摘要:

274 AnaZyst, April, 1973, Vol. 98, pp. 274-288 The Determination of Trace Amounts of Cobalt and Other Metals in High-purity Water by Using Ion-exchange Membranes BY H. JAMES (Atomic Energy Establishment, Winfrith, Dorchester, Dorset) Microgram amounts of cobalt, chromium, copper, iron, nickel and zinc are concentrated on ion-exchange resin impregnated membranes from large volumes of reactor cooling waters. Atomic-absorption measurement on the acid-extracted membranes has permitted the determination of cobalt down to 0-01 pg 1-1 in water samples, with an analytical precision of f 12 per cent. a t the 96 per cent. confidence limit, based on twelve replicate observations. Gamma-spectrometric measurement of the nuclide cobalt-60 present in the reactor cooling waters has enabled membrane efficiency to be determined ; a t cobalt levels of 0.01 and 0.1 pg 1-l, the efficiencies are shown to be 86 per cent.and greater than 99 per cent., respectively. THE determination of trace metals, nuclides and insoluble material in cooling waters from the Steam Generating Heavy Water Reactor (SGHWR) is required in order to make an assessment of corrosion, erosion and re-deposition rates in the cooling circuits. Continuous methods of analysis currently in use for the determination of iron1 and copper2 are capable of achieving a limit of detection of approximately 1 pgl-1 (p.p.b.). Determinations of cobalt, nickel and zinc are, however, required at levels considerably lower than this concentration. The pres- ence of trace amounts of cobalt in the cooling circuits is of particular interest as it is a source of the long-lived nuclide cobalt-60, which contributes significantly to radiation doses received during reactor maintenance.Various solvent-extraction methods applied to samples of relatively small volume, and semi-automated on-line techniques, were found to be incapable of determining the low trace amounts of metals in some reactor cooling waters. Trials with small columns packed with powdered cation-exchange resins and chelating resins showed a high retention of metals at the 100 pg 1-1 level. Schulek, Remport-Horviith, Lgsztity and Koros3 described the use of specially prepared carboxycellulose as a collector for nanogram amounts of metals in water. The use of columns of ion-exchange resins or carboxycellulose on reactor cooling water sampling points, however, proved difficult to operate and maintain.Blaedel and Haupert4 reviewed the analytical potentialities of ion-exchange membranes for the extraction and concentration of ionic species; by using radioactive cationic tracers they showed that 100-fold enrichment in concentration could be achieved. Campbell, Spano and Green6 studied the characteristics of cation and anion-exchange resin loaded paper discs by X-ray fluorescence. They showed that greater than 99 per cent. retention of cations such as Ca", Cr3+, Co2+, Cu2+, Fe3+, Mn2+, Ni2f and Zn2+ was attained at the 100-pg level in 50-1111 volumes of solution. A method for the determination of cobalt down to 0.05 pg 1-l has been described by Batley.6 This method is based on the oxidation of alizarin red S with hydrogen peroxide, which is catalysed by trace amounts of cobalt, and was developed specifically for the determination of cobalt in reactor cooling water circuits.However, from experimental data provided on the levels of iron throughout SGHWR cooling water circuits, and from examinations of the amount of cobalt present in associated insoluble materials, it was calculated that the levels of cobalt in some circuits would be considerably less than the detection limit of 0.05 pg 1-1 of cobalt given by the catalytic method. From initial trials it was considered that ion- exchange membranes would provide the most convenient method of sample concentration. This paper describes the investigations and development of the use of ion-exchange membranes for the quantitative collection and subsequent analysis of microgram amounts of cationic impurities obtained from large volume-integrated samples.Q SAC; Crown Copyright Reserved.JAMES 275 Cation-exchange and anion-exchange resin impregnated membranes (trade name Acropor) were obtained from Gelman-Hawksley Limited. The Acropor membranes, 47 mm in diameter, incorporate finely divided ion-exchange resin into a structure of acrylonitrile - poly(viny1 chloride) copolymer reinforced with nylon. Dispersion of the finely divided resin through the membrane produced a more effective surface area per unit mass of resin than is available with a column of powdered ion-exchange resin. Acropor membranes have a mass of approxi- mately 100 mg per disc, of which the ion-exchange resin constitutes about 20 per cent.m/m. Ion-exchange capacity is claimed to be from 0.05 to 0.1 mg-equiv per membrane, and the membranes are effective up to a working temperature of 100 "C, or 125 "C for short periods. Two types of cation-exchange membrane are available at present: Acropor, Type SA, is a strongly acidic cation-exchange membrane containing sulphonic acid groups ; and Acropor, Type CH, is impregnated with chelating resin containing iminodiacetate groups with a high preference for iron, copper and other heavy metals. In early laboratory trials it was found that a greater pressure was necessary to obtain a flow through the chelating membrane than for the strongly acidic cation-exchange membrane ; also, the inherent cobalt content was greater in the chelating membrane.For these reasons further investigations were conducted by using the Acropor, Type SAY cation-exchange membranes. Anion-exchange membranes, Acropor, Type SB, are impregnated with strongly basic anion-exchange resin containing quaternary ammonium groups. Attempts to regenerate these membranes to the hydroxide form for use as collectors of trace amounts of chloride have shown little success. However, they have proved useful for the collection and deter- mination of trace amounts of sulphate and nitrate in water. Because of the extremely fine filtration properties of Acropor membranes, it is necessary to introduce a pre-filter so as to prevent blockage of the membrane. The filtration of in- soluble species in SGHWR cooling waters has been standardised by retention of the species on microporous filters of 0.45-pm pore size.It was found to be essential to incorporate this type of pre-filter immediately before the ion-exchange membrane. The retentive capacity of the microporous pre-filter for soluble cationic species has not been investigated, but is expected to be very low. EXPERIMENTAL PRELIMINARY TESTS- Flow-rates of the capillary sampling lines on the reactor cooling water circuits vary from 10 to 50 ml min-l. For simulation purposes, a mock solution containing 100 pg each of cobalt, copper, iron, nickel and zinc in a total volume of 3 litres of distilled de-ionised water was passed at the rate of 17 ml min-l through a single Acropor cation-exchange membrane protected by a microporous pre-filter.The mock solution (pH 5 ) of the mixed metal ions was prepared by dilution of weakly acidic standard solutions of the individual metal ions. A peristaltic pump was used to deliver the 3 litres of solution to the pre-filter membrane held in a 47 mm diameter filter-funnel. Liquid was drawn through the membrane assembly under gentle suction. The pre-filter and Acropor membrane were together digested with 5 ml of analytical-reagent grade concentrated hydrochloric acid. It was found that the nylon support fabric of the Acropor membrane was unaffected by this treatment; the copolymer and ion-exchange resin had been disrupted, giving a finely divided suspension in solution. Filtration of the solution through a small (25 mm diameter) microporous filter removed the nylon disc and most of the suspended material; successive washings with hot 2~ hydro- chloric acid removed soluble metals from the filtered residues.The filtered solution p h s washings were diluted to 25 ml for the determination of cobalt, copper, iron, nickel and zinc by atomic-absorption spectrophotometry. A reagent - apparatus blank was run with the mock solution; as a check on membrane efficiency, the 3 litres of eluate were concentrated to 50 ml by distillation in silica apparatus, and the concentrate was also analysed by atomic- absorption spectrophotometry. The results obtained are shown in Table I. It was assumed that at the nearly neutral pH of reactor cooling waters, membrane efficiencies would be greater than the values obtained for the slightly acidic mock solution.The high percentages of metals retained by the pre-filter and Acropor membrane were encouraging, especially for cobalt, copper and nickel.276 JAMES: THE DETERMINATION OF TRACE AMOUNTS OF COBALT [~‘!na&St, VOl. 98 TABLE I ACROPOR ION-EXCHANGE MEMBRANE EFFICIENCY Metal (100 p g per 3 litres of solution) Cobalt Copper Iron Nickel Zinc A I \ Retained on pre-filter and Acropor membrane (blank deducted), per cent. .. .. 99 96 95 98 93 Found in concentrated eluate, per cent. , , <2 <2 5 <2 -5 In order to determine the lower levels of impurities, such as cobalt, it was found necessary to concentrate the metals collected by the filter - membrane system into a reasonably small volume. Two methods of extraction were investigated : digestion with concentrated acid and elution of the membrane with dilute acid.Ignition of the filter and membrane with dissolution of the ash in acidic solution was considered, but it was thought that the volatile losses incurred would probably be large and erratic, in addition to which airborne radioactivity would be a hazard. Complete wet oxidation of the membrane was not considered to be necessary as all that is required, apart from dissolution of insoluble solids on the pre-filter, is the removal of the absorbed cations from the ion-exchange resin. The use of additional reagents on complete dissolution by wet oxidation would also increase blank values. Insoluble impurities present in the samples of cooling water, which had collected on the microporous pre-filter, were found to be soluble in hot concentrated hydrochloric acid.Oxidation with a few drops of concentrated nitric acid also served to dissolve the filter material. Although experience has shown that the insoluble iron found in SGHWR cooling waters is generally readily soluble in concentrated hydrochloric acid, highly intractable magnetite could, if present, be made soluble by fusion with a small amount of sodium fluoroborate or potassium 11 ydrogen sulphate. A solution containing 20 pg ml-l of copper was passed a t a flow-rate of 6 ml min-1 tlirough a pre-filter and Acropor membrane, to give a 10 per cent. breakthrough of copper. Analysis of the filtrate was carried out continuously on a Technicon AutoAnalyzer by using the zincon method.2 The copper content of the filtrate up to first breakthrough was less than 0.4 pg ml-l, indicating a membrane retaining efficiency of greater than 98 per cent.13y integration, the amount of copper collected on the filter system verified the capacity o f 0-05 inequiv per membrane. The pre-filter and Acropor membrane were eluted with five successive 10-ml portions of 2 M hydrochloric acid and the eluate fractions ( I to 5) were then analysed to determine copper by atomic-absorption spectrophotometry. In a similar experiment, the pre-filter and Acroyor membrane, loaded to 10 per cent. breakthrough with copper, were digested with 5 ml of concentrated hydrochloric acid for 15 minutes. On dilution of the solution to 10 ml, a small amount of insoluble material pre- cipitated from solution ; this material was believed to consist of ion-exchange resin fines or breakdown’ products from the copolymer matrix.The Acropor nylon support disc and suspended solids were removed by filtration through a 0.45-pm pore-size filter, which was washed with three successive 5-ml volumes of water, making the total volume of filtrate 25 ml. The 0.45-pm filter was re-treated with 5 ml of hot concentrated hydrochloric acid and washed with a total of 20ml of water. Copper was determined on the two filtrates by atomic- absorption spectrophotometry. Results from the two methods of cation extraction, acid elution and acid digestion, are given in Table 11. The results given in Table I1 show that both extraction methods gave approximately the same recovery of copper.Acid digestion was preferred, however, as this method would be more appropriate than the elution method for the treatment of samples containing filterable insoluble solids. Also, the extractant acid can be controlled to a low volume in the digestion method, which is essential for the determination of impurities below 1 pg ml-l. IN-LINE SAMPLING APPARATUS- Samples taken from the SGHWR cooling