CHAPTER 3 Methodology 3.1 NEW METHODS This Section describes novel methods of analysis that are considered to be of suficient general interest to merit discussion here as well as in the appropriate Section on specific applications. The Section also includes consideration of papers by workers who have made a detailed study of experimental parameters of widespread relevance. 3.1.1 Sample Preparation Techniques 3.1.2.1 Sample Handling and Storage.The accuracy of trace analysis is often critically dependent upon both the preservation of the sample and the minimization of contarninof ion. Unfortunately, in many routine analyses these aspeets are not given the considcration that they merit. Mizuike and Pinta (307) have reviewed contamination problems in trace analysis.Four main types were identified and discussed: airborne contamination, which could be drastically reduced by using clean rooms or hoods; reagent contamination (especially mineral acids), which could be minimized by utilizing various purification tech- niques; apparatus contamination, which could be reduced by judicious selection of materials and cleaning procedures; and finally, and an often overlooked source, the analyst himself/ herself.Guidance for the design and operation of a clean room for trace metal analyses has been given by Gardner (1449). The present status of contamination in trace analysis has been reviewed by the IUPAC Commission of Microchemical Techniques and Trace Analysis (1519). A summary of the contamination problems encountered in 93 different laboratories is given and it is shown that decomposition of the sample is the most critical stage.As an extension to previously approved nomeizclature, (Pure Appl. Chenz., 1979, 51, 43), recommendations for scales of working in analysis in which sample size and comtituent content are classified have also been published (310). Further work on the selection of sampIe containers (see also ARAAS, 1978, 8, 63) has been performed (1 1, 740).It i s generally agreed that acid-washed high-pressure polyethylene or PTFE containers are suitable for most trace element analyses. One study (1 1) found that there was no significant leaching of 11 metals from high-density polyethylene containers into water or nitric acid after 4 years, unfrozen, storage. A bigger problem however was prevent- ing loss of analyte on or into the sample container itself.A rather worrying study on the effect of the time of storage and type of container on the reliability of Cd, Cu, Hg, Pb and Zn determinations in whole blood has been published by Meranger et al. (1314). Within one week almost all determined concentrations changed by at least 10%. Except for Hg, storagc at low temperature was found not to inhibit these changes.No single type of container could be recommended for all elements. Vitreous containers were optimum for Cd and Zn; losses of Cu occurred in all types of container. Loss or gain of Hg from polyethylene and PTFE containers continues to be investigated (78). Sulphur-containing antioxidants in polyethylene have been implicated in such losses, while the addition of HNO, or KMnO, as a preservative to the sample appeared to assist passage of Hg vapour from ambient air through the walls of the sample container (1498). Freezing of the sample or the use of glass containers was advocated to minimize this problem.Matsunaga et al. (477) have recom- mended the use of glass containers, pre-heated to 500 "C or washed with HF, for the determination of Hg in seawater.The samples were acidified with H,SO, to give a final 5960 Analytical Atomic Spectroscopy concentration of 0.2M, and were allowed to stand for 20 days before being analysed. The resulting solutions were then found to be stable for at least another 40 days. The 20-day standing procedure resulted in relcase of additional Wg, which was not initially reduced by SnC1,.It also avoided the use of KMnO,, which increased blank values (see also 3.1.1.4). Additional reference on the preceding topic - 1885. 3. I J.2 Sample Homogenization, Solubilization and Dissolution Procedures. The accuracy of analysis of many food products is limited by the sampling technique. In a procedure that gave highly homogenized samples of canned foods, the contents of the entire can were mixed with 2M HNO,, blended using a high-efficiency sonic-probe homogenizer, allowed to stand for 16 hours, and then sampled after further blending (1065, 1440).The use of organic tissue solubilizers such as tetramethylammonium hydroxide (TMAH) can result in rapid dissolution of tissues with minimal blanks (see also ARAAS, 1974, 4, 148).One gram of soft animal tissue was dissolved in 2 ml of 20% m/V TMAH in methanol (107). The resulting solutions were analysed for Cd, Cr, Cu, Ni, Pb and Zn using ETA with an automatic sampler. It was essential to effect calibration by the method oi standard additions. Julshamn and Anderson (970) have compared a commercial tetra-alkyl tissue solubilizer in toluene with a conventional HNO, /HClO, digestion.For small soft tissue samples, satisfactory results for Cd, Cu and Mn were obtained using the tissue solubilizer, but not for Al. For hard tissues such as bone, the solubilizer did not give complete dissolution. Emulsioizs of oil (1670) and iodine-treated pctroleum (1635) in water have been obtained using various surfactants (see also ARAAS, 1978, 8, 77).With minimal sample preparation and the use of inorganic standards, satisfactory FAAS analyses were achieved. Ghiglione et al. (1728) have continued their work on the dissolution of metal samples using an underwater high-voltage spark discharge (see also ARAAS, 1976, 6, Ref, 315). The resulting emulsions were reasonably stable at a pH of 2.5, but sensitivities were only 60% of those of the equivalent aqueous solutions.The technique was successfully applied to the determination of Cr, Cu, Mn and Ni in low-alloy steels. The determination of trace elements in coal ash and glass has been accomplished using relatively simple dissolution techniques. Satisfactory cold digestion tcchniques with minimal blanks have been reported for glass (42) and coal fly ash (1567).The samplcs were treated with HF/ HC1 and subjected to ultrasonic agitation. An alternative sample-dissolution procedure for coal utilized slurries, produced by an ultrasonic cavitational homogenization, which were nebulized into an ICP using a Babington nebulizer (1361) (see also Section 3.1.4). 