Spectrometer Pre-burn Time and Integration Time
The sample excitation process in photoelectric spectroscopy consists of two steps. First, the sample is excited in a spark chamber filled with hydrogen. Most of the air is driven out, minimizing the effects of selective oxidation and UV absorption during the excitation discharge. However, due to complex physical and chemical processes within the sample, such as evaporation and diffusion, the spark generated by the excitation requires a certain amount of time to achieve a stable discharge. This means that the absolute and relative intensities of the spectral lines of each element become more stable. This stabilization requires a certain amount of time, which is the pre-burn phase. After the spark stabilizes, the spectrum generated by the spark is collected and integrated (much like exposure in photography). Both the pre-burn phase and the integration phase require a certain amount of time to complete, which is a key parameter in direct photoelectric spectroscopy: the pre-burn time and integration time.
The selection of the pre-burn time and integration time depends not only on the light source but also on the properties of the sample material. Generally, to obtain satisfactory excitation parameters, the pre-burn time and spark integration time can be combined with orthogonal experiments. Given a fixed light source, metals that are easier to excite (i.e., those with low melting points, such as zinc and lead) require a shorter pre-combustion time. Cast iron, which has a higher melting point and is difficult to excite, requires a longer pre-combustion time. Pre-combustion times vary for different materials and elements. Pre-combustion times for low- and medium-alloy steels can range from 4 to 6 seconds, for high-alloy steels from 5 to 8 seconds, for free-cutting steels from 10 to 30 seconds, and for aluminum alloys from 3 to 10 seconds.
The integration time depends primarily on the reproducibility of elemental analysis in the excited sample, the elemental concentration, and the selected spectral line. Generally speaking, higher element concentrations result in higher spectral intensity and a greater tendency for detector signal overflow. Therefore, the integration time should be shorter; otherwise, it can be appropriately extended. For spectral lines, exposure times are longer when the light level is low, and shorter when the light level is high. If you select a spectral line with high sensitivity, its spectral intensity will be higher than other spectral lines at a certain concentration, and detector signal overflow may occur. Therefore, the integration time should be shortened. Conversely, it can be appropriately extended. Generally speaking, for trace and micro elements, the integration time is longer; for major or high-content elements, the integration time is shorter. When selecting spectral lines, characteristically sensitive lines should be selected for trace and micro elements, while sub-sensitive lines are preferred for high-content elements.
The above is Wuxi Qianrong Analytical Instrument Co., Ltd.'s sharing on spectrometers. We hope it will be helpful.