water circuit were delivered isokinetically via stainless-steel capillary lines to a central sampling cabinet. The pre-filters and Acropor membranes were housed in stainless-steel (or aluminium) pressure filter holders supplied by Gelman-Hawksley Limited. Membranes were placed on a stainless-steel support mesh inApril, 19731 AND OTHER METALS I N HIGH-PURITY WATER 277 the holder base, a thrust ring allowing the top of the filter holder to be screwed on to the base without causing twist distortion of the membranes.The filter holders are designed to permit filtration a t pressures of up to 1.38 MN (200 p s i ) ; however, there is no restriction of flow apart from that caused by the membranes, and samples at pressures up to 5-52 MN m--2 (800 p s i . ) were taken regularly. Restriction of flow caused by blockage of the pre-filter by solids has been investigated. Capillary flow-rates during integrated-volume sampling were not affected by up to 5 mg of insoluble solids; as a control on gamma-activity levels, this amount of material represented the maximum normally collected. There was no evidence to indicate that the membranes were contaminated by pick-up of iron, nickel or chromiwm from the inner surfaces of the filter holder.However, in order to eliminate any possible metal contaminants, all inner surfaces of the holder were sprayed occasionally with a PTFE aerosol. A diagram of the filter holder is shown in Fig. 1. I t was essential to measure accurately the volume of sample that passed through the membrane in order to calculate the concentrations of metals collected. To facilitate this measurement, an integrated-volume meter was designed. The filtrate received continuously from the membrane filter holrier was passed into a siphon, made of copper tubing, of about 125-ml capacity. Tlic filtrate from the inter- mittently emptying siphon was directed into a counterbalanced receiver connected through a magnetic Reed switch to a 1000-Q coil Sodeco counting meter, operating from 48V d.c.A magnet was used to counterbalance the siphon receiver. As the balanced beam tilted during an emptying cycle of the siphon, the magnet operated the Reed switch and actuated the counter so as to record each siphonful delivered. Ordinary metal contacts can be used in place of the magnetic Reed switch and magnet system. Integrated-volume counters were made so as to provide one for each sample point on the cooling water circuits in order to complete a full survey over the same period of time. Flow-rates of the capillary sample lines were observed to be between 0.6 and 2.5 1 h-l, depending on their position in the circuit. The precision of the volumes measured by using integrated-volume counters at flow-rates between 0-5 and 3 1 h-l for volumes up to 20 litres was within &3 per cent. The precision is expected to apply to sample volumes greatly in excess of 20 litrcs.A diagram of the integrated-volume meter is shown in Fig. 2. TABLE I1 COMPARISON OF ACID ELUTION AND ACID DIGESTION Copper Cumulative, Technique Fraction removed/mg per cent. removed Acid elution* .. . . 1 1.90 84.0 2 0.60 84.2 3 0.32 94.9 4 0.12 99.0 5 0.03 100.0 - Total 2-97 Acid digestiont . . .. ‘39.0 100.0 * Elution with five successive 10-ml portions of 2 M hydrochloric acid. t (i) I;iltrate (plus washings) from digest of pre-filter and Acropor membrane; and (ii) filtrate (plus washings) from re-digest of 0.45-pm filter. METHOD APPARATUS- Gamma spectrometry-A Technical Measurement Corporation (TMC, Model 401 D) 400-channel pulse-height analyser coupled to a resolver - integrator (Model 522A), printer (Model 500A), and equipped with an 8-cm3 lithium-drifted germanium crystal (20th Century Electronics Ltd.) coupled to the TMC analyser through “Harwell 2000 Series” units, was used for all gamma-spectrometric measurements. Counter geometry was standardised by278 JAMES: THE DETERMINATION OF TRACE AMOUNTS OF COBALT [Analyst, VOl.98 measurement of 16*0-ml volumes contained in screw-capped 60-cm3 polyethylene bottles. Standard nuclide solutions were obtained from the Radiochemical Centre, Amersham, Bucks. , and all sample measurements were calculated to to. When long-duration samples were taken , for example, 7-day periods, to was calculated to the middle of the sampling period.The peak energies of the major nuclides sought are as follows- Nuclide . . .. .. .. .. . . w o &*Fe O5Zn 51Cr Gamma-spectrometric peak energy/keV . . 1173 1096 1116 320 1332 1296 Atomic absorption-A Varian Techtron AA5 instrument was used for all atomic-absorp- tion measurements, readings being displayed on a 200-mm scale slave recorder. The burner compartment was fitted with a chimney and ducting to take radioactive gases derived from reactor cooling water samples into a series of filters for purification. Standard solutions of chromium, cobalt, copper, iron, nickel and zinc were prepared by dissolving accurately weighed amounts of high-purity metals (obtained from Koch-Light Laboratories Ltd.) in Aristar grade hydrochloric and nitric acids.Stock standard solutions containing 1 mg ml-1 of metal were diluted to the required levels with Acropor-filtered de- mineralised water. Blank values were found to be very low; for example, the apparatus blank reading obtained by aspiration of air measured at the peak absorption sensitivity for cobalt was not affected by acidic reagent plus water blanks. Atomic-absorption calibrations for the six elements sought were checked daily by direct standardisation with the particular element, and checked regularly by the method of mixed standard additions. Wavelengths of maximum sensitivity were used for measurements of chromium, cobalt, nickel and zinc; concentrations of copper and iron in the Acropor digest solutions were measured at less sensitive wavelengths so as to obviate the need for dilution.I Capillary Gland nut Securing ring Filter top O-R ing Pre-filter lon-exchange filters Support screen. Underdrain disc Filter base Outlet to counter Fig. 1. In-line filter holderApril, 19731 AND OTHER METALS IN HIGH-PURITY WATER Inlet from filter Perspex case I Externa I 279 Fig. 2. Integrated volume counter (scale reduction 2*4:1) Optimum wavelengths, range and limits of detection applicable to air - acetylene gas mixtures are shown in Table 111. TABLE I11 EXAMINATION OF ACROPOR DIGEST SOLUTIONS WITH VARIAN TECHTRON AA6 Concentration Element Wavelength/nm rangelpg ml-l Chromium . . .. .. 367.8 0 to 10 Cobalt . . . . .. 240.7 0 to 5 Copper .. .. .. 324.7 0 to 10 217.9 6 to 25 Iron .... .. 240.3 0 to 6 Nickel . . .. . . 232.0 0 to 5 Zinc .. .. .. 213.9 0 to 2 372.0 5 to 100 Limit of detection/pg ml-l 0.02 0.016 0.01 0.02 0.02 0.006 For sampling, 47 mm diameter microporous filters, 0.45-pm pore-size [available from Millipore (U.K.) Ltd.], were used. Also used were types SA and SB 47 mm diameter cation- and anion-exchange Acropor membranes and 47 mm diameter stainless-steel or aluminium filter holders (available from280 jilizalyst, Vol. 98 Gelman-Hawksley Ltd.), and a gland nut and O-ring for the union between the capillary line and the filter holder (available from North Hants Engineering Co. Ltd.). For sample preparation, 25 mm diameter microporous filters, 0.8-pm pore-size, and a 25 mm diameter micro-filtration flask and funnel [Millipore (U.K.) Ltd.] were used.REAGENTS- JAMES: THE DETERMINATION OF TRACE AMOUNTS OF COBALT The concentrated acids used were Aristar grade reagents. Hydrochloric acid, concentrated, sp. gr. 1.18. Nitric acid, concentrated, sp. gr. 1.42. De-mineralised water used for the dilution and preparation of samples and standard solutions was purified by passing it through a mixed stack of two cation- and two anion- exchange Acropor membranes protected by a microporous pre-filter. PROCEDURE- Cafdlary line sampling-The radioactive impurities present in reactor water circuits were efficiently concentrated by the Acropor membranes and gave high levels of activity. Gloves, safety spectacles and protective clothing were worn during sampling, preparation and analysis.Place one anion-exchange membrane on the photo-etched screen in the filter holder base, followed by three cation-exchange membranes. Finally, place one millipore pre-filter (0.45 pm) on top of the membranes in order to complete the stack. Ensuring that the large O-ring in the filter holder top is in place, screw down the securing ring (hand-tight) to complete the filter holder assembly. Fit the gland nut, washer and small O-ring to the filter holder top and pass the capillary sample line through the filter holder top to within 1 cm of the pre-filter disc. Tighten the gland nut so as to make a leak-free seal with the filter holder and capillary line. When sufficient sample has been collected, slacken off the gland nut to allow the capillary line to be withdrawn from the holder.Read the integrated-volume meter counter for subsequent calculation of total volume passed. Keeping the filter holder upright, apply gentle suction to the filter holder outlet so as to remove surplus liquid through the membrane stack. This prevents loosely held solids from being washed off the pre-filter on to the lower Acropor membranes when the holder is dismantled. A cro#or sample preparation-If filterable “insoluble” and filtrate “soluble” species are required, separate the pre-filter from the membrane stack by using chisel-edged plastic tweezers. Lay the membrane discs flat on the bottom of Pyrex beakers with an internal diameter slightly greater than the discs. With a pipette, add 5-0 ml of Aristar grade concen- trated hydrochloric acid to each beaker and cover it with a watch-glass. Digest the contents of the beaker with the acid nearly at its boiling-point on a hot-plate for about 15 minutes.Add five drops of Aristar grade concentrated nitric acid at this stage and continue the digestion for a further 10 minutes or until all traces of insoluble solids have dissolved. (The pre-filter is completely dissolved by this treatment.) Dilute the “insoluble” solution to 25 ml in a calibrated flask. Diluted solutions prepared from the acid digest of the Acropor membranes were found to contain a small amount of very finely divided insoluble material derived from the membrane matrices in addition to the intractable nylon support discs. Dilute the acid extract solution from each Acropor membrane stack so that the con- centration of acid is less than 6 M and filter it slowly through a single 25-mm diameter 0.8-pm pore-size Millipore filter-pad held in a microfiltration apparatus.Pulp the nylon discs and transfer the pulp from the beaker to the Millipore pad, pressing it with a PTFE rod while applying gentle suction to the filtration flask. Wash the digestion beaker, PTFE rod and pulped nylon pad with successive 3-ml portions of hot 1 M Aristar grade hydrochloric acid. Continue the rinsing and washing so as to give a total filtrate volume of 25 ml. It was found that occasionally a small amount of the white organic material precipitated from the filtrates on standing. No changes in atomic-absorption measurements were observed, however, with addition of standard solutions of the cations cobalt, copper, iron, nickel and zinc to blank Acropor digest filtrates containing relatively large suspensions of organic material.Prepare blank solutions by digesting unused Millipore filters, and Acropor membranes, with the same amounts of reagents as those used for sample solutions. Filter and wash the Acropor blank solutions in the same manner as that used for the Acropor sample solutions Special shielding was necessary for some samples.April, 19731 AND OTHER METALS I N HIGH-PURITY WATER 281 and finally dilute the solution to 25 ml. If separation of “insoluble” and “soluble” species is not required, digest the whole stack of pre-filter and membranes together, filter and wash them to give a total volume of 25 ml; the blank containing one pre-filter and the requisite number of membranes is prepared accordingly.RESULTS CATION-EXCHANGE MEMBRANE EFFICIENCY- Initial laboratory trials showed that the retention of a single cation-exchange membrane was greater than 95 per cent. for cobalt, copper, iron and nickel a t the 30 pg 1-1 level. It was considered, therefore, that a stack of three such membranes would be sufficient to remove almost 100 per cent. of the cations, assuming an equal efficiency for the second and third membranes in collecting decreasing concentrations of cations. In consideration of handling radioactivity levels concentrated by the Acropor technique, samples were taken over periods from 24 hours for the highly active samples, to 7 days for the low-activity samples. Generally, the integrated sample volumes varied accordingly between 50 and 350 litres; samples of large volume were taken for the determination of small trace amounts of impurities such as cobalt.Samples of cooling water were taken at points showing the widest variations in trace-metal content and flow-rate. Acid digest solu- tions were prepared from the separated pre-filters and individual Acropor membranes for analysis by atomic-absorption spectrophotometry and gamma spectrometry. TABLE IV COLLECTION OF CATIONS ON ACROPOR MEMBRANES Atomic-absorption results are given as total microgram amounts collected on the pre-filter and separated Acropor membranes; results for gamma spectrometry are given in microcuries. All results have been corrected for blank values and background counts Sample A (flow-rate 35 ml min-l; total volume collected 80 litres) 7 h \ “Soluble’ ’ Method absorption Atomic Gamma spectrometry Method absorption Atomic Gamma spectrometry “Insoluble” First Second Third (0.45-pm Acropor Acropor Acropor pre-filter) membrane membrane membrane - +--7 Cation Nuclide p g pCi p g i 2-i p g pCi c o c u Fe Ni Zn SOCO 68Fe 65zn 1.5 7 860 11 <1 2.9 0.95 <o-1 10 750 12 16 30 11.3 <0.1 0.76 0.6 110 5 5 7 0- 6 <0.1 0.2 <0.6 <2 (6 <1 <6 <0.01 (0.1 <O.l Sample B (flow-rate 300 ml min-l; total volume collected 20 litres) A < \ “Soluble” r h \ “Insoluble’’ First Second and Third Fourth and Fifth (0.45- pm Acropor Acropor Acropor pre-filter) membrane membranes membranes Cation Nuclide p g pC1 pg pCi p g pCi pg pCi -.