February, 19611 SMYTHE AND WHITTEM 83 Analytical Chemistry of Beryllium A Review* BY L. E. SMYTHE AND R. N. WHITTEM (A4 ustrailian Atomic Energy Commission Research Establishment, Sydney, New South Wnles, Azsstmlia) SUMMARY OF CONTENTS Introduction Materials requiring chemical analysis General chemical and radiochemical methods Gravimetric Volumetric Colorimetric and fluorimetric Ion exchange Solvent extraction Chromatographic Polarographic Radiochemical Determination of impurities in beryllium Spectrometric methods Emission X-ray Mass spectrometry BEFORE 1939, the analytical chemistry of beryllium dealt mainly with the analysis of beryilium ores, a limited number of beryllium compounds and a few useful alloys with such metals as aluminium (introduced in 1918) and copper (introduced in 1926).During the past 20 years new uses have been found for beryllium in the electrical, chemical and metal industries and, more recently, in the field of atomic energy. The increasing use of beryllium and its com- pounds led to the recognition, in the early 1940’s, of beryllium disease causing respiratory illness and certain kinds of skin reactions. Investigations of this disease and the control of occupational levels of beryllium required the development of methods for detecting small traces of beryllium in a variety of materials (see Table I). Accurate analytical methods were also required for the whole range of macro to micro amounts of beryllium. Although a Russian1 review was published in 1957 and a specialised review2 in 1958, many papers have appeared in the literature during the past 3 years.This review is presented to assist analytical chemists with a coverage of the more recent methods. MATERIALS REQUIRING CHEMICAL ANALYSIS Materials that may require examination are listed in Table I. GENERAL CHEMICAL AND RADIOCHEMICAL METHODS General chemical and radiochemical methods for determining beryllium may be con- veniently grouped under nine headings. This grouping, although convenient for review purposes, is not rigid, since an analytical procedure might involve a combination of methods. GRAVIMETRIC- Gravimetric procedures for determining beryllium are based on the formation of com- pounds insoluble under certain conditions ; some of the more “insoluble” beryllium compounds are listed in Table 11.It should be noted that the exact compositions of many of the compounds listed in Table I1 are unknown and that this is a limitation to their use in accurate gravimetric methods. The literature of beryllium is overburdened with compounds that have been assigned formulae simply from the chemical analysis of the solid phases-mixed crystals, residues from evaporation or indefinite gummy precipitates obtained under various con- dition~.~ For example, the halides of beryllium are hydrolysed by water, and, by careful * Reprints of this paper will be available shortly. For details, please see p. 142.84 SMYTHE AND WHITTEM: ANALYTICAL CHEMISTRY TABLE: I BERYLLIUM-CONTAINING MATERIALS [Vol. 86 Material Beryllium ores (generally 3BeO.A1,0,.6SiO,) Beryllium metal (commercial or high- purity powder, flake or fabricated) Beryllium oxide and hydroxide Beryllium alloys Beryllium compounds (carbide, sulphate, Air Water (or effluent) Filter-paper smears or swabs Biological materials Soils Miscellaneous (e.g., filter elements) halides, organo-metallic, etc.) r Constituents determined Be, Al, $3, K, Na, Fe, Ni, Li, Mg, Cr, Mn, Ca, etc.MetaZs--.Al, Fe, Si, Ca, Mg, Cu, Mn, Cr, Ni, Cd, B, lanthan- Non-mettzZs---O, H, N, C, halogens, He, 3H, etc. As for beryllium metal As for beryllium metal, but larger amounts of alloying Mainly major constituents, e.g., carbide, sulphate, halogen, ides, etc. elements such as Th, U, Pu, etc. etc. Traces of Be or Be compounds NoTE-Eeryllium metal, alloys or compounds Will Contain active constituents after irradiation in high-flux materials-testing reactors.Radiochemical analysis is necessary in such instances. manipulation of the evaporation residues, products of almost any degree of basicity can be prepared. It follows that many compounds of beryllium cannot be prepared by methods involving the use of aqueous solutions. Owing to lack of many insoluble beryllium compounds of definite composition, the most common and reliable method for determining beryllium gravimetrically involves precipitation of beryllium hydroxide and subsequent ignition to the o ~ i d e . ~ s ~ ~ ~ ~ ~ The method is com- paratively straightforward, although appropriate health precautions should be taken with ignited beryllium oxide.' Because of the colloidal nature of beryllium hydroxide, the results of gravimetric determinations are likely to be high, owing to adsorption and occlusion of impurity elements and compounds.Special precipitation procedures are used involving precipitation of beryllium hydroxide from near-neutral solution. Appropriate separation procedures are required in the presence of aluminium, silica, the hydrogen sulphide group, iron, titanium, zirconium, lanthanides, chromium, tungsten, vanadium and thorium. TABLE :[I INSOLUBLE BERYLLIUM COMPOUNDS Compound Notes Beryllium hydroxide, Be(OH),* Beryllium oxide, hydrate, BeO.xH,O* Beryllium oxide, Be0 Beryllium sulphate, BeSO, Sodium fluoroberyllate, Na,BeF,* Potassium fluoroberyllate, K,BeF,* Barium fluoroberyllate, BaBeF,* Beryllium carbonate, basic, [BeCO, + Be(O:H),j * Beryllium ammonium phosphate, BeNH,PO,* Beryllium - cobalt complex, [ (H,O),Be,(CO,),(OH),] Beryllium acetate, Be(C,H,O,),* Beryllium acetylacetonate, Be(C5H,0,), Beryllium - tannin complex* Beryllium - quinaldine complex Beryllium - oxine complex Beryllium - naphthaldehyde complex Beryllium - mercaptobenzothiazole complex Beryllium stearate, Be(C,,H,,O,), Amorphous powder or gel Decomposes on heating giving Be0 Stable to above 2000" C Hydrate (.4H,O) is soluble No normal carbonate [Co(NH,),] .3H,O* * Exact composition unknown.Other gravimetric methods based on the isolation of insoluble beryllium compounds of rather indefinite composition (see Table 11) require close control and careful assessment of interfering elements. These methods include isolation of beryllium as the beryllium - cobalt- ammine complex,8 ,9 barium fluoroberyllate,1° ,l1 beryllium mercaptobenzothiazole,l2 berylliumFebruary, 19611 OF BERYLLIUM.A REVIEW 85 naphthaldehyde,13 ammonium beryllium phosphate,14 the beryllium - tannin complex4 or as its complexes with benzylamine, triethanolamine or oxine.15 Gravimetric methods are suitable for determining milligram to gram amounts of beryl- lium. With careful control the precision and accuracy are to approximately 0.1 to 1 per cent. VOLUMETRIC- Unfortunately there are few specific reactions that can be used for the volumetric deter- mination of beryllium. A reliable volumetric procedure suitable for microgram to milligram amounts of beryllium would be invaluable. One volumetric method for b e r y l l i ~ m ~ ~ ~ 6 ~ ~ 7 is based on formation of the extremely stable complex BeF42-.If an excess of alkali fluoride (e.g., potassium or sodium fluoride) is added to a suspension of beryllium hydroxide, the reaction proceeds almost quantitatively in accordance with the equation- Be(OH), + 4F- -+ BeF42- + 20H- The free base liberated is proportional to the beryllium present and can be titrated with standard hydrochloric acid. However, it should be noted that, because the reaction is not strictly stoicheiometric, it is necessary to use an empirically determined titre for beryllium for the standard hydrochloric acid. Another volumetric method is that in which quinalizarin is used to detect the end- point.4 Iron interferes in this method and is removed by reducing the mixture with hydrogen and selectively dissolving the iron in hydrochloric acid.The quinalizarin reagent is used in a colour-comparison test in the presence of sodium hydroxide. Several modifications of this method have been described, and it is said to be suitable for amounts of beryllium in the microgram to milligram range. Other volumetric methods for beryllium include the salicylate - fluoride method,l* 8-hydroxyquinaldine with a volumetric finish,lg indirect complexometric titration of beryllium with ethylenediaminetetra-acetic acid (EDTA),20y21 potassium iodate - sodium thiosulphate hydrolysis method,22 titration of beryllium oxine with potassium b r ~ m a t e ~ ~ and bismuth oxychloride t i t r a t i ~ n . ~ ~ Volumetric methods for determining beryllium are possibly the least satisfactory of the chemical methods and their reliability under various conditions cannot be stated with any certainty .COLORIMETRIC AND FLUORIMETRIC- Several reliable colorimetric and fluorimetric methods are available for beryllium. Most of these are suited to determining microgram to low milligram amounts of beryllium. For example, a fluorimetric method for determining