.1 M NaOH solution was selected as the supporting electrolyte.ANALYST, JANUARY 1986, VOL. 111 13 Calibration Graph, Accuracy and Precision A calibration graph of quarter-wave potential versus cyanide concentration was obtained for concentrations between 0.01 and 0.1 pg ml-1 (the chronopotentiograms obtained are shown in Fig.3). A series of ten solutions of cyanide concentrations of 0.014.1 pg ml-1 were prepared and their concentrations were determined using the calibration graph. The results obtained are given in Table 1. The results indicate that the proposed method is accurate, with a relative error of less than 2% and a precision, expressed as the relative standard deviation, of less than or equal to 1%. Determination of Cyanide in the Presence of Interferents Determinations of cyanide in the presence of different amounts of chloride, sulphide, sulphate, carbonate and phosphate were made. The cyanide concentration was 0.05 pg ml-l.The maximum tolerable concentrations of these interferents were 7 pg ml-1 and 0.02 pg mi-1 for chloride and sulphide, respectively, and 0.1 M for the others. At higher concentrations, these substances caused changes in the shape of the potential - time graph, producing positive errors. Determination of Cyanide in Waste Waters The proposed indirect method was applied to the determi- nation of cyanide in waste waters. Spectrophotometry is widely applied for the determination of cyanide in waste waters and is usually based on the reaction of cyanide with chloramine-T to form cyanogen chloride, which combines with pyridine and a cyclic amine to form a dye.375>6 Potentiometry with a cyanide-selective electrode is also used.5.6 Both methods have a similar sensitivity and precision with a relative error and relative standard deviation of less than 2%.”10 For the proposed method the sample is made highly acidic with sulphuric acid, and heated under reflux while bubbling air through the solution.The hydrogen cyanide evolved is absorbed in a 1.0 M NaOH solution; this separates cyanide from any interfering substances.3.5 Under these conditions only sulphide interferes. This can be eliminated by adding a cadmium salt before cyanide separation . 3 3 The results obtained for the determination of the cyanide concentration in several waste waters are given in Table 2. These values are in agreement with those obtained by the benzidine - pyridine method,3 having similar precision, ranging between 2 and 5% (owing to the recovery efficiency).In this way the determination of cyanide using the chrono- potentiometric method gives results comparable to those obtained by the standard method. The method is simple and the analysis time is approximately the same as that of the spectrophotometric and cyanide-selective electrode methods. However, there is no need to prepare and store several reagent solutions as in the spectrophotometric method because the proposed method only requires inexpensive 10-2 M formaldehyde solution. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. References Procopio, J. R., PhD Thesis, Facultad de Ciencias, Universi- dad Autdnoma de Madrid, 1985. Van Effen, R. M., and Evans, D. H., J. Electroanal. Chem., 1980, 107, 405. American Public Health Association, American Water Works Association and Water Pollution Control Federation, “Stan- dard Methods for the Examination of Water and Waste- waters,” Fifteenth Edition, American Public Health Associa- tion, New York, 1980. Kolthoff, I. M., and Elving, P. J., “Treatise on Analytical Chemistry, Part 11,” Volume 13, Interscience, New York, 1966. Csikai, N. J., and Barnard, A. J., Anal. Chem., 1983,55,1677. Pohlandt, C . , Jones, E. A., and Lee, A. F., J. S. Afr. Znst. Min. Metall., 1983, 83, 11. Aldridge, W. N., Analyst, 1945, 70, 474. Nagashima, S., Anal. Chim. Acta, 1978, 99, 197. Murty, G. V. L. N., andviswanathan, T. S.,Anal. Chim. Acta, 1961,25, 293. Cussbert, P. J., Anal. Chim. Acta, 1976, 87, 429. Paper A51215 Received June 17th, 1985 Accepted August 12th, 1985

ISSN:0003-2654    

DOI:10.1039/AN9861100011

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, JANUARY 1986, VOL. 111 15 Simultaneous Determination, by Hydride Generation and Inductively Coupled Plasma Atomic Emission Spectrometry, of Arsenic, Antimony, Selenium and Tellurium in Silicate Rocks Containing the Noble Metals and in Sulphide Ores L. Halicz" Geological Survey of Israel, 30 Malkhe Yisrael St., Jerusalem, Israel and G. M. Russell Council for Mineral Technology, Private Bag X30 15, Randburg 2 125, Republic of South Africa A method is described for the continuous generation of the hydrides of arsenic, antimony, selenium and tellurium and the simultaneous determination of these elements by an atomic emission spectrometer with a 5-kW nitrogen - argon inductively coupled plasma source. After digestion of the sample, the analytes are separated from the matrix by coprecipitation with iron(ll1) hydroxide at pH 2.40.A standard additions technique is used for quantification. This method is relatively free from interferences and is applied to the determination of arsenic, antimony, selenium and tellurium in silicate rocks containing gold and the platinum-group metals (noble metals), and also in sulphide ores rich in transition metals and lead. Keywords: Hydride generation; inductively coupled plasma atomic emission spectrometry; arsenic, antimony, selenium and tellurium determination; silicate rocks; sulphide ores The purpose of this investigation was the development of a method for the simultaneous determination of trace amounts of arsenic, antimony, selenium and tellurium in complex geochemical and industrial matrices. The simultaneous determination by inductively coupled plasma atomic emission spectrometry (ICP-AES) of these elements after the generation of their hydrides was first described by Thompson and co-workers,1-3 who established the best compromise conditions for the generation of the hydrides from 5 M hydrochloric acid using a 1% solution of sodium tetrahydroborate(II1).Wolnik et aZ.4 and Nygaard and Lowry5 also described methods for the simultaneous and sequential determination of the volatile hydride-forming elements. It is well known that arsenic, antimony, selenium and tellurium commonly exist in solution in two oxidation states. Unfortunately, reduction with tetrahydroborate(II1) is not efficient for these metals in high oxidation states. Potassium iodide has been used as a pre-reducing agent before final production of the hydrides with sodium tetrahydrobor- ate(III).s7 In the determination of total selenium and tellurium,l the addition of potassium bromide377 and boiling of the sample in 4 M hydrochloric acids10 for pre-reduction has been found to be beneficial.Almost all publications on hydride generation mention possible inter-elemental interferences. Smith12 carried out the first systematic study of the effects of 48 elements on the determination of hydride-forming elements. Smith's findings12 and those of Thompson et a1.2 indicate that interference effects are less severe in the determination of arsenic and antimony but that, in the determination of selenium and tellurium, the analytes must usually be sepa- rated from interfering elements such as the transition metals, gold and the platinum-group metals. This can be effected partly by the coprecipitation of the analytes on lanthanum hydroxide (a method devised by Bkdard and Kerbyson13) or by the coprecipitation of the analytes with iron(II1) hydrox- ide.14915 A variety of procedures for the digestion and * To whom correspondence should be addressed.decomposition of the sample are described in the literature as being satisfactory. Dissolution techniques are considered extremely important because losses of the analytes may occur.1G18 Experimental Apparatus Continuous hydride generation was accomplished by the use of three channels of a four-channel peristaltic pump (Gilson Instrument Co., Minipuls 11). The sample solution, sodium tetrahydroborate(II1) reagent and potassium iodide solution were delivered to a modified separator based on the design of Thompson et aZ.1 and similar to that of De Oliveira et aZ.19 A schematic representation of the hydride-flow manifold, which is similar to that of Nygaard and Lowry,S is shown in Fig.1. The gaseous hydrides and the hydrogen are swept from the separator into the plasma by a continuous flow of argon. I 1 7 Fig. 1. H dnde-generation manifold. (1) Flow-rate of argon, 2.1 I min-1; (2; flow-rate of sam le, 9.5 ml min-1; (3) flow-rate of 1% NaBH4 in 0.1 M NaOH, 4.7 mfmin-1; (4) flow-rate of 10% KI in 20% HCI, 9.5 ml min-1; 5 , gas exit to plasma torch; (6), phase separator; and (7), drain16 ANALYST, JANUARY 1986, VOL. 111 A Hilger Analytical Polyvac El000 spectrometer, with a Radyne R50P r.f.generator (frequency 27.12 MHz) was used for the detection of the hydrides of the elements. An Orion pH meter (Research 501) with an Orion glass electrode was used for the adjustment of the pH of the solution. Table 1. Experimental parameters Torch . . . . . . . . . . . . Incident power . . . . . . . . Coolant outer gas (nitrogen) . . . . Intermediate gas (argon) . . . . . . Carrier gas (argon) . . . . . . . . Observation height . . . . . . . . Wavelength: As1 . . . . . . . . . . . . Sb I . . . . . . . . . . . . Se I . . . . . . . . . . . . TeI . . . . . . . . . . . . Integration time . . . . . . . . Sample matrix . . . . . . . . . . Sample flow-rate . . . . . . . . Sodium tetrahydroborate(II1) flow-rate Potassium iodide flow-rate .. . . Greenfield type 4.75 kW 23 1 min-1 16.8 1 min-1 2.1 1 min-1 9.0 mm 197.197 nm 206.833 nm 196.026 nm 214.281 nm 20 s 1 + 1 hydrochloric acid 9.5 ml min-1 4.7 ml min-1 9.5 ml min-1 Table 2. Effect of selected ions on hydride production Concentration/ Suppression of analyte signal, YO Interferent pg ml-1 As* Sb* Se* Te* 500 2 0 40 0 Pb(I1) . . . . 400 10 30 40 90 100 0 6 10 65 Au(II1) . . . . 1 0 10 85 >95 Pt(1V) . . . . 1 20 20 30 >95 Pd(I1) . . . . 1 20 20 70 >95 Fe(II1) . . . . 5000 4 3 65 5 Ir(1V) . . . . 1 0 0 0 0 Rh(II1) . . . . 1 0 0 10 0 Ru(1V) . . . . 5 0 0 3 8 Au+PGMt . . 0.2each 5 0 48 89 * Analyte concentration 0.1 pg ml-1. t Platinum-group metals. Table 3. Efficiency of coprecipitation with Fe(OH), at pH 2.40 in the presence of 10% NH&l Concentration before precipitation/ Element pg ml-1 As .. . . . . . . . . . . 20 Sb . . . . . . . . . . . . 20 Se . . . . . . . . . . . . 20 Te . . . . . . . . . . . . 20 Pb . . . . . . . . . . . . 200 c u . . . . . . . . . . . . 200 Au, Pt, Pd, Ir, Rh . . . . . . 10 Ru . . . . . . . . . . . . 10 0.1 0.1 0.1 0.1 Recovery, % 100 100 100 99 100 99 100 94 c0.2 <0.2 <2 15 Reagents De-ionised water and analytical-grade reagents were used throughout the experimental work. Hydrochloric acid, relative density 1.18. Nitric acid, relative density 1.40. Hydrofluoric acid, 40% mlm. Perchloric acid, 70% mlm. Sodium peroxide, 95% mlm. Merck. Sodium hydroxide, 99% mlm. Merck. Ammonium chloride, 99.5% mlm. Saarchem UnivAR grade. Sodium tetrahydroborate (III), solution, 1 YO.A mass of 10 g of sodium tetrahydroborate(II1) was dissolved in 1 1 of 0.1 M sodium hydroxide solution. Potassium iodide solution, 100 g 1-1 in 20% VIV hydro- chloric acid. Arsenic standard solution, 1.00 g 1-1. Arsenic trioxide was dissolved in aqua regia and diluted with 3 M hydrochloric acid. Antimony standard solution, 1.00 g 1-1. Antimony (gran- ules) was dissolved in aqua regia and diluted with 3 M hydrochloric acid. Selenium standard solution, 1 .OO g 1-1. Selenium (granules) was dissolved in aqua regia and diluted with 3 M hydrochloric acid. Tellurium standard solution, 1.00 g 1-1. Tellurium (gran- ules) was dissolved in hydrochloric acid - nitric acid - water (1 + 1 + 1) without heating and diluted with 3 M hydrochloric acid.The optimum conditions for the formation of the hydrides of arsenic, antimony, selenium and tellurium and the com- promise instrumental parameters are given Table 1. Decomposition of Silicate Rocks A mass of 1.000 g of finely ground sample was treated with 10 ml of nitric acid and 10 ml of perchloric acid in a Teflon beaker. This solution was evaporated to 2-3 ml on a hot-plate, 10 ml of hydrofluoric acid and 5 ml of perchloric acid were added to the residue and the solution was evaporated nearly to dryness. After decomposition, the residue was dissolved in 30 ml of 1 + 1 hydrochloric acid and heated on a water-bath for 1 h. Decomposition of Sulphide Ores A mass of 1 .OOO g of finely ground sample was fused with 3.0 g of sodium peroxide in a zirconium crucible.The melt was cooled and then dissolved in 40 ml of 1 + 1 hydrochloric acid, after which the solution was heated on a water-bath for 1 h. Separation of Arsenic, Antimony, Selenium and Tellurium from the Matrix The acid solution was diluted to 125 ml with water and 15 g of ammonium chloride were added. The solution was heated to approximately 50 "C, neutralised with pellets of sodium hydroxide and finally adjusted to a pH of 2.40 with a 0.2 M solution of sodium hydroxide. The solution was heated on a water-bath for 2 h and the precipitate obtained was filtered through a Whatman No. 542 filter-paper. The precipitate of Table 4. Effect of ammonium chloride on the efficiency of the coprecipitation with Fe(OH), at pH 2.40 Recovery, % I 11 14-1, YO As* Sb* Se * Te * Aul- Ptt Pdt Irt Rht Rut 0 25 25 33 17 5 12 6 17 25 73 2.5 97 98 94 60 <2 3 <2 9 10 55 5 99 99 98 75 <2 (2 <2 <2 <2 40 10 100 99 98 94 <2 (2 <2 <2 <2 15 * Analyte concentration 0.1 pg ml-1. t Analyte concentration 10 pg ml-1.ANALYST, JANUARY 1986, VOL.111 17 iron(II1) hydroxide (only a partial precipitation of iron is effected), including arsenic, antimony, selenium and tel- lurium, was dissolved in 50 ml of hot, concentrated hydro- chloric acid, transferred into a 100-ml calibrated flask and diluted to volume with water. Determination of Arsenic, Antimony, Selenium and Tellurium The compromise conditions for reduction and measurement (Table 1) were used for the determination of the elements. A portion of the sample solution was spiked with a mixed standard solution of arsenic, antimony, sellenium aqd tel- lurium to give an additional concentration of 100 ng ml-1 of each of the elements.The concentration of the elements was calculated from the net signal for each element and compared with the net signal of the addition. Results and Discussion Silicate material is usually decomposed by fusion with sodium hydroxide, sodium peroxide or lithium metaborate. Decom- position by fusion can be used only as a preliminary step, as silicic acid must be removed. If the latter is not removed, the silica separates as a gel when the solution is acidified. This gel contains the hydride-forming elements. A more commonly used method for the decomposition of silicates is to heat the samples with nitric and perchloric acids followed by a further treatment with perchloric and hydrofluoric acids.14 This combination of acids has the advantage that no arsmic,16 antimony,l6 selenium,1618 or tellurium20 is lost. Sulphide ores containing low levels of silica are decomposed by fusion with sodium peroxide at 600 "C for 5 min to prevent the loss of the hydride-forming elements. The advantage of a fusion over the acid digestion previously discussed is that the sulphides are completely converted into Table 5. Effect of residual gold and platinum-group metals on hydride production after coprecipitation with Fe( OH), Initial concentrations of individual Suppression of analytical signal, % metals/ No. of pgml-* precipitations As* Sb* Se* Te* 2 1 4 5 46 50 10 1 6 5 55 90 10 2 7 6 40 35 * Analyte concentration 0.1 pg ml-1.sulphates, whereas acid digestion can result in the formation of a considerable amount of elemental sulphur. Each digestion procedure is followed by heating of the strong hydrochloric acid. This results in the reduction of selenium(V1) and tellurium(VI)+11 to selenium(1V) and tellurium(IV), respectively, the +4 oxidation state being preferred for quantitative hydride generation.1 However, arsenic(V) and antimony(V) remain unchanged and must be reduced to arsenic(II1) and antimony( 111) , respectively, with an auxiliary reducing agent such as potassium iodide before their hydrides can be produced. Unfortunately, pre-reduction with potassium iodide also reduces the oxidation state of selenium to zero, from which no hydride can form. It was found that the addition of the potassium iodide to the sample after the sodium tetrahydroborate(II1) had been added allowed the hydride of selenium to form before the oxidation state of the selenium could be reduced to zero, while allowing arsenic(V) and antimony(V) to be reduced successfully to arsenic(II1) and antimony(III), respectively.For the equi- valent production of the arsenic and antimony hydrides to be obtained in the absence of a pre-reduction step with potassium iodide, a potassium iodide solution of 100 g 1-1 in a 20% V/V hydrochloric acid medium must be used at a flow-rate of 9.5 ml min-1. The flow manifold is detailed in Fig. 1. The detection limits obtained with this system were calculated according to the equation used by Winge et aZ.21 and were 1.1 ng ml-1 for arsenic, 0.8 ng ml-1 for antimony, 0.7 ng ml-1 for selenium and 2.2 ng ml-1 for tellurium.The calibration graphs were linear up to 5 pg ml-1 for arsenic, antimony and selenium, and up to 3 pg ml-1 for tellurium. The coprecipitation of the hydride-forming elements with lanthanum hydroxide at pH 9.0 greatly reduced the interfer- ence effects caused by copper, nickel, cobalt, zinc, cadmium and related matrix elements. 13-21 Unfortunately, this method involves the coprecipitation of iron, lead, gold and the platinum-group metals with the lanthanum hydroxide. The interference due to iron is minimal (Table 2), and quantitative analysis is possible by the use of a technique in which the analyte solutions are spiked. However, the interference effects caused by lead, gold and the plantinum-group metals are extremely high (Table 2), especially in the production of the selenium and tellurium hydrides, and a more efficient separation of the interfering elements is necessary.The coprecipitation of arsenic, antimony, selenium and tellurium Table 8. Concentration of the major and minor components in anode slime (Mintek 1/77)22 Table 6. Concentrations of major elements in in-house reference materials Concentration, % Mintek No. c u Fe Pb S Zn 3 1/74 0.35 9.06 1.95 27.43 44.77 32/74 1.07 3.38 71.06 NR* 3.15 33/74 20.25 20.80 16.93 26.96 6.30 * NR = not reported. Concentration, Concentration, Component YO Component Y O Pt . . . . . . 0.04* Ag . . . . 22.5 Sb . . . . . . 7.60 As . . . .1.0* Se . . . . . . 5.03 Au . . . . 1* c u . . . . 6.15 SiOz . . . . 4.45 Ni 2.06 Sn 4.32 Te . . . . 1.36 Pb . . . . 17.82 Pd . . . . 0.2* . . . . . . . . . . . . * Tentative value. Table 7. Analytical results for arsenic, antimony, selenium and tellurium in selected standards As/pg gg1 Sblpg g-1 Se/pg g-1 Telpg g-1 Material This work Reported This work Reported This work Reported This work Reported Mintek31/7422 . , . . 3.6 k 0.3 NR* 1 4 f 3 1 9 f 5 1 k 0.3 NR 1 k 0.4 1.5 k 0.7 Mintek3217422 . . , , 2.5 f 0.5 4.0 k 0.8 NDt NR 3.2 k 0.3 4.4 k 1 1 f 0.4 NR Mintek3317422 . . . . 3.640.5 2.6$ k 0.8 ND NR 1.6 4 0.4 1.5$ k 0.5 4 4 0.5 NR NBS1633 . . . . . . 5 5 f 3 61 6 f 0.5 7$ 10 & 0.5 9.4 0.5 f 0.2 NR * NR = Not reported. t ND = not determined. $ Tentative value.18 ANALYST, JANUARY 1986, VOL.111 Table 9. Analytical results for arsenic, antimony, selenium and tellurium in mixtures of standards Aslpg g-1 Sblpg g-’ Selpg g-’ Te1p.g g-1 Calculated* Calculated Calculated Calculated Material This work value This work value This work value This work value SARM 4 - 1/177 (2500+ 1) . . . . 4.5 kO.3 4.0 21 + 2 30 f 6 2 0 f 2 20+1 6.2 + 0.5 5.4 k 0.5 (5OOO+ 1) . . . . . . 2.4k0.3 2.0 1 2 k 1 1 5 k 3 1 0 k 1 10 k 0.5 3.2 +. 0.4 2.7 k 0.3 SARM 4 - 1/77 * Calculated from tentative value. with iron(II1) hydroxide at pH 2.40 in the presence of 100 g 1-1 ammonium chloride solution has the advantage that almost 100% of the analyte elements are recovered with minimum coprecipitation of the interfering elements (Table 3). Therefore, this technique is recommended.The high concentration of ammonium chloride is necessary to ensure good separation of the gold and the platinum-group metals and complete coprecipitation of the hydride-forming elements (Table 4). In the analysis of samples with a total platinum-group metals content of less than 200 pg g-1, only one coprecipita- tion step is necessary. However, for high-grade ores and concentrates, it may be necessary for the original precipitate to be dissolved and coprecipitated a second time. This reduces the suppression caused by the interfering elements sufficiently for an analysis to be carried out (Table 5). It is also theoretically possible for losses of the analyte elements to occur during the coprecipitation stage, which would also reduce the analytical signal.This hypothesis was tested by the analysis of a synthetic solution containing a known concentration of the hydride-forming elements and iron, gold and platinum-group elements. After separation of the interfering elements, an aliquot of the solution was spiked with the hydride-forming elements to give a final concentra- tion equivalent to twice their concentration prior to separa- tion. A comparison between the net analytical signal of the unspiked sample and the relative increase due to the spike addition indicated that the recovery of the analytes was excellent. These experiments also confirmed the need for additions of the analytes to be used for quantification instead of calibration with synthetic solutions. Analyte addition compensates for the suppression caused by residual gold and platinum-group metals in the final solution (Table 5).Results were also obtained for arsenic, antimony, selenium and tellurium on the “in-house” reference materials of the Council for Mineral Technology (Mintek),22 viz., Mintek 31/74, 32/74 and 33/74, and in the standard reference material NBS 1633 (coal fly ash) (Tables 6 and 7). Owing to the lack of suitable international reference materials containing gold and the platinum-group metals, an in-house reference material was prepared for arsenic, antimony, selenium and tellurium by mixing of the South African reference material SARM 4 (norite) with Mintek 1/77 (anode sludge)22 in the proportions 2500 + 1 and 5000 + 1 (Table 8). The analytical results indicate good agreement with the calculated values (Table 9).Conclusions An analytical method has been developed for the simul- taneous determination of arsenic, antimony, selenium and tellurium in silicate rocks containing gold and the platinum- group metals and in sulphide ores containing lead and transition elements. The method utilises a separation tech- nique in which the hydride-forming elements are coprecipi- tated with iron(II1) hydroxide in the presence of ammonium chloride at pH 2.40. Interference effects are reduced to a minimum. This paper is published by permission of the Council for Mineral Technology (Mintek). The authors extend their thanks to Mr. R. V. D. Robert for many useful discussions on hydride-generation chemistry. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.13. 14. 15. 16. 17. 18. 19. 20. 21. 22. References Thompson, M., Pahlavanpour, B., Walton, S. J., and Kirk- bright, G. F., Analyst, 1978, 103, 568. Thompson, M., Pahlavanpour, B., Walton, S . J., and Kirk- bright, G. F . , Analyst, 1978, 103, 705. Pahlavanpour, B., Pullen, J . H., and Thompson, M., Analyst, 1980, 105, 274. Wolnik, K. A., Fricke, F. L., Hahn, M. H., andcaruso, J. A., Anal. Chem., 1981, 53, 1030. Nygaard, D. D., and Lowry, J. H., Anal. Chem., 1982,54,803. Nakahara, T., Anal. Chim. Acta, 1981, 131, 73. Azad, J., Kirkbright, G. F., and Snook R. D., Analyst, 1980, 105, 79. Thompson, M., Pahlavanpour, B., and Thorne, L. T., Water Res., 1981, 15, 407. Nadkarin, R. A., Anal. Chim. Acta, 1982, 135,363. Verlinden, M., Talanta, 1982, 29, 875. Nazarenko, V. A., “Analytical Chemistry of the Elements: Selenium and Tellurium,” Israel Program for Scientific Trans- lations, Wiley, New York, 1972, p. 190. Smith, A. E., Analyst, 1975, 100,300. BCdard, M., and Kerbyson, J. D., Anal. Chem., 1975,47,1441. Nakashima, S . , Analyst, 1978, 103, 1031. Nakashima, S . , Anal. Chem., 1979, 51, 654. Bajo, S . , Anal. Chem., 1978, 50, 649. Chan, F. L., and Riley, J. P., Anal. Chim. Acta, 1965,33, 36. Bock, R., and Jacob, B., Fresenius 2. Anal. Chem., 1964,200, 81. De Oliveira, E., McLaren, J. W., and Berman, S. S . , Anal. Chem., 1983,55, 2047. Nazarenko, V. A., “Analytical Chemistry of the Elements: Selenium and Tellurium ,” Israel Program for Scientific Trans- lations, Wiley, New York, 1972, p. 190. pp. 204-205. Winge, R. K., Peterson, V. J., and Fassel, V. A., Appl. Spectrosc., 1979, 33, 206. Stoch, H., and Ring, E. J., Report M104, Council for Mineral Technology, Randburg, 1983. Paper A51 70 Received February 20th, 1985 Accepted August 8th, 1985

