Category Archives: Mass-spectrometry

by sergei

PSU for vacuum gauge ZJ-52T

ITS40  GC/MS ( chromatomasspectrometer ) was produced  since 1985  year of 20th sectury in cooperation of Finnigat MAT and Varian – very  relieble  longlasting device. Two of them are  still running at my laboratory.  But it has no gauge to check vacuum  produced by forevacuum pump. This article is about schematic   how to measure quality of vacuum by means of gauge ZJ-52T which can be bought on Aliexpress.

Method of measurement is  very simple – special octal tube has filament wire ( pins 2 and 3 ), when we supply some voltage to it,  becomes  hot.  Special thermoresistor connected to pins 1 and 4   and current through it depends of the quality of vacuum – as better is vacuum, as stronger is current.

PSU and measurement schemcatic is on the picture below

Vacuum_meter_ZJ_52T_PSU_1

Secondary winding of the transformer T1 produces 20 V AC voltage, which after diode bridge and filtering gives 24 VDC volatage before the volage regulator T3 on LM317, which is connected as a current source – it’s value can be checked on mA meter.  It’s value can be adjusted in 50 – 100 mA range by variale resistor R9. This current then applied to  Wheatstone bridge on resistors R1 – R3, and as a fourth resistor of this bridge is used filament of the gauge ZJ-52T.  Zero on the measurement microampermeter ( vacuum indicator in pct )  can be adjusted by means of  resistor  R14. Maximal range – 100 % can be adjusted by the resistor R5.  I have used 100 uA microampermeter.

In order to extend  life of the gauge longer, do not supply voltage to filament until good enough vacuum is maintained.

by sergei

Retention indexes ( RI ) of solvents on phase RTX-1701

Liquid phase RTX-1701 from Restek is one of the most suitable for application in GC analyses of organic solvents.  This study is about GC separation of mixtures of organic solvents on 0.25mm ID capillary column installed into Varian 3400 GC, as a detector was used  Finnigan MAT ion trap mass-spectrometer ITS40.  Liquid phase film thickness is 1 um, column length 30m.  Owen of the gas chromatograph programmed from 50 deg. C  ( 1 minute ),  8 deg/min to 180 deg.C.

As a standard solution used C5 – C14 mixture of n-Alkanes with each component content about  200 ppm ( wt )  in HPLC grade Acetonitrile, or 156 mg per ml, or  156 ng per 1 ul.  Injector of GC was  adjusted to split ratio 1:50, so as a result each alkane’s peak  load was about 3 ng if 1 ul of the standard solution is injected.

To determine RI index of solvents,  special sample solution was prepared  by mixing 0.2 ul of each solvent standart ( min 99 % purity ), same amount of n-Octane was added  as  internal standard.  No solvent was used in this case and for injecting used headspace sample – by adding of 0.5ul of test mixture to 12ml glass bottle ( with laboratory air inside ) and 50 ul of this headspace sample was injected into CG.

At the same time, if peak square of each solvent is measured , we can determine relative intensity indexes K  for MS detector to each sample solution component.  Values of K we can use later for quantitative analyses of a mixture with  unknown composition using same HS method of sample preparation and using n-Octane as internal standard.

Most popular solvents for paits were used to prepare test sample, here is list of solvents for determination, totally 27 components:

  • n-Octane ( internal standard )
  • Methanol
  • Ethanol
  • n-Propanol
  • IPA ( iso-Propyl Alcohol )
  • n-Butanol
  • iso-Butanol
  • 2-Butanol
  • 1-Methoxy-2-Propanol
  • 2-Ethoxy-1-Ethanol
  • Acetonitrile
  • Acetone
  • 2-Butanone ( MEK )
  • Cyclohexane
  • Methylene Chloride
  • iso-Octane
  • 1,4-Dioxane
  • n-Butyl-Acetate
  • iso-ButylAcetate
  • EthylAcetate
  • MethylAcetate
  • MTBE
  • Diisopropyl Ether
  • 1-Methoxy-2-Propyl Acetate
  • Toluene
  • p-Xylene
  • Cumene

50 ul of  this mixture’s headspace contains about 120 ng of each component, what after  1/50 split in injector is acceptable load for 1 um liquid phase film.

Now about the tuning of mass-spectrometer. It was made using Varian Saturn 5.2 software:

  • manifold temperature – 220 deg C
  • transfer line temperature – 230 deg C
  • filament emission current – 20 uA
  • multiplier voltage – 1550 Volts
  • AGC target TIC – 20 000 counts
  • one microscan time – 100 us
  • scans per second – 3

Varian  3400 CG injector temperature 250 deg.C, injector 1075 type with split valve ( open ), inlet helium pressure 12 PSI. For injection is used Hamilton 1ul ( for  liquids ) and 100 ul  ( for headpace ) syringe with 70mm needle.

