Analytical
Currents
Turnip SPECTROSCOPY mosaic virus by SERS The rod-shaped turnip mosaic virus can infect more than 20 families of dicotyledonous plants such as magnolias, geraniums, and roses. Its host specificity is determined primarily by the composition and spatial structure of its coat protein (MW 20,000). Surface-enhanced Raman spectroscopy (SERS), several orders of magnitude more sensitive than normal Raman spec troscopy, is used in biological macromolecular studies because it has almost no detrimental effects on the structure and activity of the sample. Hongying Deng of Wuhan University (China) and colleagues examined the sec ondary structure of the virus coat protein by both normal and surface-enhanced Ra man spectroscopy. The normal Raman spectrum showed three amide ΠΙ bands and two amide I bands that arise from the β-sheet, random coil, and α-helix struc tures. The surface-enhanced Raman spec trum showed three amide ΙΠ bands and one amide I band that arise from the ahelix. From these and other results, con formational structures are deduced. (SpectrochimicaActa 1993,494,1709-14) Noninvasive intracellular [Mg] and pH by 3 1 P NMR The concentration of intracellular free magnesium is important physiologically because Mg binds to ATP, but its role in metabolism has not been fully estab lished because it is hard to measure accu rately in living systems. 31P NMR has been used to determine free Mg ion indi rectly by measuring the chemical shifts of the α and β Ρ sites on ATP, but the pH must be known a priori for the determina tion to be accurate. Gerald Williams, Timothy Mosher, and Michael Smith of The Pennsylvania State University College of Medicine have developed a method for simultaneously determining pH and intracellular [Mg]/
[ATP] that uses the γ-α and γ-β shifts as well. Those shifts have been shown to reflect the local pH and both [Mg] and pH, respectively, so pH can be deter mined simultaneously with [Mg]. The γ-β chemical shift may be more sensitive than the α-β shift at high pH, and it avoids the problem of resonance overlaps with dinucleotide phosphates. {Anal. Biochem. 1993,214,458-67) BIOANALYTICAL Two
sites are better than one for cytochrome c binding
C. Martinez-Lozano, V. Tomas, and O. Val of the University of Murcia (Spain) have developed an automated method that couples flow injection analysis to a photochemical reaction for the determina tion of two catecholamines, epinephrine and L-dopa, in pharmaceutical prepara tions. The method is based on the strong inhibition by these catecholamines of the photoreduction of phloxin by EDTA which is monitored by the fluorescence intensity of the dye. At a sampling fre quency of 35 samples per hour, epineph rine and L-dopa can be determined in the 1.9-26.4^g/mLand 1.5-12.7^g/mL range, respectively. (Talanta 1993,40, 1625-30)
The binding stoichiometry of cy tochrome c with cytochrome c peroxidase has been pre Atmospheric sented in various reports as 1:1 or as 2:1. ELECTROANALYTICAL particles and Brian Hoffman and Jian Zhou of North failed western University have used fluores devices cence quenching of the cytochrome upon Researchers study electron transfer as a titration indicator ing the degrada for complexing it with its peroxidase. tion of electronic They found that the quenching rate devices and atmo constant increases with the addition of spheric corrosion should consider the the peroxidase up to a ratio of 1:2 for en effects of airborne submicrometer parti zyme to substrate. Further enzyme addi cles. In many urban indoor environments, tion causes it to decrease. Decomposition the mass concentrations of these parti of the titration curve into the contribu cles and their arrival rates at surfaces are tions of quenching rate constants from comparable to the mass concentrations two assumed binding sites on the peroxi and arrival rates of corrosive gases such dase reveals that, although the concen as S0 2 and NCv tration of 1:2 complex (fully occupied per Working to understand these pro oxidase) is only 0.1% that of the 1:1 cesses in real-world environments, complex, the 1:2 complex causes most of R P. Frankenthal, D. J. Siconolfi, and the quenching. (J. Am. Chem. Soc. 1993, J. D. Sinclair of AT&T Bell Laboratories 115,11008-09) constructed an accelerated life test chamber for electronic devices, circuit Automated method for boards, and assemblies. It provides paral catecholamines lel airflow at velocities up to 35 m/min, generates particles 0.01-1 μπι in diame Catecholamines are important metabolic ter at concentrations > 1 χ 1010/m3, and compounds produced in the brain. The ensures uniform and constant particle determination of catecholamines in bio concentration by having all particles logical samples requires the use of very sensitive trace analysis techniques. When travel the identical distance and encoun ter the same type and number of obstruc used in pharmaceuticals, however, cate tions. The average acceleration factor for cholamines are present in much larger quantities and thus do not require the use particle deposition is 100. (J. Electrochem. of such sensitive methods. T. Perez-Ruiz, Soc. 1993,140,3129-34) Analytical Chemistry, Vol. 66, No. 1, January 1, 1994 21 A