ISSN:0003-2654    

DOI:10.1039/AN9861100015

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, JANUARY 1986, VOL. 111 19 Determination of Gallium in Phosphorus Flue Dust and Other Materials by Graphite Furnace Atomic Absorption Spectrometry David C. Barron and Benjamin W. Haynes US Department of the Interior, Bureau of Mines, 4900 Lasalle Road, Avondale, MD 20782, USA A simple, rapid method for the determination of gallium in inorganic matrices using Zeeman-corrected graphite furnace atomic absorption spectrometry (GFAAS) is described. The method uses an acid dissolution technique, Mg(NO& as a matrix modifier and the method of standard additions. The 294.4-nm wavelength is used to improve the signal to noise ratio without loss of sensitivity. Gallium was determined in phosphorus flue dust and also in coal fly ash, copper ore and steelmaking flue dust. The procedure is used as an alternative to neutron-activation analysis (NAA) and is intermediate in sensitivity between flame atomic absorption spectrometry and NAA.A comparison of GFAAS and NAA results is presented. Keywords: Gallium determination; graphite furnace atomic absorption spectrometry; matrix modification; mineral wastes An ongoing project of the Bureau of Mines is the recovery of gallium from high-volume mining and metallurgical wastes. A rapid method was needed to provide gallium concentrations when determining optimum parameters for its extraction and recovery. High-volume metallurgical wastes such as phospho- rus flue dust, coal fly ash and electric furnace steelmaking flue dust were studied as potential materials for gallium recovery. The determination of trace levels of gallium by neutron- activation analysis (NAA) and by graphite furnace atomic absorption spectrometric (GFAAS) analysis in conjunction with solvent extraction pre-concentration has been repor- ted.1-3 The method of Lo et aZ.,2 used in determining trace levels of transition metals in sea water, was applied to gallium using dithiocarbamate complexes to extract the gallium and subsequent back-extraction into nitric acid using Hg2+. This method gives good results, but the use of high concentrations of mercury in the graphite furnace and its subsequent vaporisation into the laboratory were not desired. The use of this same method for NAA using Pb2+ as a back-extraction agent was described by Yu and Wai.1 The use of NAA for determining gallium is very sensitive, but it is not generally available for routine use.The use of the alternative wavelength of 294.4 nm has been reported to give a sensitivity that is equal to or better than that of the primary wavelength of 287.4 nm for gallium in GFAAS.3 The use of the L’vov platform in this GFAAS method gives enhancement over normal tube wall atomisation of the analyte.4 Based on very limited testing, Botha and Fazakas3 suggested that ascorbic acid may be a suitable matrix modifier. This study was carried out with dilute aqueous solutions of gallium in 0.05% V/V nitric acid. Shan et aZ.5 used Ni(N03)2 as a matrix modifier and the 287.4 nm line. In their testing for suitable matrix modifiers, the relative sensitivities for Ni(N03)2 and Mg(N03)2 were similar, with Mg(N03) being slightly better.The samples used in their analysis were digested using HC104, thereby adding C1- to the matrix. The chloride effect was overcome in this method by adding a second modifier of NH4N03 to remove the chloride effect.5 The high volatility of chlorides6 in the graphite furnace was avoided in this proposed method, which required only the use of Mg(N03)2. To avoid the use of solvent extraction and mercury2 in the laboratory and chloride536 in the graphite furnace, a simple GFAAS procedure was desired. The availability of NAA was such that sample analysis would take several weeks. The proposed method uses a sample digestion and analysis procedure modified from Haynes ,7 polarised Zeeman back- ground-corrected GFAAS, and avoids the presence of chloride.Although only Zeeman GFAAS was used, standard GFAAS using deuterium arc background correction should also provide adequate precision. Experimental Reagents All acids used were of analytical-reagent grade. Distilled, de-ionised water (DDW) was used throughout. A 1000 mg 1-1 gallium standard (Aldrich Chemical Co.) was diluted to 1 mg 1-1 with 2% V/VHN03 in DDW. This solution could be used for up to a month without change in concentration. The matrix modifier was a 1% V/V solution of Mg(N03)2 in DDW. Instrumentation A Perkin-Elmer Model 5000 Zeeman atomic absorption spectrometer* and an HGA-400 graphite furnace controller were used. An AS-40 autosampler was used to inject the samples into the furnace. Pyrolytically coated graphite tubes and a L’vov platform were used for all determinations. A standard gallium hollow-cathode lamp was used at 294.4 nm, a current of 12 mA and a slit width of 0.7 nm.Sam p 1 e s Phosphorus flue dust samples were obtained from elemental phosphorus production furnaces in Tennessee and Idaho. The stainless-steel electric furnace dust was a blend of 12 dust samples from various furnaces.* A sample of mixed copper ore was obtained from the St. George Mine in Utah. The coal fly ash was National Bureau of Standards (NBS) Standard Reference Material (SRM) 1633a that contained a reference (non-certified) value for gallium of 58 mg kg-1. Procedure Dry the samples overnight at 140°C and store them in a desiccator to cool. Weigh 0.5 g of sample to the nearest 0.1 mg and place it in a Teflon beaker.Add 25 ml of DDW, 5.0 ml of HN03 and 5.0 ml of HF. Heat the samples on a hot-plate at moderate heat until dry, usually 1-1.5 h. Cool the samples and then add 20 ml of DDW and 5.0 ml of HN03. Re-heat the samples at low temperature for 5-10 min. Filter each sample into a 100-ml calibrated flask, washing the filter-paper thoroughly with DDW. Cool the samples to room tempera- * Reference to specific products does not imply endorsement by the Bureau of Mines.20 ture and dilute to 100 ml. Serial dilution of the sample may be required and HN03 should be kept at 1% V/V in these dilutions. Table 1 gives the graphite furnace conditions developed and used in this method. All readings are in absorbance units in the peak-area mode using a 5-s integration time.The argon purge gas is interrupted during atomisation. The sample volume is 20 pl and is followed by 5 pl of Mg(N03)2 solution. This 5-p1 volume provides 50 pg of Mg(N03)2 to the L'vov platform. The use of Mg(N03)2 as an ashing aid here is similar to its use in other methods.7.9 All samples are analysed by the method of standard additions using dilutions of the sample plus additions of 0, 5 , 10 and 15 yg 1-1 of gallium. Results and Discussion Optimisation of Parameters Initial work was performed using the primary gallium wavelength of 287.4 nm. Erratic results were obtained at this wavelength using Mg(N03)2 as the matrix modifier and high background absorbance readings were observed. Recent studies by Wibetoe and Langmyhrlo on spectral interferences in Zeeman background-corrected AAS indicated a back- ground overcompensation for gallium in the presence of iron.This introduces serious negative systematic errors at the 287.4-nm line. This overcompensation is due to the presence of an iron line close to the 287.4-nm gallium line whose 0 components overlap the gallium analyte line. Under the same conditions using deuterium arc background correction, these errors are positive. 10 The spectral interferences were avoided by using the alternative wavelength for gallium of 294.4 nm. The parameters shown in Table 1 were the result of tests to determine optimum charring and atomisation temperatures. Using 2 0 4 aliquots of 25 pg 1-1 aqueous gallium standard, a 2000 "C atomisation temperature and varying the charring temperature, the effect of Mg(N03)2 matrix modifier on gallium recovery was determined.The results are depicted in Fig. 1. Using the same parameters for the tests shown in Fig. 1 but with 20-pl aliquots of a dissolved phosphorus flue dust sample, the effect of Mg(N03)2 on gallium recovery was again determined and is shown in Fig. 2. Finally, using Mg(N03)2 as a matrix modifier and a 1200°C charring temperature, the effect of varying atomisation temperature on gallium recovery was determined for an aqueous gallium standard and a dissolved sample of NBS SRM 1633a coal fly ash. These results are presented in Fig. 3. From Figs. 1-3, an optimum char temperature of 1200°C and an optimum atomisation temperature of 2000°C were obtained. The results in Fig. 2 indicate that a slightly higher signal is obtained at lower temperatures by not using the Mg(N03)2 modifier in the phosphorus flue dust samples.However, the decreased background obtained with the modifier at the higher char temperature of 1200 "C gave better precision. This increased precision at the higher char temperature was determined to be more important than the small increase in signal intensity at lower char temperatures without the modifier. Therefore, Mg(N03)2 was used with all samples in this study. The maximum power heating mode was used in all tests to provide Table 1. Conditions in GFAAS for gallium at 294.4 nm Temperature/ Argon flow-ratel Step "C Ramp/s Hold/s ml min-1 1 160 1 60 300 2 1200 45 20 300 3 2000 O* 5 0 4 2650 1 5 300 5 20 10 5 300 * Maximum power heating mode.0.1 50 0.125 ~ 0.100 0 m + 0 0.075 2 0.050 0.025 n ANALYST, JANUARY 1986, VOI 1 I I I I 111 "400 600 800 1000 1200 1400 1600 1800 Tem peratu rePC Fig. 1. Effect of Mg(N03)2 on the recovery of gallium by varying the charring temperatures with atomisation at 2000 "C. Sample, a ueous standard solution. A, With Mg(N03)*; and B, without Mg(N8,), 1 0.175 400 600 800 1000 1200 1400 1600 Tern peratu rePC Fig. 2. Effect of Mg(N03), on the recovery of gallium by varying the charring temperature with atomisation at 2000 "C. Sample, phospho- rus flue dust sample. A , With Mg(N03),; and B, without Mg(N03)2 0.175 0.150 0.125 8 c 0.100 + s 0 2 0.075 0.050 0.025 0 A 1600 1800 2000 2200 2400 2600 Temperature/"C Fig. 3. Effect of Mg(N03)2 on the recovery of gallium by varying the atomisation tem erature with charring at 1200 "C.Samples: A, aqueous standart and B, coal fly ash, both with Mg(N03)2ANALYST, JANUARY 1986, VOL. 111 21 Table 2. Gallium concentrations in various samples determined by GFAAS and NAA Gdmg kg-1 GFAAS* NAAt Sample Matrix type N x (7 C.V., Yo N x PFD-2 Phosphorus flue dust 10 315 28 8.8 2 300 PFD-1 Phosphorus flue dust 8 512 43 8.4 2 505 2 530 PFD-3 Phosphorus flue dust 2 531 2 840 PFD-4 Phosphorus flue dust 2 830 NBS 1633a$ Coal fly ash 8 61 5 8.2 2 58 NDP NDQ ss-1 Stainless-steel flue dust 3 50 3.6 7.2 - 2 270 - - - - MCO-1 Mixed copper ore 2 253 - * N = Number of replicate samples; X = average of replicate gallium determinations; u = standard deviation; C.V. = coefficient of t Neutron-activation analysis performed under the direction of A.B.Whitehead, Salt Lake City Research Center. $ Not certified, NBS reference value 58 mg kg-1. 0 ND = Not determined. variation. rapid, even heating to the platform for atomisation with a final burnout temperature at 2650 “C to clean the graphite furnace prior to introduction of the next sample aliquot. To determine if standard additions methods were neces- sary, slopes of calibration graphs were determined for aqueous gallium standards, phosphorus flue dust samples and coal fly ash samples using the method of standard additions. Using linear regression analysis, sample solution graphs gave slopes different from that of the aqueous calibration graph. These results led to the use of the method of standard additions for all samples.Using 20 p1 of a 50 p1-1 (1.0 ng) gallium standard, a peak-area absorbance of 0.280 was routinely obtained. Analysis of Samples Using the above procedure, four phosphorus flue dust samples, one coal fly ash sample, one stainless-steel flue dust sample and one mixed copper ore sample were analysed for gallium. All samples except the stainless-steel flue dust were also analysed in duplicate by standard NAA procedures; comparative results are given in Table 2. The lack of certified standards for gallium in reference materials makes it difficult to assess the accuracy of this procedure, but the results of GFAAS and NAA compare well. The coefficient of variation was between 7.2 and 8.8. Conclusions This method for gallium determination using Zeeman- corrected GFAAS and the L’vov platform is intermediate in sensitivity between flame AAS and NAA.Although not as sensitive as NAA, this method is more rapid than NAA and can be performed in laboratories equipped with graphite furnace AAS. It does not require the use of a reactor or other associated equipment for storing and counting radioactive decay products. A lower limit of about 0.8 pg 1-1 of gallium can be determined in aqueous solution. The method emplovs a straightforward dissolution technique and the U V af Mg(NO& as a single matrix modifier. All samples involved in this study required standard additions. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Yu, J. C., and Wai, C. M., Anal. Chem., 1984, 56, 1689. Lo, J. M., Yu, J. C, Hutchison, F. I., and Wai, C. M., Anal. Chem., 1982,54,2536. Botha, P. V., and Fazakas, J., Anal. Chim. Acta, 1984, 162, 413. Slavin, W., Manning, D. C., and Carnrick, G. R., At. Spectrosc., 1981, 2, 137. Shan, X.-Q., Yuan, 2.-N., and Ni, Z.-M., Anal. Chem., 1985, 57, 857. Slavin, W., Carnrick, G. R., and Manning, D. C., Anal. Chem., 1984, 56, 162. Haynes, B. W., At. Absorpt. Newsl., 1978, 17, 49. Law, S. L., Lowry, W. F., Snyder, J. G., and Kramer, G. W., “Characterization of Steelmaking Dusts from Electric Arc Furnaces,” Report of Investigation, RI 8750, National Bureau of Mines, Washington, DC, 1983,26 pp. Slavin, W., Carnrick, G. R., Manning, D. C., and Pruszkow- ska, E., At. Spectrosc., 1983, 4, 69. Wibetoe, G., and Langmyhr, F. S., Anal. Chirn. Acta, 1984, 165, 87. Paper A.5/194 Received May 28th, 1985 Accepted July 29th, 1985

