Rapid Analysis of Perchlorate in Drinking Water at Partsper Billion Levels Using Microchip Electr

Letters to Analytical Chemistry

Rapid Analysis of Perchlorate in Drinking Water at Parts per Billion Levels Using Microchip Electrophoresis

Jana C.Gertsch,?Scott D.Noblitt,?Donald M.Cropek,?and Charles S.Henry*,?

Department of Chemistry,Colorado State University,Fort Collins,CO,and Construction Engineering Research Laboratory,U.S.Army Corps of Engineers,Champaign,IL

A microchip capillary electrophoresis(MCE)system has been developed for the determination of perchlorate in drinking water.The United States Environmental Protec-tion Agency(USEPA)recently proposed a health advisory limit for perchlorate in drinking water of15parts per billion(ppb),a level requiring large,sophisticated instru-mentation,such as ion chromatography coupled with mass spectrometry(IC-MS),for detection.An inexpen-sive,portable system is desired for routine online moni-toring applications of perchlorate in drinking water.Here, we present an MCE method using contact conductivity detection for perchlorate determination.The method has several advantages,including reduced analysis times relative to IC,inherent portability,high selectivity,and minimal sample pretreatment.Resolution of perchlorate from more abundant ions was achieved using zwitterionic, sulfobetaine surfactants,N-hexadecyl-N,N-dimethyl-3-ammonio-1-propane sulfonate(HDAPS)and N-tetradecyl-N,N-dimethyl-3-ammonio-1-propane sulfonate(TDAPS). The system performance and the optimization of the separation chemistry,including the use of these surfac-tants to resolve perchlorate from other anions,are dis-cussed in this work.The system is capable of detection limits of3.4(1.8ppb(n)6)in standards and5.6( 1.7ppb(n)6)in drinking water.

In recent years,scienti?c literature and popular media have been pervaded by reports on perchlorate,its persistence in the environment,its detection by various analytical methods,and its effect on human health.1-11Long-term exposure can disrupt thyroid hormone production by competitively inhibiting the uptake of iodide into the thyroid.Reduced thyroid hormone production has been linked to a number of developmental and neurological disorders in newborns and infants,such as cerebral palsy and cretinism.2-5Such adverse health effects have invoked the need for a method to routinely monitor perchlorate in drinking water.

Perchlorate contamination in watersheds is ostensibly at-tributed to the use of Chilean fertilizers up to the1950s and the manufacturing of NH4ClO4in missile and rocket fuels.4-11In 2004,California introduced a public health goal of6parts per billion(ppb)perchlorate in drinking water,and since then,several other states have adopted similar advisory levels.4,6While per-chlorate exposure is recognized nationally as a water quality issue and human health concern,the toxicity impact is not quantitatively understood.The USEPA has not set regulatory levels of perchlo-rate in drinking water,but recently issued an Interim Drinking Water Health Advisory,determining that a level of15ppb is protective of all subpopulations.12

Perchlorate has been mainly analyzed by ion chromatography (IC)with either conductivity detection(CD)or mass spectrometry (MS).13-16Currently,USEPA employs methods314.0,331.0,and 332.0for perchlorate analysis.While these methods are capable of isolating,detecting,and quantifying perchlorate with low limits of detection(0.02-0.005ppb),the instrumentation is costly, complex,and lacks portability.A system that can monitor

*Corresponding author.

?Colorado State University.

?U.S.Army Corps of Engineers.

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Published on Web03/25/2010

perchlorate levels online is desirable,particularly during reme-diation efforts for contaminated drinking water supplies.

We present here a microchip capillary electrophoresis(MCE) method capable of measuring perchlorate with low sample and reagent consumption,reduced analysis times relative to IC,and low detection limits.The optimization of the separation chemistry as well as the use of contact conductivity detection,incorporating a recently reported bubble cell design,allow for low limits of detection and fast analysis times(approximately1min).17Two zwitterionic sulfobetaine surfactants,N-hexadecyl-N,N-dimethyl-3-ammonio-1-propane sulfonate(HDAPS)and N-tetradecyl-N,N-dimethyl-3-ammonio-1-propane sulfonate(TDAPS),were compared for the selective manipulation of perchlorate retention time.At concentrations above the critical micelle concentration(CMC), micellar interactions slow the migration of perchlorate,separating the analyte from common,higher mobility anions found in water. TDAPS was found to provide more reproducible results than HDAPS.Finally,the novel separation chemistry was used to analyze perchlorate in drinking water samples with99%recovery and detection limits of5ppb.

EXPERIMENTAL SECTION

Materials.All chemicals are reagent grade unless otherwise noted.Silicon wafers(100mm)were purchased from University Wafer(Boston,MA).Poly(dimethylsiloxane)(PDMS)and Sylgard 184elastomer were obtained from Dow Corning(San Diego,CA). SU-83025photoresist was purchased from Microchem(Newton, MA).Sodium?uoride,1,3-propane disulfonic acid disodium salt, and N-tetradecyl-N-N-dimethyl-3-ammonio-1-propane sulfonate (TDAPS)were purchased from Sigma-Aldrich(St.Louis,MO). Chloride,nitrate,and sulfate(potassium salt)were obtained from Fisher(Fair Lawn,NJ).Potassium perchlorate was obtained from J.T.Baker(Phillipsburg,NJ).Nicotinic acid was purchased from Fluka(Buchs,Switzerland).N-Hexadecyl-N,N-dimethyl-3-ammo-nio-1-propane sulfonate(HDAPS)was obtained from Anatrace,Inc. (Maumee,OH).Tungsten microwires(13μm diameter)were purchased from GoodFellow Corp.(Huntingdon,UK).Solutions were prepared in18.2M?water from a Millipore Milli-Q puri?cation system(Billerica,MA).

