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Flow injection analysis has been used to determine lactate in precipitated serum samples employing the NADH-LDH method. The method is suitable for determinations in the concentration range 0.2-20 mmoles per litre of lactate. The procedure has been tested against a manual routine procedure and the results were in good agreement.
Flow injection analysis (FIA) has become a versatile tool for rapid and automated analyses. As its capabilities have increased, so have the complexity and operation of the apparatus. We have been investigating ways to simplify both the apparatus and the application of injection techniques. A novel cam-driven syringe pump and the development of sequential injection analysis (SIA) are reviewed, and some applications presented. Flow injection coulometric titrations are presented as a means to further alleviate reagent stability and calibration problems. These systems have potential for automatically carrying out many drug assays.
Flow-injection analysis is a precise, elegant, and economical technique, but its most troublesome feature is the mode of injection of the sample slug. We describe an alternative approach in which the sample is aspirated by the sample probe. In the simplest version the probe normally rests in reagent; when sampling is to take place, the pump is stopped and the probe is transferred to the sample container. The pump makes a predetermined angular movement, the probe is returned to reagent, and the pump is restarted. In more advanced versions the same approach is combined with the merging zone technique. The system is economical, precise, and capable of full automation in a multichannel discretionary analyzer.
Combining flow injection analysis with a biosensor is a novel biosensing process which has allowed speedy and accurate analysis. Diagnostic analysis is the most important application for biosensing flow injection analysis, but other applications include bioprocess monitoring, analysis of food and agricultural products, as well as environmental analysis. In addition, the analysis of compounds, such as explosives and abused drugs, and monitoring of Salmonella, the microorganism that causes food poisoning, have been reported.
A flow injection analysis (FIA) procedure is described for the determination of chlorocresol in a parenteral pharmaceutical formulation. The product is directly injected into a carrier stream of water and subsequently reacted with a reagent stream of nitrous acid. The resulting brown nitro-derivative is determined spectrophotometrically at 400 nm. The method has been validated and should be applicable to chlorocresol in other pharmaceutical products and to compounds containing a phenolic ring, assuming absence of matrix interference.
A flow injection analysis procedure with chemiluminescence detection for the determination of both thiol-containing drugs and the amino acid cysteine is described. Procedures are based on the inhibition by the drugs of the chemiluminescence generated in the copper-catalysed oxidation of luminol by hydrogen peroxide. The proposed methods were applied to the determination of cysteine, N-acetylcysteine, penicillamine, 2-mercaptopropionylglycine and thiouracil in pharmaceuticals.
A flow injection analysis (FIA) procedure is described for the determination of pentavalent antimony (Sb5+) in the drug, sodium stibogluconate, in a parenteral pharmaceutical formulation. The sample solution is injected directly into a carrier stream of iodide ion which is then mixed with an acid stream in situ. Sb5+ is determined by the redox reaction with acidified iodide to liberate iodine, which is monitored spectrophotometrically at 350 nm. The closed conditions prevent interference from atmospheric oxygen and the rapid reaction time assists in minimizing interference from side reactions. The use of tartaric acid as a solvent for sample and standard solutions ensures obedience of Beer's law over the Sb5+ concentration range 0.01-0.2% (w/v). The method is specific for the higher oxidation state in an ionic mixture of Sb5+ and Sb3+, and has been fully validated for use in a pharmaceutical preparation. Assuming absence of matrix interference it is applicable to Sb5+ from other sources and should be applicable to other reducible ionic species.
Two flow injection analysis (FIA) methods, using spectrophotometric detection, are proposed for the determination of penicillamine or tiopronin [N-(2-mercaptopropionylglycine)]. The procedures are based on the formation of yellow complexes between these thiol-containing drugs and Pd(II), in a 1 M or 0.25 M HCl medium, respectively. With peak height as a quantitative parameter, penicillamine is determined over the range 1.0 x 10(-5)-7.0 x 10(-4) M; for tiopronin the range is 1.0 x 10(-5)-6.0 x 10(-4) M. The methods have been applied to the routine determination of the drugs in pharmaceutical preparations.
