Toshiaki Asakai

Investigation of iodine liberation process in redox titration of potassium iodate with sodium thiosulfate

Potassium iodate is often used as a reference material to standardize a sodium thiosulfate solution which is a familiar titrant for redox titrations. In the standardization, iodine (triiodide) liberated by potassium iodate in an acidic potassium iodide solution is titrated with a sodium thiosulfate solution. The iodine liberation process is significantly affected by the amount of acid, that of potassium iodide added, the waiting time for the liberation, and light; therefore, the process plays a key role for the accuracy of the titration results. Constant-voltage biamperometry with a modified dual platinum-chip electrode was utilized to monitor the amount of liberated iodine under several liberation conditions. Coulometric titration was utilized to determine the concentration of a sodium thiosulfate solution on an absolute basis. Potassium iodate was assayed by gravimetric titration with the sodium thiosulfate solution under several iodine liberation conditions. The liberation process was discussed from the changes in the apparent assay of potassium iodate. The information of the appropriate titration procedure obtained in the present study is useful for any analysts utilizing potassium iodate to standardize a thiosulfate solution.

Certification of water content in NMIJ CRM 4222-a, water standard solution 0.1 mg g−1, by coulometric and volumetric Karl Fischer titration

The precise determination of water content is a very important issue and in high demand in many fields. To ensure precise and reliable measurements, certified reference materials (CRM) of water standards, whose concentrations are traceable to the International System of Units (SI), are required. The National Metrology Institute of Japan (NMIJ) has issued a CRM of water in mesitylene (0.1 mg g−1) (NMIJ CRM 4222-a), with a very small uncertainty, for use in controlling the quality of analyses of trace water contents and confirming the validity of Karl Fischer (KF) titrators. This CRM is homogeneous, stable and low-hygroscopic under normal laboratory conditions; therefore, complex sample handling is not required. Characterization of the CRM was performed by coulometric and volumetric KF titrations. The certified value of the CRM (mass fraction of water) is 0.134 mg g−1, and its expanded uncertainty is 0.004 mg g−1 with a coverage factor of 2, and is metrologically traceable to SI. We describe the measurement procedures and assays of trace water contents with linkage to SI and the technical details of the characterization of water in NMIJ CRM 4222-a. The developed CRM is particularly suitable for the quality control and validation of coulometric KF instruments and will be valuable in analyzing trace water contents.

Comparison of three electrochemical end-point detection methods to assay potassium dichromate by coulometric titration

Coulometric titrations with three electrochemical end-point detection methods were performed to assay potassium dichromate as a standard for oxidation–reduction titration. The assay as an oxidizing agent was carried out with ferrous ions produced by electrolytically reducing ferric ions. Three end-point detection methods were employed and compared with each other: constant potential amperometry, potentiometry, and constant voltage biamperometry (a dead-stop method). The last one was found to provide high accuracy in the coulometric titration of potassium dichromate. Solution form samples were also measured to confirm the possible existence of chromium(III) in potassium dichromate by both coulometric titration and ion-exchange chromatography with inductively coupled plasma time-of-flight mass spectrometry.

Final report of key comparison CCQM - K105 'Electrolytic conductivity at 5.3 S⋅m-1'

The aim of key comparison CCQM-K105 was to demonstrate the measurement capabilities of the participating institutes with respect to the conductivity of multi-component aqueous salt solutions. Practical salinity results are currently not traceable to metrological references consistent with the International System of Units (SI). Nevertheless, salinity is one of the most important input quantities for oceanographic models, whose measurement data must be accurate on very long timescales. Thus, in order to determine the practical salinity value, there is a strong interest on the part of oceanographic researchers in establishing the traceability to the SI of conductivity measurements. To this end, the conductivity of a standard seawater sample, provided by the support laboratory (PTB), was measured in a way that was traceable to the SI. The nominal conductivity values of the solution were 5.3 S m-1 at 25 ?C and 4.3 S m-1 at 15 ?C. Thirteen institutes taking part in the comparison had to measure the conductivity values of the sample at both temperatures. The median was chosen for both values as an estimator for the KCRV, evaluated on the basis of the Monte Carlo method. An institute requested to be excluded from the determination of the KCRV because of contact problems of its cell. At 25 ?C the KCRV is 5.3024 S m-1 with an interval of confidence (at the 95.45% level of significance) from 5.3005 S m-1 to 5.3044 S m-1. At 15 ?C the KCRV is 4.2892 S m-1 with an interval of confidence (at the 95.45% level of significance) from 4.2877 S m-1 to 4.2907 S m-1. For the how far the light shines statement the CMCs can cover the range 1 S m-1 to 15 S m-1 for the values 5.3 S m-1 at 25 ?C and 4.3 S m-1 at 15 ?C. This comparison is a follow-up of the CCQM Pilot Study P111. Main text. To reach the main text of this paper, click on Final Report. The final report has been peer-reviewed and approved for publication by the CCQM.