Microchip Fabrication.Construction of PDMS microchips was performed using previously reported methodologies.18-20 Channels were50μm×50μm as determined by pro?lometry. Microwire spacing was120μm,and the waste reservoir was2 mm after the detection zone.The sample and buffer channels were 2cm in length,the sample waste was1.5cm,and the separation channel was5cm.Microchips used in this study were fabricated with a bubble cell,and the design,fabrication,and optimization of the bubble cell are previously described.17A schematic of the microchip is shown in the Supporting Information,Figure1S.

Instrumentation and Data Acquisition.Contact conductivity detection was performed with a Dionex CD20conductivity detector as described previously.17A National Instruments USB-6210DAQ and LabView8.0software,running a custom Virtual Instrument,were used to monitor the output of the detector at a collection rate of20kHz with2000point boxcar averaging.No additional data?ltration or smoothing was performed.A?fth-order,polynomial baseline?t was subtracted from the raw data to account for baseline drift resulting from reagent evaporation, ion depletion,and temperature?uctuations.A previously pub-lished,custom-built,?oating high voltage power supply(HVPS) was used for electrophoresis.21

Electrophoresis.Separations were performed in counter-EOF mode,in which the migration of analytes toward the detection zone is opposite the direction of electroosmotic?ow(EOF).22 Microchips were prepared by rinsing for～30s each with18.2 M?·cm water and buffer.Gated injection was used throughout this study.23,24Each sample was made in18.2M?·cm water and mixed with10%background electrolyte(BGE)to ensure conduc-tivity consistency.24Zwitterionic surfactants,HDAPS and TDAPS, were used in the buffer system.25-28Propane disulfonate(PDS) was used as an internal standard.

Drinking water was collected from a potable water source in the chemistry building at Colorado State University,Fort Collins, CO.Sample preparation consisted of the addition of10%BGE.In addition,water samples were spiked with known concentrations of perchlorate for recovery studies.

RESULTS AND DISCUSSION

Several factors were considered when optimizing separation conditions,including buffer pH,?eld strength,injection time,and sulfobetaine surfactant composition and concentration.The use of sulfobetaine surfactants is based on previous work by Lucy29 and Haddad30focusing on the ability of zwitterionic head groups to interact with the polarizable perchlorate ion.Nicotinic acid(10 mM)was chosen as the background electrolyte because of its relatively low pI(3.6)and its lack of electrochemically active functional groups.31-33Using a low pH electrolyte causes partial protonation of the surface silanol groups,reducing the EOF. Additionally,low pH is integral in the preventing interference by other anionic compounds in the https://www.sodocs.net/doc/11106628.html,pounds with p K a values greater than the buffer pH will be partially or fully protonated,slowing or preventing their migration toward the detector.The EOF was approximately-1.2±0.5×10-5 cm2·V-1·s-1and was calculated from the migration time of the internal standard.34

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Sulfobetaine surfactants were used as BGE additives to improve the resolution of perchlorate from other anions.A series of electropherograms collected as a function of TDAPS surfactant concentration are shown in Figure 1.In the absence of surfactant,perchlorate migrates faster than the internal standard.While perchlorate is resolved from chloride,nitrate,and sulfate,the resolution was deemed insuf?cient for real samples where the concentrations of these anions will exceed perchlorate by at least 1000-fold.At concentrations above the CMC,micelles selectively interact with perchlorate,reducing its apparent mobility.29,30Therefore,the migration time of perchlorate could be manipulated by varying surfactant concentration.Initially,HDAPS was tested because of its low CMC (～0.1mM).27HDAPS appeared to be an excellent initial candidate for this separation;however,over time,it was found to produce inconsistent migration times.The average retention time of perchlorate was 73s but the RSD was 48%(Supporting Information,Figure 2S).The cause of the instability is not currently understood but likely lies in the poor reproduc-ibility of HDAPS -PDMS adsorption.35,36

We,next,tested TDAPS.Similar to HDAPS,TDAPS was selected for its relatively low CMC (0.4mM).30Furthermore,TDAPS has been used successfully by the Henry group.37The optimization of TDAPS concentration in the BGE can be deduced from examination of Figure 1.Perchlorate is effectively separated from chloride and nitrate and migrates after the internal standard when the TDAPS concentration is >0.5mM.The optimal concen-tration of TDAPS,based on resolution and peak shape,was determined to be 1.0mM.Employing this buffer system,a

signi?cant improvement in reproducibility was observed.The average retention time for perchlorate was 53.5s with an RSD of 8.6%.

In addition to surfactant studies,?eld strength and injection time were also investigated.These parameters were optimized for both standards and drinking water samples.A ?eld strength of -200V/cm was used for optimizing surfactant concentrations;however,in later experiments,the ?eld strength was increased to reduce analysis time.The progression of electropherograms from -200to -500V/cm for standards can be seen in Figure 3S (Supporting Information).Analysis time is reduced as ?eld strength increases;however,a signi?cant increase in noise was observed at ?eld strengths >-400V/cm.The optimal ?eld strength was determined to be -350V/cm.Increasing the ?eld strength from -200to -350V/cm reduced the analysis time from 100to 60s.In contrast,current IC techniques require run times of 15-30min.

Increased injection times result in a greater amount of sample introduced into the separation channel for gated injections.Since chloride and sulfate have the highest ion mobilites in drinking water,more chloride and sulfate will be introduced into the microchip than other anions in a single injection (Figure 2).The large peaks generated from chloride,nitrate,and sulfate in higher ionic strength matrixes,such as drinking water,can interfere with perchlorate analysis when injection times are long (>10s).Additionally,peak shapes are compromised due to effects of a larger sample plug.The best injection time for standards ranges between 1and 5s,while the optimal injection time for drinking water samples is 10s.

