Spectrophotometric determination of silicon in ultrapure, dilute hydrofluoric acid solutions

A new analytical procedure is described for the spectrophotometric determination of silicon in ultrapure, dilute hydrofluoric acid (HF) solutions. The method is a variation of the classical molybdenum blue method, but adds optimised quantities of boric acid to eliminate any HF interference in the colorimetric process. Its sensitivity and detection limit have been evaluated as, respectively, (180 ± 9) · 10^− 5/(μg/L Si) and 7.6 μg/L Si, and its reproducibility has been confirmed. The method has also been successfully applied and validated for the determination of the etch rate of single crystalline silicon surfaces in ultrapure 2% v/v HF solutions.     

离子色谱法测定蚀刻槽废氢氟酸中的六氟硅酸

建立了一种新的检测蚀刻槽废氢氟酸中六氟硅酸的离子色谱方法。色谱柱为Metrosep A Supp 7阴离子交换柱,流动相为3.2 mmol/L碳酸钠-1.0 mmol/L碳酸氢钠,流速为0.7 mL/min。六氟硅酸经过抑制型电导检测器后进行衍生化反应,在360 nm波长下用紫外检测器检测。六氟硅酸的线性范围为2.4~120 mg/L,相关系数r²大于0.999,定量限为0.24 mg/L,平均加标回收率为97.2%。本方法还可以同时利用电导检测器检测废氢氟酸中的氢氟酸、醋酸、盐酸、硝酸、磷酸和硫酸的含量。该方法快速、准确,适用于蚀刻槽液中六氟硅酸的检测。     

Elimination of hydrofluoric acid interference in the determination of antimony by the hydride generation technique

For the determination of antimony by hydride generation techniques a pretreatment procedure has been developed for the reduction of Sb(V) to Sb(III) in order to remove the effect of hydrofluoric acid which strongly interferes with the reduction of pentavalent antimony to the trivalent state. It is based on the combined action of l-cysteine and boric acid at 80 degrees C. The pretreatment is effective in both nitric and hydrochloric acid media. Quantitative recoveries are obtained in less than 60 min. Under these conditions antimony is reduced to the trivalent state in acid media containing both nitric and hydrochloric acid. The method has been applied to the determination of total antimony in certified reference materials of sediments after pressurized microwave digestion with HNO(3)-HCl-HF. Good agreement is obtained by using both analytical techniques: continuous flow hydride generation atomic fluorescence spectrometry and flow injection electrothermal atomic absorption spectrometry with in-situ trapping of stibine in a graphite atomizer.     

Determination of trace arsenic in hydrofluoric acid by hydride generation and atomic absorption spectrometry

Practical procedures are given for determination of arsenic(III) and (V) in hydrofluoric acid by means of hydride generation and atomic absorption spectrometry. Arsenic(III) can be determined by direct generation of arsine with sodium borohydride in hydrochloric/hydrofluoric acid medium, arsenic(V) being only slightly reduced under the conditions used. For its determination, arsenic(V) has to be prereduced with potassium iodide, and even then its reduction to arsenic(III) and then arsine is far from complete. It is possible to determine it in presence of arsenic(III) by a difference method, but this is recommended only if the As(V)/As(III) ratio is greater than 1. Total arsenic can be determined after oxidation of As(III) and evaporation of most of the hydrofluoric acid. The limit of determination is 5 g/l for arsenic(III) and 0.25 g/l for total arsenic; the relative standard deviation is about 10%.     

Decomposition procedure with aqua regia and hydrofluoric acid at room temperature for the spectrophotometric determination of phosphorus in rocks and minerals

A rapid spectrophotometric method for the determination of phosphorus in rocks and minerals is described. The sample solution is prepared by treatment with hydrofluoric and aqua regia at room temperature. Unreacted fluoride ions are complexed with boric acid. As fluoride ions do not have to be removed by heating, the method is rapid and avoids the use of platinum ware.     

Determination and characterization of reversed-phase bonded ligands by chemical cleavage with aqueous hydrofluoric acid

A simple and rapid method for the determination and characterization of chemically bonded ligands on reversed-phase packing materials is described. The method consists of cleavage with aqueous concentrated hydrofluoric acid and analysis of the reaction product by GC, NMR and mass spectrometry. It is confirmed from (13)C-NMR spectra that the structure of the bonded ligand is not altered by aqueous hydrofluoric acid. Several commercial reversed-phase packing materials have been analysed by mass spectrometry and because the cleavage reaction proceeds quantitatively, the alkylsilyl groups used are completely converted into the corresponding fluoride derivatives. In the proposed method the cleavage reaction is so fast that the determination takes only 15 min for the steps prior to the chromatographic and spectrometric analyses. The relative standard deviation is 3-4%.     