3.1.1.3 Sample Digestion and Oxidation Procedures.In view of the increasing sophistica- tion of analytical instrumentation, it is surprising that so little agreement on digestion and oxidation procedures has been achieved. The accuracy of many analytical methods would now appear to depend on the sample preparation technique rather than the type of instru- mentation used. Bock's comprehensive book on decomposition methods for both inorganic and organic materials has now been translated into English (156), and over 3000 references are listed. Various problems concerning dry ashing or wet digestion of organic and biological materials continue to be reported.There still seems to be considerable diszgreement over the relative merits of wet and dry ashing (963). Fetteroff and Syty (1037) found that for the determination Pb in chewing-gum, dry ashing at 500 "C followed by dissolution of the residue in HNO, did not result in complete recovery.It was necessary to evaporate theMethodology 61 HNO, leachates to dryness and re-ash for a further 2 h in order to obtain quantitative recovery. Dry ashing at 480 "C followed by dissolution of the ash in HCl/HF has been recommended (1609) for the analysis of a wide range of elements in refuse. A useful description of the sampling procedure used for this difficult type of sample is given.Prasad and Spiers (1035) found that wet digestion of plant materials with H,SO,/H,O, resulted in poor recovery of Ca and, surprisingly, of Fe and Zn. They recommended dry ashing the samples at 475 "C followed by dissolution of the residue in 2M HCl; this procedure gave results equivalent to a conventional HNO, /HC10, wet digestion.Other workers (773), how- ever, have found problems with a similar dry ashing technique in the determination of Cd, Cu, Mn and Zn in vegetable matter. When this was dry ashed at 450 "C losses were observed from volatilization (typically 5-1 5 % ) and also from conversion of the analytes into forms that were not quantitatively recovered by conventional acid leaching.Both types of losses were found to increase with increasing temperature and at 800 "C the latter type of loss was typically 40-60%. Etherington and Davies (468) have presented evidence that loss of Fe from plant material as iron pentacarbonyl can occur with dry ashing at 500 "C or even with conventional acid digestions.Additional reference on the preceding topic - 331. Polytetrafluoroethylene pressure digestion vessels have been successfully used for many difficult digestion procedures. One such procedure is the digestion of mineral oils by heating 100 mg of oil with 2 ml HNO, at 160 "C for 16 h (1483). The method was compared with dry ashing and oxygen flask combustion and found to possess significant advantages.Price et al, (1574), for the determination of 12 elements, used a PTFE pressure vessel to dissolve a wide range of aluminium alloys using an HNO,/HF digcstion followed by addition of W$O, to complex excess fluoride and minimize interelement effects (see also ARAAS, 1978, 8, 62). A pressure digestion vessel constructed from glassy carbon (1482) has been recom- mended for the decomposition of organic matrices.The main problem with conventional pressure digcstion devices is that they cannot be readily applied to large batches of samples. A method to overcome this, utilizing a miniature multiple-pressure digestion device, has been described (161 1). Thirty-six 1.5 ml polypropylene tubes were held in an aluminium box-section tube rack by their rims and a sheet of silicon rubber was sandwiched over thc top of the tubes, Up to 20 mg of sample could be digested under pressure with the appropri- ate acids, The use of polypropylene however, rather than PTFE, limited the upper working temperature. 3.1.1.4 Sample Preparation for Mercury Analysis. Considering the vast amount of effort that has been expended on the analysis of Hg (see also Section 1.5.2) in environmental samples there is remarkably little consensus of opinion as to the optimal sample prepara- tion procedures, The prodigious rate of publications on this topic shows no signs of abating. Low recoveries of Hg in wet-digested settled sewage and humus tank effluent samples were observed (38) unless the organic material present was completely oxidized by wet digestion on a boiling water bath with an excess of a suitable oxidizing agent.Similarly, other workers (470) have found that digestion with KMnO,/HNO, at 80 "C for 18 h only gave 90% recovery of organic Hg in natural waters. hlillward and Le Bihan (8) have also shown that if inorganic Hg is allowed to equilibrate with humic material in natural waters for 90 min, some of the resulting mercury species were more stable than methylmercury salts, Very poor recoveries were obtained when a standard SnCl, reduction was used.Photochemical oxidation at pH 1 was recommended as a means of destroying the organic matter. This is an increasingly popular method of destroying organic material prior to Hg analysis (8, 470, 496, 1512, 1719); however, the recovery of Hg has been reported to be significantly reduced in the presence of significant amounts of suspended solids (470).The determination of Hg62 Analytical Atomic Spectroscopy in fish tissue usually requires prolonged digestion. Velghe et al. (1048) have rapidly digested fish tissue with H,SO, and injected the resulting solution directly into a Hg generation cell containing SnCl, /CdCl, in acid in order to determine inorganic and phenylmercury, excess of NaOH was then added to liberate methyl- and ethyl-mercury (see also ARAAS, 1973, 3, Ref. 132).An alternative rapid method for total Hg involved a 20-min digestion procedure in which the sample was refluxed with H,S0,/HN0,/V,05 (1047). The procedure was also applied to the determination of Se. 3.1.1.5 Sample Preparation for Hydride Generation Techniques. A particular problem with hydride generation techniques (see also Section 1.5.1) is the production of foam when incompletely digested biological samples react with NaBH,. This has been effectively overcome (1980) by using a new commercial antifoaming agent (DB llOA, Dow Corning, U.S.A.). Undigested urine samples were found to give a complete recovery of As when compared to fully digested samples.Calibration using aqueous standards containing the antifoaming agent was possible. The determination of Pb by hydride generation has been further investigated (632) (see also ARAAS, 1977, 7 , Ref. 295). A comparison of the use of K2Cr207, H,S,O,, and KMnO, as the preliminary oxidizing agent before addition of 5% m / V NaBH, solution was carried out.A sample solution containing 0.25M K,Cr,O, and 0.25M malic acid was recommended. 