Simultaneous multi-element determination of trace metals in sea water by inductively-coupled plasma atomic emission spectrometry after coprecipitation with gallium

Coprecipitation with gallium hydroxide is studied for the preconcentration of trace metals in sea water before multi-element analysis by inductively-coupled plasma/atomic emission spectrometry. Gallium precipitates at pH 9 only when magnesium is present. Optimum conditions are established for multi-element preconcentration and removal of matrix elements. The method is almost free from contamination because of the use of highly pure gallium meetal and only a small amount of sodium hydroxide for pH adjustment. Spectral interferences from gallium are negligible and a concentratioin factor of more than 200 can be obtained. Detection limits range from a few ng l^?1 to 150 ng l^? for Al, Co, Cr, Fe, La, Mn, Ni, Ti, V, Zn, Y and Pb. Artificial and natural sea-water samples can be analyzed with adequate precision.     

Polymerization of mono-substituted acetylenes with a liquid crystalline moiety by Ziegler–Natta and metathesis catalysts

Polymerization of five monomers, 1-[p-(trans-4′-alkylcyclohexyl)phenoxy]alkyne (i.e., PCH001A, where PCH, 0, 01 and A represent phenylcyclohexyl mesogenic moiety, number of carbon in an alkyl group attached to cyclohexyl group, ether linkage + number of methylenic units in the spacer between phenoxy and acetylenic groups, and terminal acetylene, respectively) were carried out using Ziegler-Natta and metathesis catalysts. All polymers were soluble in organic solvents such as benzene, chloroform, and THF. A liquid crystalline phase was observed in the polymers of PCH303A and PCH503A through the polarized optical microscope and DSC measurements. Polymerization of PCH003A by the Fe(acac)₃-AlEt₃ catalyst yielded a high-molecular-weight polymer with M_w = ca. 3 × 10⁶. © 1993 John Wiley & Sons, Inc.     

Thermodynamic properties of binary mixtures: Hexamethylphosphoric triamide (HMPA) with a non-polar liquid at 25°C

Excess isobaric heat capacities C _p ^E , densities and speeds of sound u of HMPA+heptane and+benzene were measured at 25°C. C _p ^E of both mixtures were positive in the range of small x and negative in the other region. The mixture containing benzene showed higher C _p ^E than the heptane mixture. They both exhibited considerably smaller C _V ^E than C _p ^E . V^E was positive for HMPA+heptane and negative for HMPA+benzene. The compressibilities K _s ^E and K _p ^E of both mixtures were negative. In both mixtures, non-random mixing is expected and [(CH₃)₂N]₃PO molecules are inhomogeneously distributed.     

Simple fluorophotometric determination of cobalt(II) with p-hydroxy-2-anilinopyridine and hydrogen peroxide

Summary A simple and sensitive determination of cobalt(II) is based on its fluorescence reaction with p-hydroxy-2-anilinopyridine and hydrogen peroxide. The relative standard deviation is 2.5% (n=5). An application to pharmaceutical preparations is recommended.The application of diarylamine compounds in analytical chemistry. IV.-Part III see ref. [1]     

Mechanistic study of the oxidation of -ascorbic acid by chloranil at the nitrobenzene water interface

The redox reaction between -ascorbic acid in water and chloranil in nitrobenzene has been studied by means of polarography with an ascending water electrode as well as cyclic voltammetry with a stationary interface. Through accurate measurement of the limiting currents, it has been suggested that the redox reaction should be a two-electron reaction rather than a one-electron reaction described previously. A spectrophotometric technique has also been used to observe that the redox reaction proceeds spontaneously under certain conditions even without electrochemical control. Based on these findings, it has been concluded that the present heterogeneous charge transfer reaction is the ion transfer of chloranil semiquinone radical, which is driven by the homogeneous electron transfer between ascorbic acid and chloranil in the aqueous phase.     

Thermally assisted magnetic recording with bit-patterned media to achieve areal recording density beyond 5 Tb/in

Thermally assisted magnetic recording (TAR) with bit-patterned media was investigated by micromagnetic simulation. The media were assumed to be FePt layers. The effective head-field margin as well as the increase in temperature margin and down-track shift margin was investigated. Conditions of the head and medium that lead to a recording density beyond 5 Tb/in² were proposed.     

Helically Assembled Pyrene Arrays on an RNA Duplex That Exhibit Circularly Polarized Luminescence with Excimer Formation

Circularly polarized luminescence (CPL) was observed in pyrene zipper arrays helically arranged on an RNA duplex. Hybridization of complementary RNA strands having multiple (two to five) 2′‐O‐pyrenylmethyl modified nucleosides affords an RNA duplex with normal thermal stability. The pyrene fluorophores are assembled like a zipper in a well‐defined helical manner along the axis of RNA duplex, which, upon 350 nm UV illumination, resulted in CPL emission with pyrene excimer formation. CPL (g_lum) levels observed for the pyrene arrays in dilute aqueous solution were +2×10^?2–+3.5×10^?2, which are comparable with |g_lum| for chiral organic molecules and related systems. The positive CPL signals are consistent with a right‐handed helical structure. Temperature dependence on CPL emission indicates that the stable rigid RNA structure is responsible for the strong CPL signals. The single pyrene‐modified RNA duplex did not show any CPL signal.