A flow injection analysis (FIA) method for the determination of histamine is described. Control of reaction timing allows exploitation of a transient, chemical-kinetic increase in selectivity that occurs when o-phthalaldehyde reacts with histamine. The molar fluorescence ratio (selectivity) of histamine/histidine reaches a maximum value of 800 in 32 s, precluding the need for separation of histamine from histidine, spermidine, and other potential interferences in biological samples. On-line dilution prevents matrix effects and affords a linear response up to approximately 4.45 mM histamine, or 500 mg of histamine free base/100 g. Under these conditions the detection limit (3 times peak-to-peak baseline noise) is 5.5 pg (corresponding to 0.60 mg of histamine free base/100 g of sample) and throughput is 60 injections per hour. The high sensitivity and high selectivity of the method allow the rapid determination of histamine in fish with minimal sample conditioning and will find application in the determination of endogenous histamine as well, such as in blood plasma and brain tissue.
A flow injection analytical system based on a gas diffusion membrane module for ammonia and an ammonium flow-through potentiometric detector has been set up for measurement of L-glutamine and ammonium ions in hybridoma cell cultures. The main feature of the system is that the same basic analytical concept and equipment is used in both measurements, the only difference being for the determination of L-glutamine, in which the sample flows through an immobilized glutaminase cartridge. The conditions to enable the performance of both analysis consecutively, avoiding potential interferences by unwanted deamination of other compounds in the samples, have been determined. Finally, the proposed system has been compared with reference analytical methods for batch hybridoma cell culture experiments.
A flow injection system, incorporating an acetylcholinesterase (AChE) single bead string reactor (SBSR), for the determination of some organophosphorous (azinphos-ethyl, azinphos-methyl, bromophos-methyl, dichlorovos, fenitrothion, malathion, paraoxon, parathion-ethyl and parathion-methyl) and carbamate insecticides (carbofuran and carbaryl) is presented. The detector is a simple pH electrode with a wall-jet entry. Variations in enzyme activity due to inhibition are measured from pH changes when the substrate (acetylcholine) is injected before and after the passage of the solution containing the insecticide. The percentage inhibition of enzyme activity is correlated to the insecticide concentration. Several parameters influencing the performance of the system are studied and discussed. The detection limits of the insecticides ranged from 0.5 to 275 ppb. The determination of these compounds was conducted in Hepes buffer and a synthetic sea water preparation. The enzyme reactor can be regenerated after inhibition with a dilute solution of 2-PAM and be reused for analysis. The immobilized enzyme did not lose any activity up to 12 weeks when stored at 4 degrees C.
A flow injection spectrophotometric method for the determination of captopril involving measurement of the absorbance of the captopril complex with palladium(II) in a 0.12 M HCl medium at 400 nm is presented. The calibration graph was linear over the range 2 x 10(-5)-6 x 10(-4) M. The sampling frequency was 90 h-1 with sample injections of 70 microliters. The proposed method was applied to the determination of captopril in pharmaceutical samples.
A flow injection spectrophotometric procedure with enzymatic hydrolysis was developed for determination of orthophosphate, phytate and total phosphorus in cereal samples. Phosphorus species were extracted from cereals with 0.05 mol L(-1) potassium hydrogen phthalate buffer solution at pH 5.7. Orthophosphate was directly determined in the extracts by molybdenum blue spectrophotometric method. The phytate was hydrolyzed by the enzyme phytase coupled to a solid phase packed into an enzymatic reactor, and the resulting hydrolyzed orthophosphate was also determined by spectrophotometry at 650 nm. After optimization for phosphorus species extraction and enzymatic hydrolysis, a linear calibration graph was obtained up to 196 x 10(-6) mol L(-1) orthophosphate (P conc = -2.67 + 0.52x, r = 0.9998). Measurements are characterized by relative standard deviation of 1.6% for a standard of 72 x 10(-6) mol L(-1) orthophosphate and no baseline drift was observed during 4 h operation periods. It provides 72 measurements per hour, with 2.4 x 10(-)6) mol L(-1) and 7.9 x 10(-6) mol L(-1) as detection and quantification limits, respectively.
A flow injection method for the determination of ammonia in whole blood and plasma is described. The method utilizes diffusion of ammonia into a stream of a pH-sensitive indicator, which is monitored by a photometer. A volume of 90 microliter is needed and the result is obtained within 1 min. Ammonia concentrations increase during storage due to deamination. It is proposed to use plasma samples, which could be stored frozen at - 20 degrees C without significant change.