The detection limit for perchlorate in standards was determined utilizing the optimized separation conditions.Standards were prepared in 18.2M ?·cm water and diluted with 10%(v/v)BGE to provide consistent sample conductivity.Electropherograms showing the separation of PDS and perchlorate at concentrations

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.

Figure 1.Electropherograms showing the changes in perchlorate retention with increasing TDAPS concentrations.Resolution for perchlorate and PDS is 1.87(0.21,2.84(0.19,and 10.1(0.23when the TDAPS concentration is 0.5,1.0,and 2.0mM,respectively.Sample contains 5μM analytes:0.17ppm chloride,0.31ppm nitrate,0.50ppm perchlorate,and 1.2ppm PDS in 18.2M ?·cm water.Conditions:10mM nicotinic acid BGE,-350V/cm,3.0s injection.Detector range:100μ

S.

Figure 2.Electropherograms showing the changes in peak areas with increasing injection time.Sample contains 100ppb perchlorate and 0.124ppm PDS in drinking water.The peak area for perchlorate increased from 11.4mV ·s (0.06to 18.9mV ·s (0.02,to 34.9mV ·s (0.02,and to 50.8mV ·s (0.08for 3.0,5.0,7.0,and 10s injections,respectively.Conditions:10mM nicotinic acid,1mM TDAPS BGE,-350V/cm.Detector range:100μS.

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between 1and 50ppb are shown in Figure 4S (Supporting Information).The LOD was 3.4±1.8ppb for perchlorate (34±18nM),S/N )3.Perchlorate measurements were linear between 5and 1000ppb (r 2)0.9982).The detection limit and linear range are within the USEPA proposed health advisory limits and are comparable to that achieved by IC-CD systems.

Possible interference from anions in drinking water was also investigated.Anions of greatest concern include chloride,nitrate,sulfate,and ?uoride because of their ubiquity in drinking water.The separation of perchlorate from all interferences considered is shown in Figure 5S (Supporting Information).Early experiments proved the separation conditions capable of resolving perchlorate from sulfate,chloride,and nitrate,and under the described conditions,?uoride

was not detected within a 120s experimental window.Fluoride is not observed because the p K a value of the ?uoride ion (3.17)is near the pH of the buffer (3.6)so that a substantial fraction of ?uoride ions are protonated,slowing its migration.38

Drinking water collected from the Colorado State University Chemistry building was analyzed for perchlorate.Perchlorate was not detected in the native water sample;however,when spiked with 100ppb perchlorate and 248ppb PDS,both compounds were detected with 99%recovery for perchlorate,as calculated relative to PDS,rendering the microchip and separation conditions capable of analyzing perchlorate in this matrix.Separations of drinking water samples spiked with perchlorate and PDS are shown in Figure 3.The limit of detection for perchlorate in drinking water was 5.6±1.7ppb (56±17nM),S/N )3,and measurements were linear between 10and 1000ppb (r 2)0.9984).A calibration curve is shown in Figure 6S (Supporting Information ).CONCLUSIONS

A microchip capillary electrophoresis method has been devel-oped for the detection of perchlorate in drinking water.Separation chemistry,including the comparison of two zwitterionic sulfobe-taine surfactants,has been optimized.The device is capable of analyzing perchlorate over a relatively large linear range,with a detection limit of 5ppb in drinking water which exceeds the USEPA regulatory requirement.Additionally,analysis times for the method are approximately 15to 30times shorter than current IC techniques.This is the ?rst step toward development of a ?eldable platform for online,routine perchlorate monitoring in drinking water.

NOTE ADDED AFTER ASAP PUBLICATION

This paper was published on the Web March 25,2010with the second author of the manuscript not included.The corrected version was reposted April 2,2010.

SUPPORTING INFORMATION AVAILABLE

Additional information as noted in text.This material is available free of charge via the Internet at https://www.sodocs.net/doc/11106628.html,.Received for review December 20,2009.Accepted March 17,2010.

AC9029086

(38)Harrison,C.R.;Sader,J.A.;Lucy,C.A.J.Chromatogr.,A 2006,1113,

123–129

.

Figure 3.Electropherograms showing separation of drinking water samples spiked with 0.12ppm PDS and concentrations of perchlorate between 1and 1000ppb.Conditions:-350V/cm,10s injection,BGE )10mM nicotinic acid,1.0mM TDAPS,pH 3.6.Detector range )50μS.

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英语中的比较级与最高级 详解

比较级与最高级 1.as...as 与(not) as(so)...as as...as...句型中，as的词性 第一个as是副词，用在形容词和副词的原级前，常译为“同样地”。第二个as是连词，连接与前面句子结构相同的一个句子(相同部分常省略)，可译为“同..... He is as tall as his brother is (tall) . (后面的as 为连词) 只有在否定句中，第一个as才可换为so 改错: He is so tall as his brother.（X） 2.在比较状语从句中，主句和从句的句式结构一般是相同的 与as...as 句式中第二个as一样，than 也是连词。as和than这两个连词后面的从句的结构与前面的句子大部分情况下结构是相同的，相同部分可以省略。 He picked more apples than she did. 完整的表达为: He picked more apples than she picked apples. 后而的picked apples和前面相同，用did 替代。 He walked as slowly as she did.完整表达为: He walked as slowly as she walked slowly. she后面walked slowly与前面相同，用did替代。

