Anion and Cation analysis with Professional IC - automatic dilution and sample preparation with SPM

Transcription

1 IC Application Work AW CH Anion and Cation analysis with Professional IC - automatic dilution and sample preparation with SPM Branch: Chemical industry; Water, wastewater, environmental protection, Mining branch Keywords IC / 850 / 858 / ProfIC / Metrosep A Supp 5-150/4.0 / Metrosep C 4-150/4 / chloride / nitrite / bromide / nitrate / sulfate / thiocyanate / cyanate / sulfide / sodium / ammonium / potassium / magnesium / UV detection / automatic dilution / / / / extension module / SPM / / branch: chemical, water, wastewater, environmental protection, mining Summary The application work shows the possibilities of Professional IC instruments and the Software MagIC Net. The determination of standard anion, standard cation, cyanate, thiocyanate and sulfide was prepared in unknown samples of process water from a mine. The samples were injected after the automatic dilution and automatic cation removal procedure with the SPM module. The automatic sample preparation with the SPM module, was compared with the manual sample preparation using sodium cartridges. Reagents Anion Eluent: 3.2 mmol/l sodium carbonate 1.0 mmol sodium bicarbonate in ultra pure water (resistivity >18 M ) Cation Eluent: 1.7 mmol/l nitric acid, 0.7 mmol/l dipicolinic acid MSM Regeneration solution: 100 mmol/l sulfuric acid, 100 mmol/l oxalic acid in ultrapure water (resistivity >18 M ) MSM Rinsing solution: ultra pure water (resistivity >18 M ) SPM Regeneration solution: 100 mmol/l EDTA, Titriplex III solution (Merck) SPM Rinsing solution: 100 mmol/l sodium carbonate in ultra pure water (resistivity >18 M ) with 10 mmol/l ethylendiamine Dilution solution: 2 mmol/l ethylendiamine (EDA) in ultrapure water (resistivity >18 M ) Rinsing solution for special beaker: 0.1 mol/l sulfuric acid in ultrapure water (resistivity >18 M ) Sample 3 different samples of process water from a mine. The samples contain cyanide, thiocyanate, sulfide, the standard anions and cations. Standards and calibration procedure A multipoint calibration was carried out by applying different dilution factors to standard 1 (= stock solution). The stock solution for calibration of sulfide was prepared separately with 20 mg/l. The 1000 ppm sulfide standard was prepared from sodium sulfide (Fluka 71975). The purity was 35%. 704 mg of Sodium sulfide was diluted in a 100 ml flask with 100 mmol/l sodium hydroxide (= ppm). The diluted sulfide standards were dissolved in 10 mmol/l sodium hydroxide. Because of the contamination with other sulfur species, the sulfide calibration was run separately. Standards stock solutions: TraceCERT Standards for IC from Sigma-Aldrich Concentrations of the anion standards (in the MagIC Net standard table). [mg/l] Chloride Nitrite Cyanate Bromide Nitrate Sulfate Thiocyanate Sulfide* *Concentrations calculated due to the used sodium sulfide weight. Concentrations of the cation standards (in the MagIC Net standard table). [mg/l] Sodium Ammonium Potassium Calcium Magnesium Apparatus and Accessories 850 Professional IC AnCat Professional Sample Processor Professional UV/VIS Detector Dosino Stirrer Dosing Unit 10 ml

2 Anion and cation analysis with Professional IC - automatic dilution and sample preparation with SPM page 2/ Extension Module Suppression SPM Rotor A IC equipment for dilution Metrosep A Supp 5-150/ Metrosep C 4-150/ Metrosep C 4 Guard Metrosep A Supp 4/5 Guard MagICNet 2.2 Professional Analysis The samples and standards were injected with the 858 Professional Sample Processor after the automatic dilution and the sample preparation with a SPM module. For cation analysis the diluted sample was injected directly. For anion analysis the diluted sample passed the SPM Module for cation removal. Parameters for anion analysis: Flow 0.7 ml/min Polarity + Temp. coefficient 2.3 %/ C Column temperature 30 C Sample Loop 20 µl for cation analysis: Flow 0.9 ml/min Polarity - Temp. coefficient 1.5 %/ C Column temperature 30 C Sample Loop 20 µl for Sulfide analysis with the UV Absorption: Flow 0.7 ml/min Wavelength 215 ± 20 nm Reference 260 ± 20 nm Measuring duration 300 ms Column temperature 30 C Sample Loop 20 µl Calculation: Automatic integration with MagIC Net 2.2 software using peak area for all analytes. Results Sample concentrations in [mg/l]; Mean of N=3 Analyte Rica Brine E 7 Chloride Nitrite Cyanate Bromide Nitrate Sulfate Thiocyanate Sulfide Sodium Ammonium Potassium Calcium Magnesium Comments A benefit of this setup is the automatic multi-point calibration from one stock solution. All necessary dilution and sample preparation steps of samples or standards run fully automated by the system, reducing handling and error sources. The matrix of the analyzed customer samples had a big influence on the sulfide analysis. After one injection of the nondiluted sample E7, there was no possibility to detect sulfide at all, even not in the standard. The exchange of the column and the guard column allowed to solve this problem. To check the sulfide analysis with the sample matrix, the samples were diluted first 1:50. These samples were spiked with 2 ppm sulfide and analyzed immediately after spiking. Depending on the sample matrix the recoveries of sulfide were 80% (Rica), 60% (Brine), 55% (E7). The sample preparation step with Sodium cartridges before spiking improved the recoveries for Rica and Brine by about 10%, but not for the sample E7. So, these samples probably contained components that complexe or eliminate sulfide. The goal of further investigations was to develop a sample preparation which allowed the sulfide standard analysis, besides the sample matrix in the setup. The automatic dilution of the samples (1:50), was not sufficient enough to guarantee the sulfide analysis. The 20 ppm sulfide standard which ran after every diluted sample, showed a strong decrease of sulfide response. After the first sample analysis the recovery was lowered to 50%. The sample residue (which we could see due to the yellow color) in the dilution vessel and tubing influenced the sulfide analysis, too. To remove the impurities a rinsing step with 0.1 mol/l sulfuric acid was introduce into the procedure which ran during the analysis time.

