Gerald G. Vurek

Fluorometric method for the determination of nanogram quantities of inulin

The fluorometric determination of 15 or fewer nanograms of inulin can be made with a precision of ±5.3%. Inulin reacted with dimedone in concentrated o-phosphoric acid produces a moderately fluorescent product which can be excited by the 366 nm mercury lines and which has its fluorescence peak around 400 nm. The reaction conditions, 5 min at 100°C, are such that the presence of five times more glucose than inulin does not introduce significant error in the estimation of inulin.

A fiber optic PCO2 sensor

The theory, construction and performance of a catheter tip optical PCO2 probe is described. The sensor, called the Opticap, is made with plastic fiber optics. One fiber carries light to the sensitive tip which is a silicone rubber tube 0.6 mm dia. × 1.0 mm long filled with a phenol red-KHCO3 solution. Ambient PCO2 controls the pH of the solution which influences the ooptical transmittance of the phenol red. A second fiber carries the transmitted signal to a receiver; the resulting electrical signal is linearly related to the PCO2 over the range of 2.7 to 10.7 kPa. The probe was tested as a tissue PCO2 sensor on the cerebral cortex of the cat and as arterial PCO2 sensor. Drift over one days use was 0.6 KPa or less and individual probes have been used as long as 12 weeks.

Helium-Glow Photometer for Picomole Analysis of Alkali Metals.

The low-power electricglow discharge in helium can excite efftctively the characteristic emission lines of sodium and potassium. The helium-glow photometer used to generate the glow and measure the light is a relatively simple apparatus; it can be used to analyze samples containing 10-14 mole or more of sodium and potassium. Overall precision of the apparatus and method is 5 percent or better.

CONSTANT VOLUME, SELF-FILLING NANOLITER PIPETTE: CONSTRUCTION AND CALIBRATION.

Pipettes with volumes ranging from less than one nanoliter to 200 nanoliters can be constructed by means of a simple mechanical system and calibrated by radioisotope and fluorescence techniques. Biological fluids can be transferred with a repeatability of 1 percent by this self-filling pipette of constant volume.

Capillary-Tube Scanner for Mechanized Microbiology A photoelectric scanner measures growth in agar-filled capillaries and gives a new approach to microbiology

Growing microcolonies of bacteria can be detected by their light-scattering property. We have described a system in which growing bacteria in glass capillaries filled with nutrient agar are counted as the capillaries move through a narrow beam of light. Increased counts after incubation indicate the presence of viable organisms in the original sample; the equipment can detect colonies when they grow to a diameter of 8 �m. Aerobic, anaerobic, and facultative organisms can grow in the capillary environment. The sensitivities of several organisms to antibiotics were determined by adding antibiotics to the agar before the capillaries were filled.

Picomole quantitation of ammonia by flow-through fluorometry

A new fiber optic fluorometer has been used to measure picomole amounts of ammonia. The method is based on the enzymatic conversion of alpha-ketoglutaric acid and ammonium ion to glutamate with associated oxidation of NADH. The decrease in NADH fluorescence is used to quantify sample ammonia content. The method is rapid and reproducible and is capable of resolving differences as small as 0.3 pmol between samples containing 0-7 pmol.

Flow-through Nanocolorimeter for Measurement of Picomole Amounts of Magnesium and Phosphate

Abstract This paper describes the construction of a colorimeter with a working volume of 230 nL and light path of 11 mm. The performance of the apparatus is demonstrated by the measurement of magnesium and inorganic phosphate in simulated biologic fluid. Sensitivity is less than 10−12 mole.

Calcium measurement: Picomole quantitation by continuous-flow colorimetry

Abstract A new microcolorimeter with a 220-nl volume, 1.1-cm light path cuvet and solid-state photometric components is described. It has been used in a continuous-flow analysis system for the colorimetric measurement of total calcium in biologic fluids. The sensitivity is 0.5 pmol and it is linear beyond 50 pmol.

Fiber-optic colorimeter for submicroliter samples.

Abstract We have described the construction and testing of a microcolorimeter which has a 1.2 cm path and requires a sample volume of less than 0.2 μl. In addition, we have described the results of some tests which indicate the limits and potentials of the use of fiber-optic material for microfluo ometers as well as for microcolorimeters.

Assay of Sodium and Potassium Activated Adenosine Triphosphatase in Submicrogram Fragments of Renal Tubules

Abstract An improved method for measuring Na, K-ATPase in submicrogram fragments of single renal tubules approximately one millimeter long is described. The activity is determined by coupling ATP hydrolysis stoichiometrically to pyruvate kinase and the oxidation of NADH by lactic dehydrogenase. NADH oxidation is followed fluorimetrically using an instrument specially modified for increased sensitivity and stability.