Spectrophotometric extractive titrations for the determination of traces of metals

A modification of extractive titrations, spectrophotometric end-point determination, is proposed. There is no need to discard the organic layer after each extraction because specially constructed titration cells are used. Precise, rapid and selective determination of microgram amounts of single cations, and in favourable cases pairs of cations, is possible.     

Determination of trace impurities in gallium arsenide by NAA

GaAs is not an ideal matrix for INAA because elements yielding activation products with half-lives up to about 5 d cannot be measured due to the interference by⁷²Ga and⁷⁶As (t_1/2=14.1 h and 26.4 h, respectively). The measurement of radionuclides with longer half-lives is interfered with by⁷⁴As (t_1/2=17.7 d), generated by fast neutrons. However, using an irradiation facility with a very low flux of fast neutrons, in which the generation of⁷⁴As is minimal, five elements could be determined in GaAs (Cr, Co, Zn, Ag, and Hg). For 27 elements the detection limits were below 1 g/g and for ten of them below 10 ng/g. The determination of nitrogen in GaAs has been carried out using the (n, p)-reaction on¹⁴N, which is induced by thermal neutrons. The activation product,¹⁴C, can be effectively separated and purified via¹⁴CO₂ and counted with high efficiency in a liquid scintillation counter, and nitrogen can be determined with fairly low detection limits if sufficiently high neutron fluxes and long irradiation times are applied. The procedure described is based on a reactor irradiation with a thermal flux of 2·10¹⁴ n·cm^–2·s^–1 for 51 days. 0.16±0.09 g/g N in GaAs were determined and the detection limit was about 3 ng/g.     

Spectrophotometric determination of selenium with dithizone

Microgram amounts of selenium(IV) are determined by measuring the decrease in absorbance of dithizone in carbon tetrachloride solution at 620 nm. Relative standard deviations for samples containing 0.20 and 1.00 μg of selenium(IV) are 0.6% and 0.4%, respectively. Of several metals tested only copper (at the 1.0-μg level) and iron (at the 100-μg level) interfere but high concentrations of nitric or perchloric acid cause low results. A reinvestigation of the reaction of selenium(IV) with dithizone suggests a formula Se(HDz)₄ for the dithizonate.     

Determination of iron in high purity gallium arsenide, gallium and arsenic as the bathophenanthroline complex

Summary A spectrophotometric method is described for the determination of iron in high purity GaAs and As or Ga, having a limit of detection of 3.5×10^–5% and 7×10^–5% Fe, resp. After sample dissolution and pre-reduction of Fe³⁺ to the bivalent state with hydroxylammonium chloride the red iron(II)-bathophenanthroline complex is formed in the presence of sodium citrate, ascorbic acid and perchlorate. It is extracted into chloroform and optical density of the resulting extract is measured at 533 nm. The effect of copper is discussed. The procedure is stated to be rapid and applicable not only to Ga, As and GaAs, but also to other materials.

---

Zusammenfassung Es wird eine spektralphotometrische Methode zur Eisenbestimmung in Ga oder As und GaAs mit Nachweisgrenzen von 3,5 · 10^–5% bzw. 7,0 · 10^–5% Fe beschrieben. Nach Lösung der Probe und Vorreduktion des Eisens mit Hydroxylammoniumchlorid wird in Anwesenheit von Natriumcitrat, Ascorbinsäure und Perchlorat ein roter Komplex von Eisen(II)-bathophenanthrolin gebildet, der mit Chloroform extrahiert wird und dessen optische Dichte bei 533 nm gemessen wird. Der Einfluß des Kupfers wird diskutiert. Die vorgeschlagene Methode ist schnell durchfÜhrbar und kann nicht nur fÜr Ga, As und GaAs, sondern auch fÜr andere Materialien angewendet werden.

     

Determination of chromium in gallium arsenide by electrothermal atomic absorption spectrometry

The sample is decomposed with 50% (v/v) aqua regia and the diluted solution is injected into the graphite furnace. The temperature program developed minimizes non-specific background signals, so that correction is not required. For a 100-mg sample, the 3σ detection limit is 70 ng Cr g^?1. The relative standard deviation of the overall procedure is 5–7%.     

