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Hollow Cathode Lamps

Overview
Atomic absorption spectroscopy (or AAS) in its modern form came from principles developed by Australian physicist Dr. A. Walsh in 1955.
Atomic absorption spectroscopy is ideal for analyzing minute quantities of metallic elements because its operating principle and analysis method offer relatively simple measurement with high accuracy.
Hamamatsu Photonics provides a full line of hollow cathode lamps(空心陰極燈管) developed by our discharge tube manufacturing technology accumulated over long years of experience. These lamps provide the sharp, high-purity spectral lines essential for high accuracy measurement.
 
原子吸收光譜法(或AAS)的現代形式來自澳大利亞物理學家A.Walsh博士於1955年開發的原理。
原子吸收光譜法(或AAS)是理想的分析微量金屬元素的工作原理及分析方法,提供相對簡單的高精度量測。
累積了多年放電管生產製造技術與經驗,Hamamatsu Photonics提供全系列的空心陰極燈管(hollow cathode lamps )。這些空心陰極燈管(hollow cathode lamps )提供了原子吸收光譜法(或AAS)的高精度測量所需的尖銳,高純度的光譜。
 
 
 
Type of hollow cathode lamps
Hollow cathode lamps(空心陰極燈管) consist of single-element lamps and multi-element lamps. Single-element lamps are usually superior to multi-element lamps in absorption sensitivity and analytical line radiant intensity. Although multielement lamps offer the advantage of simultaneous determination of multiple elements, their cathode composition must be determined by taking the properties of the metals to combine fully into account, so fabricating cathodes from an optional combination of elements is not possible.
 
Applications
Atomic absorption spectrophotometers (原子吸收光譜儀)
● Atomic fluorescence spectrophotometers 
● Multi-element analyzers
● Environmental analytical instruments
 
Construction
 
As shown in Figure 1, a hollow cathode lamp is constructed with a bulb having a window (④ in Figure 1) made of quartz or UV-transmitting glass or borosilicate glass for spectral line emission, and into which a hollow cylindrical cathode (② in Figure 1) and a ring-shaped anode (① in Figure 1) are assembled. Noble gas is also sealed inside at a pressure of several hundred pascals. The cathode is made of a single element or alloy of the element to be analyzed to ensure sharp analytical spectral lines with an absolute minimum of interfering spectral components.
 
Operating Principle
 
The hollow cathode lamp is a type of glow discharge tube that uses a hollow cathode to enhance the emission intensity. Compared to parallel plate electrodes, using a hollow cathode increases the current density by more than 10 times and this is accompanied by a significant increase in light intensity and a lower voltage drop in the lamp. This is known as the hollow cathode effect (or hollow effect). 
When a voltage is applied across the electrodes of a hollow cathode lamp to cause a discharge in the lamp, electrons pass from the interior of the cathode to the cathode-fall region and flow through the negative glow region toward the anode. This causes ionization of the gas within the lamp through inelastic collisions with the gas atoms. Positive ions generated by the gas ionization are accelerated by the electric field and collide with the cathode surface. The kinetic energy of ion impact causes the cathode materials to sputter (or fly) away from the cathode surface in the form of an atomic vapor. This metallic vapor consists primarily of single atoms in the ground state and they are thermally dispersed within the hollow cathode.
Meanwhile an electron bunch or cluster is accelerated by the electric field toward the anode. The accelerated electrons collide with the groundstate metallic atoms being diffused and excite the metallic atoms. The excited metallic atoms return to the ground state again in an extremely short transition time of about 10-8 seconds. At this point, monochromatic light characteristic of those atoms is emitted at an energy corresponding to the energy difference between the excited state and the ground state.
This transition of electrons occurs not only in the target element for quantitative analysis but also in other elements of the cathode materials, causing a variety of energy transitions to occur. So, in a wide spectral range, many spectral lines of those elements and the filler gas can be observed. Transition metal elements such as Ni, Co and Fe in particular result in an extremely large number of spectral lines.
 