ISSN:0003-2654    

DOI:10.1039/AN9861100019

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST JANUARY 1986 VOL. 111 23 Determination of Nitrogen-I5 by Optical Emission Spectrometry Using an Atomic Absorption Spectrometer Michael H. Timperley Taupo Research Laboratory Division of Marine and Fresh water Science Department of Scientific and Industrial Research P. 0. Box 4 15 Taupo New Zealand and John C. Priscu Department of Biology Montana State University Bozeman MT 59717 USA The determination of 15N percentage abundance by optical emission spectrometry (OES) using an atomic absorption spectrometer (AAS) with an inexpensive radiofrequency generator (27.5 MHz 20 W) and a specially designed cavity is described. Sample tubes for micro-Dumas combustion are easily constructed as required and nitrogen spectra in duplicate for each sample are recorded in 20 s for two-peak or 30 s for three-peak spectra.Because of the cavity design the technique tolerates masses of N per sample tube between 1 and 110 pg. The precision coefficient of variation <6% is equivalent to that reported for other OES techniques and statistical analysis suggested that a large proportion of the analytical variability is introduced during sample preparation. Many laboratories have access to AAS and this together with the cavity and inexpensive r.f. generator makes 15N technology widely available at low cost. Keywords Nitrogen-I5 determination; optical emission spectrometry; atomic absorption spectrometer; micro-Dumas combustion Optical emission spectrometry (OES) is now a widely used technique for measuring the percentage abundance of 15N, particularly in applications involving only a few micrograms of N and also in laboratories for which the cost of mass spectrometry the alternative technique is prohibitive.Mass spectrometry has the advantage of high accuracy and sensi-tivity but requires several hundred micrograms of N in each sample a feature which is a disadvantage for example in studies with phytoplankton. Both OES and mass spectro-metric methods have been reviewed in considerable detail by Fiedler and Proksch.1 Analysis by OES involves two distinct operations. In the first sample N is converted into N2 gas and in the second the N2 either alone or mixed with an inert gas is excited by microwave or radiofrequency energy to emit a spectrum that is analysed to determine the intensities of the emission lines from the 28N2 29N2 and 30N2 molecules.The relative intensities are proportional to the relative amounts of the three molecules in the sample N. Converting sample N usually organic N into N2 can be achieved by the Kjeldahl - Rittenberg procedure in which ammonium produced by Kjeldahl digestion is subsequently oxidised with alkaline hypobromite solution. 1 Alternatively a more direct technique the Dumas method can be used.2.3 In this method sample N is combusted with CuO (plus Cu if N03- is present) and the gases produced with the exception of N2 are absorbed by CaO. The Dumas method is commonly used alone but has also been applied to ammonium produced from sample N by Kjeldahl digestion46 and catalytic ammoni-fication.7 These latter procedures are necessary for large heterogeneous samples5 and where subsamples e.g.for Kjeldahl N analysis are required but for small samples these procedures with their potential for contamination do not offer any advantage over the direct Dumas method.* Purchase of a 15N emission spectrometer was not an option available to the Taupo Research Laboratory but an atomic absorption spectrometer is part of its instrumentation. When preliminary trials confirmed that identical principles were involved in generating an N2 emission spectrum and in generating a spectrum from an electrodeless discharge lamp (EDL) a light source common in atomic absorption spec-trometry,g the possibility of using an atomic absorption spectrometer for emission spectrometric analysis of 15N was recognised.Despite being one of the most widely distributed analytical instruments their use for 15N OES has not been previously reported. In this paper we describe methods for sample preparation, the r.f. generator and design of the r.f. cavity recording the N2 spectrum using the atomic absorption spectrometer and the performance of the system. Experimental Sample Preparation Sample tubes are made as required by sealing one end of a borosilicate glass tube 8 mm o.d. 5 mm i.d. and 200 mm long. The tubes are combusted at 500 "C overnight to remove any nitrogenous substances from the glass surfaces1 and stored in a desiccator until required. Our samples for 15N analysis include phytoplankton on glass-fibre filters liquids either in capil-laries or dried on to glass-fibre filters and finely ground solid matter.Each sample is placed in a tube and oven-dried overnight at 75 "C. Using a small spatula CaO (approximately 15 mg) and a CuO - Cu mixture (approximately 15 mg) are then placed in each tube. Before use the CaO powder is heated at 900 "C for 2 h and stored in a minimum volume desiccator. Re-heating is necessary once each week while the container is being frequently opened. The CuO powder is heated at 500 "C for 2 h mixed with Cu metal granules (4 + 3 m/m) and stored in a desiccator. A small plug of cotton-wool is inserted approximately 20 mm into the open end of each tube to prevent CaO - Cu powder from being carried into the vacuum manifold and the tubes are then immediately attached to the vacuum line.The manifold incorporates six sample tube attachment ports with a tap for each port a vacuum sensing head (Pirani G5C2) a detachable cold trap (liquid N2) an oil diffusion pump (Edwards E203D) and a backing pump (Jayvac JDX 60). Sample tubes are attached to ports by short (25 mm) lengths of neoprene vacuum hose ( 5 mm i.d.). Evacuation of the sample tubes is hastened by brief application of a high-frequency discharge (e.g. Teslar coil) to each tube. When the pressure is less than 2 x 10-4 Torr each tube is sealed by a small gas torch at a point 110 mm from the closed end. The sealed tubes are then combusted at 500 "C for 6 h an 24 ANALYST JANUARY 1986 VOL. 111 Beam aperture 11 3 7 5 I - . Base plate (Al) Coil 9 0.d. Quartz tube 28.7 0.d.25.2 i.d. Coil coated Cu wire swg 20 .Shield (Al) 45.0 0.d. 42.0 i.d. Coaxial connector Supports (All 10 ,+ Beam aperture 38 *I- 7 i Fig. 1. Detail of the cavity designed for optical emission spec-trometry of N contained in straight-sided sample tubes. Dimensions in millimetres allowed to cool slowly. Immediately before analysis a Teslar coil is again briefly applied to each tube. Instrumentation The r.f. energy source (Scientific Associates Hamilton New Zealand) has a maximum output of 20 W at 27.5 MHz with controls for power output and for matching the output to the cable cavity and tube. A shielded coaxial cable leads the signal to the r.f. cavity (Fig. 1) which was specially designed to match the generator output and the size of the sample tubes.Although the structure of this cavity is relatively simple, materials often vary in composition and precise dimensions depending on the supplier and the optimum dimensions of the coil need to be matched (Le. with a grid dip meter) to the generator. A sample tube is placed in the cavity the r.f. activated and the matching controls are adjusted to give maximum emission intensity. Cooling is achieved by an air jet directed into the top of the cavity. The cavity is fitted into an atomic absorption spectrometer (Perkin-Elmer Model 4000 reciprocal dispersion 0.65 nm mm-1) at the position normally occupied by the light source. The cavity can also be placed in the flame position but the physical arrangement is less convenient. The PE 4000 has push-button control of all functions necessary for recording the N2 emission spectrum including wavelength setting scan speed gain forward and reverse scan base-line zero and recorder expansion.The spectrometer is operated in the emission mode with a band pass of 0.07 nm a signal integration constant of 0.2 s and a scan rate of 5 nm min-l. The chart recorder is set to run at 10 cm min-1. Recording the N2 Spectrum Immediately the sample tube begins to emit the following operations are performed: 1. Set the wavelength to 299.3 nm. Zero the base line (AZ on the PE 4000). 2. Set the wavelength to 297.7 nm if there is <35% or to 298.3 nm if >35% of 15N adjust the gain to give a reading of approximately 1.2 units (this is achieved automatically on the PE 4000 by pressing GAIN).Set the chart expansion to full scale for an emission signal of 1.5 units (1500 RECEXP on the PE 4000). Set the wavelength to 297.4 nm. Turn on the chart drive. Scan towards higher wavelength (SCAN + control on the PE 4000). The 28N2 emission line will be recorded at 297.7 nm. Immediately the recorder pen reaches the base line ( i e . , ca. 298.0 nm) after the 28N2 peak change the recorder expansion as required (e.g. 50 RECEXP on the PE 4000 for <1% of 15N) to record the 29N2 emission line at 298.3 3. 4. 5. 6. > v) C a, C t 0 v) c .-c .-.-.-E w 0.366% A A A A A 1.91% A A A Wavelength Fig. 2. Examples of N emission spectra (recorded in duplicate) for samples containing different atom-% 15N contents.A 28N2; B 29N2; C 30N2. A Change of chart expansion; A change of wavelength scan direction; 3 0 ~ = chart expansion relative to 28N2 peak. Broken lines are base lines for the determination of peak height (see text) nm. If required ( i e . at >12.5% of 15N) continue the scan to record the 30N2 emission line at 298.9 nm. Immediately the scan is complete reverse the direction of scanning (SCAN - on the PE 4000) and re-record the spectrum in reverse by changing the recorder expansion at the appropriate wavelengths. This procedure gives two scans for one sample in 20 s if only the 28N2 and 29N2 peaks are recorded or in 30 s if the 30N2 peak is also required. By recording two scans reliable results can be obtained from tubes with decreasing emission intensity (a common feature of tubes containing <1 pg of N) because the two spectra are symmetrical about the centre point and the peak-height averages are therefore unaffected by signal drift.Examples of the spectra obtained for different concentra-tions of 15N are given in Fig. 2. The positions of the operational changes described above are shown. 7. Calculation of Atom- % 15N Irrespective of peak size and spectral interference from other gases the base lines for the 28N2 and 30N2 emission peaks are easily found as shown in Fig. 2. The low wavelength side of the 29N2 peak coincides with a small peak possibly due to CO,8 which confuses the 29N2 base-line position. Comparisons of the measured per cent. of 15N with the actual per cent. of 15N in a series of standard samples using a variety of methods for determining the 29N2 peak base line showed the following procedure to give the most consistent accuracy.The recorder trace was marked at positions 0.17 nm on both sides of the highest point of the 29N2 peak and the line between these two marks was taken as the correct base line. For given scan and chart speeds the required positions were conveniently expressed in chart units or millimetres. Examples of these base lines are shown in Fig. 2. Peak heights were taken from the highest point vertically down to the base line and then multiplied (or divided) by the chart expansion. At low 15N concentrations these base lines gave smaller peak heights than those calculated from our data by other methods.5.8 Standard equations1 were used to calculate 15N concentra-tions: 30N2 + 0.5 29N2 15N (atom-%) = 30N2 + 29N2 + 28N2 x 100 .. (1) 100 2 x 28N 2 * 1 15N (atom-%) = I 1 . . . . . *9N2 where the symbols e.g. 30N2 represent the peak heights. Equation (1) gave more precise results and was preferre ANALYST JANUARY 1986 VOL. 111 25 whenever the 30N2 emission signal was significant i.e. >2% of the 28N2 peak height. This corresponds to approximately 12.5% of 15N. Equation (2) was used when 15N < 12.5%. At 12.5% of 15N the difference between the values given by the two equations was about 0.2% of 1jN. Method Performance Tests The major disadvantage of OES compared with mass spec-trometry for measuring 15N abundance is its lower precision, and accordingly part of this study involved an examination of factors contributing to precision.This examination considered the measured 15N concentration at natural 15N abundance (0.366%)1 in sets of tubes containing different masses of N per tube each set prepared on a different day and replicate analyses of these tubes on the same and different days. A solution containing 1 mg 1-1 of N [(NH4)2S04 BDH Chemicals Aristar grade] was prepared in distilled de-ionised water. One glass-fibre filter (Whatman GF/F 25 mm, combusted at 500 "C for 2 h washed in 1 M HCl overnight, rinsed and stored in distilled de-ionised water) was added to each of six tubes. The filter in each tube was dried over a small flame and aliquots (10 pl = 10 pg of N) of the (NH4)2S04 solution were applied to the filter to give a set of six tubes containing 10 20 30 40 50 and 60 pg of N.The tubes were dried at 75 "C sealed and combusted as described above and analysed for 15N. 'l'he first experiment to evaluate the effects on measured 15N concentration of re-analysing each tube on the same and different days involved analysing one set of six tubes containing between 10 and 60 pg of N with six determinations per tube on each of four days. For the second experiment, designed to assess the effect of tube preparation a new set of tubes was prepared and analysed with six determinations per tube on each of four days. At low 15N abundance (i.e. <1% of ISN) the values determined by OES are usually higher than the true Val-ues,7,8JO probably because of residual C02 in the tubes dissociating to CO in the discharge and producing an emission peak coincident with the 29N2 line.This problem is usually overcome by applying a calibration graph to the values determined by OES. This graph was determined from 11 standard solutions containing differing 15N concentrations prepared by mixing appropriate aliquots of two stock solu-tions one prepared from (NH4)2S04 (BDH Chemicals, Aristar grade) and the other from 15N-enriched (NH4)$04 (99 atom-% 15N) (Amersham International). Both stock and standard solutions contained 200 pg ml-1 of N. For each standard solution three sample tubes were prepared as described above using 100 pl of solution per tube. Six determinations of the 15N concentration in each tube were made.Upper and lower limits on the amount of N per tube necessary to give a measurable spectrum were determined using seston (mostly phytoplankton) from a culture of lake water. Water from Lake Rotorua a eutrophic lake in the centre of the North Island of New Zealand was collected from 1 m below the surface and screened (0.25 mm) to remove zooplankton. Eight litres of this water were supplemented with 3000 pg of 15N [(NH4)2S04 99 atom-% lsN] and 300 pg of P (KHZPO,) and cultured with occasional agitation at 18.5 "C under fluorescent light (100 pE m-2 s-1),* 18 h light 6 h dark. After 5 d the total N in the seston was measured11 and different volumes of the culture were filtered (GF/F filter 25 mm) ranging from the volume giving a just discernible green colour on the filter (approximately 3 pg of N) to the maximum volume filtered in 20 min (approximately 110 pg of N).Triplicate tubes were prepared for each mass of N and each tube was analysed six times for 15N. * E = einstein; 1 E = 1 mol of photons. Our research includes studies on the kinetics of nitrogen uptake by phytoplankton and the following experiment was conducted to assess the precision of the 15N technique for this type of experiment. Water from Lake Rotorua was cultured exactly as described above except that the volume was 9 1 instead of 8 1 and continuous light was used. After each time interval a sample (300 ml) of the culture was taken and six subsamples (50 ml) were filtered (GF/Ffilter 25 mm). At time zero before 15N was added 12 subsamples were taken.Six determinations of 15N were made for each subsample giving 36 measurements at each sampling time except at t = 0 when 72 measurements were made. Results In the first experiment one set of six tubes containing between 10 and 60 pg of N was re-analysed with six determinations per tube on each of four different days. The total data set 144 values had a mean and standard deviation of 0.468 and 0.033% of 15N respectively. Analysis of variance (ANOVA) showed that replicate analysis of sample tubes on the same day (main effect A) did not make a significant contribution to the total sum of squares (ss) and also that re-analysing the tubes on different days (main effect B) and the first-order inter-actions involving A and B (A:B A:C B:C) were not significant.These effects and interactions represent the non-random influence of the spectrometer and this ANOVA showed that neither short nor longer term changes in spectrometer performance were identifiable contributors to the data variability. These non-significant effects and inter-actions were combined with the second-order interaction (A B C) to give the error ss. This (ANOVA) is summarised in the upper part of Table 1. The other main effect the mass of N per tube (C) was a highly significant contributor (31%) to the total ss but as C also included the influence of tube preparation unambiguous interpretation of effect C was not possible from this experiment. The second experiment consisted of four sets of six tubes containing between 10 and 60 pg of N per tube each set prepared and analysed with six determinations per tube on each of four days.This data set had the same dimensions as the data set from the first experiment and the mean and standard deviation 0.456 and 0.031% of 15N respectively were similar. A summary of the ANOVA for this experiment is given in the lower part of Table 1. As was found in the first experiment main effect A the influence of daily changes in spectrometer performance was not significant. Preparing and analysing tubes on different days (D) was the most significant main effect and this contributed 12.9% of the total ss. Although D included the influence of daily changes in spectrometer performance the first experiment showed that this was not significant. The mass of N per tube (B) included the effect of tube preparation and made a small contribution (8.7%) to the total ss but its significance was low.The interaction between B and D (B D) was significant. This experiment showed that tube preparation was an identifiable contributor to data variability but its importance depended on how much of effect B could be attributed to the mass of N per tube. The means of the six determinations made on each tube prepared in the second experiment were not correlated with the mass of N per tube ( r = 0.090 n = 24) and, although this does not preclude the existence of a non-linear relationship it does suggest that the mass of N per tube was not an important component of effect B. The extreme possibility is that the mass of N per tube at least between 10 and 60 pg had no influence on data variability (this was supported to some extent by the results given in Table 3 and discussed below) and this leads to the conclusion that tube preparation contributed 31% and 49% of the total ss in the first and second experiments respectively.The remaining data variability represented by the error ss can be considere 26 ANALYST JANUARY 1986 VOL. 111 Table 1. Analysis of variance (ANOVA) of data matrices obtained by analysing atom-% l5N in samples of (NH4),S04 (0.366 atom-% 15N). First ANOVA is for data from one set of six tubes containing 10 20 30,40,50 and 60 pg of N per tube each tube analysed six times on each of four days. Second ANOVA is for data from four sets of six tubes containing 10 20 30 40 50 and 60 pg of N per tube with six determina-tions per tube each set prepared and analysed on a different day.A = Replicate analyses on the same day; B = analysis on different days; C = mass of N per tube; and D = preparation and analysis on different days Sum of Degrees of Mean Variance Dimension squares freedom square ratio Significance First ANOVA: Main effect: . . . . . . . . . . . . . . . . 12.54 0.001 0.04846 5 0.00969 c Error: A + B + A B + B C + A C + A B C . . 0.10661 138 0.00077 Total sum of squares 0.15507 143 B . . . . . . . . . . . . . . . . 0.01193 5 0.00239 4.12 0.01 D . . . . . . . . . . . . . . . . 0.01771 3 0.00590 10.17 0.001 B:D . . . . . . . . . . . . . . 0.03804 15 0.00254 4.37 0.001 A + A B + A D + A B D Total sum of squares 0.13741 143 .. . . . . . . Second ANOVA: Main effects: 1st-order interaction: Error: . . . . . . 0.06972 120 0.00058 . . . . . . . . TaMe 2. Data used for establishing a calibration graph. Each measured value is the mean of six determinations on one sample except for standard 1 which is the mean of 24 samples with six determinations per sample. Each coefficient of variation (C.V.) was calculated from three tubes six determinations each i.e. 18 values except for standard 1 for which 24 tubes were used 15N Yo Measured Standard 1 2 3 4 5 6 7 8 9 10 11 12 True 0.366 0.588 0.751 1.14 1.91 3.45 6.56 12.9 25.0 49.7 74.4 99.0 1 0.644 0.886 1.18 1.96 3.53 6.53 -12.8 25.9 50.9 75.7 95.9 2 0.634 0.857 1.18 1.95 3.46 6.47 -12.7 24.8 50.6 76.4 96.0 3 0.662 0.835 1.18 1.93 3.45 6.55 -12.8 23.5 50.8 76.3 96.2 Mean 0.456 0.647 0.859 1.18 1.95 3.48 6.52 12.8 24.7 50.7 76.1 96.1 C.V.Yo 6.8 4.8 4.5 3.1 3.5 2.5 3.0 2.5 4.9 1.1 0.6 0.2 Table 3. Effect of different amounts of seston N per tube on measured 15N concentration. Samples taken from Lake Rotorua water cultured with added (15NH4)2S04 (see text). Each mean and standard deviation are for triplicate samples tubes six determinations per tube 15N Yo Volume filtered/ml 5 10 50 100 150 200 Particulate N/ 2.8 5.6 28 56 84 110 Standard Mean deviation 40.8 1.25 43.6 0.67 47.6 0.89 47.5 0.47 47.4 0.70 46.7 1.27 as the analytical noise and this accounted for 51-69% of the total ss.Calibration data are given in Table 2. The measured value for natural 15N abundance 0.456 atom-% was that obtained from the second experiment described above. The means of both measured and true values were transformed by adding 1 to the base 10 logarithm of each value to give symmetrical distributions of positive values for stepwise multiple regres-sion analyses. The calibration equation derived explained 99.99% of the total ss in the measured values and was log (7') = 1.1055 log M - 0.1473 [ln(l + log M)]2 - 0.0332 where T = true value and M = measured value. This equation predicted the 15N concentration in the 12 standards (0.366-99 atom-%) with average and maximum errors of 0.007 and 0.017% of 15N respectively.The results obtained for the measured per cent. of 15N with different amounts of seston per tube are shown in Table 3. Masses of N per tube between 28 and 110 pg had no significant effect on the measured per cent. of 15N. The intensity of the discharge decreased with increasing amount of N per tube and at 110 pg of N the discharge was only 10 mm long and confined within the small coil. Despite this the discharge was perfectly stable as it was for all tubes in this experiment. The tubes containing 2.8 and 5.6 pg of N showed evidence of contamina-tion by 14N. The amount of contaminant 14N was calculated to be 0.50 pg from the tubes containing 2.8 pg of particulate N and 0.46 pg from tubes containing 5.6 pg of particulate N.A third estimate made from the tubes containing (NH4)2S04 (99 atom-% 15N) used for the calibration experiment (Table 2), gave a value of 0.60 pg for contaminant N. The origin of this 14N was not established but it must have been derived from the solid material (e.g. glass surfaces CaO or CuO - Cu mixture) in the tubes as the amount of residual atmospheric N in the tubes was only about 5 x The incorporation of 15N into seston from Lake Rotorua water over a period of 48 h is shown in Fig. 3. For the purposes pg ANALYST JANUARY 1986 VOL. 111 27 I I I Time/h Fig. 3. Change with time of measured 15N concentration in seston (retained by Whatman GF/F membrane 0.7 pm nominal pore size) from Lake Rotorua water cultured with added (15NH&S04 (see text for culture conditions).Vertical height of each point spans mean f 1 s.d. of six sample tubes with six determinations per tube except at t = 0 when 12 sample tubes were measured of demonstrating the precision of the 15N technique in this type of experiment the number of replicates taken at each time (i.e. twelve at t = 0 six at other times) was greater than would normally be taken ( e . g . triplicates at each time). The vertical dimension of each data point spans the mean k one standard deviation of the measured per cent. of 15N. The coefficient of variation for all data points lies between 1.3 and 4.7%. Discussion Several features of this OES procedure for determining 15N abundance offer distinct advantages over the attributes of other published techniques.Foremost among these advan-tages is that of cost. The main component of this technique is the atomic absorption spectrometer and although these instruments are expensive their cost is usually justified by their normal function i.e. the analysis of metals. Extending the use of these instruments to determine 15N abundance is a bonus at little extra cost. Further these instruments are widely distributed throughout the scientific world and although some may require the addition of a wavelength scanning device most could be readily adapted to the technique described here. The r.f. generator is a modified unit from a large radio transmitter and accordingly it was inexpensive. Many laboratories with atomic absorption spectrometers use EDLs and the r.f.generators for these need only have the special cavity attached to be suitable for 15N work. The vacuum manifold represents the major expense but this cost is essential irrespective of the type of spectrometer used to record the N2 spectrum. Most spectrometers for OES analysis use sample tubes with constrictions or other complex shapes but in this system simple straight-sided tubes gave the best results and were inexpensive and convenient to make. The main factor in the successful use of these sample tubes was the cavity design, which caused the discharge to concentrate in the small coil, giving the same effect as the narrow section in constricted tubes.8 The design also contributed to one of the most important attributes of the system.Often in experimental work e . g . with phytoplankton the amount of N retained on a filter or placed directly in a sample tube is either not known or cannot be controlled and for OES techniques that require a relatively narrow range of masses of N per sample tube2JJ2 this must be a substantial disadvantage. The method described here is not restricted in this way and in phytoplankton studies the upper limit is determined by the amount of seston that blocks a 25 mm glass-fibre filter and the lower limit at which contamination becomes important corresponds to a just discernible green colour on the filter. Smaller amounts of N can be determined e.g. 0.5-1 yg but allowance is then necessary for approximately 0.5 pg of contaminant 14N (see references 4 and 13 for a discussion on contamination).The precision (coefficient of variation) achieved by this method from 6.8% at natural 15N abundance to 0.2% at 99% of 15N can be compared with that reported by others for OES techniques e.g. 6.l-O.2% for 0.363-11% of 15N7778J2J4 However most of these precision data either were based on very few samples i.e. <lo or were for sample preparation techniques other than the micro-Dumas method used here. There have been no previous attempts to identify the causes of low precision in OES 15N analyses despite this being a major limitation of the method particularly when micro-Dumas combustion is used.8 In this study at least 13% and possibly 49% of the data variability at natural 15N abundance originated during the preparation of the sample tubes but careful attention to the procedures used did not substantially improve the precision.The type of glass used for sample tubes can influence the shape of the calibration graph but apparently does not affect the precision.15 One further source of data variability was thought to be inadequate recorder response. At the relatively high scan rate used of 5 nm min-1 the peak, i.e. 0.1 nm of the 28N2 emission signal was scanned in approximately 1 s which is close to the recorder response time of 0.5 s. This suggests that the precision would be improved by either a faster response recorder or direct computer acquisi-tion of the emission signal from the atomic absorption spectrometer. Measurements by other OES techniques of 15N at levels close to natural abundance are often higher than the true values and this was found to be so for the technique described here.The procedure used for finding the base line for the 29N2 emission peak gave smaller and more reproducible peak heights than those calculated by other methods and this reduced the amount of curvature of the calibration graph. Our technique for finding the base line is similar to that of Lloyd-Jones et aZ.5 Their method uses the dips on each side of the 29N2 peak but we found that the emission intensities at these dips relative to that at the 29N2 peak varied independently of the 15N concentration possibly because of emission from dissociation products of water16 not absorbed by the CaO. Some workers have advocated the use of a number of linear regression lines to span the calibration graph75,7J7 but this was unnecessary for the calibration data presented in Table 2.After the data had been transformed to give an approximately symmetrical distribution stepwise multiple regression analy-sis gave a single equation with an accurate fit over the entire range of 15N concentrations. A programmable calculator is used to calculate the true 15N concentration from peak heights. Recording the emission spectrum is a rapid operation, taking 20 or 30 s for duplicate records of two- or three-peak spectra. This is achieved by a high scan rate of 5 nm min-l, although at the expense of a small but tolerable loss of precision from the slow recorder response. The limit on the rate of analysis is sample preparation and with the vacuum line described 18 tubes can be evacuated and sealed in 1 h.After combustion these tubes can be analysed in 30-40 min. The system has been in use now for almost 2 years and has successfully analysed more than 1000 samples for marine productivity studies17 and many other samples from lakes.18 Conclusions The wide availability of atomic absorption spectrometers in scientific laboratories and the low cost of the generator an ANALYST JANUARY 1986 VOL. 111 cavity offer a simple and convenient facility for laboratories unable to acquire alternative instrumentation for 15N technol-ogy. This development has greatly expanded nitrogen research in the Taupo Research Laboratory and has the potential if adopted in other laboratories to advance substantially research on nitrogen in biological systems.The authors thank the following staff of the Taupo Research Laboratory Max Gibbs for contributions to the cavity design, Vaughan Wilkinson Rosemary Vigor-Brown and Paul Woods for conquering the vacuum line and for analysing the first 1000 samples and Jan Simmiss for typing the various drafts of this manuscript. 1. 2. 3. 4. 5. References Fiedler R. and Proksch G. Anal. Chirn. Acta 1975 78 1. Murphy T. P. Can. J. Fish. Aquat. Sci. 1980 37 1365. Lernasson L. and Pages J. J. Exp. Mar. Biol. Ecol. 1983, 67 33. Paasche E. and Kristiansen S . Estaurine Coastal Shelf Sci., 1982 14 237. Lloyd-Jones C. P . Hudd G. A. and Hill-Cottingham D. G., Analyst 1974 99 580. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. Ronner U. Sorensson F. and Holm-Hansen O. Polar Biol. 1983 2 137. Goeyens L. G. Stichelbaut L. W. Post E. J . and Baeyens, W. F. Analyst 1985 110 135. Fiedler R. and Proksch G. Plant Soil 1972. 36 371. Barnett W. B. At. Absorpt. Newsl. 1973 12 142. Karlsson L. and Middleboe B . in “Proceedings of a Symposium on Isotopes and Radiation in Soil - Plant Relation-ships Including Forestry,” IAEA Vienna 1972 p. 211. Priscu J. C. and Priscu L. R. Mar. Biol. 1984 81 31. Blackburn T. H. Appl. Environ. Microbiol. 1979,37 760. Lloyd-Jones C. P. Adam J. S. Hudd G. A. and Hill-Cottingharn D. G. Analyst 1977 102 473. Kanazawa S . and Yoneyama T. Soil Sci. Plant Nutr. 1976, 22 489. Lloyd-Jones C. P. Adam J. and Salter D. N. Analyst 1975, 100 891. Burridge J. C. and Hewitt I. J. Anal. Chirn. Acta 1980,118, 11. Priscu J. C and Downes M. T. 1985 Estuarine Coastal Shelf Sci. 1985 20 529. White E. Law K. Payne G. and Pickrnere S. N.Z. J . Mar. Freshwater Res. 1985 19 49. Paper A51207 Received June 1 Oth 1985 Accepted July 22nd I98

