Zepto

In order to increase the precision of realization of the base unit meter, the definition based on the wavelength of a krypton-86 radiation was replaced in 1983 by one based on the speed of light. Also added were the prefixes zetta (Z) for 10, zepto (z) for 10 , yotta (Y) for 10 , and yocto (y) for 10 . 

Prefix deci- centi- milli- micro- nano- pico- fcmto- atto- zepto-... 

Good to excellent Good to excellent Zepto to nanomoles ppm... 

Absolute detection Zepto to nano moles Nano to micro moles Nano to micro moles... 

Zepto (symbol = z) BPTl Bovine pancreatic trypsin inhibitor... 

A more sophisticated mode of LIE detection is the multiphoton-excitation (MPE) fluorescence [47], which is based on the simultaneous absorption of more than one photon in the same quantum event and uses special lasers, such as femtosecond mode-locked laser [48] or continuous wave laser [49], This mode of LIE detection allows mass detection limits at zeptomole level (1 zepto-mole=10 mol) due to exceptionally low detection background and extremely small detection volume, whereas detection sensitivity in concentration is comparable to that of traditional LIE detection modes. A further drawback is the poor suitability of MPE-fluorescence detection to the on-column detection configuration, which is frequently employed in conventional LIE detection. 

For example, if 1 pi of a 1 ppb solution (1 pg) is injected into a chromatograph, this will represent 10 femtomoles for a compound with a molecular weight of lOOg/mol The analyst must become accustomed to using prefixes that have seldom been used before femto- (1(T15), atto-(10-18), zepto- (10-21). Thus the zepto-mole contains only 602 molecules. These limits tend towards single atoms or molecules - the ultimate trace. 

One of the ways we will learn to express quantities in Chapter 1 is by using prefixes such as mega for million (I06), micro for one-millionth (10-6). and atto for 10-18. The illustration shows a signal due to light absorption by just 60 atoms of rubidium in the cross-sectional area of a laser beam. There are 6.02 X 1023 atoms in a mole, so 60 atoms amount to 1.0 X 10-22 moles. With prefixes from Table 1-3, we will express this number as 100 yoctomoles (ymol) or 0.1 zeptomole (zmol). The prefix yocto stands for I0-24 and zepto stands for 10-21. As chemists learn to measure fewer and fewer atoms or molecules, these strange-sounding prefixes become more and more common in the chemical literature. 

Table C Metric Multipliers tera, peta, exa come from tetra, penta, hexa with one letter removed zetta, yotta come from zeta, iota, with one letter added atto comes from Danish "atten" for 18 zepto comes from Latin "septem" or Greek "hepta" (1000 7) and yocto comes from Greek "octo" (1000-8) with one prefix letter added...

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