Table of the components content on test mixture of 27 compoments

g/cm cub ml wt, g % wt  ug/1ul Peak load
ng
n-Octane 0.703 0.2 0.1406 3.07 26.0 108 2.2
iso-Octane 0.69 0.2 0.138 3.01 25.6 106 2.1
Cyclohexane 0.774 0.2 0.1548 3.38 28.7 119 2.4
Toluene 0.867 0.2 0.1734 3.78 32.1 134 2.7
p-Xylene 0.861 0.2 0.1722 3.76 31.9 133 2.7
Cumene 0.863 0.2 0.1726 3.76 32.0 133 2.7
Acetonitrile 0.785 0.2 0.157 3.42 29.1 121 2.4
Methanol 0.791 0.2 0.1582 3.45 29.3 122 2.4
Ethanol 0.78 0.2 0.156 3.40 28.9 120 2.4
n-Propanol 0.803 0.2 0.1606 3.50 29.7 124 2.5
iso-Propanol 0.785 0.2 0.157 3.42 29.1 121 2.4
n-Butanol 0.81 0.2 0.162 3.53 30.0 125 2.5
iso-Butanol 0.802 0.2 0.1604 3.50 29.7 124 2.5
2-Butanol 0.806 0.2 0.1612 3.52 29.9 124 2.5
1-Methoxy-2-Propanol 0.913 0.2 0.1826 3.98 33.8 141 2.8
MTBE 0.741 0.2 0.1482 3.23 27.4 114 2.3
DiisoPropyl Ether 0.725 0.2 0.145 3.16 26.9 112 2.2
1,4-Dioxane 1.033 0.2 0.2066 4.51 38.3 159 3.2
Methyl Acetate 0.938 0.2 0.1876 4.09 34.7 145 2.9
Ethyl Acetate 0.895 0.2 0.179 3.90 33.1 138 2.8
n-Butyl Acetate 0.881 0.2 0.1762 3.84 32.6 136 2.7
iso-Butyl Acetate 0.87 0.2 0.174 3.80 32.2 134 2.7
1-Methoxy-2-Propyl Acetate 0.966 0.2 0.1932 4.21 35.8 149 3.0
2-EthoxyEthanol 0.93 0.2 0.186 4.06 34.4 144 2.9
Acetone 0.786 0.2 0.1572 3.43 29.1 121 2.4
2-Butanone 0.8 0.2 0.16 3.49 29.6 123 2.5
Methylene Chloride 1.326 0.2 0.2652 5.78 49.1 205 4.1
  SUM 0.849 5.4 4.5848 ng/1ul ng, split 1/50
g/cm.cub ml g 50 ul of HS ( 1ul/12ml)

Resulting figures are listed below.

First of all it is chromatogramm of standard solution C5 – C14, on Y axis is TIC ( Total Ion Current ):

C5_C14

and table of retention times:

Carbon N RT, min
4 1.214
5 1.961
6 2.708
7 4.02
8 5.956
9 8.182
10 10.469
11 12.683
12 14.784
13 16.761
14 18.78
15 20.799

Values for first and last rows are obtained by extrapolation.

Chromatogram of the mixture of 27 compoments:

27_labels

As seen,  three components –  IPA,  Methyl Acetate and MTBE ( mentioned in sequence as RI grows ) are not separated on this column and comes out as one peak. In AMDIS using SIM plots and data from mass-spectra of three above mentioned substances ( m/z=45 is main peak for IPA – red curve, m/z=43 is  peak for Methyl Acetate – yellow curve, and m/z=73 is main peak for MTBE – blue curve ) we still can get both three components separated and to calculate their RT and RI:

MTBE_IPA_MetAc

and finally – table of RI ( Retention Indexes ) of all solvents and calculated relative to n-Octane index K, which shows, how much times intensity of the substance ( TIC )  is higher ( if K < 1 ) or lower ( if K > 1 ), then intensity of the same amount (  by wt ) of n-Octane. As a result for future analyses we have  possibility  of quantification for  chromatograms with n-octane as the internal standard.

