ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 29 Analysis of Sodium in Blood Plasma Using a New Mini Ion-selective Electrode Martin Telting-Diaz, Malcolm R. Smyth and Dermot Diamond* School of Chemical Sciences, National Institute for Higher Education, Glasnevin, Dublin 9, Ireland Eileen M. Seward, Gyula Svehla and Anthony M. McKervey Department of Chemistry, University College, Cork, Ireland The popularity of ion-selective electrodes is well recognised today. Numerous medical centres use them on a routine basis for the analysis of the most relevant physiological ions in clinical practice, e.g., Na+, K + , CaI+ and H+.l As regards sodium, the development of the sodium glass membrane has permitted the potentiometric analysis of various body fluids: whole blood,? serum,3.4 plasma2.5 and urine.z.4.h Today much modern equipment uses this analytical method for sodium measurements in clinical laboratories.The advantages of the electrodes are well catalogued in the literature.7 in particular when they are compared with more sophisticated methods of sodium analysis, such as flame photometry or atomic absorption. PVC sodium selective membranes based on neutral carriers have not yet achieved the popularity of the glass membrane, even though it is well known that the performance of electrodes based of these membranes is superior to that of the glass electrode in terms of lower membrane resistance, lack of contamination by proteins depositing on the membrane surface, the obvious easy construction. general robustness and the possibility of implanting micro-PVC electrodes into the human body.Derivatives of calix(.l]arenes have shown an ability to complex alkali metal ions.s.y X-ray crystallographic studies of some of these macrocyclic compounds have established a cuplike configuration, with polar groups facing towards the cavity. and ordered in such a way as to promote ion binding.]" The cavity of the ligand used in this research (methyl p-tert-butylcalix[.l]aryl acetate) (Fig. 1) is formed from polar phenolate and ester oxygen atoms.' I When incorporated into plasticised PVC membranes. a surrounding highly lipophilic layer ensures a good compatibility with the non-polar PVC plasticiser . Electrodes based on such ion-sensitive membranes have been found to respond to variations in ion activity in a Nernstian manner. i.e., E = E" + S log u, where a, are primary ion activities in sample solution; E is the measured potential: E" is the standard potential: and S is the Nernst slope factor.i.e., 2.303 RT/z,F, in which R is the gas constant. T the absolute temperature. 2 , the charge on the primary ion and F the Faraday constant. Ideally. a selective ionophort contained in a liquid or PVC membrane draws only one type of cation [the primary ion (i)] Author to whom correspondence 4hould be addressed. into the membrane phase. In reality, all ion-selective elec- trodes respond to cations other than the primary ion. The effect of these interfering ions 0) on the membrane potential is given by the Nikolski - Eisenman equation: E = E" + s log [a;+ T' a;,='] where all the symbols have their conventional meaning.12 Experimental methods for estimating selectivity coefficients have been outlined by Moody and Thomas.13 Fig.1. The ionophore methyl p-tert-butylcalix[j]aryl acetate (ligand 1C) showing the cone conformation with a separation between adjacent phenolic oxygen atoms of 0.3 1-0.33 nrnl' (oxygen atoms filled circles) Materials and Methods Chemicals and Samples All of the electrolyte solutions were prepared in Milli-Q water and the salts were of analytical-reagent grade. The calibration solutions and those used to determine selectivity coefficients for the separate-solution method were made up by serial dilution of 0.1 M stock salt solution.ANALYTICAL PROCEEDINGS, JANUARY 1989. VOL 26 The synthesis of the calixarene ester has been described earlier. 