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Micro-flowcell conductometric sweat analysis for cystic fibrosis diagnosis.
This paper describes a device specifically designed to facilitate neonatal sweat testing. The components are sized appropriately for attachment to the limbs of newborns. Iontophoretic electrodes, with pilocarpine gel inserts, are latched into small holders attached by straps to the limb. The holder at the anodic site remains in place to receive and align the sensor cell, which uses a conical collecting surface to channel the sweat directly and anaerobically from the sweat ducts to the continuous flow-through conductivity cell within its body. A crib-side analysis unit incorporates an iontophoretic power supply and displays a continuous readout of sweat electrical conductivity. The average conductivity during a specific time interval and the initial sweating rate are automatically displayed. The method, which simplifies sweat tests, is currently being assessed in three neonatal clinical trials to test its ability to reduce test failures in the newborn due to insufficient sweat.
Spectroscopic and electrochemical investigation of ternary complexes of D- or L-aspartic acid containing polyacrylamides-Cu(2+)-bovine serum albumin and their radio-stability.
D- or L-aspartic acid containing polyacrylamides were synthesized. Binary and ternary complex formation between these polymers with copper and bovine serum albumin was studied by spectroscopic and electrochemical measurement. Depending on the ratio of the polymer/copper and protein/polymer, the mixture exhibited water-soluble and insoluble character. A hypothetical structural scheme for the formation of ternary complexes is proposed. The effect of radiation on these complexes was also investigated.
Karl Fischer titration and coulometry for measurement of water content in small cartilage specimens.
This study evaluated the efficiency of Karl Fischer titration and coulometry for measurement of water content in small intact and defective cartilage specimens. Cartilage from the main weight-bearing zone of the medial condyle of 38 fresh sheep knees was used. Of these, 20 condyles had an intact cartilage, while defects (14 grade I and 4 grade II) were found in the rest. The mechanical hardness was determined as Shore A. Cartilage specimens of approximately 5 mg were analyzed in special devices for moisture measurement and then continuously heated up to 105 degrees C. The actual measurement was performed in an electric cell (coulometry). An electrode was laminated with hygroscopic phosphorus pentoxide. In the electrochemical reaction, H and O are liberated from the electrode. The requirement for electric energy correlates with the amount of water in the specimen. The water content in intact cartilage was 66.9%. Grade I (72.6%) and grade II (77.8%) defects had significantly higher water content. Significantly higher and faster spontaneous evaporation was observed in cartilage defects at room temperature. The water content and spontaneous water evaporation correlated with significantly lower mechanical hardness. The experimental design (combined method of thermogravimetry, Karl Fischer titration, and coulometry) was sufficient for evaluating the water content in small cartilage specimens. It is also possible to measure the temperature-dependent water liberation from cartilage specimens.
Derivation of the photo-electric efficiency of photoreceptors and a method of extracellular measurement of nerve current. I.
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The mechanism of transmission of the cardiovascular sound. An experimental study of the conduction velocity of sound on the chest wall.
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The interaction of DNA with dopamine by spectroscopic and electrochemical methods.
It has recently been reported that dopamine may show some biological activities in antitumor and cell apoptosis. We have thoroughly investigated the interaction between dopamine and DNA by CD, UV, fluorescence and electrochemical methods. The results of spectroscopic measurements have indicated that a binding event occurs in a dopamine-DNA system. Besides the electronstatic interaction between a negatively charged DNA molecule and a positively charged dopamine molecule, other binding modes, such as hydrogen-bond and intercalation may also exist in this system. The interaction parameters, including the equilibrium constant and binding numbers, were estimated by an electrochemical method based on the redox current and formal potentials. Both of the two calculation methods showed that the 1:1 type of complex was formed in the dopamine-DNA system and that its equilibrium constant was about 5.85 x 10(6) M(-1). Based on the results of UV, fluorescence and electrochemical experiments in the present study, dopamine may be employed as an effective probe for a DNA assay.
Spectroscopic and voltammetric study on the binding of aluminium(III) to DNA.
