İletkenlik dedektörlü iyon kromatografi ile çeşitli örneklerde siyanür, siyanat, tiyosiyanat, krom (VI) ve metal-siyanür kompleksleri tayini
Determination of cyanide, cyanate, thiocyanate, chromium (VI) and metal-cyanide complexes in various samples by ion chromatography with conductivity detector
- Tez No: 442795
- Danışmanlar: DOÇ. DR. GÜLÇİN YILMAZ
- Tez Türü: Doktora
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2016
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Kimya Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 104
Özet
Siyanür iyonu (CNˉ), canlılar için çok zehirlidir. Siyanür bileşikleri, geniş bir yelpazede metallerle kararlı kompleksler oluşturabildiklerinden madencilik, metalurji, elektrokaplama, fotoğrafçılık, gibi alanlarda kullanılmaktadırlar. Ayrıca elektrokaplama endüstrisinde kullanılan diğer zehirli anyon krom(VI)' dır. Hidrojen siyanatın (HCNO) ayrışma sabiti (pKa = 3,66) iletkenlik dedektörüne yanıt vermeye yetecek kadar yüksek olduğu için siyanür, siyanata alkali pH'da kloramin-T kullanılarak dönüştürülmüştür. Bu çalışmada siyanat, tiyosiyanat ve dikromat doğrudan eşzamanlı analizi için seçici, hassas ve güvenilir bir iletkenlik dedektörlü iyon kromatografi yöntemi geliştirilmiştir. Serbest siyanür, zayıf asit ayrışabilen siyanür türleri ve tiyosiyanat, pH 12'de yükseltgen olarak kloramin-T kullanılarak tamamıyla siyanata dönüştürülürken, kuvvetli metal-siyanür kompleksleri pH 12'de fotooksidasyon önişlemini takiben kloramin-T reaksiyonu ile tayin edilmiştir. Geliştirilen yöntemlerle elde edilen toplam siyanat iyon kromatografi sistemi ile analizlenmiştir. Anyon değiştirici kolonda kromatografik ayırımlar eluent olarak NaOH kullanarak optimize edilmiş çok-adımlı gradient eluent programıyla başarılmıştır. Optimize kromatografi koşulları: 0 – 15 dakika 2 mM NaOH (izokratik), 15 – 25 dakika 2 mM'dan 30 mM'a NaOH (gradient), 25 – 30 dakika arası 30 mM NaOH (izokratik), 30 – 31 dakika 30 mM'dan 2 mM'a gradient NaOH, ve bir sonraki analize hazırlık aşaması yani yeniden şartlandırma için 31 – 35 dakika 2 mM NaOH (izokratik); Suprasör akımı 19 mA; Kolon kompartman sıcaklığı ve dedektör hücre sıcaklığı sırasıyla 35 °C ve 40 °C; Hareketli faz akış hızı 0,250 mL/dak ve örnek loop hacmi 10 µL idi. Geliştirilen yöntem siyanür ve dikromat eşzamanlı analizi için elektrokaplama havuz çözeltilerine ve endüstriyel atık suyu numunesine uygulanmıştır. Siyanür ve dikromat sırasıyla 0,6 – 962 µM ve 0,9 – 119 µM doğrusal dinamik aralıklarda ölçülebilmişlerdir. Optimize edilmiş koşullarda siyanür için tespit sınırı (S/N = 3) ve tayin sınırı (S/N = 10) 0,2 ve 0,6 µM iken bu değerler dikromat için 0,3 ve 0,9 µM olarak bulundu. Sonuç olarak bu tezde İletkenlik Dedektörlü İyon Kromatografi ile çeşitli örneklerde siyanür, tiyosiyanat, siyanat, krom(VI) ve metal siyanür kompleksleri tayini için güvenilir yöntemler geliştirilmiştir.
Özet (Çeviri)
Cyanide ion (CNˉ) and hexavalent chromium (Cr(VI)), which are highly toxic compounds, are extensively used in electroplating industry. Since cyanide compounds can form stable complexes with metals in a wide spectrum, they are used in mining, metallurgy, manufacture, photography, etc. The complexes of zinc, nickel, copper and cadmium metals with cyanide can be ionized in acidic medium and they are known as weak acid dissociable (WAD) species. In addition to free cyanide, WAD species, metal-cyanide and strongly complexed metal-cyanides, thiocyanate, cyanogen chloride, and cyanate show very distinct differences in terms of toxicity, reactivity, and effect on the environment. The ionization constants of metallocyanides have significant differences with oxidation state, pH, temperature, and photodegredation playing as important factors. The toxicity of metallocyanides exhibits diversity according to their stabilization constants. The concentration of cyanate gradually increases with time as the cyanide concentration decreases in environment due to oxidation of cyanide. The most harmful cyanide species to the environment are shown to be free and WAD cyanides. Inhalation of hydrocyanic acid (prussic acid (HCN)) or digestion of cyanide salts causes fast-appearing symptoms. HCN vapors are formed by mixing the salts with acids or in the stomach following oral ingestion. The lethal dose is probably 100 mg for hydrocyanic acid while it is 300 mg for potassium cyanide. Furthermore, according to US EPA, the maximum contaminant level for cyanide in drinking water is 0.2 mg/L. Cyanide shows its toxic action by binding to the heme-type iron complex in cytochrome oxidase, causing an inhibition in the last step in oxidative phosphorylation in the cycle. There are many proteins and metalloenzymes affecting negatively from cyanide. Apart from binding to metals as a strong-field ligand, it also reacts with enzymes having carbonyl group in the active centers, producing cyanohydrins. In addition, it causes elimination of sulfur in disulfide-type enzymes, xanthine oxidase, and forms thiocyanate, thereby cancelling the enzymatic activity. Chromium is generally used as an additive for alloys or materials to donate some properties such as strength, hardness, permanence, hygiene, color and resistance to temperature, wear and corrosion. Chromium species can be released into environment through industrial activities such as textile dyeing, preservation of wood, tanning, paint and pigment production, electroplating and metallurgy. As for the effects of chromium on health, Cr(VI) can be toxic, mutagenic, and carcinogenic. Cr(VI) damages to the skin, the respiratory tract, the kidneys and augments risk of lung cancer depending on exposure type. Toxic effect of Cr(III) is ignored and even it may be an essential trace element for proper functioning of lipid, glucose, and protein metabolism in mamalians. The US EPA has set the maximum contaminant level for Cr(VI) in drinking water and inland surface waters as 0.05 and 0.10 mg/L, respectively. Industrial wastewaters containing chromium have to be refined prior to discharging into the environment because Cr(VI) concentration must be lower than the permitted limits. Therefore, the control of these compounds in electroplating baths and wastewater is crucial issue. Though many different methods have been described in literature for the determination of cyanide and Cr(VI) individually, no study has focused on simultaneous analysis. It is clear that simultaneous determination of Cr(VI) and cyanides in wastewaters is challenging task. In this thesis, a new method was developed for simultaneous determination of cyanide and Cr(VI) by ion chromatography with suppressed conductivity detector. Cyanide was converted to cyanate for being measurable with a conductivity detector, because the dissociation constant of hydrogen cyanate (HCNO) is highly sufficient (pKa = 3.66) to give a reasonable response. In addition, direct simultaneous determination of cyanate, thiocyanate and Cr(VI) was performed. Furthermore, we also determined total cyanide content including strongly complexed metal-cyanides by using photo-oxidation following chloramine-T treatment. To the best of my knowledge, chloramine-T has not been used with photo-oxidation method to form cyanate from strong metal-cyanide complexes. The ion chromatographic analysis was performed on an ICS-3000 (Thermo Scientific, Waltham, MA, USA) equipped with a suppressed conductivity detector (ASRS ULTRA II-2mm suppressor and conductivity cell). An IonPac AG20 guard column (50 mm × 2 mm, I.D.), Thermo Scientific, Waltham, MA, USA) and an IonPac AS20 separation column (250 mm × 2 mm) were used as the analytical columns. The mobile phase gradients were generated on-line from ultra-pure water using the Reagent-Free (RF) EGC-NaOH EluGen II cartridge and then polished off from the contaminants using Continuously Regenerating Trap Column (CR-ATC). Data acquisition and instrumental control were performed via a Chromeleon Client (6.80) software (Thermo Scientific, Waltham, MA, USA). The Reagent-Free Ion Chromatography (RFIC) system provides avoiding potential contamination compared to systems with manually prepared eluents. The instrument was also equipped with a pump attached to an AS autosampler. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) (Perkin Elmer ELAN DRC-E) analyses were conducted for determination of elemental content of samples. The optimized chromatographic conditions: the eluent gradient was 0-15 min 2 mmol/L NaOH isocratic, 15-25 min gradient from 2 to 30 mmol/L NaOH, 25-30 min 30 mmol/L NaOH isocratic, 30-31min gradient from 30 to 2 mmol/L NaOH, 31-35 min 2 mmol/L NaOH isocratic (recondition step). The suppressor current was 19 mA. Column compartment temperature and detector cell temperature were kept constant with a thermostate at 35 °C and 40 °C, respectively. The flow rate was 0.250 mL/min and the sample loop was 10 µL. Thiocyanate can be also oxidized with chloramine-T to form cyanate at alkaline pH when heated. Therefore, a positive error may occur if a sample has a previously uncontrolled presence of cyanate and thiocyanate. In order to investigate percentage of conversion of thiocyanate to cyanate, 10 mL of the thiocyanate standard solutions were adjusted to pH ≥ 12 and 20 µL of 5 % chloramine-T solutions were added, vortexed, then kept at 80 °C for 20 minutes. The solutions were allowed to reach room temperature, than loaded into IC autosampler vials. The recoveries from thiocyanate standard solutions at 37.88 µmol/L, 57.68 µmol/L, and 77.48 µmol/L were found as 102.0 ± 0.2 %, 94.2 ± 1.2 %, and 89.4 ± 0.2 %, respectively. Solutions containing various amounts of cyanide, thiocyanate, and cyanate were also investigated to measure the conversion percentage to cyanate. 10 mL of the solutions were adjusted to pH ≥ 12 and 20 µL of 5 % chloramine-T solutions were added, vortexed, then kept at 80 ºC for 20 minutes. The solutions were allowed to reach room temperature, then loaded into IC autosampler vials. In the final solutions, the theoretically equivalent total concentrations of 23.85, 47.70, and 95.40 µmol/L of CNˉ were prepared. Good recovery results were also obtained for triple mixture of cyanide, thiocyanate and cyanate. Decomposition of strong metal-cyanide complexes were investigated under varying parameters such as use of portable UV apparatus (4W, 366 nm) or photoreactor, temperature, and presence of chloramine-T as the oxidant. Standard metal-cyanide complex solutions except for Fe(CN)64ˉ and Fe(CN)63ˉ were prepared by mixing the metal cations and cyanide ion in stoichiometric amounts. 10 mL of the metal-cyanide complex solutions at pH ≥ 12 was transferred into the quartz cell and stoppered. A handheld UV light source and the quartz tube were placed vertically with minimum distance between them, and the illumination system was tightly closed with aluminum foil. The other UV light source, the photoreactor, was fitted with 12 of 20 cm-long lamps operating at 366 nm and 254 nm. 10 mL of the solutions was put into the quartz tube, stoppered, and put into the center of the photoreactor. The distance between each lamp and the tube was 12 cm. When 10 µL and 20 µL of 5 % chloramine-T solutions (pH = 12, 80 ºC for 20 min) were added to tetracyanonickelate(II) solutions, 85 % and 100 % recovery values obtained, respectively. Procedure (I) was as follow: A 10.0-mL of the solution was mixed with 30 - 40 µL of 10 M NaOH, thus the pH value adjusted to ≥ 12, then 50.0 µL of 5 % chloramine-T solution was added, vortexed for 1 minute, then kept in a water bath at 80 ºC for 20 minutes. Although we added 50 µL of 5 % chloramine-T solution, procedure (I) gave low yields for decomposition of hexacyanoferrate (II) and hexacyanoferrate(III). Thereafter, we firstly focused on iron-cyanide complexes. After adjustment of 10.0 mL solutions for these two complexes to pH ≥ 12, they were irradiated for 180 minutes to UV radiation (12 lamps, λ366) and cyanide recoveries were found to be 102.2 and 106.2 % for hexacyanoferrate(III) and hexacyanoferrate(II), respectively. Similarly, another set of solutions were added 10 µL of chloramine-T and irradiated for 90 minutes, with cyanide recovery values of 96.3 and 99.3 %, respectively. Another experiment involved hexacyanoferrate(III) and hexacyanoferrate(II) solutions with 10 µL of chloramine-T added and subjected to UV radiation for 90 minutes (portable handheld UV source, λ=366 nm). Then they were kept in a hot water bath at 80 ºC for 20 minutes and cyanide recoveries were 98.3 % and 101.8 %, respectively. However, tetracyanocuprate(II), and pentacyanocobaltate(II) gave approximatelly 40-50 % recovery values with this procedure. When these solutions had a slightly different procedure of addition of chloramine-T followed by irradiation for 120 minutes at 80 ºC water bath (λ=366 nm), there was no significant change in the results and even more, there were too many unidentified peaks due to the decomposition of chloramine-T. This motivated us to concentrate our efforts on pentacyanocobaltate(II) complex. A 10 mL of pentacyanocobaltate(II) solution at pH ≥ 12 was applied as per the procedure II. Procedure (II) was as follow: To a 10.0 mL of solution, to