- - A c o 2.5 1-5 < 0.5 < 0-5 c u 10 380 130 4 Fe 1300 140 30 10 Ni 23 12 10 2 Zn 2.5 20 10 6 SOCO 6.0 1.6 0.4 < 0.02 68Fe 3-0 (0.1 cO.1 < o m 1 66Zn 0.1 0-5 0.2 <0*1282 JAMES: THE DETERMINATION OF TRACE AMOUNTS OF COBALT [AutdySt, VOl. 9 Five Acropor membranes were used for the collection of cations in sample B taken from a 0.8-mm bore line that delivered at a flow-rate of 300mlmin-l. An integrated-volume counter was not used for volume measurement at this high flow-rate and regular readings of timed flow-rates were taken instead. Some typical results of these investigations are shown in Table IV. An assessment of the ratio of “insoluble” to “soluble” metals can be made from the results obtained. For example, iron is shown to be a largely filterable particulate species, whereas copper and zinc are mainly present in “soluble” ionic form.Although the figures for cobalt obtained by atomic-absorption spectrophotometry show values of “less than 0.5 pgJ’ in each instance after the first Acropor membrane, the very sensitive gamma-spectrometric results on the same solutions define a diminishing level of cobalt-60 in the lower membranes. The sum of the particulate and cationic forms of cobalt collected, in terms of the integrated volume passed, indicate a measured level of 0.14 pg 1-1 of cobalt for sample A and 0-20 pg 1-1 of cobalt for sample B. The two samples were taken from different parts of the water circuit. It is essential to use reagents and water of the highest purity, especially for the deter- mination of impurities below the parts per billion level, even though they have been con- centrated approximately 1000-fold by the Acropor technique.Blank values for the micro- porous pre-filter, three Acropor cation-exchange membranes and reagents were determined by atomic-absorption measurements of the 25 ml of extraction solutions of pre-filters and membranes. The results shown in Table V have been calculated as total microgram amounts in extraction solutions; the results are the mean values of thirty determinations. BLANK VALUES- TABLE V ACID-EXTRACTION BLANKS Microporous pre-filter Three Acropor Reagent blank in 25 ml cation-exchange membranes in 25 ml (25 ml) Cobaltlpg . . .. < 0-4 < 0.4 < 0.4 CoPPerlPLg * - .. 1.5 1 0.5 Nickel/pg . . .. 1.5 1 0.8 Iron/pg . ... 5 5 1 Zinc/pg . . .. 5 6 2 Hence, the blank levels of combined pre-filter and three Acropor membranes, applied to a 100-litre integrated sample, would be equivalent to 0.1 pg 1-1 for iron and zinc, 0.03 pg 1-1 for copper and nickel and <0404pg1-1 for cobalt. CATION COLLECTION LOSSES- It was considered that cations could be displaced from membrane to membrane down the stack during sampling with subsequent loss of cations in the membrane eluate. In order to determine the magnitude of possible losses, membrane eluates were sampled and con- centrated by distillation. Atomic-absorption measurements on 100-fold concentrations were found to be at the limits of detection for cobalt, copper, iron and nickel. Consequently, for an assessment of membrane stack efficiency, the long-lived isotopes cobalt-60 and iron-59 present in the eluate concentrates were compared with cobalt-60 and iron-59 found in the membrane digest solutions. Eluates were collected in 2.5-litre glass bottles containing 0.5 ml of analytical-reagent grade concentrated hydrochloric acid ; eluate fractions were taken just after the start of a sampling period and just before the end of the period.The eluates were concentrated to 15 ml for gamma-spectrometric measurement. The results summarised in Table VI show the percentages of cobalt-60 and iron-59 retained on one microporous pre-filter and three Acropor cation-exchange membranes. In a similar experiment with the short-lived copper-64 isotope in the cooling water sample as a tracer, the retention efficiency of an Acropor stack was shown to be 98 per cent.at the 1 pg 1-1 of copper level; eluate samples were taken at the beginning and end of a 7-day sampling period, 340 litres being passed. The cobalt content of sample C shown in Table VI at O * O l O p g 1-1 concentration is retained by the Acropor stack at 85 per cent. efficiency. Only a slight improvement inApril, 19731 AND OTHER METALS I N HIGH-PURITY WATER 283 retention efficiency at this level of cobalt was achieved by doubling the number of cation- exchange membranes used. Sample D, which contained almost ten times the cobalt content of sample C, is shown to be 99 per cent. retained. Cobalt-60 activities in the final eluates of samples C and D are similar to the activities in the initial eluates, indicating that no washing out or breakthrough of cobalt collected occurred.It is assumed that membrane retention efficiencies will decrease below 85 per cent. for cobalt levels lower than 0-01 pg 1-1 and a correction is made for any samples at this level. However, it is possible that at these very low levels, the membrane stack efficiency would increase for flow-rates of less than the 2 1 h-1 delivered at sample point C. Sample point . . .. Flow-rate/l h-l . I Element sought . . Integrated volume/litres Retained on stack . . Activity on stack . . Initial activity in eluate Final activity in eluate Activity retained on stack, per cent. . . TABLE VI CATION LOSSES IN MEMBRANE ELUATE C D D Cobalt Cobalt Iron 250 60 60 2 2.5 2.5 0.095 eg 1-’ of Co 140 nCi 1-1 of 6oCo 0.9 nCi 1-1 of 6oCo 1.1 nCi 1-l of 6oCo 85 99.3 > 99.6 0.010 pg 1-1 of Co 1-70 nCi 1-1 of aoCo 0.29 nCi 1-l of 6oCo 0.31 nCi 1-l of 8oCo 45-8 pg 1-l of Fe 92 nCi 1-1 of 69Fe <0*3 nCi 1-l of 4uFe <0.3 nCi 1-l of 6@Fe E Chromium 66 2.6 2.0 pg 1-1 of Cr 730 nCi 1-l of 61Cr 500 nCi 1-1 of Wr 960 nCi 1-l of Wr -60 In gamma-spectrometric examinations the efficiency of the lithium-drifted germanium crystal used for the detection of iron-59 is low; also, the abundance of iron-59 in SGHWR cooling waters is small.Therefore, evaluation of losses in the eluate by measurement of iron-59 has been limited to sample D, which contained the relatively high iron content of 45 pg 1-1. Concentration of eluates to a greater extent than 100-fold would be necessary to detect iron-59 in samples containing less than 45 pg 1-1 of iron.Generally, iron in the cooling waters has been found to be material that can be removed by filtration; even at the lower levels of about 10 pg 1-1 of iron and less, 90 per cent. of the total iron collected is removed by the microporous pre-filter. The poor retention of chromium-51 shown in Table VI was investigated; it was believed that the chromium may not have been present in a cationic form in sample E. Laboratory trials showed that soluble chromate was quantitatively collected on Acropor anion-exchange membranes with the resin in the chloride form. It was also shown that the chromate collected was completely removed from anion-exchange membranes by elution with 2 N sodium hydroxide solution or by digestion with hot concentrated hydrochloric acid solution.An integrated sample of cooling water was collected on a stack of membranes comprising, in order, a microporous pre-filter, three cation-exchange membranes and two anion-exchange membranes at the bottom of the stack. A sample of eluate taken at the end of a 24-hour sampling period and concentrated by distillation from 2.5 litres to 15 ml was examined for chromium-51 and zinc-65 content by gamma spectrometry. The pre-filter, cation- and anion-exchange membranes were separated for analysis in order to determine the proportions of “insoluble,” cationic and anionic species of chromium and zinc in the circuit. The results given in Table VII show a high retention of chromium and zinc on a mixed stack of Acropor membranes.The con- centration of chromium collected on the anion-exchange membranes is in close agreement TABLE VII COLLECTION OF CHROMIUM AND ZINC ON CATION- AND ANION-EXCHANGE MEMBRANES Sample F: integrated volume 58 litres A f \ Chromium/ W r / Wr, Zinc/ 66Zn/ BSZn, Pg 1-1 nCi 1-1 per cent. pg 1-1 nCi 1-1 per cent. Retained on pre-filter . . . . 0.3 440 26.1 0.16 6.2 9.7 Retained on cation-exchange membranes . . .. . . 0.9 310 18.4 0.9 43.0 80.7 Retained on anion-exchange membranes . . .. . . 2-6 930 55.2 0.1 4.1 7-7 In final eluate . . .. . . 0.04 6 0-3 (0.1 1.0 1.9284 JAMES: THE DETERMINATION OF TRACE AMOUNTS OF COBALT [A.iZdySt, VOl. 98 with the over-all losses incurred on a stack consisting totally of cation-exchange membranes, as shown in Table VI, which indicates that the chromium lost from a stack of cation-exchange membranes is anionic and not a colloidal or non-ionic species.It is obvious from the elemental and gamma-spectrometric results shown in Table VII that the particulate and soluble ionic forms of chromium possess different specific activities; this conclusion can also be deduced for cobalt, iron and zinc from the results given in Table IV. The differences in the specific activities of soluble and insoluble species is due to their indi- vidual points of origin in the cooling water circuits and life-cycle through the reactor core. SAMPLE PREPARATION LOSSES- Use of the gamma-spectrometric measurement of long-lived radioisotopes present in the water samples was extended to investigate the loss of cations during sample preparation.The acid digestion of membranes was used in preference to the method involving elution with acid; however, this procedure involved removal of the membrane support material by filtration, which may have entrained cationic species. Membranes from an integrated-volume sample taken from the cooling circuit were treated in the normal manner by digestion with 5ml of concentrated hydrochloric acid and oxidised with nitric acid. The nylon support disc and insoluble resin-dispersion polymer were removed by filtration and washed with hot dilute hydrochloric acid to give a total volume of filtrate of 25 ml. Filtered solids were made soluble by wet oxidation with concentrated sulphuriq and nitric acids, and examined for cobalt-60, iron-59 and zinc-65 by gamma spectrometry.However, the losses are very low in comparison with the levels of cations sought. For example, a loss on the filter of 1 per cent. of cobalt at the 0.1 pg 1-1 level, plus the 1 per cent. loss in sample eluate (Table V) is within the expected precision limits of the method, including collection, extraction and analysis. The results given in Table VIII show slight losses on the filter. TABLE VIII FILTRATION LOSSES BY MEMBRANE EXTRACTION OF NUCLIDES Total activity in extract filtrate/nCi 1-1 4.05 x 103 1-76 x loa 0.92 x 10s Total activity on extract filter/nCi 1-1 . . 50 6 18 Activity retained on filter, per cent. . . 