beryllium in which morin (2‘,4’,3,5,7- pentahydroxyflavone) reagent is used is said to have a detection limit of 0.004 pg and is precise to 0.8 per cent. on 0.2 pg at the 95 per cent. confidence The procedure and precautions to be observed to achieve this precision ( e g . , control of temperature, concentra- tions of morin, sodium hydroxide, salts, etc.) are rather time-consuming. However, with simple fl uorimetric equipment and without any special precautions, measurements can easily be made at levels down to 0.1 pg.Although good colorimetric methods for beryllium are also available, fluorimetric methods appear to have greater sensitivity and are more suitable for the microgram range. The colorimetric methods involve use of adsorption indicators or formation of suit able stoicheiometric complexes. Fluorimetric methods reported in the literature include morin preceded by selective electrolysis26 or selective e ~ t r a c t i o n , ~ ~ 8-hydroxyquinaldine and successive extraction with final fluorimetric determinati0n,~8,~~ quinizarin (1,4-dihydroxyanthraquinone) ,30 l-amino-4- hydroxyanthraq~inone~~ and a rapid routine method for determining sub-microgram and microgram amounts of beryllium in filter-~aper.~~ Colorimetric methods involve use of chrome azurol S,32 s33 8-hydroxyq~inaldine,~~ Erio- chrome cyanine R,34 aluminon (ammonium aurintricarboxylate) ,36 936 chrome blue K (also known as mordant blue 31 or 4-sulpho-2-hydroxyphenylazo-l,8-dihydroxynaphthalene-3,6- disulphonic acid) ,37 gossypin (a glycoside of the flavanol gossypetin) ,38 neothorin (arsenazo),39 thoron [ l-(o-arsonophenylazo)-2-naphthol-3,6-d.isulphonic acid] ,40 s 4 1 alberon (Solochrome brilliant blue B) ,a miscellaneous hydroxyq~inones,~~ salicylic acid,43 beryllon I1 [S-hydroxy- naphthalene-3’, 6‘-disulphonic acid-( l-azo-2’)-1’, S’-dihydroxynaphthalene-3‘, 6’-disulphonic acid, di- or tetra-sodium salt] ,14944,46 quinalizarin (1,2,5,8--tetrahydroxyanthraquinone) ,4*%86 SMYTHE AND WHITTEM : ANALYTICAL CHEMISTRY [Vol.86 hapthazarin (5,6-dihydroxy- 1,4-naphthaquinone) ,47 4- (9-nitrophenylazo) -0rcinol,~8 zenia (9-nitrobenzeneazo-orcinol) ,49 curcumin (diferuloylmethane) ,4 y50 molybdophosphoric acid,51 Naphthochrome green G,52 Naphthochrome azurine 2B,53 quini~arin,~~ 954 5-sulphosalicylic acid,55 l-amino-4-hydroxyanthraquinone30 and acetyla~etone.~~ Generally, the choice of reagent is governed by the material to be analysed and the interfering elements. Masking agents, solvent extraction, ion exchange, chromatography and electrochemical separation have all been used in conjunction with a colorimetric finish. Currently available colorimetric methods are not generally applicable in the sub-microgram range, and the lower limit for normal spectrophotometric precision is approximately 10 pg, with an upper limit in the milligram range.A wide choice of colorimetric reagents for beryllium is therefore available. ION EXCHANGE- Ion exchange has not been extensively used in the determination of microgram amounts of beryllium. Some promising methods have recently been reported, and it is likely that ion-exchange methods will receive more attention. The new ion-exchange chelating resins containing such groups as iminodiacetate, e.g., Dowex A1 chelating resin (The Dow Chemical Co., Midland, Michigan, U.S.A.), or the sodium. diallgl phosphate complexing resins57 may prove promising as the basis of new analytical procedures. The ion-exchange separation of beryllium with salicylate analogues has been studied by Schubert, Lindenbaum and Westfal158 and might also form the basis of an analytical procedure.It was shown that beryllium can be selectively eluted from a cation-exchange resin with sulphosalicylic acid (0.02 to 0.1 M) at pH 3.5 to 4.5. The ions Cu2+, UO,2+ and Ca2+ are not removed under these conditions; however, at pH 4.5 to 4.7 the ion U022+ is eluted. At pH values above 6 in the presence of sulphosalicylic acid, beryllium is strongly adsorbed by an anion-exchange resin. The separa- tion of milligram amounts of beryllium can be carried out on a cross-linked polystyrene cation- exchange resin, such as Amberlite IR-112 or Zeo-Karb 225, in the presence of a complexing agent. 