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The different types of instruments used for monitoring pharmaceutical dissolution testing are presented. Their features and the need for automation are critically discussed. The advantages of flow injection analysis in this respect are illustrated by a variety of examples clearly showing its adaptability to the different problems posed by other automatic and non-automatic alternatives.
Serum samples were analyzed for their urea content using fluorescence flow injection analysis incorporating an immobilized urease bioreactor and a gas permeable separator. The urease was immobilized under mild and facile conditions to a hydrophilic 2-fluoro-1-methylpyridinium-activated support. The ammonia released as a result of urease-catalyzed urea hydrolysis diffused through a gas permeable membrane into a constant stream of o-phthaldehyde solution to form a highly fluorescent product with lambda ex at 340 nm and lambda em at 455 nm. Up to 25 serum samples can be analyzed per hour. The within-day coefficient of variation (CV) was 1.12% and the day-to-day CV was 1.25% for serum containing 10.50 mg urea nitrogen dl-1. The bioreactor shows excellent storage (at 4 degrees C) and operational stabilities (at 37 degrees C).
Post-column, on-line photolytic derivatization in liquid chromatography with electrochemical detection for some inorganic anions is described. Flow injection analysis and ion-pair reversed-phase chromatography followed by photolysis and electrochemical detection were used for the determinations of anions. Several operation conditions, such as mobile phase, lamp used for the photolysis, flow-rate, and applied potential, have been optimized for the determinations. Analytical figures of merit were determined. Method validation was carried out by the analysis of single blind, spiked samples. Inherent from the advantages of electrochemical detection in liquid chromatography, the method is of high sensitivity and selectivity for anion analysis.
Problems associated with the use of biosensors in process control, e.g. difficulties of sterilization and sensor fouling, are shortly displayed, and possibilities to overcome them are outlined. The advantages of flow injection analysis (FIA) are demonstrated and examples for efficient sampling systems connected with this method are reviewed. Special emphasis is given to problem-orientated sample pretreatments, preventing fast inactivation of immobilized enzymes in the analysis system. Examples of problem-orientated sample pretreatment units are given. A proposal for a computer-controlled self-calibrating FIA system is given.
Milk samples were analyzed for their lactose content using flow injection analysis and incorporating immobilized beta-galactosidase or beta-galactosidase/mutarotase and glucose oxidase/peroxidase bioreactors. These enzymes were immobilized, under mild conditions, on to a 2-fluoro-1-methylpyridinium salt-activated Fractogel support. The use of a phosphate buffer (0.15 M) was found to facilitate the rapid mutarotation of alpha-D-glucose and hence could obviate the need for the more expensive mutarotase. The chromogenic agents of choice for monitoring the reaction were 3-methyl-2-benzothiazolinone hydrazone and 3-dimethylaminobenzoic acid. Linearity was observed over the concentration range 16-160 micrograms/ml using lactose standards (r = 0.996). Between 30 and 40 milk samples/h can be analyzed. Comparisons are made with existing HPLC and alkaline methylamine methods for a range of milk matrices. The FIA method consistently gives the lowest standard deviations and coefficient of variation for the various milk matrices analyzed.
Studies of drug-protein binding constants (ka) and of the degree of binding (%B) in biological fluids have been carried out by means of flow injection analysis (FIA). The association constants found for clinically relevant concentrations agree with the literature data. The degree of binding found for discoumarol, phenytoin and sulfisoxazole is also in agreement with the literature whereas that of warfarin is slightly lower.
Bovine adrenal medullary cells have been cultured on microbeads which are placed in a low-volume flow system for measurements of stimulation-response parameters. Electronically controlled stream switching allows stimulation of cells with pulse lengths from 1 s to many minutes; pulses may be repeated indefinitely. Catecholamines secreted are detected by an electrochemical detector downstream from the cells. This flow-injection analysis technique provides a new level of sensitivity and precision for measurement of kinetic parameters of secretion. A manual injection valve allows stimulation by higher levels of stimulant in the presence of constant low levels of stimulant. Such experiments show interesting differences between the effects of K+ and acetylcholine on cells partially desensitized to acetylcholine.