 
For conventional atomic absorption spectroscopy (原子吸收光譜儀)
Lineup of Hollow Cathode Lamps (空心陰極燈管)

 

● L233 series (38 mm diameter): Single-element hollow cathode lamps (66 lamps) ①

Element

Atomic
Number

Type No.
(suffix)

Analytical Line
(nm)

Operating Current
(mA)

Maximum Current
(mA)

Ag

Silver

47

-47NB

  328.07 *
338.28 

10

20

Al

Aluminium

13

-13NB

  309.27 *
396.15

10

20

As

Arsenic

33

-33NQ

  193.70 *
197.20

10

12

Au

Gold

79

-79NQ

  242.80 *
267.59

10

16

B

Boron

5

-5NQ

  249.68 *
249.77

10

20

Ba

Barium

56

-56NB

  553.55 *

10

20

Be

Beryllium

4

-4NQ

  234.86 *

10

20

Bi

Bismuth

83

-83NQ

  223.06 *
306.77

10

12

Ca

Calcium

20

-20NU

  422.67 *

10

18

Cd

Cadmium

48

-48NQ

  228.80 *

5

12

Co

Cobalt

27

-27NU

  240.73 *
346.58

10

20

Cr

Chromium

24

-24NB

  357.87 *
425.44

10

20

Cs

Caesium

55

-55NB

  852.11 *

10

20

Cu

Copper

29

-29NB

  324.75 *
327.40

10

20

Dy

Dysprosium

66

-66NB

  404.59 *
421.17

15

15

Er

Erbium

68

-68NB

  400.79 *
415.11

15

15

Eu

Europium

63

-63NB

  459.40 *
462.72

15

15

Fe

Iron

26

-26NU

  248.33 *
371.99

10

20

Ga

Gallium

31

-31NU

287.42
  294.36 *

4

6

Gd

Gadolinium

64

-64NB

407.87
  422.58 *

12

12

Ge

Germanium

32

-32NU

  265.16 *

10

20

Hf

Hafnium

72

-72NU

  286.64 *
307.29

20

25

Hg

Mercury

80

-80NU

  253.65 *

4

6

Ho

Holmium

67

-67NB

  410.38 *
416.30

15

20

In

Indium

49

-49NB

  303.94 *
325.61

10

15

Ir

Iridium

77

-77NQ

  208.88 *
266.47

20

20

K

Potassium

19

-19NB

  766.49 *
769.90

10

15

La

Lanthanum

57

-57NB

357.44
  550.13 *

10

20

Li

Lithium

3

-3NB

610.36
  670.78 *

10

20

Lu

Lutetium

71

-71NB

328.17
  331.21 *

15

15

Mg

Magnesium

12

-12NU

  285.21 *

10

18

Mn

Manganese

25

-25NU

  279.48 *
403.08

10

20

Mo

Molybdenum

42

-42NB

  313.26 *
320.88

10

20

Na

Sodium

11

-11NB

  589.00 *
589.59

10

15

Nb

Niobium

41

-41NB

  334.91 *
405.89

20

30

Nd

Neodymium

60

-60NB

463.42
  492.45 *

15

15

Ni

Nickel

28

-28NQ

  232.00 *
341.48

10

20

Os

Osmium

76

-76NU

  290.90 *
305.86

15

15

Pb

Lead

82

-82NQ

  217.00 *
283.30

10

15

Pd

Palladium

46

-46NQ

  244.79 *
247.64

10

20

Pr

Praseodymium

59

-59NB

  495.13 *
513.34

15

15

Pt

Platinum

78

-78NU

  265.95 *
299.80

10

20

Rb

Rubidium

37

-37NB

  780.02 *
794.76

10

20

Re

Rhenium

75

-75NB

  346.05 *
346.47

20

25

Rh

Rhodium

45

-45NB

  343.49 *

10

20

Ru

Ruthenium

44

-44NB

  349.89 *

20

25

Sb

Antimony

51

-51NQ

  217.58 *
231.15

10

15

Sc

Scandium

21

-21NB

390.74
  391.18 *

10

15

Se