Retention Time (min.) Area RI g K relative
to n-Octane
1.933 59870 498 Methanol 0.1582 6.98
2.369 335630 557 Ethanol 0.156 4.10
2.647 1013000 594 Acetone 0.1572 2.16
2.695 527600 601 IPA 0.157 2.20
2.724 3550283 603 Methyl Acetate 0.1876 1.59
2.735 3696900 604 MTBE 0.1482 1.50
2.85 2198000 612 Methylene Chloride 0.2652 0.47
2.959 1717000 621 Diisopropyl Ether 0.145 0.33
3.134 425955 634 Acetonirtile 0.157 1.43
3.583 286471 668 n-Propanol 0.1606 2.17
3.708 2396000 678 Cyclohexane 0.1548 0.25
3.778 685293 683 Ethyl Acetate 0.179 1.01
3.848 1924000 688 iso-Octane 0.138 0.28
3.98 470826 698 Butanone-2 0.16 1.32
4.092 362567 705 2-Butanol 0.1612 1.72
4.7 416271 736 iso-Butanol 0.1604 1.49
5.41 370475 773 1-Methyl-2-Propanol 0.1826 1.91
5.448 455108 775 n-Butanol 0.162 1.38
5.772 198077 792 1.4-Dioxane 0.2066 4.04
5.938 545056 800 n-Octane 0.1406 1.00
6.421 313887 823 EthylCellosolve 0.186 2.30
6.56 473259 829 Toluene 0.1734 1.42
6.859 472836 842 iso-Butyl Acetate 0.174 1.43
7.811 460222 885 n-Butyl Acetate 0.1762 1.48
8.908 644390 934 para-Xylene 0.1722 1.04
9.535 580913 961 MPA 0.1932 1.29
10.124 853490 987 Cumene 0.1726 0.78

K indexes for IPA ( m/z 45), Methyl Acetate ( m/z=75 ) and MTBE ( m/z=73 ) have been calculated for SIM mode plots.

Thanks to Dmitrijs Dmitrijevs, who have helped me to find some pure solvents for making standard mixtures.

************************************************************************************************

by sergei

Varian Saturn 5.2 software for Finnigan MAT ITS40 GC/MS system

Finnigan MAT ITS40 it is somewhat unical device, it is GC/MS system, which consists of Varian 3400 gas chromatorgaph and Finnigan MAT ion trap as  detector. This kind of apparatus were produced in  90th, and it is almost miracle, that two devices with serial numbers #IS 003138 and #IS 000150 which I have in my lab still works ! First one I have purchased in 2011 from Germany ( LabExchange ). Another one –  in 2022 for spare parts directly from US,  but it was in pritty good condition and I also have managed to get it working !   One of devices ( #IS 003138 ) have equipped with Restek   30m 0.25mm capillary column 1um  RTX-1701 phase for solvents and in another ( #IS 000150 )  was  installed J&W also 30m 0,25mm capillary column with 0.25um DB-5 phase – for heavier compounds.   On the picture below is #IS 003138 purchased on 2011 from Germany:

img_6629_2

Due to my careless,  in 2018 year happened  one problem with first device ( #IS 003138 ), as due to discharge of BIOS battery of PC and failure of it’s hard disk ( what a misfortune, both happened almost simultaneosly ) I have lost all original ITS40 software.  I had in mind and it was my mistake, that  floppies, which were enclosed to the device from LabExchage in accesoary box contains copy of the software…. but a misfortune again – there was software for another Finnigan MAT device – ion trap ITD800, but it is not compatible with  ITS40.   So, what to do ?  In order to keep device running I have purchased Vx software from Adron Systems. It is quite good option, it can be run on Win7 instead of DOS, what of course  is very convenient. But Vx software contains only part of all service, which is available in  original ITS40 program.   And in 2023 finally happened to find good way  to get my ITS’s  on almost original SW !  Of course, it is almost hopeless idea to find nowadays original ITS40 software.  At  Chromatofraphy forum I seen interesting offer how this issue to solve.   ITS40 appears to work fine with Varian Saturn 5.2 software, it is a bit newer, released in  1995 year or so, but still it is DOS based and very similar to ITS40. Only is necessary to change ( or to reprogram old ones )  two EPROMs in ITS40 SAP board.   And I am very happy that in 2023 I have contacted Walter Lehmann, former Varian employee, with question about spare parts for my devices.  Also asked him about software for ITS40.   And finally it worked !! He offered me Varian Saturn software just for nothing and I only  paid  EUR 120.- for set of EPROMs. At his web-site you can find offer for EPROMS for Varian Saturn and here is also reference on software   https://www.ms-parts.ch/varian.htm .