An automated assay for the determination of penicillin in formulations suitable for use in pharmaceutical quality control is presented. The method is based on the classical iodometric penicillin assay which is incorporated in a flow injection analysis (FIA) system. The required hydrolysis is performed on-line by using an immobilised penicillinase reactor. Packed-bed and single-bead-string enzyme reactors are compared. It turns out that a packed-bed penicillinase reactor (10 cm x 1.5 mm i.d.) provides complete hydrolysis within short residence time, while only little back-pressure is generated. This enzyme reactor is stable for at least 9 months. Enzymatic hydrolysis of the beta-lactam ring results in the formation of the corresponding penicilloic acid, which consumes iodine. The iodine consumption is determined colorimetrically by measuring the decrease of the absorbance of the blue coloured iodine/starch complex. The optimum reactor length and flow rate for the colourimetrical detection reaction are determined. The optimised method is applied to the assay of penicillin in formulations and the results are compared with the "true" results obtained with a reference method: a mercurimetric titration. The reliability of the flow injection method is evaluated quantitatively by determining the maximum total error (MTE). The reliability is shown to be highest when measuring at a 0.3-mM level. Eight formulations including capsules, tablets and injectables containing penicillin G, amoxicillin or flucloxacillin are assayed. The MTE does not exceed the 6% level and the most probable MTE is between 1.5 and 3.5%.
Our experience in industrial bioprocess monitoring and environmental control let us develop a concept for biosensor research which distinguishes itself from other, more popular, approaches. Biosensors must improve and/or simplify existing state-of-the-art analysis systems. Only the parallel development of biosensors and their complementary metrology leads to industrially sound solutions. The combination of flow injection analysis with immobilized enzymes in the form of enzyme columns is already used today for the solution of on-line analytical problems in bioprocesses and environmental control.
This automated spectrophotometric method for determination of cholinesterase activity in erythrocytes and plasma is based on measurement of the choline produced at 30 degrees C by the hydrolysis of acetyl-, butyryl-, or succinylcholine. Blanks, standards, and samples are prepared by a Gilson robotic unit. Use of flow-injection analysis for detection allows use of smaller volumes of reagent and sample. We applied this method to the study of 91 healthy subjects and members of two families with succinylcholine sensitivity. Results with use of the three different substrates for determination of activity in plasma correlated well (r greater than 0.94). Results for plasma and erythrocytes from healthy subjects are lower in women less than 50 years old than in women greater than 50 years or men. Values for plasma obtained with succinylcholine substrate (range: 31 to 100 U/L) allow detection of very sensitive subjects--AA phenotypes (less than 10 U/L)--but do not distinguish the UA from the UU phenotype.
Glucose oxidase (GOD) and Horseradish peroxidase (HRP) were covalently coupled to alkylamine controlled pore glass by means of glutaraldehyde. About 700-800 U/g of immobilized GOD and 300-400 U/g of immobilized HRP were obtained. Some factors of affecting enzyme immobilization were discussed. The immobilized enzymes were packed into a plastic tube and used in flow-injection analysis (FIA) for glucose in serum. A good linearity range was observed for this immobilized enzyme system at 20 mg/mL to 1000 mg/dL D-glucose, the recovery was 95.4-103.5%, the within-batch imprecision was 0.8-2.2%, and the between-batch imprecision was 2.2-4.2%. More than 100 samples were measured within an hour. One enzyme column with five units of immobilized GOD and HRP, applied for 50 assays/d, has been used for more than 2 mo.
A flow injection system is described for the parallel determination of pullulan and glucose during a fermentation of the fungus Aureobasidium pullulans. The polysaccharide was hydrolyzed by pullulanase and amyloglucosidase, immobilized to controlled-pore glass (CPG). The glucose produced was oxidized by glucose dehydrogenase and the NADH formed determined photometrically. The pullulan concentration was calculated from the difference to the response obtained for free glucose. The calibration curves for monomer and polymer were both linear between 2 mg dm-3 and 20 mg dm-3. Analysis of one sample for the determination of glucose and pullulan took about 10 min.
