Michael S. Epstein

Definitive measurement methods

Abstract This paper describes the use of ‘definitive’ methods in the certification of reference materials. The definitions, variations, and limitations of definitive methods are considered and related to analytical methods considered to be definitive.

The independent method concept for certifying chemical-composition reference materials

Abstract Certified values for chemical-composition reference materials are often derived from results generated by two or more independent and reliable measurement methods. This paper examines the concept of method independence from both philosophical and practical standpoints, drawing examples from actual certification data. Methods are compared based on specific criteria and an attempt is made to define the degree of independence necessary to qualify methods as independent.

A new river sediment standard reference material.

The collection, processing and certification of a new sediment Standard Reference Material (SRM), SRM 2704, is described. Collected from the bottom of the Buffalo River in New York State during the fall of 1986, SRM 2704 is certified for 25 elements with information provided on another 22 elements. Improvements in analytical methods as well as the application of well-defined quality-control procedures for collection, processing and analysis have resulted in a reference material that is more completely characterized than previous NIST sediment reference materials.

Determination of mercury in zinc ore concentrate reference materials using flow injection and cold-vapor atomic absorption spectrometry

A flow-injection, cold-vapor atomic absorption spectrophotometric method was developed for the determination of trace amounts of mercury in a proposed zinc ore concentrate Standard Reference Material (SRM 113b). The samples were digested with nitric and hydrochloric acids in closed Teflon digestion vessels. The experimental details for sample preparation and the flow injection method are discussed. The effect of matrix and various acid concentrations on the extraction and subsequent analysis of mercury were also studied. The method has a detection limit of 0.08 mug Hg/g in the sample. A certified reference material (CZN-1) was analyzed and the results obtained agreed well with the certified value.

The Determination of Low Concentrations of Sodium in Cement by Flame Emission Spectrometry without Sample Preparation

The determination of low concentrations of sodium using atomic spectrometric methods is often limited by environmental contamination in the sample preparation step. Wet digestion techniques must be carried out in a clean environment and require that samples be dissolved in plastic containers with the use of high-purity acids. Fusion methods require the use of high-purity flux materials to avoid contamination. Such materials are often difficult to obtain and are expensive. The analytical blank usually defines the lower limit of detection for sodium determinations when either wet digestion or fusion methods are used to prepare the sample. Direct sample introduction methods which require no sample preparation would significantly minimize contamination problems related to dissolution.

A spectral interference in the determination of arsenic in high-purity lead and lead-base alloys using electrothermal atomic absorption spectrometry and Zeeman-effect background correction

Abstract Arsenic, antimony, and tellurium are determined at part-per-million concentration levels in bullet lead, lead-base alloy, and high purity lead using electrothermal atomization atomic absorption spectrometry (ETAAS) with Zeeman-effect background correction. A spectral interference by lead absorption lines resulting from excited state transitions is observed on both primary arsenic analysis lines, at 193.696 nm and 197.197 nm. Analytical bias caused by the interference at 197.197 nm is eliminated by using temperature programming and temporal resolution.