Analytical Currents expensive; with so many pesticides on per derivatization are obtained for each the market, methods that use GC with enantiomer. Quality control samples yield element-sensitive detectors can require RSDs of 17% for the low-concentration multiple gas chromatographs for a com samples and 7% for the middle- and highprehensive determination. Ion trap MS concentration samples. (A- Chromatogr. A with methane chemical ionization (CI) 1993, 653,253-59) has been tested with mixed success as an alternate detection method for the GC Diffusion separator for eluates; full-scan data reflected hybrid semivolatile organic spectra that could not compared with compounds pesticide spectral libraries. The gas/particle distributions of semiThomas Cairns' group at the Food and volatile organic compounds are of inter Drug Administration has used single-ion est because the atmospheric lifetime and area measurement to determine 250 pes fate of pollutants depend in part on this ticides in mixed standards, with deuteri partitioning. The accuracy of results ob um-labeled internal standards for quanti tained with traditional samplers, how fication. In comparison with results from ever, is affected by gas-phase adsorption GC with element-sensitive detection, the on filter media and volatilization from ion trap method was better for determin collected particles in traditional samplers. ing target pesticides at sub-ppm levels Peter H. McMurray and co-workers of (RSD < 10% and a correlation coefficient the University of Minnesota have con > 0.995). A few pesticides, mostly sulfur- structed a low flow rate system to avoid containing compounds, gave unaccept redistribution between the two phases able data because of low sensitivity of during sampling of compounds such as detection. The authors note that sample PAHs and PCBs. cleanup will be necessary before quantifi A laminar flow diffusion separator re cation is acceptable for all 250 target moves a known fraction of the gas phase compounds. (Rapid Commun. Mass Spec- from the ambient aerosol. This fraction is Amino acid trom. 1993, 7,971-88) collected downstream from the separator MASS SPECTROMETRY sequencing and extracted with supercritical C02; the MS is a well-estabextract is then analyzed by GC/MS. The Chiral , lished method for particle-phase concentration is obtained ibuprofen " peptide sequenc SEPARATIONS as the difference between the measured by HPLC ing, both by fasttotal compound concentration and the Ibuprofen (2,4atom bombard isobutylphenyl pro gas-phase concentration. (Environ. Sci. ment (FAB) and by pionic acid), a non Technol. 1993,27,2441-49) collision-induced dissociation (CID). Al steroidal anti though cn ions are commonly observed in inflammatory FAB spectra as a consecutive series, they CZE with isotachophoretic drug, is commonly sold under the trade appear sporadically in CID spectra, lead preconcent ration ing Klaus Biemann and Kevin Downard of name Advil or Nuprin. Because of the N. J. Reinhoud, U. R Tjaden, and J. van presence of an asymmetric carbon atom MIT to postulate that cn formation under der Greef of Leiden University (The α to the carbonyl function, ibuprofen ex CID conditions may be more sequenceNetherlands) have devised a strategy to ists in two enantiomeric forms and is fre improve the limits of detection for CZE dependent than the remainder of the quently sold as a racemic mixture of (R)backbone fragment ions. Therefore, cn analysis of biological samples. ions could provide a means of elucidating and (S)-enantiomers. Evidence suggests, An intial CZE run using indirect UV however, that anti-inflammatory activity (or at least verifying) the structure of a absorbance detection provides insight peptide when sequence ambiguities exist. is stronger for the (S)-enantiomer and into analyte ions and the migration order that the drug undergoes a unidirectional They discovered that the formation of of leading and terminating ions as well as inversion from the inactive (#)-enanticn ions is promoted by the nature of the the ionic composition of the sample ma omer to the active (S)-enantiomer in vivo. trix. The next step is to select and tune amino acid C-terminal to the cleavage site, whereas the nature of the residue D. Nicoll-Griffith and colleagues at the ΓΓΡ separation window to achieve N-terminal to the cleavage site has little the Merck Frosst Center for Therapeutic sample cleanup before CZE is begun. effect on cn ion formation. They also pro Research (Quebec) have developed an The approach can be used for cationic pose a mechanism for cn ion formation automated method for determining ibu and anionic modes of analysis. Its useful and discuss its applicability to their ob profen enantiomers as their amide deriva ness is demonstrated in the determina served results. (J. Am. Soc. Mass Spec- tives using HPLC. An autosampler mixes tion of three cationic antimuscarinic trom. 1993,4,874-81) the crude sample with the derivatization drugs in spiked urine and plasma sam reagents; on-line solid-phase extraction ples; concentrations of homatropine and traps excess derivatization reagents prior scopalamine down to 100 ng/mL were Ion trap MS detects mixed to analytical separation on a (3,4-dinidetermined using this procedure com pesticide residues Determining pesticide levels in fruits and trobenzoyl)-phenylglycine (DNBPG) chi bined with liquid-liquid extraction. (J. ral column. Detection limits of 7.5-200 μg Chromatogr. A 1993,653,303-12) vegetables can be both cumbersome and Folic acid in seawater Folic acid, a water-soluble Β vitamin, is ubiquitous in living systems and likely is present in natural waters because of the organisms that inhabit those waters. However, its occurrence and distribution have not been reported because analytical techniques that could detect low levels of the compound were not available. Anne-Christine Le Gall and Constant M. G. van den Berg of the University of Liverpool describe a method based on cathodic stripping voltammetry preceded by adsorptive collection on a hanging mercury drop electrode to determine folic acid in sea and estuarine waters. In seawater, the best sensitivity is obtained at pH 8.5 at a deposition potential of-0.25 V using square-wave modulation between 25 and 100 Hz. The voltammetric re sponse for 60-s adsorption increases lin early with concentration from the detec tion limit of 0.09-500 nM. The concentration of folic acid was found to increase as salinity decreased. (Anal. Chim. Acta 1993,282,459-70)
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Analytical Chemistry, Vol. 66, No. 1, January 1, 1994