3.1.2 Pre-concentration Techniques A large number of pre-concentration techniques have been published, yet the interlabora- tory agreement of the results of ultratrace level analysis would appear to leave much to be desired. (1452, 1858; see also ARAAS, 1978, 8, 68).An interlaboratory ccmparison of As, Mo and Se analyses from uranium mill tailings has been reported. (Dreesen, D. R., Gladney, E. S., and Owens, J. W., J. Wat. Pollut. Control Fed., 1979, 51, 2447’). This paper quoted results from an interlaboratory comparison exercise in which Se was determined in a groundwater sample. The results ranged from 40 to 1840 pg 1-1 with a standard deviation of 499pg 1-1.The depressing conclusion was that compliance with regulations for Se in discharges is difficult to justify at present. Problems arise when published methods are adopted for the routine analysis of large numbers of samples since they often require con- siderable attention to detail not immediately obvious from the author’s description. Two useful reviews on pre-concentration techniques have been published (475, 670) and it was generally agreed that no single type of pre-concentration technique could be specifically recommended for a wide range of elements. 3.1.2.1 Solvent Extraction.Multi-element extractions of natural waters using APDC / DDC / CHCl, for Cd, Cu, Ni and Zn followed by ETA analysis (1070) and APDC/2,6-dimethyl-4- heptanone for Cd, Co, Cr, Cu, Fe, Mo, Ni, Pb, V and Zn followed by FAAS (1467) have been reported.The general need for pretreatment of the samples before the extraction step was stressed (1467). Laqua et al. (852) found it necessary to use a third Ar flow to prevent carbon deposition in a 5 kW ICP after an APDCIMIBK multi-element extraction and nebulization of the organic solvent into the plasma.Intense band spectra (see also Section 1.2) limited the usefulness of the technique to elements having their emission lines below 280nm. Additional references on the preceding topic - 31, 171, 638, 1052. Three further solvent extraction systems for lead have been reported: 4-capryl-3-methyl- 1 -phenyl-5-pyrazolone / MIBK (631); Na,S,O, / trioctylmethyl ammonium chloride / MIBK (1126); and ‘Alamine 336’ OT ‘Aliquat 336S’/xylene (10). These appeared to have no significant advantage over conventional systems using APDC and/or DDC.Methodology 63 A method for the selective determination of As(ZZZ), As(V) and organo-arsenic com- pounds has been described by Akemi et al.(354). The samples were solubilized in 6M HCl and the As(II1) extracted into toluene; the As(V) was then reduced to As(II1) by KI and again extracted into toluene.The As in the two toluene extracts was then back extracted into water and determined. The organo-arsenic compounds retained in the aqueous samples were wet ashed and also determined. The As in orchard leaves was found to be wholly inorganic, while 90-100% of the element in algae and shark muscle was organic.Organo-silicones in water (777) have been extracted into pentanol/MIBK (1 : 1) at pH 5-7. Tetramethyldisiloxane-1,3-diol (TMDS) was used as a standard. An RSD of 0.095 at a 1 pgml-1 level of TMDS was claimed (see also ARAAS, 1978, 8, Ref. 1251). A novel method for the determination of barium in the presence of a large excess of Ca has been reported (374).The Ba was selectively extracted as its 18-crown-6 ether into nitrobenzene (this reagent is highly toxic !). Three extractions were necessary. The Ba was then re-extracted in 1M HNO, and determined by AAS using a N,O/C,H, flame. The Ca concentration in the final solution was 0.1% that of the original sample solution. A PTFE porous film disc with a 40pm pore diameter, which allowed the passage of organic solvents but impeded the passage of water (466), was found to be ideally suited for microextractions when only small volumes of organic solvents were used. It is, however, only applicable to solvents heavier than water.The method was tested on orchard leaves, bovine liver and rat whole blood by extraction of Cd and Pb into CC1, using various chelating agents.Other reference of interest - N,O/H, flame for organic solvents: 1715. 3.1.2.2 Ion-exchange Methods. The precision of ion-exchange pre-concentration was found to be improved significantly if a peristaltic pump was used to control the flow of samples through the resin columns (37). Chelex 100 resin has been used to concentrate Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn from seawater (456).After adjustment of the pH to 5.2 the sample was passed through the column. Alkali and alkaline-earth metals were eluted with ammonium acetate prior to elution of the analyte elements with 2x5 ml of 2.5M HNO,. The final extracts were analysed by ETA. Additional references on the preceding topic - 670, 1070. The direct ETA anatysis of small mounts (--I rng) of ion-exchange resins, after passage of the sample solution through a small quantity of the resin, is becoming popular (172, 644, 946, 1043, 1496). This approach has the advantage that natural water samples can be passed through the resin at the time of collection and hence the problems associated with preserva- tion of the sample solutions are effectively overcome, Barnes et al.(1546) have passed 25Oml urine samples through columns containing 100mg of a polydithiocarbamate resin, washed the resin with water and then digested it in 2ml HNOB/H2S0,, to give a 125-times concentration step for trace metals. The resulting solutions were nebulized into an ICP.A similar technique has been applied to geological analysis (1309). It should be stressed (yet again) that it is possible that some elements present in natural waters or biological samples are associated with natural organic com- pounds and are not quantitatively extracted unless a pretreatment step, such as photo- chemical oxidation or wet digestion, is used.The fact that spikes of the analyte are recovered from these types of samples does not guarantee recovery of endogenous analyte. Other references of interest - Au, Pt, ion-exchange pre-concentration: 229.Development of specific ion-exchange resins: 73.64 Analytical Atomic Spectroscopy Non-boiling concentration: 465. Polyurethane foam / 142 pyridylazo)-2-napthol: 293. Speciation /ion-exchange studies: 88. Se, electrochemical pre-concentration: 1493. TI, anion-exchange pre-concentration: 1074. 3.1.2.3 Adsorption Concentration. Concentration of Ag, As, Bi, Cd, Cu, Hg, Se, Sn, Te and Zn has been achieved (1615, 2033) by passing the sample solution at pII 3-6 through a freshly prepared homogenous layer of CuS, MnS or ZnS. The layer was 300-400nm thick and was supported on a 40 mm diameter cellulose nitrate or PTFE filter with a pore size of less than 1 pm. The resulting precipitate was dissolvcd in 2 ml aqua regia and the elements determined by ETA.By using large sample volumes (0.1-6 litres) detection limits of a few ngl-1 were obtained. An additional advantage of the technique was that tlic filters could also be analysed using XRF. Isolation of the analyte from the matrix can occasionally be achieved with simple methods. Jackwerth (628) has Concentrated many trace elements from a lead matrix by dissolving the lead in 20% V / V HNO,, evaporating the solution to near dryness and extracting the precipitated Pb(NO,), with 65% V/V HNO,, Gold has been concentrated from aqueous solutions by adding a large excess of Hg2+ ion, adding SnCl, solution, collect- ing the resulting Hg globule containing the Au and dissolving it in a small volume of aqua regia (729).Additional reference on the preceding topic - 112. 