ISSN:0003-2654    

DOI:10.1039/AN9861100023

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST JANUARY 1986 VOL. 111 29 Studies on the Determination of Mercury in Human Beard Shavings by Neutron-activation and y-Ray Analysis J. G. Pritchard and S. 0. Saied* Department of Physical Sciences North East London Polytechnic Stratford London E 15 4LZ UK The determination of mercury by instrumental neutron-activation analysis has been studied with particular emphasis on hair as the matrix. The well known analytical standards orchard leaves and Bowen's kale have been compared and the value 0.164 k 0.013 p.p.m. found for the level of mercury in Bowen's kale. Hence the likely accuracy is _+ 8% when matrices similar to Bowen's kale are analysed for mercury by the method described. All factors affecting the precision are discussed. Powdered hair and the standards were shown to be easily homogenisable; however beard shavings were found to be generally inhomogeneous with respect to mercury distribution especially when the mercury content was much in excess of ca.2 p.p.m. owing to exposure of subjects to mercury in the professional working environment. The beard shavings of non-occupationally exposed human beings contained 0.1-1.5 p.p.m. of mercury. Difficulties with the establishment of a mercury mass standard for use with the method are discussed. Keywords Mercury determination; hair; beard shavings; neutron-activation analysis; y-ray analysis In a previous report on the determination of mercury in hair by cold vapour atomic absorption spectrometry,lJ it was noted that the instrumental neutron-activation analysis method had been widely applied to the determination of mercury in hair but had given some results that appeared much too high and was unattractive as too few experimental details were available from which the procedure might be judged.2-6 In the course of continued work on the determi-nation of mercury in human hair we have taken the opportunity to examine the neutron-activation method in detail and to report on its reliability in this application.In principle the neutron-activation method seems simple. Samples and standards should be irradiated under the same conditions in the high neutron flux of an atomic reactor then the gamma radiation from both should be compared quantita-tively by means of a germanium crystal scintillator.7-9 Nat-urally occurring mercury consists of a mixture of seven (non-radioactive) isotopes but only the excitation of 196Hg and 202Hg yields products that involve y-ray half-lives long enough to allow a convenient analytical procedure.10 The radio-chemical reactions for 202Hg the major isotope of mercury of natural abundance 29.7% are as follows: Activation 2gtHg + An += 2ziHg ~ ~ 4 7 d ' 2z:T1* + P- (210 keV) 203 * 2:T1 + y(279 keV) 'lT1 T ' z 3 x 10-los ' Here An indicates a neutron p- an electron (of energy 210 keV) y a gamma ray an asterisk a nuclear excited state and T4 the decay half-life.The P-rays are mainly absorbed in material located between the sample and the detecting crystal and essentially only the y-emission is measured in this instance at 279 keV. However a background is picked up by the detector, owing mainly to scattered X-rays (bremsstrahlung) that arise from the absorbed P-rays.Although of only 0.2% natural abundance the 196Hg is far more easily activated12 to 197Hg in both the nuclear ground state and an excited state.11J2 The complicated decay scheme of these species results in ';;Au as the final product with the emission of a principal y-ray of energy 77 keV the over-all decay half-life being ca. 3 d.ll * Present address Department of Mathematics and Physics, University of Aston Gosta Green Birmingham B4 7ET UK. During the early part of the decay period the y-ray spectrum of a mercury-containing substance shows a 77-keV peak that is much higher than the 279-keV peak but the much shorter half-life of the former is not conducive to a convenient analysis in our view when large batches of samples are involved.Rather the 279-keV peak with Ti = 47 d allows relatively easy measurement scheduling and the necessity for decay corrections is rare. Moreover preliminary experiments showed that the accuracy and precision of measurement of the 77-keV signal were seriously compromised by a "noisy" sloping background whereas the 279-keV signal appeared against a much clearer and flat background. Hence the 279-keV peak was used for the analysis in this work. In this instance a small' correction was necessary to the lowest mercury levels observed owing to interference from sel-enium trace amounts of which almost always occur in the hair of healthy persons.13 In this method accuracy requires (a) that analytical samples be irradiated at the same time and in the same location as aliquots of material that has been standardised with respect to mercury content so that variations in neutron flux within the reactor can be compensated and (b) that standards and samples be of the same physical form and be sufficiently homogeneous in bulk with respect to mercury so as to yield reproducible aliquots for the analysis.Samples of cut hair strands taken at random in aliquots of 0.1-0.2 g differ seriously in mercury content and are therefore unsuitable, whereas similar sized aliquots of powdered hair taken from thoroughly mixed batches have been shown to be uniform in mercury content within an experimental error of 4 5 % .2 Moreover thorough testing of the powdered and easily homogenised standard orchard leaves has shown that con-sistent results can be obtained provided that aliquots of not less ,than 0.25 g are used for the analy~is.1~ We therefore undertook to compare 0.25-g samples of powdered hair with very similar samples of analysed standard materials of which two were found suitable orchard leaves and Bowen's kale.14J5 Both of these contain mercury at the lowest level likely to be found in hair 0.1-0.2 p.p.m.and were free from interferents except for a small amount of selenium for which a correction could easily be applied. (River sediment ,I6 contain-ing multifarious interferences and heterogeneous owing to its broad distribution of particle sizes and high density and bovine liver,17 with far too high a selenium content were rejected.) Loss of mercury by evaporation during the analytical process is an ever present problern.lJ8 Polythene capsules 30 ANALYST JANUARY 1986 VOL.111 which contained no serious interferences were selected to enclose the samples and standards. A relatively cool atomic pile was selected together with a modest degree of excitation to ensure the integrity of the analytical specimens. (The sealing of hair samples in quartz tubes was rejected because of suspected loss of mercury during the hot-sealing process and serious interference from selenium in the silica.) Within the above context this paper reports an exploration of the neutron-activation method and aims to provide an assessment of its precision internal consistency and accuracy with respect to atomic absorption spectrometry.2 The range of mercury concentration in the hair samples examined extends from the normal range 0.1-2 p.p.m.towards 100 p.p.m. by inclusion of hair from dentists occupationally exposed to mercury vapour. Experimental Materials Batches of electric-razor hair shavings usually in amounts from 0.5 to 1 g were collected from several dentists and other persons. Their accumulated daily shavings in the compart-ments behind the cutting rotors of the electric razors were simply tipped out into clean paper or polythene envelopes and sealed until taken for the analysis. In some instances large accumulations of up to 10 g of shavings were collected. The dentists were all in active practice with mercury and amalgam continuously in the immediate working environment whereas the other persons had no unusual contact with mercury other than from their normal daily food and a usual number of dental restorations.Standard Reference Materials Nos. 1571 (orchard leaves) , 1645 (river sediment) and 1577a (bovine liver) were supplied by the Office of Standard Reference Materials National Bureau of Standards Gaithersburg MD USA (supplies of orchard leaves were no longer available after 1983). Bowen’s kale was supplied by Professor H. J. M. Bowen University of Reading Berkshire UK.15 One millicurie of 203Hg was obtained in the form of a solution of ca. 10 mg of mercury(I1) acetate in 2-3 cm3 of dilute acetic acid at a pH in the range 2-3 from Amersham International Amersham Buckinghamshire UK.Nitric and acetic acids were of Aristar grade and sodium sulphide selenium dioxide mercury(I1) oxide and thio-acetamide were GPR-grade reagents from BDH Chemicals, Poole Dorset. Equipment Polythene capsules of pill-box shape with tightly fitting separate heat-sealable lids external dimensions 5 x 15 mm diameter capacity 0.50 cm3 (“size-l”) were purchased from Precision Machining Engineering (Harrow) Ltd. South Harrow. Polythene canisters external dimensions 75 x 25 mm diameter capacity 30.0 cm3 for containment of batches of pill-boxes were obtained from Gallenkamp Griffin London. Filled canisters were irradiated in core tubes of the University of London Research Reactor at Imperial College of Science and Technology Silwood Park Sunninghill Ascot , Berkshire UK.This reactor is water cooled fuelled by 235U, operates at a maximum power of 100 kW for 7-8 h during the normal working day and generates maximum thermal neutron fluxes of approximately 10’2 neutrons cm-2 s-1 and maximum temperature ca. 60 “C in the core tubes.19 The detection - recording system for measurements of the y-ray spectra of irradiated samples was as follows. A Canberra Model 7226 lithium-drifted germanium crystal detector was used in conjunction with a Canberra Model 3002 3-kV stabilised d.c. power supply (supplying 2.5 kV). The 4-ps pulse signal from the detector pre-amplifier was fed into a Canberra Model 2011 shaping amplifier slotted into the front panel of a 4096-channel Canberra Model 8524 pulse-height analyser.The detecting crystal was a coaxially drifted hollow cylinder of 22.7 cm3 active volume with one closed end of 12.6 cm2 area facing upwards to the sample and situated 5 mm below a 51 mm diameter beryllium window recessed by 1 mm into the top of the detector housing. The crystal was cooled by conduction from a copper finger protruding from the bottom of the detector and maintained in liquid nitrogen. The nominal resolution of the crystal was reported as 1.97 keV at 1332 keV, and its efficiency as a nominal 3.4% measured arbitrarily with 1332-keV y-ray emission from 6OCo with respect to a high-efficiency sodium iodide crystal detector of low resolution.20 The analyser incorporated a video-screen display automatic timing and numerous programmable control facilities and was interfaced to separate output units, namely a Centronics Model 739 dot-matrix printer a Hewlett-Packard Model 7470A graphics plotter and a Radio Shack Realistic Minisette-9 Model 14-812 compact cassette recorder (Canberra Model 5421MK).The analyser energy scale was 0.45 keV per channel. The sample holder was an 85 mm diameter Perspex disc of 2.5 mm thickness ruled with concentric circles to allow precisely reproducible positioning of the pill-box sample capsules. The disc was attached to a brass annulus that could be adjusted up and down along the length of a rigid vertical brass rod calibrated in millimetres. At the lowest point in its adjustment the sample holder was in contact with the top of the detector housing. The multi-channel analyser recorded automatically a net integral count and its statistical variation.2I Typically chan-nels 526-536 ( N channels) accumulating in the range 276.8-281.3 keV were pre-set to cover the whole of the 203Hg band.Also typically channels 523-525 and 537-539 (2n channels), symmetrically situated either side of the 276.8-281.3 keV band were pre-set to calculate a mean background count per channel rn. Then a total background count of ( N + 2n)rn = B may be projected over the entire 2n + N channels considered. If the total background count ( B ) is subtracted from the total count over the 2n + N channels (T) then the count attributable to the 203Hg is T - B = A and its standard deviation is calculated as [A + B + (2n + N) B/2n]&. In this expression in addition to the total number of counts recorded, an additional number of background contributions is added according to the ratio of the total number of channels considered to the number of channels used to estimate the mean background.Clearly if the latter is not a large number compared with the former then additional uncertainty (apart from the random nature of the natural radioactivity compris-ing the total number of counts) is introduced by virtue of the method used to estimate the unknown background incorpor-ated in the 267.8-281.3 keV band. The analyser automatically recorded a percentage error function approximately equiv-alent to the 90% confidence limits of the net count A due to 203Hg which were calculated as k1.65 x 100 [ A + B + (2n + N)B/2n/VA.The relative standard deviation is this function with the factor 1.65 omitted which could be equally well programmed into the analyser output. Preliminary Experiments and Calibration The complete spectra of irradiated blank pill-box capsules, several encapsulated 1-pg samples of selenium dioxide and 0.25-g samples of hair and the standard materials were recorded. The 277-281 keV band net integral due to 203Hg was measured for a particular hair sample containing ca. 5 p.p.m. of mercury over a period of 36 d and several hourly counts were repeated systematically over a 48-h period. Aliquots of 0.25 g were selected from certain large batches of powdered beard shavings in some instances after thorough mixing of the batch and in other instances on a take-it-as-it-comes basis and irradiation and counting analysis was carried out with respect to 0.25-g aliquots of either orchard leaves or Bowen’s kale a ANALYST JANUARY 1986 VOL.111 31 the only y-ray component in the range of interest is a peak at 237 keV which does not interfere with an analysis for standards. Several aliquots of each standard were tested against one another. The mercury(I1) acetate solution containing 203Hg was suitably diluted to a level well below 0.1 pg p1- in dilute acetic acid to give an easily manageable level of radioactivity. A Jencons Finnpipette was used to transfer aliquots of the diluted 203Hg solution in multiples of 5 p1 on to 13-mm circlets of Whatman No. 4 filter-paper fitted into the bottoms of the polythene capsules. These transfers were made on to filter-paper that was previously (a) untreated (b) treated with like aliquots of a 2 pg pl-1 solution of sodium sulphide and (c) treated with like aliquots of a 2 pg pl-l solution of thi0acetamide.1~ This was repeated with a 0.2 pg p1-1 solution of non-radioactive mercury(I1) oxide in 0.2 M nitric acid.The radioactive capsules were closed with lids and counted. The non-radioactive capsules were closed with lids sealed, irradiated and counted. the measurement laboratory in lead containers of thickness not less than 25 mm. (Any vehicle employed for this purpose need not be specially labelled in the UK when the radiation dose-rate does not exceed 0.5 mrem h-l at any part of the exterior surfaces of such lead containers and when no more than 80 mCi of 203Hg are so transported.22) Handle and open the canisters by remote control and handle the capsules with 6-in long forceps.Place each capsule in the sample holder of a suitable y-ray detecting and scaling system and count the radiation for a time sufficient to generate not less than 3000 counts in the 277-281 keV band. Apply corrections for the counting dead-time if appreciable the contribution of 75Se if any to the 277-281 keV peak and for the decay of the 203Hg if counted a significant period of time after counts with which comparison is to be made. The corrected count rates for analytical samples and standards may then be directly compared. Recommended Procedure Results Dry the orchard leaves in an oven at 85 "C for 4 h before use as prescribed.14 Dry the Bowen's kale in an oven at 90 "C for 20 h before use as recommended.15 Weigh exactly 0.25 g of powdered hair or dried powdered vegetable standard into a pill-box capsule filling it almost completely and put the lid into place immediately.Heat-seal each capsule by running a hot iron around the tight join between pill-box and lid. Install 10 or 11 pill-boxes in each canister so that they remain immobile. (Samples may be identified by numbers written on the polythene capsules with Staedtler water-proof permanent-ink pens.) Allow not less than three standards per canister. Irradiate the canisters in a thermal neutron flux of ca. 1012 n cm-2 s-1 for ca. 24 h. Allow not less than 7 d for the radioactivity of the canisters to decay to a manageable level before transportation or measurement of the samples is attempted.Transport the canisters from the reactor area to y-Ray Spectra Fig. 1 shows the y-ray spectrum of an irradiated hair sample containing ca. 6 p.p.m. of mercury. The energy range shown here is from 25.4 to 480.3 keV the cooling-off period ca. 20 d and the count time 1208 s. The band due to 203Hg appears well defined in the 277-281 keV range. The 90% confidence limits calculated automatically for the likely variation of the net area measurement of the band are +3.5%. No peaks due to selenium are in evidence. The only other isotopes that might conceivably give rise to y-rays in the 277-281 keV range are either extremely rare of short half-life or both.23 The 77.6-keV peak due to 197Hg is evident as the right-hand member of the irregular quadruplet located on the characteris-tically raised and distinctly spikey background to the left-hand side of the spectrum and the accompanying mercury X-ray peaks are at 68.9 and 72.9 keV.The completely blank background counted for 10 000 s showed no peaks of any consequence above 100 keV. Fig. 2 shows the y-ray spectrum of a typical irradiated hair sample containing ca. 0.5 p.p.m. of mercury. The energy range shown is 48-645 keV the decay period ca. 20 d and the count time 72 000 s. The 203Hg band is still very clearly defined with respect to its background. The mercury X-ray region is off-scale at the far left of the spectrum. Peaks due to 75Se are clearly evident at 122 136 and 265 keV and there is also a small peak at 400 keV; the 203Hg peak needs to be corrected for a small contribution due to selenium in instances such as this as discussed below.When counted for equally long periods irradiated blank capsules gave peaks of variable intensity due to gold 198Au at 412 keV (Tj= 2.7 d), chromium 51Cr at 321 keV (Th = 28 d) and antimony 124Sb at 604 keV (Tr = 61 d).24,25 Such peaks could also be seen i 32 ANALYST JANUARY 1986 VOL. 111 peak at 145 keV is probably a combination peak due to simultaneity of the 77-keV 197Hg y-ray and 69-keV mercury X-ray events.9 The separately run spectrum of selenium (irradiated as the dioxide) gave well defined peaks at 121,135,265,280 and 400 keV in the approximate ratios 0.9 2.6 1.0 0.4 0.2 (uncor-rected.for variation of crystal efficiency with energy). The ratio of net count rates for the 265- and 280-keV 75Se peaks, measured on 12 different samples gave a mean of 0.42 with a standard deviation (s.d.) of 0.03. This ratio was used to correct the net counts for the 203Hg bands obtained from certain hair samples that contained less than 2 p.p.m. of mercury as discussed later. The y-ray spectrum of orchard leaves was similar to Fig. 2. The 203Hg peak stood equally well above the background. In the earlier stages of the decay however orchard leaves showed particularly strong peaks due to 48Sc and 124Sb and also 122Sb at 565 keV (7’4 = 2.8 d). The y-ray spectrum of Bowen’s kale was relatively free from background peaks, except those due to Sc and Cr. When counted after decay periods of 15 d the correction to the 203Hg band due to 0.08 p.p.m.of selenium in orchard leaves was about -4% and for 0.14 p.p.m. of selenium in Bowen’s kale it was ca. -6%. Stability of the Instrumentation and Half-life of 203Hg A set of ten 60-min counts taken over a 48-h period for the 203Hg band of a strongly radioactive hair sample (yielding net counts of ca. 13 500 associated with backgrounds of ca. 2500) had after correction for an assumed half-life of 47 d a relative standard deviation (r.s.d.) of 1.6%. The r.s.d. values com-puted by the multi-channel analyser for the same set ranged from 1.0 to 1.2%. The difference from 1.6% is not significant and the results reflect essentially only the random nature of nuclear disintegrations.The stability of the detector and electronic amplifying and counting system was thus demon-strated at least over a 48-h period. The ratio of pulse counting time to count time the detector “dead time,” was zero (<0.1%) throughout the work owing to the low level of radioactivity involved. Four plots of log(net count rate) against mean clock time for the count obtained from four independent sets of hourly count data taken with high-activity irradiated hair samples over a 36-d period yielded least-squares lines with correlation coefficients of ca. 0.99 and a mean value of 47.7 d (s.d. 0.5 d) for the apparent half-life of 203Hg in our system. The half-life of 203Hg is variously quoted,ls127 26-30 the most reliable value being 46.91 k 0.14 d.11728 The lower 95% confidence limit of our range is equal to this standard value and confirms the identity and quality of the 203Hg peak in our system.Our value for the half-life may have been slightly raised by a small contribution to the 277-281 keV band from a trace amount of 75Se of half-life 122 d. The stability of the apparatus over a period of weeks was hence established. Homogeneity of Powdered Hair Samples The position of the capsules on the counting platform of the detector could be reproduced to within +_ 0.3 mm horizontally and vertically and the results in Table 1 show that no measurable error could be introduced by any slight misadjust-ment. When counted right way up and upside down typical sample capsules containing irradiated stir-mixed powdered hair gave identical results within the replicate count error discussed above.Ten similarly irradiated 0.25-g aliquots taken from a several-gram amount of well mixed beard shavings containing ca. 6 p.p.m. of mercury gave results with an r.s.d. of 5.4%. A repeat of this exercise with 11 aliquots from shavings containing ca. 30 p.p.m. of mercury yielded an r.s.d. of 2.9%. The shavings therefore appeared reasonably homogeneous in bulk. This variation also includes any non-uniformity of the neutron flux in the atomic reactor and any haphazard Table 1. Effect of vertical and horizontal displacement of sample from the centre of the counting platform Effect of displacement on the count rate* Displacement/mm 0 4 8 12 20 30 40 Vertical? 