Selenium

34

-34NQ

  196.03 *

20

25

Si

Silicon

14

-14NU

  251.61 *
288.16

10

20

Sm

Samarium

62

-62NB

  429.67 *
484.17

15

20

Sn

Tin

50

-50NQ

  224.61 *
286.33

20

20

Sr

Strontium

38

-38NB

  460.73 *

10

20

Ta

Tantalum

73

-73NU

  271.47 *
275.83

10

20

Tb

Terbium

65

-65NB

431.88
  432.64 *

15

15

Te

Tellurium

52

-52NQ

  214.27 *

10

15

Ti

Titanium

22

-22NB

  364.27 *
365.35

10

20

Tl

Thallium

81

-81NU

  276.78 *
377.57

7

10

Tm

Thulium

69

-69NB

  371.79 *
410.58

10

15

V

Vanadium

23

-23NB

306.64
  318.40 *

10

20

W

Tungsten

74

-74NU

  255.14 *
400.87

10

25

Y

Yttrium

39

-39NB

  410.23 *
412.83

15

15

Yb

Ytterbium

70

-70NB

346.43
  398.79 *

10

10

Zn

Zinc

30

-30NQ

  213.86 *
307.59

7

15

Zr

Zirconium

40

-40NB

  360.12 *
468.78

20

20

D2

Hydrogen

1

-1DQ

240
(peak value)

30

35


● L733 series (38 mm diameter): Multi-element hollow cathode lamps (11 lamps)

Element

Atomic
Number

Type No.
(suffix)

Analytical Line
(nm)

Operating Current
(mA)

Maximum Current
(mA)

Na-K

Sodium
Potassium

11
19

-201NB

Na  589.00 *
K    766.49 *

10

15

Ca-Mg

Calcium
Magnesium

20
12

-202NU

Ca  422.67 *
Mg  285.21 *

10

18

Si-Al

Silicon
Aluminium

14
13

-203NU

Si   251.61 *
Al   309.27 *

10

20

Fe-Ni

Iron
Nickel

26
28

-204NQ

Fe  248.33 *
Ni   232.00 *

10

20

Sr-Ba

Strontium
Barium

38
56

-205NB

Sr   460.73 *
Ba  553.55 *

10

20

Al-Ca-Mg

Aluminium
Calcium
Magnesium

13
20
12

-321NU

Al   309.27 *
Ca  422.67 *
Mg  285.21 *

10

18

Ca-Mg-Zn

Calcium
Magnesium
Zinc

20
12
30

-322NQ

Ca  422.67 *
Mg  285.21 *
Zn  213.86 *

10

15

Cu-Mo-Co-Zn

Copper
Molybdenum
Cobalt
Zinc

29
42
27
30

-401NQ

Cu  324.75 *
Mo  313.23 *
Co  240.73 *
Zn  213.86 *

10

15

Cd-Cu-Pb-Zn

Cadmium
Copper
Lead
Zinc

48
29
82
30

-402NQ

Cd  228.80 *
Cu  324.75 *
Pb  217.00 *
Zn  213.86 *

10

15

Cu-Fe- Mn-Zn

Copper
Iron
Manganese
Zinc

29
26
25
30

-405NQ

Cu  324.75 *
Fe  248.33 *
Mn  279.48 *
Zn  213.86 *

8

15

Co-Cr-Cu- Fe-Mn-Ni

Cobalt
Chromium
Copper
Iron
Manganese
Nickel

27
24
29
26
25
28

-601NQ

Co  240.73 *
Cr   357.87 *
Cu  324.75 *
Fe  248.33 *
Mn  279.48 *
Ni   232.00 *

10

20

Analytical lines marked with an asterisk (*) indicate the maximum absorption wavelength of each element. Since each element has two or more spectral emission lines, select the spectral line that best suits the sample concentration.
NOTE: 
The guaranteed lifetime is defined by the product of the operating current and the accumulated operating time and is specified as 5000mA·hrs except for the guaranteed lifetimes of As, Ga and Hg which are specified as 3000 mA·hrs.
 

