Cyanide and sulfide analysis using amperometric detection and Metrosep A Supp /4.0

Transcription

1 Metrosep A Supp /4.0 Branch Environment, Food, Beverages Keywords IC; 850; 858; Metrosep A Supp /4.0; Cyanide; Sulfide; ; DC Mode Summary The determination of sulfide and cyanide in standard solutions was investigated on the Metrosep A Supp /4.0 column using sodium hydroxide eluent. The influence of chloride in the sample matrix regarding the sulfide and cyanide determination was also tested. Samples Spiked Herisau tap water analyzed on Metrosep A Supp / 4.0 column. Instruments 881 Compact IC pro Cation Professional Sample Processor IC Amperometric Detector Wall - Jet Cell Spacer 50 µm Ag Working Electrode Pd Reference Electrode Metrosep A Supp / Metrosep A Supp 10 Guard/ Reagents Sulfide standard stock solution, 1 g/l. The 1000 ppm sulfide standard was prepared from sodium sulfide (Fluka 71975). The purity was 35%. 695 mg of Sodium sulfide was diluted in a 100 ml flask with 100 mmol/l sodium hydroxide (= 1000 ppm). The 1000 ppm cyanide standard was prepared from potassium cyanide (Fluka 60179). The diluted cyanide and sulfide standards were dissolved in 100 mmol/l sodium hydroxide. Sodium hydroxide solution 30% Suprapur (Merck ) IDRANAL III standard solution 0.2 mol/l (Fluka 35102) Solutions Eluent 100 mmol/l sodium hydroxide mmol/L EDTA in ultra pure water (resistivity >18 M ) Standard solutions Concentration of the cyanide and sulfide standards in the MagIC Net standard table in [µg/l] Standards Sulfide Cyanide Std Std Std Std Std Std Std Std Sample preparation No sample preparation was required. Page 1 of 7

2 Analysis The samples and standards were injected with the 858 Professional Sample Processor. Parameters Flow Mode Cell potential Range Damping Channel 1.0 ml/min DC 0.0 V Auto on current Column temperature 35 C Detector temperature 35 C Sample Loop 20 µl Calculation Automatic integration with MagIC Net 2.3 software using peak area. The calculation of the injection precision based on twelve injections of the 6 ppb standard. Area (na) x min Mean (5) % RSD % Recovery Cyanide Sulfide The recovery is calculated according to double injection of a standard with the same concentration as the spiked samples. Comments Before the first usage only, the column needs an pretreatment. Rinsing with 50 mmol/l EDTA solution with standard flow for 3 h, followed by conditioning with the eluent for 12 h. The EDTA concentration in the eluent depends on the column. The EDTA push the sulfide and cyanide peaks on the A Supp 10 to the front of the chromatogram, while the system peak doesn`t move. In this case the correct concentration of EDTA helps to separate the sulfide from the system peak. Conc. [µg/l] Mean (12) % RSD Cyanide Sulfide Results The recovery of sulfide and cyanide was tested with the Herisau tap water. The water was spiked with 10 ppb cyanide and sulfide. Additional sodium hydroxide up to 100 mmol/l was added. Conc. [µg/l] Mean (3) % RSD Cyanide Sulfide Date Thursday, December 1, 2011 Author Gabriele Zierfels Competence Center Ion Chromatography Metrohm International Headquarters Appendix Result chromatograms with peak table, calibration curves. The influence of chloride in the sample matrix was investigated. Therefore standard solutions with 15 ppb cyanide and 2.5 ppb sulfide together with different concentrations of chloride (0 3 g/l) were analyzed on an A Supp /4.0 column. The chromatograms displayed a chloride disturbance peak. The cyanide peak flattens with increasing chloride concentration. With a chloride concentration of 0.6 g/l in the sample and higher, the cyanide peak could not be calculated automatically. Page 2 of 7

3 Appendix Standard 2 (the peak at 3.2 min is the system peak) Standard 6 Page 3 of 7

4 Chromatograms of the spiked standards (15 ppb cyanide and 2.5 ppb sulfide) with g/l chloride. Analysis on A Supp / g/l chloride g/l chloride g/l chloride g/l chloride g/l chloride g/l chloride g/l chloride g/l chloride g/l chloride g/l chloride 11 - standard solution without chloride Calibration curves: Page 4 of 7

5 Stability check To check stability of the measurement a 10 ppb standard solution of sulfide and cyanide was injected 69 times from different vials. Page 5 of 7

6 Stability check Cyanide Reproducibility check For this test another standard solution of 10 ppb cyanide and sulfide was prepared and analyzed 14 times according the same chromatographic conditions. Page 6 of 7

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