Marijuana is listed as a Schedule I substance under the American Controlled Substances Act of 1970. As more U.S. states and countries beyond the U.S. seek legalization, demands grow for identifying individuals driving under the influence (DUI) of marijuana. Currently no roadside DUI test exists for determining marijuana impairment, thus the merit lies in detecting the primary and the most sought psychoactive compound tetrahydrocannabinol (THC) in marijuana. Salivary THC levels are correlated to blood THC levels making it a non-invasive medium for rapid THC testing. Affinity biosensing is leveraged for THC biomarker detection through the chemical reaction between target THC and THC specific antibody to a measure signal output related to the concentration of the targeted biomarker. Here, we propose a novel, rapid, electrochemical biosensor for the detection of THC in saliva as a marijuana roadside DUI test with a lower detection limit of 100 pg/ml and a dynamic range of 100 pg/ml – 100 ng/ml in human saliva. The developed biosensor is the first of its kind to utilize affinity-based detection through impedimetric measurements with a rapid detection time of less than a minute. Fourier transform infrared spectroscopy analysis confirmed the successful immobilization of the THC immobilization assay on the biosensing platform. Zeta potential studies provided information regarding the stability and the electrochemical behavior of THC immunoassay in varying salivary pH buffers. We have demonstrated stable, dose dependent biosensing in varying salivary pH’s. A binary classification system demonstrating a high general performance (AUC = 0.95) was employed to predict the presence of THC in human saliva. The biosensor on integration with low-power electronics and a portable saliva swab serves as a roadside DUI hand-held platform for rapid identification of THC in saliva samples obtained from human subjects.

The paper describes an investigation into a number of the chemical reactions employed in photometric analysis for the determination of silicon, manganese, chromium, nickel, vanadium, titanium, copper, iron and molybdenum. The influence of a large number of variables has been studied in order to establish the optimum solution conditions for the development of stable and reproducible colours irrespective of the class of material in which the clement to be determined may occur.

No abstract

275 to 325 m p and from 400 to 450 mp, the corresponding peak absorbancy indices (g per litre per cm) being 1.1 and 0.055, respectively. Unfortunately light of the first waveband is subject to serious interference from many elements, including iron, molybdenum, niobium, zirconium and so on. Many of these difficulties do not arise with the higher waveband and, since the applicability of this technique was just as important as the best accuracy, investigations were limited to the higher waveband. Moreover, since the ultimate accuracy attainable in a determination is dependent on the largest single error from any one operation of the procedure, extensive experiments were carried out to assess the degree of control needed for the attainment of maximum accuracy under these conditions. PRINCIPLE OF DETERMINING MAXIMUMACCURACY-0.05 per cent. Let C, = the concentration of the reference solution, C, = the concentration of the test solution, A , = the theoretical absorbancy of the reference solution under standard conditions A , = the theoretical absorbancy of the test solution under standard conditionsThe concentration error at any point on a spectrophotometric calibration graph is in a 1-0-cm cell, and in a 1-0-cm cell.

BY A. BACON Several German workers have described the use of Eriochrome Cyanine-R for the photometric determination of aluminium. This reagent was not available through the normal British supplies and Solochrome Cyanine-RS was suggested as the British equivalent. The paper describes the application of this reagent to the determination of aluminium in magnesium alloys containing alloying additions of aluminium in the ranges 0 to 0.35 per cent. of aluminium and up to 14 per cent. of aluminium, and also to the detection of trace amounts of aluminium up to 0.02 per cent.Interference by zinc, nickel, manganese and cadmium is negligible ; copper and iron interference is discussed in detail. The determination of aluminium in the presence of phosphate is also described. For alloying additions in the ranges stated, the method has an accuracy of + 1 per cent. of the maximum of the aluminium range covered. With metal containing less than 0-025 per cent, of aluminium the results are reproducible to 0.0005 per cent. of aluminium.MANY authors have described the use of Eriochrome Cyanine-R for the determination of aluminium. Snell and Snelll claim that 4 hours at room temperature or 1 hour a t boiling temperature is required to attain a constant depth of colour at a pH of 3.8, although at higher pH (5.4 to 6.0) several days are required. This seems to be taken from a paper by Richter,2 who also states that various preparations of Eriochrome Cyanine-R exhibit different reactions, which are expressed either in the character of the calibration graph or in different values for the lake. Two years earlier Rauch3 had applied the same reagent to the determination of aluminium in magnesium alloys and had described sources of error experienced both in the photo-electric measurement and in developing the colour. Much of the work described in this paper was carried out in 1944, at which time Eriochrome Cyanine-R was not available from the usual sources of supply in England, but Solochrome Cyanine-RS was stated to be similar in properties. As early tests showed that the dye changed from red to yellow over the pH range of 3.0 to 8-0 and that aluminium salts reacted to form a purple lake, it was decided to investigate the reaction in detail and compare the results with the earlier reports on the Eriochrome Cyanine-R reagents.Choice ofJiZters-To select the most suitable colour filters, a solution containing 0.05 g of Solochrome Cyanine-RS per litre and an excess of an aluminium salt was buffered at pH 5-8 by means of sodium acetate and acetic acid, and the absorption measured on a Spekker absorptiometer at different wavelengths with Ilford colour filters and a tungsten filament lamp. The drum readings were plotted against the wavelength of maximum transmission of the colour filters. From Fig. 1 it can be seen that maximum sensitivity occurs with green filters. In the same figure is included an absorption curve of a solution containing only the reagent, and it is apparent that the dye alone absorbs strongly in the green waveband. At first it m...