Normal phase-liquid chromatography-tandem mass spectrometry with atmospheric pressure photoionization for the purity assessment of 17ß-estradiol.

A normal phase-liquid chromatography-hybrid tandem mass spectrometry (NP-LC-MS/MS) method utilizing atmospheric pressure photoionization (APPI) without dopant has been developed and implemented for the simultaneous determination of several estrogenic steroid hormones. The combination of both NP-LC and APPI-MS/MS tolerates the use of solvents that have the advantages of being self-doping for APPI and, at the same time, inhibit the in situ formation of estrogen dimers as frequently observed for conventional reversed phase (RP)-LC methods. The NP-LC-APPI-MS/MS method has been validated in-house, and its performance characteristics (linearity, repeatability, limits of detection, etc.) were assessed for use in the quantification of estrogens. Moreover, the method was used to characterize and determine the inherent related structure impurities in batches of ß-estradiol, required for the establishment of reference measurement systems for clinical chemistry and laboratory medicine, which served as candidate reference material for an organic purity assessment interlaboratory study (CCQM-K55.a) organized by the International Bureau of Weights and Measures (BIPM) Chemistry Department and carried out within the framework of the Organic Analysis Working Group (OAWG) of the Consultative Committee for Amount of Substance-Metrology in Chemistry (CCQM).

Mass balance method for the SI value assignment of the purity of organic compounds.

A mass balance method is described for determining the mass fraction of the main component of a high purity organic material. The resulting assigned value is established to be traceable to the SI and can be determined with a small associated measurement uncertainty. Pure organic materials with values and uncertainties determined in this way are necessary as primary calibrators of reference measurement systems in order to underpin the metrological traceability of routine measurement results. The method has been applied to materials in which the main components were respectively theophylline, digoxin, 17ß-estradiol, and aldrin. Its performance has been validated in international comparisons coordinated by the BIPM and is in principle applicable to a wide structural range of stable, nonvolatile organic compounds. It has been successfully applied to mass fraction assignments when the main component is present in the range of (950-1000) mg/g and can achieve associated standard uncertainties ranging from 0.5 mg/g (for high purity materials or those containing well-characterized, stable minor components) to 2 mg/g (materials with a significant number or variety of impurities). It is in principle equally applicable to materials with a smaller mass fraction content of the main component.

Simultaneous determination of various cardiac glycosides by liquid chromatography-hybrid mass spectrometry for the purity assessment of the therapeutic monitored drug digoxin.

A high performance liquid chromatography-hybrid tandem mass spectrometry (LC-MS(n)) method utilising electrospray ionisation has been developed and implemented for the simultaneous determination of several cardiac glycosides (CGs) as well as their corresponding aglycones formed by and extracted from herbaceous plants of the genus Digitalis. The method has been validated in-house and its performance characteristics (linearity, repeatability, limits of detection, etc.) were assessed for use in the quantification of CGs and their corresponding aglycones. LODs from 38 to 936pgg(-1) in solution, corresponding to mass fraction impurity levels from 0.0009 (or 0.00008%) to 0.019mgg(-1) (or 0.0019%) detectable in the pure materials have been realized. Moreover, the method was used to characterize and to determine the inherent CG impurities in batches of the therapeutic monitored drug digoxin which served as candidate reference material for an organic purity assessment inter-laboratory study (CCQM-P20.f) organised by the BIPM Chemistry Section and carried out within the framework of the Organic Analysis Working Group (OAWG) of the Consultative Committee for Amount of Substance - Metrology in Chemistry (CCQM). Digoxin was selected from materials required for the establishment of reference measurement systems for clinical chemistry and laboratory medicine.

Production of certified reference materials for mycotoxins: IRMM's view on the assessment of uncertainties.

Analytical difficulty and the economic importance of controlling mycotoxin levels in food and feed led the Community Bureau of Reference (BCR) to prepare a series of certified reference materials (CRM) for various mycotoxins. Because of the wide acceptance of these CRM and the need to ensure the comparability and traceability of measurements in the future it is necessary to prepare and certify new batches of mycotoxin reference materials (RM). In the following text two different approaches for evaluation of the characterisation uncertainty of CRM will be compared using the certification of aflatoxin M(1) (AfM(1)) in milk powder as an example. The conventional approach is based on evaluation of characterisation exercise data; the alternative approach is based on measurement uncertainties of the employed analytical methods. Because laboratories are using totally different approaches to estimate the measurement uncertainties, combination of the uncertainties obtained from the participating laboratories was not recommended. Therefore, a new integrated approach for assessment of the measurement uncertainties of the analytical methods on the basis of additional data collected during the characterisation exercise will be described. The conventional approach was found to be the most appropriate and economical approach to evaluate the characterisation uncertainty as a characterisation exercise must be performed anyway to establish the property values of candidate (C)RM, irrespective of whether or not reliable measurement uncertainties can be provided by the laboratories. An integrated approach for assessment of measurement uncertainties based on additional characterisation data as applied here to enable use of an uncertainty-based approach provides more information but is too time-consuming and cost-intensive to become common practice.

Production of a calibrant certified reference material for determination of the estrogenic mycotoxin zearalenone.

Several previous interlaboratory studies in the field of mycotoxin analysis have revealed considerable problems, apparent as high between-laboratory standard deviations, or rather non-comparable and non-traceable results. A major reason is lack of proper calibrants for external calibration. Public awareness of substances that mimic or interfere with the activity of natural hormones (endocrine disrupters) has led to increased interest in mycotoxins with estrogenic potential, e.g. zearalenone (ZON). During a large-scale standard measurement and testing (SMT) project of the European Commission (EC) dealing with the preparation and certification of reference materials for determination of the mycotoxin ZON in maize, a ZON calibrant in acetonitrile was prepared and intensively checked for purity, homogeneity, and stability. Preparation of the material, study of its homogeneity and stability, and characterisation of the calibrant on the basis of its preparation, with discussion of the results obtained, are described in this paper. The certified value of 9.95 micro g mL(-1) for ZON in acetonitrile and its corresponding expanded uncertainty of +/-0.30 micro g mL(-1) were calculated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM).