Many calcified structures produce periodic growth increments useful for age determination at the annual or daily scale. However, age determination is invariably accompanied by various sources of error, some of which can have a serious effect on age-structured calculations. This review highlights the best available methods for insuring ageing accuracy and quantifying ageing precision, whether in support of large-scale production ageing or a small-scale research project. Included in this review is a critical overview of methods used to initiate and pursue an accurate and controlled ageing program, including (but not limited to) validation of an ageing method. The distinction between validation of absolute age and increment periodicity is emphasized, as is the importance of determining the age of first increment formation. Based on an analysis of 372 papers reporting age validation since 1983, considerable progress has been made in age validation efforts in recent years. Nevertheless, several of the age validation methods which have been used routinely are of dubious value, particularly marginal increment analysis. The two major measures of precision, average percent error and coefficient of variation, are shown to be functionally equivalent, and a conversion factor relating the two is presented. Through use of quality control monitoring, ageing errors are readily detected and quantified; reference collections are the key to both quality control and reduction of costs. Although some level of random ageing error is unavoidable, such error can often be corrected after the fact using statistical (‘digital sharpening)’ methods.

Accuracy, precision and quality control in age determination, including a review of the use and abuse of age validation methods

Manual for the geochemical analyses of marine sediments and suspended particulate matter

In accomplishing successful electrospray ionization analyses, it is imperative to have an understanding of the effects of variables such as analyte structure, instrumental parameters, and solution composition. Here, we review some fundamental studies of the ESI process that are relevant to these issues. We discuss how analyte chargeability and surface activity are related to ESI response, and how accessible parameters such as nonpolar surface area and reversed phase HPLC retention time can be used to predict relative ESI response. Also presented is a description of how derivitizing agents can be used to maximize or enable ESI response by improving the chargeability or hydrophobicity of ESI analytes. Limiting factors in the ESI calibration curve are discussed. At high concentrations, these factors include droplet surface area and excess charge concentration, whereas at low concentrations ion transmission becomes an issue, and chemical interference can also be limiting. Stable and reproducible non-pneumatic ESI operation depends on the ability to balance a number of parameters, including applied voltage and solution surface tension, flow rate, and conductivity. We discuss how changing these parameters can shift the mode of ESI operation from stable to unstable, and how current-voltage curves can be used to characterize the mode of ESI operation. Finally, the characteristics of the ideal ESI solvent, including surface tension and conductivity requirements, are discussed. Analysis in the positive ion mode can be accomplished with acidified methanol/water solutions, but negative ion mode analysis necessitates special constituents that suppress corona discharge and facilitate the production of stable negative ions.

Practical implications of some recent studies in electrospray ionization fundamentals.

▪ Abstract Manganese(IV) oxides produced through microbial activity, i.e., biogenic Mn oxides or Mn biooxides, are believed to be the most abundant and highly reactive Mn oxide phases in the environment. They mediate redox reactions with organic and inorganic compounds and sequester a variety of metals. The major pathway for bacterial Mn(II) oxidation is enzymatic, and although bacteria that oxidize Mn(II) are phylogenetically diverse, they require a multicopper oxidase-like enzyme to oxidize Mn(II). The oxidation of Mn(II) to Mn(IV) occurs via a soluble or enzyme-complexed Mn(III) intermediate. The primary Mn(IV) biooxide formed is a phyllomanganate most similar to δ-MnO2 or acid birnessite. Metal sequestration by the Mn biooxides occurs predominantly at vacant layer octahedral sites.

Biogenic manganese oxides: Properties and mechanisms of formation

Antimony in the environment: a review focused on natural waters: I. Occurrence

Preconcentration of trace elements from seawater with silica-immobilized 8-hydroxyquinoline

Pre-concentration of trace metals from sea-water for determination by graphite-furnace atomic-absorption spectrometry.

The application of inductively coupled plasma mass spectrometry (ICP-MS) to the determination of eight trace metals in a coastal seawater reference material is described. Accurate calibration has been achieved for Mn, Co, Ni, Cu, Zn, Cd, and Pb by standard additions techniques, while stable isotopes dilution has been applied for Cr, Ni, Cu, Zn, Cd, and Pb. In both cases the race metals were separated from the seawater and concentrated 50-fold by adsorption on silica-immobilized 8-hydroxyquinoline prior to instrumental determination. Detection limits are in the range from 0.2 to 2 ng L/sup -1/, low enough to permit the analysis of even open ocean samples. 12 references, 4 figures, 3 tables.

Determination of trace metals in seawater by inductively coupled plasma mass spectrometry with preconcentration on silica-immobilized 8-hydroxyquinoline

The arsenic species present in a dogfish muscle reference material (DORM-1) have been identified by using high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICP-MS), thin-layer chromatography, and electron impact mass spectrometry and quantified by using HPLC/ICP-MS and graphite furnace atomic absorption spectrometry. The major species is arsenobetaine (15.7 +/- 0.8 ..mu..g of As/g of DORM-1), constituting about 84% of the total arsenic. For this species, the HPLC/ICP-MS detection limit was 0.3 ng of As.

Identification and quantitation of arsenic species in a dogfish muscle reference material for trace elements.

La realisation preliminaire en ligne d'une etape de preconcentration ameliore les limites de detection de plusieurs elements d'un facteur 2 a 7

Shier S. Berman

Papers

Preconcentration of trace elements from seawater with silica-immobilized 8-hydroxyquinoline

Pre-concentration of trace metals from sea-water for determination by graphite-furnace atomic-absorption spectrometry.

Determination of trace metals in seawater by inductively coupled plasma mass spectrometry with preconcentration on silica-immobilized 8-hydroxyquinoline

Identification and quantitation of arsenic species in a dogfish muscle reference material for trace elements.

Determination of trace metals in reference water standards by inductively coupled plasma mass spectrometry with on-line preconcentration