100 66.5 54.5 44 30 21 15 Horizontal$ 100 97 90 83 60 35 24 * Normalised to 100% for zero displacement.t Effect on the 1332-keV peak of a 6OCo point source. $ Effect on the 279-keV peak from a capsule containing Z03Hg in a typical hair sample. Table 2. Losses of mercury(I1) acetate containing 203Hg from filter-paper soaked in sulphur-containing reagents Relative count in presence of reagent Timeld None Na,S Thioacetamide 0 100 100 100 1 72 80 100 4 45 60 100 evaporation of mercury from the hair in the capsules which are evidently unappreciable. All effects are within +lo% at the outside limits. Linearity of the Detection System with Mass of Mercury and Mercury Losses The accurately measured volume increments of mercury(I1) acetate solution containing 203Hg that were placed at room termperature on filter-paper impregnated with thioacet-amidel3 gave count rates accurately proportional to mass of mercury within the counting error.The range of linearity tested was the equivalent of up to 50 p.p.m. of mercury in a 0.25-g sample of hair. However omission of the thioacet-amide in this test revealed a characteristic and seemingly mysterious loss of mercury (Table 2). Experiments on the irradiation and subsequent counting of accurately measured aliquots of non-radioactive mercury solutions even in conjunction with thioacetamide showed the disappearance of 3&90% of the mercury from “sealed” capsules and experiments on the establishment of an absolute standard for mercury were not continued (see further discus-sion below).Calibration of the Detector and Standardisation of the Method Table 3 details the results of repeated calibration of the instrumentation with the selected standards. The count rates and their instrumental r.s.d. values are listed for five separate runs in which each orchard leaves capsule was compared with two Bowen’s kale capsules. The count rate listed is integral count in the 276-282 keV band minus background per 105 s. The percentage recovery is calculated as net count rate per nanogram of mercury for Bowen’s kale divided by the same for orchard leaves times 100 with respect to the reported mean mercury content (and standard deviation) values of 0.155 k 0.008 pg g-1 for orchard leaves,l4 and 0.174 k 0.030 yg 8-1 for Bowen’s kale.15 The mean recovery of mercury in Bowen’s kale with respect to orchard leaves is 94.2% with an s.d.of 6.2% on 14 results (only just significantly different from Analysis of eight 0.25-g aliquots of homogenised beard shavings at different times with respect to different samples of Bowen’s kale yielded a mean value of 0.54 p.p.m. with an s.d. of 0.05 p.p.m. (r.s.d. 9%). The result of the analysis of the 100%) ANALYST JANUARY 1986 VOL. 111 33 Table 3. Calibration of y-ray detector and direct comparison of 250-mg lots of orchard leaves and Bowen’s kale Orchard leaves Bowen’s kale Count rate 4447 4447 4948 4948 4124 4124 4236 5659* 4704 4704 4183 4183 2095t 2095t Relative standard deviation, O/O 7.9 7.9 6.7 6.7 9.1 9.1 9.1 10.3 7.3 7.3 9.7 9.7 12.7 12.7 Count rate 4537 4509 4652 4862 4661 4840 4423 6293 * 5131 5209 4048 4403 2169t 23781-Relative Recovery of standard mercury from deviation Bowen’s kale, YO YO 9.1 90.9 7.9 90.3 9.7 83.7 8.5 87.5 9.1 100.7 8.5 104.6 12.7 93.0 10.3 99.0 7.9 97.2 7.9 98.6 12.1 86.2 9.1 93.7 17.6 92.1 8.5 101.1 * Amplifier adjustment in this single instance.t Substantially longer decay time elapsed before measurement in these instances. Table 4. Results demonstrating the heterogeneity of dentists’ beard shavings with respect to mercury Dentist Mercury content of consecutive aliquots * p.p.m. A . . . . . . 4.9 4.9 5. I 2.4 B . . . . . . 2.9 3.2 3.8 4.6 c . . . .. . 3.3 4.0 6.3 8.6 D . . . . . . 6.3 11.1 15.9 40.0 E . . . . . . 13.8 19.1 20.9 26.9 F . . . . . . 42.4 56.8 59.0 68. I value are in italic type. * Values within +lo% of their mean with a nearest neighbouring same hair by the previously developed atomic absorption method with respect to a weighed mercury standard was 0.5 p.p.m. with a likely error of k 0.05 p.p.m. ,2 corroborating the accuracy of both methods. Analysis of Beard Shavings from Control Subjects and Selected Dentists Analysis of the individually homogenised beard shavings from 13 randomly selected control subjects with respect to Bowen’s kale as standard gave the following spread of results: 1.33 1.0 0.7 0.65 0.5 0.45 0.4 0.4 0.4 0.3 0.2 0.15 and 0.1 p.p.m. These values are the means of duplicate determina-tions taken to the nearest 0.05 p.p.m.Five of the values below 0.6 p.p.m. were for vegetarian or modest fish- and meat-eating subjects. The range obtained previously for the scalp hair of non-occupationally exposed persons was 0.35-2.7 p.p.m.2 Results obtained on several aliquots taken at random from unmixed hair samples obtained from certain dentists are shown in Table 4 and demonstrate the heterogeneity of this material. In general more than two determinations are necessary to demonstrate the heterogeneity as duplicates may be misleading. Thus a span of up to +lo% can be expected in populations of results obtained on homogeneous hair by this neutron-activation technique when the mercury level is several parts per million as demonstrated above.Hetero-geneity is demonstrated if duplicate results differ by more than this span. If for case A in Table 4 the determinations were made in the order left-to-right homogeneity would be assumed if no more than three determinations were perfor-med. In case B any two consecutive determinations would be insufficient to demonstrate heterogeneity. Dentists C and D both have very heterogeneous shavings and any two of the four determinations in each instance would reveal some degree of heterogeneity. With dentists E and F the matter depends on which samples might be picked. Correction for Selenium and Limit of Detection No correction was necessary for selenium when the mercury content of the hair was above ca. 2 p.p.m. For 0.5-2 p.p.m. of mercury the contribution from 75Se to the net count rate of the 203Hg band was in the range 0-13% and for 0.1-0.4 p.p.m.the correction was variously 13-30%. The trend to lower corrections as the mercury level increases is due merely in our view to the relatively greater signals from mercury. In noting no correlation between the mercury and selenium levels in hair we are in agreement with Sakurai et ~1.31 (although a correlation has been reported32). The limit of detection is defined as three times the square root of the background count.33734 The longest count times were required for the standards and the occasional sample containing 0.1-0.2 p.p.m. of mercury and here the limit of detection was within the range 0.01-0.02 p.p.m. This is comparable to the level of correction usually required for selenium.Conclusion Suitability of Neutron-activation Analysis for the Determina-tion of Mercury in Biological Samples such as Hair and the Use of Standards During the early 1970s disparaging remarks were made about the accuracy of the neutron-activation technique by analysts who preferred an exacting micro-electroanalytical technique35 and in their masterly review Westermark and Sjostrandg suggested specifically that mysterious discrepancies of 70-90% in mercury recovery were general. The UK Atomic Energy Authority in 1978 noted that neutron-activation analysis gave an inexplicably high value for mercury in hair compared with a value only SOo% as great obtained by cold vapour atomic absorption spectrometry.36 Also studies in Italy have shown an apparent range of 0.3-32 p.p.m.for mercury in the hair of non-occupationally exposed people determined by neutron-activation analysis ,37 whereas the result by atomic absorption spectrometry is more plausibly 0.1-3.6 p.p.m.2.38 A low recovery of mercury in a standard would of course give too high a result for the mercury in an unknown sample. The experiments carried out in this work strongly suggest the disappearance of mercury salts by volatilisation during the irradiation process (however implausible this might seem). The use of thioacetamide to render the mercury salt non-volatile was successful at room temperature but not so when irradiation was involved. Japanese workers have stated that the thioacetamide should be kept wet during the irradiation process and then the standards should be stable,39 yet the ranges they have reported for mercury in the hair of non-occupationally exposed people are still suspiciously high, 0.99-13.2,39 0.6-1840 and 1-16 p.p.m.,31 and may not be explained wholly on the basis of a high content of fish in the Japanese diet.This recovery problem is not insurmountable but is unquestionably a difficult one. Indeed the National Bureau of Standards have reported that 18 man-months of effort were required in their laboratory to correct problems with the absolute standard in connection with their certified value for mercury in orchard leaves.41 However the consistency of the numerous experiments carried out with orchard leaves and Bowen’s kale in this work shows that there are no haphazar 34 ANALYST JANUARY 1986 VOL.111 gains or losses of the biologically combined mercury from these materials in the course of the neutron-activation process to which they were subjected. We therefore strongly advocate their use as secondary standards in this application. The NBS report mean values of (a) 0.155 pg 8-1 for mercury in orchard leaves by neutron-activation analysis on 0.25-g samples (b) 0.160 pg 8-1 by a cold vapour atomic absorption technique in which samples of 2-3 g were digested and (c) 0.145 pg g-1 by stable-isotope dilution spark-source mass spectrometry in which 5-g samples were digested.42 They quote 0.155 pg g-1 for general use with approximately two standard deviations 0.015 yg 8-1 representing the outside limits of all the results obtained.14 This exhaustive work leaves little doubt as to the proper value.(The recently reported range of 0.154-0.162 pg 8-1 based on atomic absorption work,43 offers some independent corroboration.) The neu-tron-activation method as tested in this work for the 0.5 p.p.m. level in hair has given results with this secondary standard that agree well with results obtained by the previ-ously reported atomic absorption method,2 and may be taken as accurate. As supplies of NBS orchard leaves are now exhausted we put forward our standardisation of Bowen’s kale against the NBS material. Taking 0.155 p.p.m. as the standard value for orchard leaves with r.s.d. 5% and the found value for Bowen’s kale as 94.2% of 0.174 p.p.m. with r.s.d. 6.2% (Table 3) we arrive at 0.164 p.p.m.with s.d. 0.013 p.p.m. for the level of mercury in Bowen’s kale. The standard deviation can be taken as the likely accuracy of individual determina-tions by the procedure described i.e. 8%. Matters Affecting the Precision of the Neutron-activation Method The best precision r.s.d. 1-2% was obtained with the large signals from the repetitive experiments designed merely to test the stability of the instrumentation. In the large-signal test of homogeneity of hair shavings and neutron flux carried out with respect to one standard the r.s.d. range was increased to >5%. If the variability introduced by analyses carried out in different runs with different standards is now added in particular for hair containing a low normal level of ca.0.5 p.p.m. of mercury the r.s.d. is increased to ca. k970 as noted in the calibration and standardisation section above (see also the population of r.s.d. values shown in Table 3). The precision is limited by the low level of mercury in the secondary standard. The r.s.d. of 9% can be apportioned as ca. 8% to the standard (which contains the minimum 0.1-0.2 p.p.m. of mercury) and 4% to the sample (containing 0.5 p.p.m.). Hence ca. 8% is the lower limit for the likely reproducibility of determinations on hair that contains 0.5 p.p.m. or more of mercury whereas the imprecision must rise to at least ca. 12% for samples of hair that contain only 0.1-0.2 p.p.m. of mercury. This is probably increased to say 15% by the need for high corrections for the contribution of 75Se to the 203Hg mercury band.This represents a span of 30% in standard deviation alone (albeit for the worst possible situations to be met with in practice) and we have therefore quoted the lower mercury levels only to the nearest 0.05 p.p.m. Several replicate determinations are required in order to ensure reasonable precision in the determination of these lower mercury levels. The precision may be raised by a number of measures that would give larger signals. Another homogeneous secondary standard that contains more mercury might be sought. Longer and more costly irradiation times and count times might be employed. A higher neutron flux with an attendant higher core temperature could be used with increased risk of chemical attack on the samples standards and containers.To take measurements earlier in the decay period however does not greatly improve the signal to noise ratio as then the general background is higher in addition to the signal of interest. Scope of the Neutron-activation Method and Alternative Methods World-wide interest in neutron-activation analysis continues, in particular for the determination of mercury in dentists’ hair,44,45 and in general for the simultaneous determination of several elements in hair.46-48 Studies emphasising accuracy and precision are rare although for example it has been reported that preliminary precipitation of mercury as the thiocyanate prior to activation can give a very low limit of detection (ca. 0.001 ~ g ) . ~ 9 Several modifications of the basic cold vapour atomic absorption technique2>50-59 and even some spectrophotometric methodsW62 have been preferred for the determination of mercury in biological samples such as hair, probably because by these means the analyst has the analysis under his complete control within the resources of his own laboratory.Radiometric recovery checks in such methods are rare63 and results may come into question. The neutron-activation method used carefully as described here with a suitable secondary standard is straightforward safe and reliable with regard to accuracy and precision and need not be considered only the province of the specialist. We thank Dr. Susan J. Parry and Mr. G. D. Burholt of the Imperial College Research Reactor Centre for freely discuss-ing their own analytical work and for making smooth arrangements at minimum cost for our programme.We also thank Dr. L. R. Day of NELP for his interest and support and Mr. Alan Wates for invaluable help with the maintenance of equipment and delivery of radioactive samples. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. References Pritchard J. G. McMullin J. F. and Sikondari A. H. Br. Dent. J. 1982 153 333. McMullin J. F. Pritchard J. G. and Sikondari A. H., Analyst 1982 107 803 and references cited therein. Iyengar G. Y. Kollmer W. E. and Bowen H. J. M. “The Elemental Composition of Human Tissue and Body Fluids,” Verlag Chemie Weinheim 1970 p. 52 and references cited therein. Nixon G. S . and Smith H. J. Oral Ther. Pharmacol.1965,1, 512. Coleman R. F.,. Cripps F. H. Stimson A. and Scott H. D., Atom 1967 Nos. 1-3 12. Sinclair P. M. Turner P. R. and Johns R. B. J. Prosthet. Dent. 1980 43 581. Bowen H. J. M. Adv. Act. Anal. 1969,1,101 and references cited therein. Girardi F. and Guzzi G. Adv. Act. Anal. 1969 1 137 and references cited therein. Westermark T. and Sjostrand B. Adv. Act. Anal. 1972,2, 57 and references cited therein. Aliev A. I. Drynkin V. I . Leipunskaya D. I. and Kasatkin, V. A. translated by Benny B. “Handbook of Nuclear Data for Neutron Activation Analysis,” Program for Scientific Translations Jerusalem 1970 p. 19. Dzhelepov B. S . and Peker L. K. translated by Allan D. L., “Decay Schemes of Radioactive Nuclei,” Pergamon Press, London 1961 pp. 606-607.The Radiochemical Centre “The Radiochemical Manual Part 1 Physical Data,” HM Stationery Office London 1962 p. 37. Sairenji E. Moriwaki K. Shimizu M. and Noguchi K., International Conference on Mercury Hazards in Dental Practice West of Scotland Health Boards Glasgow Scotland, September 2-4 1981 Proceedings and Discussion Volume, Paper 15 ANALYST JANUARY 1986 VOL. 111 35 14. 15. 16. 17. 18. 19. 20. 21. 22, 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. Cali J. P. “Standard Reference Material No. 1571 Revised Certificate of Analysis August 31 1977,” National Bureau of Standards Gaithersburg MD. Bowen H. J. M. At. Energy Rev. 1975 13 451. Uriano G. A. “Standard Reference Material No. 1645, Revised Certificate of Analysis November 16 1978,” National Bureau of Standards Gaithersburg MD.“Certified Standard Reference Material No. 1577A,” National Bureau of Standards Gaithersburg MD. Gorsuch T. T. “The Destruction of Organic Matter,” Pergamon Press Oxford 1970 pp. 79-84. University of London Reactor Centre “Brief Guide to the Irradiation of Samples in the University of London Reactor,” Imperial College Silwood Park March 1980. “Series 7000 Ge(Li) Spectrometer Systems Instruction Man-ual,” Section 7.3 Detector Specifications Canberra Industries, Meriden CT 1973. “Series 85 Multichannel Analyser Operator’s Manual,” Can-berra Industries Meriden CT 1981 Appendix A . l . Department of the Environment “Code of Practice for Carriage of Radioactive Materials by Road,” HM Stationery Office London 1975.Madson A. A. in Crouthamel C. E. Editor “Applied Gamma-ray Spectroscopy,” Pergamon Press London 1960, pp. 365 and 366. Parry S . J. Imperial College of Science and Technology, London personal communication 1983. Parry S . J. “Evaluation of Low Density Polyethylene for Irradiation Capsules,’’ Report ULRC/RES/34 University of London Reactor Centre Imperial College Silwood Park, March 1981. Cook G. B. and Duncan J. F. “Modern Radiochemical Practice,” Clarendon Press Oxford 1952 p. 384. Slater D. N. “Gamma-Rays of Radionuclides in Order of Increasing Energy,” Butterworths London 1962 p. 77. Eichholz G. and Krzyzewski A. Can. J. Phys. 1956 34, 1167. Thiry H. Bull. SOC. R. Sci. Li&e 1957 26 No.1 29. Crouthamel G. E. “Applied Gamma-ray Spectrometry,” Pergamon Press London 1960 p. 365. Sakurai S. Tsunoda H. Terai M. Yukawa M. Tomura, K. and Suzuki-Yasumoto M. in “Nuclear Activation Tech-niques in the Life Sciences 1978,” Proceedings of an Interna-tional Symposium on Nuclear Activation Techniques in the Life Sciences held by the International Atomic Energy Agency in Vienna 22-26 May 1978 International Atomic Energy Agency Vienna 1979 pp. 573-581. Mangal P. C. and Gulati N. Proc. Nucl. Phys. Solid State Phys. Symp. 1978 21B 356; Chem. Abstr. 1977 98 104. Currie L. A. Anal. Chem. 1968 40 586. Stranshiskii A. G. Khomyakov C . K. Shakun N. A., Serykh N. V. and Sevenn N. F. Biofizika 1975,4 621. Pillay K. K. S. Thomas C. C. Jr. Sondel J. A. and Hyche, C.M. Anal. Chem. 1971 43 1419. Collier T. R. “Experience of Using the Magos Atomic Absorption Method for the Determination of Mercury in Biological Materials,” Environmental and Medical Sciences Division Atomic Energy Research Establishment Harwell, Memo AERE-M2930 Reference HL 781399 (C5) February 1978. Clements G. F. Rossi L. G. and Santaroni G. P. in “Nuclear Activation Pechniques in the Life Sciences 1978,” Proceedings of an International Symposium on Nuclear Activa-tion Techniques in the Life Sciences held by the International Atomic Energy Agency in Vienna 22-26 May 1978 Interna-tional Atomic Energy Agency Vienna 1979 pp. 527-543. Pallotti F. Bencivenga B . and Simonetti T. Sci. Total Environ. 1979 11 69. 39. 40. 41. 42. 43. 44. 45.46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. Takeuchi T. Hayashi T. Takoda J. Koyama M. Kozuka, H. Tzuji H. Kusaka Y. Ohmori S . Shinogi M. Aoki A., Katayama K. and Tomiyama T. in “Nuclear Activation Techniques in the Life Sciences 1978,” Proceedings of an International Symposium on Nuclear Activation Techniques in the Life Sciences held by the International Atomic Energy Agency in Vienna 22-26 May 1978 International Atomic Energy Agency Vienna 1979 p. 545. Imahori A. Fukushima I. Shiobara S. Tomura K., Suzuki-Yasumoto M. Yukawa M. and Terai M. in “Nuclear Activation Techniques in the Life Sciences 1978,” Proceedings of an International Symposium on Nuclear Activa-tion Techniques in the Life Sciences held by the International Atomic Energy Agency in Vienna 22-26 May 1978 Interna-tional Atomic Energy Agency Vienna 1979 pp.563-571. La Fleur P. D. J. Radioanal. Chem. 1974 19 227. Alvarez R. National Bureau of Standards Gaithersburg, MD personal communication 1984. Lau 0.-W. Hon P.-K. Cheung C.-Y. and Wong M.-C., Analyst 1984 109 1175. Yatim S. Majalah BATAN 1983,16,60; Chem. Abstr. 1983, 101 105296h. Lin S . M. Chiang C. W. Tseng C. L. and Yang M. H., Radiochem. Radioanal. Lett. 1983 56 261. Kim N. B. Report IAEA-R-2 535-F (1982) INIS Atomindex, 1983 14 Abstr. 753711; Chem. Abstr. 1983 99 83323a. Das H. A. Hoede D. Nieuwendijk B. J. T. Van der Sloot, H. A. Teunissen G. J. A. and Woittiez J. R. W. Rep. ECN-131 Netherlands Energy Foundation 1983; Chem. Abstr. 1983,99 3558211. Cortes E. Cassorla V. and Munoz L. Radiochem. Radio-nal. Lett. 1981 50 177. Biso J. N. Cohen I. M. and Resnizky S. M. Radiochem. Radioanal. Lett. 1983 58 175. Roschig M. and Wuenscher R. G. Zentralbl. Pharm. Pharmakother. Laboratoriumsdiagn. 1982 121 893. Shiwastava A. K. and Tandon S . G. Int. J. Environ. Anal. Chem. 1982 11 22. Dmitriev M. T. Grasovskii E. I. and Shashchev A. Y. Gig. Sanit. 1983,50; Chem. Abstr. 1983,99 186595. Campe A. Velghe N. and Claeys A. At. Spectrosc. 1982, 3 122. Yamamoto J. Yoshida M. and Kaneda Y. Eisei Kagaku, 1983 29 418. Baba T. Ohmiya S. Hosokawa M. and Ishibashi T., Seikatsu Eisei 1983,27,258; Chem. Abstr. 1983,100,114127k. Yanagisawa M. Suzuki H. Kitagawa K. and Tsuge S., Spectrochim. Acta Part B 1983 38 1143. Robinson J. W. and Skelly E. M. Spectrosc. Lett. 1981 14, 519. Gardner D. and Dal Pont G. Anal. Chim. Acta 1979 108, 13. Peter F. and Strunc G. Clin. Chem. (Winston-Salem NC), 1984,30 893. Chung K. C. Chungang Uitaechi 1982 7 1; Chem. Abstr., l982,97,3945a. Voronin V. M. Lamentova T. G. Nikolaeve E. C. and Rubtsov A. F. Sud.-Med. Ekspert. 1981 24 47; Chem. Abstr. 1982,97 18505f. Krylova A. N. and Rubtsov A. F. Sud.-Med. Ekspert. 1982, 25 48; Chem. Abstr. 1982 97 176299~. Lendero L. and Krivan V. Anal. Chem. 1982,54,579. 62. 63. Paper A5lI 82 Received May I7th I985 Accepted August 6th 198