3 Anion and cation analysis with Professional IC - automatic dilution and sample preparation with SPM page 3/17 With this procedure, a blind value for sulfate (6 ppm) was observed. However, sulfuric acid was necessary to properly clean the dilution vessel and the capillaries. So, for sulfate result blank value was substracted. Sample preparation with sodium cartriges. Summary of the recovery tests Technique Samples % Recovery % Rec. after sample preparation (Na + cartrige) Before the analysis, every sample was diluted manually (1:50). 15 ml of this solution was filtrated slowly (1 ml/min) through a precleaned cartridge. The manual sample preparation on the Sodium cartridges (to get rid of metals) took 15 min per sample. The recovery of a 20 ppm sulfide standard was > 90%. The standard was analyzed after every 25 prepared samples. The sulfide standard was injected without dilution. Sample preparation with SPM Module. With the 872 Extension Module Suppression equipped with the sample preparation module (SPM) the cation exchange could be done automatically. The samples for analysis had to be filtrated with a membrane filter prior to the analysis. Otherwise the switch valve on the 858 Professional Sample Processor could clog. The 40 ppm sulfide standard, which was analyzed after every sample, was diluted (1:2) with UPW from a Dosino. The recovery was 92% (11 analyses). If the sulfide standard was diluted (1:20) the recovery decreased to 50%. To improve the recovery of sulfide up to 90%, the UPW in Dosino was set to ph 9 with ethylendiamine (EDA). This amine did not influence the analysis of anions and cations. EDA eluted after 30 min in the cation chromatogram as a large peak. The customer samples had to be diluted (1:50) prior analysis. To check this procedure for the sulfide analysis a 100 ppm standard was used with the automatic dilution. The analyses were done after every diluted customer sample. In 7 analyses the sulfide recovery was 76%. If the analysis was prepared without the diluted customer samples in between, the sulfide recovery was by 90% (9 analyses). Spike test with 2 ppm Sulfide in samples Analysis with 20 ppm sulfide between samples Rica Brine E Rica << 50 > 90 Brine << 50 > 90 E7 << 50 > 90 Technique Samples % Recovery after sample preparation (SPM Module) Analysis with 100 ppm Sulfide (1:50) between samples Analysis with 100 ppm Sulfide (1:50) without samples between standard Rica Brine E (N=7) 90 (N=9) So, the sample preparation with SPM module of customer samples could reduce the matrix content. The prepared solutions contained still components that eliminated sulfide. Appendix Installation diagram, accessories list and calibration curves. Result chromatograms with peak table and statistics. Additional information for the method and setup. Date Friday, Name G. Zierfels; Competence Center Ion Chromatography Metrohm International Headquarters; Switzerland