Cyclic voltammetry (CV) and ultraviolet (UV) spectroscopy were used, for the first time, to study the interaction between aluminium(III) and calf thymus DNA under neutral pH conditions. Thus obtained data confirmed the existence of a relatively strong interaction between Al(III) and DNA. The binding site for aluminium(III) on DNA chains is not the bases, but the phosphate groups on the DNA backbones, the same as that for [Co(phen)3](3+/2+) that binds non-specifically and electrostatically to the deoxyribose phosphate backbone of DNA. When coexisting, Al(III) binds more favorably to DNA than [Co(phen)3](3+/2+), which implies the relatively strong binding of Al(III) to the phosphate backbone of DNA under neutral pH conditions. The nature of the binding of Al(III) to DNA is also discussed.
A disposable voltammetric cell for determining the titratable acidity in vinegar.
A disposable voltammetric cell using three pencil leads as working, reference, and counter electrodes was developed for determining the titratable acidity, i.e. the acid content in vinegar. The materials of the pencil leads were graphite-reinforcement carbons (GRCs). A voltammetric determination of acid was made by measuring the reduction prepeak current of 3,5-di-t-butyl-1,2-benzoquinone (DBBQ) due to the presence of acids in unbuffered solution. The potential stability of the pseudo-reference electrode of GRC was examined. The prepeak current was found to be proportional to the acetic acid concentration from 0.05 to 2.7 mM with a correlation coefficient of 0.999. The cell-to-cell reproducibility for 1 mM acetic acid was evaluated with ten individual disposable cells. The RSD of the prepeak current and the SD of the prepeak potential were 2.56% and 0.008, respectively. The titratable acidity in five vinegar samples was determined by voltammetry using disposable cells and compared with that of the titratable acidity determined by the conventional potentiometric titration method. We then observed the results by both methods, and found a correlation coefficient of 0.972. As such, the voltammetry using disposable-cell required only one thousandth the volume of a vinegar sample for the titration method. The disposable cell was superior to the conventional electrochemical cell, in terms of facility, environment-friendly, and economy, and thus a sensor using the present cell would be useful for routine work in the quality control of vinegar.
Single channel analysis of the inward rectifier K current in the rabbit ventricular cells.
The inward rectifier K channel in rabbit ventricular cells was studied by the patch-clamp method. Single channel currents were recorded in giga-sealed cell-attached patches with 150 mM K+ in the pipette. The slope conductance in the membrane potential range from -140 to -40 mV was 46.6 +/- 6.7 pS (mean +/- S.D., n = 16), and was reduced by decreasing [K+] in the pipette (20 or 50 mM). The channel was blocked by an application of Cs+ or Ba2+ (0.04-1 mM) in the pipette. Outwardly directed current, recorded with 50 mM K+ in the pipette, revealed the inward rectification of the single channel current. The probability of the channel being open was 0.33 +/- 0.05 (n = 10) at the resting potential (RP=-81.7 +/- 1.7 mV, n = 16) with 150 mM K+ in the pipette, and it decreased with hyperpolarization. The mean open time of the channel was 178 +/- 25 msec (n = 6) at RP. The closed time of the channel seemed to have two exponential components, with time constants of 11.0 +/- 2.0 msec and 1.92 +/- 0.52 sec (n = 6) at RP. The slower time constant was increased with hyperpolarization. The averaged patch current recorded upon hyperpolarizing pulses demonstrated a time-dependent current decay as expected from the single channel kinetics. The results indicated that the inward rectifier K+ current has time- and voltage-dependent kinetics.
Conductometric determination of CO2 in air samples.
A new procedure enables the CO2 concentrations of air samples to be determined and automatically registered. The CO2 contents of the air samples are absorbed in an Sr(OH)2 solution. The resulting decrease in electrical conductivity of the solution is automatically registered by a d.c. strip-chart recorder in such a way that the decline of the curve is proportional to the amount of CO2 absorbed. In each analysis, quantities of CO2 up to about 8 mumol can be determined with an error of less than 0.02 mumol, and, accordingly, CO2 quantities of 2 to 8 mumol contained in samples of at least 150 ml of fresh atmospheric air or about 1 ml of carboxygen or expired air can be analysed with an accuracy of better than +/- 1.0% of their CO2 content.
Evaluation of a method for determination of the subcutaneous blood flow in the forefoot continuously over 24 h.
A method is presented which allows for continuous registration of forefoot blood flow over 24 h. Blood flow was estimated by the radioactive Xenon washout method and a portable CdTe detector system was used to measure the tracer disappearance rate. Since the semiconductor detector is placed very close to the tracer depot the washout rates registered are a mixture of rate constants due to tracer removal by blood flow and diffusion of the tracer depot away from the detector. Rate constants only due to diffusion were obtained over 24 h from amputated feet and similarly from normal feet with circulatory arrest in several 20 min periods during 24 h. The rate constants due to blood flow could thus be calculated by subtraction of the appropriate diffusion rate constants from the recorded rate constants. Blood flow in the forefoot during 24 h was measured in 10 experimental subjects with normal peripheral circulation. Blood flow during daytime did not differ between the first and second day. Blood flow during night-time was about twice that during daytime.
Electrogenic anion absorption in rabbit distal colon.
The mechanisms of anion transport in the rabbit distal colon were investigated in vitro under short-circuit conditions by examining the effects of transport inhibitors (the stilbene derivatives SITS and DIDS) under a variety of conditions. These agents consistently inhibited Jm-sCl: SITS (10(-3) M) reduced both unidirectional chloride fluxes to the same degree and did not alter JnetCl. In contrast, 10(-4) M DIDS had no effect on Js-mCl and had a significant chloride antiabsorptive effect. DIDS had no effect on either tissue cyclic AMP levels or on basal flux of potassium. The effects of SITS and the cyclic AMP-related secretagogue theophylline on Isc were independent. Additionally, there was no significant alteration of intracellular potential difference or apical membrane fractional resistance elicited by SITS during microelectrode impalement of colonic surface epithelial cells. These results suggest a complex mechanism of anion transport in the distal colon, with a component of electrogenic anion absorption inhibited by the stilbenes. The subsequent changes in current, conductance, and chloride fluxes are dependent upon additional, independent anion transport processes. These pharmacologic agents exhibit an antiabsorptive effect, rather than a stimulation of electrogenic chloride secretion.
Impedance microbiology: applications in food hygiene.
Impedance microbiology is a rapid method that enables qualitative and quantitative tracing of microorganisms by measuring the change in the electrical conductivity. With direct impedance technology, the change in the conductivity of a liquid culture medium serves as a measuring parameter, whereas with indirect impediometry, the change in the electrical conductivity of a reaction solution, which occurs through the absorption of gases from the inoculated bacterial culture, is measured. Most investigations concerning the applicability of impediometry in food microbiology deal with the impedimetric detection or enumeration of Enterobacteriaceae, especially the detection of Salmonella. However, impediometry has been applied to other bacterial groups or species as well. Furthermore, a great number of published findings concern the impedimetric determination of the total bacterial count. The successful application of this fast method on further areas of food hygiene, such as tracing antibiotics and testing additives for their antimicrobiological effect, has also been described. In general the use of impediometry for the application areas stated has been judged positively. However, the time and expense required by the user to optimize the method, the deficits when testing slightly contaminated sample material or determining the bacterial count in those cases in which the microorganisms are sublethally damaged, and the necessity of performing individual calibration for each food category limit the applicability of impediometry.
Evaluation of a selective broth for detection of Staphylococcus aureus using impedance microbiology.
Experiments were conducted to evaluate a selective nutrient broth containing acriflavine and nalidixic acid for detection of Staphylococcus aureus using an impedance microbiological method. Nine species of bacteria, other than S. aureus, were evaluated using the selective broth to determine if these species could be inhibited. A total of 10 ppm of nalidixic acid inhibited the gram-negative species tested, with the exception of Pseudomonas aeruginosa. Similarly, 10 ppm of acriflavine suppressed the Staphylococcus spp. examined; however, S. aureus retained the ability to proliferate. Nutrient broth solution containing 10 ppm of nalidixic acid and 10 ppm of acriflavine (S. aureus impedance broth [SIB]) inhibited multiplication of most of the bacterial species tested and allowed S. aureus to be detected in an average of 16.4 h. Fresh chicken carcass rinses and cooked chicken rinses were inoculated with Escherichia coli and S. aureus and assayed using SIB in conjunction with impedance. Results demonstrated that S. aureus could be detected in less than 11.5 h, although the presence of E. coli decreased detection times. Additionally, impedance assays were conducted using five different poultry products to evaluate the sensitivity of the broth for detecting S. aureus. S. aureus could be detected on poultry products when present at low levels (10(1) CFU/ml) in less than 24 h. These studies demonstrated that SIB may be used in conjunction with impedance for rapid detection of S. aureus. However, without further modification, this method should not be used for enumeration of S. aureus from samples containing mixed microflora.
