Pesticides Identification at the Residue Level - ACS Publications

1 Possible Limits of Ultramicro Analysis

Downloaded via 185.252.219.61 on November 13, 2018 at 04:30:26 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

GUNNAR

WIDMARK

Institute of Analytical Chemistry, University of Stockholm, Stockholm 50, Sweden

This paper discusses reached

by modern

the possible methods

ment trends in analytical paths, both marked leads toward terized

the

by the

complex

traditional

information.

especially (DAS). foreseen

when A further when

for

using

data

the combination

analysis

are

(MS)

by

can

systems

and selectivity is

The ultimate

illustrated

for

sensitivity,

acquisition

of instruments

to cover the GC/MS/DAS/computer. ultramicro

second employing

at high

in sensitivity

path charac-

The

and mass spectrometry on-line

main

with the need

instruments

identification

increase

two

The first

simplicity.

be

Develop-

seem to follow

Combination for

to

analysis.

sensitivity.

to identification,

(GC)

information

of sensitivity

goal of quantitation,

demand

leading

gas chromatography produce

chemistry

by increasing

strong

path is hopefully

limits

of residue

a "map

is

extended limits of of

tracer

cosmos."

T o u r i n g t h e past t w o decades there has b e e n a r e m a r k a b l e increase i n sensitivity analysis. figures

of

chemical

analysis, e s p e c i a l l y

i n pesticide

residue

It is f r o m this field m o r e t h a n a n y other t h a t h i g h s e n s i t i v i t y

s u c h as p p m , p p b , a n d p p t h a v e b e e n b r o u g h t to the p u b l i c b y

t h e n e w s m e d i a . U n f o r t u n a t e l y , the p u b l i c has h a d f e w o p p o r t u n i t i e s to u n d e r s t a n d the d i m e n s i o n s of these

figures;

i l l u s t r a t i n g the b i o l o g i c a l

significance of a n a l y t i c a l l y h i g h s e n s i t i v i t y figures is o b v i o u s l y a n e v e n m o r e difficult task.

Ultimate Sensitivity at Ultramicro Analysis I t is reasonable to ask the a n a l y s t i f t h e r e exists a n u l t i m a t e p o s s i b l e l i m i t of d e t e c t i o n of s m a l l q u a n t i t i e s i n c h e m i c a l analysis. A s i n m o s t 1

Biros; Pesticides Identification Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2

PESTICIDES

IDENTIFICATION

cases associated w i t h p e s t i c i d e c h e m i s t r y , there are o n l y c o m p l e x answers to this v e r y s i m p l e q u e s t i o n . W h a t is a c t u a l l y q u e s t i o n e d is the l i m i t of s e n s i t i v i t y at w h i c h u s e f u l a n a l y t i c a l results c a n be o b t a i n e d .

T h u s , any answer w o u l d d e m a n d a

d e f i n i t i o n of the c o n c e p t of usefulness. T h e e x p e r i e n c e d analyst k n o w s t h a t the extreme u l t i m a t e of sensit i v i t y of one m o l e c u l e

( o r one a t o m after d e c o m p o s i t i o n )

per

sample

u n i t is not foreseen f o r p r a c t i c a l a n a l y t i c a l w o r k . N e v e r t h e l e s s , t h e e a r l y s c h o o l of n u c l e a r p h y s i c i s t s w e r e a b l e to detect single e l e m e n t a r y p a r t i c l e s w h e n using very simple instrumentation. T h e tremendous

improvements

i n i n s t r u m e n t a t i o n since t h e n w o u l d c e r t a i n l y m a k e a n y t y p e of single m o l e c u l e detectable, b u t n o t i n a m i x t u r e a n d n e v e r i n a n u n k n o w n s a m p l e g i v e n to the analyst. I n the s a m p l e of the o l d p h y s i c i s t , the e m i t t e d p a r t i c l e d i f f e r e d sufficiently f r o m the b a c k g r o u n d to b e d e t e c t e d — w h e n

not

absorbed!