59 When a buffer solution (pH 3-5 to 5.0) containing beryllium, aluminium, chromium, titanium and a slight excess of EDTA is passed thxough the resin in the ammonium form, only beryllium is adsorbed.The beryllium can be eluted with ammonium chloride solution and determined by a suitable method. Belyavskaya. and Fadeeva developed a method60 for the quantitative separation of beryllium from copper and nickel; they used SBS cation-exchange resin in the ammonium form. The separation was carried out in amrnoniacal medium (con- taining ammonium carbonate) at pH 8.5 to 9.0 atnd subsequent elution was with ammonium carbonate solution; full details were not available to us. Another method for determining milligram amounts of beryllium in beryl was described by Nadkarni, Varde and AthavaleGI; beryllium was separated from iron, aluminium and titanium by ion exchange.After fusion with sodium fluoride, digestion with sulphuric acid and addition of EDTA, the solution at pH 3-5 was passed through a cation-exchange resin (Amberlite IRA-120 or Zeo-Karb 225) in the sodium form. Beryllium was retained and the iron and aluminium complexes passed through. The beryllium was then eluted and determined gravimetrically, as BeO. Ion exchange has been used for the concentration of beryllium from sea water.56 Only 10ml of Dowex 50-X8 resin (200 to 400 mesh) converted to the ferric form and hydrolysed with ammonia were required for 50 litres of sea water. The standard deviation of results by ion-exchange methods for beryllium in the milligram range appears to be about 5 per cent., and these methods cannot as yet be recommended for sub-microgram amounts of beryllium.SOLVENT EXTRACTION- Only a limited number of different solvent-extraction systems have been used in the determination of beryllium. Extraction systems based on chelate formation appear to be the most promising for analytical purposes. Six-membered ring systems including beta-diketones and hydroxycarbonyls have proved valuable. Little work, however, has been carried out on analytical ion-association extraction systems in which beryllium may be contained in the cationic or anionic member of the ion pair. Analytical methods based on the solvent extraction of beryllium as acetylacetonate have received the most attention.62 to 68 The method has been applied to metallurgical analysis,65 to radiochemical analysis6* and in conjunction with masking agents.es ss9 MostFebruary, 19611 OF BERYLLIUM.A REVIEW 87 finishes after this extraction are colorimetric. Other solvent-extraction methods for deter- mining beryllium include a fluorimetric method involving semi-micro purification of the beryllium solution by extraction with ethyl acetate and diethyldithi~carbamate~~; sodium hydroxide and sodium ~ u l p h i d e ~ ~ ; 8-hydroxyquinaldine and chloroform70 ; separation as basic acetate and extraction with chl~roform~~ ; extraction with thenoyltrifl~oroacetone.~~~~~ Solvent-extraction methods for beryllium are applicable from microgram to macro amounts. Under carefully controlled conditions recoveries of 95 per cent. and higher can be achieved.In the microgram range the standard deviation is 5 to 10 per cent., with a lower extraction limit of about 1.0 pg. CHROMATOGRAPHIC- Chromatographic methods for determining beryllium have not yet gained wide accept- ance. The disadvantages of such methods for beryllium include (a) lengthy procedures, ( b ) close control is required, (c) results are mostly semi-quantitative and (d) the range of concentrations is restricted. An electrochromatographic method for beryllium has been described by Majumdar and Si11gh.7~ The migration sequences of beryllium and seven other elements were determined in various electrolytes; separations were possible with some mixtures containing up to four constituents. A semi-quantitative determination of beryllium, lithium and boron in minerals by partition chromatography has been de~cribed,’~ but cannot be recommended for routine use.Amounts of beryllium between 10 and 90 pg have been separated from uranium and titanium by paper chromatography, a mixture of isopropyl alcohol, acetylacetone and hydro- chloric acid being used as solvent.76 After separation, the ions were detected with an ethanolic solution of quercetin and a solution of potassium ferrocyanide, and the planimetric method was used for quantitative evaluation of the separated spots. Values of RF for beryl- lium, uranium and titanium were also reported. The average error in the analysis of a (1 + 1) mixture of beryllium and uranium did not exceed 10 per cent. The determination of beryllium after separation by paper chromatography has been described by Elbeih and Abou-Elnaga, 77 who used visual comparison of the oxine complex under ultra-violet illumina- tion.POLAROGMPHIC- Recently, Venkataratnain and Raghava Rao stated79 that, in an 0.5 M lithium chloride supporting electrolyte at pH 3.4, the diffusion current at the first stage of reduction remained proportional to the concentration of beryllium in solution up to 8 x 1 0 - 3 ~ . Earlier workers, however, have failed to detect any “steps” for the reduction of beryllium from aqueous solutions of its salts.