A flow injection-spectrophotometric determination at 540 nm of hydroxyamphetamine is reported. The procedure is based on a coloured reaction with 2-hydrazono-3-methylbenzothiazole (MBTH) and ceric ammonium nitrate (CeIV) as the oxidation reagent. Under optimised conditions, the determination of hydroxyamphetamine is achieved in a range of 0.01-0.2 mmol.l-1 with a relative standard deviation of 0.78% for 0.05 mmol.l-1 (n = 10) and a sample throughput of 75.h-1. The method was used for the determination of medicinal drug in the mass-produced dosage form of Czech origin: Pedrolon drops, Galena a.c.
A flow-injection analysis (FIA) system based on fibre optic detection of oxygen consumption using immobilized glucose oxidase (GOD) and lactate oxidase (LOD) is described for the on-line monitoring of glucose and lactate concentrations in animal cell cultures. The consumption of oxygen was determined via dynamic quenching by molecular oxygen of the fluorescence of an indicator. GOD and LOD were immobilized on controlled pore glass (CPG) in enzyme reactors which were directly linked to a specially designed fibre optic flow-through cell covering the oxygen optrode. The system is linear for 0-30 mM glucose, with an r.s.d. of 5% at 30 mM (five measurements) and for 0-30 mM lactate, with an r.s.d. of 5% at 30 mM (five measurements). The enzyme reactors used were stable for more than 4 weeks in continuous operation, and it was possible to analyse up to 20 samples per hour. The system has been successfully applied to the on-line monitoring of glucose and lactate concentrations of an animal cell culture designed for the production of recombinant human antithrombine III (AT-III). Results of the on-line measurement obtained by the FIA system were compared with the off-line results obtained by a glucose and lactate analyser from Yellow Springs Instrument Company (YSI).
A flow injection analysis (FIA) system coupled with a fluorescence detection system using diphenyl-1-pyrenylphosphine (DPPP) was developed as a highly sensitive and reproducible quantitative method of total lipid hydroperoxide analysis. Fluorescence analysis of DPPP oxide generated by the reaction of lipid hydroperoxides with DPPP enabled a quantitative determination of the total amount of lipid hydroperoxides. Use of 1-myristoyl-2-(12-((7-nitro-2-1,3-benzoxadiazol-4-yl)amino) dodecanoyl)-sn-glycero-3-phosphocholine as the internal standard improved the sensitivity and reproducibility of the analysis. Several commercially available edible oils, including soybean oil, rape-seed oil, olive oil, corn oil, canola oil, safflower oil, mixed vegetable oils, cod liver oil, and sardine oil were analyzed by the FIA system for the quantitative determination of total lipid hydroperoxides. The minimal amounts of sample oils required were 50 microg of soybean oil (PV = 2.71 meq/kg) and 3 mg of sardine oil (PV = 0.38 meq/kg) for a single injection. Thus, sensitivity was sufficient for the detection of a small amount and/or low concentration of hydroperoxides in common edible oils. The recovery of sample oils for the FIA system ranged between 87.2+/-2.6% and 102+/-5.1% when PV ranged between 0.38 and 58.8 meq/kg. The CV in the analyses of soybean oil (PV = 3.25 meq/kg), cod liver oil (PV = 6.71 meq/kg), rapeseed oil (PV = 12.3 meq/kg), and sardine oil (PV = 63.8 meq/kg) were 4.31, 5.66, 8.27, and 11.2%, respectively, demonstrating sufficient reproducibility of the FIA system for the determination of lipid hydroperoxides. The squared correlation (r2) between the FIA system and the official AOCS iodometric titration method in a linear regression analysis was estimated at 0.9976 within the range of 0.35-77.8 meq/kg of PV (n = 42). Thus, the FIA system provided satisfactory detection limits, recovery, and reproducibility. The FIA system was further applied to evaluate changes in the total amounts of lipid hydroperoxides in fish muscle stored on ice.
A flow-injection analysis (FIA) system was developed to study the enzyme-catalyzed hydrolysis of synthetic peptides, each of which contained one scissile bond. The concentrations of alpha-amino groups in reactions mixtures were determined by FIA with o-phthalaldehyde as a fluorescence reagent. The method allows a rapid, precise, and sensitive determination of kinetic constants for proteases acting on extended peptide substrates.