3.谓语的替代 在as和than 引导的比较状语从句中，由于句式同前面 主句相同，为避免重复，常把主句中出现而从句中又出现的动词用do的适当形式来代替。 John speaks German as fluently as Mary does. 4.前后的比较对象应一致 不管后面连词是than 还是as,前后的比较对象应一致。The weather of Beijing is colder than Guangzhou. x than前面比较对象是“天气”，than 后面比较对象是“广州”，不能相比较。应改为: The weather of Bejing is colder than that of Guangzhou. 再如: His handwriting is as good as me. 应改为: His handwriting is as good as mine. 5.可以修饰比较级的词 常用来修饰比较级的词或短语有: Much,even,far,a little,a lot,a bit,by far,rather,any,still,a great deal等。 by far的用法: 用于强调，意为“...得多”“最最...”“显然”等，可修饰形容词或副词的比较级和最高级，通常置于其后，但是若比较级或最高级前有冠词，则可置于其前或其后。

人教版(新目标)初中英语形容词与副词的比较级与最高级

人教版（新目标）初中英语形容词与副词的比较级与最高级 （一）规则变化： 1．绝大多数的单音节和少数双音节词，加词尾-er ，-est tall—taller—tallest 2．以不发音的e结尾的单音节词和少数以-le结尾的双音节词只加-r，-st nice—nicer—nicest , able—abler—ablest 3．以一个辅音字母结尾的重读闭音节词或少数双音节词，双写结尾的辅音字母，再加-er，-est big—bigger—biggest 4．以辅音字母加y结尾的双音节词，改y为i再加-er，-est easy—easier—easiest 5．少数以-er，-ow结尾的双音节词末尾加-er，-est clever—cleverer—cleverest, narrow—narrower—narrowest 6．其他双音节词和多音节词，在前面加more，most来构成比较级和最高级 easily—more easily—most easily （二）不规则变化 常见的有： good / well—better—best ; bad (ly)/ ill—worse—worst ; old—older/elder—oldest/eldest many / much—more—most ; little—less—least ; far—farther/further—farthest/furthest

用法： 1．原级比较：as + adj./adv. +as（否定为not so/as + adj./adv. +as）当as… as中间有名字时，采用as + adj. + a + n.或as + many / much + n. This is as good an example as the other is . I can carry as much paper as you can. 表示倍数的词或其他程度副词做修饰语时放在as的前面 This room is twice as big as that one. 倍数+as+adj.+as = 倍数+the +n.+of Your room is twice as larger as mine. = Your room is twice the size of mine. 2．比较级+ than 比较级前可加程度状语much, still, even, far, a lot, a little, three years. five times,20%等 He is three years older than I (am). 表示“（两个中）较……的那个”时，比较级前常加the（后面有名字时前面才能加冠词） He is the taller of the two brothers. / He is taller than his two brothers. Which is larger, Canada or Australia? / Which is the larger country, Canada or Australia? 可用比较级形式表示最高级概念，关键是要用或或否定词等把一事物（或人）与其他同类事物（或人）相分离 He is taller than any other boy / anybody else.

英语中的比较级和最高级

大多数形容词有三种形式,原级,比较级和最高级, 以表示形容词说明的性质在程度上的不同。 形容词的原级: 形容词的原级形式就是词典中出现的形容词的原形。例如: poor tall great glad bad 形容词的比较级和最高级: 形容词的比较级和最高级形式是在形容词的原级形式的基础上变化的。分为规则变化和不规则变化。 规则变化如下: 1) 单音节形容词的比较级和最高级形式是在词尾加 -er 和 -est 构成。 great (原级) (比较级) (最高级) 2) 以 -e 结尾的单音节形容词的比较级和最高级是在词尾加 -r 和 -st 构成。wide (原级) (比较级) (最高级) 3)少数以-y, -er, -ow, -ble结尾的双音节形容词的比较级和最高级是在词尾加 -er 和 -est 构成。 clever(原级) (比较级) (最高级) 4) 以 -y 结尾,但 -y 前是辅音字母的形容词的比较级和最高级是把 -y 去掉,加上 -ier 和-est 构成. happy (原形) (比较级) (最高级) 5) 以一个辅音字母结尾其前面的元音字母发短元音的形容词的比较级和最高级是双写该辅音字母然后再加 -er和-est。 big (原级) (比较级) (最高级) 6) 双音节和多音节形容词的比较级和最高级需用more 和 most 加在形容词前面来构成。 beautiful (原级) (比较级) (比较级) difficult (原级) (最高级) (最高级) 常用的不规则变化的形容词的比较级和最高级: 原级------比较级------最高级 good------better------best many------more------most much------more------most bad------worse------worst far------farther, further------farthest, furthest 形容词前如加 less 和 least 则表示"较不"和"最不 形容词比较级的用法: 形容词的比较级用于两个人或事物的比较,其结构形式如下: 主语+谓语(系动词)+ 形容词比较级+than+ 对比成分。也就是, 含有形容词比较级的主句+than+从句。注意从句常常省去意义上和主句相同的部分, 而只剩下对比的成分。

