A new flow-injection determination of glucose based on the redox reaction of hydroquinone with iron(III) in the presence of 1,10-phenanthroline.

A new spectrophotometric flow-injection (FI) method is proposed for the determination of glucose based on the redox reaction of hydroquinone with iron(III). When a glucose solution containing quinone is passed through the immobilized glucose oxidase column introduced in FI system, quinone is reduced to hydroquinone by glucose. In the presence of 1,10-phenanthroline (phen), iron(III) is then quantitatively reduced by hydroquinone to iron(II) followed by the formation of iron(II)-phen complex (lambda(max)=510 nm). An FI peak observed at 510 nm corresponds to the concentration of glucose. The wide dynamic range for glucose was obtained in the range of 1x10(-6)-1x10(-3) mol l(-1) at a sampling rate of 24 h(-1) and the detection limit (S/N=3) was 5x10(-7) mol l(-1). Relative standard deviations were 0.78, 0.44 and 0.23% (n=5) for 5x10(-6), 5x10(-5) and 5x10(-4) mol l(-1) of glucose, respectively. The proposed method was successfully applied to the determination of glucose in control blood sera, human blood plasma and wine.

New spectrophotometer equipped with long light path length cells and two channel FIA for trace metals.

New spectrophotometer was designed for the simultaneous assay of copper and iron using flow injection analysis and moreover, new 50 mm light path cells were equipped in the spectrophotometer to enhance the sensitivity. Both copper and iron at 2-10 ppb level were determined simultaneously and rapidly using water soluble reagent, 5-Br-PSAA. Determination limits were 1 ppb for copper and 1 ppb for iron. Relative standard deviations were about 1%.

Flow injection determination of iron by its catalytic effect on the oxidation of 3,3',5,5'-tetramethylbenzidine by hydrogen peroxide.

A flow injection-photometric method has been developed for the determination of iron(II+III). The method is based on the catalytic effect of iron(III) on the hydrogen peroxide oxidation of 3,3',5,5'-tetramethylbenzidine to form a blue compound (lambda(max)=650 nm). In this catalyzed reaction, 1,10-phenanthroline acted as an effective activator. Iron(II) is also determined, being oxidized by hydrogen peroxide. Calibration graphs for iron(II) and iron(III) obtained under the optimized conditions were identical with each other and linear in the range 0.2-200 ng ml(-1) with a detection limit of 0.05 ng ml(-1) iron. The reproducibility was satisfactory with a relative S.D. of 1.0% for ten determinations of 5 ng ml(-1) iron(III). The proposed method was successfully applied to the determination of iron in river and lake water samples and can be determined free iron species.

Potentiometric flow titration of iron(II) and chromium(VI) based on flow rate ratio of a titrant to a sample.

A new potentiometric flow titration has been proposed based on the relationship of the flow rates between titrant and sample solutions. A sample solution is pumped at a constant flow rate. The flow rate of the titrant solution is gradually increased at regular time intervals and a flow rate for the titrant solution in the vicinity of the equivalence point is obtained. The concentration of the sample is calculated by C(S) (mol l(-1))=(R(T) (ml min(-1))xC(T) (mol l(-1)))/R(S) (ml min(-1)), where C(S), C(T), R(S), and R(T) denote the unknown sample concentration, titrant concentration in the reservoir, the flow rate of the sample solution which is a constant rate, and the flow rate of the titrant solution at an inflection point, respectively. The potentiometric flow titration of iron(II) with cerium(IV) and of chromium(VI) with iron(II) has been presented. The titration time of the proposed method is about 10 min per sample. An R.S.D. of the method is 0.77% for seven determinations of 1x10(-3) mol l(-1) iron(II). Similarly, the flow titration of chromium(VI) with iron(II) is carried out over the range 1x10(-4)-1x10(-3) mol l(-1) chromium(VI) and is successfully applied to the determination of chromium in high carbon ferrochromium.

Catalytic flow injection determination of vanadium by oxidation of N-(3-sulfopropyl)-3,3',5,5'-tetramethylbenzidine using bromate.

A catalytic flow-injection (FI) method was developed for the determination of 10(-9) mol l(-1) levels of vanadium(IV, V). The method is based on the catalytic effect of vanadium(V) on oxidation of N-(3-sulfopropyl)-3,3',5,5'-tetramethylbenzidine (TMBZ.PS) using bromate as oxidant to form a yellow dye (lambda(max)=460 nm). The use of 5-sulfosalicylic acid (SSA) as an activator enhanced the sensitivity of the method. The calibration graphs with a working range 0.05-8.0 ng ml(-1) were obtained for vanadium(V). Vanadium(IV) was also determined, being oxidized by bromate. The detection limit (signal/noise, S/N=3) was 0.01 ng ml(-1) (ca. 2x10(-10) mol l(-1)) vanadium. The relative standard deviations (R.S.D.) for 15 determinations of 0.5 ng ml(-1) vanadium, and for ten determinations of 0.1 and 1.0 ng ml(-1) vanadium were 0.41, 2.6 and 0.25%, respectively, with a sampling rate of 15 samples h(-1). The proposed method was successfully applied to the determination of vanadium in natural waters.