A l t h o u g h less s e n s i t i v e l y d e t e c t e d , the same h o l d s t r u e to some extent f o r electron-capturing compounds,

s u c h as D D T , w h e n present i n a n o r d i -

n a r y b i o l o g i c a l s a m p l e . T h e m a i n difference is t h a t there are o n l y a f e w e l e m e n t a r y p a r t i c l e s to b e c o n s i d e r e d , w h e r e a s there is a vast n u m b e r of electron-capturing compounds.

T h u s , the E C D response

w i l l not

be

i n t e r p r e t a b l e i n p r o p e r c h e m i c a l terms. T h e m a i n factor h a m p e r i n g a n increase of s e n s i t i v i t y i n c h e m i c a l a n a l y s i s — s u c h as r e s i d u e a n a l y s i s — i s the l a r g e n u m b e r of

compounds

p o s s i b l y present i n a n o r d i n a r y - s i z e sample—e.g., 1 g r a m .

The

n u m b e r of c o m p o u n d s makes it l i k e l y that m a n y of the c o m p o u n d s

large will

h a v e c h e m i c a l p r o p e r t i e s too close for d i f f e r e n t i a t i o n b y o r d i n a r y m e t h ods of d e t e c t i o n a n d s e p a r a t i o n . H o w e v e r , because most m o d e r n schemes of analysis c o n t a i n one or s e v e r a l s e p a r a t i o n a n d c o n c e n t r a t i o n

steps,

t h e r e is no m o r e reason to m a k e a n o m e n c l a t u r e d i f f e r e n t i a t i o n b e t w e e n u l t r a m i c r o analysis a n d h i g h s e n s i t i v i t y analysis.

I n b o t h cases, h i g h

s e n s i t i v i t y d e t e c t i o n is a s k e d for, a n d b y c o n c e n t r a t i o n steps the

com-

p o u n d s w i l l finally b e d e t e c t a b l e i n a v e r y s m a l l s a m p l e .

Tracer Cosmos A l t h o u g h a n enormous n u m b e r of c o m p o u n d s are constituents of a n y 1-gram

s a m p l e , as m e n t i o n e d ,

this n u m b e r

is n e v e r

unlimited.

Ap-

p r o a c h i n g the l o w e s t levels of c o n c e n t r a t i o n , w h e r e o n l y a f e w orders of m a g n i t u d e of e a c h m o l e c u l e are present, the n u m b e r of possible

con-

stituents is s u c h t h a t the use of the n a m e " t r a c e r c o s m o s " is justified, e m p h a s i z i n g the a n a l y t i c a l difficulties foreseen to r e a c h the l o w e r levels. I n F i g u r e 1, a n a t t e m p t is m a d e to i l l u s t r a t e b y the h e a v y l i n e s , t h e sides

of the triangles, the m a x i m u m n u m b e r

of

compounds


possibly

1.

Limits of Ultramicro

W I D M A R K

3

Analysis

Levels of Concentration

Levels of Molecules

- in"3

•+f't--+\+ i.i i + + V. + +/-t- + •+• -+- •+- -K«f • M i l l i r i i i • & • + + + + ++ + + 4-Vt + -!"•«-Is + I i i I iM r n 1/1 i i i i •+* + + + •!-•»++ + -r/+- +• -t + 1- •»- - •t + + + +\J-i / i i l I i i I l I i i i K I +/++•+•+-1-1-1 - --r -t--t- -t- + -f, •+-/+-•»- + +-+ t -t--- + + 1 - 4-4—*- •»-+. + • H i/i i i i i i i i i I I I I I I I'M il ft

:

10

10

10

I0

V

10

10'

10

Moximum Number of Compounds ot Each Level of Concentration Figure 1.

Map of tracer cosmos

present o n each d e c i m a l l e v e l of concentration.