英语比较级和最高级的用法归纳

英语比较级和最高级的用法归纳 在学习英语过程中，会遇到很多的语法问题，比如比较级和最高级的用法，对于 这些语法你能够掌握吗？下面是小编整理的英语比较级和最高级的用法，欢迎阅读！ 英语比较级和最高级的用法 一、形容词、副词的比较级和最高级的构成规则 1.一般单音节词和少数以-er，-ow结尾的双音节词，比较级在后面加-er，最高级 在后面加-est; (1)单音节词 如：small→smaller→smallest short→shorter→shortest tall→taller→tallest great→greater→greatest (2)双音节词 如：clever→cleverer→cleverest narrow→narrower→narrowest 2.以不发音e结尾的单音节词，比较在原级后加-r，最高级在原级后加-st; 如：large→larger→largest nice→nicer→nicest able→abler→ablest 3.在重读闭音节(即：辅音+元音+辅音)中，先双写末尾的辅音字母，比较级加-er，最高级加-est; 如：big→bigger→biggest hot→hotter→hottest fat→fatter→fattest 4.以“辅音字母+y”结尾的双音节词，把y改为i，比较级加-er，最高级加-est; 如：easy→easier→easiest heavy→heavier→heaviest busy→busier→busiest happy→happier→happiest 5.其他双音节词和多音节词，比较级在前面加more，最高级在前面加most; 如：bea utiful→more beautiful→most beautiful different→more different→most different easily→more easily→most easily 注意：(1)形容词最高级前通常必须用定冠词 the，副词最高级前可不用。 例句： The Sahara is the biggest desert in the world. (2) 形容词most前面没有the，不表示最高级的含义，只表示"非常"。 It is a most important problem. =It is a very important problem.

英语比较级和最高级的用法

More than的用法 A. “More than+名词”表示“不仅仅是” 1)Modern science is more than a large amount of information. 2)Jason is more than a lecturer; he is a writer, too. 3) We need more than material wealth to build our country.建设我们国家，不仅仅需要物质财富. B. “More than+数词”含“以上”或“不止”之意，如： 4)I have known David for more than 20 years. 5)Let's carry out the test with more than the sample copy. 6) More than one person has made this suggestion. 不止一人提过这个建议. C. “More than+形容词”等于“很”或“非常”的意思，如： 7)In doing scientific experiments, one must be more than careful with the instruments. 8)I assure you I am more than glad to help you. D. more than + (that)从句，其基本意义是“超过（=over）”，但可译成“简直不”“远非”.难以，完全不能（其后通常连用情态动词can） 9) That is more than I can understand . 那非我所能懂的. 10) That is more than I can tell. 那事我实在不明白。 11) The heat there was more than he could stand. 那儿的炎热程度是他所不能忍受的 此外，“more than”也在一些惯用语中出现，如： more...than 的用法 1. 比……多，比……更 He has more books than me. 他的书比我多。 He is more careful than the others. 他比其他人更仔细。 2. 与其……不如 He is more lucky than clever. 与其说他聪明，不如说他幸运。 He is more （a）scholar than （a）teacher. 与其说他是位教师，不如说他是位学者。 注：该句型主要用于同一个人或物在两个不同性质或特征等方面的比较，其中的比较级必须用加more 的形式，不能用加词尾-er 的形式。 No more than/not more than 1. no more than 的意思是“仅仅”“只有”“最多不超过”，强调少。如： --This test takes no more than thirty minutes. 这个测验只要30分钟。 --The pub was no more than half full. 该酒吧的上座率最多不超过五成。-For thirty years，he had done no more than he （had）needed to. 30年来，他只干了他需要干的工作。 2. not more than 为more than （多于）的否定式，其意为“不多于”“不超过”。如：Not more than 10 guests came to her birthday party. 来参加她的生日宴会的客人不超过十人。 比较： She has no more than three hats. 她只有3顶帽子。（太少了） She has not more than three hats. 她至多有3顶帽子。（也许不到3顶帽子） I have no more than five yuan in my pocket. 我口袋里的钱最多不过5元。（言其少） I have not more than five yuan in my pocket. 我口袋里的钱不多于5元。（也许不到5元） more than, less than 的用法 1. （指数量）不到，不足 It’s less than half an hour’s drive from here. 开车到那里不到半个钟头。 In less than an hour he finished the work. 没要上一个小时，他就完成了工作。 2. 比……（小）少 She eats less than she should. 她吃得比她应该吃的少。 Half the group felt they spent less than average. 半数人觉得他们的花费低于平均水平。 more…than,/no more than/not more than (1)Mr．Li is ________ a professor; he is also a famous scientist． (2)As I had ________ five dollars with me, I couldn’t afford the new jacket then． (3)He had to work at the age of ________ twelve． (4)There were ________ ten chairs in the room．However, the number of the children is twelve． (5)If you tel l your father what you’ve done, he’ll be ________ angry． (6)－What did you think of this novel? －I was disappointed to find it ________ interesting ________ that one． 倍数表达法 1. “倍数+形容词（或副词）的比较级+than+从句”表示“A比B大（长、高、宽等）多少倍” This rope is twice longer than that one.这根绳是那根绳的三倍（比那根绳长两倍）。The car runs twice faster than that truck.这辆小车的速度比那辆卡车快两倍（是那辆卡车的三倍）。 2. “倍数+as+形容词或副词的原级+as+从句”表示“A正好是B的多少倍”。