Finally all seems nice ! But it was not easy to get this software running  on modern PCs. And here is my story how all it happened. Main problem here is that Saturn software runs under MS-DOS only, but one equisition file has up to 700 – 800 MB, and it must be copied to some memory carrier  to pass it for  further processing to another, more powerfull  PC.  To use floppy disks for this purpose is troublesome – even HD 1.44MB floppies has too small memory.  USB flash card would be fine, but there is no USB ports in old DOS PCs…. Where is solution ?

Solution is here – USB emuator, which is produced by Bulgarian company Nalbantov Electronics.   They started to produce special USB  boards, which can be installed into old PCs instead of 3.5 or 5.25  inch drives. Initially it was intended for musicians, but later same boards were used as upgrade for old industrial equipment.  Boards are available on e-Bay, but here is reference on Nalbantov Electronics web-page: https://floppyusbemulator.com/ .

Some information about the PC, which I have purchased in 2011 together with ITS40 – it was Compaq 386/20e Deskpro.  And I  became a fan of Compaq.   It is fantastic reliable device.  I have installed on that original Compaq software – MS-DOS ver. 5.0.   Only two parts been replaced since it was produced in 1989 – BIOS battery and hard drive. Instead of crashed Conner type 33  I have installed SeaGate ST31722A Medalist, with 1.28 GB of total  memory, FAT16 formatted  to 640MB. Here is  pictures of my PC with Nalbantov card installed ( both ITSs are connected to the same Compaq – I never run ITSs simultaneously ):

IMG_20230616_190307

Lef side on the wall you can see my Chemical Angel – present of my wife.   It is my safeguard !

IMG_20230714_184929

IMG_20230714_214253

and two main boot files:

 

autoexec.bat

 

@ECHO OFF

PROMPT $p$g

PATH C:\DOS

SET LMOUSE=C:\MOUSE1

C:\MOUSE1\MOUSE

SET TEMP=C:\DOS

 

config.sys

 

DOS=HIGH

DOS=UMB

DEVICE=C:\DOS\HIMEM.EXE

FILES=30

BUFFERS =32

DEVICE=C:\DOS\CEMM.EXE RAM 1024

DEVICEHIGH=C:\DOS\VDISK.SYS 1024/E:8

DEVICEHIGH=C:\DOS\CACHE.EXE 1024 /EXT

And now about the reason why Saturn 5.2 may not work on modern PCs. First of all  –  file system. If you have FAT32, you need to reformat your hard drive to FAT16.  Another reason  is memory. Saturn software uses for communication with MS a pease of RAM memory starting with C800.  Take a look into BIOS of your PC – if this region is already  occupied  ( most probably by video-card or BIOS ROM  ), this PC will not communicate correctly with your GPIB card.

Am very grateful to Walter Lehmann for Saturn 5.2 software and assistance in it’s installation.

Also many thanks to my acquaintance  Stanislav, who have helped me with selection of hard drive for Compaq PC.

Wish you good luck !

 

by sergei

Калибровка хроматомасспектрометра ITS40 для количественного анализа смесей растворителей

Как известно, хроматомасспектрометр раскрывает перед нами колоссальные возможности в обнаружении и идентификации примесей. Однако как и у всего в этом мире,  у этого уникального прибора есть и недостатки. Один из них – трудности количественного анализа смесей, ввиду того, что   МС ( масс-спектрометр )  обладает различной чувствительностью к различным соединениям и , как следствие,  чтобы определить количественный состав смеси  требуется отдельная калибровка по каждому  компоненту.

Для определения коэффициентов относительной чувствительности при количественном  анализе методом нормировки,  были сделаны ряд анализов контрольных смесей, в состав которых входят:

  • метанол
  • ацетонитрил
  • ацетон
  • МЕК
  • н-бутанол
  • толуол
  • п-ксилол
  • 1-метокси-2-пропилацетат
  • этилацетат
  • бутилацетат
  • 1-метокси-2-пропанол
  • изо-бутанол

каждого компонента взято по 0.8 мл,  было сделано 4 разных состава и компоненты подобраны так, чтобы  в каждой смеси не было неразделенных пиков.  На колонке с фазой RTX-1701 от Restek  неудовлетворительно разделяются следующие компоненты:

ацетон – метилацетат – изопропанол

метоксипропанол  ( MP )- н-бутанол

метоксипропилацетат ( MPA ) – о-ксилол.

Методика подготовки проб для анализа. 1 микролитр испытуемой смеси через мембрану  вводится микрошприцом в  пустую 12 мл пробирку с крышкой и  пробирка кладется на 3 минуты в термостат при 80 градусов цельсия для полного испарения пробы. Затем микрошприцем на 100 мкл из пробирки отбирается 70 микролитров пробы и вводится в испаритель хроматографа.