Note on the L233 and L733 series current values
The operating current and maximum current values listed above are specified as a peak current value. However, instruments using a pulse lighting system may indicate the lamp current value as the mean value. So, when using such an instrument, verify which current value (mean or peak) it indicates and use the specified current value to operate lamps correctly.
 
 
 
 
For atomic absorption spectroscopy (原子吸收光譜儀) using the S-H method background correction
Lineup of Giant-pulse Hollow Cathode Lamps

 

● L2433 series (38 mm diameter): Single-element hollow cathode lamps (46 lamps)

Element

Atomic
Number

Type No.
(suffix)

Analytical
Line
(nm)

Low ①
Current
(mA)

High ①
Current
(mA)

Accumulated ②
Lifetime
(mA·ms·h)

Operating ②
Lifetime
(h)

Ag

Silver

47

-47NB

  328.07 *
338.28

10

400

20 000

500

Al

Aluminium

13

-13NB

  309.27 *
396.15

10

600

30 000

500

As

Arsenic

33

-33NQ

  193.70 *
197.20

12

500

7500

150

Au

Gold

79

-79NQ

  242.80 *
267.59

10

400

20 000

500

B

Boron

5

-5NQ

  249.68 *
249.77

10

500

5000

100

Ba

Barium

56

-56NB

  553.55 *

15

600

30 000

500

Be

Beryllium

4

-4NQ

  234.86 *

10

600

6000

100

Bi

Bismuth

83

-83NQ

  223.06 *
306.77

10

300

6000

200

Ca

Calcium

20

-20NU

  422.67 *

15

600

30 000

500

Cd

Cadmium

48

-48NQ

  228.80 *

8

100

5000

500

Co

Cobalt

27

-27NU

  240.73 *
346.58

15

400

20 000

500

Cr

Chromium

24

-24NB

  357.87 *
425.44

10

600

12 000

200

Cu

Copper

29

-29NB

  324.75 *
327.40

10

500

25 000

500

Dy

Dysprosium

66

-66NB

  404.59 *
421.17

15

600

6000

100

Er

Erbium

68

-68NB

  400.79 *
415.11

15

500

5000

100

Eu

Europium

63

-63NB

  459.40 *
462.72

10

600

6000

100

Fe

Iron

26

-26NU

  248.33 *
371.99

12

400

20 000

500

Ga

Gallium

31

-31NU

287.42
  294.36 *

4

400

4000

100

Ge

Germanium

32

-32NU

  265.16 *

20

500

5000

100

Hf

Hafnium

72

-72NU

  286.64 *
307.29

20

600

6000

100

Hg

Mercury

80

-80NU

  253.65 *

12

400

4000

100

Ho

Holmium

67

-67NB

  410.38 *
416.30

10

600

6000

100

K

Potassium

19

-19NB

  766.49 *
769.90

10

600

30 000

500

La

Lanthanum

57

-57NB

357.44
  550.13 *

20

600

9000

150

Li

Lithium

3

-3NB

610.36
  670.78 *

15

500

25 000

500

Mg

Magnesium

12

-12NU

  285.21 *

10

500

25 000

500

Mn

Manganese

25

-25NU

  279.48 *
403.08

10

600

30 000

500

Mo

Molybdenum

42

-42NB

  313.26 *
320.88

10

600

9000

150

Na

Sodium

11

-11NB

  589.00 *
589.59

10

600

12 000

200

Ni

Nickel

28

-28NQ

  232.00 *
341.48

10

400

20 000

500

Pb

Lead

82

-82NQ

  217.00 *
283.30

10

300

15 000

500

Pd

Palladium

46

-46NQ

  244.79 *
247.64

10

300

3000

100

Pt

Platinum

78

-78NU

  265.95 *
299.80

10

300

3000

100

Ru

Ruthenium

44

-44NB

  349.89 *

20

600

6000

100

Sb

Antimony

51

-51NQ

  217.58 *
231.15

15

500

7500

150

Se

Selenium

34

-34NQ

  196.03 *

15

300

4500

150

Si

Silicon

14

-14NU

  251.61 *
288.16

10

500

10 000

200

Sm

Samarium

62

-62NB

  429.67 *
484.17

15

600

6000

100

Sn

Tin

50

-50NQ

  224.61 *
286.33

20

500

25 000

500

Sr

Strontium

38

-38NB

  460.73 *

10

500

25 000

500

Te

Tellurium

52

-52NQ

  214.27 *

15

400

4000

100

Ti

Titanium

22

-22NB

  364.27 *
365.35

10

600

12 000

200

V

Vanadium

23

-23NB

306.64
  318.40 *

10

700

7000

100

Y

Yttrium

39

-39NB

  410.23 *
412.83

15

600

6000

100

Yb

Ytterbium

70

-70NB

346.43
  398.79 *

5

200

2000

100

Zn

Zinc

30

-30NQ

  213.86 *
307.59

10

300

15 000

500

Analytical lines marked with an asterisk (*) indicate the maximum absorption wavelength of each element.
Since each element has two or more spectral emission lines, select the spectral line that best suits the sample concentration.
NOTE:
① Maximum discharge current: Peak current (See the current waveform charts for the low current and high current waveform specifications.)
② When lamps are operated at a current less than the maximum discharge current specified for each element:
     The accumulated lifetime(mA·ms·h) is defined by the operating time including the lamp preheat time multiplied by the product of the low current and its time width or the product of the high current and its time width, whichever is larger.