1.2 0.3 1.9 Nuclide GOCO 69Fe 6sZn The results shown in Table VIII were obtained for a sample taken from a high-tempera- ture region of the cooling water circuit.From the low iron-59 activity retained on the filter it was concluded that the iron, which from this sample point was generally difficult to dissolve, had effectively been made soluble by the acid-digestion procedure. DETERMINATION OF IRON- The total iron content determined by the Acropor technique on numerous samples containing insoluble solids was found to be invariably higher than the total iron results obtained by the automated 2,4,6-tripyridyl-l,3,5-triazine (TPTZ) method.1 In the automated method particulate iron is dissolved by treatment with 1 per cent. V/V thioglycollic acid solution in a time-delay coil at 95 “C; digestion time in the delay coil is about 20 minutes. Dissolved iron is then determined by continuous absorptiometric measurement of the coloured complex formed with TPTZ.A number of 200-ml “grab” samples were taken from two capillary lines (sampling time about 6 minutes) into bottles containing thioglycollic acid. The acidified samples were divided into two equal portions; one series of samples was introduced directly into a Technicon AutoAnalyzer for determination of iron and the other series was digested in a boiling water bath for 1 hour prior to analysis in the AutoAnalyzer. Therefore, the second series had combined periods of digestion of 1 hour at 100 “C and 20 minutes at 95 “C. The results for iron summarised in Table IX show the effect of increasing the digestion time with thioglycollic acid in the automated procedure. Also included in Table IX are the Acropor results obtained on daily integrated samples covering the short-period “grab” samples. The mean results for iron shown in the top half of the table were obtained from determinations carried out at steady power and during plant operations for water clean-upApril, 19731 AND OTHER METALS I N HIGH-PURITY WATER 285 (Powdex re-coats.) The eight individual results are shown in Fig.3. Also shown in Fig. 3, for comparison, are nine daily results for iron obtained by the TPTZ and Acropor methods during a typical reactor start-up period. Incomplete dissolution of insoluble iron by the normal TPTZ method is indicated by the values shown in Table IX, especially for the high iron content of sample Y, and is confirmed by the single determinations shown in the lower half of the table; the portions of “grab” sample receiving additional digestion with thiogly- collic acid gave results in close agreement with the value for total iron obtained by Acropor collection.Steady power period (with water clean-u p) -1 Reactor start-up period -I- I- “G ra b” sarn p le ‘ * TPTZ result 5 40 < I .- X \ \ \ \ \ I - X ‘ \ I 1 i L \ \ \ \ \ I 9 Days -- 8 Days 1- -- I Fig. 3. Daily determination of iron: comparision of results obtained by TPTZ and Acropor methods Perturbations in the cooling water circuits cause short-term fluctuations in the amount of solids in circulation. It is possible that during such a release of solids the “grab” sample of small volume may miss the resultant high iron content; however, it was found that continuous in-line analysis by the normal TPTZ method also gave lower iron results than the Acropor system.In addition, a direct comparison of the two methods has been obtained by determining the iron by the TPTZ “grab” method and the Acropor technique on twin capillary lines at sample point Y. Identical volumes were collected over a period of 2 hours; the normal TPTZ method gave 28 pg 1-1 of iron compared with the Acropor result of 50 pg 1-l.286 JAMES: THE DETERMINATION OF TRACE AMOUNTS OF COBALT [Analyst, VOl. 98 TABLE IX COMPARISON OF RESULTS FOR IRON BY THE TPTZ AND ACROPOR METHODS Iron in “grab” Iron in Iron in sample by integrated “grab” TPTZ method Iron on sample on sample by (additional Acropors pre-filter TPTZ method*/ digestion) */ (“soluble”)/ (“insoluble”) / Sample point Pg 1-1 CLg 1-1 pg 1-1 Pg I-’ X (mean of 13 determinations) 4.9 - 0.6 6.8 Y (mean of 8 determinations) 13.0 - 1-6 26 X (single determination) (2 6 Y (single determination) 16 20 1.4 18.4 Y (single determination) 22 61 1-9 68 - - - - X (single determination) <2 4 * Iron results obtained by Mr.R. E. H. Rolfe, SGHWR Chemistry Laboratory. DETERMINATION OF COPPER- Total iron/ 6.4 27-6 7 6 19.8 69.9 CLg 1-1 Routine copper determinations on “grab” samples by using the automated zincon method2 have shown close agreement with the copper results obtained by the Acropor- integration technique, the limit of detection for copper by the former method being 1 pg 1-1. Of the fifteen results obtained for sample X, seven indicated 2 pg 1-1 of copper, three 1 pg 1-1 and five less than 1 pg 1-l.The “less than 1 pg 1-l” values were taken as 0.5 pg 1-1 of copper for calculation of the mean value. Copper determined by the Acropor-integration technique is shown in Table X to be present mainly as a “soluble” cation. There is no difficulty in dissolving it for the continuous method as there is for the iron determination. TABLE X COMPARISON OF RESULTS FOR COPPER CONTENT BY THE ZINCON AND ACROPOR METHODS Copper in integrated sample r Copper in “grab” On 0; sample by Acropors pre-filter Total zincon method/ (“soluble”)/ (“insoluble”) / copper/ Sample point Pg 1-1 Pf3 1-1 Pg 1-1 Pg I-’ X (mean of 16 determinations) 1.3 1.0 0.1 1-1 PRECISION- An assessment of analytical precision was achieved by atomic-absorption determination of known amounts of cations added to Acropor membranes. Twelve separate determinations were performed by using a mixture of standard solutions containing 1 pg of cobalt, 90 pg of copper and 950 pg of iron per 100 ml added to each single cation-exchange membrane.Following a water wash, the membranes were digested with concentrated hydrochloric acid, insoluble organic material was filtered off and the solutions were diluted to 25-ml volumes for analysis by atomic-absorption spectrophotometry. The varied levels of added cations were chosen to simulate approximate ratios of cobalt, copper and iron found in SGHWR cooling waters. The results are summarised in Table XI as the concentrations of cations in the digest extract solution. Y (mean of 9 determinations) 17 17-6 0-6 18.0 TABLE XI PRECISION OF ATOMIC-ABSORPTION ANALYSES Cobalt Copper Iron (Co2+) (CUS+) (Fe*+) Concentration in extract solution (25 ml) / Precision at 96 per cent.confidence limit pg ml-l . . .. .. .. .. 0-041 3.6 38 (12 determinations)/pg ml-1 . . . . f0.006 (f12%) f0-066 (fl*6%) ,t0.96 (f2.6%) Calculations of the precisions in terms of a volume of cooling water sample of 100 litres are: cobalt 0.01 & 0.001 p g l-l, copper 0.9 f 0.02 pg 1-1 and iron 9.6 f 0.26 pg 1-l.April, 19731 AND OTHER METALS I N HIGH-PURITY WATER 287 With standard solutions of cobalt, copper, iron, nickel and zinc, there does not appear to be any interference in the determination of any one element caused by the presence of the other four in the ratios generally found in SGHWR cooling waters.These ratios for the metals in the order given are 1 : 100: 1000: 10: 10. The mean value of the total cobalt content of thirteen integrated samples, taken from one capillary sample point over a period of 15 weeks, was found to be 0.014 pg 1-1 with a standard deviation of &0-005 pg 1-l. The variation included a number of short-term circuit disturbances that caused slight fluctuations in the concentration of solids, and hence cobalt content, in addition to the analytical errors. Reproducibility of results has also been shown by analysis of ten duplicate 300-litre integrated samples to determine cobalt. These samples were taken on a weekly basis from two capillary lines fed from one multi-headed sample point. Results of the duplicate samples shown in Table XI1 are, on average, within &0-002 pg 1-1 of cobalt at the 0.01 to 0.02 pg 1-1 level.TABLE XI1 COMPARISON OF COBALT CONTENTS FROM TWIN CAPILLARY LINES Results expressed as pg 1-1 of cobalt Run 1 Run 2 Run 3 Run 4 Run 6 Capillary XI . . . . 0.012 0.016 0.0 16 0.012 0.0 19 Capillary XI1 . . . . 0.012 0.017 0-016 0.010 0.020 Difference . . . . Nil 0.001 0.001 0.002 0.001 DISCUSSION The method of collection on Acropor cation-exchange membranes has been in use for over 1 year for the determination of trace-metal impurities in SGHWR cooling water circuits. During that time the method has been developed to enable cobalt to be determined down to the 0.01 pg 1-1 level. At this level, the three-membrane stack system has been shown by gamma-spectrometric measurement of cobalt-60 to be approximately 86 per cent, efficient.Further investigation would be required to establish membrane efficiency and analytical precision at levels lower than 0.01 p.p.b. A major advantage of the Acropor collection system over the determination of impurities in “grab” samples, or in-line continuous methods, is the relative reduction of blank levels. Reagent and apparatus blank values arising from the preparation of samples by the Acropor technique are very low in comparison with the amounts of metals collected from an integrated- volume sample. On a routine basis, sampling time, and hence frequency, depends on the concentration of metals in the water at a particular sampling point. For example, if only the major impurity, such as iron, is to be determined, and it is present in relatively high concentration with respect to blank levels, then a small integrated volume should suffice.On the other hand, if the interest lies in the determination of very small trace amounts of impurities such as cobalt, then a long-duration integrated sample would be necessary. The separation of “insoluble” filterable impurities by means of a single microporous pre-filter of nominal pore size 0.45 pm is an arbitrary measure. No work has been conducted on the investigation of possible retention of “soluble” cations on a bed of solids collected on the pre-filter during the sampling period. It is considered, however, that any retention would be extremely small; the “insoluble” material consists mainly of oxides of iron, and the amount collected does not generally exceed 0-3 mg cm-2 of filter area for any sample.The microporous pre-filter also allows the sample to be spread from a narrow jet issuing from the capillary line into a relatively slow-moving “column” of water through the ion- exchange membrane stack. Dissolution of oxides of iron by treatment with thioglycollic acid in a mixing coil at 95 “C has been shown to be incomplete for some SGHWR cooling waters that probably contain magnetite. The results obtained for iron by the normal con- tinuous TPTZ method on samples containing relatively high concentrations of insoluble solids (greater than 20 pg 1-1 of iron) are approximately half the values obtained by the Acropor method with concentrated acid digestion. Gamma-spectrometric measurements of the long-lived isotopes cobalt-60, iron-59 and zinc-65, coupled with atomic-absorption determinations of cobalt, iron and zinc on both “insoluble” and ‘soluble” species, has provided useful information on the specific activities of these isotopes and their fate in the reactor cooling water circuits.288 JAMES Anion-exchange resin impregnated membranes have been used to demonstrate the presence of anionic zinc and chromium, probably as zincate and chromate, in SGHWR waters. Analytical applications of the anion-exchange membranes have not yet been fully investi- gated; however, preliminary determinations of sulphate and nitrate at concentrations below the parts per million level have shown promise. CONCLUSION The method described provides a simple and efficient concentration system for the determination of extremely small trace amounts of cations in water. The final determination of extracted metals by atomic-absorption measurements greatly reduces the relatively high blank levels inherent in solvent-extraction and colorimetric methods. In comparison with in-line continuous methods of analysis, the Acropor integrated system does not provide early information for plant control. However, the integrated sample enables positive determina- tions of metals in water to be carried out at levels considerably lower than those which could be detected by current chemical methods. Much detailed information on plant efficiencies, steam carry-over and corrosion rates has been obtained from the atomic-absorption and gamma-spectrometric measurements of the filterable “insoluble” and “soluble” species collected by the Acropor system. This paper is published by permission of the United Kingdom Atomic Energy Authority. The author thanks Mr. E. Bowell, Head of Analytical Services, A.E.E., Winfrith, for valuable discussions; Mr. T. R. Holland for experimental preparations and design of the integrated flow meter; and Messrs. R. K. Alty and W. J. Symons for technical assistance. REFERENCES 1. 2. 3. 4. 5. 6. Dawes, C. A., Tetlow, J . A., and Wilson, A. L., CERL Report No. RD/L/R1399, 1966. Wilson, A. L., CERL Report No. RD/L/N162/67, 1968. Schulek, E., Remport-HorvAth, Zs., LAsztity, A., and Koros, E., Talanta, 1969, 16, 323. Blaedel, W. J . , and Haupert, T. J., Analyt. Chem., 1966, 38, 1306. Campbell, W. J., Spano, E. F., and Green, T. E., Ibid., 1966, 38, 987. Batley, G. E., Talanta, 1971, 18, 1226. Received October 4th, 1972 Accepted November 29th. 1972

