Glucose monitoring gets under the skin Elevated glucose is not just a symptom of diabetes; it is a cause of the pathology, says Mark Shults of the University of Wisconsin Medical Center and the company Markwell Medical (Racine, WI). The open-chain aldehyde form of glucose reacts nonenyzmatically with proteins throughout the body. After years of exposure to such glycosylated proteins, many organs, including the eyes, kidneys, and heart, are severely damaged. Although insulin can be given to lower gluose levels, it must be given cautiously to avoid driving glucose too low, which results in serious insulin reactions. One proposed solution to this dilemma involves an implantable glucose sensor that could provide a "rich stream" of glucose data to the patient so that insulin can be used optimally. That goal is moving closer to reality. Shults and his co-workers have taken their
amperometric glucose sensors based on glucose oxidase chemistry, implanted them in dogs, and obtained clinically relevant data for as much asfourand a half months. They have received clearance from the U.S. Food and Drug Administration to begin limited human clinical trials with up to five individualss One of the most difficult aspects of designing an implantable glucose sensor is in tricking the body to use its defense mechanisms in the sensor's favor. Any time an object is introduced into the body, the body produces a "foreign body capsule", or FBC, that is intended to isolate the intrusive object. The FBC needs its own blood supply as it develops, but, unless something is done to sustain the process, angiogenesis (the creation of new blood vessels) stops. The FBC then loses its vascularization, becoming a tough,fibrousmembrane with such poor blood circulation that the loses its analyte. The researchers have developed an outer layer for the sensor membrane from a pro-
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Britt EricksonreportsfromSt. Louis
Rapid, simultaneous detection of triazine herbicides Atrazine is one of the most widely used herbicides in the world. Methods for detecting it in water and soil are challenging because of its many degradation products. In addition, related triazine herbicides, such as simazine and cyanazine, are often found in the sample matrix. David S. Hage and co-workers at the University of Nebraska have developed a new method based on high-performance affinity chromatography for the simultaneous detection of atrazine and its related compounds. The method relies on an immunoaffinity column, which contains a covalently attached monoclonal antibody (mAb) that is specific for triazine compounds. The triazine herbicides are extracted from water samples upon passing through the immunoaffinity column. A set of standard reversed-phase (RP) HPLC columns is then used to reconcentrate and separate the extracted solutes. According to Hage, the method requires much smaller sample volumes than traditional GC methods and it
prietary material, the texture of which seems to promote angiogenesis. In addition, the sensor membrane must have a stable layer that can protect the underlying layers from macrophages mat attempt to degrade the sensor. This bioprotective layer can be constructed of polymers such as PTFE and polypropylene. When the sensor is operating in vitro, the 90 % response time to an increase in glucose levels is 3-5 min. In vivo ii is snly slightly slower, indicating a good blood supply to the sensor. The sensor responds over the clinical range of interest, 50-500 mg glucose/100 mL ((.8-28 mM). The fully implanted sensor transmits data using radiotelemetry. Interestingly, most sensor failures have little to do with the reaction chemistry. The prototype sensors are not in hermetically sealed packages, which limits long-term in vivo operation of electronics. This problem could be overcome by using the same techniques as in pacemaker construction.
ANDI moving ahead offers a lower detection limit of 0.1 ppb for a 250-uL sample injection. This limit is well below the EPA maximum allowance of 3 ppb in drinking water. Sample throughput can be increased by running samples simultaneously, says Hage. Because the system contains both an immunoaffinity column and standard RP columns, you can have multiple samples, one on each column, at the same time, he explains. The direct analysis of samples can be completed in as little as 12 min for ramples with hpp levels of triazine compounds and in 30 min for those with pptr levels, he says. .n addition, no sample pretreatment, other than simplefiltration,is required. The method has been used for monitoring triazine herbicide contamination in surface and river waters. In addition, it has been used to study the degradation rates of atrazine in groundwater and for evaluating new purification strategies in water treatment plants. With a different mAb, the method can also be used for the measurement of other contaminants in the environment. Hage says that they are currently developing a similar method for the detection of alachlor, another widely used herbicide.
In an ongoing effort to develop data standards for the instrumentation industry, a subcommittee of the American Society for Testing and Materials (ASTM) is closing in on guidelines—dubbed the Analytical Data Interchange Protocols (ANDI)—for mass spectrometry and chromatography. At a May 4 meeting in Attanta, the committee finalized the eraft for rhromatography. Those standards should be available on the ASTM web site (http://www.astm.org) soon, says Lynn Matthews, president of Thru-put Systems, Inc. (Orlando, FL) and chair of the subcommittee. The standards are designed to allow manipulation and archiving of data long past the life span of the instrument that collected it. The plan calls for specifications to handle raw data, results, the full dataprocessing method, the full chemical method, and good laboratory practice (GLP) information. Only specifications for raw data and results have been completely defined in the current round of protocols, says Mike McConnell, director of engineering at PE Nelson and a. technical cochair of an early ANDI committee on chromatography.
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