Flow injection analysis. Part VII. use of ion-selective elctrodes for rapid analysis of soil extracts and blood serum. Determination of potassium, sodium and nitrate

Bubanale V. Effect of centrifugation force and time on the analysis of lactate dehydrogenase and potassium in the serum samples

Introduction and Aim: Any imperfection that occurs during any stage of the testing process is described as laboratory error. Increasing requirements of biochemical tests, numerous patient samples and automation has forced laboratory work to be carried out at a faster speed. Few studies are shown to investigate the influence of settings of centrifugation of less than 10 minutes on the laboratory result in serum. Thus, our study was aimed to see the effect of centrifugation force and time on the analysis of lactate dehydrogenase(LDH) and potassium from serum samples.   Methodology: Samples were collected from 61 healthy volunteers. 5ml was taken in two separate BD vacutainer serum tubes. Tube 1 was centrifuged for 2000g for 10 minutes, tube 2 for 5 minutes 3000g, and analysed for LDH and potassium.   Results: A significant difference was observed between 5 min (U/L) (3000g) and 10 min (U/L) (2000g) with LDH and 5 min (mmol/l) 3000g and  10 min (mmol/l) 2000g with potassium.   Conclusion: LDH and potassium levels were found to be raised by increasing the centrifugal force to 3000g. Hence, the standard centrifugation protocol of 10 min at 2000 or 2500 rpm is to be followed to get the accurate results.

Impedance-based sensor for potassium ions

A conductometric sensor for potassium ions in solution is presented. Interdigitated, planar gold electrodes were coated with a potassium-selective polymer membrane composed of a poly(vinyl chloride) matrix with about 65 wt% of plasticiser and 2-5 wt% of a potassium-selective ionophore. The impedance of the membrane was measured, using the electrodes as a transducer, and related to the concentration of potassium in a sample solution in contact with the membrane. Sensitivity was optimised by varying the sensor components, and selectivity for potassium over sodium was also shown. The resulting devices are compact, miniature, robust sensors which, by means of impedance measurements, eliminate the need for a reference electrode. The sensor was tested for potassium concentration changes of 2 mM across the clinically relevant range of 2.7-18.7 mM.

Recent advances in flow injection analysis

A dynamic development of methodologies of analytical flow injection measurements during four decades since their invention has reinforced the solid position of flow analysis in the arsenal of techniques and instrumentation of contemporary chemical analysis.

Flow analysis in Brazil: contributions over the last four decades

Timeline with the main contributions of Brazilian researchers to flow analysis.

Determination of Trace Sodium in the Water-Steam System of Power Plants Using an FIA/ISE Method with an Automatic Penetration and Alkalization Apparatus

A new method for the rapid determination of trace-level sodium ion based on flow-injection analysis (FIA) and an ion selective electrode (ISE) is proposed. Various effects on the sensitivity of the method such as the flow rate and alkalinity of the carrier, sampling volume, temperature, length of reaction coil, length and thickness of alkalization tube, concentration of the alkalizing reagent etc. were investigated. The optimum conditions were ascertained. The method showed good linearity in the concentration ranges of 0.5 - 10 microg L(-1) and 10 - 100 microg L(-1), and could deal with 40 - 50 samples per hour. The consumption of the sample is only 0.80 mL per time. The relative standard deviation was 0.55%, and the recovery range was 98 - 103%. By designing a hermetically sealed single-line FIA-ISE manifold, a problem removing the interference of sodium ion from air could be solved, and automatic alkalization of the sample was realized. This method has been used for successfully determining the trace-level sodium ions in the water-steam system at fossil power plants.

In-soil potassium sensor system

A potentiometric sensor system based on potassium ion-selective electrodes was developed for agricultural purposes. Sensors were built using PVC ion-selective membranes over an inner solid contact prepared with graphite-epoxy composites. A copper plate was used as a reference electrode. A two-stage electronic circuit composed of current and voltage amplifiers was designed to interface the sensors to a distributed data acquisition system. Three ion-selective sensors and three off-the-shelf temperature sensors and their associated circuits were mounted in a PVC tube to set up a soil probe. The electronic controls were placed in an airtight box fixed at the upper part of the probe. The system was evaluated in the field, where the sensors presented sensibility within the range of 69-71 mV dec(-)(1). Extracts of soil samples were analyzed by a current flame photometry approach, and the results, compared with the probe measurements, showed a linear relationship (r (2) = 0.992 and 0.995, respectively, to 5 and 20 cm depths), which implies viability and instrumentation reliability for agricultural applications.

Vitamins B1 and B6 tubular electrodes as FIA detectors; their use in the analysis of pharmaceutical products

Ion-selective electrodes without an inner reference solution and tubular potentiometric detectors for the determination of vitamins B1 and B6 in pharmaceutical preparations by flow injection analysis (FIA) are reported. The membranes were prepared with the vitamin tetra(2-chlorophenyl)borate (TCPB) dissolved in o-nitrophenyloctyl ether (o-NPOE) and immobilized on PVC. Intrinsic behaviour of the tubular detectors was assessed using a low-dispersion single-channel FIA manifold and was compared with conventionally-shaped electrodes using the same membrane. Data obtained in the determination of vitamins B1 and B6 in pharmaceutical preparations with a double channel flow injection manifold incorporating the tubular detectors are presented and compared with those obtained by the U.S. Pharmacopeia method and by direct potentiometry with conventionally-shaped electrodes.