A conductance method for the identification of Escherichia coli O157:H7 using bacteriophage AR1.
The feasibility of using a specific phage (AR1) in conjunction with a conductance method for the identification of Escherichia coli O157:H7 was evaluated. The multiplication of strains of E. coli O157:H7 was inhibited by AR1; therefore, a time point (detection time, DT) at which an accelerating change in conductance in the culture broth was not obtained. Bacterial strains were subcultured on sorbitol-MacConkey agar and incubated at 35 degrees C for 24 h, and the ability of the bacteria to ferment sorbitol was recorded. An aliquot of 0.5 ml of the bacterial suspension (10(7) CFU/ml) and 0.5 ml of the phage suspension (10(8) PFU/ml) were added to the conductance tube of a Malthus analyzer containing 5 ml of culture broth. The tubes were incubated at 35 degrees C, and conductance changes in the tubes were continuously monitored at 6-min intervals for 24 h by the instrument. A positive reaction was defined as an E. coli strain that could not utilize sorbitol and caused no conductance change (i.e., no DT) within an incubation period of 24 h. Of the 41 strains of E. coli O157:H7 tested, all produced positive reactions. When a total of 155 strains of non-O157:H7 E. coli were tested, 14 did not have a DT within 24 h. However, among these 14 strains, 13 were sorbitol fermenters, and the remaining one was a nonfermenter. Therefore, by definition, only one strain produced a false-positive reaction. The sensitivity and specificity of the present method were 100% (41 of 41) and 99.4% (154 of 155), respectively. The present method incorporating conductimetric measurement and phage AR1 for the identification of E. coli O157:H7 was simple and capable of automation.
Could conductivity be used as a parameter in urinalysis?
Conductivity is a non-linear function of electrolyte concentration in solutions and could be used as an indirect method. The aim of this study was to determine the feasibility of urine conductivity measurement, which is a simple, cheap and not time consuming method, in the evaluation of renal functions. Seventy-two patients whose primary diseases were not taken into consideration were enrolled in this study. First morning urine specimens were obtained from all the patients and evaluated for osmolality, conductivity, pH, specific gravity, protein, creatinine, urea, uric acid, glucose, sodium, potassium, chloride, inorganic phosphate and calcium levels. There was a significant positive relation between osmolality and creatinine, urea, sodium, potassium, chloride, inorganic phosphate, uric acid, conductivity and specific gravity. Conductivity was also determined to be positively related to osmolality (r: 0.390, p < 0.01), sodium (r: 0.326, p < 0.01) and uric acid (r: 0.345, p < 0.01). The patients were grouped as those with a urine osmolality of less or more than 290 m Osm/kg. H2O (group A and B respectively). Urine conductivity was 6.84 +/- 5.35 (0.16-23.2) mScm-1 in group A and 10.6 +/- 5.25 (0.12-192) mScm-1 in group B. The difference was statistically significant (p = 0.005). When the spectrum of conductivity values were evaluated separately in each group, 74% of the patients in group A and 33.9% of the patients in group B were determined to have a conductivity level of less than 7.338 mScm-1. In conclusion, urine conductivity has a positive relation with osmolality. In addition, while osmolality and specific gravity are effected by many non-electrolyte molecules, conductivity is only related to sodium and uric acid concentrations. In addition, urine osmolality and conductivity levels could be used to interpret the concentration of uncharged glucose molecules. These results suggest that conductivity could be used as a parameter in routine urinalysis.