For optical purity analysis and separation of optical Isomers
The
Second Wave of Pirkle Columns from Regis The first wave Based on a n approach developed by Dr. William H. Pirkle of the University of Illinois, a first wave of chiral columns was introduced by Regis in 1982. These columns were packed with silica-bonded dinitrobenzoyl (DNB) derivatives of phenylglycine and, later, leucine. Today these columns are finding wide use in separating optical isomers from many classes of aromatic compounds such as alcohols, sulfoxides, bi-βnaphthols, β-hydroxysulfides, and agents related to propranolol.
The second wave Now Begis introduces a second wave: The new Pirkle covalent naphthylalanine HPLC columns. These columns are especially designed for separating the DNB derivatives of amines, amino acids, alcohols, and thiols. These new columns are startlingly selective, w i t h relative retentions as high as 16.5 already reported. These second wave columns are also characterized by typical Regis advantages: They are covalent, highly efficient, based o n spherical silica, and strongly guaranteed. The guarantee: If, for any reason, you are not satisfied w i t h the performance of y o u r Regis column, simply r e t u r n it for a full refund.
How supplied The first wave, stUl available and widely used Ionic 8S em columns B-Pnenyl Glycine L-teuoine Covalent 35 cm columns D-Phenyl Glycine L-Phenyl Glycine D,L-Fhenyi Glycine i-Iteucine ï h e beginning of the second wave Covalent 25 cm columns D-
.me
L-Naphthyl Alanine D,L-Napnthyl Alanine Regis Plrkle column literature available upon request from your Regis Distributor, or write:
jP| Regis Chemical Co. HJ 8210 Austin Avenue Morton Grove, Illinois 60053 USA CIRCLE 180 ON READER SERVICE CARD
Focus monitoring drugs, toxins, and naturally occurring biochemicals in various body fluids such as cerebral spinal fluid, amniotic fluid, or even the interstitial fluids of soft tissue. Other researchers are designing fiber-optic biosensors that use enzymatic, immunochemical, or other biocatalytic reactions instead of the traditional dye indicator reactions. For example, Mark Arnold of the University of Iowa has designed a fiber-optic chemical sensor in which an isolated enzyme is immobilized at the surface of a bifurcated optical fiber bundle (3). Response of the sensor is based on directly measuring the enzymatic generation of a spectrophotometrically detectable product. Immunosensors
Researchers are designing fiber-optic biosensors that use enzymatic, immunochemical, or other biocatalytic reactions instead of the traditional dye indicator reactions. are being developed by both Sepaniak and by Hirschfeld's group, and like the enzyme-based sensors, these are highly specific and have the potential for determining many different biomedically important analytes. Fluorescence-based fiber-optic chemical sensors have been aimed primarily at the determination of pH and blood gases (CO2 and O2), although Sepaniak's group is also working on an optical-fiber fluoroprobe for clinical determination of drugs in body fluids or tissue. Blood gas sensors have been developed by several researchers, including Peterson, Hirschfeld, and Otto Wolfbeis of the Institut fur Organische Chemie in Graz, Austria. This is the only type of fiber-optic sensor that is commercially available. Cardiovascular Devices of Irvine, Calif., currently the only company selling fiber-optic sensing devices (although it is likely to have some competition in the near future), offers two such sensors: an extracorporeal sensor for use in an externally diverted bloodstream (such as during openheart surgery) and a catheter for actual in vivo use. Affinity sensors
The newest trend in fiber-optic sensor development is that of affinity sensors, which combine fluorescence
768 A · ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
detection with competitive-binding reactions. In addition to their inherent high selectivity, these sensors can use analytical reactions that don't directly produce an optical change. A competitive-binding affinity sensor for glucose was developed several years ago by J. S. Schultz (4). In this sensor, the specific glucose-binding reagent concanavalin A is immobilized on the inner wall of a hollow fiber, and glucose competes for binding sites with fluorescein-labeled dextran. In the absence of glucose, the dextran is bound to the concanavalin A substrate, but when the glucose concentration increases, some of the dextran is driven off into the optical path, and there is an increase in the fluorescence intensity proportional to the glucose concentration. At the 1986 Pittsburgh Conference held last March in Atlantic City, Rudolf Seitz of the University of New Hampshire presented preliminary work on the development of a sensor that uses fluorescence energy transfer as an alternative to visualization of the dextran displacement by glucose. In Seitz's approach, both the dextran and concanavalin A are labeled with fluorophores, one with a donor and one with an acceptor. As with Schultz's sensor, dextran is bound to the concanavalin A in the absence of glucose, and the distance between donor and acceptor is short enough that the excited donor transfers energy to the acceptor. Added glucose displaces the dextran from the concanavalin A and causes a decrease in the efficiency of energy transfer. Efforts are under way to develop conditions in which the energy transfer process not only quenches donor emission but also leads to significant acceptor emission intensities. This would allow a single ratio measurement of donor-to-acceptor emission intensity, and such a ratio measurement would be inherently more stable than a single intensity measurement. Also at this year's Pittsburgh Conference, Seitz introduced a competitive-binding sensor designed to determine fluoride, chloride, and nitrite anions using fluorescein-labeled dextran and Texas-Red-labeled polyethylenimine confined by a dialysis membrane. Seitz is also developing a sensor for determination of alkali metal ions based on competition of the metal ions and fluorescein-labeled polyethylenimine for crown ether binding sites. Future fiber-optic sensor development is expected to make use of increasingly sophisticated optical techniques. For example, in a REPORT published in the January 1984 issue of