I n this

figure,

a s s u m e d t h a t a l l c o m p o u n d s h a v e a m o l e c u l a r w e i g h t o f 60. T h i s

it is figure

is too l o w , b u t 600 is b e l i e v e d t o b e f a r too h i g h . U n i t s o f c o n c e n t r a t i o n n o w i n use at p o l l u t i o n studies are g i v e n o n t h e axes. T h e d o t t e d lines o f F i g u r e 1 refer t o the a s s u m p t i o n t h a t w e a r e d e a l i n g w i t h a 1-gram s a m p l e o f 9 9 % p u r i t y , a n d t h a t t h e a m o u n t o f i m p u r i t y is e q u a l l y d i v i d e d o n e a c h o f t h e p o s s i b l e d e c i m a l levels o f c o n c e n t r a t i o n . N a t u r a l l y , t o m e e t this a s s u m p t i o n , there are n o t e n o u g h materials a v a i l a b l e f o r the 1 % o r for the 0 . 1 % l e v e l . H o w e v e r , one i s u n l i k e l y to find f r o m n a t u r a l sources a n e v e n d i s t r i b u t i o n o f c o n t a m i n a n t s l i k e t h i s , o r one a t w h i c h there are the s a m e n u m b e r o f c o m p o u n d s o n e a c h l e v e l . T h e same h o l d s t r u e for the other extreme, t h a t a l l t h e t r a c e constituents are present o n t h e s a m e l e v e l o f c o n c e n t r a t i o n .

I t seems

more realistic to assume—excluding a detailed discussion—that i m p u r i -


4

PESTICIDES

IDENTIFICATION

ties are g r o u p e d as " i s l a n d s " o n the t r i a n g u l a r m a p of t h e t r a c e r c o s m o s ; p r e s u m a b l y , the islands w i l l b e densest at the top.

D e p e n d i n g o n the

c h e m i c a l n a t u r e of these i s l a n d s — l i p i d or h y d r o p h i l i c — t h e y w i l l m o v e upwards or downwards on their respective maps w h e n brought i n contact w i t h a system of r e v e r s e d character. T h u s , a w a t e r s a m p l e w i l l lose p a r t of its d i s s o l v e d l i p i d m a t e r i a l s to s u s p e n d e d

particles h a v i n g a fatty

surface. P a r t i c l e s a b l e to a b s o r b l i p i d m a t e r i a l s are a l w a y s present i n n a t u r a l w a t e r s a n d a i d i n the t r a n s p o r t of the l i p i d m a t e r i a l s — i n c l u d i n g s o m e t e c h n i c a l c o m p o u n d s , e.g.,

D D T — t o l i v i n g organisms, thus c a u s i n g ac-

c u m u l a t i o n . M o r e o v e r , i t is a s s u m e d t h a t the fatty surface of the p a r t i c l e s protects p a r t l y l i p i d m a t e r i a l s f r o m c h e m i c a l d e g r a d a t i o n .

However, it

w o u l d b e of great interest to k n o w m o r e a b o u t the reactions o c c u r r i n g i n w a t e r at v e r y l o w c o n c e n t r a t i o n levels w h e r e the h i g h l y r e a c t i v e p r o d u c t s of

H2O-O2

e q u i l i b r i u m are to b e

found—e.g., the h y d r o x y r a d i c a l .

K n o w l e d g e f r o m this field w o u l d p r o b a b l y i n d i c a t e t h a t f e w

organic

c o m p o u n d s are l i k e l y to s u r v i v e at the l o w e s t levels of c o n c e n t r a t i o n . T h e short d i s c u s s i o n i n the p r e c e d i n g p a r a g r a p h s illustrates t h e usefulness of p e s t i c i d e r e s i d u e analysis at m u c h l o w e r levels of c o n c e n t r a t i o n t h a n those p r e s e n t l y a v a i l a b l e . A s i n d i c a t e d b y T a b l e I , there are a n u m b e r of o t h e r fields w h e r e a n a l y t i c a l m e t h o d s of i m p r o v e d s e n s i t i v i t y w i l l be

needed. Table I.