ISSN:0003-2654    

DOI:10.1039/AN9739800274

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, April, 1973, Vol. 98, $9. 289-292 Indirect Complexometric Titration of Barium and 289 Strontium after Stepwise Precipitation as Sulphate from Homogeneous Solution BY €3. C. SINHA AND S. K. ROY (Central Glass and Ceramic Research Institute, Calcutta-32, India) An indirect method has been developed for the stepwise titration of barium and strontium with EDTA, based on precipitation of the elements as sulphate from a homogeneous solution. Barium, strontium and other multivalent cations are complexed by titration with EDTA a t pH 10.0 by using a mixed indicator comprising Eriochrome black T, Titan yellow and Naphthol green B. Barium is then selectively replaced from its EDTA complex and precipitated as the sulphate with an excess of magnesium sulphate solution. The excess of magnesium is determined by titration with EDTA and the equivalent concentration of barium is calculated.Strontium is determined in the same solution in the same way, with an excess ?f zinc sulphate solution. The optimum conditions for precipitation and the interfercnces due to various anions and cations have also been studied. Copper, nickel, cobalt and iron interfere and a second method for the determination of barium alone has been derived wherein the interfering elements are comglexeql with triethanolamine, potassium cyanide and ascorbic acid. Phosphate and chromate interfere and require to be separated. 1 VARIOUS methods based on direct and back-titrations of barium and strontium withlEDTA (disodium salt) are reported in the literat~re.l-~ In all of the methods, these elements, and other alkaline earth elements, if present, are co-titrated and therefore prior separation of the individual elements is essential for their determination.Belcher, Gibbons and West6 reported a method for the determination of barium sulphate that entailed dissolving it in an excess of a strongly ammoniacal ( 9 ~ ) solution of EDTA and then back-titrating the excess with magnesium ions from magnesium chloride solution. Precipitation of barium as sulphate from a homogeneous solution of its EDTA complex by the replacement reaction with mag- nesium and nickel in the presence of sulphate ions has been reported for the gravimetric determination of b a r i ~ m . ~ , ~ However, precipitation from a homogeneous solution has not yet been utilised in complexometric titration of the element in the presence of other alkaline earth elements.This paper describes a method in which barium, strontium and other alkalihe earth elements are complexed by titration with EDTA at pH 10.0 with the use of a mixed indicator. Barium and strontium are then precipitated stepwise as their sulphates at the same pH from a homogeneous solution by displacement reactions with a known (excess) volume of magnesium sulphate and zinc sulphate, respectively, according to the following equations- Ba[EDTA] + MgSO, = BaSO, + Mg[EDTA] Sr[EDTA] + ZnSO, = SrSO, + Zn[EDTA] (log k = 7.76) (log k = 8.69) (log k = 8-63) (logk = 16.26) The excess amounts of magnesium and zinc ions are then titrated stepwise with EDTA solution. Barium and strontium are calculated from the equivalent amounts of magnesium and zinc consumed during their respective displacement reactions.REAGENTS AND SOLUTIONS- EXPERIMENTAL All reagents were of analytical-reagent grade quality unless otherwise stated. Calcium chloride solution, 2.0 mg ml-1. Barium chloride solution, 2.0 wag ml-I. Strontium chloride solution, 2.0 mg ml-I. @ SAC and the authors.290 SINHA AND ROY: INDIRECT COMPLEXOMETRIC TITRATION OF BARIUM AND [ATZa&St, Vol. 98 Magnesium sulphate sohtion, 0.05 M. Zinc szclphate solution, 0-05 M. Standard magnesium solution, 0.05 M-Dissolve 1.2160 g of pure magnesium turnings in 1 + 1 hydrochloric acid, almost neutralise the solution with 1 M sodium hydroxide solution and dilute to 1 litre with water. Mixed indicator solution-Dissolve Eriochrome black T (0.03 g), Titan yellow (0.04 g) and Naphthol green B (0.01 g) in 25 ml of triethanolamine.EDTA solution, 0.05 M-Dissolve 18.6125 g of the disodium salt of EDTA in water and dilute the solution to 1 litre. Standardise the EDTA solution thus obtained with the mag- nesium sulphate solution at a pH of 10.0 by using mixed indicator and calculate the equivalent amounts of barium oxide and strontium oxide per millilitre of EDTA solution. Bufler solution, PH 10.0-Dissolve 67.5 g of ammonium chloride in 250 ml of water and 570 ml of ammonia solution (sp. gr. 0.88), dilute to 1 litre and mix thoroughly. PROCEDURE I. STEPWISE DETERMINATION OF BARIUM AND STRONTIUM OXIDES IN THE Transfer a portion of the solution containing barium, strontium, calcium and magnesium into a 250-ml conical flask.Add 2 to 3 g of ammonium chloride, followed by dilute ammonia solution (1 + 4) dropwise until the contents of the flask smell of ammonia. Add 10 to 15 ml of buffer solution and titrate the mixture with 0 . 0 5 ~ EDTA solution in the presence of 10 to 12 drops of mixed indicator until a sharp green colour is obtained. DETERMINATION OF BARIUM OXIDE- Dilute the complexed solution to 100 ml, heat it to 50 to 60 "C on a hot-plate and add an excess (3 to 5 rnl) over the theoretical requirement of sulphate ions of 0.05 M magnesium sulphate solution (1 ml of 0.05 M magnesium sulphate solution for every 7.67 mg of barium oxide content) slowly from a pipette, keeping the mixture on the hot-plate for 10 minutes.Cool the mixture, add 5 ml of buffer solution and 10 ml of absolute ethanol and titrate the excess of magnesium in the solution with 0.05 M EDTA solution to the sharp green end-point. Reserve the solution for the determination of strontium oxide. BaO (mg) = ( A - a) x f where A ml is the volume of EDTA equivalent to the volume of magnesium sulphate solution added, am1 is the volume of EDTA solution required to titrate the excess of magnesium sulphate andfis the equivalent of barium oxide in milligrams per millilitre of EDTA solution. DETERMINATION OF STRONTIUM OXIDE- To the solution reserved after the determination of barium, add 0.06 M zinc sulphate solution (5 ml for every 10 mg of strontium oxide) and 5 g of potassium sulphate. Boil the mixture for 10 minutes in order to precipitate strontium sulphate, then cool it, add 10ml of buffer and 16 to 20 ml of absolute ethanol.Titrate the excess of zinc with 0.05 M EDTA PRESENCE OF CALCIUM AND MAGNESIUM- Then , solution to the sharp green end-point. Then, SrO (mg) = (B - b) x g where B ml is the volume of EDTA equivalent to the volume of zinc sulphate solution added, b ml is the volume of EDTA solution required to titrate the excess of zinc sulphate, and g is the equivalent of strontium oxide in milligrams per millilitre of EDTA solution. PROCEDURE 11. DETERMINATION OF BARIUM OXIDES IN THE PRESENCE OF VARIOUS CATIONS- To a portion of the solution in a 250-ml conical flask add 5ml of 0 . 0 5 ~ magnesium sulphate solution. Dilute the mixture to 50m1, add 2 to 3 g of ammonium chloride and then ammonia solution (1 + 4) dropwise until the contents of the flask smell of ammonia.Acidify the solution to pH 3 to 4 by adding 10 per cent. V/V hydrochloric acid and then add a 1-ml excess of the acid. Add 10 ml of 30 per cent. V/V triethanolamine while shaking the flask, followed by 10ml of buffer solution, 5 to 10ml of 10 per cent. m/V potassium cyanide solution and 1 g of ascorbic acid. Heat the solution to 70 to 80 "C to remove the iron colour, cool it and titrate it with 0.05 M EDTA solution to the sharp green end-point in the presence of 10 to 12 drops of mixed indicator solution.April, 19731 STRONTIUM AFTER PRECIPITATION FROM HOMOGENEOUS SOLUTION 291 Proceed in the same way as described in procedure I for the determination of barium oxide and calculate the amount of barium oxide from the same equation.RESULTS AND DISCUSSION The sulphate ion plays an important r6le in the stepwise precipitation of barium and strontium from homogeneous solution because of its replacement reactions with magnesium and zinc sulphates, respectively. Firsching' studied the co-precipitation of alkaline earths during the homogeneous precipitation of barium sulphate from an equimolar solution of these elements in a 1-5 mM sulphate-ion concentration and reported the co-precipitation of strontium to be less than 4 per cent. In the present study, it was observed that the co- precipitation of strontium increased with the increase of excess of sulphate-ion concentration. An excess of 1.6 to 2.5 mM magnesium sulphate concentration over the theoretical requirement of sulphate ions calculated as magnesium sulphate (1 ml of 0.05 M magnesium sulphate solution for every 7.67 mg of barium oxide content) was found to be satisfactory.Addition of magnesium sulphate in the procedure instead of magnesium chloride and ammonium sul- phate7 improved the granular nature of the barium sulphate precipitate. For precipitation of strontium sulphate, however, a large excess of sulphate ions (more than 0.25 M) is preferable. Temperature is also an important factor in the procedure. Quantitative precipitation of barium sulphate at room temperature takes too long, while with boiling solutions, co- precipitation of strontium sulphate (in an equimolar solution) increases. A temperature of 50 to 60 "C is found to be a suitable compromise for barium sulphate precipitation.However, the precipitation of strontium sulphate requires the solution to be boiling. The ratio of strontium to barium is also very important in the precipitation of barium sulphate. The determination is possible in solutions containing a molar ratio of up to 1.0, or slightly greater (1.481) when the concentration of strontium oxide is not higher than 20.0 mg per 100 ml of solution (Table I). With increase in strontium-ion concentration, the co-precipitation of strontium sulphate also increased. TABLE I STEPWISE DETERMINATION OF BARIUM AND STRONTIUM IN THE PRESENCE OF CALCIUM (20 mg) AND MAGNESIUM (20 mg) SrO takenlmg 6 10 20 6 10 20 30 10 20 20 20 BaO takenlmg 10 10 10 20 20 20 20 40 40 60 80 Molar ratio, SrO : BaO 0.740 1.48 2.96 0.37 0.74 1.48 2-22 0-37 0-74 0.49 0.37 BaO found* /mg 10.02 10.02 Drifting of end-point 20.20 20.12 20.20 Drifting of end-point 40.02 40.10 69.68 79.73 SrO found*/mg 6.19 10.07 Drifting of end-point 6.14 10.07 20.10 Drifting of end-point 10.18 20-26 20.36 20-25 Difference ( BaO) Img + 0.02 + 0.02 - + 0.20 +0*12 + 0.20 + 0.02 + 0.02 - 0.32 - 0.27 Difference Fro) Img +O.lS + 0.07 + 0.14 + 0.07 +om10 +0*18 + 0.26 + 0.36 + 0.26 * Mean of three titrations.The metallochromic indicator Eriochrome black T is often used in the direct titration of barium and strontium with EDTA solution in the presence of calcium and magnesium at pH 10.0. However, the end-point, from red to blue, is not very sharp and is sometimes confusing. In an attempt to improve the end-point by producing a change from red to green, additions of yellow dyes such as methyl orange,s methyl y e l l o ~ , ~ , ~ Tropaeoline 009910 and methyl redl1-l3 have been reported.In the present work, we used Titan yellow in conjunction with Eriochrome black T and Naphthol green B and this mixed indicator gave a very sharp change from red to green in the titration of barium with EDTA solution. The end-point during the titration of excess of zinc with EDTA solution (procedure I) in the absence of absolute ethanol, however, reverted from green to pink within a few seconds, probably as a result of the greater solubility of strontium sulphate. The addition of 10 to292 SINHA AND ROY 15 ml of absolute ethanol so as to reduce the solubility of strontium sulphate was necessary in order to eliminate this effect.The stepwise determination of barium and strontium is possible in the presence of calcium, magnesium and lead. However, iron and manganese, even at a concentration of 1 p.p.m., affected the end-point by causing the colour of the indicator to fade. Copper, nickel and cobalt interfered by inactivating the indicator. In the presence of any of these interfering elements, the procedure for the stepwise determination of barium and strontium fails. Pro- cedure 11, in which the interferences due to iron (5-45 mg), aluminium (11.0 mg), titanium (2.0 mg), nickel (31.8 mg), cobalt (20-0 mg), manganese (9.0 mg) and copper (32.0 mg) were eliminated (see Table 11) by complexing with triethanolamine and potassium cyanide, and the iron and manganese complexes were subsequently reduced with ascorbic acid, was found to facilitate the determination of barium in the presence of these ions.Higher concentrations of aluminium caused co-precipitation of magnesium during the heating stage of the procedure. TABLE I1 DETERMINATION OF BARIUM IN THE PRESENCE OF VARIOUS CATIONS BaO taken = 20.0 mg Ion Added/mg BaO found*/mg Differcncelmg Sr 8.46 19.97 - 0.03 Fe 2.62 19.89 -0.11 Fe 5.24 20-04 + 0.04 A1 5.50 20.12 3-0.12 A1 22-00 21.10 + 1-10 Ti 0.30 20.04 + 0.04 Ti 1-50 20.20 + 0.20 M n 3.00 19.89 -0.11 Aln 8.95 20.04 + 0.04 Ni 12.59 20.20 + 0.20 Ni 31-80 20.20 + 0.20 c u 16.00 20.20 -t 0.20 c u 32.00 20.04 + 0.04 c o 20.00 20.04 + 0.04 *Mean of three titrations. Manganese, titanium and zirconium, when present in higher concentrations than those men- tioned above, were also precipitated during heating.In such instances, the removal of iron, aluminium, titanium and zirconium by precipitating them as hydroxideswitli ammonia solution was found to be satisfactory. Phosphate and chromate ions, even in small amounts, precipi- tated the alkaline earth elements and thus interfered in both procedures. Chromate could be removed as hydroxide together with R,O,-type elements after reduction with ethanol. Phosphate, when present, is required to be removed as zirconium phosphate. The authors thank Mr. K. D. Sharma, Director, Central Glass and Ceramic Research Institute, Calcutta, for permission to publish this paper, and Dr. S. Kumar for taking a keen interest in the work. 1. 2 . 3. 4. 5. 6. ~ 7. 8. 9. 10. 11. 12. 13. REFERENCES Welcher, F. J ., “The Analytical Uses of Ethylenediaminetetraacetic Acid,” 13. Van Nostrand West, T. S., “Complexometry with EDTA and Related Reagents,” Third Edition, BUEI Chemicals Manns, T. J., Reschovsky, M. U., and Certa, A. J., Analyt. Chent., 1952, 24, 908. Sijderius, I<., Analytica Chim. Acta, 1954, 10, 517. Belcher, R., Gibbons, D., and West, T. S., Chem. G. Ind., 1954, 127; Chem. Abstr., 1954, 48, 5730. Gordon, L., Salutsky, M. L., and Willard, H. H., “Precipitation from Homogeneous Solution,” Firsching, F. H., Analyt. Chem., 1961, 33, 1946. Gerlach, K., Angew. Chem., 1955, 67, 178; Chern. Abstr., 1955, 49, 7439. Brunisholz, G., Genton, M., and Plattner, E., Helv. Chim. Ada, 1953, 36, 782; Chew. Abstr., 1953, Ballczo, H., and Doppler, G., 2. analyt. Chem., 1956, 152, 321. Hol, P. J., and Leferink, G. H., Chem. Weekbl., 1953, 49, 733. Kimbel, K. H., Hoppe-Seyler’s 2. Physiol. Chem., 1953, 293, 273; Chem. Abstr., 1955, 49, 13346. Rehell, B., Scand. J . Clan. Lab. Invest., 1954, 6, 335; Chem. Abstr., 1955, 49, 9724. Received October 17th, 1972 Accepted November 29th, 1972 Company Inc., New York, 1961, p. 143. Ltd., Poole, Dorset, 1969, pp. 171 and 205. John Wiley & Sons, New York, and Chapman & Hall Ltd., London, 1959, p. 103. 47, 9208.

