Ions, absorption, detection

A flow-injection system with electrochemical hydride generation and atomic absorption detection for the determination of arsenic is described. This technique has been developed in order to avoid the use sodium tetrahydroborate, which is capable of introducing contamination. The sodium tetrahydroborate (NaBH ) - acid reduction technique has been widely used for hydride generation (HG) in atomic spectrometric analyses. However, this technique has certain disadvantages. The NaBH is capable of introducing contamination, is expensive and the aqueous solution is unstable and has to be prepared freshly each working day. In addition, the process is sensitive to interferences from coexisting ions. 

Neve et al. [547] digested the sample with nitric acid. After digestion the sample is reacted selectively with an aromatic o-diamine, and the reaction product is detected by flameless atomic absorption spectrometry after the addition of nickel (III) ions. The detection limit is 20mg/l, and both selenium (IV) and total selenium can be determined. There was no significant interference in a saline environment with three times the salinity of seawater. 

Determination of Inorganic and Organic Arsenic Species by Ion Chromatography Using an Atomic Absorption Detection System , Ricci, G. Colovos, G. Hester, N. Shepard, L Anal. Chem., accepted for publication 1980. 

The ESR spectra of the V-ion-implanted titanium oxide catalysts were measured before and after calcination of the samples in O2 at around 723-823 K, respectively (Fig. 11). Distinct and characteristic reticular V" ions were detected only after calcination at around 723-823 K. It was found that only when a shift in the absorption band toward visible-light regions was observed, the reticular V ions could be detected by ESR. No such reticular V ions or shift in the absorption band have ever been observed with titanium oxides chemically doped with V ions [16,18,19]. 

Figure 9. Illustration of the use of extracted ion-current profiles obtained with LC-MS, moving-belt interface, for the detection of carbamate and other pesticides. T op, extracted ion-current profile for 17 major ions second from top, extracted ion-current profile for m/z = 151 to m/z = 181 third from top, extracted ion-current profile for m/z = 86 to m/z = 305 bottom, UV absorption detection at 220 nm. (Reproduced with permission from reference 53. Copyright 1982 Preston Publications.)...

By far most of the work discussed in this review has been based on LIF detection, usually with an 488 nm Ar-ion laser as the excitation source. Only very few other examples exist in the literature where other detection principles were investigated. One of these exceptions is an integrated detection cell for chip CE that has been described by Liang et al. [78]. In combination with the U-shaped separation channel, two additional well aligned channels to take up the excitation and collection fibers where micromachined in a glass plate. The U-cell provides a longitudinal path of 120 -140 pm in length parallel to the flow direction and can be used both for absorption and fluorescence measurements. The absorption detection limit was 0.003 AU ( 6 pM of a fluorescein dye) in the fluorescence mode a detection limit of 3 nM fluorescein (20 000 molecules) was achieved. 

The precise measurement of eluent ion absorption is also extremely important in indirect photometric detection. It is known from classical spectrophotometry [31] that the photometric error is only small in an absorbance range between 0.2 and 0.8. There-... 

Figure 7A Chromatogram obtained with 0.2 mM 2,6-dimethylpyridine at pH 6.35 as eluent by use of (a) direct conductivity and (b) indirect UV absorption detection. Sample 15 pL of a solution containing 2 X 10 M of each of the indicated ions. From Ref. [8] with permission.

In isotachophoresis, electrical detection is most commonly used, although thermal and UV-absorption detection are also used(3). For capillary zone electrophoresis, UV-absorption and fluorescence detection have proven most useful so far. The principles behind the optical detection modes are fairly obvious. However, the electrical and thermal detectors deserve further explanation. As described earlier, in isotachophoresis, each zone is an individual "pure" band of sample ions. The zones travel in order of decreasing mobility. To compensate for each successive... 

We have no definite evidence for the presence of (CH3)2COH radicals although a weak unidentified absorption, detected at high gain, is present in the wings of the spectrum shown in Figure 3A. Acetonyl radicals could also be produced by an ion-molecule reaction such as Reaction 12. 

LIF (Ezekiel and Weiss, 1968 Cruse, et al., 1973 Zare and Dagdigian, 1974 Kinsey, 1977) is an example of an indirect technique for the detection of a one-photon resonant upward transition. There are many other indirect detection techniques (optogalvanic, optothermal, photoacoustic, cavity ringdown), but Multi-Photon Ionization (MPI) is a special type of indirect technique uniquely well suited for combining absorption detection with other useful functionalities (see Section 1.2.1.1). In MPI, photo-ion detection replaces photon detection. The one-color, singly-resonant-enhanced (n + m) REMPI f process consists of an n-photon resonant e, v, J <— e",v",J" excitation, followed by a further nonresonant m-photon excitation into the ionization continuum... 

B. A. Petersson, Z. Fang, J. RMidka, and E. H. Hansen, Conversion Techniques in Flow Injection Analysis. Determination of Sulphide by Precipitation with Cadmium Ions and Detection by Atomic Absorption Spectrometry. Anal. Chim. Acta, 184 (1986) 165. 

In previous studies [3, 4], we had pointed out that the interphase formation mechanisms result from dissolution of the metallic surface layers, concomitantly with ion diffusion through the liquid prepolymer. In order to detect the dissolution phenomenon, pure amine (either DETA or IPDA) was previously applied to chemically etched metallic sheets (either A1 or Ti alloys were used, and had hydroxidic surfaces). After 3 h, the metallic surfaces were scraped with a PTFE spatula. The modified amine (i.e., the amine reacted with the metal) was analyzed. Whatever the natures of the amine and the metal were, metal ions were detected in the modified amines by ICP analysis and new peaks were detected by infrared spectroscopy [5]. To indicate hydroxide dissolution, a very thin layer of liquid amine was applied to chemically etched aluminum, and Infrared Reflection - Absorption Spectroscopy (IRRAS) spectra were recorded every 5 min (the hydroxide band intensity variation at ca. 3430 cm was followed). The OH group peak intensity decreased when the amine-metal contact time increased [5]. Conversely, if pure DGEBA monomer was apphed to the metal surfaces, even after 3 h in contact with the metallic surfaces, no metal ion was detected by ICP in the DGEBA recovered, and the infrared spectra remained identical before and after the contact with the metal. Finally, if pure amine monomer was applied to gold-coated substrates, no chemical reaction was observed (by either IGP or FTIR analyses). 

PH2 ions were detected by IR absorption spectra of MPH2. Pure and solvent-free crystalline MPH2 could be isolated at room temperature after reacting excess PH3 gas with M or MNH2 in liquid NH3 (M = K, Rb, Cs) at -35"C. X-ray diffraction methods did not allow to locate the H atoms within the PHg ion librations and quasi-free rotations of the ions were assumed [24]. X-ray diffraction on single crystals of KPHg and RbPH2 (obtained from solutions in DMF) was done by [25]. 

An unknown X shows a hroad absorption band in the infrared at 3200-3550 cm but none in the 1620-1780 cm region. It contains only C, H, and O. A 116-mg sample was treated with an excess of methylmagnesium bromide, producing 48.7 mL of methane gas collected over mercury at 20 °C and 750 mm Hg. The mass sp>ectrum ofXhas its molecular ion (barely detectable) at 116 w/zand a fragment peak at 98. What does this information tell you about the structure of X ... 

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