Multielement cations

Ammonium and hydrogen ions (protons) are both present in the soil solution as multielement cations. Ammonia gas reacts with water to produce the ammonium cation, NH4+ (Figure 5.8, equation 1). Ammonium acts as a cation in all senses and will be attracted to cation exchange sites on soil particles. Ammonium in the soil solution and on exchange sites is available to plants. 

Many of the different pillaring agents reported in the literature (organic compounds, metal trischelates, organometallic complexes, metal cluster cations, metal oxide sols, polyoxocations, etc.) have drawbacks such as low reactivity or lack of thermal stability, and polyoxocations are by far the most widely employed. Many different polyoxocations (Al, Ni, Zr, Fe, Cr, Mg, Si, Bi, Be, B, Nb, Ta, Mo, Ti, and, more recently, Cu, Ga, and Ce) have been reported in the open and patent literature and clays with multielement or doped pillars also have been claimed [2,8,9,19,20,68-70,73-75]. However, the chemical composition, structure and charge are at present well defined only for the Al-polyoxocation, in which the Keggin ion [Al,304(0H)24(H20)i2] is identified. 

A Perkin Elmer Optima 3000 Spectrometer was used to determine the cation content of solutions. Samples and multielement standards (0,1,10 and 100 mgL" ) were diluted with 5% nitric acid. All vials used were cleaned with 1 M sulphuric acid. Detection limits are 3, 5, 0.1, 5, and 70 igL for Fe, Al, Ca, Na, and K, respectively. 

Ion chromatography gained general acceptance as fast and sensitive multielement detection method for the determination of alkali and alkaline earth metals, heavy and transition metals, actinides and lanthanides, as well as selected organic cations, allowing detection limits in the range of microgram per liter and analysis time of less than 20 min. 

LAMM A. Laser microprobe mass analysis was specifically developed to complement other microanalytical techniques to determine intracellular distributions of physiological cations and toxic constituents in biological tissues. LAMMA is an analytical methodology capable of simultaneous multielement analysis of metals and their distribution on a cellular or subcellular scale, with a measurement sensitivity of 10" to 10" " g for most metals. LAMMA has received somewhat widespread use in the analysis of essential and toxic metals in tissues and cell preparations (Drueke 1980 Goebel et al. 1990 Schmidt and Barckhaus 1991 Schmidt et al. 1980, 1986 Vandeputte et al. 1985 Verbueken et al. 1984 Visser et al. 1984). The detection sensitivity of LAMMA for lead is 5 /rg/g, with a limit of detection of approximately 2 X 10" g (Schmidt and Barckhaus 1991). 

---