adjust the pH to ≥ 12, 30 - 40 µL of 10 M NaOH was added and transferred into a quartz tube without adding the oxidant, and irradiated in a photoreactor having four lamps at 254 nm and eight lamps at 300 nm for 5 hours, then 50.0 µL of 5 % chloramine-T solution was added, followed by keeping in a water bath at 80 ºC for 20 minutes. We obtained a recovery value of 95.1 %. To a hexacyanoferrate(II) solution, theoretically having a cyanide concentration of 0.142 mmol/L, procedure II was applied with varying times. After 60 minutes, cyanide left the complex completely from this complex. A standard mix solution of 61.5 µmol/L cyanide and 7.4 µmol/L Cr(VI) was added to 30-40 µL of 10 M NaOH, thus the pH value adjusted to ≥ 12, then 20.0 µL of 5 % chloramine-T solution was added, vortexed for 1 minute, then kept in a water bath at 80 ºC for 20 minutes. The solution was allowed to reach room temperature, than loaded into IC autosampler vials. Under optimum IC conditions, cyanate and Cr(VI) were successfully separated from other anions such as fluoride, chloride, nitrite, bromide, nitrate, carbonate, sulphate, phosphate which are commonly found in water samples. Yet, among these anions only high concentrations of nitrite anion exhibited positive error on cyanate results while high concentrations of phosphate ion showed intereference to Cr(VI). The tolerance limits of nitrite-to-cyanate and phosphate-to-Cr(VI) were calculated 11-fold and 23-fold, respectively, at molar ratio. The method tolerated a large amount of the other common anions. Interference effects of metals on Cr(VI) determination were also investigated in detail. For this purpose, equivalent moles of Ni2+, Cd2+, Co2+, Zn2+, Fe3+ ve Cu2+ ions were added into Cr(VI) solutions at a concentration of 23.15 µmol/L. Direct analysis of binary mixtures gave excellent results for recoveries of Cr(VI). Chloramine-T and photo-decomposition treatment were also applied to metal-Cr(VI) mixtures. In addition, the Cr(VI) species possibly occurring from the oxidation of Cr(III) might be cause an error. Therefore, interference effect of Cr(III) was also investigated. For this purpose, same procedures were applied to 1.92 mmol/L Cr(III) solution before IC analysis. Cr(III) did not interfere with determination of Cr(VI) and there was no any Cr(VI) signal occurring from Cr(III). The developed method was validated. Cyanide and dichromate could be measured in the linear dynamic ranges of 0.6 – 962 µM and of 0.9 – 119 µM, respectively. Under optimized conditions, the limit of detection (S/N = 3) and the limit of quantification (S/N = 10) of cyanide were 0.2 and 0.6 µM, and these values for dichromate were 0.3 and 0.9 µM, respectively. Electroplating bath solutions, effluent and refined wastewaters from industrial estate were collected from the İstanbul, İkitelli region. The samples were tightly stoppered and immediately transferred to the laboratory to keep at + 4 °C. The samples were pretreated as soon as reaching to room temperature after taking out of the refrigerator and analyzed with IC.Appropriate amount of 10 M NaOH was added to 10 mL of sample solutions to adjust the pH value to ≥ 12. In some samples, metal hydroxide precipitates were centrifuged at 3000 rpm for 3 minutes. When needed, the samples were adequately diluted until the concentration of the analytes reached in their linear calibration ranges. All solutions were filtered through a Polyethersulfone (PES) filter whose pore size was 0.2 µm. The samples were divided into three portions. I) 2 mL of the first portions were directly injected into the IC system at optimum conditions. Concentrations of CNOˉ, SCNˉ, and Cr(VI) were obtained. II) Another 2-mL portion in a test tube was mixed with 20 µL 5 % chloramine-T solution, stoppered, and kept in a hot water bath (80 ºC) for 20 minutes in order to convert cyanide to cyanate. The sample solutions were allowed to reach the room temperature before loading IC autosampler vials. III) Third 2-mL portions were subjected to irradiation for 5 hours by the lamps (four at 254 nm and eight at 366 nm) in the photoreactor. Then the same operations applied to the second portions described above were repeated for third portions, which led to the determination of total cyanide content. In conclusion, in this thesis reliable ion chromatography with conductivity detection methods were developed for determination of cyanide, thiocyanate, cyanate, chromium(VI), and metal cyanide complexes in various samples. Total cyanide content including strongly complexed metal-cyanides was also determined by using photo-oxidation following chloramine-T treatment. Proposed methods were applied to electroplating bath solutions and industrial wastewater. The procedures are reliable, precise, selective, sensitive and suitable for routine analysis. Acceptable recoveries and relative standard deviation (RSD) values were obtained both standard solutions and real samples. The presented methods are suitable for controlling cyanide and Cr(VI) concentrations in wastewater samples which has a great importance for environmental health.
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