初中英语比较级和最高级讲解与练习

初中英语比较级和最高级讲解与练习 形容词比较级和最高级 一．绝大多数形容词有三种形式,原级,比较级和最高级, 以表示形容词说明的性质在程度上的不同。 1. 形容词的原级: 形容词的原级形式就是词典中出现的形容词的原形。例如: poor tall great glad bad 2. 形容词的比较级和最高级: 形容词的比较级和最高级形式是在形容词的原级形式的基 础上变化的。分为规则变化和不规则变化。 二．形容词比较级和最高级规则变化如下: 1) 单音节形容词的比较级和最高级形式是在词尾加-er 和-est 构成。 great (原级) greater(比较级) greatest(最高级) 2) 以-e 结尾的单音节形容词的比较级和最高级是在词尾加-r 和-st 构成。 wide (原级) wider (比较级) widest (最高级) 3) 少数以-y, -er, -ow, -ble结尾的双音节形容词的比较级和最高级是在词尾加 -er 和-est构成。 clever(原级) cleverer(比较级) cleverest(最高级)， slow(原级) slower(比较级) slowest (最高级) 4) 以-y 结尾,但-y 前是辅音字母的形容词的比较级和最高级是把-y 去掉,加上-ier 和-est 构成. happy (原形) happier (比较级) happiest (最高级) 5) 以一个辅音字母结尾其前面的元音字母发短元音的形容词的比较级和最高级是双写该 辅音字母然后再加-er和-est。 原形比较级最高级原形比较级最高级 big bigger biggest hot hotter hottest red redder reddest thin thinner thinnest 6) 双音节和多音节形容词的比较级和最高级需用more 和most 加在形容词前面来构 成。 原形比较级最高级 careful careful more careful most careful difficult more difficult most difficult delicious more delicious most delicious 7)常用的不规则变化的形容词的比较级和最高级: 原级比较级最高级 good better best 好的 well better best 身体好的 bad worse worst 坏的 ill worse worst 病的 many more most 许多 much more most 许多 few less least 少数几个 little less least 少数一点儿 （little littler littlest 小的） far further furthest 远（指更进一步，深度。亦可指更远） far farther farthest 远（指更远，路程）

英语比较级和最高级

形容词比较级和最高级的形式 一、形容词比较级和最高级的构成 形容词的比较级和最高级变化形式规则如下 构成法原级比较级最高级 ①一般单音节词末尾加 er 和 est strong stronger strongest ②单音节词如果以 e结尾，只加 r 和 st strange stranger strangest ③闭音节单音节词如末尾只有一个辅音字母， 须先双写这个辅音字母，再加 er和 est sad big hot sadder bigger hotter saddest biggest hottest ④少数以 y, er(或 ure), ow, ble结尾的双音节词， 末尾加 er和 est(以 y结尾的词，如 y前是辅音字母， 把y变成i，再加 er和 est，以 e结尾的词仍 只加 r和 st) angry Clever Narrow Noble angrier Cleverer narrower nobler angriest cleverest narrowest noblest ⑤其他双音节和多音节词都在前面加单词more和most different more different most different 1) The most high 〔A〕mountain in 〔B〕the world is Mount Everest，which is situated 〔C〕in Nepal and is twenty nine thousand one hundred and fourty one feet high 〔D〕 . 2) This house is spaciouser 〔A〕than that 〔B〕white 〔C〕one I bought in Rapid City，South Dakota 〔D〕last year. 3) Research in the social 〔A〕sciences often proves difficulter 〔B〕than similar 〔C〕work in the physical 〔D〕sciences. 二、形容词比较级或最高级的特殊形式：

高中英语的比较级和最高级用法总结

比较级和最高级 1.在形容词词尾加上―er‖ ―est‖ 构成比较级、最高级： bright（明亮的）—brighter—brightest broad（广阔的）—broader—broadest cheap（便宜的）—cheaper—cheapest clean（干净的）—cleaner—cleanest clever（聪明的）—cleverer—cleverest cold（寒冷的）—colder—coldest cool（凉的）—cooler—coolest dark（黑暗的）—darker—darkest dear（贵的）—dearer—dearest deep（深的）—deeper—deepest fast（迅速的）—faster—fastest few（少的）—fewer—fewest great（伟大的）—greater—greatest hard（困难的,硬的）—harder—hardest high（高的）—higher—highest kind（善良的）—kinder—kindest light（轻的）—lighter—lightest long（长的）—longer—longest loud（响亮的）—louder—loudest low（低的）—lower—lowest near（近的）—nearer—nearest new（新的）—newer—newest poor（穷的）—poorer—poorest quick（快的）—quicker—quickest quiet（安静的）—quieter—quietest rich（富裕的）—richer—richest short（短的）—shorter—shortest slow（慢的）—slower—slowest small（小的）—smaller—smallest smart（聪明的）—smarter—smartest soft（柔软的）—softer—softest strong（强壮的）—stronger—strongest sweet（甜的）—sweeter—sweetest tall（高的）-taller-tallest thick（厚的）—thicker—thickest warm（温暖的）—warmer—warmest weak（弱的）—weaker—weakest young（年轻的）—younger—youngest 2.双写最后一个字母,再加上―er‖ ―est‖构成比较级、最高级： big（大的）—bigger—biggest fat（胖的）—fatter—fattest hot（热的）—hotter—hottest red（红的）—redder—reddest sad（伤心的）—sadder—saddest thin（瘦的）—thinner—thinnest wet（湿的）—wetter—wettest mad（疯的）—madder—maddest 3.以不发音的字母e结尾的形容词,加上―r‖ ―st‖ 构成比较级、最高级：able（能干的）—abler—ablest brave（勇敢的）—braver—bravest close（接近的）—closer—closest fine（好的,完美的）—finer—finest large（巨大的）—larger—largest late（迟的）—later—latest nice（好的）—nicer—nicest ripe（成熟的）—riper—ripest

