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Quantitation of the trace amount of DNA by counting individual DNA molecules using a high-sensitivity flow cytometric setup has been developed and evaluated for the purpose of establishing a reference analytical procedure. Model DNA molecules, represented by lambda (λ) viral DNA (48 502 bp, double-stranded), were electro-focused to form a tightly bound flow stream on a detection point situated on the centre axis of fused silica tubing measuring 50 µm × 50 µm. The individual DNA particles that were stained with a fluorescent dye were detected individually with a high-sensitivity laser-induced fluorescence (LIF) detection system. Assuming all DNA particles in a given sample volume were detected and counted ('exhaustive counting'), its molar concentration can be calculated without the need for calibration materials. The validity of the proposed measurement method was thoroughly examined and discussed.

Trace impurity elements in high purity copper metal (4 nine class) put on the market were analyzed by Instrumental Neutron Activation Analysis (INAA) and the results compared with those from Graphite Furnace Atomic Absorption Spectrophotometry (GFAAS) and Inductively Coupled Plasma Atomic Emission Spectrophotometry (ICP-AES). The sample irradiation was done at the irradiation facilities (thermal neutron flux, 5.1012 n.cm 2.s 1) of the TRIGA Mark-III research reactor in the Korea Atomic Energy Research Institute. Four unalloyed copper standards (NIST SRM # 393, 394, 395 and 398) were used to identify the accuracy and precision of the analytical procedure. The homogeneity of samples was assessed by means of the elements such as Ag, As, Co, Sb, Se and Zn. The analytical results of INAA, GFAAS and ICP-AES were in good agreement within expected uncertainties each other and showed the possibility of using them for the analytical quality control.

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