*O Proximity of the hydrogen steps resulting from hydrolysis of Be2+ ions plus the need for accurate pH control is likely to cause difficulties in measuring step height. A more promising field of investigation would be polarographic methods based on the reduction of beryllium - organo complexes of the hgdroxyazo type or amperometric methods.s1 $82 RADIOCHEMICAL- Several interesting radiometric-titration, tracer,56 photo-neutron and activation methods for beryllium have been described.Neutron-activation methods for impurities in beryllium are referred to in the next section. A promising method, based on earlier work by Gaudin and PannelP and by Aidarkin and his co-workerss4 has been further developed by Milner and Edwardsg5 The method is based on measuring the photo-neutron flux produced when samples containing beryllium are irradiated with photons from an antimony-124 source. The method is rapid, interferences are small (with the exceptions of boron, cadmium, samarium and gadolinium) and, under the best conditions, the lower limit of detection is less than 0.002 per cent., as BeO.Radio- metric-titration procedures involving use of phosphorus-3ZS6 ss7 and ir0n-59~~ have been described. The phosphorus-32 method is said to be suitable for determining milligram amounts of beryllium in alloys and concentrates. Beryllium, as sulphate, is added to a buffer solution at pH 5 to 5.5 and is titrated with 0.1 M diammonium hydrogen orthophos- phate (containing phosphorus-32) of activity 20,OOO to 30,000 counts per minute per ml. At intervals, 0 6 m l aliquots are withdrawn, spun in a centrifuge and counted, and the equivalence point is found graphically. The precision of current radiometric procedures is Published work on the polarographic determination of beryllium is limited.7888 SMYTHE AND WHITTEM: ANALYTICAL CHEMISTRY [Vol.86 not as good as those of colorimetric and fluorimetric methods. Beryllium has been deter- mined88 in beryl by using radioactive iron-59. A preliminary oxalate precipitation is in- volved, and the procedure in its present form does not appear to be suitable for microgram amounts of beryllium. A beryllium-hazard detector in which polonium-210 alpha particles are used has been described.8s A 2.6-curie polonium-210 source provides a flux of alpha particles, to which samples of beryllium dust on filter-paper are exposed. The gamma-ray yield of the reaction sBe(a, n, y)12C is used to measure the beryllium content. The method is applicable in the range 0.2 to 100 pg of beryllium and a determination can be completed in 5 to 10 minutes.The method, however, necessitates a large capital cost for the source and detection equipment and cannot be recommended for routine use. DETERMINATION OF IMPURITIES IN BERYLLIUM-- Considerable attention has been devoted to the determination of impurities in beryllium, and nearly all the analytical methods described in this review, with the addition of methods such as vacuum fusion extraction, have been applied. Despite the demand for improved analytical methods, few analyses have been carried out on beryllium with very low levels of impurities such as oxygen, hydrogen and nitrogen. In fact, the solid solubility limits for oxygen, hydrogen and nitrogen have apparently never been deter~nined.