Cation-exchange behaviour of several elements in hydrofluoric acid-organic solvent media

The cation-exchange characteristics of 15 elements with the strongly acidic cation-exchange resin Dowex 50 x 8 were investigated in media containing varying concentrations of organic solvents and aqueous hydrofluoric acid. The determination of the distribution coefficients was carried out in 0.15-1.2 M hydrofluoric acid solutions containing 0-90% of the organic solvents methanol, ethanol, n-propanol, isopropanol, methyl glycol, acetone, tetrahydrofuran, and acetic acid. Based on these distribution data the possibilities of separations of the various elements are indicated and discussed.     

Ion chromatographic analysis of anions in ammonium hydroxide,hydrofluoric acid,and slurries,used in semiconductor processing

In this study, ion chromatography (IC) with suppressed conductivity detection was used for the determination of trace anions in 29% (w/w) ammonium hydroxide, 49% (w/w) hydrofluoric acid and slurries. For these samples, various sample pretreatment methods were applied to eliminate matrix interferences. For concentrated ammonium hydroxide, an on-line electrochemical neutralizer (SP10 AutoNeutralization module) was used to neutralize the base prior to the IC analysis. For concentrated hydrofluoric acid, a heart cutting technique with an ion-exclusion column was used to separate the anions of interest prior to an IC separation. A method was also developed to analyze chloride in silica slurries by IC.     

Atomic absorption spectrometric determination of trace metals in technical and reagent-grade sulfuric and hydrofluoric acids and ammonia solution

Atomic absorption spectrometric methods are described for the determination of some trace metals (cadmium, copper, iron, lead, manganese and zinc) in technical and reagent-grade sulfuric and hydrofluoric acid and ammonia solution. The methods have lower limits of determination of about 1 p.p.b. Compared to conventional procedures for the determination of trace metals in inorganic acids and ammonia solution, the proposed methods have the advantages of requiring small sample amounts (10–250 μl) and no addition of reagents; the time of analysis is thus considerably reduced and the risk of introducing contamination diminished. The methods are also applicable to the analysis of other liquid inorganic or organic chemicals.     

Decomposability in hydrofluoric acid of the main and some minor and trace minerals of silicate rocks

The decomposability in hydrofluoric acid of a selection of 28 main and some minor and trace minerals of silicate rocks was investigated. 21 minerals were decomposed successfully by heating on the water bath ; the remainder - with the exception of topaz-were found to be decomposable at the higher temperatures of a teflon-lined bomb. The results indicate that hydrofluoric acid alone is more effective as decomposing agent than a mixture containing another mineral acid.     

Cation-exchange of 43 elements from hydrofluoric acid solution

The cation-exchange behaviour of 43 elements in 1-24M hydrofluoric acid has been investigated by means of the radiotracer technique. Under certain conditions the alkali, alkaline-earth, rare-earth and bivalent transition metal ions are retained on Dowex-50W x 8, whereas ions forming stable anionic fluoro-complexes are not.     

Acidity constant of hydrofluoric acid

A detailed experimental investigation of the association (acidity) constant of hydrofluoric acid has been made at 25°C in sodium perchlorate media at ionic strengths between 0.01 and 0.5M. Results were obtained by potentiometry using a fluoride ion-selective electrode in conjunction with three types of reference electrode, all involving cells with liquid junction. After careful consideration of possible errors in the present results and a critical study of the literature, a zero ionic strength pK _a ^o (HF) value of 3.18±0.02 is recommended until existing contradictions can be resolved.     

Ion pairs and the strength of hydrofluoric acid

The available spectroscopic data do not support the current theory on the nature of aqueous hydrofluoric acid: namely, undissociated HF molecules in dilute solutions (weak acid), and HF^?₂ or more complex ions at higher concentrations (strong acid). A different model is proposed, involving as a dominant species ion pairs of hydorxonium fluoride H₃O⁺…F^?linked by an exceptionally strong hydrogen bond. This model is also more consistent with various other properties of the H₂O-HF system.     

