Method ruggedness studies incorporating a risk based approach: a tutorial

This tutorial explains how well thought-out application of design and analysis methodology, combined with risk assessment, leads to improved assessment of method ruggedness. The authors define analytical method ruggedness as an experimental evaluation of noise factors such as analyst, instrument or stationary phase batch. Ruggedness testing is usually performed upon transfer of a method to another laboratory, however, it can also be employed during method development when an assessment of the method's inherent variability is required. The use of a ruggedness study provides a more rigorous method for assessing method precision than a simple comparative intermediate precision study which is typically performed as part of method validation. Prior to designing a ruggedness study, factors that are likely to have a significant effect on the performance of the method should be identified (via a risk assessment) and controlled where appropriate. Noise factors that are not controlled are considered for inclusion in the study. The purpose of the study should be to challenge the method and identify whether any noise factors significantly affect the method's precision. The results from the study are firstly used to identify any special cause variability due to specific attributable circumstances. Secondly, common cause variability is apportioned to determine which factors are responsible for most of the variability. The total common cause variability can then be used to assess whether the method's precision requirements are achievable. The approach used to design and analyse method ruggedness studies will be covered in this tutorial using a real example.     

Study of Complex Formation Between Dicyclohexano-18-Crown-6 (DCH18C6) with Mg 2+, Ca2+, Sr 2+, and Ba2+ Cations in Methanol–Water Binary Mixtures Using Conductometric Method

The complexation reactions between Mg²⁺,Ca²⁺,Sr²⁺ and Ba²⁺ metal cations with macrocyclic ligand, dicyclohexano-18-crown-6 (DCH18C6) were studied in methanol (MeOH)–water (H₂O) binary mixtures at different temperatures using conductometric method . In all cases, DCH18C6 forms 1:1 complexes with these metal cations. The values of stability constants of complexes which were obtained from conductometric data show that the stability of complexes is affected by the nature and composition of the mixed solvents. While the variation of stability constants of DCH18C6-Sr ²⁺ and DCH18C6-Ba²⁺versus the composition of MeOH–H₂O mixed solvents is monotonic, an anomalous behavior was observed for variations of stability constants of DCH18C6-Mg²⁺ and DCH18C6-Ca²⁺ versus the composition of the mixed solvents. The values of thermodynamic parameters (ΔH_c°, ΔS_c°) for complexation reactions were obtained from temperature dependence of formation constants of complexes using the van’t Hoff plots. The results show that in most cases, the complexation reactions are enthalpy stabilized but entropy destabilized and the values of thermodynamic parameters are influenced by the nature and composition of the mixed solvents. The obtained results show that the order of selectivity of DCH18C6 ligand for metal cations in different concentrations of methanol in MeOH–H₂O binary system is: Ba²⁺>Sr²⁺>Ca²⁺> Mg²⁺.     

Traceability system for elemental analysis

A complete metrological traceability system for measurement results of chemical analysis was set up. Core components are pure substances (national standards) characterised at the highest metrological level, primary solutions prepared from these pure substances and secondary solutions deduced from the primary solutions and intended for sale. The relative uncertainty of the element mass fraction of the primary substances and solutions is < 0.01 and < 0.05%, respectively. For the certification of transfer solutions and for stability testing, a precision measurement method for element contents has been developed by means of optical emission spectrometry (ICP OES) by which uncertainties between 0.1 and 0.05% can be achieved. The dissemination to field laboratories is effected with the aid of a calibration laboratory of the German Calibration Service (DKD) which certifies the element content of the secondary solutions with an uncertainty ≤ 0.3%. Calibration with these solutions enables the user to establish traceability of his measurement results to the International System of Units (SI). Currently, the system comprises Cu, Fe, Bi, Ga, Si, Na, K, Sn, W, and Pb.     

