Seven synthetic analogues of somatostatin helped clarify structural requirements for suppression of growth hormone secretion in rats. Size of the ring is not critical; deletions of serine-13, lysine-4 or asparagine-5 result in peptides which retain an appreciable fraction of the activity. The analogue des-Ala1, Gly2, Asn5-somatostatin lowers plasma growth hormone and insulin levels without affecting plasma glucagon levels significantly.

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Chlorine is widely used to safeguard the water supply. Chlorine concentrations must be monitored to ensure proper application and effective disinfection. The N,N-Diethyl-p-phenylenediamine (DPD) colorimetric method is commonly used to measure the free chlorine residual in potable water supplies.The DPD colorimetric method (as described in AWWA Standard Method 4500-Cl-G) requires the addition of sample, DPD, and buffer in separate steps. Reagent preparation is time consuming, and the method can be technique dependent. The indicator solution, if improperly stored, can increase in background and possibly skew results. The test has become more convenient to perform because of advances in DPD reagents in the form of stabilized liquids, powder dispensers, pre-packaged powders, and tablets, but each of these methodologies has its own limitations.Liquid systems demand accurate measurement or may require drop counting, which is prone to error. Powder dispensers, although convenient, have been known to clog when moisture enters the unit and causes the powder to cake. It is also known that DPD powders do not always completely dissolve in the sample. Pre-measured, pre-packaged powders resolve the problems caused by moisture but can be difficult to open. Transfer of the packet contents can be hit-or-miss, resulting in spills and the possibility that an inadequate amount of DPD entered the test sample. There have been reports of allergic reactions to DPD, so the spills also represent a possible exposure risk to sensitized individuals. Tablets can be difficult to crush, and slow to dissolve.A new method of DPD delivery has been developed. This method, trademarked as the DPD ReagentStrip™, addresses many of the limitations listed above. Indicator, buffers, and EDTA in proportions as identified in AWWA Standard Method 4500-Cl-G are impregnated onto laboratory grade paper and dried. The paper is cut into strips that are stable and protected from moisture. The reagent pads are never touched, so there is no contact exposure risk. The strips are of a size that is easy to handle, and in unitary packaging that is easy to open. Spillage is not a problem because the reagents are not released until the strip is dipped in the water sample. During the 20-second dip time the correct amount of reagent is dispensed and simultaneously mixed into the sample, so there is no concern about poor dissolution or improper dosing.Test results using the new delivery method show excellent correlation with widely used EPA compliant colorimeters that use current delivery technology. In one study water was collected at more than 70 distribution points from around Rock Hill, SC. Water samples were tested at the collection point using both powder pillows and the DPD Reagent Strip™. A Hach DR100 Pocket Colorimeter was used to read the color and determine the concentration of the samples. The same curve was used for both methods. Upon comparison a slope of 0.9961 and a correlation coefficient (R 2 ) of 0.9996 (n=72) were obtained, demonstrating excellent agreeme...