On the interaction of copper with defects in gallium arsenide

The behavior in gallium arsenide of copper introduced through the melt has been investigated. Measurements have been made on the electrical and photoluminescent properties of single crystals that had either been quenched from T_cryst, slowly cooled after crystallization or thermally annealed at 1100°C after completion of the growth. On quenching from T_cryst, formation of very shallow acceptors is observed. On slow cooling or annealing at 1100°C, acceptor levels are formed of the order of 0.12 and 0.02 eV. The concentration of carriers for both levels diminishes with lower temperatures of annealing and with concentration of copper added. The 0.12 eV level is assigned to the center (Cu_GaV_Ga)⁻.     

Spectrophotometric and polarographic methods for the determination of silicon at ng/g levels in gallium arsenide

Summary Spectrophotometric and differential pulse polarographic determinations of silicon in gallium arsenide as heteropoly acid have been established. The analysis comprises decomposition with a mixture of hydrochloric acid and bromine in a PTFE vessel, elimination of matrix elements by evaporation of arsenic as arsenic trichloride and extraction of gallium as gallium tetrachloro-complex anion by di-isopropyl ether, and finally spectrophotometric determination of silicomolybdenum blue or polarographic determination of -silicomolybdic acid. Optimization of sample pretreatment procedures and instrumental determination have been carefully elaborated. The detection limits of the developed methods were found to be 7 ppb and 5 ppb, respectively, for spectrophotometry and polarography. The proposed methods have been practically applied to the analysis of various Si-doped samples. The results obtained by the chemical methods are compared with those from the electrical measurement and the discrepancies found are discussed.

---

Spektralphotometrische und polarographische Bestimmung von Silicium in Galliumarsenid im ng/g-Bereich

Zusammenfassung Die beschriebenen Verfahren beruhen auf der Si-Bestimmung als Heteropolysäure. Sie umfassen den Aufschluß der Probe mit Salzsäure und Brom im PTFE-Gefäß, Eliminierung der Matrixelemente (Verdampfung von Arsen als Arsentrichlorid und Extraktion von Ga als Tetrachlorokomplex mit Diisopropylether) sowie anschließende spektralphotometrische Bestimmung als Silicomolybdänblau oder polarographische Bestimmung als -Silicomolybdänsäure. Die Optimierung der Vorbehandlungstechnik sowie der instrumentellen Analysenparameter wird beschrieben. Die Nachweisgrenzen liegen bei 7 ppb bzw. 5 ppb. Die vorgeschlagenen Methoden wurden auf verschiedene Sidotierte Proben angewendet. Die Ergebnisse werden verglichen und Unterschiede diskutiert.

---

---

Presented at the Colloquium Spectroscopicum Internationale XXIV, September 15–20, 1985, Garmisch-Partenkirchen, FRG     

Determination of carbon impurity in gallium arsenide crystals by photon activation analysis

Determination of carbon impurity in GaAs crystals has been investigated by photon activation analysis using the¹²C(, n)¹¹C reaction. Chemical isolation of the radiocarbon as CO₂ was carried out by the combustion method using Pb₃O₄ as a fusing agent and/or oxidizing accelerator in a high flow rate of oxygen stream. The CO₂ was then collected by passing through a double trap containing NaOH solution, and precipitated finally as BaCO₃. By measuring positron annihilation gamma-rays due to the isolated radiocarbon, it was proved that determination of the above carbon impurity can be achieved easily and favourably. On the basis of the results obtained, a conversion factor for the LVM absorption of carbon at room temperature in Fourier-transform infrared spectroscopy was found to be 1.4·10¹⁶ atoms · cm^–1.     

Determination of 17 trace elements in gallium arsenide by reactor neutron activation analysis

A method has been developed for the simultaneous determination of 17 trace elements in gallium arsenide. The method involves reactor neutron irradiation of the samples, distillation of the arsenic matrix activity and Ge(Li) γ-ray spectrometry. For a sample size of 0.1 g and a 10-day irradiation at 2·10¹³ n cm^-2 s^-1, the detection limits vary from 70 p.p.b. (tin) down to 5·10^-3 p.p.b. (scandium).     