3.1.3 Indirect Methods Indirect methods can prove very useful for specific applications, but it is important to appreciate that the reaction of the determinand with the element finally determined is often not specific. Hence, interference effects can be quite severe and the methods tend to have limited application.The ittdirect determiiiation of phosphate by measuring the Mo or V in phosphovanado- molybdic acid has been recommended for the analysis of iron and steels (724) and biological tissue (1369). The method was claimed t o be an improvement over the more common phosphomolybdic acid system (see also ARAAS, 1978, 8, 65). The formation of phospho- molybdic acid has been used, however, for the analysis of bottom sediments for phosphate (1 778).Vierkorn-Rudolph and Bachmann (1002) have determined nanogram levels of chloride by utilizing the following reactions : C,H,Hg NO, + C1- + C,H,Hg Cli- NO,- CrO, + 2H+ +2C1- -+ CrO,Cl, The covalent reaction products were extracted using CHCl, or CC1, and the Hg or Cr subsequently determined by ETA. +H,O Additional reference on the preceding topic - 338.The determination of the total carboxyl and phenolic content of coat and lignite residues has been achieved (565) by treating the coal with 1M NaOH, washing it with water, then removing the adsorbed Na with HCl and determining the Na by FES. When NaHCO, was substituted for NaOH, only the carboxyl group adsorbed sodium, and thus the carboxyl content could be determined.Carbon disulphide has been determined in fuel gases (927) by absorption in alcoholic KOH and reaction with Cu2f ion to form insoluble cuprous xanthate. This was separated byMethodology 65 filtration, dissolved in acid and the Cu determined by AAS. Other workers (1854) have adsorbed the CS, onto a chromatographic support and subsequently determined the CS, by monitoring S, emission in a cool flame.Non-ionic detergents in natural waters have been determined by extraction into ethyl acetate, evaporation of the extract to dryness, followed by reaction with phospho- molybdic acid in the presence of BaCl, to form an insoluble Mo species. The residual Mo in the filtrate was measured by FAAS (1828). A somewhat simpler method has been pro- posed by Crisp et al.(1487) who used the extraction of a neutral adduct with potassium tetrathiocyanozincate into 1,2-dichlorobenzcne. The Zn was subsequently determined by FAAS after back extraction into 0.1M HCl. Anionic detergents have been determined (305) in natural waters at the ngml-1 level by reaction with Cu(I1) and ethylenediamine to form a ternary complex, which was then extracted into CHC1, and the Cu subsequently deter- mined using ETA.At very low levels interference by natural organic chelating agents was minimized by preferential U.V. photochemical oxidation of the chelating agents prior to the analysis. Zndirecr AAS methods have also been proposed for: As (33), chluroprothixene (1231), cyanates (1612), esters (1 1291, ethinyloestradiol (703), fluoride (1649), sulphate (1248, 1443, 171 7), tannins (1 159) and thiols (1712).Zndirect emission methods have bccn proposed for aliphatic amines and amino acids (1565), fluoride (1540, 1686), sulphate (564, 580) and total sulphur (1468). 3.1.4 Nebulization, Vaporization and Atomization The Babington nebulizer (see ARAAS, 1978, 8, 8, and 1977, 7, 24) continues to gain popularity (546, 591, 592, 1738) and is being used for a wide variety of difficult applications. This nebulizer can satisfactorily nebulize solutions containing a high level of dissolved solids, viscous solutions and even solutions containing suspended solids, such as homogen- ized tissue (546).It can also operate at low Ar flow rates and is thus ideally sl-lited to ICP as well as FAAS analyses. The reported FAAS detection limits were similar to those obtained with a conventional pneumatic nebulizer (591).Ape1 and Duchane (569) described a fritted disc pneumatic nebulizer that was fabricated from a 15 ml Buchner funnel containing a fine frit. The sample was supplied to one side of the frit by a peristaltic pump and, simultaneously, gas was forced through from the other.Nebulization efficiences greater than 60% were obtainable. The device can be thought of as a Babington nebulizer with multiple orifices (see also Section 1.2). Cresser (1364, 1504) has described an impact cup that can be easily fitted to most commercial AAS pneumatic nebulizers. The PTFE cup replaced the impact bead and was positioned so that the nebulized sample was directed on to the inside of the cup.The resulting absorbance signal f o r most elements was rcduced about 12 times and thus the Ca, Mg and Na content of many natural waters could be determined without sample dilution. The fine spray produced resulted in less condensed phasc interference effects. It was possible to incorporate both the cup and the conventional impact bead in the spray chamber and to changc from one to the other without extinguishing the flame.Slurry injection where the solid sample i s ground to a small size, suspended in a suitable solution, such as 0.5% m/V aqueous Triton X-100, and directly nebulized into a flame or plasma is becoming increasingly popular (see ARAAS, 1975, 5, Ref. 1239). The technique has proved extremely useful for coal analysis using conventional pneumatic iiebulization (215, 530, 1694), Babington nebulization (546, 1361) and ETA (215).Compared to conven- tional wet ashing, approximately 15 min of operator time per sample was saved and, in addition, the typical turn-round time was reduced from 2days to 2 h (530). The main66 Analytical Atomic Spectroscopy disadvantage of the technique is decreased accuracy because of increased matrix effects.Careful calibration preferably using slurries containing typical samples that have previously been analysed after conventional wet or dry ashing is recommended. Additional references on the preceding topic - 12, 546, 591, 1444, 1501, 1568, 1588, 1694, 1981. FAAS detection would appear to be ideally suited for flow injection analysis.Some promising results using small volumes of analyte and automated sample injection have been reported (495, 1708). Ure et al. (1464) have mounted a water-cooled silica tube in an air/C,H, flame to concentrate Cu from solutions nebulized into the flame for a fixed period. At the end of the period the cooling