Fields Requiring More Sensitive Analysis

S t u d i e s of disappearance of t e c h n i c a l c h e m i c a l p r o d u c t s i n n a t u r e ; e.g., p l a s t i c , p a i n t , pesticides, d r u g s ( t o t a l fate s t u d i e s ; a c c u m u l a t i o n , e.g., a t t h e e n d of f o o d chains) I d e n t i f i c a t i o n of u n k n o w n s f o u n d i n n a t u r e ( c o n d i t i o n for legislation) S t u d i e s of n a t u r a l l y - o c c u r r i n g c o m p o u n d s a t p p m - p p b levels S t u d i e s of m a i n c o m p o n e n t s of i n d i v i d u a l cells N e w w a y s to d e t e r m i n e degree of t o x i c i t y (at n o r m a l l y s u b t o x i c levels) Quality control and monitoring E a r l y w a r n i n g systems (e.g., h e a l t h control)

Limits of Detection; Quantitation and Identification •

Sensitivity limits must be i m p r o v e d for both quantitation a n d i d e n t i fication

of p e s t i c i d e residues. A l t h o u g h the f o r m e r m e t h o d is m o r e sensi-

t i v e t h a n t h e latter, u n t i l recently m o s t progress

has b e e n m a d e

in

i m p r o v i n g the s e n s i t i v i t y of q u a n t i t a t i v e analysis. S i n c e there is a d e p e n d ence b e t w e e n the t w o m e t h o d s , sensitive m e t h o d s of i d e n t i f i c a t i o n h a v e


1.

W I D M A R K

Limits

of Ultramicro

SEPARATION

Analysis

5

IDENTIFICATION 10 nq (pg)

(lOOng) Figure 2. Flow chart of separation and identification processes in pesticide residue analysis. Solid line indicates that on-line combinations are available; thick line indicates that they are in common use; dotted line, manipulations. b e c o m e e v e n m o r e d e s i r a b l e . F i g u r e 2 demonstrates t h e c o n n e c t i o n t w e e n the m e t h o d s

be-

o f s e p a r a t i o n a n d o f i d e n t i f i c a t i o n ; differences i n

sensitivities are i n d i c a t e d . Quantitation. T h e most easily i n t e r p r e t e d p a r t of a q u a n t i t a t i v e r e s i d u e analysis is the r e c o r d i n g o f a detector response f o u n d l i n e a r to c o n c e n t r a t i o n w h e n c h e c k e d b y s t a n d a r d solutions. It has to b e v e r i f i e d also that t h e response of s a m p l e a n d s t a n d a r d s o l u t i o n w i t h a specific m e t h o d is o b t a i n e d at t h e same a n a l y t i c a l position—e.g., o n a gas c h r o m a t o g r a m . T h e use of b l a n k s w i l l demonstrate the d e g r e e o f influence of i n t e r f e r i n g materials a n d thus e x h i b i t the d e t e c t i o n l i m i t o f the r e c o r d i n g system. H o w e v e r , because o f the f u n d a m e n t a l l i m i t a t i o n o f a n y

monodetector

system, o n l y c o n s i d e r a b l e k n o w l e d g e of the s a m p l e w i l l m a k e a q u a n t i t a t i v e r e s i d u e analysis r e l i a b l e . A c h e m i c a l analysis is not o n l y the r e c o r d i n g o f a detector s i g n a l but a very complex

matter.

I n T a b l e I I , the extent o f t o t a l r e s i d u e

analysis i s s k e t c h e d , a n d at e a c h step errors c a n b e m a d e w h i c h w i l l influence the a n a l y t i c a l result. W h e n serious, these errors w i l l the r e c o r d e d a n a l y t i c a l result i n t o nonsense.

convert

W h e n less i m p o r t a n t , these

errors w i l l o n l y l o w e r the o v e r - a l l s e n s i t i v i t y o f the analysis. T h u s , the s e n s i t i v i t y l i m i t o b t a i n a b l e b y t h e detector alone is i n r e a c h o n l y w h e n the e n t i r e scheme o f the analysis is successfully p e r f o r m e d .


6

PESTICIDES

Table II.

IDENTIFICATION

T h e Analytical Process

Planning before the actual analysis in collaboration with, e.g., biologists D i s c u s s i o n s w i t h biologists of the purpose of a n a l y s i s D i s c u s s i o n of the t y p e of s a m p l e t o be chosen P i l o t tests; use of s i m p l i f i e d models Suggestions—criticism S m a l l series are a n a l y z e d A g r e e m e n t s o n p u r p o s e , size, e c o n o m y , etc.

