Detection limit polarography

The improvements manifested in the differential method yield sensitivities that are often an order of magnitude better than those of normal pulse polarography. Detection limits as low as 10 M can be achieved, but doing so requires close attention to selection of the medium. See Section 7.3.6 for more details. 

Under optimum conditions LPS voltammetry is an order of magnitude more sensitive than polarography (i.e., the detection limit is about 10 M). As in classical polarography, somewhat higher sensitivity and selectivity can be attained when using a differential version (i.e., when recording, as a function of potential, not the current but its derivative with respect to potential). 

At the end of four weeks of continued use, during which 4 liters of eluate were collected, samples were sterile and non-pyrogenic. Isotonicity was confirmed (NaCl = 8.94 .03 mg/ml) and neutrality maintained (pH = 6.27 0.16). No tin was detected in generator eluates by differential pulse polarography above a detection limit of 0.1 lig/ml. The radionuclidic identity of Rb-82 is easily confirmed by verification of its 76 sec half-life or through gamma spectrometry. 

The use of polarographic assays for the determination of drugs in blood is the most demanding on the detection limitations of the technique. Differential pulse polarography, stripping voltammetry, and LCEC are the only electrochemical methods currently available for routine determination of drugs below 1.0 ng/mL of blood. 

The determination of diazepam in plasma with detection limits of 0.03-0.2 fjLg/mh by cathode ray [189] and pulse polarography [174,190] has been described. The first reported pulse assay [174] differs from the other polarographic assays [189,190] in that a more polar solvent is employed to ensure quantitative extraction, followed by TLC separation and determination of diazepam and its major blood metabolite, N-desmethyldiazepam, to ensure specificity. 

Pulse polarography has also been used to measure dantrolene in plasma [181] and trimethoprim [192] and nitroimidazoles in blood [193,194]. The overall recovery of the trimethoprim assay was reported to be 81.7 6.3% (SD) with a detection limit of 0.5-0.75 fxg/mL of blood. There was no interference from the sulfamethoxazole, which is administered simultaneously. Glibomuride [195], phenobarbital, and diphenylhydantoin [97] have all been determined as their nitro derivatives after extraction from blood. The recovery of phenobarbital and diphenylhydantoin from blood was 72.3 6.5% (SD) and 76.6 2.3% (SD), respectively, with a detection limit of 1-2 fxg/mL. A modified assay [97] for the determination of both compounds in blood with TLC separation was also described. A differential pulse polarography determination of cephalosporin antibiotics in human serum samples has recently been described [196]. 

A differential pulse CSV method for the determination of traces of butyltin species in water was compared with two other voltammetric methods, namely differential pulse polarography and ASV (Schwartz et at., 1995). The butyltin species were accumulated on the mercury drop electrode as their tropolone complexes. Detection limits were 5 mg 1 1 for tributyltin (TBT), 0.5 mgl-1 for dibutyltin (DBT) and 0.5 mgl-1 for monobutyltin (MBT). These detection limits were better than the corresponding values obtained in the other analytical methods. 

Song et al. [11] developed a polarographic method for the determination of mefenamic acid in tablets, which was based on rapid nitrosation of mefenamic acid with sodium nitrite in acetic acid, and subsequent measurement of the A-nitroso derivative of mefenamic acid by linear-sweep polarography. The method is simple, sensitive, and specific, and was characterized by a detection limit of 2 x 10 7 mol/L. 

With the differential pulse polarography [245], the antibiotics can be determined at low concentration, if necessary, at the ppm or even sub-ppm level. Tetracycline hydrochloride is determined in aqueous acetate buffer pH 4 (detection limit 0.1 ppm), but for the analysis of chlortetracycline hydrochloride, oxytetracycline hydrochloride and free tetracycline, a non-aqueous medium must be used. Streptomycin sulphate is analysed in alkaline solution, trace quantities of zinc being masked by Na2EDTA, and the detection limit is 1 ppm. A determination in blood serum or urine is also possible but the peak potentials are shifted here to more negative values. The polarographic determination is preceded by ultrafiltration. Penicillin G potassium and ampicillin must be first functionalised by nitrosation. The authors also recommend an analysis of mixtures which is however demonstrated only with chloramphenicol and tetracycline, at 2.4 and 4.2 ppm, respectively. 

Arsenic(III) and arsenic(V), monomethylarsonate and dimethylarsinate have been determined by differential pulse polarography after separation by ion-exchange chromatography detection limits for the latter two are 18 and 8ppb, respectively. Diphenylarsenic acid has been studied polarographically. ... 

Anodic stripping voltammetry has been used to determine total arsenic spedes . Pulse polarographic methods have been applied to aqueous and non-aqueous solutions of methyl- and dimethylarsenic adds at concentration levels down to 0.1 /rg/ml . These arsenicals are electroactive in aqueous buffers and in non-aqueous media in which the acidic supporting electrolyte, guanidinium porchlorate, is employed. A direct method of analysis, based on differential pulse polarography, is reported. Detection limits of roughly 0.1/xg/ml (for MMAA) and 0.3p[Pg.190]

Phenylarsine oxide is used as a titrant for the direct and indirect determination of residual chlorine and ozone in water and wastewater. Preliminary investigations on the direct measurement of PAO by differential pulse polarography (DPP) indicate that this technique is a promising method for lowering the detection limits in the indirect measurement of these oxidants. The control of pH is a necessary consideration in free and combined chlorine analysis with as well as the stability and measurement of... 

A method based on polarography of the product formed by alkaline hydrolysis followed by heating with formaldehyde at pH5 had a detection limit of 10 pg/ml for amoxicillin in plasma [184], Obviously any penicilloic acid in the sample will also respond in this method. 

The detection limit for classical polarography is about I O - M. Routine determinations usually involve concentrations in the mM range. 

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