ISSN:0003-2654    

DOI:10.1039/AN9739800289

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, April, 1973, Vol. 98, $9. 293-296 293 Molecular Interaction Errors in Phase-solubility Analysis BY D. THORBURN BURNS, J. B. GALLAGHER, R. J. STRETTON AND J. S. WRAGG (Department of Chemistry, University of Technology, Loughborough, Leicestershire, LE11 3 T U) (Analytical Research, Quality Control, The Boots Company Ltd., Pennyfoot Street, Nottinglzam) Results are presented for the assay by phase-solubility analysis of ibufenac (4-isobutylphenylacetic acid) and of saccharin in the presence of various impurities. The results for impurities obtained for ibufenac mixtures were almost twice those expected, while those for saccharin mixtures were normal. From a consideration of these results, the effect of compound formation by molecular interaction is discussed. THE theoretical and practical aspects of phase-solubility analysis have been reviewed by Mader,l Higuchi and Connors2 and by Outch3 and its use has been suggested for purity determination.The technique has recently been applied by the National Bureau of Standards to the determination of the purity of cholesterol, urea and creatinine, which were to be used as clinical reference materials4 Only Higuchi and Connors, in discussing the limitations of the technique, emphasised that the solubility of each component must be unaffected by the presence of the other components although this aspect has been mentioned ez~rlier.~-s Wilkin- son and Wraggg obtained anomalous results by phase-solubility analysis for the impurity content of an insecticide (butacarb) when compared with those obtained by the use of gas - liquid chromatography, infrared spectroscopy and isotopc dilution analysis.They suggested that compound formation by interaction between components of a mixture was a serious limitation to the application of the procedure. To investigate further the possibilities of molecular-interaction compound formation and its effect on the results obtained, the anti-inflammatory, antirheumatic compound 4-isobutylphenylacetic acid (ibufenac) , and the artificial sweetener o-sulphobenzoic imide (saccharin), were chosen for- phase-solubility studies in model systems. EXPERIMENTAL AND KESULTS APPARATUS AND TECHNIQUE- The apparatus used was that described by Garratt, Johnson and Kinglo and the procedure was based on that outlined by Mader.ll Solvents were selected to give solubilities in the range 0.1 to 7.5 per cent., as suggested by Mader, and the results obtained were calculated by using the least-squares method.The compounds were examined by using various equili- bration times from 2 to 14 days. The marked scattering of points in the phase-solubility diagrams after equilibration for 2 days indicated that equilibrium conditions were not obtained in this period. However, results obtained after equilibration for 4 days were more consistent and were indistinguishable from those obtained by using longer equilibration periods. The reliability of the techniques used in this investigation was checked by using the insecticide (butacarb) previously examined in detail by Wilkinson and Wragg. Crude butacarb was purified by recrystallisation from light petroleum (boiling range 40 to 60 "C).A mixture containing 3,5-di-t-butylphenol (5 per cent. m/m) and purified butacarb (95 per cent. m/m) was prepared. This mixture and the purified butacarb were assayed by phase- solubility analysis by using n-hexane as solvent and an equilibration period of 7 days at 31 "C. Solution compositions were determined gravimetrically by evaporating off tlic solvent at room temperature under a stream of nitrogen and finally drying the residue to constant mass at 75 "C. The impurity content of the purified butacarb was found to be 0 per cent. [confidence limits (P = 0.95) & 0.14 per cent.] and that of the mixture 11.7 per cent. [confidence limits (P = 0-95) The latter result was rather more than twice the value expected in the absence of interaction, and was in agreement with results obtained by Wilkinson and Wragg.0.72 per cent.]. @ SAC and the authors.294 THORBURN BURNS et al. : MOLECULAR INTERACTION ERRORS [AIzalySt, VOl. 98 Phase-solubility determination of ibufenac-A commercial sample of ibufenac was purified by recrystallisation from light petroleum (boiling range 40 to 60 "C) and the resulting crystals were ground in a glass mortar. The drug formed a liquid phase when equilibrated with solvent mixtures of water and methanol or water and acetone, but remained crystalline and had the desired solubility in the non-polar solvents n-hexane, n-heptane, n-octane and 2,2,4-tri- methylpentane. Mixtures of known composition were prepared by adding known amounts of benzoic acid (impurity I), phenylacetic acid (impurity 11) and 2-(4-isobutylphenyl)propionic acid (ibuprofen) (impurity 111) to the purified ibufenac.Each of the added impurities was previously purified, impurity I by vacuum sublimation and I1 and I11 by recrystallisation from light petroleum (boiling range 40 to 60 "C). Homogeneity of the mixtures (Table I) was ensured by dissolving the weighed components in the minimum volume of methanol and evaporating the solution to dryness at 66 "C with the aid of a stream of oxygen-free nitrogen. The residues were dried to constant mass over silica gel under partial vacuum and then ground in a mortar. TABLE I COMPOSITION (PER CENT. m/m) OF PREPARED IBUFENAC MIXTURES No. 1 2 3 4 6 6 7 8 Recrystallised ibufenac Impurity I 90.0 10.0 96-0 6.0 98.0 2.0 96.0 - 98-0 - 96-0 - 98.0 - 90.0 7.0 Impurity I1 Impurity I11 - - - - - - 6.0 - 2.0 - - 6.0 - 2-0 3.0 - The purified ibufenac and each of the mixtures were assayed by phase-solubility analysis, with an equilibration temperature of 28 "C and an equilibration period of 4 days.To deter- mine the solution composition, the solvent was removed at 66 "C under a stream of oxygen- free nitrogen and the residue dried over silica gel under partial vacuum. The above procedure was used to assay a sample of commercial ibufenac in 2,2,4-tri- methylpentane and the recrystallised drug in n-hexane, n-heptane and n-octane. In order to test for solid-solution formation in the mixtures Nos. 2 to 7, the solid phases from tubes in the saturated segment of the phase diagrams were separated from the solution phases, washed with a small amount of pure solvent and dried.The solid phases were combined and then assayed by the phase-solubility method. The results for the phase-solubility analysis are summarised in Table 11. The confidence limits (P = 0.96) for the percentage impurity results were in the range &O-4 to h1.0 per cent. The solubility of pure ibufenac was found to be 39-4rngg-l. TABLE I1 RESULTS OF THE ASSAY OF IBUFENAC BY PHASE-SOLUBILITY ANALYSIS Sample Mixture 1 . . .. .. 2 .. .. .. 2 .. .. .. 3 .. .. .. 4 .. .. .. 6 .. .. .. 6 .. .. .. 7 .. .. .. 8 .. .. .. Recrystallised ibufenac . . Commercial ibufenac . . Solid phases . . .. Equilibration period/da ys 4 4 7 4 4 4 4 4 4 14 4 4 4 4 4 4 Impurity, per cent.m/m - Solvent Added Found 2,2,4-Trimethylpentane 10.0 26.9 6-0 12.3 6-0 11.6 2-0 6.3 6.0 16.6 2-0 3.1 6.0 14-5 2.0 3.3 10.0 22.6 0.4 0-3 0.8 0.3 0.6 3-7 0.1 - - n-Hexane - n-Octane - n-Hep tane - 2,2,4-Trimethylpentane -April, 19731 I N PHASE-SOLUBILITY ANALYSIS 295 Phase-solubility determination of sacckarin-Saccharin was purified by recrystallisation from methanol. Mixtures of known composition were prepared by adding known amounts of o-toluenesulphonamide (impurity IV) and $-sulphonamidobenzoic acid (impurity V), both of which had been previously purified by recrystallisation from water, to the purified saccharin. The procedures for phase-solubility analysis and preparation of mixtures were the same as those adopted with ibufenac except that all residues were dried to constant mass at 106 "C.Samples of recrystallised saccharin, commercial saccharin and the mixtures given in Table I11 were assayed by using as solvents acetone - chloroform (3 + 7 V/V) and pure chloroform; the equilibrium temperature was 34 "C and the period of equilibration was either 4 or 14 days. TABLE I11 COMPOSITION (PER CENT. mlm) OF PREPARED SACCHARIN MIXTURES A 90.0 10.0 - B 96-0 6.0 - C 96.0 - 6-0 D 90.0 7.0 3.0 Mixture Saccharin Impurity IV Impurity V To determine the solution composition, the solvent was removed by evaporation under a stream of oxygen-free nitrogen and the residue dried at 105 "C. The samples were also analysed by argentimetric titration based on the procedure of Parikh and Mukherji.13 The results for the phase-solubility analysis are summarised in Table IV. The confidence limits (P = 0.95) for the percentage impurity results were in the range k0.2 to k0.8 per cent.The solubility of pure saccharin was found to be 19.4 mg g-1. TABLE IV RESULTS OF THE ASSAY OF SACCHARIN BY PHASE-SOLUBILITY ANALYSIS Sample Equilibration period/days Solvent Mixture A . . .. .. 4 Acetone - chloroform (3 + 7) A .. .. .. 14 B .. * . .. 4 c .. .. .. 4 D .. .. .. 4 14 Commercial saccharin . . 4 Recrystallised saccharin . . 4 Percentage of total compounds other than saccharin h Phase- solubility Titration Added analysis method 10.0 10.4 8.8 10.0 10.4 - 6.0 5.4 6.9 6.0 4.3 2.2 10.0 9.7 8.3 - 0.02 0.8 - 0.06 - 1.8 1.3 - DISCUSSION AND CONCLUSIONS Phase-solubility analysis of ibufenac mixtures consistently gave impurity contents of approximately twice the expected values.This behaviour is similar to that which gave rise to the high results obtained by Wilkinson and Wraggg with butacarb. Of the possible sources of error, procedural errors, optical isomerism , solid-solution formation and unique ratio can be ruled out. Polymorphism has been suggested as an explanation for high assay results,l but, unlike the behaviour in the present instance, such a phenomenon would cause erratic results and could be overcome by increasing the period of equilibration. It is therefore likely that a soluble compound is formed between the major components and their chemically similar impurities. The interactions responsible for s*uch compound formation would not be covalent bonds but much weaker forces such as those due to van der Waals' interactions or to hydrogen bond- ing.Both the carboxylic acids of the ibufenac mixtures and the carbamate and phenolic species of the butacarb mixtures fulfil the requirements for weak electrostatic interaction, and it is therefore probable that hydrogen bonding is the most important type of interaction in these systems.296 THORBURN BURNS, GALLAGHER, STRETTON AND WRAGG For the ibufenac systems studied the situation is not clear; even if an error of 10 per cent. in the nominal composition of the mixture is accepted, the results do not conform to those anticipated for simple 1 : 1 compound formation. It is therefore probable that dispersive intermolecular forces, in addition to hydrogen bonding, are involved and that compound formation in these systems is the result of competition between several reactions.Such interactions are sensitive to the nature of the solvent, hydrogen bonding being favoured by non-polar solvents such as those used for the butacarb and ibufenac assays, while dispersive interaction is favoured when non-polar materials are dissolved in polar solvents. It can be seen that the criteria for low solubility in phase-solubility analysis will demand the use of such systems and the compound formation is likely to be a common occurrence. The inter- actions will be particularly apparent with several molecules the association of which is not hindered by structural factors. Phase-solubility analysis of saccharin mixtures in acetone - chloroform (3 + 7) gave results close to the expected values.The results obtained with chloroform alone as solvent were less satisfactory, possibly because the equilibration periods of up to 14 days were too short for equilibrium to be fully established. Use of the argentimetric method confirmed the results for mixtures containing o-toluenesulphonamide(1V) but gave low results for those mixtures which contained P-sulphonamidobenzoic acid (V), probably because of the formation of the silver salt of the latter. An explanation for the satisfactory analysis of saccharin mixtures can also be given on the basis of solvent effects. In the acetone - chloroform solvent the forces of solute - solvent, particularly of solute - acetone, interactions are presumably sufficiently strong to eliminate the possibility of solute - solute interactions.The related extraction - solubility procedure13 has recently been used14 to examine compounds of relatively high purity possessing a variety of functional groups, which were prepared as analytical standards. Several difficulties were noted, including those concerned with the choice of solvent, and, in particular, instances of unsatisfactory results when non-polar solvents were used. From the present results and those reported earlier,9 we conclude that non-polar solvents should be avoided when assaying substances that are prone to hydrogen bonding, and, further, that the results of any phase-solubility analysis should not be considered to be reliable unless recovery experiments on appropriate mixtures of known composition indicate the absence of complex formation by molecular interaction. The carboxyl group is a common feature of an appreciable number of therapeutically active substances, and, unless suitable precautions are taken, anomalous results might be expected to arise with some frequency as such substances are subjected to phase-solubility analysis.1. 2. 3. 4. 6. 6. 7. 8. 9. 10. 11. 12. 13. 14. REFERENCES Mader, W. J., Crit. Rev. Analyt. Chem., 1970, 1, 193. Higuchi, T., and Connors, K. A., “Advances in Analytical Chemistry and Instrumentation,” Outch, W. T., Australas. J . Pharm., 1961, 42, 1277. Meinke, W. W., Analyt. Chem., 1971, 43, May, 28A. Thorpe, D., J . Soc. Chem. Ind., 1946, 65, 414. Bennett, G. M., Analyst, 1948, 73, 191. Webb, T. J., Analyt. Chem., 1948, 20, 100. Willermain, M., Analytica Chim. Acta, 1949, 3, 206. Wilkinson, J. V., and Wragg, J. S., Analyst, 1966, 91, 600. Garratt, D. C., Johnson, C. A., and King, R. E., J. Pharm. Pharmac. Suppi., 1963, 15, 206T. Mader, W. J ., “Organic Analysis,” Interscience Publishers, New York and London, 1954, Volume 2, Parikh, P. M., and Mukherji, S. P., Analyst, 1960, 85, 26. Stenger, V. A., Gummett, W. B., and Kramer, W. R., Analyt. Chem., 1953, 25, 974. Hummel, R. A., and Gummett, W. B., Talanta, 1972, 19, 363. Interscience Publishers, New York, London and Sydney, 1966, Volume 4, p. 117. p. 263. Received April 27th, 1972 Accepted November 13th, 1972