4 page 4/17 Appendix Installation Information Connect the 800 Dosino (Anion UPW) to MSB 1 of 858 Professional Sample Processor Connect the 801 Stirrer to MSB 2 of 858 Professional Sample Processor Configuration Information Rack: Define the external position of the 858 Professional Sample Processor. External Position 1: Angle = ; Work position = 110 mm Column: Give a name to the icolumn Configuration: set the `CV` Volume to 9 ml Eluent: Solution: Method Add an Eluent to the Configuration Copy the settings of the Dosing Unit Anion UPW to the used Dosing Unit Devices Link the Column to the Analysis Link the Eluent to the Pump Link the Solution Anion UPW to the Dosino, which is connected to MSB 1 of the Sample Processor Link the Rack to the Sample Processor used, the standard table needs to be set in the following way: [mg/l] Cl The red numbers are the dilution factors of the standards. For the anion standard analysis the vial with the first - 1 concentration was set in SD Position. The vial for the cation standard analysis 1 was set in the SD Position + 1. The vial for the sulfide standard analysis was set in the SD Position + 2. Only the position of the first anion calibration standard is described in the sample table. The positions of the cation and sulfide standards are read out from the program. The first standard was injected without dilution from one vial. For the injection of the diluted standards (2 to 20) a second vial set is necessary. Check of the setup prior analysis. The sample analysis for anion and cation was prepared of the same 9 ml volume in the dilution vessel. The time condition indicates the time used for the injection of anions and cations. It can change, because of longer capillaries between the 858 valves and the SPM and/or different pressure set on the peristaltic tubing. In this setup the capillaries between the 858 valves and the SPM were 40 cm long (see installation diagram on page 6). The check procedure gives an impression if the method needs time changes in the subprograms. Test description: - Work in the manual mode. - Place 9 ml UPW in the dilution vessel. - Set the switch valve on the 858 sample processor to inject. - Set the pump speed of the peristaltic pump to Start the peristaltic pump and record the time needed for removing all water from the vessel. If the vessel is empty within 2 min, this setup is comparable to the original system. Run this test twice. - Place again 9 ml UPW into the vessel. - Set the switch valve on the sample processor to fill. - Start the peristaltic pump (speed 10) and record the time until all water is removed from the vessel. If the vessel is empty within 5.5 min, the setup compared to the original system. The method should work without changes in the subprograms. Otherwise, the method should be adjusted to the new time values in all subprograms. Evaluation Standard For the calibration from one stock solution dilution factors of 1, 2, 5, 10 and 20 were used. The final concentrations resulting from the respective dilution were set in the standard calibration table. If a stock solution of 10 mg/l is Time program The time program was set up with five sub-programs (direct injection, calibration, dilution, calibration sulfide, rinsing). The sub program direct injection was used for an injection of undiluted standard or sample. The calibration program was used for the injection of the standard stock solution, with different dilution factors. The sub program calibration sulfide was used for a parallel preparation and analysis of the sulfide standards. The sub program dilution was used for injection of samples with a known dilution factor. The sub program rinsing was used for rinsing steps with diluted acid and water, after the injection of diluted or nondiluted samples.

5 page 5/17 Appendix The analysis UV_Anion helped to verify the result for nitrite, bromide, nitrate and thiocyanate. Workplace For the determination of samples with automatic dilution it is necessary to prepare a calibration first. System check up before starting the sulfide analysis (recommended for already used instruments). Sample matrix (such as transition metals) or different impurities in the capillaries and in the instrument could influence the sulfide response enormously. Begin the check up with pulling the sulfide standard solution from the waste side: - Connect a piece of new PEEK capillary to the injection port of the anion valve. - Place the second end of the PEEK capillary in one 200 ml volumetric flask with 20 ppm sulfide solution. - Connect the end of the waste capillary (anion) to the pump tubing for pulling the sulfide standard. Connect the second end of the pump tubing to the next capillary to waste bottle - Prepare the connection from the anion valve to a new analytical column, bypass the MSM, MCS and connect the outlet of the capillary to the UV detector. The MCS shouldn`t be use for sulfide analysis, because of strong peak broadening. - Prepare 8 analyses with this configuration. The peak response should be nearly the same (retention time 20 min; impurities of sulfate, sulfite were detected after sulfide). - In the next step connect the MSM in the flow path; prepare next 8 analysis with the same sulfide solution. All responses should be in the same range, otherwise the MSM is not running well. - Prepare all connections with a new capillary set as shown in the installation diagram. Prepare next 8 direct analyses with the same sulfide solution as before. If every capillary or tubing was clean enough, the 8 result should give the same response. Even if the instrument runs well, it may happen that the first and second analysis of the sulfide standard show growing peaks. After the second analysis the peak response should stay on the same level. Otherwise there is a problem with the used setup.

6 page 6/17 Appendix Installation Diagram Accessories List Quantity Article No. Description Professional IC AnCat Professional Sample Processor Dosino Magnetic Stirrer Dosing Unit 10 ml IC equipment set for dilution Transfer Tubing with holder 10 ml Adapter UNF 10/32 outer / M6 inner Round glass bottle / 1000 ml / GL Professional UV/VIS Detector Extension Module Suppression SPM Rotor A

7 page 7/17 Appendix Calibration curves

8 page 8/17 Appendix

9 page 9/17 Appendix

10 page 10/17 Appendix

11 page 11/17 Appendix

12 page 12/17 Appendix

13 page 13/17 Appendix Chromatogram of first anion calibration standard Chromatogram of the first cation calibration standard

14 page 14/17 Appendix Standard chromatogram of 10 ppm Sulfide Anion Chromatogram of the diluted sample Rica (dilution 1:50)

15 page 15/17 Appendix Cation Chromatogram of the diluted sample Rica (dilution 1:50) Anion Chromatogram of the diluted sample Brine (dilution 1:50)

16 page 16/17 Appendix Cation Chromatogram of the diluted sample Brine (dilution 1:50) Anion Chromatogram of the diluted sample E7 (dilution 1:50)

17 page 17/17 Appendix Cation Chromatogram of the diluted sample E7 (dilution 1:50)