·    When lamps are operated at the maximum discharge current specified for each element:
     The guaranteed lifetime (operating lifetime) is defined by the accumulated operating time including the lamp preheat time.
The guaranteed lifetime is specified by either of the above definitions.
 
Note on L2433 series current values
● Low current operation
   Absorption of the target element occurs when a lamp is operated at a low current.
   While making sure not to exceed the low current value listed for the lamp, set the current at which the best analytical sensitivity is obtained.
● High current operation
   When a lamp is operated at a high current, a self-reversal effect occurs in the lamp to absorb the background. As in low current operation, set the current while making sure not to exceed the high current value listed for the lamp.
 
● Time width
    Do not operate the lamps in a state where the time width of the discharge current waveform exceeds the maximum time width shown in the above charts.
 
 
Lamp Current and Absorption Sensitivity
 
The ideal analytical line profile of the light emitted by a hollow cathode lamp should exhibit no spectral line broadening other than natural broadening. In actual operation, however, the spectral lines are emitted along with a certain broadening. The causes of such broadening include
Doppler broadening, self-absorption line width distortion, Lorentz broadening (pressure broadening), Holtzmark broadening (resonance broadening), Zeeman effect broadening, and Stark effect broadening. Among these, Doppler broadening and self-absorption line width distortion are major factors in broadening so that broadening related to other causes is usually small enough to be ignored.
Doppler broadening depends on the random thermal motion of the light-emitting atoms, which is affected by the temperature of the gas. Spectral line broadening does not occur as long as the thermal motion of the atoms is within a plane perpendicular to a line connecting the observation point and the light source. However, if the thermal motion of the atoms is parallel to that line (forward and back motion as seen from the observation point), the frequency at the emitted light observation point will increase (shift to shorter wavelength side) during motion toward the observation point and decrease (shift to longer wavelength side) during motion away from the observation point. This phenomenon is the socalled Doppler effect. Light-emitting atoms in a hollow cathode have a random thermal motion that causes the spectral lines to broaden. The width λ0 of this Doppler broadening can be expressed by the following equation:
where c is the velocity of light, R is the gas constant, T is the absolute temperature of the gas, and Ma is the atomic weight.
Self-absorption occurs when there is a temperature gradient within the atomic vapor layer inside the cathode hollow, in other words, it occurs when the atomic vapor within the cathode hollow is flowing out of the hollow. In this state, atoms in the higher-temperature atomic vapor layer within the hollow are more excited than those in the lower temperature atomic vapor layer outside the hollow, and so cause light emission.
When the emitted light passes through the relatively low temperature atomic vapor layer outside the hollow, it is absorbed by the atoms in the ground state. This phenomenon is termed self-absorption and just as with the Doppler effect results in broadening of analytical line width and a loss of absorption sensitivity.
As stated above, deterioration in the analytical line profile depends on the lamp current, so care must be taken since increasing the lamp current may cause an excessive increase in atomic vapor. In actual measurement, it is essential to operate the lamp at an optimal current that takes into account both the analytical line output intensity and absorption sensitivity.
The self-absorption effect is large for high-vaporization-pressure elements such as Cd (Cadmium) and small for low-vaporization-pressure elements such as Mo (Molybdenum). The typical operating current for the former is usually specified as a low value.
 