~~ It is doubtful if ultra-high-purity beryllium has ever been prepared and submitted to comprehensive analysis.A comprehensive review dealing with methods for the detection of twenty-one compon- ents in beryllium has been published,2 but no such review covers the literature of the past 2 years. Conventional methods have been used for detecting common anions, such as chloride and sulphate, in beryllium compounds. Spectrographic methods have been extensively used for determining metallic impurities in beryllium and beryllium compounds and are detailed later. Vacuum fusion extraction procedures have been extensively used for determining hydrogen, oxygen and other gases in beryllium. A wide variety of chemical and radio- chemical methods has also been used. Some of the more important papers are summarised in Table 111.EMISSION- The major advantages of emission spectrornetry are specificity, high sensitivity, rapid processing of large numbers of samples and the relatively small samples. Against this, limitations are imposed by the empirical nature of the method when quantitative results are required. For every form and composition of sample, it is necessary either to have a range of standard samples or to carry out more or less extensive sample preparation to ensure that standards and samples can be directly compared. Even when this is done, spectrographic analyses for major elements show a considerably higher standard deviation than do most other methods. Thus, although many spectrographic techniques have been described for determining beryllium in bery1,134,136J38 it is our opinion that this determination is prefer- ably carried out by conventional “wet” chemical methods. This section will therefore deal with methods for determining traces of beryllium and its compounds and with methods for determining traces of impurities in beryllium and beryllium oxide.Determination of very small amounts of beryllium-Several techniques have been described for determining traces of beryllium in various materials, for example, plutonium,137 thoria,138 bismuth - uranium alloys139 and ~ 1 a n t s . l ~ ~ The major effort, however, appears to have been directed to meet the requirements of speed and sensitivity limits set for environmental moni- toring by smears, air-sampling, etc., reviewed recently by Br00ks.l~~ A wide variety of techniques has been used, the highest sensitivity claimed being obtained by the cathode- layer technique.In this method,136s142,143 the sample, as a powder or a solution dried on the graphite cathode, is arced at 10 to 15 amps, and only light originating very near the cathode is allowed to enter the spectrograph. g of beryllium has been ~1airned.l~~ Conventional d.c. arc techniques, in which the sample is placed on the anode and light from all the gap is admitted to the spectrograph have also been de~cribed.1~~~1~~ Thallium was used as internal standard in both these methods, and Landis and Coons145 claimed that, by adding barium chloride as carrier, higher sensitivity and reproducibility were obtained over the range 0-002 to 0.1 pg of beryllium. Another d.c.arc technique is the “iron-flux” method used by Garton, Webb and Sayer,146 who covered the range 0.006 to 4 pg of beryllium with a single exposure. SPECTROMETRIC METHODS A limiting sensitivity of 2 xFebruary, 19611 OF BERYLLIUM. A REVIEW 89 Fred, Nachtrieb and Tomkinsl47 were able to detect 0.002 pg of beryllium with a copper spark. Davis, Parker and Webb148 used a condensed spark between graphite electrodes, on one of which the sample, collected on a paper pad, was glued; with a direct-reading spectrograph, these workers were able to detect 0.003 pg of beryllium. Aluminium was used as internal standard, aluminium sulphate solution being placed on the pad (by pipette) before sparking. Spark techniques have also been described. TABLE I11 SUMMARY OF METHODS FOR DETERMINING IMPURITIES IN BERYLLIUM AND ITS COMPOUNDS Impurity determined Oxygen (as BeO) in Be .. Oxygen in Be . . .. .. Helium and tritium in Be . . Free carbon in Be . . . . Combined carbon in Be . . Fluorine in Be . . .. . . Oxygen in Be0 and Be . . Chlorine in Be0 and Be . . Combined nitrogen in Be . . Beryllium oxide in BeF, . . Fluorine in Be compounds . . Lanthanides in Be . . . . Various metals in Be . . . . Silicon in Be . . . . .. Iron in Be . . . . . . Chromium in Be . . . . Nickel in Be . . . . .. Cadmium in Be .. .. Uranium in Be.. .. . . Silicon in Be compounds . . Free Be and carbide-C in Be Various impurities in Be Copper in Be . . . . . . Manganese in Be . . .. Tungsten in Be . . . . Iron in Be compounds . . . . - Solution methods have .. . . . . . . .. . . . . . . .. .. . . . . . . .. .. .. . . .. . . . . . . . . . . . . . . .. been Literature reference* 91 92 93 ‘1 94, 95 96, 97 98 99 100 101 102 94, 95 105 106 107 108, 109, 110 111, 112, 113 112, 114 115, 116, 117 118, 119 120 121, 122, 123, 124 125 126 127, 128 129 130, 131 132 133 2 i { 2 Remarks Chemical method (methanol - Br,) ; error -&O.Ol per cent., as Be0 Chemical method (HCl) Activation method (lSN measured) ; relative error &5 per cent. Micro vacuum fusion; coefficient of variation 15 to 20 per cent. a t 0.01 per cent. level Fusion and extraction Solution, ignition and gasometric finish Solution and gasometric finish Absorptiometric method Chemical method (CuSO,) Chemical method Vacuum fusion method Chemical method (Kjeldahl) Chemical method (diffusion) Chemical method Chemical method Chemical method (oxalate) Spectrographic methods Absorptiometric methods Absorptiometric methods Absorptiometric methods Absorptiometric methods Absorptiometric method Absorptiometric and volumetric methods Absorptiometric method X-ray fluorescence spectroscopy Absorptiometric method Chemical methods Chemical methods Activation analysis Review of various methods - * See reference list, p.91. described. Feldman149 and Owen and his c o - w ~ r k e r s ~ ~ ~ used a porous-cup- spark technique in which the sample was fed into the discharge by percolation through the thin base of a hollow graphite electrode. A closely allied technique is the rotating-disc method in which the lower electrode is a rotating disc of graphite partly immersed in the sample solution.This has been used by Smith and his co-workersl61 and by the U.K. Atomic Energy A~th0rity.l~~ The latter workers used scandium as internal standard and, by choosing various beryllium and scandium lines, covered the range 0.03 to 50 pg of beryllium. Since air and smear samples are usually collected on filter-paper, most of the techniques mentioned above involve considerable chemical pre-treatment, such as wet ashing and separa- tion of interfering elements. Since these determinations are most usually carried out for Health Physics purposes, it seems to us that speed is more important than accuracy, especially when “spills” give rise to suspected contamination. Accordingly, in these laboratories, smear- and air-sample analyses are carried out by a modification of the method described by Davis, Parker and Webb,l** in which the filter-paper samples are glued to graphite electrodes 10 mm in diameter.A pulsed-arc discharge is used, with the sample as cathode and a blunt graphite anode 6 mm in diameter; the gap is 4 mm. Results are reported in the range (0.01 to >2 pg of beryllium by making visual comparison with standards prepared by90 SMYTHE AND WHITTEM 1 ANALYTICAL CHEMISTRY pol. 86 drying solutions of beryllium sulphate on similar filter-papers. If a stock of machinedelec- trodes is maintained, a batch of twenty samples can be processed by one operator in about 90 minutes. The main disadvantage of the method is that results may vary appreciably with different physical forms and chemical compositions of the beryllium contamination.How- ever, as the biological effects vary far more with the particle size and chemical state of the beryllium, the method is regarded as acceptable for Health Physics control. The speed of the method is invaluable in assessing the spread of contamination after a “spill.” Churchill and Gilliesonlm introduced a technique for the continuous monitoring of air for beryllium by drawing a constant flow of air across a spark gap. The light from the spark was dispersed by a grating monochromator set for the beryllium doublet at 3130 A and was continuously recorded by means of a photomultiplier, d.c. amplifier and circular-chart recorder. An improved version of this monitor has been described1” in which integration over a short time was used rather than continuous recording.Other refinements were higher dispersion to improve sensitivity, backgroundL correction and periodic standardisation (involving a discharge between beryllium - copper electrodes to generate particles of beryllium oxide). It was claimed that, by re-designing the spark gap and using a pulsed-arc discharge axially in the air stream, rather than a condensed spark across it, results were independent of the particle size and chemical composition of the beryllium aerosol. A similar instrument is being constructed in these laboratories. Here, very high dispersion is used, since it has been found that titanium interferes if the monochromaator “window” is set to admit both lines of the beryllium doublet at 3130 A.Our monochroinator has a band pass of 0.1 A, sufficient to resolve one beryllium line from titanium. A number of the refinements made by Webb, Webb and Wildyl” have been omitted, since we require specificity