water was turned off and the liberated Cu absorbance pulse (10-20s duration) was monitored.A characteristic concentration of 0.8 pg 1-1 was observed (see also RRAAS, 1976, 6, Ref. 1288). Gold, Pd and Pt have been vaporized (1628) by heating silicate samples in a stream of chlorine at 850 OC for 15 min. The volatile metal chlorides were condensed on to a water- cooled gat-top electrode and the metals subsequently determined by OES in a 10 A a.c.arc. Standards were prepared by mixing silica with small portions of the metal chlorides. Two sample preparation techniques were compared for hollow-cathode excitation (805). In the first technique, the cup cathode was coated with a benzene solution of Apiezon N grease and then 20Opl of the sample solution placed in the cup and evaporated to dryness under an i.r. lamp. In the second technique, the electrode was dipped in the sample solution, which was then evaporated to dryness, The first technique was found to be optimal for “cooled” cathodes, while the second was recommended for “hot” cathodes.The use of element-specific spectroscopic detectors for GC and HPLC continues to increase (see Section 1.2.2.3). Plasma detectors are the most popular and these include d.c.Ar plasmas (59, 60, 454), MIP (75, 89, 91, 193, 608) and ICP (1610). Flinn and Aue (129) used a cool flame detector to determine Se in GC effluents by monitoring Se, emission at 475 nm. The response was quadratic as for S, emission. Various methods for coupling flames to HPLC systems have been reported (39, 40, 101, 436, 481, 526). A direct interface to an ETA system (230) has been used to detect Se; Ni was incorporated into the final liquid stream to prevent loss of Se during the dry ashing step.The direct aitalysis of solid samples can result in considerable labour saving, but the main problems are still sample homogeneity and establishing reliable calibration procedures. Langmyhr (1681) has produced a comprehensive review on this subject and concluded that it has great potential, particularly in medicine, biology and environmental analysis.The use of graphite powder was found to improve atomization efficiency and prevent sample fusion in direct ETA of solids, and if the correct operating conditions were employed it was often possible to use simple aqueous standards for calibration (531). Van Loon (1751) has mounted metal samples (in the form of rods or nails) in graphite rods and inserted these into a flame. Refractory samples could be mounted on a Pt wire for insertion.A HC1 solution wds simultaneously nebulized into the flame and the determination carried out by AAS. The results were matrix-dependent but could be used for semi-quantitative sorting of sample types. Uranium determination b y A AS is notoriously insensitive; the characteristic concentra- tion in the N,O/C,H, flame has been improved 5 times by the addition of 10 mg ml-1 Ga to all solutions (1870).Tarui and Tokairin (636) have determincd U by ETA in a graphite tube device and avoided a significant memory effect from carbide formation by placing thc sample in a small Ta boat that was inserted into the tube.Methodology 67 L’Vov and Pelieva (1839) successfully determined cerium in steel in the 0.05-0.23% concentration range by ETA.A comprehensive study of the factors affecting Ce determina- tion was presented and from these studies the authors found that a Ta-lined furnace and the use of the 567 nm absorption line gave the best results. The determination of boron and phosphorus by ETA is limited by poor sensitivity and memory effects.Szydlowski (502) enhanced the B sensitivity and minimized carbide formation by the addition of 1000 pug ml-1 Ba to all solutions. Natural waters were success- fully analysed by this method using a Massmann graphite tube ETA device. Khavezov et al. (1890) used Zr carbide coated graphite tubes to achieve increased P sensitivity, long tube life and to avoid the necessity of adding La to the samples (see also ARAAS, 1978, 8, 66).A P detection limit of 0.05 pgml-1 for a 50 pl sample injection volume was claimed. Garnys and Smythe (463) improved the rate of ETA analyses by pre-drying and ashing samples on a long graphite filament. The filament was inserted through the graphite tube, the temperature raised for atomization and then the filament rapidly moved on to the next sample.The rate of analysis was increased three fold. Other references of interest - ETA-Determination of Tc: 458. ETA-Use of CCI, and CF,Cl, for vaporization: 1009. Graphite capsule in flame atomizer: 717. New pneumatic nebulizer: 1596. Use of organic acids to improve FAAS signal stability: 571. 3.2 DETECTION LIMITS, PRECISION AND ACCURACY Impressive detection limits or good precision are not synonymous with high accuracy. More attention should be given to improving accuracy rather than detection limits, on which considerable eff art and ingenuity are frequently expended. Boumans and Bosveld (1475) and Winge et al. (1730) have independently carried out investigations in computing the relative ZCP sensitivities for up to 10 prominent lines of some 70 elements.Detection limits were estimated from the ratio of peak-to-background intensity for each line, The results were presented in tabular form arranged alphabetically by element. A specific study of optimum ICP emission wavelengths for 18 impurity elements in TiO, has been made (63). Demers (617) has presented the results of an evaluation of the “end-on” viewed ZCP, operating in the horizontal position.It was claimed that with aqueous samples much lower detection limits were obtained than with the conventional configuration, but precision and chemical interference effects were similar (see also ARAAS, 1978, 8, Ref. 1415 and Section 1.2). A method for determining the contribution of separate noise componerzts with respect to source and type, the “noise-study” method, has been tested using an automated AE/AF spectrometer system (602).An evaluation of modulation methods and flame types was used to demonstrate how the magnitude and source of precision limiting noise call be determined. The use of a resistor-capacitor damping device for improving the SNR of transient AA signals was described by Wall and Catterick (41).The authors demonstrated the advantages of the device by using it in conjunction with two commercially available instruments having alternatively digital and analogue damping systems. The accuracy of most methods is critically dependent upon the rnerhod of cdibru~iort. Standard addition was the subject of a detailed study by Ratztaff (1999). Equations were given to demonstrate the effect of increment size on the precision of a standard addition or subtraction method.Use of a “generalized” standard addition method has been postulated (1844) as a means of detecting and quantifying the magnitude of interference effects. The68 Analytical Atomic Spectroscopy determination of Ca in Portland cement employing calibration by standard addition (1643) was shown to result in errors of up to 2896, whereas with matching standards, errors were less than 2%.A wide concentration range calibration method for furnace AAS was described (159) in which the peak width at a chosen fixed height was measurcd. It was claimed that the results obtained by this method were not affected by the numerous optical and electronic factors which cause non-linear response in AAS.The authors reported that a 100-1000 fold range of concentration could be covered by this method. It has been shown that calibratioii graphs for Cr determination by FAAS, in the optimized luminous air/C,H, flame, can exhibit inflexions and/or regions of negative slope (144). ‘The shape of the graph was found to be dependent upon the age of the standards, even when made up in 10% V / V IiNO,.Thcse efects were not observed if a non-luminous flame was used; however this resulted in a significant loss of sensitivity. Other references of interest - Analytical range test: 859. Detection limits of rare earths by ICP-OES: 1275. Preeision and noise in FAAS: 929. Preeision of flame emission measurements : 6 19.Seleetio n and pre-concentration of trace substances: 629. Use of the cathode layer line enrichment to reduce detection limits for noble metals: 13. 3.3 STANDARDS AND STANDARDIZATION 3.3.1 Standards A timely report on the worldwide availability and application of CRMs for trace analysis has been prepared by Koch (308). This report was originally proposed at the 26th IUPAC conference in 1971 and should prove to be extremely useful particularly for those concerned with routine analytical quality control.Alvarez (52) described the preparation and methodology for certification of six plant tissue and food product CRMs issued by the National Bureau of Standards (N.B.S.). The value of such CRMs in the development of reliable methods for obtaining accurate data on the chemical composition of foods in agricultural studies was stressed (1434).The area of fossil fuel analysis has been somewhat neglected in the preparation of CRMs, particularly in view of the increasing use of these fuels as a primary energy source. Reed and Uriano (86) have described two currently avail- able CRMs in this field as wcll as plans for expanding the range.A set of six new silicate “Geochemical Exploration” samples has been produced by the US. Geological Survey (1554) and, in view of inhomogeneity problems with the previous series, work has been carried out on 42 elements by more than 100 laboratories on a co-operative basis. Stoch et al. (Geos. Newsl., 1979, 3, No. 1, 25) have described in a very thorough report the preparation and certification of two samples of Bushweld type chromitc, dctailed statistical treatment of results from 32 laboratories throughout the world was presented .Other references of interest - Feasibility study for preparation of high purity reagent RMs: 6x3. Investigations into homogeneity of metallurgical materials for solid sample ETA: 1119. Pepperbush powder RM: 1934.Methodology 69 3.3.2 Standardization Studies Smith (1452, 1858) has produced a report summarizing interluboratory comparison studies carried out by the South African National Institute for Water Research.Results and methods used for mineral (Part IV) and trace metal (Part V) analysis by 14-16 laboratories were given. For the trace metal study, solutions were prepared by additions of proprietory standard solutions to deionized-distilled water and circulated in polythene containers.The two groups of elements studied were: Group I: Al, Cd, Co, Cry Cu, Fe, Mn, Ni, Pb and Zn; Group 11: Ag, As, Ba, Be, I-Ig, Li, Se, Sr, and V. Almost 95% of the determinations were carried out using AAS techniques. Of the results received, 67% were considered acceptable, 25% acceptable but questionable, and 8% unacceptable.Insufficient data was received for As, Hg and Se. As a result of tests involving 22 laboratories under the auspices of the BITC (Bureau International Technique de Chlore), two methods for the determination of total Hg in water involving the cold vapour technique have been accepted for recommendation as referee methods (171 9).The breakdown procedures recommended were (i) oxidation with HNO, /H,SO,/KMnO, /K2S,08 for domestic waters and domestic and industrial waste and, (ii) U.V. irradiation in the presence of K,Cr,O, and H,SO, or HNO,. Several interlaboratory method studies have been carried out on the determination of Pb in blood (1116, 1198, 1316, 1621). These have shown that there is room for improvement in such areas as the preparation of standard materials and the selection of laboratories with relevant experience (see also Section 3.1.2).The accuracy of 2 reference methods for Na and K in serum by FAES has been confirmed in a survey carried out by 12 laboratories in which manual and semi-automated pipetting techniques were used (325). In an intercomparison of analytical methods for the analysis for traces of Pt and Pd in alloys, Pauwels (19) has shown that both AAS and activation techniques can be used for determining the lower levels of these elements with precision and accuracies equivalent to the uncertainties of the referenee material.XRF, OES and spark source MS, however, were less accurate. The samples used in the study were synthetic alloys prepared by doping pure Cu with Pt and Pd using high-frequency levitation melting.A comparison of two methods for the dissolution of iron ores was studied in a round- robin test on the determination of trace levels of Cr, Cu, Mn, Ni, Pb, Ti, V and Zn by AAS (1898). An acid dissolution procedure involving HCl was found to give more accurate results than a Na,BO, /Na2C0, fusion procedure.With this latter procedure lower values for Cu and Pb were observed and this was attributed to alloy formation with the Pt crucibles during the fusion step. A very large amount of collaborative effort is required before a Standard Method can be published with confidence. Such a method for the analysis of wood preservatives and treated timber containing As/Cr/Cu formulations has been issued (1 160).Arsenic, Cr and Cu are leachcd from the wood by dilute H2S0,/H,0, solution before analysis by FAAS. An alternative photometric procedure is given. The U.K. Department of the Environment / National Water Council has issued tentative AAS mcthods for the determination of Hg and Ca in waters and sewage effluents (1076, 1426) as part of a series of rccommended methods for the determination of water quality.Methods for the determination of both inorganic and organo-mercury