(完整版)初中英语比较级和最高级的用法

英语语法---比较级和最高级的用法 在英语中通常用下列方式表示的词:在形容词或副词前加more(如 more natural,more clearly )或加后缀 -er(newer,sooner )。典型的是指形容词或副词所表示的质、量或关系的增加。英语句子中，将比较两个主体的方法叫做“比较句型”。其中，像“A比B更……”的表达方式称为比较级；而“A最……”的表达方式则称为最高级。组成句子的方式是将形容词或副词变化成比较级或最高级的形态。 一、形容词、副词的比较级和最高级的构成规则 1．一般单音节词和少数以-er，-ow结尾的双音节词，比较级在后面加-er，最高级在后面加-est； （1）单音节词 如：small→smaller→smallest short→shorter→shortest tall→taller→tallest great→greater→greatest （2）双音节词 如：clever→cleverer→cleverest narrow→narrower→narrowest 2．以不发音e结尾的单音节词，比较在原级后加-r，最高级在原级后加-st； 如：large→larger→largest nice→nicer→nicest able→abler→ablest 3．在重读闭音节（即：辅音＋元音＋辅音）中，先双写末尾的辅音字母，比较级加-er，最高级加-est； 如：big→bigger→biggest hot→hotter→hottest fat→fatter→fattest 4．以“辅音字母＋y”结尾的双音节词，把y改为i，比较级加-er，最高级加-est； 如：easy→easier→easiest heavy→heavier→heaviest busy→busier→busiest happy→happier→happiest 5．其他双音节词和多音节词，比较级在前面加more，最高级在前面加most； 如：beautiful→more beautiful→most beautiful different→more different→most different easily→more easily→most easily

初中英语形容词比较级和最高级讲解与练习

初中英语形容词比较级和最高级讲解与练习 形容词比较级和最高级 绝大多数形容词有三种形式,原级,比较级和最高级, 以表示形容词说明的性质在程度上的不同。 形容词的原级: 形容词的原级形式就是词典中出现的形容词的原形。 例如: poor tall great glad bad 形容词的比较级和最高级: 形容词的比较级和最高级形式是在形容词的原级形式的基础上变化的。分为规则变化和不规则变化。 规则变化如下: 1) 单音节形容词的比较级和最高级形式是在词尾加 -er 和 -est 构成。 great (原级) (比较级) (最高级) 2) 以 -e 结尾的单音节形容词的比较级和最高级是在词尾加 -r 和 -st 构成。 wide (原级) (比较级) (最高级) 3)少数以-y, -er, -ow, -ble结尾的双音节形容词的比较级和最高级是在词尾加-er 和-est 构成。 clever(原级) (比较级) (最高级) 4) 以 -y 结尾,但 -y 前是辅音字母的形容词的比较级和最高级是把 -y 去掉,加上 -ier 和-est 构成. happy (原形) (比较级) (最高级) 5) 以一个辅音字母结尾其前面的元音字母发短元音的形容词的比较级和最高级是双写该辅音 字母然后再加-er和-est。 big (原级) (比较级) (最高级) 6) 双音节和多音节形容词的比较级和最高级需用more 和 most 加在形容词前面来构成。 beautiful (原级) (比较级) (比较级) difficult (原级) (最高级) (最高级) 常用的不规则变化的形容词的比较级和最高级: 原级------比较级------最高级 good------better------best many------more------most much------more------most bad------worse------worst far------farther, further------farthest, furthest 形容词前如加 less 和 least 则表示"较不"和"最不"

(完整)初中英语比较级和最高级

◇下列形容词和副词没有比较级和最高 （即表示“最高程度”或“绝对状态”的形容词和副词没有比较级和最高级） empty, wrong, perfect, unique, extreme, excellent, favourite, true, right, correct, extremely ... 形容词副词比较级最高级使用注意事项 ◇比较应在同类事物之间进行。 误：Your English is better than me. 正：Your English is better than mine. ◇比较级前可以有一个表示程度的状语，最常见的三大修饰词是：a little, much, even。 以下单词也可用来修饰：any, far, still, a lot, yet, rather。 My sister is a little taller than me. Their house is much larger than ours. 另外，名词短语也可修饰比较级，说明程度。 I’m three years older than he. 特别提醒：very, quite, too不可修饰比较级。 ◇避免重复使用比较级。 误：He is more kinder to small animals than I. 正：He is much kinder to small animals than I. 误：He is more cleverer than his brother. 正：He is cleverer than his brother. ◇比较要符合逻辑，在同一范围内比较时，避免将主语含在比较对象中，这时需使用other来排除自身。 误：China is larger that any country in Asia. 正：China is larger than any other country in Asia. 误：John studies harder than any student in his class. 正：John studies harder than any other student in his class. 正：John studies harder than any of the other students in his class. 正：John studies harder than anyone else in his class. ◇比较要遵循前后一致的原则，注意前后呼应。 The population of Shanghai is larger than that of Beijing. It is easier to make a plan than to carry it out. ◇序数词通常只修饰最高级。 Africa is the second largest continent. The Yellow River is the second longest river in China. This is the third most popular song of Michael Jackson. ◇为避免重复，我们通常用that, those, one, ones代替前面出现的名词。that 代替可数名词单数和不可数名词，those代替可数名词复数。one既可指人又可指物，只能 代替可数名词。 The weather in China is different from that in America. The book on the table is more interesting than that(或the one)on the desk. A box made of steel is stronger than one made of wood. 误：In winter, the weather of Beijing is colder than it of Shanghai. 正：In winter, the weather of Beijing is colder than that of Shanghai. ◇“否定词 + 比较级”相当于最高级。

英语比较级和最高级

英语比较级和最高级

一、比较级和最高级的讲解 变化规则 1．一般单音节词和少数以-er，-ow结尾的双音节词，比较级在后面加-er，最高级在后面加-est； （1）单音节词 如：small→smaller→smallest short→shorter→shortest tall→taller→tallest great→greater→greatest （2）双音节词 如：clever→cleverer→cleverest n arrow→narrower→narrowest 2．以不发音e结尾的单音节词，比较在原级后加-r，最高级在原级后加-st； 如：large→larger→largest nice→nicer→nicest able→abler→ablest 3．在重读闭音节（即：辅音＋元音＋辅音） 中，先双写末尾的辅音字母，比较级加-er，最高级加-est；