ISSN:0003-2654    

DOI:10.1039/AN9739800293

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, April, 1973, Vol. 98, $$. 297-302 297 Analytical Methods Committee REPORT PREPARED BY THE FLUORINE SUB-COMMITTEE A Critical Examination of Procedures for the Assay of Sodium Fluoride THE Analytical Methods Committee has received the following Report from its Fluorine Sub-committee. The Report has been approved by the Analytical Methods Committee and its publication has been authorised by the Council. REPORT The constitution of the Sub-committee was: Dr. E. J. Newman* (Chairman since October, 1969), Mr. R. W. Fennell" (Chairman until October, 1969), Dr. A. W. Davison, Mr. J. K. Foreman, Mr. G. S. GOB,* Mr. R. J. Hall, Dr. R. F. Milton, Mr. J. W. Ogleby," Mr. B. T. Saunderson, Dr. J. M. Skinner* and Mr. C. A. Watson,* with Mr. P. W. Shallis as Secretary. The members marked with an asterisk took part in the work of the Milligram Group of the Sub-committee, which was responsible for the preparation of this Report.In addition, the following were corresponding members of the Sub-committee, although those marked with an asterisk took part in the early stages of the work : Professor R. Belcher, Mr. H. A. Foner," Mr. H. Green,* Mr. R. Waspe* and Dr. J. E. Whitley. INTRODUCTION The Milligram Group of the Fluorine Sub-committee set up by the Analytical Methods Committee in 1965 concentrated its efforts initially on trying to establish a suitable direct method for the assay of sodium fluoride. The main objective was that material thus charac- terised could then be used in work on methods that required calibration, such as titration with thorium nitrate, colorimetry or potentiometric measurement by means of the fluoride- selective electrode.A survey of the literature and the experiences of the members of the Sub-committee with various procedures indicated that the precipitation of lead chloro- fluoride, followed either by a final weighing or by a titration procedure, might prove to be satisfactory, although it was recognised from the outset that the procedure was lengthy and more open to operator errors than was ideally desirable. Finally, a favoured, although not entirely satisfactory, lead chlorofluoride precipitation procedure was compared with an indirect ion-exchange method. All the members of the Group had had some experience of at least one of the variants of the method described by Hoffman and Lunde1l.l After some preliminary trials, an agreed procedure was established and a collaborative trial undertaken.The results summarised in Table I were reported for both gravimetric determination, and, after the precipitate in the filter crucible had been dissolved in dilute nitric acid, for titrimetric determination. Common sources of solid sodium fluoride and of silver nitrate solution were used; each determination was made on a solution containing 25 mg of fluorine, as sodium fluoride. TABLE I FIRST COLLABORATIVE TRIAL-LEAD CHLOROFLUORIDE METHOD Gravimetric determination Mean recovery, Standard No. of Laboratory per cent. deviation results A r \ A 101.19 0.34 10 B 98-45 0.96 6 C 100.33 0.87 6 D 102.10 0.63 6 E 103.62 0-84 6 @ SAC. Titrimetric determination Mian recovery, Standard No.bf per cent.deviation results 101.21 0-61 10 98-08 0.82 5 100.06 0.91 6 101.50 0.60 6 104.39 3.79 6298 ANALYTICAL METHODS COMMITTEE A CRITICAL EXAMINATION OF [AWZlySt, VOl. 98 In view of the wide discrepancies between the results obtained in the different labora- tories, a detailed examination of the individual manipulative techniques used in each laboratory was made and the following aspects were noted- (i) different percentage mass losses were observed between laboratories and between different amounts of sample on drying the sodium fluoride; and (ii) some operators took the mass of lead chlorofluoride as the difference between the mass of the crucible plus precipitate and the original mass of the crucible, whereas others took the difference between the mass of the crucible plzcs precipitate and the final mass of the crucible, i.e., after the precipitate had been dissolved in nitric acid.Most, but not all, operators recorded a loss in mass of the crucible after the lead chlorofluoride precipitate had been dissolved in nitric acid. A second collaborative trial was carried out, for which the details of the procedure were more strictly laid down. Only the gravimetric technique was used, as the titrimetric procedure did not appear to offer any advantage. Again in each test a solution containing 26 mg of fluorine, as sodium fluoride, was used; the results are summarised in Table 11. TABLE I1 SECOND COLLABORATIVE TRIAL-LEAD CHLOROFLUORIDE METHOD Laboratory Mean recovery, per cent.Standard deviation No. of results A 101-30 0.48 6 B 97-96 1-06 4 C 101.62 0.19 6 D 103.06 0.34 6 F 99-23 0-32 6 These results are similar to those in Table I for laboratories A to D, although results for laboratories C and D both show an improved precision but a higher mean recovery than those obtained previously. The behaviour of the sodium fluoride on drying indicated that this particular batch was suspect, although not sufficiently variable to invalidate the general picture of the results obtained. In the procedure used so far the lead had been added to the fluoride-containing solution as solid lead nitrate. Other methods of precipitating lead chlorofluoride that might have offered advantages in terms of speed, accuracy and precision were available. In order to make a preliminary assessment of the merits of the various procedures, two analysts in one laboratory each carried out six determinations by the five methods listed below.I Gravimetric, solid lead nitrate. I1 I11 Gravimetric, lead chloronitrate solution.2 IV Gravimetric, lead acetate solution.s V Gravimetric, lead chloride solution.* Titrimetric, solid lead nitrate; precipitate filtered on to, and then dissolved from, a paper-pulp pad instead of a filter crucible. A common stock fluoride solution was used by the analysts who took part in this work and for each determination a solution containing 25 mg of fluorine, as sodium fluoride, was used. The results obtained are shown in Table 111, from which it can be seen that no single method is outstandingly better than the others, although method IV is significantly inferior in terms of precision.The percentage recovery figures are for comparison only; the TABLE I11 FIRST COMPARISON OF METHODS FOR FLUORIDE DETERMINATION Analyst 1 r Mean recovery, Standard Method per cent. deviation I 101.46 0.79 I1 101.08 0.61 111 98.63 0.50 IV 101.26 1-78 V 98.19 0.62 Analyst 2 & Mean recovery, Standard per cent. deviation 100.66 0.84 99-93 0.74 98.13 0-78 100.72 0.93 98-59 0.78 Grand mean, per cent. 101*00 100.43 98-33 100.99 98.47 Pooled standard deviation 0.81 0.68 0.66 1.41 0.66April, 19731 PROCEDURES FOR THE ASSAY OF SODIUM FLUORIDE 299 purity of the sodium fluoride used to make up the stock solution was not known although it was believed to be high. As no definite conclusion could be reached from this test, a standardised solution of sodium fluoride was circulated, and members of the Group were requested to determine its fluoride content by as many of the above methods as they could apply and also by a method based on the indirect ion-exchange method used for the assay of commercial sodium fluoride.5 For the lead chlorofluoride procedure, each determination was carried out on a solution containing 25 mg of fluorine, as sodium fluoride, and for the ion-exchange method solutions containing 50 mg of fluorine, as sodium fluoride, were used except in laboratory A, which used solutions containing 40 mg of fluorine.The results obtained are summarised in Table IV. TABLE IV SECOND COMPARISON OF METHODS FOR FLUORIDE DETERMINATION Method .. I Laboratory A B C D E F G Method . . Laboratory A B C n E F G r a 101.35 101.23 99.60 98-06 101-45 98.43 99.67 - 7 a - - - b 0.34 0.73 0.21 0.68 0-48* 0.16 0.68 IV b - )r - - - I1 P a b c V P a b c - - 100.33 0.12 6 - - I11 - a b t 98.27 0*03* 2 - - - Ion exchange m 99-68 100.16 98.31 100*16 100~00 100.34 - - 0.09 4 0.07 6 0.27 6 0.05 4 o-oo* 2 0.23 6 - - - - a represents mean recovery, per cent.; b, standard deviation; and c, number of results, * Range. Despite the heterogeneity of the results in Tables I11 and IV, it was possible to derive (i) method IV could be discounted on grounds of poor precision; (ii) better precision could be expected with the ion-exchange method than with any (iii) there was a strong indication that the ion-exchange method was without bias; and (iv) although a negative bias could be expected, method I11 might have better precision than method I, which tended to have a positive bias.Those members of the Group who had tried method I11 agreed that the procedure was simpler than those for methods I, I1 or V. A collaborative trial was arranged in which three determinations by both method I11 and the ion-exchange method were made on three separate days, when possible by two analysts. Four laboratories were able to complete the full pro- gramme, a fifth could spare only one analyst. The full results, given as percentage recovery, are shown in Table V. A new common supply of sodium fluoride, shown not to have variable characteristics on drying, was used for these tests. The amounts of fluoride taken for deter- mination were as before, i.e., 25 mg for method I11 and 50 mg for the ion-exchange procedure, except for laboratory A in which 40 mg were taken.An analysis of variance was applied to the results, starting with those reported by individual laboratories. Highly significant differences between the two methods were found for each laboratory, and significant differences between analysts occurred at some labora- tories for method 111. Variations from day to day were much larger than would be expected some general conclusions- of the other methods tried;300 ANALYTICAL METHODS COMMITTEE : A CRITICAL EXAMINATION OF [Analyst, Vol. 98 TABLE V COLLABORATIVE TRIAL-LEAD CHLORONITRATE (METHOD 111) AND Results are percentage recoveries ION-EXCHANGE METHODS Laboratory Day A 1 2 3 C D F 1 2 3 1 2 3 1 2 3 G 1 2 3 Method I11 1 Analyst I Analyst I1 98.27 08-03 98-08 97.82 98-50 97.92 98.45 98-08 98.59 97.83 98.27 97.99 98-55 98-54 98.50 98.52 98.49 98.54 98.74 99.00 98.76 98.75 99.08 98.97 98.70 99.05 99-38 98.99 99.1 1 98.95 99.67 99-45 99-43 99.32 99.32 99-40 99.07 - 99-32 - 100-04 - 100.67 - 100.77 - 100.86 - 99.33 - 99.7 1 - 99-38 - 99.58 99.52 99.42 99-52 99.44 99.44 99.42 99.90 99-22 99.30 99-30 98.99 99-38 99.06 99-44 99-10 99.56 98.92 96-33 97.86 96.75 98-58 96.80 96.96 97.75 97.38 97-35 97.1 6 96.33 97.1 2 95.80 98.33 96-40 98.21 95.1 3 98.55 Ion exchange Akalyst I 99-61 99-66 99-52 99-68 99.48 99-39 99.48 99.44 99.48 100.40 100.21 100.40 100.02 100-02 100.02 99-83 99-83 100.02 - - - - - - - - - Analysi I1 99-48 99.62 99.57 90.47 99.56 99-52 99.56 99.47 99.66 100.21 100.2 1 100.02 100-2 1 100.02 100.02 99-83 100.02 99-83 99-52 99-45 90.63 99.8 1 9!,.99 99.45 99.63 99.99 100.17 All results 99.7 to 99.8.90.88 100.26 100.26 100.64 100.26 100.08 100.26 100.64 100.46 100.20 100.26 100.26 100.26 100.46 100.08 100.26 99.88 100.46 * Results rounded to 0-05 ml of titrant. from variability within sets of three readings. However, these day-to-day variations did not affect the two methods in the same way; a high result by the gravimetric procedure could occur with a low result by the ion-exchange method. Results, expressed as standard deviations in percentage recovery, were- The methods were then examined separately over all laboratories. Method I11 Ion exchange Between laboratories .. .. .. .. 0.94 0.33 Between analysts in a laboratory . . .. 0.4 1 -+ Between days for one analyst .. .. 0-35 0.08 Within sets of readings .. .. . . 0.31 0.13 ID Only three sets of results were available.April, 19731 PROCEDURES FOR THE ASSAY OF SODIUM FLUORIDE 301 It is apparent that, as might be expected, laboratory variability is a dominant factor. That this variability is not caused by the common source of sodium fluoride that was used in each laboratory for making up the solutions is illustrated in Table VI, which is a summary of the results given in Table V. It can be seen, for example, that low results by method I11 do not coincide with low results by the ion-exchange method. It can also be seen that the ion- exchange method is substantially without bias, whereas the gravimetric method I11 has a negative bias of at least 1 per cent.CONCLUSIONS None of the methods tried was entirely satisfactory as an assay (or referee) method for sodium fluoride. The ion-exchange procedure provided the nearest approach on grounds of both accuracy and precision. It has, however, the following dkadvantages- (i) it provides a measure of the total anions present in the solution under test and is therefore completely unspecific ; (ii) it depends on the accurate standardisation of the alkaline titrant; and (iii) it depends on the efficient functioning of the ion-exchange resin column. On the other hand, it is simpler to manipulate and considerably more rapid than any of the precipitation procedures. Laboratory A C D F G Analyst I I1 I I1 I I1 I I1 I I1 TABLE VI SUMMARY OF RESULTS IN TABLE V Method I11 Ion-exchange method 1 Mean P Mean recovery, recovery per cent.Standard deviation per cent. Standard deviation 98.41 0.17 99-62 0.09 98.14 0.31 99.63 0.06 99.13 0.36 100.1 1 0.2 1 99-10 0.24 100-06 0.16 99.91 0.70 - - - - 99.74 0.26 99.42 0.1 1 99.7, - 99.31 0.32 99.76 96-62 0.78 100.30 0.26 97.79 0.69 100.24 0.18 The collaborative work on lead chlorofluoride precipitation confirmed the impression held in individual laboratories that the method was subject to operator variability, whichever particular procedure was used. The most complete trial of a precipitation procedure was that reported last, wherein lead chloronitrate was used as precipitant (method 111), the results of which are summarised in Table VI.The variability in the results, both means and standard deviations, achieved by different analysts is clearly demonstrated. It is of interest to note the consistency between the pairs of means obtained by the analysts in laboratories A, C and F, although the laboratory means vary by about 1 per cent. Another interesting feature, illustrating the variability possible between operators in the same labora- tory, is given by laboratory G’s results for method I11 in Tables IV and VI; the results in Table IV are much more in line with those of the other laboratories reported in Table VI, where laboratory G’s results can be seen to be outstandingly poor. Laboratory A, on the other hand, reported remarkably consistent mean results on different occasions for this procedure (see Tables 111, IV and VI) , although these were lower than those reported by most other analysts. Similar observations can be made on the earlier work on the “lead nitrate” (method I) procedure although the figures obtained were much more variable.It can be concluded, therefore, that although the lead chloronitrate precipitation pro- cedure is not suitable as a referee method, it can give reasonably consistent results under302 ANALYTICAL METHODS COMMITTEE conditions that apply in a given laboratory and is to be preferred to the other procedures tried. The following disadvantages are noted- (i) a negative bias can be expected; (ii) the method is significantly less precise than the ion-exchange method; and (iii) the procedure requires manipulative skill and is lengthy, requiring a period of Anionic interference is, however, less than that for the ion-exchange method, the analytical standing overnight for precipitation. factor is good and the method is direct, i.e., the fluorine being determined is precipitated. REFERENCES 1. 2. 3. 4. 5. Hoffman, J. I., and Lundell, G. E. F., J . Res. Natn. Bur. Stand., 1929, 3, 581. Belcher, R., and Macdonald, A. M. G., Mikrochirn. Ada, 1957, 610. Hawley, F. G., Ind. Engng Chem., 1926, 18, 573. Belcher, R., and Tatlow, J. C., Analyst, 1951, 76, 593. “ ‘AnalaR Standards for Laboratory Chemicals,” Fifth Edition, British Drug Houses Ltd. and Hopkin & Williams Ltd., 1957, p. 389.