ISSN:0003-2654    

DOI:10.1039/AN9861100029

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, JANUARY 1986, VOL. 111 37 Automated Determination of Fat, Crude Protein and Lactose in Ewe Milk by Infrared Spectrometry Wendy M. Harris National Institute for Research in Dairying, Shin field, Reading RG2 9AT, UK An instrumental method is described for the automated determination of fat, crude protein and lactose in ewe milk by infrared spectrometry. When ewe milks are analysed for fat, crude protein and lactose on an instrument that has been calibrated for cow milk, differences occur between the instrument readouts and absolute values as determined by chemical methods. This work identifies these errors and also looks at the different storage conditions that may be used for samples that have to be analysed over a prolonged experimental period. Keywords: Ewe milk; infrared analysis; fat; protein; lactose The use of the infrared milk analyser is well established in the dairy industry for the analysis of bovine milk. The automatic determination of fat, crude protein and lactose in 1500 individual cow milks is carried out each week at the National Institute for Research in Dairying (NIRD).The instrument is calibrated according to the manufacturer's instructions' and its performance is monitored daily by analysing sub-samples of a bulk milk. The concentrations of fat, crude protein and lactose in this bulk milk are determined by standard chemical methods.2 The infrared milk analyser measures fat at a wavelength corresponding to a C-H vibration, protein by absorption of the peptide linkages between amino acids of protein molecules and lactose by absorption of the hydroxy groups in the lactose molecule.Wide variations in the composition of individual fatty acids and amino acids are found in milks taken from different mammalian species. Consequently, an instrument calibrated for cow milk will register incorrect results if used for the analysis of ewe milk. A review of the literature revealed little information on infrared analysis on mammalian milk other than cow. Barbosa and Miranda3 analysed goat milk for fat, crude protein and lactose, both by standard chemical methods and by an infrared analyser, which was calibrated for cow milk. Marked differ- ences were found, where the instrument overestimated for fat and lactose and underestimated for crude protein concentra- tion. A research project at NIRD required the automated analysis of fat, crude protein and lactose in ewe milk.This was carried out using an infrared analyser that had been calibrated for cow milk. Ng-Kwai Hang and Hayes4 used potassium dichromate at varying concentrations to preserve cow milk and noted the effects of subsequent storage on fat, crude protein and lactose levels, using infrared spectrometry. Samples with a concentra- tion of potassium dichromate of 8 mg ml-1 of milk were stored at room temperature for up to 10 d. Fat concentrations remained constant, but marginal changes in crude protein levels were observed. This concentration of potassium dichro- mate can cause allergic reactions in laboratory staff. Sjaunjas reported that bronopol (2-bromo-2-nitropropane-1,3-diol) is used in Sweden in preference to potassium dichromate, because of the health hazard that may stem from the use of the latter.This work identifies the errors involved in analysing ewe milk on an infrared instrument calibrated for cow milk. It also determines the storage conditions that can be used for samples that have to be taken over a long experimental period. Such storage permits large batches to be analysed at one time with the minimum of work time accorded to calibration. Experimental Apparatus A Milkoscan Model 203B Infrared Milk Analyser [Foss Electric (UK) Ltd., York], fitted with a double-beam infra- red spectrophotometer and a two-stage mechanical homo- geniser, was used. This model measures fat at a wavelength of 3.48 ym, protein at 6.50 pm and lactose at 9.55 pm.Dilu-vials disposable plastic vials of 20 ml capacity (supplied by Elkay Laboratories, Basingstoke, Hampshire) and a Model 243 polarimeter (Thorn Automation Ltd., New Basford, Notting- ham), fitted with a 20 mm sample cell, were also used. Reagent Potassium dichromate ( K2Cr207). Supplied as Lactabs Mark I11 tablets from Thompson and Capper, Runcorn, Cheshire. One tablet contained 30 mg of potassium dichro- mate and 20 mg of sodium chloride. Dilution of Milk It was necessary to dilute the ewe milks with de-ionised water, so that the concentrations of fat and protein, in particular, were brought within the parameters of instrument calibration. All analyses were then carried out on diluted samples and corrections made for the differences between fat, crude protein and lactose concentrations as determined by the instrument and against those measured by chemical methods.Test Samples Morning and evening milks from Mule sheep were individu- ally composited and the pooled sample diluted (25 ml of sample + 25 ml of de-ionised water). Sub-samples of 20 ml of the diluted test milks were prepared to give two separate batches of 59 individual samples, which were stored over the experimental period of 9 weeks. Further aliquots of the diluted test milks were prepared, to give three batches of 12 individual samples. These were used to monitor any changes in composition due to the effects of storage. Storage The first batch of 59 milks was stored frozen at - 18 "C and the other was preserved with potassium dichromate (1 Lactab Mark 111 per 20 ml of milk) and stored in a refrigerator at 4 "C.The other 36 sub-samples were split into three separate batches of 12 milks each. One was analysed fresh, another38 ANALYST, JANUARY 1986, VOL. 111 Table 1. Composition of fat crude protein and lactose in diluted and undiluted ewe milks. Results are in grams of constituent per 100 g of milk Fat Crude protein Lactose Sample Undiluted Diluted Corrected Undiluted Diluted Corrected Undiluted Diluted Corrected 1 4.70 2.38 4.76 6.12 3.07 6.14 2.53 1.26 2.52 2 5.43 2.72 5.44 6.37 3.21 6.42 4.25 2.10 4.20 3 4.90 2.49 4.98 6.35 3.20 6.40 4.73 2.38 4.76 4 6.62 3.31 6.62 6.19 3.11 6.22 4.03 2.01 4.02 5 4.76 2.40 4.80 6.23 3.14 6.28 4.92 2.48 4.96 6 5.02 2.55 5.10 5.87 2.96 5.92 4.88 2.46 4.92 Over-all mean 5.24 Range .. 4.70-6.62 5.28 6.19 5.87-6.37 6.23 4.22 2.53-4.92 4.23 Table 2. Comparison of methods for the determination of lactose in diluted ewe milk. Results are in grams of constituent per 100 g of milk Polarimeter Chloramine-T Sample 1 2 4 5 6 Over-allmean . . Standard deviation . . Range . . . . Result 4.78 4.66 4.38 4.34 4.38 4.40 4.48 4.46 4.58 4.52 4.60 4.64 Mean 4.72 4.36 4.39 4.47 4.55 4.62 4.52 0.14 4.36-4.72 Result 4.66 4.66 4.36 4.22 4.40 4.44 4.36 4.36 4.50 4.46 4.60 4.58 Mean 4.66 4.29 4.42 4.36 4.48 4.59 4.47 0.14 4.29-4.66 after frozen storage and the other after storage in the refrigerator, with added preservative. These periods of storage were in line with those applied to the batches of 59 milks. Reference Samples These samples were used to compare the composition of fat, crude protein and lactose, as determined by standard chemical methods and by infrared spectrometry.Eight fresh samples were selected to give reasonable coverage of the range of compositional values as expected in the test samples. These were prepared and diluted following the same procedure used for the test milks and then analysed immediately. Analysis All the stored samples were analysed at the end of the 9-week period by the infrared analyser, which had been calibrated for cow milk. The frozen milks were rapidly thawed by immersion in a water-bath, set at 40 L- 2 "C. Occasional mixing helped to accelerate thawing and when the samples were conditioned to 40 "C, they were well mixed by inversion and presented for analysis.The preserved samples that had been stored at 4 "C were conditioned in the same manner and analysed imme- diately. British Standard methods were used for the chemical analysis.2 The Rose - Gottlieb method for the determination of fat was used in preference to the Gerber technique, The Kjeldahl procedure, employing a mercury catalyst, was accepted for the determination of the total nitrogen. The total nitrogen includes non-protein nitrogen, which was not deter- mined in this work. The nitrogen results were converted into crude protein (TN x 6.38). Anhydrous lactose was deter- mined by the chloramine-T method. Results and Discussion Composition of Fat, Crude Protein and Lactose in Diluted and Undiluted Ewe Milks It was considered necessary to ascertain that the dilution of ewe milk did not alter the accuracy of the chemical methods used.Duplicate analyses were carried out on both dilute and undiluted fresh samples for fat, crude protein and lactose. The results are given in Table 1. The over-all means for fat, crude protein and lactose on the undiluted and corrected diluted milks show only marginal differences and it was concluded that dilution of ewe milk did not alter compositional values as determined by the chemical methods used in this study. Determination of Lactose in Diluted Ewe Milk The chloramine-T method is non-specific for lactose and consequently it was decided that the method be evaluated against the polarimetric procedure given by Grimbleby.6 Duplicate analyses were carried out on diluted samples for each method and the results are given in Table 2.Results for both methods are in good agreement and it was concluded that the chloramine-T method was acceptable for the determina- tion of lactose in diluted ewe milk. Differences in Instrument Readout and Results of Chemical Analyses on Ewe Milk The results reported in Table 3 show the differences in instrument readouts and results of chemical analysis on the eight reference samples. Instrument minus chemical results for fat, crude protein and lactose all showed differences with the greatest margin being found for fat, giving a mean difference of +0.39 (standard deviation, s.d. 0.06). Crude protein showed a difference of +0.34 (s.d. 0.08) and lactose -0.32 (s.d. 0.07). The standard deviation figures for fat and crude protein compare well with the expected levels for cow milks (s.d.0.05), although it was noted that for the lactose it was higher than normally found in routine laboratory analysis. Composition of Fresh and Stored Ewe Milk To test the effect of storage on the composition of ewe milk, fresh, preserved and frozen samples were analysed by an infrared milk analyser for fat, crude protein and lactose. The results of analyses on 12 samples for each treatment are given in Table 4. The fat results for the frozen milks are slightly lower than those reported for fresh and preserved milks. Fat emulsion is sensitive to freezing and the oil can separate out on thawing, thus accounting for decreased infrared absorption. As fat destruction appears to be linked with the fat level, the dilution of the ewe milks may have reduced this effect.ANALYST, JANUARY 1986, VOL.111 39 Table 3. Differences in the composition of ewe milk as determined by chemical and instrumental* methods. Results are in grams of constituent per 100 g of milk Fat Crude protein Lactose Sample 1 2 3 4 5 6 7 8 Mean . . Standard deviation Range . . Infrared 6.10 5.42 5.46 5.28 5.66 6.20 5.24 3.90 5.41 Chemical - Chemical infrared 6.44 +0.34 5.90 +0.48 5.86 +0.40 5.56 +0.28 6.10 +0.44 6.60 +0.40 5.66 +0.42 4.26 +0.36 5.80 +0.39 0.06 4.26-6.60 * Instrument calibrated for cow milk. Infrared 4.78 4.94 4.66 4.50 4.60 4.46 4.98 4.44 4.67 Chemical 5.02 5.30 4.94 4.90 4.96 4.82 5.24 4.92 5.01 4.82-5.30 Chemical - infrared +0.24 +0.36 +0.28 +0.40 +0.36 +0.36 +0.26 +0.48 +0.34 0.08 Infrared 5.06 4.66 4.66 4.78 4.82 4.88 5.32 5.26 4.93 Chemical 4.66 4.29 4.42 4.36 4.48 4.59 5.00 5.04 4.61 4.29-5.04 Chemical - infrared -0.40 -0.37 -0.24 -0.42 -0.34 -0.29 -0.32 -0.22 -0.32 0.07 Table 4.Composition of fresh versus stored ewe milk. Results are in grams of constituent per 100 g of milk Fat Crude protein Lactose Fresh Preserved Frozen Fresh Preserved Frozen Fresh Preserved Frozen Over-all Range . . 7.20-9.52 5.34-6.54 2.96-5.58 mean* . . 8.12 8.10 8.01 5.98 6.00 6.05 4.34 4.39 4.37 * Mean values of the analysis of 12 samples for each treatment. Table 5. Composition of frozen and preserved ewe milks. Results are in grams of constituent per 100 g of milk Fat Crude Protein Lactose Preserved Frozen Preserved Frozen Preserved Frozed Over-all mean* .. 6.04 6.04 4.34 4.29 5.22 5.27 Correlation Range . . . . . . 4.82-7.38 3.62-5.28 4.52-5.70 coefficient . . . . 0.964 0.998 0.993 * Mean of analysis of 59 samples. Composition of Frozen and Preserved Ewe Milk Potassium dichromate was used at a reduced level of 1.5 mg ml-1 of milk, compared with 8 mg ml-1 as used by previous workers.4 This was carried out in order to minimise the health hazard that may stem from the use of higher concentrations of potassium dichromate. The fat , crude protein and lactose concentrations in frozen and preserved ewe milks are given in Table 5. The results show that there is no difference in the over-all mean for fat and only marginal differences between those for crude protein and lactose. Correlation coefficients give a slightly lower estimate for fat (0.964), compared with crude protein and lactose (0.998 and 0.993).This may be due to the effects of freezing on the fat emulsion. Conclusion Diluted ewe milk may be routinely analysed for fat, crude protein and lactose, using an infrared milk analyser, provided adjustments are made for the differences in composition that occur when using an instrument calibrated for cow milk. The automatic infrared milk analyser at NIRD is used almost exclusively for bovine milk and therefore it was considered impractical to alter the calibration to meet an infrequent demand for ewe milk. Project leaders were given results for diluted milks and advised of the adjustments (plus their relative standard deviations) to make to the fat, crude protein and lactose figures to give more precise data. For continuous analysis of ewe milk, it may be more accurate to re-align the instrument calibration, to give the absolute levels of fat, crude protein and lactose. Infrared analysis on ewe milk can be carried out on diluted samples that have been stored over a period of weeks, either by preserving with potassium dichro- mate or by frozen storage. The author thanks Mr. E. Florence, NIRD, for helpful discussions during the course of this work. References 1. 2. “Milkoscan 203B, Manual of Operation,” A / S N. Foss Electric, HillerBd, Denmark, 1984. “Methods for the Chemical Analysis of Liquid Milk and Cream,” BS 1741 : 1963, British Standards Institution, London. 3. Barbosa, M., and Miranda, R., “Addendum to Special Publication No. 49. Challenges to Contemporary Dairy Analy- tical Techniques,” Royal Society of Chemistry, London, 1984. Ng-Kwai Hang, K. F., and Hayes, J. F., J. Dairy Sci., 1982,65, 1895. Sjaunja, L. A., Actu Agric. Scand., 1984, 34, 273. Grimbleby, F H., J . Dairy Res., 1956, 23, 229. 4. 5. 6. Paper A51122 Received April lst, 1985 Accepted August 14th, 1985