1 1 Plasticiser-mediator 2-nitrophenyl octyl ether (2- nPOE), potassium tetra-p-chlorophenylborate (KTpCIPB), poly(viny1 chloride) (PVC) and tetrahydrofuran (THF) were obtained from Fluka AG.while salts of Tris buffer were obtained from Sigma. The plasma samples were collected at St. James Hospital, Dublin. The samples had previously been analysed by means of a sodium glass electrode using the Technicon method,lj which involves dilution of the sample six times before it is screened. One aliquot of each sample was taken and adjusted to pH 7.4 with Tris buffer. The samples were then diluted ten times. The composition of the membrane cocktail used throughout this research is given in Table 1. Table 1. Membrane cocktail composition Component O/o m/m Ligand 1C 1.3 2-nPOE 65.0 KTpClPB 0.3 PVC 33.3 Electrodes and Instruments Electrodes were constructed by introducing a chloridised silver wire (Johnson Matthey Ltd.) into a 1 mm i.d.PVC tube (EMS Medical Group Ltd., Stonehouse, Gloucestershire) about 16 cm long. One end of the wire was soldered to a 2 mm plug, which was subsequently fixed to the tube by glueing with an epoxy adhesive. At the other end, the wire was cut to size and a 4 5 mm porcelain tip (Morgan Matroc Products Ltd.). glued in place with a drop of tetrahydrofuran (Fig. 2). To coat the PVC membrane on to the porcelain, the tip was submerged several times in the membrane "cocktail" and left to dry by evaporat- ing the THF for 24 h at room temperature. The electrode was C d e Fig. 2.Schematic representation of a PVC mini-ion-selective elec- trode: ( a ) , chloridised silver wire; ( b ) . PVC electrode body ( 1 mm i.d.); ( c ) , internal reference electrolyte (0.1 M NaCI); ( d ) , ion sensitive PVC membrane; (e), porcelain tip; ( f ) . 2 mm electrical DIUE next filled with the internal solution (0.1 M sodium chloride) by injecting it with a fine syringe into the PVC tube body. The electrode was then left to condition in 0.1 M sodium solution for 1 h prior to use. The indicator electrodes constructed were used with a Metrohm AG 9100 Herisan reference electrode, connected to a Philips PW 9421 digital pH/mV meter and a Linseis 16512 chart recorder. The meter was standardised and used according to the recommendations of the manufacturer. The e.m.f.measurements were carried out on cells of the type: Hg, Hg2C12/KCl(satd)/ Reference Sample/ PVC membrane/O. 1 M NaCVAgC1,Ag ISE Selectivity Coefficients and Electrode Function To determine the slope of the electrodes, potentials were measured in six standard solutions of NaCl over the range 10-'-10-6 mol 1 - 1 . The response to a number of possible interfering ions over the same range is shown for comparison in Fig. 3. Selectivity coefficients wi (tabulated in Table 2) were obtained by the separate-solution method," using the expres- sion E,-E, = log KF;"' 2.303 RTIF where E, and E j are the potentials measured in solutions of the various interfering ions (j) and the primary ion (i) at equal activities (0.1 M). Corrections for experimental e.m.f. values were made for estimated variations in liquid junction potential using the Henderson formula.15 The activity coefficients were calculated on the basis of the Debye - Huckel formalism.li Table 2. Comparison of selectivity coefficients and slopes for a variet!, of sodium ion selective electrodes. See reference 4 for glass membrane electrode Selectivity coefficients (log Kilo') Mini-electrode* based on Ion ligand 1C Cs + H i K+ NH' + Li + Mg'+ SlopeimV Ca2 t -1.51 -1.88 -2.47 -2.74 -2.78 -3.12 -3.74 58.1 f 0.8 ETH 227 -2.24 -0.1 0.0 -1.7 0.5 -1.5 57.5 k 0 . 1 - 3 3 &.A Glass ETH 157 electrode - 1 .5+ -3.0 0.7 3 . 0 -0.4 -3.0 - 1 .O+ -4.5 -1.7 -3.0 -3.3 - -3.1 - 60.1 k 0.7 * Determinations obtained by the separate-solution method by using 0.1 M solutions. The values for the membranes denoted as ETH 227 and ETH 157 have been obtained by Simon and co-workers' and correspond to two different Na + ionophores. + Values obtained with macro-electrode.Procedures For studies involving determinations of selectivity coefficients, sets of up to 10 electrodes were assayed and the electrode that presented less drift was selected to perform the analysis. The e.m.f. values used for calculations were the mean of the potential measured at 10 and 15 min after immersing the electrodes in the sample. The measurements were performed at 20 + 1 "C throughout.ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 - E 140 m cs i, 130 B 31 ' 1 I I /+ Na- i 1 J Log activity Fig. 3. Calibration curves for important cations obtained ivith mini-ion-selective electrode based on ligand 1 C.Solutions range from 10 f1 to 10- I 51 (all CI salts except MgSO,) -6 -5 -4 - 3 -2 -1 0 In order to determine the e.m.f. of plasma samples. six sodium calibration solutions were made up and the slope of the electrode function calculated before attempting any measure- ment. These stock solutions contained 50.0. 125.0. 130.0. 155.0, 200.0 and 500.0 mmol 1 - 1 of Na+ with a constant ion background of K+ (4.0 mmol 1 - 1 ) . Caz+ (1.1 mmol 1-1) and Mg'+ (0.6 mmol l-I). When taking measurements. 1 ml of each stock solution was removed, 2 ml of Tris buffer added (pH 7.4) and the volume made up to 10 ml. A similar procedure was used with blood samples, i.e., 2 ml of Tris buffer (pH 7.4) were added to 1 ml of blood plasma and the total volume made up to 10 ml.To obtain the plasma, the blood samples were centrifuged at 3500 rev min-1 for 10 min. After every third or fourth sample the electrode response was checked in the calibration solutions. Two electrodes were used to analyse a total number of 44 plasma samples (see Results and Discussion). Results and Discussion PVC sodium mini-ion-selective electrodes have been construc- ted by using methyl p-tert-butylcalix[4]aryl acetate as iono- phore for the application of sodium analysis in blood plasma. The values obtained for selectivity coefficients were reprodu- cible and found to agree well with those obtained in earlier studies for the same ionophore.16 The pattern of selectivity against interferents shown in Fig. 3 is broadly similar to that 160, 1 2 0 ' + L 120 130 140 150 Glass electrode: C,; :mmol I ' 160 Fig.4. Correlation between t\vo indirect potentiometric methods for the measurement of sodium concentration in 24 plasma samples. The slope of the electrode is 58.1 k 0.8. Smac Analyser (sodium glass electrode). sample diluted six times: mini-electrode (based on ligand 1C). sample diluted ten times. The ideal correlation between both wts of results is shown by the segmented line obtained by phase-transfer studies. 1 1 The comparison shown in Table 2 includes two PVC membranes which are currently available, and the traditional glass membrane. Ligand 1C exhibits better selectivity towards K+ and Li+ than ETH 227 and ETH 157, and a similar sensitivity towards these ions compared with the glass membrane. Ligand 1C presents the best selectivity against H+ ions.Fig. 4 shows results obtained with mini-ISE's in 24 plasma samples compared with the Technicon method. Although a good correlation was obtained (coefficient = 0.94) a small but systematic error was evident (3.1 mmol 1 - 1 average). A second batch of 20 plasma samples showed a similar pattern (Fig. 5 ) with a good correlation (coefficient = 0.95) but with a constant slightly negative error in this instance (4.6 mmol 1 - 1 average). The origin of the systematic error is at present unknown but could arise from differences in the hospital or our own calibration procedures. - - 150 r------------l / /' + 120 ' I 120 130 140 150 160 Glass electrode: CNa+ immol I - l Fig. 5. Correlation of sodium measurements in 20 diluted plasma samples. Other details as for Fig.1. The slope of the electrode obtained prior to measurements is 54.5 ? 0.3 At this stage the error is being investigated by comparing new sets of results with a reference photometric method. As more precision and reproducibility in the technique is desir- able, further work will involve using the electrodes in a flow injection system. 1. 3. 4. 3. 6 . 7. 8 . 9. 10. 11. 13,. 13. 14. 15. 1 &. 16. References Arnold. M. A , . and Solsky. R . L.. And. Chem., 1986.58. X4R. Ladenson, J . H.. Chi. Chern., 1979. 25. 757. Langloff. E . . and S e i n e s . I . , Clin. Chem., 1982. 28. 170. Anker, P.. Jenny. H. B.. Wuthier. U . . Asper. R . . Ammann. D.. and Simon. W . . Clin. Chern., 1983. 298. 1508. Preusse, C . J . , and Fuchs.C., J . Cliri. Chern. Clin. Hiochern.. 1979. 17. 639. Graves, S . W.. Koch. D. D . . and Ladenson. J . H.. Clin. Cliern., 1982. 28. 1631. Ladenson. J . H.. Anal. Proc.. 1983. 20. 554. Chang. Suk-Kyu. and Cho. Iwhan. J . Chem. Soc. Perkin Trutis. I , 1986. 