Performance of analysis Field sampling Packing—storing Transportation S t o r i n g a t the l a b Mechanical treatment E x t r a c t i o n , etc. Cleaning up C h e m i c a l reactions P r e p a r a t i o n of final s o l u t i o n , s t a n d a r d , a n d b l a n k s Instrumental

Analysis

R e c o r d i n g of response Checks

Report Calculations W r i t t e n report Statistical treatment Bookkeeping

After report D i s c u s s i o n s w i t h biologists Criticism Corrections I m p r o v e m e n t of a n a l y t i c a l m e t h o d A f u r t h e r n e g a t i v e influence o n the p o s s i b l e l i m i t of d e t e c t i o n

of

r e s i d u e analysis is g i v e n b y the t y p e of r e s i d u e u n d e r i n v e s t i g a t i o n . T h e r e is a m a r k e d difference i n detector s e n s i t i v i t y i n analysis of, e.g., mates a n d D D T - t y p e pesticides.

carba-

T h e g e n e r a l difficulties of e a c h class

h a v e to b e c o n s i d e r e d , as is d e m o n s t r a t e d i n T a b l e I I I . Identification. T h e f u n d a m e n t a l l i m i t a t i o n o f gas c h r o m a t o g r a p h y i n i d e n t i f i c a t i o n studies is that b y this m e t h o d , one c a n o n l y state n o n presence of a k n o w n c o m p o u n d w h i c h is a v a i l a b l e as a s t a n d a r d i n a considerably

pure

form.

T h u s , gas

chromatography

is a n

excellent


1.

W I D M A R K

Limits of Ultramicro Table III.

7

Analysis

Objects of Analytical Investigation

C o m p o u n d (s) sought C o m p o u n d s slightly changed b y : Isomerization Polymerization Photoreaction

Autoxidation Hydrolysis

M e t a b o l i t e s ( m i g h t v a r y w i t h ecosystem) R e a c t i o n s i n the ecosystem e.g., M e t h y l a t i o n I n d u c e d changes i n the ecosystem e.g. H o r m o n e effects, " H i t a n d r u n " effects

Possible Complications Isomers a n d homologs Related compounds a) used for t h e same purpose b) n o t used for the same purpose—e.g., P C B Contamination; impurities m e t h o d to d e m o n s t r a t e that a k n o w n p e s t i c i d e is n o t present at a g i v e n l e v e l of concentration—e.g.,

the one a c c e p t e d b y the a u t h o r i t i e s . H o w -

ever, n o p o s i t i v e i n f o r m a t i o n as to the i d e n t i t y of the p e a k - f o r m i n g c o m p o u n d is o b t a i n a b l e b y o r d i n a r y gas c h r o m a t o g r a p h y .

Some information

m i g h t b e c o l l e c t e d u s i n g a t w o - d e t e c t o r system, b u t o n l y i f one of t h e detectors gives a response i n t e r p r e t a b l e i n c h e m i c a l terms.

As critical

e x a m i n a t i o n w i l l s h o w , the gas c h r o m a t o g r a p h i c detectors n o w u s e d as c o m p l i m e n t s to E C D are i m p e r f e c t i n this respect.

I n general, more

i n f o r m a t i o n is g a i n e d b y u s i n g a l t e r n a t i v e m e t h o d s

of s e p a r a t i o n , as

s h o w n at the left of F i g u r e 2. firmatory

T h e s e operations w i l l also serve a c o n -

purpose.

T h e great a d v a n t a g e of mass s p e c t r o m e t r y o v e r other m e t h o d s

of

i d e n t i f i c a t i o n is t h a t the response is g i v e n b y i n t e g e r mass u n i t s , a n d t h u s the response w i l l b e m o r e a p t for c h e m i c a l i n t e r p r e t a t i o n t h a n is v a l i d f o r other types of detectors.