Catalytic determination of cobalt at sub-nanogram levels using the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline by manual and flow-injection methods.

A catalytic photometric method was developed for the determination of sub-nanogram levels of cobalt. The method is based on the catalytic effect of cobalt(II) on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (DAOS) to form a colored dye (lambda(max)=525 nm) in the presence of hydrogen peroxide. In this reaction system, 1,2-dihydroxybenzene-3,5-disulfonate (Tiron) acted as an effective activator for the catalysis of cobalt(II). Variation of reaction time between 5 and 10 min allows the determination range to be extended from 0.01 to 1.0 ng ml(-1). The reaction system can also be successfully adapted to flow-injection analysis (FIA). The dynamic range of the proposed flow-injection method was 0.01-1.0 ng ml(-1) and detection limit (signal/noise, S/N=3) was 5 pg ml(-1) at a sampling rate of 30 h(-1). Manual and flow-injection methods were applied to the direct determination of cobalt in pepperbush as a standard material.

Flow-injection determination of copper(II) based on its catalysis on the redox reaction of cysteine with iron(III) in the presence of 1,10-phenanthroline.

A redox reaction of cysteine with iron(III) proceeds slowly in the presence of 1,10-phenanthroline (phen). However, this reaction is accelerated in the presence of copper(II) as a catalyst, producing an iron(II)-phen complex (lambda(max)=510 nm). A sensitive spectrophotometric flow-injection method is proposed for the determination of copper(II) based on its catalytic action on this redox reaction. The dynamic range was 0.1-10 ng ml(-1) of copper(II) with a relative standard deviation of 1.0% (n=10) for 1.0 ng ml(-1) of copper(II) at a sampling rate of 30 h(-1). The detection limit (S/N=3) is 0.04 ng ml(-1). The proposed method was successfully applied to the determination of copper in river water as a certified reference material.

Flow-injection determination of trace amounts of dopamine by chemiluminescence detection.

A flow-injection analysis (FIA) for the determination of dopamine has been developed. The method is based on the inhibition effect of dopamine on the iron(II)-induced chemiluminescence (CL) of 10,10'-dimethyl-9,9'-biacridinium dinitrate (lucigenin). The presence of a non-ionic surfactant, polyoxyethylene (23) lauryl ether (Brij 35), caused an increase in the inhibition effect. The present method allows the determination of dopamine over the range 1x10(-8)-2x10(-7) mol dm(-3). The relative standard deviation was 0.7% for eight determinations of 6x10(-8) mol dm(-3) dopamine. The detection limit (S/N=3) was 2x10(-9) mol dm(-3) with the sampling rate of 40 samples h(-1). The effect of other catecholamines and compounds of similar structure on the lucigenin CL reaction was studied: quinone, hydroquinone, norepinephrine, pyrocatechol and l-dopa suppressed the CL intensity.

Kinetic-catalytic determination of traces of iron by the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline.

A new kinetic-catalytic method by the initial rate procedure for the determination of nanogram level of iron(III) is developed, which is based on its catalytic effect on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone (MBTH) with N,N-dimethylaniline (DMA) to form an indamine dye (lambda(max)=590 nm) in the presence of hydrogen peroxide. Iron(II) is also determined, being oxidized to iron(III) by hydrogen peroxide. Calibration graphs obtained by the initial rate method are linear in the range 1-1000 ng ml(-1) Fe and as low as 10(-8) M Fe(II, III) can easily be determined. The relative standard deviations are 6.6, 2.5 and 1.5% for ten determinations of 1, 20 and 60 ng ml(-1) of Fe(III), respectively. The method is applicable to the determination of iron in natural waters without preconcentration and separation.

Simultaneous flow injection determination of iron(III) and vanadium(V) and of iron(III) and chromium(VI) based on redox reactions.

A flow injection analysis (FIA) method is presented for the simultaneous determinations of iron(III)-vanadium(V) and of iron(III)-chromium(VI) using a single spectrophotometric detector. In the presence of 1,10-phenanthroline (phen), iron(III) is easily reduced by vanadium(IV) to iron(II), followed by the formation of a red iron(II)-phen complex (lambda(max) = 510 nm), which shows a positive FIA peak at 510 nm corresponding to the concentration of iron(III). On the other hand, in the presence of diphosphate the reductions of vanadium(V) and/or chromium(VI) with iron(II) occur easily because the presence of diphosphate causes an increase in the reducing power of iron(II). In this case iron(II) is consumed during the reaction and a negative FIA peak at 510 nm corresponding to the concentration of vanadium(V) and/or chromium(VI) is obtained. The proposed method makes it possible to obtain both positive (for iron(III)) and negative (for vanadium(V) or chromium(VI)) FIA peaks with a single injection.

Determination of ultratrace amounts of copper (II) by its catalytic effect on the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline.

A spectrophotometric method was developed for the determination of ultratrace amounts of copper(II) based on its catalytic effect on the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline to produce an intensely coloured dye (lambda(max) = 525 nm) in the presence of hydrogen peroxide. In this reaction, pyridine acted as an effective activator for the catalysis of copper(II). By measuring the absorbance of the dye, copper(II) can be determined at the 0.002-0.1 ng cm(-3) (3.1 x 10(-11)-1.6 x 10(-9) mol dm(-3) level. The relative standard deviation for ten determinations of 0.06 ng cm(0-3) of copper(II) was 2.6%. The proposed method was successfully applied to the determination of copper(II) in tap water and biological material.

Flow-injection photometric determination of sub-nanogram amounts of cobalt by its catalysis of the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline in a micellar medium.

A catalytic flow-injection photometric method was developed for the determination of levels of cobalt as low as 10(-10) mol 1(-1). The method is based on the catalytic action of cobalt(II) on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline to form a colored dye (lambda(max) = 590 nm) in the presence of hydrogen peroxide. The extremely activating effect was obtained in the presence of 1,2-dihydroxybenzene-3,5-disulfonate (Tiron) and sodium hydrogencarbonate as activators. Furthermore, the sensitivity of the method was enhanced by adding sodium dodecylsulfate as a surfactant. Linear calibration graphs were obtained over the range 0.04-0.2 ng ml(-1) and 0.1-0.5 ng ml(-1) cobalt(II). respectively, at a sampling rate of 30 per hour. The detection limit (signal/noise = 3) was 5 pg ml(-1) and the relative standard deviations for 0.1 and 0.04 ng ml(-1) cobalt (n = 10) were 1.0 and 2.3%, respectively. The method was applied to the determination of cobalt in pepperbush.

The movements of fetuses with congenital myotonic dystrophy in utero.

The movements in two fetuses with congenital myotonic dystrophy were recorded on fetal actocardiograms. The two fetuses showed gross movements associated with FHR accelerations as normal fetus. One of them showed swallowing on amniofetogram, and hiccuping on fetal actocardiogram. Both, however, were extremely hypotonic and neither displayed any gross movement, respiratory movement or swallowing postnatally. Intubation and nasal feeding were required for a long period of time after birth in both cases. The buoyancy of amniotic fluid may help the affected fetus to make gross movement in utero.

[Non-reactive pattern diagnosed by ultrasonic Doppler fetal actocardiogram and outcome of the fetuses with non-reactive pattern].

The accuracy of diagnosis by means of ultrasonic Doppler fetal actocardiogram in non-stress test (NST) was examined in 100 fetuses at 32 to 42 weeks of gestation. Fourteen fetuses were diagnosed as non-reactive by conventional NST which monitored fetal heart rate, but only 4 of the 14 fetuses were found to be "non-reactive" when the fetal actocardiogram was used. Thus the false positive rate obtained with conventional NST in judging the non-reactive pattern was 71.4% (10/14). We next examined the outcome for 25 fetuses (including 20 IUGR cases) with a "non-reactive pattern" who were diagnosed by fetal actocardiogram. Fetal distress occurred in 19 of these fetuses (76.0%), and mostly developed within 5 days after the diagnosis of "non-reactive pattern". The outcome for 20 IUGR fetuses with a "non-reactive pattern" was compared with that for fetuses with a "reactive pattern". IUGR fetuses which were "non-reactive" had a significantly higher fetal distress morbidity rate, and higher cesarean section rate. The sensitivity and specificity of the prediction of the development of fetal distress in IUGR fetuses with a "non-reactive pattern" were 81.0% and 84.2%, respectively. The present results strongly suggest the need to use the ultrasonic Doppler fetal actocardiogram at the time of NST after 32 weeks of gestation.

Reverse flow injection analysis of complexing agents and its application to estimation of complexing capacity.

A redox reaction of copper(II) with iron(II) proceeds slowly in the presence of neocuproine, although the reaction would not take place in its absence. This reaction is accelerated by the presence of complexing agents such as EDTA, DTPA, CyDTA, EDTA-OH, NTA, citrate, pyrophosphate, producing a copper(I)-neocuproine complex (lambda(max) = 454 nm). A reverse flow injection analysis (r-FIA) method is presented for the determination of trace amounts of complexing agents by measuring the increase in absorbance at 454 nm. Complexing agents at the 10(-6)M level can be determined at a rate of 120 samples/hr. By using this r-FIA system, a new procedure for the measurement of complexing capacity with metal ions such as Al(III), Cu(II), Zn(II), Cd(II) and Pb(II) has been developed. Complexing capacity for each metal ion can be measured at a rate of 120 samples/hr.