2 1 1. Ferguson. G., Kaitner. B.. McKervey, M. A , . and Seward. E . M.. J. Chem. Soc. Chern. Commun., 1987. 584. Edmonds. T. E . . "Chemical Sensors." Blackie. Glasgow and London. 1988. pp. 17-69. McKervey. M. A . . Seward. E. M.. Ferguson, G . . Ruhl. B . . and Harris. S . J.. J . Chem. Soc. Cherii. Commun., 1985, 388. Ammann. D.. Morf. W. E.. Anker. P . . Meier, P. C.. Pretsch. C.. and Simon. W . . loti Selecri1.e Electrode Rev., 1983. 5 . I . Moody. G . J.. and Thomas. J . D. K.. "Selective Ion-Sensitive Electrodes," Merrow.Watford. 1971. " S MAC Tech n icon Me t hod . '* Tech n icon I n s t r u me n t s Co rpo r - ation. Tarrytown, New York. USA. Meier. P. C.. Ammann. D.. Morf, W. E.. and Simon. W., in Koryta. J . , Editor. "Medical and Biological Applications of Electrochemical Devices. John Wiley. Chichester. 1980. p. 13. Diamond. D.. Svehla. G.. Seward. E. M., and McKervey. M. A . . A n d . Chirn. Actn. 19x8. 204, 223.32 ANALYTICAL PROCEEDINGS. JANUARY 1989, VOL 26 A Semi-continuous Flow Method for the Trace Analysis of Dissolved Inorganic Antimony A. T. Campbell and A. G. Howard Chemistry Department, The University, Southampton SO9 5NH Antimony is found in most unpolluted natural waters at concentrations which are normally below 300 ng 1-1, a level at which there are comparatively few suitable analytical methods.Methods based on hydride generation AAS offer the required sensitivity and the opportunity of providing some degree of information on speciation. There are two main approaches to such methods. The large volume “batch” approach, in which the reaction is carried out in a chamber (e.g.. the methods of Andreae et a/.‘ and Apte and Howard*) and the continuous flow hydride generation methods that are constructed from automated analysis components (e.g., the methods of Goulden and Brooksbank,’ Schmidt et al. ,4 Arbab-Zavar and Howard’ and Yamamoto et al.6). The detection limits of these methods can be improved by using a variety of collection procedures prior to transfer to the atomiser; these include balloons, pressurised chambers.collec- tor solutions and cryogenic traps (see reviews by Godden and Thomerson7 and Nakaharas). The lowest concentration detec- tion limits are generally obtained by using batch generation methods from large sample volumes and pre-concentration of the analyte. Such methods are, however, time consuming and involve much manual manipulation. and this results in a comparatively low sample throughput. Continuous flow methods, on the other hand, generally have better reproduci- bility and more rapid sample throughput, but, having no analyte pre-concentration step, lack the required sensitivity that would be required for the analysis of dissolved inorganic antimony in uncontaminated natural waters. The system to be described is a development of a technique that we have used for some years for the speciation of arsenic (Arbab-Zavar and Howardy and AptelO).This paper sum- marises the chemical and system parameters required to permit the method to be capable of the analysis of dissolved antimony in natural waters at the ng 1 - 1 level. Experimental Reagents All of the reagents used were of analytical grade unless otherwise stated. Glassware and plasticware were cleaned by overnight soaking in 1Ooh V/V hydrochloric acid followed by rinsing with distilled water. Stock standard solutions contain- ing 100 mg 1-1 of antimony(II1) and 250 mg 1-1 of antimony(V) were prepared from potassium antimony1 tartrate and potas- sium antimonate (laboratory-reagent grade). respectively. in 10% V/V hydrochloric acid.These were cross-calibrated by using flame atomic absorption spectrometry. Lower concentra- tion standards were prepared by dilution on the day of use. Sodium terrahydroborate. Laboratory-reagent grade material was dissolved in distilled water to give an unstabilised solution (2% mlV). The sodium tetrahydroborate has a significant antimony blank but can be purified by the slow addition of 2 cm3 of hydrochloric acid (1 + 9). whilst bubbling nitrogen through the solution. Potassium iodide. Potassium iodide was used to prepare a 1 M solution. This was stabilised by the addition of 2.4 g 1-1 sodium hydroxide