Two methods for the determination of N-acetyl-p-aminophenol (APAP) in plasma that differ in principle from the diazotization procedure of Brodie and Axelrod (1) are described. One method based on the differential absorption peak of APAP at 266 mµ, which corresponds to the isosbestic point of common drugs such as acetylsalicylic and salicylic acids, is simple and most specific for APAP. The other method employs a free-radical dye diphenylpicrylhydrazyl which extracts a hydrogen atom from the APAP molecule and is progressively decolorized. The dye method is the least complex and most sensitive. All three methods exhibited satisfactory replication, recovery of added APAP, and comparable plasma levels of the drug.

The method of Axelrod and Reichenthal for the determination of caffeine in serum and urine was modified. The benzene used in the extraction of caffeine was shown to alter the spectral absorbance curve of this compound. A method based on the differential absorbance spectrums of caffeine and related compounds is described. Both methods exhibited satisfactory replication, recovery of added caffeine, and comparable serum levels of the drug.

Recently there have been new trends in global consumption toward fresh foods that are sources of healthy bioactive compounds, as is the case with pitaya. However, pitaya cultivation is a relatively recent phenomenon and little is known about its management. The objective of this work is to determine the most appropriate annual fruiting pruning method for pitaya in order to obtain a regular annual yield of quality fruit and an intense shoot renewal that guarantee future production. This study compared the response of Hylocereus undatus to spur, cane, and combined pruning. As control plants, we left some plants where only sanitary pruning was performed. The results indicate that spur pruning greatly reduced flowering (seven times less than controls) and did not promote intense vegetative growth. Cane pruning, on the contrary, allowed greater flowering which is compatible with a higher number of new shoots (8% more than controls). The vigor of the new shoots was equal in all treatments. Fruit size and quality did not differ either among treatments. Spur pruning only seems applicable as a rejuvenation pruning. Combined pruning gave an intermediate response and seems of no interest given the good shoot renewal provided by cane pruning. Performing sanitary pruning alone may be an interesting option, but only in the first years of cultivation.

The shift in the UV spectral absorption curves of acetylsalicylic acid (ASA) and salicylic acid (SA) produced by a change in pH has been used in the development of a method for the quantitation of these compounds. The differential spectral absorption curve of ASA exhibits a maximum at 300 mµ, while that of SA shows a maximum at 319 mµ and an isosbestic point at 300 mµ. The method is simple and specific for ASA and capable of determining the concentration of the ASA and SA in the blood after the ingestion of 10 gr. of aspirin.