ISSN:0003-2654    

DOI:10.1039/AN9861100037

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, JANUARY 1986, VOL. 111 41 Use of Orthogonal Polynomials for Unequal Intervals to Eliminate Interference in Spectrophotometric Analysis. Simultaneous Determination of Ephedrine Hydrochloride and Diphenhydramine Hydrochloride in Two-component Mixtures M. A. Korany,” Mona Bedair and F. A. El-Yazbi Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, University of Alexandria, Alexandria, Egypt A general method is outlined for the use of orthogonal polynomials for unequal intervals to eliminate interferences in two-component spectrophotometric analysis. The method is particularly useful when ( i ) the optimum conditions of Vierordt’s method are not fulfilled and (ii) the two absorption spectra have considerable overlap. The method is illustrated by the determination of ephedrine hydrochloride and diphenhydramine hydrochloride in binary mixtures.The results obtained are encouraging and suggest that the method can be widely applied to similar problems. Keywords: Ephedrine hydrochloride determination; diphenh ydramine hydrochloride determination; orthogonal polynomials for unequal intervals; spectrophotometry A mixture of two absorbing compounds can be analysed spectrophotometrically without prior separation by the clas- sical Vierordt two-wavelength method described by Heil- meyer,l which involves the solution of a set of two linear equations. Glenn2 formulated Vierordt’s method in terms of absorbance ratios (modified Vierordt’s method), which are independent of concentration. Pernarowski et al. 3 and Cho and Pernarowski4 used absorbance ratios for the analysis of binary mixtures and derived an equation similar to Glenn’s equation.5 However, in application of these methods,l-4 the presence of spectral interferences and/or spectral overlapping such as may originate from batch-to-batch differences between the “sample” and “reference standard” or from the pharmaceutical formulation matrix, would certainly lead to erroneous results.6 Other methods aiming at solving this problem have been tried, including the use of Glenn’s method of orthogonal polynomials for equally spaced intervals,6,7 pH-induced dif- ferential spectrophotometry,s orthogonal functions for equally spaced intervals with the least-squares method,g the Apj method,lo dual-wavelength spectrometry,ll derivative spectrometryl2J3 and the use of a Vidicon spectrometer.14 Despite the usefulness of these methods&l4 in solving certain problems, however, under certain conditions where the two analytes show serious overlap and heavy spectral interferences, their applicability may be limited. In this connection, a new approach was developed in this work to the use of orthogonal polynomials for unequal intervals. The basis of harmonic aqalysis is that a given function can be expanded in terms of an orthogonal function for unequal intervals. 1 5 ~ 6 Thus, wheref(h) is the absorbance at a wavelength h that belongs to a set of rz + 1 unequally spaced wavelengths, KO, K 1 , K2, K3, K4, . . ., K, are the polynomials corresponding to constant, linear, quadratic, cubic, quartic, etc., and ko, kl, k2, k3, k4, .. ., etc., are their respective coefficients. In view of the orthogonality of the polynomials, any coefficient, k,, can be calculated from a set of absorbances by the equation f(h) = koKo + klK1 + k2K2 + k3K3 + k4K4. . . k,K, n n kj= C f ( h ) i K , i / C Kj? i = O i = O ~ ~~~ * To whom correspondence should be addressed. The denominator of this equation is the sum of the squared individual values of Kji and will be denoted hereafter by Dj. The coefficients, kj, are proportional to f ( h ) , that is kj = ajC,, where aj (= kjll:,) is a constant analogous to absorptivity and C, is the concentration of the absorbing compound, a. Application of the Proposed Method In the application of orthogonal polynomials for equal intervals to spectrophotometric analysis,6J7 one can be faced with the problem that the polynomial integers (polynomial fundamental shapes) ,6918 especially higher order polynomials, P3, Pq, .. . , etc., may not exactly fit with the fine structure of the absorption curve. On the other hand, this means that the optimum value of higher order coefficients (p3, p 4 , . . . , etc.) obtained during the convolution process’s does not reflect exactly the fine structure of the absorption curves (e.g., for benzenoid compounds). In this connection, the unequal interval wavelengths were selected according to the shape of a specified segment on the absorption curve. Thus, for absorp- tion curves in 0.1 N sulphuric acid of ephedrine hydrochloride and diphenhydramine hydrochloride (Fig. 1) , the polynomials can be be calculated according to the selected wavelength intervals as follows.For Ephedrine Hydrochloride The segment abcde (Fig. 1) shows that a K4 polynomial (quartic)l7 can fit the absorption curve. Therefore, the wavelengths 250,,,., 252,in., 256,,,, , 260,i,, and 262maX. nm were selected. These wavelengths were spaced by the intervals 0, 2, 4, 4 and 2 nm (Table 1). According to the method of Grandage,l5J6 the polynomials K1, K2, K3 and K4 can be calculated as presented in Table 1. For Diphenhydramine Hydrochloride The segment fghkl (Fig. 1) shows that a K3 polynomial (cubic)17 can fit the absorption curve. Therefore, the wavelengths 236, 241, 251, 256 and 261 nm were selected. These wavelengths were spaced by the intervals 0,5,10,5 and 5 nm.These wavelength intervals were selected as a com- promise between setting a polynomial that reflects exactly the shape of the absorption segment and obtaining a polynomial with integral numbers. According to the method of Gran-42 ANALYST, JANUARY 1986, VOL. 111 1 .O 0.8 : d 0.6 0.4 0.2 0 15 10 5 9 0 -5 -10 -15 I I I I 4 I I 240 250 260 270 280 h,/n m 0 70 20 22 30 - 40 Fig. 1. Absorption gra hs of A, 0.05% m/V ephedrine hydro- chloride and B, 0.04% rnk diphenhydramine hydrochloride in 0.1 N sulphuric acid and the corresponding k4 and kr3 convoluted curves derived from them using five-point orthogonal polynomials for unequal intervals Table 1. Calculation of the polynomials, K j , and the corresponding divisors, Dj, for the determination of ephedrine hydrochloride in two-component mixtures with diphenhydramine hydrochloride Wavelength* i set(I)/nm 0 250 1 252 2 256 3 260 4 262 Di Interval/ Xi nm level Xi/2 K 1 K2 K3 K4 0 0 0 -3 +19 -6 +4 2 2 1 -2 -6 +9 -9 4 6 3 0 -26 0 +1O 4 10 5 +2 -6 -9 -9 2 12 6 +3 +19 +6 +4 26 1470 230 294 Table 2.Calculation of the polynomials, KIj, and the corresponding divisors, DIj, for the determination of diphenhydramine hydro- chloride in two-component mixtures with ephedrine hydrochloride Wavelength * i set(II)/nm 0 236 1 241 2 25 1 3 256 4 26 1 DIj * hmII = 248.5 nm. Interval/ X, nm level Xi/5 K'] Krz 0 0 0 -13 +55 -33 5 1 -8 -29 +57 5 10 15 3 +2 -68 -12 5 20 4 +7 -23 -39 5 25 5 +12 +65 +27 430 13244 6732 ~~ Table 3. Reproducibility of k41Fm* and kI3 :'&* for ephedrine hydrochloride and diphenhydramine hydrochloride Diphenhydramine Ephedrine hydrochloride hydrochloride k4 :"bO, k'3 :"&, k4 ;O&, kI3 :"bo, Experiment x 10-3 x 10-3 x 10-3 X No.(&I) (%I) (PI) (PI11 1 95.714 -19.906 11.463 -106.683 2 94.728 -19.865 11.497 -108.130 3 94.524 -19.764 10.850 -105.796 4 95.986 -19.703 11.598 -106.283 5 95.884 -19.627 11.531 -106.714 6 95.000 -19.600 11.088 -107.130 Mean 95.306 -19.732 11.338 -106.789 Standard deviation 0.633 0.133 0.298 0.80 Coefficient of variation, YO 0.66 0.67 2.63 0.75 * Determined over the concentration ranges 32-80 mg per 100 ml for,ephedrine hydrochloride and 16-32 mg per 100 ml for diphenhydr- amine hydrochloride. dage,15J6 the polynomials Krl, Kf2 and K'3 can be calculated as presented in Table 2. The polynomials given in Tables 1 and 2 fulfil the following requirements : 4 A ( i ) 2 Kii = 0 and = 0 i = O i = O A A Y (ii) K,,i K , i = 0 and K f j , i K r u , i = 0 i = O i = O where j f u and 4 4 (iii) Kj,? = Dj and Kf6? = D r j i = O i = O Calculation of the CoeMicients k4 and k'3 The coefficients k4 and k'3 are given by the following equations: Calculation of Concentration The concentration (g%) of ephedrine hydrochloride ( c e p h , ) and diphenhydramine hydrochloride (Cdiph.) in the mixture are then evaluated by solving the following pair of simul- taneous equations: * = (Ai + &)/2 = 256 nm, where m, i and fare mean, initial and final wavelengths, respectively.ANALYST, JANUARY 1986, VOL.113 43 ~~~ Table 4. Spectrophotometric determination of ephedrine hydroch- loride (EH) and diphenhydramine hydrochloride (DH) in synthetic mixtures using the proposed and modified Vierordt methods Recovery, YO ~~ ~ Amount added/ EH DH mg per 100 ml Experiment Modified Modified No.EH DH Proposed Vierordt Proposed Vierordt 1 24 24 101.1 101.4 101.1 101.9 2 56 16 101.7 98.4 101.0 105.1 3 32 40 99.0 100.7 99.9 100.8 4 64 12 101.4 99.2 101.4 107.3 5 48 20 100.3 97.8 100.9 105.4 6 40 32 100.8 100.9 99.2 100.6 Mean 100.7 99.7 100.6 103.5 Standard deviation 1.0 1.5 0.8 2.8 Table 5. Spectrophotometric determination of ephedrine hydro- chloride and diphenhydramine hydrochloride in nasal drops using the proposed and modified Vierordt methods Recovery, % Experiment No. 1 2 3 4 5 6 Mean Standard deviation Ephedrine hydrochloride Diphenhydramine hydrochloride Proposed 99.6 101 .o 99.4 101.7 101.2 100.9 100.6 0.9 Modified Vierordt 96.5 97.3 96.8 96.7 95.8 94.9 96.3 0.8 Proposed 99.8 100.4 98.9 101.9 100.0 100.4 100.2 1 .o ~ Modified Vierordt 107.7 110.2 106.3 106.6 108.5 106.8 107.6 1.5 where subscripts I and I1 represent the two wavelength sets and (k4)I and (k’3)II are the coefficients of the mixture calculated from the absorbances measured over the two wavelen th sets I and 11, respectively.a1 and a11 are the k4 i:m and k’3ftm values, respectively, for reference ephedrine hydrochloride, and PI and pII are the k4 ::m and kt3 i:m values, respectively, for reference diphenhydramine hydrochloride. Reproducibility of a and p Separate determinations of a and p were made for different concentrations of reference ephedrine hydrochloride and diphenhydramine hydrochloride in 0.1 N sulphuric acid.The results have a relative standard deviation of less than 1% for the principal kji:;, or ktjiTm, viz., aI and pII, indicating reasonable reproducibility (Table 3). The mean values of aI versus PI on the one hand and pII versus aII on the other indicate a good separation between the two convoluted curves1* (Fig. 1) at the selected wavelength sets ( h , ~ and AmII). Experimental Apparatus A Perkin-Elmer Model 550s UV - visible spectrophotometer was used. Reagents Reference drug solutions. Dissolve 25 mg of ephedrine hydrochloride or 20 mg of diphenhydramine hydrochloride in 50 ml of 0.1 N sulphuric acid. Synthetic mixtures. Dissovle 400 mg of ephedrine hydro- chloride and 200 mg of diphenhydramine hydrochloride in 100 ml of 0.1 N sulphuric acid.In six 50-ml calibrated flasks, prepare the following dilutions: FlaskNo. . . . . . . 1 2 3 4 5 6 Added ephedrine hydrochloride/ml . . 3 4 5 6 7 8 Added diphenhydramine hydrochloride/ml . . 6 10 8 5 4 3 Make up each solution to 50 ml with 0.1 N sulphuric acid. Nasal drops. Contained 1000 mg of ephedrine hydro- chloride, 100 mg of diphenhydramine hydrochloride, 500 mg of chlorbutol and 50 mg of menthol per 100 ml of water. Diluted nasal drops solution. Pipette 5 ml of the nasal drops solution into a calibrated flask and dilute to 100 ml with 0.1 N sulphuric acid. Spectrophotometric Analysis Measure the absorbances of 1-cm path lengths of the prepared synthetic mixture solution, dilute nasal drops solution and reference standard solutions over the wavelength range 236-262 nm at 1-nm intervals using 0.1 N sulphuric acid as a blank.Results and Discussion Synthetic mixtures of ephedrine hydrochloride and diphen- hydramine hydrochloride and nasal drops containing both drugs prepared as described above were assayed for both components using the proposed orthogonal polynomials for the unequal intervals method and the modified Vierordt method2 (h, = 262 nm and h2 = 236 nm). The results obtained are shown in Tables 4 and 5. Using the proposed method, the mean recoveries for the determination of ephedrine hydro- chloride were 100.7 + 1.0 and 100.6 f 0.9% and for diphenhydramine 100.6 k 0.8 and 100.2 k 1.0% in the synthetic mixture ,and nasal drops, respectively.The assumptions that, for a good Vierordt method, ( i ) the absorption curves of the two components are sufficiently different, (ii) a wavelength is available at which the com- ponent in question contributes a reasonable proportion of the mixture’s total absorption and (iii) the amount of the irrelevant absorption is small , may explain the less satisfactory results of the Vierordt method. In this instance, the first two assumptions are not fulfilled, as indicated in Fig. 1. Also, the difference in the A itm values for the two components at the chosen analytical wavelengths is small (A i:,, at 262 nm is 6.8 and 13.5 for ephedrine hydrochloride and diphenhydramine hydrochloride, respectively, and at 236 nm 2.0 and 28.9, respectively). In the analysis of nasal drops, the presence of menthol and chlorbutol will cause interferences (irrelevant absorption) when applying the modified Vierordt method.On the other hand, the results obtained using the orthogonal polynomials for the unequal intervals method will not be affected by any interferences contributing to coefficients other than those involved in the assay coefficients. Thus, in the above assay the cubic (K’3) and quartic (K4) components (here “component” is used in the mathematical sense) are not eliminated, which means in particular that constant , linear and quadratic components of the irrelevant absorption are all rejected. Nevertheless, in common, irrelevant absorption contributes much more to the constant and linear components of the total absorption than any others.6 Errors in the proposed method can be attributed to ( i ) wavelength setting errors, which affect absorbances measured on steep slopes in the absorption curves, and (ii) over-all shifts in the wavelength calibration.However, these errors can be decreased by selecting analytical wavelengths as near as possible to the maximum and minimum absorption (as with ephedrine hydrochloride) and by measuring the standard and44 ANALYST, JANUARY 1986, VOL. 111 sample solutions side by side in a constant-temperature laboratory. 19 References 1. Heilmeyer, H., “Spectrophotometry in Medicine,” Adam Hilger, London, 1943, p. 7. 2. Glenn, A. L., J . Pharm. Pharrnacol., 1960, 12, 595. 3. Pernarowski, M., Kneval, A. M., and Christian, J . E., J. Pharm. Sci., 1961, 50, 943. 4. Cho, M. J., and Pernarowiski, M., J. Pharrn. Sci., 1970, 59, 1333. 5. Wahbi, A. M., Abdine, H., Korany, M. A., and El-Yazbi, F. A., J . Pharm. Sci., 1978, 67, 140. 6. Glenn, A. L., J . Pharm. Pharmacol., 1963, 15 (Suppl.), 123T. 7. Abdine, H. Wahbi, M., and Korany, M. A., J . Pharm. Pharmacol., 1972, 24, 522. 8. Wahbi, A. M., and Faraghaly, A. M., J. Pharrn. Pharmacol., 1970, 22, 848. 9. Wahbi, A. M., Ebel, S . , and Steffens, U., Fresenius 2. Anal. Chem., 1975, 273, 183. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. Korany, M. A., and Haller, R., J. Assoc. Off. Anal. Chern., 1982, 65, 144. Shibata, S . , Furukawa, M., and Goto, K., Anal. Chim. Acta, 1971, 53, 369. Fell. A. F.. Proc. Anal. Div. Chem. Soc., 1978. 15. 260. Korany, M. A., Wahbi, A. M., Elsayad, M. A., and Mandour, S . , Anal. Lett., 1984, 17(B12), 1373. McDowell, A. E., and Pardue, H. L., J . Pharm. Sci., 1978,67, 822. Grandage, A., Biometrics, 1958, 14, 287. Peng, K. C., “The Design and Analysis of Scientific Experi- ments,” Addison-Wesley, London, 1967, pp. 57-66. Abdine, H., Wahbi, A. M., and Korany, M. A., J. Pharm. Pharmacol., 1971, 23, 444. Agwu, I., and Glenn, A. L., J. Pharm. Pharrnacol., 1967, 19, (Suppl.), 76s. Bedair, M., Korany, M. A . , and Abdel-Hamid, M. E., Analyst, 1984, 109, 1423. Paper A5 f 128 Received April 4th, 1985 Accepted July 22nd, I985