如：big→bigger→biggest hot→hotter→hottest fat→fatter→fattest 4．以“辅音字母＋y”结尾的双音节词，把y 改为i，比较级加-er，最高级加-est； 如：easy→easier→easiest heavy→heavier→heaviest busy→busier→busiest happy→happier→happiest 5．其他双音节词和多音节词，比较级在前面加more，最高级在前面加most； 如：beautiful→more beautiful→most beautiful different→more different→most d ifferent easily→more easily→most easily 注意： （1）形容词最高级前通常必须用定冠词the，副词最高级前可不用。 例句：The Sahara is the biggest desert in the world. （2）形容词most前面没有the，不表示最高级的含义，只表示"非常"。

英语比较级与最高级的解释和种类

形容词的比较级和最高级: 绝大多数形容词有三种形式,原级,比较级和最高级, 以表示形容词说明的性质在程度上的不同。 形容词的原级: 形容词的原级形式就是词典中出现的形容词的原形。例如: poor tall great glad bad 形容词的比较级和最高级: 形容词的比较级和最高级形式是在形容词的原级形式的基础上变化的。分为规则变化和不规则变化。 规则变化如下: 1) 单音节形容词的比较级和最高级形式是在词尾加-er 和-est 构成。 great (原级) greater(比较级) greatest(最高级) 2) 以-e 结尾的单音节形容词的比较级和最高级是在词尾加-r 和-st 构成。 3)少数以-y, -er, -ow, -ble结尾的双音节形容词的比较级和最高级是在词尾加-er 和-est 构成。 clever(原级) cleverer(比较级) cleverest(最高级) 4) 以-y 结尾,但-y 前是辅音字母的形容词的比较级和最高级是把-y 去掉,加上-ier 和-est 构成. happy (原形) happier (比较级) happiest (最高级) 5) 以一个辅音字母结尾其前面的元音字母发短元音的形容词的比较级和最高级是双写该辅音字母然后再加-er和-est。 big (原级) bigger (比较级) biggest (最高级) ) 双音节和多音节形容词的比较级和最高级需用more 和most 加在形容词前面来构成。beautiful (原级)? difficult (原级) more beautiful (比较级) more difficult (比较级) 常用的不规则变化的形容词的比较级和最高级: 原级比较级最高级 good better best many more most much more most little less least ill worse worst far farther(further) farthest(furthest) 形容词前如加less 和lest 则表示"较不"和"最不" important 重要 less important 较不重要 lest important 最不重要 形容词比较级的用法: 形容词的比较级用于两个人或事物的比较,其结构形式如下: 主语+谓语(系动词)+ 形容词比较级+than+ 对比成分。也就是, 含有形容词比较级的主句+than+从句。注意从句常常省去意义上和主句相同的部分, 而只剩下对比的成分。 It is warmer today than it was yesterday. 今天的天气比昨天暖和。 This picture is more beautiful than that one.

英语单词的比较级和最高级

little:形容词比较级littler/less/lesser 形容词最高级littlest/least 副词比较级less 副词最高级least far:形容词比较级farther/further 形容词最高级farthest/furthest 副词比较级farther/further 副词最高级farthest/furthest well:形容词比较级better 形容词最高级best 副词比较级better 副词最高级best ill:形容词比较级worse 形容词最高级worst 副词比较级worse 副词最高级worst many:形容词比较级more 形容词最高级most bad:形容词比较级worse 形容词最高级worst good:形容词比较级better 形容词最高级:best old:形容词比较级:older/elder 形容词最高级:oldest/eldest good:比较级better 最高级the best hot:比较级hotter 最高级the hottest heavy:比较级heavier 最高级the heaviest fine:比较级finer 最高级the finest exciting:比较级more exciting 最高级the most exciting bad:比较级worse 最高级the worst creative:比较级more creative 最高级the most creative boring:比较级more boring 最高级the most boring far:比较级farther/further 最高级the farthest/the furthest near:比较级nearer

英语比较级和最高级的用法

英语比较级和最高级的用法 一、形容词、副词的比较级和最高级的构成规则 1.一般单音节词和少数以-er，-ow结尾的双音节词，比较级在后面加-er，最高级在后面加-est; (1)单音节词 如：small→smaller→smallest short→shorter→shortest tall→taller→tallest great→greater→greatest (2)双音节词 如：clever→cleverer→cleverest narrow→narrower→narrowest 2.以不发音e结尾的单音节词，比较在原级后加-r，最高级在原级后加-st; 如：large→larger→largest nice→nicer→nicest able→abler→ablest 3.在重读闭音节(即：辅音+元音+辅音)中，先双写末尾的辅音字母，比较级加-er，最高级加-est; 如：big→bigger→biggest hot→hotter→hottest fat→fatter→fattest 4.以“辅音字母+y”结尾的双音节词，把y改为i，比较级加-er，最高级加-est; 如：easy→easier→easiest heavy→heavier→heaviest busy→busier→busiest happy→happier→happiest 5.其他双音节词和多音节词，比较级在前面加more，最高级在前面加most; 如：beautiful→more beautiful→most beautiful different→more different→most different easi ly→more easily→most easily 注意：(1)形容词最高级前通常必须用定冠词the，副词最高级前可不用。 例句：The Sahara is the biggest desert in the world. (2) 形容词most前面没有the，不表示最高级的含义，只表示"非常"。 It is a most important problem. =It is a very important problem. 6.有少数形容词、副词的比较级和最高级是不规则的，必须熟记。 如：good→better→best well→better→best bad→worse→worst ill→worse→worst