S i n c e the mass spectrometer, w h e n

combined

w i t h a gas c h r o m a t o g r a p h , w i l l serve as a m u l t i d e t e c t o r , the c o m p u t e r i z e d d a t a a c q u i s i t i o n systems n o w b e i n g i n t r o d u c e d o n the m a r k e t w i l l i m p r o v e o u r a b i l i t y to i d e n t i f y most c o m p o u n d s s e p a r a t e d i n a r e a s o n a b l y p u r e f o r m b y gas c h r o m a t o g r a p h y . A n E C D c h r o m a t o g r a m s h o u l d n o t b e u s e d alone as a n i n d i c a t i o n of a s u c c e s s f u l s e p a r a t i o n . I n some s a m p l e s , s u c h as s e w a g e s l u d g e , there m i g h t b e a c o n s i d e r a b l e o v e r l a p b y

compounds

of l o w - c a p t u r i n g a b i l i t y . T h u s , F I D checks s h o u l d b e m a d e b e f o r e starti n g i d e n t i f i c a t i o n studies o n a mass spectrometer.


8

PESTICIDES

IDENTIFICATION

A severe obstacle i n present i d e n t i f i c a t i o n studies of a s s u m e d p e s t i c i d e residues is t h a t the mass s p e c t r o m e t e r is n o r m a l l y a less sensitive d e t e c t o r t h a n E C D . W h e n t h e mass spectrometer is set o n a s i n g l e mass n u m b e r , there is a g a i n i n s e n s i t i v i t y b u t also a n o b v i o u s loss i n selectivity.

R e c o r d i n g of o n l y a s m a l l — b u t s i g n i f i c a n t — p a r t of

t h e mass

s p e c t r u m w h i l e t h e gas c h r o m a t o g r a p h i c f r a c t i o n emerges is a n i m p r o v e m e n t f o r some i d e n t i f i c a t i o n studies, b u t c o l u m n b l e e d i n g m i g h t g i v e u n e x p e c t e d difficulties. H o w e v e r , i t is p r o b a b l e t h a t a d e s i r e d g a i n i n s e n s i t i v i t y w i l l b e a c h i e v e d soon b y i n s t r u m e n t a l i m p r o v e m e n t s o f t h e mass spectrometer, m a i n l y i n i o n i z a t i o n . I n T a b l e I V , t h e losses w h i c h are a s s u m e d at the v a r i o u s sites of c o m m e r c i a l l y a v a i l a b l e spectrometers are t a b u l a t e d . T h i s t a b l e also i n d i c a t e s t h a t the mass s p e c t r o m e t e r is o b v i o u s l y s u p e r i o r i n s e n s i t i v i t y to o t h e r i n s t r u m e n t a l t e c h n i q u e s . M o r e Table I V .

Detection Levels of Combined Instruments, G C / M S

Detector M i n i m u m 30 t o 100 ions t o g i v e a detector s i g n a l a t i d e a l s i g n a l to-noise c o n d i t i o n s

Mass Analyzer A

efficiency 1 0 ~ - 1 0 ~ l

3

M i n i m u m 300 to 1 0 ions to reach t h e mass a n a l y z e r 6

Ionization

efficiency 1 0 ~ - 1 0 ~ 3

M i n i m u m 3 X 10 to 10 5

13

Separator

8

ions t o be i n t r o d u c e d i n t o t h e ionization chamber efficiency 5 0 % or better

M i n i m u m 6 X 10 to 2 X 10 5

13

molecules t o t h e separator

T o be i n j e c t e d i n t o G C / M S , w h e n s c a n n i n g 2 - 5 0 0 mass u n i t s i n 1 sec 3 X 10 to 10 8

16

molecules

A s s u m i n g m w = 200, 5 X 1 0 ~

GC

16

to 2 X 1 0 "

8

mole

Injection T o be i n j e c t e d w h e n e l u t e d f r o m G C i n 1 sec 0.1 p g t o 4 (xg m o r e a t G C peaks of longer d u r a t i o n 0

° In practice, it is necessary to prepare sample solutions 10-100 times more concentrated.


1.

wiDMARK

Limits of Ultramicro

9

Analysis

over, gas c h r o m a t o g r a p h i c peaks o f short d u r a t i o n g i v e a n increase i n sensitivity.