and sensitivity to changes in concentration, rather than absolute accuracy. Recently, commercially constructed auto- matic monitors have become available. One of these1& is based on the rotating-disc tech- nique161 and will automatically process up to sixty samples at the rate of six per hour. The otherlE6 involves a filter tape that is directly excited in a spark, providing a result every minute. Determination of traces of impurities in beryllium and its compounds-Over the last two decades, the requirements for determining impurities in beryllium and its compounds have varied as pure forms of beryllium have becorne available.Arc methods are used almost exclusively; in general, all samples are converted to beryllium oxide before arcing. A typical early example is the method described by Lee Srnith and Fa~se1,l~~ who used a 16-amp arc and a barium hydroxide - graphite mixture as a “spectroscopic buffer’’ for determining alu- minium, calcium, chromium, iron, magnesium, manganese and silicon, mostly in the range above 100 p.p.m. The carrier-distillation method originally [developed for determining impurities in uranium168 has been used for determining silver, cadmium, molybdenum, lead, zinc, lithium and calcium,2 but the limits of detection were not stated. With lanthanum as carrier, Zaidel and his co-worker~l~~ detected gadolinium, europium and samarium in beryllium down to 0.1 p.p.m.Zaidel and othersls8 have also described an interesting method for determining very small amounts of boron in beryllium oxide. A 30-mg sample of oxide is heated in vacuo and volatile impurities are collected on a copper electrode, which is then sparked. Recently, Karabash and his co-workers7l have described a chemico-spectrographic method for determining twenty-five elements as impurities in beryllium and beryllium oxide. The sample (2 g) is converted to basic beryllium acetate and is then extracted with chloroform until about 5 per cent. of the beryllium remains in the aqueous layer, which is then separated, evaporated to dryness and converted to oxide. The oxide is then arced in a graphite cup at 12 amps.Detection limits are given as- 5 p.p.m. for Zn, 3 p.p.m. for Ca and Al, 2 p.p.m. for Ba, Ti, Fe, Sb, Te, In and T1, 1 p.p.m. for Mg, Mo, Co, Ni, Sn, Pb and Na, 0-5 p.p.m. for V, Cr, Bi and Ga, 0.3 p.p.m. for Cu, 0.2 p.p.m. for Ag, 0.1 p.p.m. for Mn and 0.05 p.p.m. for Cd.February, 19611 OF BERYLLIUM. A REVIEW 91 X-RAY METHODS- When X-ray techniques are considered for analytical problems in the beryllium field, the most notable factor is the very low absorption and scattering of X-rays by beryllium atoms. This means that the sensitivity of detection of beryllium metal is poor. On the other hand, the sensitivity of detection of impurities in beryllium metal is fairly high, particularly if thick specimens can be used. An example, now being examined in these laboratories, is the determination of beryllium oxide in beryllium, which is usually present in the range 0.3 to 1 per cent.Since the solu- bilities of oxygen and beryllium oxide in beryllium are likely to be very low, it is expected that this technique will give results for total oxygen in beryllium if the metallurgical history of the sample is such as to favour reasonable crystallite size for the beryllium oxide. X-ray fluorescence methods for many impurities are also feasible and are very sensitive. Qualitatively, chromium, copper, iron, lead, manganese, nickel, vanadium, zinc and zirconium have been detectedlZ8 in MTR shim rod; uranium was estimated at the 500 p.p.m. level. At present, we are examining a method for determining iron in beryllium and in beryllium oxide.It is planned to extend this to other common impurities, e.g., chromium, copper, manganese, nickel, zinc and uranium. MASS SPECTROMETRY- Mass spectrometry is not generally applicable to the detemination of beryllium, since beryllium and most of its compounds are insufficiently volatile for application of the usual gas-phase techniques. The use of stable-isotope dilution methods involving solid sources has not been reported, perhaps because of the difficulty of obtaining supplies of beryllium-10. However, mass spectrometry in conjunction with vacuum fusion has been used in Canadag6 and in England9’ for determining gases formed in beryllium by (n, 212) reactions; the gases found were 4He, 3He, ‘H, and 3H,. 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