Broadening and shifting of the 321-, 325- and 380-GHz lines of water vapor by pressure of atmospheric gases

Three spectral lines of the main water molecule isotope in the ground vibrational state located near 321, 325 and 380 GHz were studied at low pressures and room temperature using spectrometer with radio-acoustic detection of absorption. Self-, N₂- and O₂-pressure broadening and shifting parameters of these lines have been precisely measured. A number of parameters, in particular pressure shifts, were obtained for the first time. Complementary study of the 325-GHz line by resonator spectrometer at atmospheric pressure validated the low pressure experiment data and allowed measurement of the 325-GHz line intensity. Obtained results are discussed in comparison with previous experimental and theoretical data.     

Atom lasers: Production,properties and prospects for precision inertial measurement

We review experimental progress on atom lasers out-coupled from Bose–Einstein condensates, and consider the properties of such beams in the context of precision inertial sensing. The atom laser is the matter-wave analogue of the optical laser. Both devices rely on Bose-enhanced scattering to produce a macroscopically populated trapped mode that is output-coupled to produce an intense beam. In both cases, the beams often display highly desirable properties such as low divergence, high spectral flux and a simple spatial mode that make them useful in practical applications, as well as the potential to perform measurements at or below the quantum projection noise limit. Both devices display similar second-order correlations that differ from thermal sources. Because of these properties, atom lasers are a promising source for application to precision inertial measurements.     

Purity of potassium hydrogen phthalate, determination with precision coulometric and volumetric titration--a comparison

The mass fraction of potassium hydrogen phthalate (KHP) from a specific batch was certified as an acidimetric standard. Two different analytical methods on a metrological level were used to carry out certification analysis: precision constant current coulometric and volumetric titration with NaOH. It could be shown that with a commercial automatic titration system in combination with a reliable software for the end-point detection it is possible to produce equivalent results with the same accuracy in comparison to a definite method handled by a fundamental apparatus for traceable precision coulometry. Prerequisite for titrations are that a high number of single measurement are applied which are calibrated with a high precision certified reference material.     

Ionophoric and Complexant Properties of Lagochilin Derivatives

The ionophoric and complexant properties of synthetic derivatives of lagochilin, 3,18-O-isopropylidenelagochilin and 3,18-O-ethylidenelagochilin, were studied by BLM methods, conductometry, and IR spectroscopy. The ionophoric activity was found to be highly selective for divalent cations. Studies of the electrical conductivity of alkaline-earth metal salts in the presence of the lagochilin derivatives and analysis of their IR spectra have shown that they can form complexes with various ratios of metal ions.     

铁的理化特性对测定铁的精密度和准确度的影响

通过对铁的理化特性分析，实验设计和观察及借助数理统计分析，从根本上解释和解决水中总铁的测定精密度不好的问题。     

应用灰色系统模型提高仪器精度

文中介绍了灰色系统的原理及建模方法 ,并把它与测量仪器的使用结合起来 ,提出一种提高测量精度的新方法。实验结果证明了此方法的经济性和有效性。     

Revisiting type-A uncertainties relating to the measurement of mass fraction of lead using isotope-dilution inductively coupled plasma mass spectrometry: a way of improving measurement precision and expanded uncertainty

A quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) has been used for determination of lead in plant materials using isotope-dilution inductively coupled plasma mass spectrometry. The accuracy of the method was demonstrated by analysis of a matrix certified reference material, NIST SRM 1547 Peach Leaves. Specific instrumental parameters of Q-ICP-MS, including isotope analysis mode, integration time per point, number of points per mass, and number of measurements, were optimized to obtain the best measurement precision. The precision (expressed as relative standard deviation) associated with replicate measurement of the ²⁰⁸Pb/²⁰⁶Pb isotope ratio and its mass-bias correction factor was <0.2%. Following “Example A7” of the Eurachem/CITAC Guide, the relative expanded uncertainty, U _rel, (coverage factor k = 2) was found to be ±1.1%, which fulfilled the target value of ±2% maximum and was lower than the uncertainty of ±3.4% reported by NIST based on isotope-dilution thermal ionization mass spectrometry. Sample recovery of 99% was obtained.