T h i s i s o n e o f the factors t h a t f a v o r t h e use o f c a p i l l a r y

c o l u m n s for f u t u r e r e s i d u e studies. M o s t analysts n o w u s i n g mass s p e c t r o m e t r y alone o r i n c o m b i n a t i o n w i t h gas c h r o m a t o g r a p h y w i l l n o t b e a b l e t o u t i l i z e a l l t h e i n f o r m a t i o n o b t a i n a b l e at a series o f mass s p e c t r o m e t r i c scans. T h i s is m a i n l y b e c a u s e of i m p e r f e c t r e c o r d i n g devices w h i c h are u n a b l e t o a c c e p t a l l details i n the r a p i d flow o f signals. S o m e analysts c o m p l a i n o f b e i n g c o m p l e t e l y d r o w n e d i n p a p e r s p e c t r a . W e h a v e b e e n l u c k y e n o u g h t o h a v e one o f t h e e a r l y d a t a a c q u i s i t i o n systems c a p a b l e o f p r o d u c i n g i n s t a n t a n e o u s l y c o m p e n s a t e d a n d n o r m a l i z e d mass s p e c t r a i n d i g i t a l f o r m ( J , 2 ) .

This

system ( o n - l i n e ) has g r a d u a l l y b e e n e x t e n d e d b y a recent c o n n e c t i o n t o a s m a l l c o m p u t e r ; t h u s , w e c a n c o n v e n i e n t l y use a n y s y s t e m o f r e c o r d e d d a t a as l o n g as this o p e r a t i o n c a n b e p r o g r a m m e d .

T h e r a p i d changes

b e t w e e n different a n a l y t i c a l p r o g r a m s w i l l b e f a c i l i t a t e d b y a n e x t e r n a l disc memory n o w being installed (3).

O u r n e w system w i l l t h e n operate

as d e m o n s t r a t e d b y the flow sheet i n F i g u r e 3. H o w e v e r , d e s p i t e t h e use of a l l the electronics, the success o f a n analysis w i l l s t i l l d e p e n d m a i n l y

(or printout) digital tape on normalized spectra or raw data GC/s/MS/

H

/ OAS / J4K

Alternate methods of treating the sample to be analyzed

on

printout /Computer/ « . off | } 8K new progroms

Instant oscilloscopic inspection 'on-line 1

r

Standard analytical programs on discs

command joint planning analysts-biologists Figure 3. Flow sheet of a computerized combination gas chromatograph (GC) and mass spectrometer (MS); DAS = data acquisition system, s = separator, i = interface, d.r. = data reduction


10

PESTICIDES

o n the c o n d i t i o n of t h e gas c h r o m a t o g r a p h i c

IDENTIFICATION

column a n d the proper

h a n d l i n g o f the s a m p l e . T h e p r o g r a m m i n g of a c o m p r e h e n s i v e d a t a system i n t e g r a t e d t o a system of a n a l y t i c a l i n s t r u m e n t a t i o n w i l l c e r t a i n l y b e a v e r y e x c i t i n g task. H o w e v e r , this w i l l d e m a n d specific i n f o r m a t i o n i n a f o r m w h i c h is u s e f u l for p r o g r a m m i n g f r o m a l l t h e scientists i n v o l v e d i n t h e s t u d y o r r e s p o n sible for parts o f the s t u d y , as i n d i c a t e d b y T a b l e s I I a n d I I I . P r e s e n t difficulties i n a c h i e v i n g this t y p e of c o l l a b o r a t i o n m i g h t r e m a i n as a l i m i t i n g factor f o r i m p r o v e d l i m i t s of r e s i d u e analysis d e t e c t i o n a n d other s i m i l a r types of u l t r a m i c r o analysis.

Literature Cited (1) Bergstedt, L., W i d m a r k , G . , Chromatographia (2) I b i d . , (1970) 3, 59.

(1969) 2, 529.

(3) Bennet, P . , Bergstedt, L., W i d m a r k , G . , to be published. RECEIVED

August 24, 1970.


Pesticides Identification at the Residue Level - ACS Publications

Recommend Documents