 
 
Spectral Bandwidth (S.B.W.) and Absorption Sensitivity
 
In the vicinity of an analytical line, the presence of other spectral lines from the same element or a different element will cause the absorption sensitivity to drop. (These spectral lines in the vicinity of the analytical line are known as proximity lines.) When these proximity lines are present, the spectral bandwidth (SBW) should be narrowed to reduce the effect of proximity lines by narrowing the slit width of the spectrophotometer (原子吸收光譜儀).
 
 
Time Stability of Analytical Line Radiant Intensity
 
As described in the section dealing with the emission process of spectral lines, sputtered metal atoms are thermally diffused during repeated inelastic collisions with electrons. In this process, during the period required for the metal atom density to reach equilibrium, the radiant intensity of the analytical lines varies. This variation usually occurs in the direction of increased intensity for 10 to 20 minutes after the lamp has started, although
it will vary depending on the element and operating current. After reaching equilibrium, the radiant output intensity at the analytical line wavelength is extremely stable. 
In high-vapor-pressure element lamps, operation at excessive current levels causes excessively vaporized metal atoms to flow out of the hollow cathode space in the direction of the optical axis. This causes a temperature gradient to occur and might lower the analytical line output intensity due to phenomena such as self-absorption.
After a lamp has been left unused for a long period of time, some amount of time may be required for analytical line output intensity to reach initial stabilization, which results from changes in the cathode surface over time and depends on the element (especially alkaline element). Even in such cases, once the lamp is operated, it will light up normally from the next time.
 
 
Life
 
The life of a hollow cathode lamp (空心陰極燈管) is greatly affected by the operating current. This is due to the increase in the energy of positive ions colliding with the cathode surface which causes violent sputtering. During pulse operation as well, there is no change in the energy of the ions colliding with the cathode surface at each pulse, so lamp life is determined by the peak current and the pulse width (time width).
The following phenomena may be observed when a lamp has reached its life end:
(1) Discharge does not occur at the hollow cathode and the current does not vary even if the current control knob is changed. The analytical line output is not detectable.
(2) Extreme variations occur in analytical line intensity and the lamp current may also vary in some cases.
(3) The analytical line intensity weakens significantly and the signal-to-noise ratio deteriorates.
The major cause of these phenomena is a drop in gas pressure within the lamp. This drop in gas pressure is caused by the "gas clean-up" phenomenon in which cathode metal atoms sputtered during discharging attracts gases while being scattered and these adhere together to the bulb wall and electrodes at a lower temperature.
As the lamp is used, the cathode hollow shape is gradually worn away and deformed by sputtering from the discharge. These characteristics will vary depending upon the element and will exhibit small differences even for lamps of the same element.
 
 
Dimensional Outlines (Unit: mm)

 

 

 

 

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