solution and stored at 4 “C in a brown-glass bottle. Sulphanilantide solution (0.1 M ) . This solution was prepared in hydrochloric acid (1 + 9). A pH 5.0 buffer was prepared from sodium acetate solution (0.1 M ) , adjusted to the required pH with glacial acetic acid.Apparatus The apparatus consists of three distinct stages (Fig. 1). Continuous flow hydride generation is carried out by using a peristaltic pump with four reagent lines, a fourteen turn delay coil and a gas-liquid separator. In the top of the separator sodium hydroxide pellets act as a water trap. Gaseous products are then swept from the separator into a cryogenic trap containing 40-mesh hydrofluoric acid etched glass beads packed in a borosilicate glass U-tube. Detection of stibine is carried out by atomisation in an electrothermally heated quartz T-tube suspended in the light path of a Varian Techtron AA5 atomic absorption spectrometer. Air -1 ?= d trap I Waste Fig.1. The semi-continuous-flow apparatus for the determination of antimony by hydride generation AAS In the continuous flow hydride generation system the sample is acidified, segmented with air and then reacted with sodium tetrahydroborate. The products are then swept through the delay coil and stripped from solution in the gas-liquid separator. The stibine is then condensed at -196 “C in the U-trap. After trapping, the liquid nitrogen is removed and the i: Blank Time - Fig. 2. Typical output from the hydride systemANALYTICAL PROCEEDINGS. JANUARY 1989, VOL 26 trap allowed to warm to room temperature. This results in the release of the stibine to the atomisation - detection system (Fig. 91 33 i). Determination of Total Antimony A 5-cm-3 aliquot of the sample is pipetted into a glass sample cup, and 0.5 cm-3 potassium iodide (1 M ) pre-reductant is added, together with any masking reagents.The U-trap is cooled with liquid nitrogen and the peristaltic pump started. The sample probe is then placed in the cup and the sample is taken up over a period of 2.5 min. Pumping is continued for a further 1.5 min to ensure complete trans- mission of the stibine to the trap. The liquid nitrogen is then removed and the trap allowed to warm, resulting in the elution of stibine into the quartz tube atomiser. The resultant spectrometer output is recorded on a Y-r chart recorder (Te kman TE200). Determination of Antimony(II1) Antimony( 111) can be selectively determined using the above system by replacing the hydrochloric acid with a sodium - acetic acid buffer adjusted to pH 5.0.Table 1 . Spectrometer conditions Source Lamp current Wavelength Spectral band pass Furnace temperature Chart speed Chart sensitivity Antimony hollow cathode lamp 6 mA 217.6 nm 0.33 nm 900- 1000 "C 30 mm min- I 10 mV fsd Results and Discussion Optimisation The above procedures were optimised by using a univariate approach, which gave the conditions shown in Tables 1 and 2. Table 2. Optimum systeni parameters Hydrochloric acid 1 + 9 2% mlV Sodium tetrahydroborate Nitrogen gas flow-rate 250 cm3 min I Potassium iodide 0.5 cm3 ( 1 M) S u I p ha n i I am i d e 0.4 cm3 (0.1 M) * Adjusted to pH 5.0 by use of concentrated acetic acid. Sodium acetate 0 . 1 M* ~~ Interferences Potential interferences were studied by the addition of a known amount of foreign ion to a sample.Table 3 shows that both the total antimony and antimony( 111) systems suffered from a number of interferences. In general, however, the concentra- tions tested were far in excess of their natural occurrence in estuarine water and seawater. The main exception to this was nitrite. which interfered down to a concentration of 100 mg 1 - 1 in both systems. This interference was overcome by the addition of 400 pl of sulphanilamide (0.1 M ) to the sample prior to analysis. With the transition metal interferences, all except copper were removed by adding 300 ul of EDTA (0.002 M ) to the sample." In the instance of copper, this interference was removed by using 300 u1 of 1,10-phenanthroline (0.015 M ) . Speciation Species selectivity was obtained by careful control of the pH of the reaction.By using the sodium acetate-acetic acid buffer system antimony( 111) was selectively detected in the presence