Режимы работы хромасса –  электронная ионизация ( EI ) , диапазон Mz 30 – 200,  время сканирования  – 0.3 с,  температура детектора – 220 град Ц,  температура переходной камеры – 230 град Ц,  программирование температуры колонки – от 50 ( 1 мин ) до 180 град Ц, скорость подъема темературы – 8 град/минуту.

Определены средние коэффициенты калибровки для каждого компонента, за единицу принят внутренний стандарт н-Октан ( в дальнейшем в использовании внутреннего стандарта нет необходимости и можно пользоваться методом  нормировки ):

Метанол – 4.22

Этанол – 3.32

Ацетон – 1.96

Метилацетат – 2.76

Изопропанол – 2.04

Ацетонитрил – 2.14

Этилацетат – 1.74

Метилэтилкетон – 1.61

Изобутанол – 1.95

н-Бутанол – 2.34

1-Метокси-2-пропанол – 2.46

Толуол – 1.2

Бутилацетат – 2.23

о-, п- и м-Ксилолы – 1.19

1-Метокси-2-пропилацетат – 1.53

 

GC_picture

 

*************************************************************************************************

 

 

 

 

by sergei

Стандартный раствор н-алканов для калибровки индексов удерживания

Да, да, не удивляйтесь дорогой читатель, другой блог мне начинать уже не охота, и теперь, дабы не плодить бумаги, блоги и другие сущности, пишу сюда все, чем приходится заниматься.  Хотя – одна  публикация на эту тему уже была –  ITS40

Следите, здесь будут интересные “расследования” –    Хромасс – это чудесный прибор, который как по отпечаткам пальцев, может определить состав любой смеси, которую в принципе  можно перевести в газообразное состояние.

После запуска Хроматомасспектрометра ITS40 фирмы Finnigan MAT ( выпуск 1989 года )  для работы нужны калибровочные смеси. Конечно, можно купить готовые, но цены в последнее время стали совсем недружественными и я купил понемногу всех необходимых мне 10 н-алканов:

пентан, гексан. гептан, октан, нонан, декан, ундекан, додекан, тридекан, тетрадекан – соответственно от 5 до 14 углеродных атомов в цепочке.

Поскольку отмерять удобнее и быстрее объем, то вот таблица плотностей н-алканов:

 

n

 

density at 20 Deg C

 

ml

 

g

 

per 738 g ( 0.938 l ) of Acetonitrile

 

 

 

 

 

 

 

 

 

   ml

   ml

 

  Пентан

5

 

0.63

 

0.2

 

0.126

 

0.117

0.234

 

  Гексан

6

 

0.664

 

0.190

 

0.126

 

0.111

0.222

 

  Гептан

7

 

0.683

 

0.184

 

0.126

 

0.108

0.216

 

  Октан

8

 

0.702

 

0.179

 

0.126

 

0.105

0.210

 

  Нонан

9

 

0.719

 

0.175

 

0.126

 

0.103

0.205

 

  Декан

10

 

0.73

 

0.173

 

0.126

 

0.101

0.202

 

  Ундекан

11

 

0.74

 

0.170

 

0.126

 

0.100

0.199

 

  Додекан

12

 

0.75

 

0.168

 

0.126

 

0.098

0.197

 

  Тридекан

13

 

0.756

 

0.167

 

0.126

 

0.098

0.195

 

  Тетрадекан

14

 

0.76

 

0.166

 

0.126

 

0.097

0.194

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1.26

g

1.038

2.076

 

 

 

 

 

 

 

 

 

 

 

 

 

В правом столбце – количества мл алканов на 1 литр ( у меня было 738 г – чуть меньше ) ацетонитрила. Ацетонитрил брал качества  HPLC от фирмы Tedia.

При этом 1 мкг такого раствора будет содержать примерно 200 нанограмм каждого алкана.  Чтобы было 100 нг – берем соседний столбик левее. Соответственно, учитывая плотность ацетонитрила – 0.786 г/см.куб.,  1 мкл такого раствора будет содержать 157.2  ( или 78.6 ) нанограмм н-алканов.

Этот раствор – для капиллярной колонки Restek RTX-1701 с толщиной фазы 1 мкм.   Для другой  моей колонки – DB-5 от Agilent с толщиной фазы 0.25 мкм нужна уже  другая смесь.

Напомню, что у меня сейчас в лаборатории работают два хромасса ITS40  с двумя  разными колонками –  для решения разного рода задач. RTX-1701 – для растворителей ( и других летучих компонентов ), и DB-5 для тяжелой химии.