Determination of traces of phosphorus in gallium arsenide by radiochemical neutron activation analysis

A radiochemical separation procedure has been developed to determine traces of phosphorus in gallium arsenide. In this procedure the indicator nuclide³²P is separated from all other long-lived activation products in high purity. The resulting eluate is sufficiently pure to allow -counting. Because of the high -energy of³²P (1710 keV) the activity can be measured via the Cerenkov effect, whereas most radionuclides, because they have essentially lower -energies, are discriminated by this technique, so that the selectivity of the measurement of³²P is improved considerably. A detection limit of 1 ng/g was achieved when using samples of 50 mg, a thermal neutron flux of _th=1·10¹³n·cm^–2·s^–1, an irradiation time of 36 hours and a measuring time of 1 hour.     

Spectrophotometric extractive titrations-IV Determination of zinc in germanium dioxide and germanium chloride

A simple and selective determination of zinc in germanium chloride and germanium dioxide is described. The sample is dissolved in sodium potassium tartrate solution and zinc is titrated spectrophotometrically at 532 mug( with a dithizone solution in carbon tetrachloride without discarding the organic phase. Interfering ions such as Bi(III), Cu(II), Cd(II), Co(II), Ni(II), Pb(II), Sn(II), Fe(II), Fe(III), Mn(II) and T1(I) are masked with bis(2-hydroxyethyl)dithiocarbamate. The detection limit is 3-23 x 10(-5)% of zinc and this may be lowered by taking a larger sample and by performing the analysis in a closed system. A simplified technique, consisting of the simultaneous titration of the sample and blank, is described.     

Spectrophotometric determination of iron and cobalt with Ferrozine and dithizone

Procedures are described whereby iron (1–50 μg) and cobalt (1–25 μg) are determined spectrophotometrically, iron as iron(II) with the disodium salt of 3-(2-pyridyl)-5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine (Ferrozine) and cobalt as the cobalt(III) dithizonate complex. The reduction to iron(II) prevents interference of iron(III) in the cobalt determination, and both metals can be determined in the same portion of sample solution. Removal of interference by other metal ions is described.     

Determination of zinc in gallium arsenide by electrothermal atomic absorption spectrometry with the L''vov platform and matrix modification

Summary A method is described for the determination of zinc in gallium arsenide by ETAAS with platform atomization and matrix modification. The sample is decomposed with nitric and hydrochloric acids, ortho-phosphoric acid is added as a matrix modifier and the diluted solution is injected into the furnace. The optical correction of the nonspecific absorbance is readily achieved by means of a conventional deuterium lamp. Platform atomization improves the peak repeatability by a factor often in comparison with wall atomization. For a 40 mg sample, with reduced argon flow rate in the atomization step, the detection limit is 0.08 g Zn g^–1 (4×10¹⁵ atoms cm^–3). Results obtained by analysing Zn-doped GaAs samples are presented. The relative standard deviation of the overall procedure is 4–8%.

---

Bestimmung von Zink in Galliumarsenid durch ETAAS mit L'vov-Plattform und Matrixmodifizierung

     

Determination of oxygen in gallium arsenide by3He activation analysis using substoichiometric precipitation

Distillation of fluoride as fluorosilicic acid and substoichiometric precipitation as lanthanum fluoride was studied for the determination of oxygen in gallium arsenide by³He activation analysis. Fluoride could be separated substoichiometrically with a good reproducibility by two distillations and successive precipitation with lanthanum. The oxygen concentration in gallium arsenide prepared by the horizontal Bridgman technique was 10 to 36 ppb and increased a little along the front, middle and tail portions in the crystal.     

Spectrophotometric determination of manganese with dithizone using the synergistic effect of pyridine

The extraction of manganese with dithizone using the synergistic effect of pyridine has been studied. A method is described for determining manganese spectrophotometrically. Trace amounts of manganese can be determined, the sensitivity being 0.0014 μg Mn/cm² at 530 nm.     

Determination of boron in silicon-doped gallium arsenide by electrothermal atomic absorption spectrometry and ultraviolet-visible spectrophotometry