An apparatus has been developed for the isolation of fluoride in biological samples through pyrohydrolysis. With this apparatus, it is possible to determine both organic and inorganic fluorocompounds with a recovery close to 100% and precision within 5%. The high recovery rate can be expected even for highly heat-resistant compounds such as CaF2, without using WO3 as a catalyst. For determination of the isolated fluoride, a separate apparatus was developed in which flow-injection analysis was used in conjunction with a fluoride ion-selective electrode as a detector. With this apparatus, fluoride in a sample solution with a volume as small as 0.2 ml, and at a concentration as low as 0.5 microgram/l, can be determined within 3 minutes with a precision of several percent. Combined use of the two apparatuses makes it possible to determine fluoride in different biological samples within 10-15 minutes with a precision of several percent, free from external contamination. By selecting suitable conditions for analysis and using a 1 g sample, it is possible to determine fluoride at a concentration as low as 5 ng/g. By employing these apparatuses, the fluoride content in different biological samples has been determine and the effectiveness of their use confirmed.
The determination of reduced nicotinamide adenine dinucleotide (NADH) by electrochemical oxidation requires a more positive potential than is predicted by the formal reduction potential for the NAD+/NADH couple. This problem is alleviated by use of 2,6-dichloroindophenol (DCIP) as a redox coupling agent for NADH. The electrochemical characteristics of DCIP at the glassy carbon electrode are examined by cyclic voltammetry and hydrodynamic voltammetry. NADH is determined by reaction with DCIP to form NAD+ and DCIPH2. DCIPH2 is then quantitated by flow-injection analysis with electrochemical detection by oxidation at a detector potential of +0.25 V at pH 7. NADH is determined over a linear range of 0.5 to 200 microM and with a detection limit of 0.38 microM. The lower detection potential for DCIPH2 compared to NADH helps to minimize interference from oxidizable components in serum samples.
Two types of polyvinyl chloride (PVC) matrix membrane electrodes responsive to the antimalarial drug chloroquine have been constructed, electrochemically evaluated, compared and used in pharmaceutical analysis. Type 1 is the classic PVC model with chloroquine-tetraphenylborate (TPB) sensor; Type 2 is a coated silver disk without internal filling solution. Both electrode types exhibited rapid linear potentiometric response to the logarithmic concentration of diprotonated chloroquine cation in the 10(-1) - 10(-6)M range with calibration slopes 28-30 mV/concentration decade over the pH range 1.8-6.2. These electrodes were sensitive enough to permit determination of chloroquine phosphate at concentrations as low as 5 microgram/mL with good accuracy and precision. Determination of chloroquine in various pharmaceutical preparations using direct potentiometry and potentiometric titration with NaTPB gave an average recovery of 98.8% of the nominal values (SD 0.5%). The Type 2 electrode was also assessed in a flow-through sandwich cell for flow injection analysis. Results were compared with data obtained by the U.S. Pharmacopeia method.
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Glucose, ethanol and lactate were determined simultaneously in a flow injection system by using a parallel configuration of immobilized enzyme reactors. Hydrogen peroxide produced was monitored amperometrically at the potential of +0.65 V vs. Ag/AgCl. Linear relations between sensor responses and each species were observed in the ranges of 0.02-10 mM (glucose), 5 x 10(-4)-0.1% (v/v) (ethanol) and 0.005-1 mM (lactate) with correlation coefficients larger than 0.999 for each species. The relative standard deviations for 10 successive injections were 1.4, 0.5 and 1.1% for glucose (1 mM), ethanol (5 x 10(-3)% (v/v] and lactate (0.05 mM), respectively. Analysis of serum samples was performed with urate-eliminating reactors which were set just before each immobilized enzyme reactor. Interference of ascorbate in a serum sample was completely eliminated by using an ascorbate-eliminating reactor which was set before the sample injection valve. Application of the system to alcoholic beverages and control serum was described and the results were compared with those of free enzymatic, spectrophotometric analysis (F-kit or C-test method).
Trimethoprim (TMP) in four pharmaceutical preparations (compound sulfamethoxazol tablets, compound tetracycline tablets, compound trimethoprim and sulfamethoxazol tablets; and compound berberine injection) is determined by solvent extraction-flow injection spectrophotometry. It can be extracted into chloroform directly, and the absorbance at a wavelength of 280 nm of the organic phase is measured after phase separation. The manifold comprises two streams. The sample is injected into a 0.2 mol/L NaOH carrier stream, and extracted with chloroform in a 200-cm coil (ID 0.7 mm) after a 50 cm reaction tube (ID 1.0 mm). Calibration graph is linear in the range of 25-150 micrograms/ml. The average recovery is 101.4% with a relative standard deviation of 1.1%. The proposed system permits the analysis of about 50 samples per hour. Precise results in agreement with those obtained with official methods are achieved.