ISSN:0003-2654    

DOI:10.1039/AN9739800297

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

AInalyst, April, 1973. Book Reviews 303 STATISTICAL METHODS IN RESEARCH AND PRODUCTION WITH SPECIAL REFERENCE TO THE CHEMICAL INDUSTRY. Edited by OWEN L. DAVIES and PETER L. GOLDSMITH. Fourth Revised Edition. Pp. xiv + 478. Edinburgh: Oliver and Boyd for Imperial Chemical Industries Limited. 1972. Price ltj5. The title of this book makes it clear that it is about the application of statistics to problems of research and production, and this must be borne in mind by the analyst who is wondering if he should buy it. For those for whom it is intended, it is an excellent exposition-logically set out, lucidly explained and with a wealth of practical examples that are fully worked out and based on 1.C.1.’~ actual experience. The last (third) edition was published in 1957. The changes that have taken place since then have led to the production of a completely revised text, only two of the contributors to the new edition being contributors to the previous one.Attention is drawn in the introduction to the implications of the availability of computers, and the consequent reduction in use of desk calculating machines. This is illustrated later in the chapter on Multiple Regression, in which techniques of much practical use are described that could not practicably be used a t all without the aid of a computer. Although the chapter headings and general arrangement of the new edition remain almost the same as in the last edition, which makes it easy for anyone familiar with the latter to use the former, every chapter appears to have been completely re-written.The analyst engaged on quality control will be interested in the extension of Chapter 10, “Control Charts,” to include the recently devised “Cusum” charts, by means of which undesirable trends can be detected sooner than with conventional Shewhart charts. The chapter on decision-making has been completely re-written; it is very well done and should be most useful at management level, although perhaps not to the analyst who only provides the data on which the decisions will be based. But the analyst in question will find the first few chapters of this book a first-class description of standard statistical techniques, many of which may be of direct service to him in increasing the productivity of his department; and he would be well advised a t least to skim through the later chapters also if he aspires to be, some day, the man a t the aforesaid management level.ERIC C. WOOD PARTICLE MEASUREMENT, SIZE AND SURFACE AREA DETERMINATION. BIBLIOGRAPHY 1969-1972. Published by the author a t the University of Bradford. This book is a very worthwhile compilation. It comprises a literature survey for the period 1969 to 1972 and contains 1132 references. The survey review of recent publications on particle size and surface area determination is pertinent and sensibly arranged. The index to this survey provides a short cut to the original literature. The arrangement of the references cannot be faulted. The book is well produced and it is to be hoped that it can be made generally available. At present, this and other similar publications are available by direct application to the authors, at the Postgraduate School of Studies in Powder Technology, the University of Bradford.This book shows commendable initiative on the part of the staff a t Bradford and they should be congratulated on their moves in this direction. By T. ALLEN. Pp. vi + 34. 1972. Price L2. D. DOLLIMORE ANALYTICAL APPLICATIONS OF EDTA AND RELATED COMPOUNDS. By R. PKIBIL. International Series of Monographs in Analytical Chemistry, Volume 52. Pp. xxii + 368. Oxford, New York, Toronto, Sydney and Braunschweig : Pergamon Press. The formation of complexes in aqueous solution is of great importance in analytical chemistry and EDTA and its derivatives provide some of the most efficient chelating agents available for these reactions.Dr. Pi.ibil is a well known authority on the reactions of these compounds and his extensive published work and stimulating lectures clearly demonstrate his mastery of their mode of action and ingenuity in their application. When confronted with a new monograph by this author, therefore, the reader is assured that the work will contain a wealth of material that will be of immediate practical value. The monograph is divided into two sections. Part I takes the form of two chapters that make up a theoretical introduction. The first of these, written by 1972. Price Ll2.60.304 BOOK REVIEWS [Analyst, Vol. 98 Prof. R. Belcher and Dr. A. Townshend, describes the development of EDTA as an analytical reagent. The second chapter, written by Prof.J. Koryta, contains an excellent brief account of the nature of the equilibria of complexes and methods of study. Part I1 commences with Chapter 3 and is devoted to the reactions of classical gravimetric analysis, titrimetric analysis, colorimetry and other instrumental techniques. The monograph is thus concerned only with the “passive” rdle of EDTA and other complexans, i.e., their screening or masking properties. The author states clearly that he considers the “active” r81e of EDTA to be in its use as a reagent in complexometric titrations, and that the latter is not included in the book as it forms an independent sector of analytical chemistry. The text contains a vast amount of information on the “passive” applica- tions of the complexans; the use of some of the metallochromic indicators] such as those derived from the triphenylmethane dyestuffs, is also considered in relation to colorimetry in Chapter 5 .This volume is a translation of an entirely new Czech manuscript, except for Chapter 2, which is essentially a translation of Prof. Koryta’s contribution to the 1957 Czech edition, and is stated to have little in common with the Czech editions published in 1953 and 1957 as regards extent or concept of the whole subject. It is authoritative, well balanced and clearly written and illus- trated; despite its relatively high price, it should be extremely valuable to all workers concerned with wet-chemical procedures for the separation and determination of inorganic species in solution. G. F. KIRKBRIGHT COURS DE CHIMIE ANALYTIQUE GI~NBRALE.Tome 11. MBTHODES ~LECTROCHIMIQUES ET ABSORPTIOMBTRIQUES, CHROMATOGRAPHIE. By GASTON CHARLOT. Pp. iv + 201. Paris: Masson et Cie. 1971. Price FF41. This book is the second of the volumes written by the author especially for students in the “Licence et MaPtrise des Sciences” course in analytical chemistry in Universities and Colleges of Technology in France. As these courses correspond approximately to the B.Sc. and M.Sc. degree courses in some U.K. universities, it is perhaps timely to consider what is thought to be appropriate for these levels by a well known advocate of analytical chemistry. There may be some desire to have closer academic relations between the universities and colleges in the countries of the E.E.C. and it is probable that we may have some transfer of professional analysts within multi- national industries.A knowledge of what is recommended for these courses may be useful. The first volume dealt with reactions in aqueous and non-aqueous solutions. This small volume is concerned with the basic theory of electrochemical reactions and their applications in analytical chemistry, as well as separation methods, including chromatography. The application of optical methods, such as absorptiometry, to photometric titrimetry is also considered. There is also a chapter dealing with accuracy and precision. The aim is reasonable but the range of subjects covered in 200 pages is so wide that much of the treatment is of necessity very superficial. The level of the work would not be accepted at the Finals level for a first degree in the U.K. It is not detailed enough in its practical aspects for L.R.I.C. courses in Colleges of Technology. As a revision text-book it is quite acceptable, and as a book for students of chemistry who do not specialise in analytical chemistry it gives a good coverage of the subject; a translation would certainly prove of value to many undergraduates in the U.K. L. S. BARK

ISSN:0003-2654    

DOI:10.1039/AN9739800303

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

304 BOOK REVIEWS Errata JULY (1972) ISSUE, p. 533, line 47. For “0-05-pCi” read “0.5-pCi.” IBID., p. 533, line 48. For “2 x IBID., p. 534, line 26. For “10 pCi” read “100 pCi.” IBID., p. 634, line 27‘. F o r “10 pCi g-l” read “10 Ci g-l.” mrad h-l” read “0.2 mrad h-l.” [Analyst, Vol. 98

ISSN:0003-2654    

DOI:10.1039/AN9739800304

出版商:RSC    

年代:1973

数据来源: RSC