Hydration structure in dilute hydrofluoric acid

We have performed the multistate empirical valence bond (MS-EVB) molecular dynamics simulations of a dilute hydrofluoric acid solution at ambient temperature to study the hydration structure associated with its weak acidity. The developed MS-EVB model showed reasonable agreement with experimental and previous ab initio molecular dynamics and reference interaction site model self-consistent field simulations for the free energy and structural properties. The local tetrahedral and translational order parameters around the fluorine atom significantly increase in the transition and product states of the HF dissociation reaction. This indicates that the angular and translational rearrangements of the hydrogen-bond topology are necessary especially around the fluorine atom. At the transition state of the proton transfer, the tetrahedral order parameters are very large, whereas the translational order parameters are not. This suggests that for the proton transfer to occur the large angular rearrangements of the hydrogen-bond topology are more necessary than the translational ones.     

The analysis of inorganic siliceous materials by atomic absorption spectrophotometry and the hydrofluoric acid decomposition technique : Part I. the analysis of silicate rocks

The analysis of various inorganic siliceous materials of geological and industrial interest is discussed. The methods proposed are based on decomposition of a single sample by hydrofluoric acid and determination by atomic absorption spectrophotometry of up to 10 constituents. General procedures are described, and details are given for the determination of silicon, aluminium, total iron, magnesium, calcium, sodium, potassium, titanium and manganese in silicate rocks. Analytical data are given for the analysis of reference rocks G-2 and W-1.     

Association of hydrofluoric acid in NaCl aqueous media under hydrothermal conditions

The apparent association constant of hydrofluoric acid Q _HF ^' in 1m NaCl aqueous media has been determined potentiometrically at pressures up to 1 kbar and temperatures up to 250°C. A concentration cell employing hydrogen electrodes was used. The association of HF increases with increasing temperature but decreases with increasing pressure.     

Trace anion determination in concentrated hydrofluoric acid solutions by two-dimensional ion chromatography II. Method performance study with a hydroxide eluent and a low noise suppressor

The two-dimensional ion exclusion chromatography/ion chromatography (ICE-IC) approach is considered to be the method of choice for the determination of trace anions in concentrated hydrofluoric acid (48-50%, w/w). In order to achieve lower detection limits, this method was for the first time used with electrolytically generated and purified hydroxide eluents in combination with a low noise electrochemical suppressor. Compared to carbonate based eluents, the achieved gain in peak height sensitivity for chloride, sulfate, nitrate and phosphate is a factor of 6, 7, 16 and 13, respectively. The instrumental detection limits, based on the background noise, are 2, 0.2, 0.4 and 1.4 microg/kg HF 50% (w/w) for the same anions. Their method detection limits, calculated according to SEMI, are all within the 6-10microg/kg HF 50% (w/w) range and thus at least 10 times lower than the current Tier C grade requirements. The chromatographic run time could be shortened with some 10 min by the use of a relatively fast high-capacity hydroxide selective anion exchange column.     

Trace anion determination in concentrated hydrofluoric acid solutions by two-dimensional ion chromatography I. Matrix elimination by ion-exclusion chromatography

Since years, ion exclusion chromatography (ICE) has been the standard method to separate strong acid analyte anions from concentrated weak acid matrices such as hydrofluoric acid (HF). In this work, the commercially available IonPac ICE-AS 1 column was used to separate trace levels of chloride, nitrate, sulfate and phosphate from HF solutions at 20% (w/w). The efficiency of the separation was studied in more detail using techniques such as ion chromatography (IC), inductively coupled plasma optical emission spectrometry (ICP-OES) and ICP-mass spectrometry (ICP-MS). For 20% (w/w) HF solutions and at a water carrier flow-rate of 0.50 ml/min, the cut window was set from 8.5 to 14.5 min. Under these conditions, analyte recoveries of better than 90% were obtained for chloride, nitrate and sulfate, but only about 75% for phosphate. The HF rejection efficiency was better than 99.9%. It was found that the ICP techniques, measuring total element levels and not species, yielded significantly higher recoveries for phosphorus and sulfur compared to IC. Evidence will be given that part of the added phosphorus (approximately 15% for an addition of 10 mg PO4/kg) is present as mono-fluorophosphoric acid (H2FPO3). In the case of sulfate, the difference between IC and ICP-MS could be attributed to an important matrix effect from the residual HF concentration.     

Spectrophotometric determination of niobium in tantalum metal

A new method for the determination of traces of niobium in tantalum metal has been developed. The niobium is separated from tantalum by solvent extraction with hexone from hydrofluoric acid-hydrochloric acid solution, and from molybdenum and tungsten by solvent extraction with oxine-chloroform solution from ammoniacal citrate solution. The niobium is then determined by the spectrophotometric thiocyanate method.