compounds using the cold vapour technique are given. It is hoped that the final version of the Ca method will give an indication as to the maximum permissible levels of potential interferents such as aluminium, phosphate and sulphate. Other references of interest - AAS techniques in food analysis: 533.Comparison between ETA and anodic stripping voltammetry for the determina- tion of Pb in geological samples: 659.70 Analytical A tomic Spectroscopy Evaluation of two mineralization methods for plant materials: 1895. Interlaboratory comparison of trace element measurements in marine organisms: 408. Metals in workplace environments, collaborative test of a “Ruggedized Method”: 115.Methods for determination of total Hg in gases: 1666. Sampling and methods for determination of Cd, Cu, Ni and Zn in sea water: 1070. Sn in foods by AAS: 45. TABLES 3.3A.1- 3.3A.5 : REFERENCE MATERIALS Table 3.3A.1 FERROUS METALS AND ALLOYS ~~ ~~ ~ Supplier Finely divided form Solid form Amt fur Standardisierung und Warenprufung (ASMW), 102 Berlin, Wallstrasse 16, D.D.R.Bundesanstalt fur Materialprufung (BAM), 1 Berlin 45, Unter den Eichen 87, Germany Bureau of Analysed Samples Ltd., Newham Hall, Newby, Middlesbrough, Cleveland TS8 9EA, England Bureau National de Metrologie (B.N.M.)., 21 rue Casimir Perier, 7500T-Paris, France Centro Nacional de Investigaciones Metalurgicas, Cuidad Universitaria, Madrid 3, Spain Gosstandart of the USSR, 9 Leninsky Prospekt, 1 1704, Moscow, U.S.S.R.Institut de Recherches de la Siderurgie Francaise, B.P. 129, 78104-Saint Germain en Laye, France Iron & Steel Institute of Japan, Japan Unalloyed & alloyed steels, cast irons, slags, ferro alloys Unalloyed & alloyed steels, slags, cast irons, ferro alloys High purity irons, unalloyed & alloyed steels, slags, cast irons, ferro alloys Unalloyed & alloyed steels, cast irons High purity irons Unalloyed & alloyed steels Unalloyed & alloyed steels, cast irons Unalloyed & alloyed steels, ferro alloys, cast irons, slags Unalloyed & alloyed Unalloyed & alloyed steels Unalloyed & alloyed steels, cast irons steelsMethodology 71 MBH Analytical Limited, Station House, Potters Bar, Herts.EN6 lAL, England Metalimpex, POB 330, H- 1 376 Budapest, Hungary National Bureau of Standards, Office of Standard Reference Materials, Washington, DC 20234, U.S.A. Spex Industries Inc., 3880 Park Avenue, Metuchen, NJ 08840, U.S.A. Swedish Institute for Metal Research, Drottning Kristinas vag 48, S-11428 Stockholm, Sweden South African Bureau of Standards, Private Bag X191, Pretoria, Transvaal 0001 , South Africa Unalloyed & alloyed steels Unalloyed & alloyed steels, cast irons, ferro alloys Unalloyed & alloyed steels, cast irons Unalloyed & alloyed steels, cast irons Unalloyed & alloyed steels, cast irons Unalloyed & alloyed steels, cast irons Unalloyed & alloyed steels, ferro-alloys, slags Ferro alloys Table 3.3A.2 NON-FERROUS METALS AND ALLOYS Supplier Finely divided form Solid form Aluminium Company of America, Alcon Technical Center, Alcon Center, PA 15069, U.S.A.Aluminium Pechiney, High-purity metals, 23 bis, rue Balzac, 75360 Paris Cedex 08, France Amt fur Standardisierung und Sn, Al, Mg base Al, Cu Warenprufung (ASMW), 102 Berlin, Wallstrasse 16, D.D.R.British Aluminium Co. Ltd., Chalfont Park, Gerrards Cross, Bucks. SL9 OOB, England Bundesanstalt fur Materialprufung (BAM), 1 Berlin 45, Unter den Eichen 87, Germany Bureau of Analysed Samples Ltd., High-purity metals, High-purity metals, Newham Hall, Newby, Middlesbrough, Pb base Cleveland TS8 9EA, England A1 base Al, Mg base A1 base Cu, Ni, Al, Mg base Al, Mg, Cu, Ni, Sn, AI.Cu, Ni base72 Analytical Atomic Spectroscopy Table 3.3A.2 NOM-FERROUS METALS AND ALLOYS- cmfinued Supplier Finely divided form Solid form BNF Metals Technology Centre, Grove Lab oratories, D c nchw o rt h Road , Wan ta ge, Oxfordshire, England Canada Centre for Mineral and Energy Technology, c / o Coordinator, CANMET, 555 Booth Street, Ottawa, Ontario K1A OGI, Canada Commissariat a 1’Energie Atomique, (C.E.A.) Cristal Tec, B.P.no 85 Centre de tri, 38041 - Grenoble Cedex, France Centre Technique des Industries de la Fonderie (C.T.I.F.), 44, Avenue de la Division Leclerc, 923 10 - Sevre, France Centre Technique du Zinc, 34, rue Collange, 92300 -Levallois Perret, France Gosstandart of the USSR, 9 Leninsky Prospekt, 11704 Moscow, U.S.S.R. Inco Europe Limited, European Research and Development Centre, Commercial Development Department, Birmingham B16 OAJ, England Japan Brass Makers’ Association, Japan Japan Light Metal Association, Japan Light Metal Smelters Association, Japan Johnson Matthey Chemicals Ltd., Orchard Road, Royston, Herts.SG8 SHE, England Cu base Cu base Cu base Al, Mg base Cu base High-purity metals, Zn base Cu base Ni base Cu base Al, Mg base Al, Mg base Hi gh-puri ty me ta 1s High-punt y me ta IsMethodology 73 MBH Analytical Limited, Station House, Potters Bar, Herts.EN6 IAL, England Mercure Industrie, 13, rue Saulnier, 92800 - Puteaux, France Metalimpex, POB 330, H-1376 Budapest, Hungary Al, Cu, Ni, Zn, Co base High-purity metals A1 base National Bureau of Standards, Office of Standard Reference Materials, Washington, DC 20234, U.S.A.High-purity metals, Al, Co, Cu, Ni, Pb, Mg, Sn, Pb, Ti, Zn, Zr base Al, Cu, Pb, Ni, Ti, Zn, Zr base Planet- Watt ohm, 05310-la Roche de Rame, France Spex Industries Inc., 3880 Park Avenue, Metuchen, NJ 08840, U.S.A. High-purity metals Cu, Pb, Sn base Table 3.3A.3 GEOLOGICAL MATERIALS Supplier Finely divided form Amt fur Standardisierung und Warenprufung (ASMW), 102 Berlin, Wallstrasse 16, D.D.R.Mn, Cr, Sn ores Bundesanstalt fur Materialprufung (BAM), 1 Berlin 45, Unter den Eichen 87, Germany Fe ores Bureau of Analysed Samples Ltd., Fe, Mn, Cr, Al, ores Newham Hall, Newby, fluorspar, sillimanite, Middlesbrough, Na & K feldspar, magnesite, dolomite Cleveland TS8 9EA, England74 Analytical Atomic Spectroscopy Table 3.3A.3 GEOLOGICAL MATERIALS - continued Supplier Finely divided form Canada Centre for Mineral and Energy Technology, c / o Coordinator, CANMET, 555 Booth Street, Ottawa, Ontario KIA OGI, Canada Sb, Co-Mo, Au, Fe, Mo ores syenite, gabbro, ultramafic rocks Centre National de la Recherche Scicntifique, Centre de Recherche Petrographiques et Geochimiques (C.N.R.S./C.R.P.G.), 15, rue Notre Dame des Pauvres, Case Officielle No. 1, 54 500 Vandoeuvre-lez-Nancy , France Commission of European Communities, Community Bureau of Reference (BCR), 200 Rue de la Loi, B-1049 Brussels, Belgium Geological Survey of Japan, Japan Gosstandart of the USSR, 9 Leninsky Prospekt, 1 1704 Moscow, U.S.S.R. International Atomic Energy Agency, Analytical Quality Control Services, Laboratory Seibersdorf, PO Box 590, A-101 1 Vienna, Austria Junta de Energia Nuclear, Cuidad Universitaria, Madrid-3, Spain L.R.M., B.P. 3013, 54000 Nancy Cedex, France National Bureau of Standards, Office of Standard Reference Materials, Washington, DC 20234, U.S.A. National Chemical Laboratory for Industry, Japan South African Bureau of Standards, Private Bag X191, Pretoria, Transvaal 0001, South Africa Ores, rocks Zn, Pb, Sn, Cu ores Rocks Fe ores U ores Lignite Rocks Fe, Al, Cu, Mo, Li, Zn, W ores, fluorspar, Na & K feldspar, clays Rocks Rocks, Fe, Cr oresMethodology 75 Table 3.3A.4 GLASSES, CERAMICS AND REFRACTORIES Supplier Finely divided form Bureau of Analysed Samples Ltd., Newham Hall, Newby, Middlesbrough, Cleveland TS8 9EA, England Centre d'Etudes et de Recherches de L'lndustrie des Liants Hydrauliques, 23, rue de Cronstadt, 750 1 5 - Paris, France Centre National de la Recherche Scientifique, Centre de Recherche Petrographiques et Geochimiques (C.N.R.S./C.R.P.G.), 15, rue Notre Dame des Pauvres, Case Officielle No. 1, 54500 Vandoeuvre-lez-Nancy, France Federation Europeenne des Fabricants de Produits Refractaires (P.R.E.), 44, rue Copernic, 75016 Paris, France L.R.M., B.P. 3013, 54000 Nancy Cedex, France National Bureau of Standards, Office of Standard Reference Materials, Washington, DC 20234, U.S.A. National Chemical Laboratory for Industry, Japan Sheffield University, Department of Ceramics, Glasses and Polymers, Northumberland Road, Sheffield S10 2TZ, England Society of Glass Technology, 20 Hallam Gate Road, Sheffield S10 5BT, England Silica brick, firebrick, magnesite-chrome Portland cement, zircon, high purity silica Cement Glasses (2 available) Refractory materials Refractory materials Lead / barium, opal, high and low boron, soda lime glasses, silica, aluminosilicate and chrome refractories, Portland cements Sodalime silica, silica, high silicic acid - high boric acid glass Potassium oxide-lead oxide-silica glass Glasses (3 available)76 Analytical Atomic Spectroscopy Table 3.3A. 5 ENVIRONMENTAL MATERIALS ~~ ~~~ Supplier Finely divided form Bureau of Analysed Samples Ltd., Newham Hall, Newby, Middlesbrough, Clcveland TS8 9EA, England Institut de Recherches de la Siderurgie Fra ncaise, B.P. 129, 78 104 - Saint Germain en Laye, France Furnace dust (LD) Furnace dust (electric) National Bureau of Standards, Office of Standard Reference Materials, Washington, DC 20234, U.S.A.Orchard leaves, bovine liver, river sediment, urban particulate matter, coal, fly ash, Theat flour, rice flour, yeast, tomato leaves, pine ncedles, spinach, oyster tissue 1 1 i 3 4 5 6 7 8 9 10 11 Table 3.3B SUPPLIERS OF SPECTROGRAPHIC GRAPHITE ELECTRODES Baird Corporation Inc., 125 Middlesex Turnpike, Bedford, MA 01 730, U.S.A.Carbon Products Division, Union Carbide Corp., 270 Park Avenue, New York, NY 10017, U.S.A. (ARL Ltd., Wingate Road, Luton, Beds., England) Labtest Equipment Co., 11828 La Grange Avenue, Los Angeles, CA 90025, U.S.A. Johnson Matthey Chemicals Ltd., 74 Hatton Garden, London EClP lAE, England Le Carbone (GB) Ltd., Portslade, Sussex, England Le Carbone Lorraine, 37-4 1 Rue Jean-Jaures, 92231 Gennevilliers, France Jarrell-Ash, 590 Lincoln Street, Waltham, MA 021 54, U.S.A.Zebac Inc., P.O. Box 345, Bevea, OH 44017, U.S.A. Ringsdorffe-Werke GmbH, 53 Bonn-Bad Godesberg, West Germany (Mining & Chemical Products Ltd., Alperton, Wembley, Middlesex HA0 4PE, England) Spex Industries Inc., 3880 Park Avenue, Metuchen, NJ 08840, U.S.A.(Glen Creston, 16 Carlisle Road, London NW9 OHL, England) Ultra Carbon Corp., P.O. Box 747, Bay City, MI 48706, U.S.A. (Heyden & Son Ltd., Spectrum House, Alderton Crescent, London NW4, England)Methodology 77 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Table 3.3C SUPPLIERS OF STANDARD METAL SOLUTIONS (MS) AND REAGENTS (R) FOR AAS Aldrich Chemical Co., Inc., 940 W.St. Paul Avenue, Milwaukee, WI 53233, U.S.A. (R) J. T. Baker Chemical Co., 222 Red School Lane, Phillipsburg, NJ 08865, U.S.A. (MS, R) Barnes Engineering Co., 30 Commerce Road, Stamford, CO 06902, U.S.A. (MS) BDH Chemicals Ltd., Poole, Dorset BH12 4NN, England (MS, R) Bio-Rad Laboratories, 2200 Wright Avenue, Richmond, CA 94804, U.S.A. (MS) Carlo Erba, Divisione Chimica Industriale, Via C . Imbonati 24, 20159 Milano, Italy (MS) Eastman Organic Chemicals, Eastman Kodak Co., 343 State Street, Rochester, NY 14650, U.S.A. (R) Fisons Scientific Apparatus Ltd., Bishop Meadow Road, Loughborough, Leics. LEll ORG, England (MS, R) Harleco, Div. of American Hospital Supply Corp., 60th and Woodland Avenues, Philadelphia, PA 19143, U.S.A. (MS) Hopkin & Williams Ltd., P.O. Box 1, Romford, Essex RM1 IHA, England (MS, R) V. A. Howe & Co. Ltd., 88 Peterborough Road, London SW6 3EP, England (MS) Instrumentation Laboratory Inc., 11 3 Hartwell Avenue, Lexington, MA 02173, U.S.A. Johnson Matthey Chemicals Ltd., 74 Hatton Garden, London EClP lAE, England (R) Koch-Light Laboratories Ltd., Colnbrook, Bucks., England (R) (Anderman & Co. Ltd., Battlebridge House, 87-95 Tooley Street, London SE1, England) May & Baker Ltd., Dagenham, Essex RMlO 7XS, England (R) E. Merck, D 61 Darmstadt, West Germany (R) Spex Industries Inc., 3880 Park Avenue, Metuchen, NJ 08840, U.S.A. (MS) ALFA Division, Ventron Corp., 152 Andover Street, Danvers, MA 01923, U.S.A. (MS) (MS) (Glen Creston, 16 Carlisle Road, London NW9 O H L , England)78 Analytical A tomic Spectroscopy 10 11 12 13 14 15 16 17 Table 3 3D SUPPLIERS OF ORGANOMETALLIC STANDARDS Angstrom Inc., P.O. Box 248, Belleville, MI 481 11, U.S.A. Baird Corporation Inc., 125 Middlesex Turnpike, Bedford, MA 01730, U.S.A. J. T. Baker Chemical Co., 222 Red School Lane, Phillipsburg, NJ 08865, U.S.A. BDH Chemicals Ltd., Poole, Dorset BH12 4NN, England Burt and Harvey Ltd., Brettenham House, Lancaster Place, Strand, London WC2, England Carlo Erba, Divisione Chimica Industriale, Via C. Imbonati 24, 20159 Milano, Italy Conostan Div., Continental Oil Co., P.O. Drawer 1267, Ponca City, OK 74601, U.S.A. Durham Raw Materials Ltd., 1-4 Great Tower Street, London EC3R SAB, England Eastman Organic Chemicals, Eastman Kodak Co., 343 State Street, Rochester, NY 14650, U.S.A. Hopkin and Williams Ltd., P.O. Box 1, Romford, Essex RM1 lHA, England E, Merck, D 61 Darmstadt, West Germany MBH Analytical Ltd., Station House, Potters Bar, Herts. EN6 IAL, England Division of Chemical Standards, National Physical Laboratory, Teddington, Middlesex TWll OLW, England National Spectrographic Laboratories Inc., 19500 South Miles Road, Cleveland, OH 44128, U.S.A. National Bureau of Standards, office of Standard Reference Materials, Washington, DC 20234, U.S.A. Research Organic/Inorganic Chemical Corp., 1 1686 Sheldon Street, Sun Valley, CA 91 352, U.S.A. ALFA Division, Ventron Corp., 152 Andover Street, Danvers, MA 01923, U.S.A. (Glen Creston, 16 Carlisle Road, London NW9 OHL, England)