Two methods have been developed for the determination of boron impurities in silicon-doped gallium arsenide (GaAs) for electronics. The first method employs the electrothermal atomic absorption spectrometry (ETAAS), the second, the UV-Vis molecular absorption spectrophotomety. In both cases the GaAs sample is decomposed with aqua regia (1+1). To prevent Ga(III) interference on the ETAAS determination of boron, a double extraction of the chlorogallic acid (HGaCl4) in diethyl ether is performed. To improve the overall ETAAS performance, the graphite tubes were pre-treated with iridium(III) and tungsten(IV). A mixed chemical modifier containing Ni(II), Sr(II) and citric acid was also used. The characteristic mass (m0) is 301 +/- 47 pg and the detection limit (3sB) is 2.4 microg g(-1). The classic UV-Vis spectrophotometric procedure using curcumin was also extended to the determination of boron in GaAs. By masking Ga(III) with EDTA and a preliminary extraction of boron with 2-ethyl-hexane 1,3-diol, performed on a semi-micro scale, a detection limit of 0.6 microg g(-1) was achieved. Both methods were applied to the analysis of two Si-doped GaAs samples which were suspected of being boron-contaminated. Results are compared with those obtained by direct analysis of the decomposed sample solution using the inductively coupled plasma atomic emission spectrometry (ICP-AES).     

Differential pulse polarographic determination of chromium in gallium arsenide

Summary The proposed method for the determination of Cr in gallium arsenide is based on the catalytic activity of chromium(VI)-DTPA complex in the presence of nitrate ions. After dissolution of gallium arsenide with hydrochloric and nitric acids and volatilization of arsenic, chromium is oxidised to chromate with potassium chlorate in nitric acid. After nitric acid removal, the 0.012 M DTPA — 2.5 M LiNO₃ supporting electrolyte buffered with 0.2 M CH₃COONa — 0.05 M CH₃COOH is directly added to the residue. Differential pulse polarography of this solution provides a detection limit of about 100 ng g^–1, with a relative standard deviation of ±2–5% and a reproducible calibration curve up to at least 1 g of Cr(VI) ml^–1.

---

Differential-pulspolarographische Bestimmung von Chrom in Galliumarsenid

Zusammenfassung Das vorgeschlagene Verfahren beruht auf der katalytischen Aktivität des Chrom(VI)-DTPA-Komplexes in Gegenwart von Nitrationen. Nach Auflösung des Galliumarsenids mit Salz- und Salpetersäure, wird Arsen verflüchtigt und Chrom mit KClO₃/HNO₃ zu Chromat oxidiert. Die Salpetersäure wird entfernt und der Rückstand direkt mit dem Trägerelektrolyt versetzt (0,012 M DTPA — 2,5 M LiNO₃, gepuffert mit 0,2 M CH₃COONa — 0,05 M CH₃COOH). Durch Differentialpulspolarographie dieser Lösung erhält man eine Nachweisgrenze von etwa 100 ng g ^–1. Die relative Standardabweichung beträgt ± 2–5%, die Eichkurve ist reproduzierbar bis 1 g Cr(VI) ml^–1.

     

Atomic absorption spectrometric determination of indium in gallium arsenide

Summary The determination of indium in heavily doped gallium arsenide (0.2–1.2 mg g^–1 In), by both electrothermal and flame AAS is reported. The sample is first decomposed with nitric acid and the diluted solution is atomized by employing the more convenient technique. The conventional air-acetylene flame is used for samples containing at least 1 mg g^–1 indium. For lower concentrations the electrothermal atomization is required and matrix-matched standards become necessary. Platform sampling is shown to improve both sensitivity and repeatability in comparison with the tube-well sampling. Dependence of the matrix effect on both the signal measurement mode and deterioration of the platform is examined. By increasing the sample mass up to 100 mg, without further dilution of the solution to be injected into the furnace but with the optical correction of the background, a detection limit (6 s) of 4.2 ng g^–1 (1.2×10¹⁴ atoms cm^–3) is achieved. The method was applied to In doped GaAs samples and the results are compared with those independently obtained by differential pulse polarography.

---

AAS-Bestimmung von Indium in Galliumarsenid

---

This work was presented at the Euroanalysis VI Conference (Paris, September 7–11, 1987)     

Rate constants for the reaction of atomic and molecular bromine with gallium arsenide

The reaction of the (100) face of a gallium arsenide single crystal with atomic and molecular bromine has been studied in a discharge flow system at temperatures between 100 and 225°C and pressures between 0.1 and 40 torr. The reaction with Br₂ was found to be first order in Br₂ only at pressures below 1 torr. Temperature dependence studies in the linear range gave the activation energy and preexponential factor for the rate controlling reaction in the low pressure regime. The results are summarized in the following Arrhenius equation: Deviations from linearity at high pressures are discussed in terms of two alternative mechanisms. The reaction of GaAs with atomic bromine was also studied as a function of temperature, and found to have a temperature dependence described by the following Arrhenius equation: