The mechanism of binding of carbamazepine (CBZ) with bovine serum albumin (BSA) has been investigated in vitro based on a new flow injection fluorometry coupled to the technique of dialysis sampling. The CBZ and BSA were mixed in different molar ratios in 0.050 mol L-1 phosphate buffer (containing 0.9% NaCl), pH 7.4, and incubated at 37±0.5℃ in a water bath. The dialysis sampler was utilized to sample free CBZ from mixed solution with a relative dialytic efficiency of 7.6%. Then the CBZ in dialysis solution was injected into carrier and on-line oxidized by lead dioxide solid-phase reactor into fluorescent product with a maximum excitation wavelength of 355 nm and a maximum emission wavelength of 478nm. The fluorescence intensity measured was linear proportional with the concentration of free CBZ in mixed solution over the range of 1×10-5 to 2×10-4mol L-1 with the detection limit of 6×10-6 mol L-1. According to the fluorescence measurement results from mixed solution, the association constant (K) estimated for CBZ–BSA binding and the number of the binding site (n) with Scatchard analysis were 1.08×104 L mol-1 and 0.94, respectively. Stern–Volmer plots indicated the presence of dynamic component in the quenching mechanism. The acting force was suggested to be mainly hydrophobic and the distance between the acceptor and donor was 3.12 nm. The estimated binding parameters agreed well with literature values.

A simple, sensitive and specific flow-injection spectrofluorimetric method has been developed for the determination of folic acid in pharmaceuticals. The method is based on use of a lead dioxide solid-phase reactor for on-line oxidation of folic acid into a strongly fluorescent compound with a maximum excitation wavelength of 281nm and an emission wavelength of 450 nm. Under optimum conditions the fluorescence intensity of oxidation product is proportional to the concentration of folic acid over the range 0.008-2.5ug mL-1. The detection limit is 0.0001ug mL-1, the relative standard deviation is 0.85% for 11 replicate determinations of 0.05ug mL-1 folic acid, and the sample throughput is 20h-1. In combination with an on-line filter and dilution, an automated drug-dissolution system was established. The proposed method has been successfully applied to the determination of folic acid in pharmaceutical preparations and dissolution testing.

A sensitive flow injection method is proposed for the determination of formaldehyde based on its catalytic action upon the redox reaction between crystal violet and potassium bromate in phosphoric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of crystal violet injected at the maximum absorption wavelength of 600nm. A calibration graph from 0.018 to 1.400mgmL 1 is obtained, and the detection limit is 0.007mgmL 1 in a sample volume of 30 mL. Up to 15 samples can be analyzed per hour with a relative standard deviation of 1.2 and 2.3%, respectively, for the determination of 1.0 and 0.1mgmL 1 of formaldehyde. The method is free from most interference. This method has been applied to the determination of formaldehyde in air, decoration boards and paints, and the results compare well with those provided by iodimetry.

A new flow injection catalytic spectrophotometric method is proposed for the simultaneous determination of nitrite and nitrate based on the catalytic effect of nitrite on the redox reaction between crystal violet and potassium bromate in phosphoric acid medium and nitrate being on-line reduced to nitrite with a cadmium-coated zinc reduction column. The redox reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of crystal violet at the maximum absorption wavelength of 610 nm. A technique of inserting a reduction column into sampling loop is adopted and the flow injection system produces a signal with a shoulder. The height of shoulder in the ascending part of the peak corresponds to the nitrite concentration and the maximum of the peak corresponds to nitrate plus nitrite. The detection limits are 0.3ng ml-1 for nitrite and 1.0 ng ml-1 for the nitrate. Up to 32 samples can be analyzed per hour with a relative standard deviation of less than 2%. The method has been successfully applied for the simultaneous determination of nitrite and nitrate in natural waters.

A flow-injection catalytic method is developed for the determination of oxalic acid based on its catalytic effect on the redox reaction between Victoria blue B and potassium dichromate in dilute sulfuric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in the absorbance ofVictoria blue B at the maximum absorptionwavelength of 618 nm. A calibration graph from 1.0 to 80.0 mgml-1 of oxalic acid and a detection limit of 0.8 mgml-1 was obtained. The sampling rate was about 22 samples per hour. The proposed method is simple and inexpensive. The applicability of the method was demonstrated by the determination of oxalic acid in vegetable food, such as spinach and mushroom.