Precise coulometric titration of cerium(IV) as an oxidising agent with electrogenerated iron(II) and reliability in cerium(IV) standardisation with sodium thiosulfate

Cerium(IV) is a useful strong oxidising agent and is often standardised against thiosulfate. In the standardisation, triiodide liberated by Ce(IV) in an acidic potassium iodide solution can be titrated with thiosulfate to determine the concentration of Ce(IV). The accuracy of the standardisation has not been established because the iodine liberation process is not well-understood. In the present study, to evaluate the iodine liberation process, Ce(IV) was assayed through two different methods: precise coulometric titration with electrogenerated ferrous ions and gravimetric titration with thiosulfate independently determined by precise coulometric titration with electrogenerated iodine. The reliability of Ce(IV) standardisation with thiosulfate is discussed on an absolute basis by coulometric titrations of both Ce(IV) and thiosulfate solutions. Finally, the accurate determination of Ce(IV) was achieved by both methods. Information on the stability of Ce(IV) solutions is also presented.

Final report on CCQM-K91: Key comparison on pH of an unknown phthalate buffer

Results of the CCQM-K91 key comparison on pH of an unknown phthalate buffer with a nominal pH value of pH ~ 4.01 at 25 ?C are reported. Measurements are performed at 15 ?C, 25 ?C and 37 ?C and optional also at 5 ?C and 50 ?C. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Potassium bromate assay by primary methods through iodine liberation reaction

Analyses of bromate are of interest, especially from the viewpoint of controlling water and food quality. Currently, the lack of a potassium bromate reference material creates problems for the reliability of analytical measurements in those areas. Bromate whose concentration is traceable to the International System of Units (SI) is needed to ensure accurate and reliable measurements around the globe; however, no one has given the procedure of an accurate assay. Several document standards and texts describe the procedure of the titration and require different, insufficient titration conditions; the authors clarified an appropriate set of titration conditions. This paper describes the measurement procedure and assay of bromate with the linkage to the SI by primary methods. Gravimetric titration with thiosulfate whose concentration was standardised by coulometric titration with electrogenerated iodine was applied to the assay of bromate through the iodine liberation reaction. The appropriate iodine liberation conditions to titrate potassium bromate with sodium thiosulfate were clarified through examinations by electrochemical methods. Finally, an accurate determination method for bromate was first established with high accuracy and traceability to the SI by primary methods.

Final report on key comparison CCQM-K73: Amount content of H+ in hydrochloric acid (0.1 mol kg−1)

This key comparison (KC), CCQM-K73, was performed to demonstrate the capability of the participating National Metrology Institutes (NMIs) to measure the amount content of H + , νH + , in an HCl solution with a nominal νH + of 0.1 mol·kg -1 . A parallel Pilot Study, CCQM-P19.2, was performed for NMIs that did not desire to participate in the KC. The comparison was a joint activity of the Electrochemical Working Group (EAWG) and Inorganic Analysis Working Group (IAWG) of the CCQM and was coordinated by NIST (USA) and CENAM (Mexico). The method of determination of νH + was left to the individual participant. All participants used either coulometry or titrimetry with potentiometric determination of the endpoint. The agreement of the results was not commensurate with the claimed uncertainties of the subset of participants that claimed small uncertainties for this determination. A workshop on technical issues relating to the CCQM-K73 measurements was conducted at the joint IAWGEAWG meeting at the Bureau International des Poids et Mesures (BIPM), Paris (Sevres) in April 2010. Several possible sources of bias were investigated, but none could explain the observed dispersion among the participants’ results. In the absence of a specific cause for the dispersion, the IAWG and EAWG decided to assign a Key Comparison Reference Value, KCRV, and standard uncertainty of the KCRV, uKCRV, based on the DerSimonian-Laird statistical estimator. The uKCRV is dominated by the between-laboratory scatter of results in CCQM-K73. The uncertainty estimates from the participants with the lowest reported uncertainties remain unsupported by this KC.

Final report on key comparison CCQM-K96: Determination of amount content of dichromate

The key comparison CCQM-K96 was organized jointly by the inorganic and electrochemistry working groups of CCQM to test the abilities of the metrology institutes to measure the amount content of dichromate. Slovak Institute of Metrology with help of KRISS acted as the coordinating laboratories. Eight NMIs took part in the comparison. All participants used high accuracy constant current coulometry. Good agreement of the results was observed. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

New Japanese certified reference materials for electrolytic conductivity measurements

The National Metrology Institute of Japan (NMIJ) has established three certified reference materials (CRMs) in electrolytic conductivity with a primary Jones-type cell: aqueous solutions of potassium chloride with different molalities (1xa0molxa0kg−1, 0.1xa0molxa0kg−1 and 0.01xa0molxa0kg−1) all supplied in glass bottles. The uncertainties were estimated from standard uncertainties of measurements (impedance, temperature and integrity of cell geometry), measurement’s repeatability, homogeneity of a batch and the storage stability of solutions. The storage stability of candidate NMIJ CRMs of upper and lower concentrations was examined with a secondary cell.