of a ten-fold excess of antimony(V). Hence. speciation information could be obtained by subtracting the concentra- tion of antimony(II1) obtained on one aliquot of a sample from the total antimony concentration obtained on a second aliquot. Table 4 shows the performance data for the system. It illustrates that the method is well suited to antimony speciation studies in the ng 1 - 1 concentration range. Even at the levels that can be determined with this method, the technique is still not suitable for the determination of antimony(II1) in unpol- luted natural water samples. It is, however, capable of providing useful information on the levels of total dissolved inorganic antimony in natural waters and may also be applicable to the analysis of sediment and tissue digests.interstitial water and industrial effluents. Table 3. Interferences Concentration of interferentimg I I 10 Antimony( 111) Pb' + (32";)' Fe'- (100%) NC+( l0Oo%) Co?+(74%,) Cr" - ( 86(!& ) Hg + (94% ) Cd'+ (100%) Mn'* (IOO'X)) Bi3-(42(Yl) Br (33%) Coz- (8%)Cr~~+(I6(%) CU"( 100°i,) Fe'+ (IOOYo) NO:-( lOO'l'o) A n t i m o n y (total) Hg ~ ( 7 . 3 % ) CU" (IOO'?") Fc"(8"4) NO?- (lOO?//;) * Percentages represent signal suppression. Table 4. Figures of merit Linear rangelng Preci 4 o n Detection limits (1 cm') ( 3 x s . d . o f h l a n k ) (5cm') Sample rate ( 1 cm3) ( 5 cm') 1 cm' 5 cm3 * I I = Number of replicates.34 ANALYTICAL PROCEEDINGS, JANUARY 1989.VOL 76 References 1 . 2. 3. 4. Andreae. M. 0.. Asmode. J . F.. Foster. P.. and Van" Dack. L.. Atiul. Chetn., 1981. 53, 1766. Apte. S . C.. and Howard. A. G.. J . At. Ahmrp. Spectrosc.. 1986. 1. 221. Goulden. P. D.. and Brooksbank, P.. Anal. Chem., 1974. 46. 1431. Schmidt. F. J . . Roger, J . L., and Muir. S . M.. Atial. Lett., 1975. 8 . 123. 5 . Arbab-Zavar. M. H.. and Howard. A. G.. Am~!\~.st. 1980. 105. 744. 6. Yamamoto. M.. Yasuda. M., and Yamamoto. Y.. Atid. Chetn., 1985. 57. 1382. 7. Godden. R. G.. and Thomerson. D. R.. AtitiITst. 1980. 105. 1137. 8. Nakahara, T.. Proj. Anal. Ar. Spectrosc., 1YX3. 6 . 103. 9. Howard. A. G.. and Arbab-Zavar. M. 14.. Atitr!\w. 1981. 106.213. 10. Apte. S . C.. PhD The5i.s. 1985. University of Southampton. The Capillary Gas Chromatography - Atomic Absorption Spectrometry of Organotin and Organolead Compounds R. C. Forster and A. G. Howard* Chemistry Department, The University, Southampton SO9 5NH The widespread use of organometallic compounds and their consequent release into the environment has lead to increasing concern over their persistence and toxicity. Organotins, and in particular tributyltin (TBT) compounds, have been widely used as biocides in marine anti-fouling paints and leaching from boat hulls results in the release of TBT into the coastal environment. Reduced shellfish numbers' have been linked to shell thickening in oysters'.' and imposex in dog whelksj; both of these conditions can result from exposure to TBT.As a result of the toxicity of TBT to non-target organisms legislation has been introduced to control the use of paints containing TBT. A level of 20 ng 1 - 1 has been proposed as a target for TBT in natural waters' but recent work would suggest that even this may be too high.6 Organolead compounds have found their major application as anti-knock agents in petrol. The release of lead into the environment occurs as both inorganic salts and as the more toxic alkylleads. As with TBT, many countries have introduced legislation that is designed to phase out their use. If the impact of organometallic compounds on the environ- ment is to be assessed then speciation of the elements at environmental levels is necessary. This paper describes the construction and development of a capillary gas chromato- graph (GC) system for the determination of organometallic species.The system employs the excellent separating power of capillary gas chromatography with the selectivity of detection shown by atomic absorption spectrometry. Improved sensitiv- ity is obtained by using on-column injection of up to SO-pl aliquots of the sample extract. Experimental Instrumentation The apparatus consists of a Pye 104 gas chromatograph (GC) interfaced to an Instrumentation Laboratory Model 25 1 