ISSN:0003-2654    

DOI:10.1039/AN9861100041

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, JANUARY 1986, VOL. 111 45 Spectrophotometric Determination of Some Anti-inflammatory Agents Using A/-Bromosuccinimide Sonia T. Hassib, Hany M. Safwat and Ramzeia 1. El-Bagry Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Cairo University, Cairo, Egypt Four non-steroidal anti-inflammatory agents have been determined titrimetrically using N- b ro m 0s u cc i n i m id e . F I u f e n a m i c a n d m ef e n a m i c acids react q u a n t i t a t ive I y with N- b ro m o s u cc i n i m id e i n a n acidic medium whereas allopurinol and indomethacin can be determined with reproducible results in an aqueous pyridine solution. The method has been successfully applied to the determination of flufenamic acid, mefenamic acid and allopurinol in their pharmaceutical formulations.In addition, a sensitive spectropho- tometric method, based on the same reaction, has been used to determine selectively indomethacin in admixture with its hydrolysis products, and for the determination of indomethacin in capsules. Keywords: Anti-inflammatory agents determination; N -bromosuccinimide; spectrophotometry; titrimetry; pharmaceutical formulations N-Phenylanthranilic acid derivatives, namely flufenamic acid (I) and mefenamic acid (11), have been determined in blood and urine using diverse chromatographic techniques. 1-4 The native fluorescence shown by these anti-inflammatory agents I II CHZCOOH OH I @CO IV H c‘r Ill in organic solvents has been used for their detection and determination .5,6 Cyclisation reactions of N-phenylanthranilic acid derivatives using formaldehyde or sulphuric acid to give benzoxazines or a mixture of acridones, respectively, have been found to be useful for sensitive fluorimetric determina- ti0ns.~.8 A spectrophotometric method for the determination of flufenamic acid, based on ion-pair formation, has also been adopted .9 Indomethacin (111) has been determined by a number of techniques: spectrophotometric,l0-’2 titrimetric,l3J4 polaro- graphic15 and chromatographic.16>17 Allopurinol (IV), which is used in the treatment of hyperuricaemia associated with gout, has been determined by quantitative chromatographic methods,l”2* in addition to electrochemical oxidation, used for its determination in the presence of uric acid.23 The British Pharmacopoeia describes a non-aqueous titra- tion for the determination of allopurinol,24 and a spectro- photometric assay following ion-exchange separation has been reported for its determination in the presence of its decompo- sition products.25 In this paper, an accurate titrimetric determination of the four mentioned anti-inflamatory agents using N-bromosucci- nimide is presented.The reaction conditions have been optimised and the stoicheiometries of the reactions ascer- tained. The method can be applied to the analysis of their pharmaceutical preparations, except indomethacin capsules, for which the titrimetric procedure cannot differentiate between indomethacin and its alkaline hydrolysis products and in this instance a spectrophotometric assay with N-bromo- succinimide was used. This method proved successful for determining indomethacin in capsules and in samples pre- pared by mixing intact and hydrolysed indomethacin.Experimental Materials and Reagents All chemicals and reagents used were of analytical-reagent or pharmaceutical grade and distilled water was used through- out. Solvents were of spectroscopic grade. Flufenamic and mefenamic acids. Flufenamic acid, Arlef capsules of Lot No. 5000, nominally containing 100 mg of flufenamic acid, mefenamic acid and Ponstan capsules of Lot No. 82545, nominally containing 250 mg of mefenamic acid, were supplied by the Nile Co. for Pharmaceutical Industries, Cairo (under licence from Parke-Davis, Detroit, MI). Zndomethacin BP. Indomethacin BP was supplied by John Bell & Croyden, London. Indocid capsules of Lot No.822667, nominally containing 25 mg of indomethacin, were supplied by Kahira Pharmaceuticals & Chemical Industries Co., Cairo (under licence from Merck Sharp & Dohme, Rahway, NJ). Allopurinol BP. Allopurinol BP and Zyloric tablets of Lot No. 14099, nominally containing 100 mg of allopurinol, were supplied by Burroughs Wellcome & Co., London. Glacial acetic acid. N- Bromosuccinimide solutions, 0.05 and 0.005 M . These were prepared by dissolving 4.45 and 445 mg, respectively, of N-bromosuccinimide (BDH Chemicals, Poole) in 500 ml of water. Sodium thiosulphate solution, 0.01 N. This solution was standardised by the dichromate method. Potassium iodide solution, 10% mlV. Apparatus A Shimadzu Graphtcord UV 240 UV - visible spectropho- tometer was used for recording the UV spectra.46 ANALYST, JANUARY 1986, VOL.111 Methods Determintion of flufenamic acid Flufenamic acid (50 mg) was placed in a 250-ml calibrated flask and dissolved in 150 ml of acetic acid, then the solution was diluted to volume with water. A volume containing 0.92-4 mg of flufenamic acid was transferred into a stoppered conical flask. Acetic acid was added, if necessary, in such amounts that the final volume before addition of N-bromosuccinimide (NBS) was 10 ml. The solution was allowed to react with 40 ml of 0.005 M NBS solution for 15 min in the dark (temperature = 25 k 2 "C). Potassium iodide solution (10 ml) was added, and the solution was titrated with 0.01 N sodium thiosulphate solution to the starch end-point. A blank determination was carried out.For the determination of flufenamic acid in capsules, the ,contents of 20 Arlef capsules were mixed thoroughly and an accurately weighed portion of the mixed powder , nominally containing 25 mg of flufenamic acid, was extracted with diethyl ether (3 X 10 ml). The residue remaining after the evaporation of diethyl ether was dissolved in acetic acid and treated as described for the determination of flufenamic acid. Determination of mefenamic acid A solution of mefenamic acid in acetic acid (0.02% mlV) was prepared. A volume of this solution containing 1.5-3.5 mg of mefenamic acid was allowed to react with 40 ml of 0.005 M NBS solution for 10 rnin in the dark (temperature = 25 k 2 "C). The procedure was followed as described for the determina- tion of flufenamic acid.For the determination of mefenamic acid in capsules the contents of 20 Ponstan capsules were mixed thoroughly and an accurately weighed portion of the mixed powder, nominally containing 25 mg of mefenamic acid, was extracted with diethyl ether (3 x 10 ml). The residue remaining after evaporation of diethyl ether was dissolved in acetic acid and the procedure was continued as described for the determination of mefenamic acid. Determination of indomethacin ( a ) Titrimetric procedure. Indomethacin (100 mg) was placed in a 250-ml calibrated flask and dissolved in 10 ml of pyridine. The solution was diluted to volume with water. An aliquot containing 5-10 mg of indomethacin was allowed to react with 40 ml of 0.005 M NBS solution for 45 rnin in the dark (temperature = 25 k 2 "C).Acetic acid (10 ml) followed by )potassium iodide solution (10 ml) were then added. The solution was titrated with 0.01 N sodium thiosulphate solution to the starch end-point. A blank determination was carried out. For the determination of indomethacin in capsules, the contents of 20 Indocid capsules were mixed thoroughly and an accurately weighed portion of the powdered capsules, nomi- nally containing 50 mg of indomethacin, was extracted with chloroform (3 x 10 ml and 1 x 5 ml). The residue left after the chloroform had been evaporated was dissolved in 10 ml of pyridine and the procedure was continued as described for the determination of indomethacin. (6) Spectrophotometric procedure. Indomethacin (25-50 mg) was dissolved in a mixture of pyridine and water (5 ml of 1 + 4 V/V); next, 40 ml of 0.05 M NBS solution were added and the reaction was allowed to proceed in the dark for 45 rnin (temperature = 25 k 2 "C).The precipitate formed was filtered and washed with water (5 x 10 ml). After decanting the water the precipitate was dissolved in hot ethanol (50 ml), cooled and transferred into a 100-ml calibrated flask. It was then diluted to the mark with ethanol. An aliquot equivalent to 0.02-0.016 mg of indomethacin was placed in a 10-ml calibrated flask and completed to volume with ethanol. The absorbance of the solution was measured at 227 nm. The indomethacin content was determined from a calibration graph prepared according to the procedure described above. For the determination of indomethacin in Indocid capsules, the contents of 20 capsules were mixed thoroughly and an accurately weighed portion of the mixed powder, nominally containing 25 mg of indomethacin, was extracted with chloroform (3 X 10 ml and 1 x 5 ml).The residue remaining after evaporation of the chloroform was dissolved in 5 ml of a mixture of pyridine and water (1 + 4) and the solution was allowed to react with 40 ml of 0.05 M NBS solution for 45 min in the dark (temperature = 25 k 2 "C). The procedure was continued as described for the spectrophotometric determina- tion of indomethacin. Determination of allopurinol Allopurinol (100 mg) was placed in a 250-ml calibrated flask. Pyridine (10 ml) was added followed by the dropwise addition of water to complete solubility.The solution was then diluted to volume with water. An aliquot containing 2-8 mg of allopurinol was reacted with 40 ml of 0.005 M NBS solution for 60 min (temperature = 25 k 2 "C). Acetic acid (10 ml) and potassium iodide solution (10 ml) were added and the solution was titrated with 0.01 N sodium thiosulphate solution to the starch end-point. A blank determination was also carried out. For the determination of allopurinol in tablets, 20 Zyloric tablets were mixed thoroughly and an accurately weighed portion of the powdered tablets, containing 50 mg of allopurinol, was extracted with a mixture of pyridine and water (1 + 4) (5 x 10 ml). The extract was diluted with water to 250 ml in a calibrated flask and treated as described for the determination of allopurinol. Results and Discussion An accurate titrimetric method for the determination of flufenamic acid, mefenamic acid and allopurinol using NBS has been developed. A study of the optimum conditions has been carried out and the stoicheiometry of the reaction of each drug with NBS has been ascertained.The conditions opti- mised were the choice of medium (for a quantitative reaction), the time required for the reaction to be completed and the amount of reagent. Under optimum conditions each of the N-phenylanthranilic acid derivatives studied was found to consume 4 mol of NBS per mole of acid in the presence of acetic acid. For flufenamic acid constant results were obtained within 10-30 min. Mefenamic acid consumed 4 mol of NBS per mole within 10-15 rnin but during the following 30 rnin a slower consumption of NBS was recorded (Fig.1). The amount of reagent used for both acids was at least three times more than the amount of NBS consumed in the reaction. The method was successfully applied to the determination of flufenamic and mefenamic acids in Arlef and Ponstan cap- sules, respectively. Both acids were extracted from their capsules using diethyl ether, which eliminates any interference from the capsules' contents other than the active ingredient. 8 1 I Timeimi n Fig. 1. and (B) mefenamic acid using NBS Effect of time on the determination of (A) flufenamic acidANALYST, JANUARY 1986, VOL. 111 47 Table 1. Titrimetric determination of anti-inflammatory agents Method of Anti-inflammatory agent determination* Flufenamic acid .. . . . . . . . . 1 Flufenamic acid . . . . . . . . . . 2 Added authentic . . . . . . . . 1 Flufenamic acid . . . . . . . . . . 4 Mefenamic acid . . . . . . . . . . 1 Added authentic . . . . . . . . 1 Mefenamic acid . . . . . . . . . . 4 Indome t hacin . . . . . . . . . . 3 Added authentic . . . . . . . . 3 Indomethacin . . . . . . . . . . 4 Arlef capsules . . . . . . . . . . 1 Ponstan capsules . . . . . . . . 1 Indocid capsules . . . , . . . . . . 3 Allopurinol . . . . . . . . . . 3 Zyloric tablets . . . . . . . . . . 3 Allopurinol . . . . . . . . . . 4 Added authentic . . . . . . . . 3 No. of experiments 9 9 10 10 5 10 9 9 5 10 14 14 4 12 8 8 6 Mass usedlmg 0.92-4.00 1.00-4.00 1.00-2.40 0.60-2.40 1 SO-3 S O 3 1.25-1 87.5 1.25-2.00 1.25-2.00 30.00-150.0 5.00-10.00 3.00-5 .OO 3.00-5.00 150.00-240 .OO 2.00-8.00 1.00-4.00 0.80-3.20 20.00-120.00 Recovery, 70 97.34-101.78 97.18-103.03 100.09-1 05.36 96.58-102.40 98.70-99.58 97.39-101.81 96.38-100.40 96.38-99.40 97.33-101.43 96.28-101.40 97.10-101.27 94.55-98.06 96.63-100.37 99.17-100.99 97.72-101.40 97.85-100.65 96.3 1-101.71 Mean recovery 99.62 f 1.18 100.40 f 2.14 103.54 f 1.38 99.09 f 1.23 99.20 f 0.39 99.77 f 0.86 97.92 f 0.90 98.25 f 0.74 100.00 f 0.80 92.12 f 1.00 100.09 _+ 0.71 99.39 f 0.95 99.76 f 2.07 99.10 f 0.81 96.99 f 0.99 99.85 f 1.44 98.54 f 1.31 ( P = 0.05), % Moles of re agent consumed per mole of anti- inflammatory agent 4 2 4 1 4 4 1 2 2 * Methods: 1, N-bromosuccinimide in an acid medium; 2, N-bromosuccinimide in hydrogen carbonate solution; 3, N-bromosuccinimide in pyridine solution; and 4, BP method.24 15 30 45 60 75 90 Tirnelmin Effect of time on the determination of (A) indomethacin and Fi .2.(B? allopurinol using NBS The results obtained for the determination of these two acids in the pure form and in capsules are summarised in Table 1, which also shows the results obtained by applying the BP method. The NBS method was found to be more sensitive than the BP method. It is noteworthy that 1 mol of flufenamic acid consumed 2 mol of NBS in the presence of potassium hydrogen carbonate; however, this determination was not as accurate as when carried out in the presence of acetic acid. A quantitative determination of allopurinol was achieved when the reaction with NBS was conducted in an aqueous solution containing a small amount of pyridine. The time required for a constant consumption of NBS was found to be within 45-90 min (Fig.2). Under optimum conditions 1 mol of allopurinol consumed 1 mol of NBS. The solubility of allopurinol in water was enhanced by pyridine, although it is, itself, almost insoluble in water. Allopurinol was extracted from Zyloric tablets using a 20% V/V aqueous solution of pyridine. (An aqueous solution was used because of the poor solubility of allopurinol in organic solvents.) TLC of the extract using methanol - chloroform (1 + 9) revealed that only allopurinol was extracted from the tablets when a 20% V/V aqueous solution of pyridine was used, The results obtained for the determination of allopurinol and Zyloric tablets are given in Table 1 and show good agreement with those obtained by the BP method.The reaction of NBS with indomethacin was studied by a titrimetric determination using a pure sample of indo- methacin. The time required for a stable consumption of NBS was between 45 and 60 min where 2 mol of NBS were Table 2. Spectrophotometric determination of indomethacin (25-50 mg) in the presence of its alkaline hydrolysis products (6 mg) using N-bromosuccinimide Concentration of indomethacin used/ mg per 10 ml 0.040 0.048 0.072 0.080 0.096 0.120 0.140 Amount of indomethacin Absorbance recoveredl Recovery, 0.273 0.0405 101.25 0.307 0.0470 97.92 0.442 0.0710 98.61 0.500 0.0805 100.63 0.578 0.0950 98.96 0.703 0.1170 97.50 0.827 0.138 98.57 Mean 99.06 Standard deviation 1.38 Standard error 0.52 Confidence limit ( P 0.05) f1.27 at 227 nm mg per 10 ml Y O consumed per mole of indomethacin.The following 15 min showed an increase in consumption to over 2 mol (Fig. 2). Good recoveries were obtained with amounts varying from 2 to 10 mg (Table 1). The titrimetric determination of indomethacin with NBS could not be applied to the determination of indomethacin when this was in admixture with its hydrolysis products, because the latter have been found to consume at least 9 mol of NBS per mole of hydrolysed indomethacin. This consump- tion is thought to be due to the indole component as, in our experience, p-chlorobenzoic acid does not consume any NBS under the applied conditions. However, it was observed that indomethacin reacted with NBS to give a pale yellow precipitate in contrast to its hydrolysis products, which did not give any precipitate under the same conditions.Making use of this behaviour led to a method that proved capable of determining the content of the intact drug in samples prepared by mixing intact and hydro- lysed indomethacin. TLC of the precipitate (after filtration and washing with water) showed an absence of indomethacin, and proved that the precipitate is a single component with an RF of 0.71 in chloroform.48 ANALYST, JANUARY 1986, VOL. 111 Table 3. Spectrophotometric determination of indomethacin in capsules (Indocid) using N-bromosuccinimide Amount of Amount of Amount of as labelled added to found in indomethacin in capsules/ capsules/ capsules/ recovered/ Recovery mg per 10 ml mg per 10 ml mg per 10 ml mg per 10 ml in capsules, YO indomethacin indomethacin indomethacin Amount of 0.020 0.030 0.040 0.050 0.060 0.032 0.048 0.064 0.080 0.020 0.030 0.040 0.050 0.060 0.016 0.024 0.032 0.040 0.0200 0.0195 0.0300 0,0300 0.3800 0.0400 0.0485 0.0500 0.0585 0.0585 0.0310 0.0160 0.0475 0.0235 0.0620 0.0320 0.0780 0.0395 Mean Standard deviation Standard error Confidence limit (P = 0.05) 100.00 100.00 95.00 97.00 97.50 96.88 98.96 96.88 97.50 97.75 1.63 0.54 1.26 Recovery of added authentic, % 97.50 100.00 100.00 100.00 97.50 100.00 97.92 100.00 98.75 99.07 1.16 0.39 0.89 Its absorption spectrum exhibited a maximum at 227 nm and a plateau around 367 nm.The absence of indomethacin in such a product justified measuring the absorbance at 227 nm. The calibration graph used for the spectrophotometric determination of indomethacin showed that Beer’s law is obeyed in the range 0.02-0.16 mg per 10 ml.A mean recovery of 99.06 k 1.27% was obtained in the determination of indomethacin in the presence of its hydroly- sis products (Table 2). The analysis of Indocid capsules gave recoveries of 97.75 k 1.26% for indomethacin in capsules and 99.07 k 0.89% when a standard additions method was applied (Table 3). Chloroform used in the extraction of Indocid capsules did not extract any excipients from the capsules, but extracted the hydrolysis products of indomethacin that were present. The BP method24 for the capsules showed negligible absorbance at 318 nm (the prescribed h) when applied to indomethacin hydrolysis products. However, the proposed spectrophotometric method is more selective.It is also more sensitive, as shown by the value, which was 595 in this method compared with 180 in the BP method. References 1. Dusci, L. J., and Hackett, L. P., J. Chromatogr., 1978, 161, 340. 2. Cotellessa, L., Riva, R., Salva, P., Marcucci, F., and Mussini, E . , J. Chromatogr., 1980, 192, 441. 3. Demetriou, B., and Osborne, B. G., J. Chromatogr., 1974,90, 405. 4. Bland, S. A., Blake, J. W., and Ray, R. S . , J. Chromatogr. Sci., 1976, 14, 201. 5. Hattori, Y., Arai, T., Mori, T., and Fujihira, E., Chem. Pharm. Bull., 1970, 18, 1063. 6. Mehta, A. C., and Schulman, S . G., Talanta, 1973, 20, 702. 7. Dell, H. D., and Kamp, R., Arch. Pharm., 1970, 303, 785. 8. 9. Schmollack, W., and Wenzel, U., Pharmazie, 1974, 29, 583. Beltagy, Y . A., Zentralbl. Pharm., Pharmakother. Labora- toriumsdiagn., 1977, 116, 925; Chem. Abstr., 1978, 88, 158545m. 10. Van der Meer, M. J., and Hundt, H. K. L., J . Chromatogr., 1980, 181,282. 11. Peterkova, M., Kakac, B., and Matousova, O., Cesk. Farm., 1980, 29, 73. 12. Krasowska, H., Krowczynski, L., and Bogdanik, Z . , Pol. J. Pharmacol. Pharm., 1973, 25, 417; Chem. Abstr., 1974, 80, 115885m. 13. “British Pharmacopeia 1980,” HM Stationery Office, London, 1980, p. 239. 14. Tajne, M. R., Kasture, A. V., and Wadodkar, S . G., Indian J. Pharm. Sci., 1978, 40, 196. 15. Nino, N., and Boneva, A., Zzv. Durzh. Znst. Kontrol Lek. Sredstva, 1979, 12, 18; Chem. Abstr., 1980, 92, 47263~. 16. Plazonnet, B., and Vandenheuvel, W. J. A., J. Chromatogr., 1977, 142,587. 17. Terweij-Groen, C . P., Heemstra, S., and Kraak, J. C., J. Chromatogr., 1980, 181, 385. 18. Endele, R., and Lettenbauer, G., J . Chromatogr., 1975, 115, 228. 19. Brown, M., and Bye, A . , J. Chrornatogr., 1977, 143, 195. 20. Kramer, W. G., and Feldman, S . , J . Chromatogr., 1979, 162, 94. 21. Putterman, G. J., Shaikh, B., Hallmark, M. R., Sawyer, C . G., Hixson, C. V., and Perini, F., Anal. Biochem., 1979, 98, 18. 22. Chang, S. L., and Kramer, W. G., J. Chromatogr., 1980, 181, 286. 23. Dryhurst, G., and De, P. K., Anal. Chim. Acta, 1972,58, 183. 24. “British Pharmacopeia 1980,” HM Stationery Office, London, 1980, p. 19. 25. Gressel, P. D., and Gallelli, J. F., J. Pharm. Sci., 1968,57,335. Paper A4/403 Received November 15th, 1984 Accepted July Ist, 1985

ISSN:0003-2654    

DOI:10.1039/AN9861100045

出版商:RSC    

年代:1986

数据来源: RSC