atomic absorption spectrometer. A resistively heated transit line is used to conduct the capillary column into a flame-in-tube atomisation cell aligned in the spectrometer light path. ~~~~ To whom correspondence should be addrefsed.Gas Chromatography Chromatography was carried out on a 0.3 mm i.d., 10 m quartz capillary column coated with an immobilised methylsilicone stationary phase (1 pm film thickness). The retention gap was 15 m of 0.32 mm i.d. trimethylchlorosilane treated capillary tubing. Nitrogen carrier gas was employed at a sub-optimal flow-rate of f3-7 ml min-I and injection was carried out by using a custom built on-column injector purged with 14 ml min-1 of nitrogen. The chromatograph was temperature programmed at the following rates: tin hydrides. 30 "C for 8 min then 20 "C min-1 to 200 "C; tetraalkyllead compounds, 30 "C for 9 min then 12 "C min-' to 120 "C. Atomic Spectroscopy The following operating conditions were employed: sources. hollow-cathode lamps operated at 5 mA; wavelength.286.3 nm (tin), 217.0 nm (lead); band pass. 0.50 nm (tin). 1.00 nm (lead). Atomisation Cell Design The flame-in tube atomiser consists of a 1 cm i.d. tube attached to the transit line using a Swagelok fitting which has been modified for the introduction of hydrogen. When employed. air is introduced opposite the capillary inlet. Several designs of atomisation cell have been investigated: firstly. a basic quartz T-tube, 14 cm long, without air introduction; secondly, a quartz T-tube, 14 cm long. with air introduction; thirdly. a short quartz atomisation cell (4 cm long); fourthly a waisted quartz tube, as in the third design, but with added 1.5 cm wide bore ends (2.2 cm i.d.) to maximise light throughput; fifthly, a very short atomisation cell (1.5 cm long); and sixthly, a Pyrex atomisation cell (4 cm long).Derivatisation of Butyltins Di- and tributyltin species were derivatised before GC by using a variation of the hydridisation method described by Matthias er 01.7 Standard solutions of the butyltin chlorides were prepared by adding between SO and SO0 pl of a 1 pg ml-1 mixed standard (in methanol) to 1 dm-3 of distilled water. One hundred microlitres of a 1 ug ml-l solution of tripropyltin chloride (in methanol) was added as an internal standard.ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 35 v) 8.5 + .- C ; 6.5 I 0 4.5 m' 2.5 0 v) c L [D - .- 0.5 1.5 Fig. 1. Tin response surface under varying air - hydrogen flow-rates 8.5 2 6.5 2 2 .- t 3 4- 4.5 g m - 2.5 2 0 v) 0.5 .- To the aqueous solution was added 10 ml of pentane, then 20 ml of 4% (mlV) aqueous sodium tetrahydroborate.The mixture was shaken for 2 min. then the upper pentane layer was separated and dried over anhydrous sodium sulphate. Finally, 80 yl of the extract was injected into the GC-AAS. Results and Discussion Atomisation Cell Design The burning characteristics of the tubes vary greatly. The basic T-tube gave rise to hydrogen flames burning at the ends; this was the least sensitive. Provision of air causes the flame to burn centrally, resulting in improved sensitivity; any excess hydrogen burns at the tube ends. but contributes little to the sensi t ivity . Table 1. Performance of the system. Detection limits based on 3 x standard deviation of the blank (17 = 3). Characteristic concentration = concentration required to give a peak height absorbance of 0.0044 RSD.(11 = 6) limiting O/" Detection Me,Pb* 5 0.28 Me,EtPb* 10 0.22 Me2Et,Pb 4 0.17 MeEt,Pb 4 0.19 Et,Pb 5 0.33 Detection lirnitipg I ~ 1 of lead 5.6 4.4 3.5 3.8 4.5 Characteristic concentration/ 17 31 17 17 20 pg 1 1 of lead RSD. Detection limit,' Characteristic ( n = 4) oftin of tin in water YI n g l - l concentration/ng 1 ~ I Bu2Sn* 4 15 130 BuSn 7 13 190 Bu,Sn 7 4 9( 1 * Me = methyl. Et = ethyl. Bu = n-butyl. I ( a ) ! DMDEL TEL TML TMEL I MTEL I 6 0.01 - e v) 0 5 10 15 Retention timeimin I 0 5 10 15 Retention timeimin Fig. 2. Example chromatogram obtained using the capillary GC - AAS system. (a). Organolead species (SO ul of a solution containing. in order 0 1 chromatographic elution. tetramethyllead.trimethylethyl- lead. dirnet hyldiethyllead. triethylmet h yllead and tetraethyllead ; approximately 2 ng of lead in each component injected. ( h ) . Organotin species its their hydrides (80 ul of an extract from water containing 500 ng I - 1 of tin as dibutyltindichloride. tripropyltinchloride. tributyltin- chloride and tetrabutyltin) With the exception of the very short tube. which gave poor sensitivity, there was little difference between the other types of tube showing minimal atom trapping. For much of the work reported here. a short Pyrex atomisation tube was therefore employed. This was easier to construct than the quartz tubes and, being short, gave the most straightforward alignment in the light beam. Gas Optimisation for Organotins With a 4 cm quartz atomiser fitted to the instrument.peak height sensitivity was measured by injecting 1 111 of a solution of tetraethyltin (20 ng of tin per microlitre) in pentane, under various flame gas stoicheiometries. From these data a response surface was constructed (Fig. 1 ) and optimum conditions were found to be 130 ml min-1 of hydrogen and 165 ml min-I of air (this was also found t o be the optimum for detection of alkyllead compounds).ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 Injection of Large Volumes The conventional injection of 1-p1 samples into a GC limits concentration based detection limits. Although as yet not widely used, the injection of large volumes on to capillary columns is possible. This can be achieved by using a custom designed on-column injector and a long retention gap.8 With a 15 m retention gap it has proved possible to inject volumes up to 80 p1 routinely, thereby significantly improving the sample based limits of detection. Performance Examples of the application of the apparatus to the determina- tion of organotin and organolead species are shown in Fig.2. The system preserves the chromatographic integrity of even the higher boiling components and no deterioration of chro- matographic performance is evident from the on-column injection of large volumes. The performance of the instrument is summarised in Table 1. Calibrations were linear up to 500 ng I-’. Conclusions The interfaced capillary GC - AAS system has proved to be a powerful tool for the analysis of organometallic species. It combines the excellent separating power of capillary gas chromatography with the selectivity of detection by atomic absorption spectrometry.Improvements in sample based detection limits have been shown to be possible by large volume on-column injection. The authors would like to thank the Trustees of the Analytical Trust Fund for the provision of an SAC studentship for the execution of this work. 1. 3 -. 3 . 3 . 5 . 6. 7. 8. References Alzieu, C., Heral, M., Thibaud, Y.. Dardignac. M. J., and Feuillet, M.. Rev. Trav. Inst. Pech. Marir., 1982, 45, 100. Waldock, M. J., and Thain, J. E., Mar. Pollur. Bull., 1986, 17. 542. Alzieu, C., Sanjuan. J., Deltreil. J. P.. and Borel. M.. Mar. Pollut. Bull., 1986, 17. 494. Bryan, G. W., Gibbs. P. E.. Hummerstone. L. G., and Burt. G. R., J . Mar. Biol. Assoc. U . K . , 1986, 66, 611. UK Department of the Environment Pollution Paper No. 25. .* 0 rg ano t i n in Anti - fo ul i n g Pain t s : E nv i ro n m c: n t a I Con si de ra - tions,” HM Stationery Office, July. 1986. Waldock, M. J.. Thain, J . E . . and Waite. M. E., Appl. Organomet. Chem., 1987. I , 287. Matthias, C. L.. Bellama, J. M., Olson. G. J., and Brinckman. F. E., Environ. Sci. Technol., 1986. 20, 609. Grob, K., Karrer. G . , and Riekkola, M.-L.. J . Chromarogr., 1985, 334, 129. THE ROYAL SOCIETY OF CHEMISTRY ANALYTICAL DIVISION EIGHTH SAC CONFERENCE-SAC 89 will be held at the University of Cambridge on July 30-August 5,1989 This Conference is organised by the Analytical Division of The Royal Society of Chemistry and sponsored by IUPAC and FECS. The scientific programme, which will be published in full in a forthcoming issue of Analytical Proceedings, will cover all aspects of analytical chemistry; there will be workshops and update courses and an attractive selection of social events for delegates and their guests. Details of the Conference and registration forms can be obtained by application to the Secretary of the Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN.